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Partial melting, melt collection and transport in the Swakane Gneiss, North Cascades crystalline core, Washington

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Partial melting, melt collection and transport in the Swakane Gneiss, North Cascades crystalline core, Washington

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Content PARTIAL MELTING, MELT COLLECTION AND TRANSPORT IN THE SWAKANE GNEISS, NORTH CASCADES CRYSTALLINE CORE, WA by Melissa Ann Boysun A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE (GEOLOGICAL SCIENCES) May 2004 Copyright 2004 Melissa Ann Boysun R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. UMI Number: 1421759 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. UMI UMI Microform 1421759 Copyright 2004 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES, CALIFORNIA 90089-1695 This thesis, written by Melissa A. Boysun under the direction of her thesis committee, and approved by all its members, has been presented to and accepted by the Director ofGraduate and Professional Programs, in partialfulfillment ofthe requirementsfor the degree of Thesis Committee Chair DEDICATION Of all the people who have influenced my life, my most heart felt thanks go to my parents Gary and Helen Boysun. Without their love, encouragement, and support over the years, I would not be where I am today. 11 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. ACKNOWLEDGEMENTS I would like to thank my advisor, Scott Paterson for his guidance and support throughout this project; my committee members, Robert Miller and J. Lawford Anderson, and the USC structure group for their advice during fieldwork and all the time spent editing; and Jennifer Matzel for her work on geochronology in the Cascades core. Funding for this project was provided by the Geological Society of America, Sigma Xi, and the University of Southern California Department of Earth Sciences. Ill R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. TABLE OF CONTENTS Dedication ii Acknowledgements iii List of Figures and Tables vi Abstract ix CHAPTER I: INTRODUCTION 1 Purpose 1 Background 2 Regional Geology 4 Swakane Gneiss and Napeequa Complex 9 Location of Field Areas 12 Columbia River Domain 13 Tamarack Creek Domain 13 Chiwawa Mountain Domain 15 CHAPTER II: ROCK DESRIPTIONS AND GEOCHEMICAL ANALYSES 21 Introduction 21 Quartz Biotite Gneiss 22 Amphibolite Schist 24 Stromatic Migmatite 25 Intrusive Rock 27 Intrusive Styles 29 Dikes and Sills 30 Sheets 32 Stocks 33 Geochemistry 35 Rare-Earth Elements 36 Trace Elements 39 Summary 39 CHAPTER ni: STRUCTURAL ANALYSIS 41 Introduction 41 Swakane Gneiss Fabric 41 Foliation and Lineations 43 Chelan Block 43 Wenatchee Block 47 Intrusive Rock Fabric and Orientation 49 Columbia River Domain 50 Tamarack Creek Domain 5 3 Chiwawa Mountain Domain 59 Summary 60 IV R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CHAPTER IV: MELTING AND MELT INJECTION 63 Introduction 63 Partial Melting in the Swakane Gneiss 64 Melting and Regional Deformation 66 Mechanical Controls on Melt Injection 68 Conclusions 71 REFERENCES 72 APPENDIX 1 79 APPENDIX 2 85 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. LIST OF FIGURES AND TABLES Figure 1-1: Tectonic Map of Western North America 5 Figure 1-2: Geologic Map of the Cascades Core 6 Figure 1-3: Swakane Gneiss and Napeequa Complex Exhumation Curve 9 Figure 1-4: Cross-section A-A' 14 Figure 1-5: Cross-section B-B' 14 Figure l-6a: Geologic Map of Chiwawa Mountain (with Station Numbers) 16 Figure l-6b: Geologic Map of Chiwawa Mountain (with Structural Data) 17 Figure 1-7: Cross-section C-C 18 Figure 1-8: Chiwawa Mountain Outcrop Map 2021 19 Figure 1-9: Chiwawa Mountain Outcrop Map 2025 20 Figure 2-1: Photomicrograph: Quartz and Biotite Inclusions 22 Figure 2-2: Photomicrograph: Opaque Inclusions 24 Figure 2-3: Photomicrograph: Amphibolite Schist 25 Figure 2-4: Photomicrograph: Partial Melt 26 Figure 2-5: Photomicrograph: Quartz Ribbons 27 Figure 2-6: Photomicrograph: K-feldspar Microstructures 28 Figure 2-7: Folded Dike with Zoning 31 Figure 2-8: Host Rock Shearing Near Dike Margins 32 Figure 2-9: Two-Mica Granodiorite Sheet 34 Figure 2-10: Muscovite Leucogranite Stock 35 Figure 2-lla: Rare Earth Element Plot 35 VI R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 2-1 lb: Trace Element Plot 35 Table 2-1: Geochemical Data 37 Figure 3-la: Stereonet Plot of Foliation in the Columbia River Domain, West Fold Hinge 44 Figure 3-lb: Stereonet Plot of Foliation in the Columbia River Domain, East Fold Hinge 44 Figure 3-2: Stereonet Plot of Foliation in the Columbia River Domain, Northeast Limb 45 Figure 3-3: Stereonet Plot of Foliation in the Tamarack Creek Domain, Northeast Limb 45 Figure 3-4: Stereonet Plot of Lineations in the Columbia River Domain, Fold Hinge 46 Figure 3-5: Stereonet Plot of Lineations in the Columbia River Domain, Northeast Limb 46 Figure 3-6: Stereonet Plot of Lineations in the Tamarack Creek Domain, Northeast Limb 47 Figure 3-7: Stereonet Plot of Foliation in the Chiwawa Mountain Domain 48 Figure 3-8: Zone of Partial Melting 49 Figure 3-9: Stereonet Plot of Lineations in the Chiwawa Mountain Domain 50 Figure 3-10: Stereonet Plot of Dike Set A Orientations in the Columbia River Domain 52 Figure 3-11: Stereonet Plot of Dike Set B Orientations in the Columbia River Domain 52 Figure 3-12: Stereonet Plot of Dike Set D Orientations in the Columbia River Domain 53 Figure 3-13: Photomicrograph and Diagram of Dike Set B Structures 54 Figure 3-14: Stereonet Plot of Dike Set C Orientations in the Columbia River Domain 55 Vll R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 3-15: Isoclinally Folded Dike in the Tamarack Creek Domain 56 Figure 3-16: Zoned Dike in the Tamarack Creek Domain 57 Figure 3-17: Stereonet Plot of Dike Orientation in the Tamarack Creek Domain 57 Figure 3-18: Conjugate Dikes in the Tamarack Creek Domain 58 Figure 3-19: Close-up of Conjugate Dikes in the Tamarack Creek Domain 58 Figure 3-20: Stereonet Plot of Foliation in the Two-Mica Granodiorite Sheet 59 Figure 3-21: Stereonet Plot of Dikes in the Chiwawa Mountain Domain 60 Figure 3-22: Histograms of the Angle Between Dike Orientations and Foliation 61 Figure 3-23: Stereonet Plot of Dikes in the Columbia River Domain 62 Figure 4-1: Melt Collection in Shear Zone 69 Plate 1: Columbia River Outcrop Maps See pocket Plate 2a: Geologic Map of Tamarack Creek (With Station Numbers) See pocket Plate 2b: Geologic Map of Tamarack Creek (With Structural Data) See pocket Vlll R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. ABSTRACT This study focused on partial melting and melt ascent in middle to deep crust. The Swakane Gneiss records the highest pressure and temperature conditions (650-725 “C/10-12 kbar) in the Cascades core, yet it is one of the youngest metamorphic units, with a protolith age of 73 Ma. Following burial, the Swakane Gneiss was subjected to partial melting by 68 Ma. Initial melt migration occurred parallel to the dominant foliation during which time strain gradients controlled migration from intergranular melt pockets to relatively lower stress sites. With increasing melt volume, the locally-derived melts were subsequently intruded into higher levels of the Swakane Gneiss as cm-scale dikes and sills, and 10 to 100 meter sheets and stocks. Stress gradients caused by heterogeneous strain, and tectonic stress controlled the emplacement of the leucogranitic intrusions, and local anisotropies e.g. foliation, folds, and shear zones had minimal effects on their ascent. IX R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CHAPTER I; INTRODUCTION Purpose The purpose of this study was to determine if local melting in the Swakane Gneiss produced leuco granite dikes in the deepest exposed sections of this unit, and to examine the influence of regional stress and local preexisting anisotropies on melt transport, from initial migration along grain boundaries to ascent from the source region. To address the question of melt ascent, I examined the Swakane Gneiss in the North Cascades crystalline core (herein called the Cascades core) in detail. In the Swakane Gneiss, deep to midcrustal migmatites, cm- to m-size granitic to granodioritic dikes and sills, and 10s to 100s m-scale granitic sheets and stocks are exposed. The migmatites are representative of near source ascent processes (Mehnert, 1968), while the sheet-like granitic bodies intruded lower structural levels of the Swakane Gneiss indicating melt ascent from the source region (Brown, 1994; Barbey et ah, 1996). In order to determine the source region of melting, I examined the composition and geochemistry of the magmatic sheets, inferred the effective viscosity of the melts during emplacement, and determined the general structural characteristics of the preserved sheet-like bodies. Furthermore, I utilized field relationships between the melts and their host rocks (e.g. foliation, lineation, and dike orientations), to determine what physical parameters controlled melt ascent in the Swakane Gneiss. hi the following chapters, I will give 1) an overview of Cascades core and Swakane Gneiss geology from previous studies; 2) a description of the three areas R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. where I conducted detailed examinations of partial melting and melt injection; 3) the results from my petrologic and structural investigations of the three areas; 4) the conclusions I have made based on these investigations; and 5) how my conclusions contribute to ongoing research on partial melting and melt ascent in deep crust, and the evolution of the Cascades core. Background Initial melt migration begins when pressure and temperature conditions in a source rock exceed the solidus for that rock type, forming anatectic migmatites (Mehnert, 1968; Brown and McClelland, 2000). This can occur in response to crustal thickening, magma underplating, fluid influx, contact metamorphism, or decompression (e.g. Whitney, 1992; Brown, 1994; Obata et ah, 1994; Gerdes et ah, 2000); and results in the dehydration breakdown of micas and/or other hydrous minerals, and the melting of felsic minerals (Rutter and Wyllie, 1988; Brown and McClelland, 2000). Continued heating of these rocks allows the melt to segregate from the restite (immobile residue) through intergranular pathways (Mehnert, 1968) and eventually form stromatic (layered) migmatite (Johannes, 1983). Terminology given to migmatite layering is as follows: leucosome (felsic, mobile minerals), melanosome (mafic, immobile minerals), and mesosome (unmelted source rock) (Mehnert, 1968). Where this layering is undisturbed, the rock is known as a metatexite, and as instabilities form and melt begins to cut across layering, the melanosome and mesosome are broken apart leaving isolated patches of the source R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. rock surrounded by leucosome forming a so-called diatexite (Mehnert, 1968; Obata et ah, 1994). The degree to which segregation occurs depends on the continuity/persistence of the heating/melting source and dictates whether melt remains in the source area to be preserved as migmatite or ascends to upper levels in the crust forming injected migmatites (e.g. dikes and sills) or more voluminous intrusive bodies (e.g. plutons, batholiths) (Brown et ah, 1995; Brown and McClelland, 2000). Determining the dominant mechanism of magma ascent; e.g. diking (Clemens & Mawer, 1992; Petford et ah, 1993; Rubin, 1995; Clemens, 1998), diaperism (Van den Eeckhout et ah, 1986; Paterson and Vernon, 1995), or pervasive magma migration (Weinberg, 1999), for an area can offer insight into host rock rheology, magma viscosity, pressure and temperature conditions, strain gradients, and regional stress fields during ascent. At lower crustal levels (> 25 km) where host rock temperatures may approach the solidus, melt is present as films along grain boundaries, which coalesce to form interconnected pathways (Mehnert, 1968; Brown et ah, 1995). At this point, initial melt migration is driven by strain gradients (Brown et ah, 1995) and preexisting anisotropies such as foliation, bedding, metamorphic layering (Mehnert, 1968; Johannes, 1983; Brown, 1994; Kisters et ah, 1998), or axial planar surfaces (Hand and Dirks, 1992; Vernon & Paterson, 2001). The mechanism by which melt is driven out of the source area is a disputed topic (e.g. Barbey et ah, 1996; Arzi, 1978; Wickham, 1987; Paterson and Miller, 1998). Some authors argue that the onset of segregation of melt from the source rock is controlled by the volume R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. of accumulated melt: 10-30% (rheologically critical melt percentage RCMP; Arzi, 1978) to 40% (critical melt fraction CMF; Wickham, 1987). Sawyer (1993) suggests this number can be as low as 10% if deformation is involved. Still others argue that the interaction between host rock and magma rheology (Rubin, 1993; Paterson and Miller, 1998) as well as local and regional deformation control ascent of magma in the crust (Brown, 1994; Vingeresse, 1999). Regional Geologv Segments of the western North American margin have been dominated by convergent plate motion for over 300 Ma (Monger et al, 1982). In the northwestem Cordillera, SW-NE contraction, crustal thickening, and arc magmatism during suturing of the Insular superterrane (Fig. 1-1) to North America in Cretaceous to early Tertiary time resulted in the formation of the Coast Plutonic Complex (CPC), which extends > 1500 km from southern Alaska to Washington state (Monger et al., 1982; Umhoefer and Miller 1996 & Miller et al., 2000). According to McGroder (1991), the plate margin was dominated by normal convergence, shifting to oblique subduction in Late Cretaceous time, resulting in orogen parallel strike slip faulting (Irving et al., 1985; Umhoefer, 1987). Based on paleomagnetic data, some authors have proposed the Baja-British Columbia hypothesis which involved the > 2000 km sinistral translation of Baja California in the late Cretaceous to early Tertiary time (Chamberlain and Lambert, 1985; Irving et al., 1985; Umhoefer, 1987). My study will not address the validity of this hypothesis, however, it does introduce important R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. \ Rocky ^ Mountain, ^ Belt / Insular Belt Intermontane| Belt Nortti Pacific 300 km Figure 1-1. Map of the major terrane boundaries of Western North ,A.merica after Monger et al. (1982). Key features include the Coast Plutonic C om plex (CPC); the O m ineca Crystalline Belt (OCB): the Ross Lake Fault (RLF); the Straight Creek Fault (SCF). The North Cascades crystalline core is located between the RLF and the SCF. The area of figure 1-2 is represented by the shaded box. Dotted line represents the 0.706 Sr’’''/SC* line (west<0.706; east>0.706). information about the regional stress directions during metamorphism and magmatism in the CPC. At the southern tip of the CPC lies the Cascades core, which is comprised of several metamorphic terranes that were amalgamated by Late Cretaceous time when metamorphism and plutonism affected the entire core (Misch, 1966; Monger et al., 1982; McGroder, 1991). This is consistent with the timing of peak metamorphism in the CPC (Whitney, 1992; Whitney et al., 1999; Valley et al., 2003). Furthermore, during Early Tertiary time, dextral strike-slip faulting resulted in translation of segments of the CPC, which in turn accommodated the relative southward displacement of the Cascades core (Fig. 1-1) (Rubin 1990; Umhoefer and Miller, 1996). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Miocene plutons Chumstick formation E h j Holden unit sfjy Swakane gneiss I' ' Eocene plutons | i i i | | 91-93 Ma Plutons 65-73 Ma plutons 7 ^ Napeequa complex W enatchee Ridge orthogneiss 7771 Chiwaukum schist ihelan complex Ingalls complex 10 km figure f j North X W enatchee Block Che an Block Figure 1-2. Geologic Map of the North Cascades crystalline core. The Entiat fault divides the Cascades core into the Chelan block to the east and Wenatchee block to the west. Dinkelman decollement (DD), White River sear zone (WRSZ), W'indy Pass tlii'ust (WPT). Station numbers represent locations where detailed mapping was conducted in the Columbia River Domain; plates are indicated with asterisks. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. The Cascades core (Fig. 1-2) is the root of a Cretaceous to Paleogene magmatic arc that exposes rocks from deep (> 40 km) to shallow (10 km) crustal levels (McGroder, 1991; Whitney et al, 1999; Miller et al., 2000; and Valley et al, 2003). The dextral Straight Creek-Fraser River fault, which separated the Cascades core from the CPC, presently marks the westernmost extent of the core (McGroder, 1991; Miller & Paterson, 2001). To the northeast, the Cascades core is bounded by the Ross Lake fault zone, a Late Cretaceous to Paleogene structure recording early reverse and late normal slip from 65 to 45 Ma (Misch, 1966; Miller and Bowring, 1990; Baldwin et al, 1997). The Windy Pass thrust fault delineates the southwestern boundary of the Cascades core (Miller, 1985), while Late Tertiary Columbia River flood basalt flows cover the core to the southeast. Early to Mid-Tertiary slip on the Entiat fault divides the core into the Chelan block to the east and the Wenatchee block to the west (Tabor et al, 1989). Offset on this structure is unconstrained, although metamorphic gradients and pluton ages are distinctly different across this structure (Mattinson, 1972; Whitney et al, 1999; and Miller et al, 2000). Magmatism in the Cascades core occurred in three main phases: 96-90 Ma, 75-72 Ma, and 50-45 Ma (Tabor et al, 1987; Miller et al, 2000). The oldest intrusions (e.g. Mount Stuart batholith. Ten Peak pluton. Dirty Face pluton) are found in the Wenatchee block (Fig. 1-2), and were emplaced following the amalgamation of the Cascades core metamorphic terranes (McGroder, 1991; Paterson et al, 2004). It is argued by several authors that intruding magmatic bodies may have contributed to some of the crustal loading of the Cascades core from ca. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 90-75 Ma (Brown and Walker, 1993; Evans & Davidson, 1999). Conversely, Mcgroder (1991) and Whitney et al. (1999) have argued for a mid-Cretaceous crustal shortening event, which was responsible for crustal thickening. Below I summarize the metamorphic evidence for this event. Peak metamorphic conditions in the Chelan Block are generally higher than in the Wenatchee Block (Whitney et al., 1999; Valley et al., 2003; Evans and Davidson, 1999), and are consistent with thrusting and pure shear thickening rather than magma loading (Whitney et al., 1999). Using U-Pb zircon ages from several localities in the Chelan block, Mattinson (1972) suggested that regional metamorphism in the Chelan block occurred from 60-90 Ma. During this time period, peak metamorphic conditions were ca. 8-12 kbar and 600-800 °C (Whitney, et al., 1999; Valley et al., 2003). Work by Evans and Davidson (1999) in the Mount Stuart area of the Wenatchee block suggests that two regional metamorphic events, with peak metamorphic conditions of 6-9 kbar and 500-700 “C, occurred between ca. 125 Ma and ca. 88 Ma. By 60 exhumation was widespread across the Cascades core (Paterson et al., in 2004) resulting in the overprinting of retrograde metamorphism (Whitney et al, 1999). Exhumation of the Cascades core occurred at a rate of ~l-2mm/year (Fig. 1- 3, Paterson et al, 2004) by nearly isothermal decompression (Whitney et al, 1999; Valley et al, 2003; Stein & Stowell, 2002) during contraction and crustal thickening (93-73 Ma), dextral transgression (73-58 Ma; Umhoefer and Miller, 1996), and transtension (55-45 Ma) (Wemike & Getty, 1997). Within both structural blocks, the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 10 20 £ & 30 Q 40 50 ■ Upper Plate (Napeequa) O Lower Plate (Swakane) 1000-1200 pegmatite Mpa * # 68 Ma ® 1000-1200 Mpa * 40 50 60 70 80 90 100 Time (ma) Figure 1-3. Graph showing the possible exhumation curves for the Swakane Gneiss and the Napeequa Complex along the Dinkelman decollement. Zircon fission track ages (ft); biotite cooling ages (bt); hornblende cooling ages (hbl); Entiat Pluton (BP); Tenpeak Pluton (TP). (*)Sawyko, 1994; (#) Valley & Whitney 2003; ((§,) Mattinson, 1972 & Matzel et al, 2002). After Paterson et al., 2004. trends in biotite cooling ages indicate that the timing of exhumation was not constant across each block. In the Wenatchee Block, cooling ages are older in the south near the Mount Stuart batholith (88-90 Ma; Evans & Davidson, 1999) and younger to the north in the Tenpeak Domain (60-70 Ma; Miller et al., 2000). In the Chelan Block, biotite cooling ages across the Dinkehnan decollement, a mid-crustal detachment (see description below), are ca. 13 Ma older in the upper plate Napeequa Complex than the lower plate Swakane Gneiss (Fig 1-3) (Miller et al., 2000; Paterson et al., 2004). Swakane Gneiss and Napeequa Complex Although the Swakane Gneiss is the youngest metamorphic terrane in the Cascades core, this dominantly fme-grained quartz biotite gneiss, records some of the highest pressures in the core (Whitney et al., 1999; Valley et al., 2003). U-Pb ages from detrital zircons in the Swakane Gneiss indicate an age of ca. 73 Ma for R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. deposition of the Swakane protolith (Matzel et al., 2002). Following deposition, this unit was buried to 40 km presumably by thrust loading (McGroder, 1991; Sawyko, 1994; Whitney et al., 1999; Valley et al., 2003). Sawyko (1994) obtained pressures and temperatures of 10-12 kbar and 580-625 °C for the Swakane Gneiss in the Chelan block, and 8-9.7 kbar and 650-700 °C in the Wenatchee block. These P-T conditions have been confirmed by Whitney et al. (1999) and Valley et al. (2003). Burial to these depths occurred by 68 Ma, the age of the first intrusions of peraluminous dikes into the deepest sections of the Swakane Gneiss (Mattinson, 1972; Matzel et al., 2002). Matzel et al. (in review) have presented the hypothesis that rapid burial was accomplished by thrusting during fore-arc or back-arc closure, or underthrusting of accretionary sediments during subduction, similar to a model proposed by Jacobson et al. (1996) and Yin (2002) for the Pelona-Orcopia-Rand Schist of southern California. By 45 Ma the Swakane Gneiss was again exposed at the surface and shedding sediments into the adjacent Chumstick Basin (Laravie, 1976; Paterson et al., 2004). Present-day exposures of the Swakane Gneiss are found in both structural blocks of the Cascades core, adjacent to the Entiat fault (Fig. 1-2). In the Wenatchee block, it is located on the northeast limb of an upright regional synform (Miller et al., 2000). In this area, the dominant foliation dips moderately to steeply to the southwest and is overturned in places near the Entiat fault. In the Chelan block, foliation was folded into a broad antiform with an axial plane striking to the northwest-southeast (Tabor et al, 1987b). The fold limbs steepen to the southwest 10 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. where they are truncated by the Entiat fault, and to the north and northwest approaching the Dinkelman decollement (Plate 2b). In both blocks, the Napeequa complex structurally overlies the Swakane Gneiss along the Dinkelman decollement (Sawyko, 1994; Alsleben, 2000; Miller et al., 2000). It is composed primarily of metachert, marble, biotite-schist, amphibolite, and metaperidotite (Paterson et al., 2004), including sheets of orthogneiss, up to 700 m thick, which are potentially related to the Entiat Pluton, near the base of the exposed section in the Chelan Block. (Paterson et al., 2004). The upper section of the Napeequa complex is dominated by metasedimentary rocks while the base is predominantly amphibolite, metaperidotite, and orthogneiss, suggesting that the protolith was an accretionary wedge complex subjected to amphibolite grade metamorphism (Tabor et al., 1989; Paterson et al., 2004). There is uncertainty as to the depositional age of the Napeequa Complex, however, U-Pb and Th-Pb zircon ages indicate contact metamorphism from 88-91 Ma in the Wenatchee block and ca. 75-73 Ma in the Chelan block, therefore representing a minimum age for the Napeequa Complex of ca. 91 ma. (Tabor et al, 1987a; Paterson et al., 2004). The Dinkelman decollement is the main structure that juxtaposes the Swakane Gneiss (lower plate) and Napeequa complex (upper plate) (Fig. 1-2). While kinematic indicators in the Napeequa complex show both north-northeast, and rare west southwest directed sense of shear, the Swakane Gneiss shows only north and northwest directed sense of shear along this structure (Alsleben, 2000; Paterson et al., 2004). Therefore, the Dinkleman decollement is thought to be a mid-crustal 11 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. detachment with initial displacement to the WSW, followed by reactivation post-73 ma with top-to-the-north and northeast sense of shear (Alsleben, 2000; Paterson et ah, 2004). Total displacement along this structure is unknown due to the lack of a piercing point in either plate. However, thermobarometric data, and biotite cooling ages (Fig 1-3) indicate a 14-22 Ma disparity between the age of presently adjacent points in the upper and lower plates (Paterson et ah, 2004). The Napeequa complex preserves peak pressures of 10-11 kbar at ca. 90 Ma while the Swakane Gneiss was subjected to pressures of about 10-12 kbar at ca. 68 Ma (Whitney et ah, 1999; Valley et ah, 2003). Biotite and hornblende cooling ages and zircon fission-track ages indicate that ductile deformation ceased in the Napeequa complex at about 57 Ma and in the Swakane by 45 Ma (Miller et ah, 2000; Valley et ah, 2003; Paterson et ah, 2004). Location of Field Areas Three field areas (Columbia River domain. Tamarack Creek domain, Chiwawa Mountain domain; see Fig. 1-2) were chosen in the Swakane Gneiss of the Cascades core to be studied in detail. The structurally deepest sections of each area contain abundant fine-grained to pegmatitic peraluminous intrusions including migmatites, dikes, sills, sheets, and stocks (Boysun and Paterson, 2001). Previous work on these peraluminous intrusions indicates that they were intruded ca. 68 Ma (Mattinson, 1972; Matzel et ah, 2002) at > 30 km depth (Valley et ah, 2003; Miller et ah, 2000), but the generation of the migmatites, the source of melt for the 12 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. peraluminous intrusions, and their ascent was poorly understood. Therefore, in each area, 1:5000 to 1:20 scale mapping of foliations, lineations, kinematics, and intrusive contacts was conducted to examine the field relationships between host rocks and melts. Samples were collected for microstructural, petrographic, geochemical and geochronologic analyses, with the locations of each sample noted in bold on Plate 1, Figure 1-2, and Figure l-6b. Below I describe in detail each area and present all structural data acquired during this study. Columbia River domain The Columbia River domain is located in the Chelan block along a fold hinge perpendicular cut through a regional antiform (Fig. 1-2 & Fig. 1-4). Located in the core and northeast limb of this fold are fme-grained to pegmatitic dikes and sills. Along Highways 97 and 91 A, 120-500 m long road-cuts allowed for detailed structural mapping (Plates la-d). Tamarack Creek domain The Tamarack Creek domain is located in the Chelan block 15 km west of the Columbia River and dissects the northeast limb of the antiform referenced above (Fig. 1-2). Peraluminous intrusions in this area include cm-scale variably deformed dikes, 100 m thick sheets, and stocks, 50-100 meter in diameter (Plate 2; Fig. 1-5). Most of the mapping in this location was conducted at 1:5000 scale although some outcrops allowed for detailed measurement of intrusive contacts (1:20). 13 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CD ■D OQ. C o CDQ. ■DCD C/) W o'o o 3 CD OO■D cq' o o o " n c o CD ■D O Q. C a o o ■O o CDQ. ■DCD (/) (/) SW NE lO O O m Swakane Chumstick 500 m - niu^oFigure 1»4. This is a cross-section from A-A’ on figure 1-2 through the Swakane Gneiss in the Columbia River domain. After Miller et al., 2000. No vertical exasperation. SW NE Swakane 1600 m peraluminous sheet M il lOOOm N apeequa 600 m Figure 1-5. This is a cross-section from B-B' on figure 1-2 through the Swakane Gniess in the Tamarack Creek domain. The location of the Dinkelman decollement was taken from mapping by Paterson. All other contacts and foliation ai*e based the data compiled in Plate 2. No vertical exaggeration. Chiwawa Mountain domain The Chiwawa Mountain domain is located in the Wenatchee block adjacent to the Entiat Fault, south of the Cloudy Pass pluton (Fig. 1-6). In this location, the Swakane Gneiss is migmatitic, and the associated leucosomes are cross-cut by cmscale dikes. The focus of mapping in this area was to determine intrusive relationships between the leucosomes and the host rock which required mapping at high resolution (1:20) (Fig. 1-8; Fig. 1-9). 15 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 7 ) CD ■ D OQ. Co CDQ. ■DCD C/) W o'o o 3 CD OO ■a cq' o o o " n c 3"O CD ■D O Q . C a o 3 ■o o CDQ. ■DCD C/) C/) LEGEND Cloudy Pass Piuton C'i Red Mountain Sheet / ChiWswj Swakane Biotite Gneiss s!>a. migmatitic IS gneiss map area 1 kilometer Figure l-6a. Geologic map of the Cliiwawa Mountain domain with station numbers. Samples for microstructural aiilayses 7J CD ■ D OQ. C o CDQ. ■DCD (/)W o'o o 3 CD OO■D‘< c q ' o QCD O’ o CD ■D O Q . C a o Q ■o o CD Q . ■DCD C/) (/) LEGEND Cloudy Pass Piuton Red Mountain Sheet S : - ”' Mm . 4C Swakane Biotite Gneiss migmatitic gneiss mg map area 1 kilometer Figure l-6b. Geologic map of the Chlwawa Mountain domain. Cross-section C-C (figure 1-7) extends beyond the area of this map. Figure 1-2 shows the whole length of the cross-section. CD ■D OQ. C o CDQ. ■DCD C/) (/) OO■D c q ' O’ Q CD ■D O Q . C a o ■o o CD Q . ssw NNE 2500 2250 2000 1750 1500 migmatitic gneiss Red Mountain Sheet ' i (•-■1- ■ .-I --Hjag.a... Figure 1-7. This is a cross-section of C-C on figure I-6b through the Swakane Tcrraiie in the Chiwawa Mountain domain. Foliation data near the Red Mountain sheet is taken fi'om figure l-6b, with the remaining data compiled from Miller et ah, 2000. No vertical exaggeration. T3 CD (/)(/) subhonzontai V 45 cm N I ;j '.• '5 psrailsfl .................................................................................................................. 45 cm ... Figure 1-8. This series of figures shows the structural relationship between foliation and dikes in the Chiwawa xMountain domain (Station 21, Fig. l-6b). Foliation is represented by dashed lines on map A, and by (x) on stereonet B. O fine to coarsegrained qtz, plag, ksp, muse + bt; • pegmatitic qtz, plag, ksp ± muse; □ fine to coarse-grained qtz, plag, ksp, bt. A. Outcrop map. Foliation is parallel to the map plane below the dotted line. B. Stereonet plot of dikes and foliation. C. Threedimenstional diagram of dikes. Foliation is parallel to the lower outcrop surface. D. 19 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 7J CD ■ DOQ. Co CDQ. ■DCD (/)(/) CDOO■D CD ■DOQ. Cao ■oo CDQ. ■DCD C/) C/) N)O Figure 1-9. This series of figures shows the structural relationship between foliation and dikes in the Chiwawa Mountain domain (Station 25, Fig. 1- 6b). Foliation is represented by dashed lines on map A, and by (x) on stereonet C. O fine to coarse-grained qtz, plag, ksp, muse ± bt; • pegmatitic qtz, plag, ksp ± muse; □ fine to coarse-grained qtz, plag, ksp, bt. A, Outcrop map. B. Three-dimenstional diagram of dikes. C. Stereonet plot of dikes and foliation. CHAPTER II: ROCK DESCRIPTIONS AND GEOCHEMICAL ANALYSES Mroduction The Swakane Gneiss is composed of 90 % quartz biotite gneiss (herein called the Swakane biotite gneiss or SBG) and 10 % amphibolite schist + garnet, rare marble, and metapelite (Tabor et ah, 1987a; Sawyko, 1994; Alsleben, 2000). The amphibolite schist, marble, and metapelite are present in the SBG as discontinuous layers and pods (Sawyko, 1994; Alsleben, 2000). Waters (1932) was the first to suggest a sedimentary protolith for the SBG, and work done by Tabor et al. (1987a & b) and Matzel et al. (2002) concur with this interpretation. Matzel et al. (2002) have recognized zircons that, display oscillatory, ingeous zoning, and have a rounded morphology suggesting a detrital history. Conversely, Martinson (1972), Cater (1982), and Sawyko (1994) suggest a sequence of dacitic lava flows as the protolith based on the geochemical homogeneity of the SBG. Although geochemical data in this area is limited and cannot disprove a volcanic protolith, they argue that to produce a sedimentary sequence as voluminous as the Swakane Gneiss, multiple sediment sources are required which would result in a more geochemically heterogeneous rock (Cater, 1982; Sawyko, 1994). All workers who have examined the Swakane Gneiss generally agree that the garnet amphibolite schist was metamorphosed from a mafic source: basalt flows or dikes (Tabor et al., 1987; Sawyko, 1994; Alsleben, 2000). Rock types listed above have been intruded by leucogranite sheets (cm to 10s of meters thick) and stocks in the lowest exposed 21 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. structural levels. Below, I describe the different rock types that comprise the Swakane Gneiss, as well as the peraluminous intrusions Quartz biotite gneiss Quartz biotite gneiss (SBG) is composed of predominantly fine-grained quartz, biotite, plagioclase, K-feldspar, + muscovite + garnet with accessory sphene, clinozoesite, apatite, ilmenite and zircon. Quartz grains show undulose extinction, subgrain formation, and recrystallization, and where quartz ribbons are present, the m mm ■ * * ■ Figure 2-1. Cross-polarized light photomicrograph of sample TCI6. Sample was taken from the quartz biotite gneiss in the Tamarack Creek domain. Inclusions of quartz (qtz) and biotite (bt) in plagioclase (plag) grain. Section is perpendicular to foliation (S,) and parallel to the lineation (L„„). FOV=2.5 mm 22 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. degree of recovery is variable. Plagioclase and K-feldspar grains show minor undulose extinction, which is overprinted by brittle fracturing. Neocrystallized plagioclase contains abundant quartz and biotite inclusions (Fig. 2-1), as well as trace zircon, apatite, ilmenite, and graphite (Fig. 2-2). Biotite and muscovite were deformed by brittle fracture, slip along cleavage planes, and minor kinking. Metamorphic garnets have been overprinted by brittle fractures. Compositional layering (Sd) within the SBG is defined by variations in muscovite and biotite content, the presence and/or change in grain-size of garnet, or an increase in Kfeldspar and plagioclase grain-size. The differences in composition, while discontinuous on a map scale, are important for determining the generations of deformation affecting the Swakane Gneiss. Alslehen (2000) and Paterson et al. (2004) recognized an increase in average garnet grain-size (2-3 mm to ~ 10 mm) approaching the Dinkelman decollement (Plate 2). Garnets, 1-2 mm in diameter, are present elsewhere in the SBG, in discontinuous lenses, but without the pattem of increasing grain-size like garnets near the Dinkelman decollement. Sawyko (1994) recognized zoned igneous plagioclase grains > 5 mm diameter in the Tamarack Creek area, and Alsleben (2000) and Paterson et al. (2004) observed > 5 mm Kfeldspar grains with abundant quartz and biotite inclusions as well as opaque inclusion trails (Fig. 2-2). However, there is no laterally continuous pattem of these minerals in map view. 23 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Amphibolite schist The amphibolite schist is typically composed of hornblende + plagioclase + garnet with accessory sphene, zircon, apatite, and sericite. Alsleben (2000) identified quartz and biotite as inclusions in plagioclase. Grain sizes range from less than 1-2 mm for hornblende and plagioclase and up to 10 mm for garnet. Hornblende forms acicular grains deformed by minor twinning, slip along cleavage planes, and brittle fracture perpendicular to their long axes. Plagioclase shows undulose extinction overprinted by brittle deformation and alteration to sericite. Figure 2-2. Plain-polarized light photomicrograph of sample TCI6. Sample was taken from the quartz biotite gneiss in the Tamarack Creek domain. Section is perpendicular to foliation and lineation. Graphite/ilmenite folded inclusion trail (S,) in plagioclase (plag). FOV == 1.25 mm. 24 R eproduced with perm ission of the copyright owner. Further reproduction prohibited wr without perm ission. Figure 2-3. Plain-polarized light photomicrograph of sample CR143So. This sample was taken from the a garnet amphibolite layer in the Columbia River domain. Section is perpendicular to foliation and lineation. Garnet (gnt) porphyroblast rimmed with plagioclase (plag) in hornblende (hbl) matrix. FOV=2.5 mm Garnet is present as initially euhedral grains, which have been rimmed by plagioclase and overprinted by brittle fractures (Fig. 2-3). Stromatic migmatite Migmatite in the SBG and is divided into two parts: leucosome and melanosome (Fig. 2-4). The leucosomes are composed of quartz + plagioclase + Kfeldspar + muscovite and trace amounts of zircon and apatite. Quartz is equidimensional and shows undulose extinction and subgrain formation. Plagioclase grains are subhedral to anhedral and preserve growth twins and weak igneous 25 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. p Figure 2-4. Cross-polarized light photomicrograph of sample CV31 a. This sample was taken from the Chiwawa Mountain domain. Section is perpendicular to foliation and parallel to lineation. Partially melted SBG wdth equigranular quartz, plagioclase (plag), and K-feldspar (ksp) and disintegrated muscovite (muse). FOV = 2.5 mm zoning, and were overprinted by minor creep causing undulose extinction, and brittle fracture. Anhedral K-feldspar grains show undulose extinction and tartan twirming overprinted by brittle fractures. Melanosomes are a homogeneous mixture of equigranular quartz -+- plagioclase + biotite + muscovite -(- K-feldspar. Plagioclase and K-feldspar grains show undulose extinction, but the dominant microstructure is brittle fracture. Proximal to the leucosomes, biotite lacks strong grain preferred orientation (GPO) or lattice preferred orientation (LPO). With increasing distance from leucosomes, finer grained biotite with larger length to width ratios are common. Muscovite grains are partially replaced by biotite, or have been broken apart and no longer form coherent grains (Fig. 2-4). 26 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Intrusive rock Granitic to granodioritic intrusive rock in the Swakane Gneiss consists of fine-grained to pegmatitic quartz + plagioclase + K-feldspar + muscovite + biotite + gamet with trace amounts of sphene, zircon, and apatite. Intrusions are generally granitic to granodioritic in composition with variability in modal biotite and gamet. Quartz grains are intensely deformed, showing undulose extinction, and minor recovery and sub-grain development. Near intmsive margins, quartz ribbons are common (Fig. 2-5) and define the solid-state foliation and a mineral lineation. Plagioclase grains preserve growth twins and oscillatory zoning that have been overprinted by deformation twins and minor amounts of undulose extinction and V Figure 2-5. Cross-polarized light photomicrograph of sample CR143Ec. Sample was taken from a pegmatitic dike in the Columbia River domain. Section is perpendicular to foliation and parallel to lineation. Quartz ribbons (qtz) in a pegmatitic dike near intmsive margin. FOV = 1.25 mm 27 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. subgrain formation. K-feldspar grains show undulose extinction and subgrain formation near grain margins. Tartan twinning, myrmekite, and perthitic texture are common in K-feldspar (Fig. 2-6). Muscovite and biotite were deformed by cleavage parallel slip and brittle fracture, and have a strong grain preferred orientation that defines the solid-state foliation within the intrusions. Garnets are euhedral and generally < 1 mm in diameter. They occur only in the pegmatitic intrusions, and were deformed by brittle fracture. Despite compositional similarity, there is significant variation in the intensity of magmatic and solid-state foliations in the intrusive bodies. The nature of these a Figure 2-6. Cross-polarized light photomicrograph of sample CR143Ec. This sample was taken from a pegmatitic dike in the Columbia River domain. K-feldspar (ksp) grain from pegmatitic dike, vein set B, showing myrmekite, tartan twinning, and perthitic texture. Section is perpendicular to foliation and parallel to lineation. FOV = 1.25 28 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. differences will be addressed as each intrusive set is defined below, but in each case, the foliation is defined by muscovite, quartz, and biotite where present. In only two instances has a magmatic foliation in the intrusive rock been preserved. One has been identified in the Columbia River domain and is defined by biotite, which has been incompletely overprinted by the solid-state foliation. The other, located in the Tamarack Creek domain, is defmed by quartz and feldspar laths aligned parallel to the intrusive margins of a large leucogranite stock. Solid-state foliations are generally sub-parallel to the dominant foliation (St) in the Swakane Gneiss, but because intmsions are variably oriented, solid-state foliation is not always parallel to intrusive margins. In the following sections I begin to define the characteristics that differentiate each style of intrusion in the Swakane Gneiss. Intrusive stvles Leucogranite intrasions in the Swakane Gneiss are compositionally similar, but differ in intrusive style, grain-size, and mica content. The four identified intrusive styles are: 1) leucosome within migmatitic rocks (see above: Stromatic migmatite), 2) cm scale dikes and sills (collectively referred to as veins), 3) 100s m scale sheets, and 4) 100s m scale stocks (Boysun and Paterson, 2001). All intrusions were emplaced syn- or post-deformation in the Swakane Gneiss (see Chapter III). The majority of differences in these intrusive bodies are structural, but below I address the intrasive styles and subtle compositional and grain size variations that distinguish each set of intrusions. 29 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Dikes and sills In the Columbia River domain, four sets of leucogranitic veins have been recognized (A,B,C, and D) based on orientation (see Chapter III for structural data), variation in biotite content, and relative age with set A being the oldest and set D being the youngest (Plate 1). Veins of set A are fine-grained to pegmatitic and were intruded parallel to the dominant foliation in the Swakane Gneiss. Sets B and D are pegmatitic and were intruded at moderate angles (15°-40°) to the dominant foliation. Set C veins are fine grained and are the only veins in the Columbia River domain that contain biotite. They were intruded parallel to the dominant foliation and have both a magmatic and solid-state foliation. The full succession described above is only recognized in the Columbia River domain, however, a similar structural pattem is also observed in the Tamarack Creek domain and is further explained in Chapter III. Two generations of dikes in the Tamarack Creek domain can be distinguished by cross-cutting relationships and intensity of deformation. The oldest and most deformed set commonly exhibits compositional zoning (Fig. 2-7). They were injected at an angle to the dominant foliation, which allowed for folding during the top-to-north deformation described in Chapter I. The youngest set of dikes, which consistently crosscuts the older, more deformed dikes, was intruded at shallow angles to the dominant foliation. Although they do have a well-developed solid-state foliation, they remain relatively planar sheets. This simple crosscutting pattem has 30 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 2-7. This photograph shows a zoned granitic dike in fme-grained quartz biotite gneiss from the Tamarack Creek domain, which has been crosscut by less defonned granitic dike. The composition of both dikes is similar (quartz, plagioclase, K-feldspar ± muscovite), with zoning defmed by grain size. The absolute age of each dike is unknown, however, the more intensely defonned dikes are typically cross-cut by less deformed dikes of similar composition. Axial planes of folds are parallel to S,. Width ofphoto is 70 cm. been identified in Tamarack Creek and along the Columbia River, but is not present in the Chiwawa Mountain domain, where no discemable pattem has been identified. Leucogranite intmsions in the Chiwawa Mountain domain have more variation in modal biotite content and no consistent crosscutting relationships; fewer than 5% of these veins were intmded parallel to the dominant foliation (e.g. Figs. 1- 8, 1-9) (Boysun and Paterson, 2002). Solid-state foliation intensity in the Chiwawa Mountain dikes is dependent on the amount of biotite and muscovite present, although the extent of this variation has not been quantified. Finer-grained, micarich dikes have a stronger fabric subparallel to the dike margin. Pegmatitic dikes 31 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 2-8. This photograph shows post injection shear in the quartz biotite gneiss host rock, parallel to a coarse-grained leucogranite dike in the Chiwawa Mountain domain. See figure 1-8 for structural data associated with these dikes and the adjacent foliation. Width of photo is 165 cm. show intense internal deformation, but internal fabrics appear weaker than finergrained dikes due to lack of mica minerals. Although the Chiwawa Mountain dikes have developed a solid-state foliation subparallel to the foliation in the host rock, some ductile deformation has been concentrated along intrusive margins, but does not extend into the dikes (e.g. Fig. 2-8). Brittle deformation overprints all of these ductile structures. Sheets Sheets of two-mica leucogranite in the Tamarack Creek domain are present as shallowly dipping bodies that were intruded subparallel to the dominant foliation. 32 R eproduced with perm ission of the copyright ow ner. Further reproduction prohibited without perm ission. Although all sheets are compositionally similar, variations in biotite and muscovite content have been identified which distinguish four phases/pulses. Figure 2-9 shows the distribution of each sheet, as well as the grain size variability. Where these sheets coalesce on the southeast side of Tamarack Creek (Plate 2), there is a weak grain size zoning that crosses compositional boundaries between the sheets. Near the center of the cluster of sheets (e.g. Fig. 1-5 & Fig. 2-9), average quartz and feldspar grain size is 2-3 mm, and as the margin of the cluster is approached, the quartz and plagioclase grain sizes decrease to less than 1 mm. The foliation in the sheets is solid-state, defmed by biotite and muscovite grains, and quartz ribbons. Foliation intensity increases with increasing mica content and is stronger with proximity to the host/intrusive contacts. Foliation crosses compositional, grain-size, and host/intrusive boundaries, and is continuous with the dominant host rock foliation (St) indicating that it formed by the same deformation responsible for the host foliation. Stocks The largest stock in Tamarack Creek is -50 meters wide and sharply crosscuts the leucogranite dikes and host foliation at high angles (Fig. 2-10). Stocks of muscovite leucogranite are fine grained, compositionally homogeneous, and have euhedral feldspar grains. These characteristics are compatible with ascent as one batch of magma and rapid cooling before zoning could occur. Muscovite, the long axes of euhedral feldspar grains, and elongate quartz grains define a magmatic R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 1 ^ — . >Trf|l * V? • ' • ' ' ' -. - '-'^ ■ ■ ‘••'■V -•;>. * ■ -'4- • ., i & m W ' ' ■ ■■■:^\".s ; . t ; ' / J : ; - ' - . T equigranular equigranular quartz, quartz, plagioclase, Kplagiodase, K- feldspar, biotite, with feldspar, 3-5mm 5-10 cm long biotite diam eter biotite enclaves. equigranular quartz, plagioclase, Kfeldspar, biotite equigranular quartz, plagioclase, K-feldspar "Twr V , i i— ■ , , - ^ ...w # | a B j ,.f / ■ • : - ■ Figure 2-9. Photographs of two-mica granodiorite sheets in the Tamarack Creek domain showing four phases of intrusion. The composition of each phase is similar, thus individual pulses are defmed by variations in mica content. Foliation of the intruded quartz biotite gneiss host rock is represented by the dotted line in (A). This series of sheets intruded subparallel to the host rock foliation (See also fig. 1-5.) Scale bar in both photographs is ca. 25 m. 34 R eproduced with perm ission of the copyright ow ner. Further reproduction prohibited without perm ission. Figure 2-10, This photograph shows a muscovite leucograiiite stock intruding fme-grained quartz biotite gneiss in the Tamarack Creek domain. The stock does not deflect foliation as it cross-cuts S, and the preexisting leucogranite dikes, and the magmatic foliation (S„,) parallels the stock margins. Width of stock is ca. 50 m. foliation. This foliation is parallel the margins of the stock and dips shallowly near the roof, steepening to sub-vertical at the walls. Host foliation does not extend into the stocks (see Fig 2-10), and there is no recognizable deformation related to emplacement of the stocks in the adjacent Swakane Gneiss. Geochemistry Geochemical analysis conducted on the Swakane Gneiss and its intrusive rocks serves to supplement structural and petrologic studies. Rock samples were prepared and analyzed by SGS XRAL Laboratories. Samples were dried, crushed to 2mm, riffle to a maximum split of 250g and mill in chrome steel equipment to 75p. 35 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. LiBOi flux was added to each sample then fused in a graphite crucible and dissolved in acid. Prepared samples were analyzed on and ICP-AES, model ArRL 3560 for trace and rare earth elements. Of the five samples analyzed, two were taken from the Tamarack Creek domain (TC26, SBG; TCPAb, granodiorite) and three from the Columbia River domain (CR143So, gamet amphibolite schist; CR142Sm, granite; CR140M, granodiorite); locations are provided on Plate la & d and Plate 2b. Table 2-1 contains the results from geochemical analyses in ppm, and normalized multi-element plots of geochemical data are displayed in Figure 2-11 using the following normalizing values; REE vs. Chondrite values determined by Evansen (1978); and trace elements vs. MORB values of Pearce (1983) and Bevins et al. (1984). Because disagreement remains as to sedimentary versus volcanic protolith for the SBG, I have also included trace element and REE values for sample TC26 (SBG) normalized to standard sedimentary compositions (Taylor and McLennon, 1981). In the following section I provide observations of the geochemical data, which will be further examined in the Chapter IV discussion of partial melting. Rare earth elements All normalized values of the samples analyzed indicate light rare-earth element (TREE) enrichment relative to heavy rare earth elements (HREE), with the intrusive samples showing a greater degree of fractionation between TREE and HREE (Fig. 2-1 la). Normalized to average sedimentary values, sample TC26 shows 36 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Table 2-1; Geochemical Data TC26* biotite-gneiss CR143SO * amphiboliteschist CR142sm # granite CR140m # granodiorite Tcpab+ granodiorite Ba 1840 122 668 338 1080 Ce 9.9 21.6 34.8 20.8 13.4 Co 4.2 39.8 6.9 1.5 2.9 Cs 2.7 1.2 2.7 0.2 1.1 Cu 11 39 11 11 10 Dy 0.61 4.72 2.08 0.49 1.08 Er 0.29 2.71 1.17 0.23 0.51 Eu 0.49 1.37 0.83 0.60 0.60 Ga 19 17 15 14 16 Gd 1.01 4.67 2.67 1.52 1.66 Hf 1 2 3 2 1 Ho 0.11 0.98 0.40 0.08 0.18 La 5.1 9.4 16.4 10.3 7.7 Lu <0.05 0.4 0.2 <0.05 0.1 Nb 7 7 6 2 4 Nd 4.7 14.6 14.8 10.5 6.4 Ni 14 126 20 7 10 Pb 35 7 16 10 27 Pr 1.2 3.0 3.7 2.6 1.7 Rb 89.6 33.5 65.4 10.7 65.8 Sm 1.2 4.0 2.8 2.1 1.6 Sr 240 240 353 590 325 Ta 0.5 0.5 <0.5 <0.5 <0.5 Tb 0.1 0.8 0.4 0.2 0.2 Th 1.7 1.2 5.5 2.4 1.6 T1 0.5 <0.5 <0.5 <0.5 <0.5 Tm 0.05 0.39 0.17 <0.05 0.07 U 1.09 1.18 1.46 0.78 1.40 V 43 308 55 10 29 Y 2.8 24.6 10.6 2.3 5.1 Yb 0.4 2.4 1.1 0.2 0.5 Zn 94 125 61 18 38 Zr 31.8 69.3 99.6 60.4 37.9 * Swakane Terrane host rock # peraluminous dike + peraluminous sheet 37 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. A. C R 143 SO TC26 s e d norm CR140M B. 1000 ■t^TC26 -B -C R 1 4 3 SO ^ C R 1 4 2 SM -^CR140M ■ m ~ TCPAB -je -T C 2 6 s e d norm 100 0.01 Rb Ba Nb Ce Sm Figure 2-11. These plots show geochemical data from selected samples in the Swakane Gneiss. Open symbols represent host rock (TC26 - quartz biotite gneiss; CRl43So - amphibolite schist); filled symbols represent intrusive rock (CR142SM - two-mica leucogranite; CR140M - muscovite pegmatite; TCPAB - two-mica leucogranodiorite). Data is provided in table 2-1. A. Rare earth element data normalized to chondrite (Evansen, 1978). B. Trace element data normalized to MORE (Pearce, 1983; Bevins et al., 1984). *In both plots, Sample TC26 is also normalized to average sedimentary values (Taylor & McLennan, 1981). 38 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. no enrichment, and has a positive Eu anomaly. Samples CR142Sm and CR140m have weak positive Eu anomalies, while TCPAb has no Eu anomaly. Trace Elements Trace element data from the five Swakane Gneiss samples typically show enrichment of incompatible elements (Rb, Ba, Th), which are preferentially concentrated in feldspars during melting. Samples CR142Sm and CR140M show the highest degree of incompatible element enrichment versus compatible element enrichment (Fig. 2-1 lb). A similar trend is observed for sample TCPAb, although there is less overall enrichment of incompatible elements. Sample TC26, when normalized to average upper crustal values (Taylor and McLennon, 1981), has no significant enrichment or depletion of compatible versus incompatible elements, and plots close to the average crustal values. Summarv The Swakane Gneiss is composed of 90% quartz biotite gneiss and 10% amphibolite schist, marble, and kyanite metapelite (Tabor et al., 1987a; Alsleben, 2000), which have been intruded by two-mica leucogranite sheets and stocks in the structurally lowest sections of the Swakane Gneiss. The intrusions are thought to be locally-derived, and therefore require thermobarometric conditions adequate to cause partial melting in the Swakane Gneiss. Direct evidence for partial melting is in the Chiwawa Mountain domain where the presence of leucosomes and adjacent 39 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. melanosomes (Fig 2-4), collectively referred to as stromatic migmatite, indicate in situ processes. Zoned igneous plagioclase grains, and books of igneous biotite suggest the presence of melt. Similarities in trace element and REE values, and patterns of enrichment versus depletion, used in combination with structural data presented in the following chapter, suggest that the SBG was partially melted to produce the peraluminous melts. 40 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CHAPTER I I I : STRUCTURAL ANALYSIS Introduction This chapter summarizes the structural data obtained over 11 weeks during two summers of fieldwork. Station locations are provided on Figures 1-2 and 1-6 and Plate 2, and structural measurements can be found in Appendix 1. All measurements of foliation, axial planes, and dike orientations are given as strike and dip using the right-hand-rule; lineations and fold axes are listed as plunge and trend. Swakane Gneiss Fabric Two foliations, and two mineral lineations have been identified in the Swakane Gneiss. The older foliation (herein called Si) is preserved as porphyroblast inclusion trails, and rootless isoclinal fold hinges (see Fig. 2-2) (Alsleben, 2000; Paterson et al., 2004). Folding of Si and compositional layering (Sd) during the Late Cretacteous to Early Tertiary exhumation of the Cascades core resulted in transposition of this fabric and the formation of a second foliation (herein called St). St is the dominant foliation observed in the Swakane Gneiss and is defined by aligned biotite, muscovite, quartz, and feldspar grains, all of which were recrystallized and rotated during top-to-north shear. Two mineral lineations are found in the plane of St: a pervasive high temperature mineral lineation, and a low temperature mineral lineation. The more pervasive lineation is medium to high temperature and is defined by elongate quartz grains and aligned biotite grains ( L m i ) . The trend of Lmi is generally north-south near the antiformal hinge, and has been 4 1 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. rotated clockwise approaching the Dinkelman decollement in the Chelan block (15 °-60 Alsleben, 2000; Paterson et ah, 2004). In the Wenatchee Block exposure, Lmi plunges shallowly to the east-southeast/west-northwest. The low-temperature mineral lineation (Lma) is defined by biotite and chlorite, and generally trends 10° to 15° counterclockwise from Lmi (Alsleben, 2000; Paterson et al., 2004). Ductile shear along the Dinkelman decollement was responsible for the formation of the dominant foliation ( S t ) and lineation ( L m i ) , and also produced the kinematic indicators described below. Kinematic indicators display top-to-north shear sense in the Swakane Gneiss, and rotate to top-to-northeast approaching the Dinkelman decollement in the Chelan Block (Alsleben, 2000; Paterson et al., 2004). Shear sense indicators include: S-C and C-C fabrics, asymmetric prophyroblast tails and microfolds, and mica fish, which are observed at the microscopic and mesoscopic scales parallel to the quartz mineral lineation and perpendicular to St (Alsleben 2000, Paterson et al., 2004). Few kinematic indicators with top-to-west shear sense have been identified in the lowermost sections of the Napeequa Complex, but none have been identified in the Swakane Gneiss (Alsleben 2000, Paterson et al, 2004). The structures I have described above are present throughout each exposure of the Swakane Gneiss, but are more pervasive (foliation and lineations) and consistent (kinematic indicators) in the Chelan Block than in the Wenatchee Block for reasons that will be addressed below. 42 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Foliation and Lineations Chelan Block In the Chelan Block, the Swakane Gneiss is exposed in an upright to gently plunging regional antiform (folded St) with a fold axis trending northwest-southeast (Fig. 1-2). According to Alsleben (2000), the fold axis has a plunge and trend of 07296°, and is located near Swakane Canyon (Tabor et al., 1987b). Based on the foliation measurements I have taken in the Columbia River domain, the trend of the axial plane is closer to -315° (e.g. Fig. 3-2 & Fig. 3-3). On the southwest limb, the average strike and dip of St is 160°/16° (Alsleben, 2000). Approaching the hinge of the antiform, near Swakane Canyon, the strike and dip of St changes to 048°/08° (Fig. 3-la) on the east side of the Columbia River, and 037°/11° (Fig. 3-lb) on the west side. The average strike of St on the northeast limb is 325° with the dip ranging from 32° - 45° approaching the Dinkelman Decollement (Fig. 3-2). In Tamarack Creek, which is located on the northeast limb, the average strike and dip of St is 344°/28°, and shallows to 357°/16° (Fig. 3-3) in the southwest approaching the antiformal hinge. The moderate- to high-temperature mineral lineation (L m i), has a north-south trend in all areas of the Swakane Gneiss except near the Dinkelman decollement where the trend rotates by 15° - 60° from north to northwest (Alsleben 2000; Paterson et al, 2004). The average plunge and trend of Lmi along the Columbia River is 08°/169° (Fig. 3-4) in the hinge region and 16°/355° (Fig. 3-5) on the northeast limb. In the Tamarack Creek area, the attitude of Lmi is more scattered 43 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Total Data : 23 Figure 3-la. Stereonet plot of foliation in the hinge of the regional antifonn in the Chelan Block. Measurements were taken in the quartz biotite gneiss along the west side of the Columbia River. Statistical average = 048708°. Total Data ; 17 Figure 3-1 b, Stereonet plot of foliation in the hinge of the regional antiform in the Chelan Block. Measurements were taken in the quartz biotite gneiss along the east side of the Columbia River. Statistical average = 037711°. 44 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Total Data : 196 Figure 3-2. Stereonet plot of foliation on the northeast limb of the regional antiform in the Chelan Block. Measurements were taken in the quartz biotite gneiss and amphibolite schist from the Columbia River. Statistical average = 316728". Total Data : 127 Figure 3-3. Stereonet plot of foliation on the northeast limb of the regional antiform in the Chelan Block. Measurements were taken in the quartz biotite gneiss from the Tamarack Creek domain. Statistical average = 334‘728". 45 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Total Data : 140 Figure 3-4. Stereonet plot of lineation on the northeast limb of the regional antifonn in the Chelan Block. Measurements were taken in the quartz biotite gniess and amphibolite schist from the Columbia River domain . Statistical average = 1673 5 5“. Total Data : 39 Figure 3-5. Stereonet plot o f lineation in the hinge of the regional antiform in the Chelan Block. Measurements were taken in the quartz biotite gneiss from the Columbia River domain. Statistical average = 0871697 46 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Total Data ; 58 Figure 3-6. Stereonet plot of lineation on the northeast limb of the regional antiform in the Chelan Block. Measurements were taken in the quartz biotite gneiss from the Tamarack Creek domain. Statistical average = 097146". due to the variability in St near intrusive sheets. The average plunge and trend of L ml is 09°/146 °, with scatter along the plane of foliation (Fig. 3-6). Wenatchee Block Foliations and lineations in the Chiwawa Mountain domain have been obscured in places due to minor faulting and fracturing during the emplacement of Miocene plutons (Cater, 1982). Foliation in this domain generally dips moderately to steeply to the southwest on the northeast limb of an upright regional synform (Fig. l-6b) (Tabor et al. 1987b). In the structurally highest levels, St is pervasive, and dips moderately to the southwest (155°/58° to 158°/35°) (Fig. 3-7a & 3-7b). Segregation of leucosome and melanosome in the SBG increases with depth to form meter-scale. 47 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Total Data : 51 Total D ata: 19 Figure 3-7. Stereonet piot of foliation in the Wenatchee Block. Measurements were taken in the quartz biotite gneiss from the Chiwawa Mountain domain. A. Foliation west of the Red Mountain sheet (Fig. 1 -6). Statistical average = 155758“. B. Foliation east ofthe Red Mountain sheet. Statistical average = 1587357 48 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. iivriiiV;^: iOlJiiiO ■ / ---------- -V ;ein-.oson'.-rf M>e;f;''.'.;fiOine m - i « pi .. F ig u re 3-8. Photograph o f a leucogranite dike cross-cutting a zone o f partially melted quartz biotite gneiss in the Chiwaw a M ountain domain. The dike is optically continuous with the stromatic m igm atites. Photo is 45 cm across. melt-rich layers that have been internally deformed (Fig 3-8; see also Fig. 2-4). Isoclinal folds within these layers are common, with axial planes are parallel to St. Lmi is the only mineral lineation present in the Wenatchee Block exposure. It is less pervasive than in the Chelan block, and generally shallow, trending east-southeast (127172°; Fig. 3-9). Intrusive Rock Fabric and Orientation Intrusive bodies in the Swakane Gneiss show variable amounts of internal fabric development and external deformation (i.e. folding and boudinage), and are dominated by solid-state fabrics. The exception to this observation is in the Tamarack Creek domain where a stock intruded at a high angle (> 70°) to the 49 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total D a ta : 14 Figure 3-9. Stereonet piot of lineations in the Wenatchee Block exposure of the Swakane Ten'ane. Measurements were taken in the quartz biotite gneiss from the Chiwawa Mountain domain. Statistical average = 127172“. dominant foliation and contains one magmatic foliation parallel to the intrusive margins (see Fig. 2-12). Dikes in the Swakane Gneiss are dominated by solid-state deformation with foliations developed subparallel to intrusive margins and/or St, depending on the orientation of the dike with respect to the host rock foliation. Although solid-state foliation intensity has not been quantified, it typically increases with decreasing grain size and increasing muscovite and biotite content. Columbia River Domain As presented in Chapter II, there are four sets of leucogranite intrusions in the Columbia River domain (Plate 1), and while compositionally similar, their orientations and cross-cutting relationships are distinct (Boysun and Paterson, 2001). Veins from set A along the Columbia River section have an average strike and dip of 50 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. 282730 ° (Fig. 3-10) with the majority of these veins injected subparallel to St. The solid-state foliation of these veins, which is defined by muscovite and quartz, is generally parallel to intrusive margins and therefore St. Any magmatic fabric that was present at the time of cooling was completely overprinted by subsolidus ductile and brittle deformation. Sets B and D are identical in composition and average attitude, and are distinguished only by cross-cutting relationships. The orientation of individual dikes in these two sets is variable. As seen in Plate 1, the orientation of each dike and its thickness changes over short distances resulting in scatter of measurements. Average strike and dip of set B is 206716° (Fig. 3-11); set D is 293°/34° (Fig. 3-12). Measurements from station 141 (Plate lb; Fig. 1-2) were excluded because ofthe open folding of the Swakane Gneiss, but are included in Appendix 1. The dominantly pegmatitic nature of these dikes and the lack abundant micas make internal foliations weak and difficult to measure accurately. Where the injected material is finer grained and muscovite or biotite rich, foliations are random. The only consistent fabric observed in these dikes is found near the intrusive contacts where quartz ribbons define a weak, solid-state foliation that is parallel to dike margins (Fig. 2-5). Veins from set C are typically parallel to St and contain two fabrics: solidstate and magmatic (Fig 3-13). The average strike and dip of set C is 209723° (Fig. 3-14). Solid-state foliation is parallel to vein margins and therefore St, and is defined by biotite grains and quartz ribbons. The magmatic fabric is formed by a second 51 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total D ata: 86 Figure 3-10. Stereonet plot of the average orientation of leucogranite vein set A in the Columbia River domain. Statistical average = 280730°. Total D ata; 31 Figure 3-11. Stereonet plot of the average orientation of leucogranite vein set B in the Columbia River domain. Statistical average = 206716°. 52 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total Data : 40 Figure 3-12. Stereonet plot of the average orientation of leucogranite vein set D in the Columbia River domain. Statistical average = 293734". population of biotite grains and to a lesser extent by K-feldspar crystals. Igneous microstructures, such as growth twins and oscillatory zoning, have been overprinted, but the orientation of the grains has been preserved. Grains form an arcuate pattern consistent with folding during magma flow (e.g. Fig. 3-13). The axes of these folds are parallel to the high-temperature mineral lineation in the Swakane Gneiss (167355°; Fig 3-4) and the axial planes are parallel to St (316728°; Fig 3-2). Tamarack Creek Domain Intrusions in the Tamarack Creek domain can be divided into three groups by relative age. The oldest dikes are zoned and intensely deformed, (e.g. folding and boudinage; see Fig. 2-7). The average initial orientation of these dikes is unknown 53 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. m m Figure 3-13. A. Schematic diagram of biotite leucogranite veins of set C showing magmatic and solid-state foliations. Black and gray ellipses represent biotite grains defining the solid-state foliation. Dashed lines represent the magmatic foliation. B. Photomicrograph is from Sample CR142Sm in cross-polarized light, mag = magmatic foliation; ss = solidstate foliation. Field of view is 2.25mm. 54 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total Data : 19 Figure 3-14. Stereonet plot of the average orientation of leucogranite vein set C in the Columbia River domain. Statistical average = 209723“. because continued deformation has transposed their original orientation and most of the foliation that existed at the time of injection. Igneous microstructures have been overprinted and intravein compositional contacts are sharp, which may be relict from multiple periods of injection predating isoclinal folding (Fig. 3-15 and 3-16). Solidstate foliation in these dikes is parallel to and continuous with St, regardless of dike orientation. Isoclinal folding of entire veins is common (Fig 3-15), and axial planes are subparallel to St. The second set of dikes shows less extemal deformation than the first and preserves only one period of injection per dike. The average orientation of these dikes is 341730° (Fig. 3-17), which is similar to the average orientation of St. However, field relationships clearly indicate that these dikes are not parallel to St (Fig. 3-18). Internal foliation is defined by quartz ribbons and muscovite where 55 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Figure 3-15. This photograph shows the isoclinal folding of aperaluminous vein typical in the Tamarack Creek domain. The axial plane is parallel to the dominant foliation (St) in the biotite gneiss (sbg). The vein is composed of quartz, plagioclase, K-feldspar, and muscovite; layering is defined by grainsize. Width of photo is 90 cm. present, and is parallel and continuous with St (Fig. 3-19). Foliation in the sheets and stocks is less intense than in the dikes and sills. The peraluminous sheets were intruded subparallel to St (Fig. 1-5), and internal solid-state foliation, defined by mica grains and quartz ribbons, is continuous with StAverage strike and dip of foliation in the sheets is 358716° (Fig. 3-20). Peraluminous stocks in the Tamarack Creek domain (Fig. 2-10) were intruded at a high angles to St. The dominant foliation in these stock is magmatic, defined by euhedral to subhedral feldspar grains, and is parallel to the margins of the stock. Near the roof the strike and dip of foliation is 000724° and at the northern contact it steepens to 076778°. 56 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Figure 3-16. Photograph of zoned dike in the Tamarack Creek domain. The host rock is composed of quartz biotite gneiss (sbg), and the dike contains pegmatitic quartz, plagioclase and K-feldspar at the margins, with a muscovite aplite core. In this case, zoning was caused by reinjection of the pegmatite dike rather than gradual cooling, which would result in a gradational contact. Width of photo is 95 cm. Total D ata; 23 Figure 3-17. Stereonet plot of the average leucogranite dike orientation in the Tamarack Creek domain. Statistical average=341730". 57 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Figure 3-18. This photograph shows the typical conjugate pattern of leucogranite dikes intruding quartz biotite gneiss in the Tamarack Creek domain. Foliation is represented by dashed lines. Northwest is to the left. Width of photo is 4.5 meters. riT . ■ ■ Figure 3-19. This is a close-up photograph of the area shown in figure 3-18. Pictured are two conjugate granitic dikes intruding the quartz biotite gneiss (sbg) in the Tamarack Creek domain. Foliation (S,) is continuous with and parallel to foliation in the dikes regardless of intrusion angle. Width of photo is 75 cm. 58 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total D ata: 45 Figure 3-20. Stereonet plot of foliation in the leucogranite sheets (see Plate 2). Measurements were taken in the Tamarack Creek domain. Statistical average = 358716". Chiwawa Mountain Domain The dikes that intrude the Chiwawa Mountain domain clearly crosscut the former partial melt. Margins are generally sharp, with no mingling between dike and host rock. In few cases, distributed slip with inconsistent kinematics has occurred along dike margins, and is confined to the host rock (Fig. 2-8). The orientation of dikes that have intruded this section of the Swakane Gneiss have no pattern, either by composition or relative cross-cutting relationships (Fig. 3-21). Therefore, the conclusion that can be drawn from the structural data is that the majority of dikes cut across the foliation at acute to high angles. 59 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. Total D ata: 141 Figure 3-21. Stereonet plot ofthe average orientation of leucogranite dikes in the Chiwawa Mountain domain. Summary The dominant foliation and compositional layering in the Swakane Gneiss is folded into a broad upright antiform in the Chelan block with an axial plane striking to the northwest. In the Wenatchee block, the foliation and compositional layering dip moderately to the southwest. Leucogranite dikes and sills intrude the Swakane gneiss in both structural blocks. Based on the calculated angle between foliation and dike or sill orientation from the three field areas, I have determined that 25 % of all leucogranite intrusions are sills that were intruded parallel to the dominant foliation (Fig. 3-22 a-c). In the Columbia River and Tamarack Creek domains, the percentage is approximately 30 % while in the Chiwawa Mountain domain, less than 5 % of all leucogranite intrusions are parallel to foliation. Statistically, the leucogranite intrusions in the Tamarack Creek and Columbia River domains plot as a conjugate 60 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. CD ■D OQ. C o CDQ. ■DCD C/) (/) OO■ D cq' CD ■D OQ. C a o ■o o CDQ. ■DCD C/) C/) A. Columbia River 30 25 10 0-5 6- 11- 16- 21- 26- 31- 36- 41- 46- 51- 56- 61- 66- 71- 76- 81- 86- 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 89 B. 7 6 5 ■ I ■ P ' 2 1 0 Tamarack Creek )-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 angle c. Chiwawa Mountain 0-5 6- 11- 16- 21- 26- 31- 36- 41- 46- 51- 56- 61- 66- 71- 76- 81- 86- 10 15 20 25 30 35 40 46 50 55 60 65 70 75 80 85 89 angle Figure 3-22. These histograms show the calculated acute angle between dominant foliation (St) and average granitic dike orientation. Measurements from 288 dikes in the Columbia River domain (A), the Tamarack Creek domain (B), and the Chiwawa Mountain domain (C) Total Data : 176 Figure 3-23. Stereonet plot of all leucogranite dike orientations in the Colmnbia River domain. Filled circles = set A; open squares = set B; open circles = set C; filled squares = set D. pattern (Figs. 3-17; 3-23), with an extrapolated maximum principle stress direction generally trending SW-NE when foliation is restored to subhorizontal (Boysun and Paterson, 2003). This orientation is subparallel with the maximum principle stress that was required to form the folds observed elsewhere in the Cascades core (see Fig. 1-2). 62 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. CHAPTER IV; MELTING AND MELT INJECTION Introduction The Swakane Gneiss has been described as enigmatic because it contains no arc related magmatic bodies (Tabor et al., 1987a; Sawyko 1994; Alsleben, 2000; Paterson et al., 2004) and has a Sr isotopic ratio greater than 0.706 yet lies well outboard of the 0.706 line (Mattinson, 1972) (see Fig. 1-1 & 1-2). Recent work by Matzel et al. (2002) has revealed that the Swakane gneiss is relatively young (<72 Ma) compared to other metamorpbic terranes in the Cascades core, and work conducted by Whitney et al. (1999) and Valley et al. (2003) shows that this unit records some of the highest temperatures and pressures (650-700 °C, 10-12 kbar) of any unit in the Cascades core. Several authors have sought to address these atypical aspects of the Swakane Gneiss in order to understand the deposition, burial (Mattinson, 1972; Tabor et al., 1987a; Sawyko, 1994; Matzel et al., in review) and exhumation of the (Whitney et al., 1999; Paterson et al., 2004; Valley et al, 2003) Cascades core during Cretaceous to Tertiary time. However, there are still unanswered questions regarding melting and melt injection in the Swakane Gneiss: 1) Metamorpbic data suggest subsolidus conditions yet evidence of partial melting is preserved as stromatic migmatites and locally derived, leucogranite dikes. 2) Pervasive deformation formed a strong anisotropy in the Swakane Gneiss; however, with sufficient melt volumes, anisotropy had only a small effect on the overall ascent of melt. In order to address these issues, 1 63 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. summarize my evidence for partial melting of the Swakane Gneiss, the possible causes of melting, and the mechanical controls on melt injection. Partial Melting in the Swakane Gneiss Direct evidence for partial melting is present in the Chiwawa Mountain domain where stromatic migmatites have been preserved (see Chapter II, Stromatic migmatite). In this area, the increasing segregation of mafic and felsic minerals from relatively homogeneous SBG to strong cm-scale compositional layering with increasing inferred paleodepth suggests that migmatite formation was an in situ process (e.g. Fig. 2-4 & Fig. 3-8). Figure 2-4 is an example of the typical migmatite in the Chiwawa Mountain domain displaying leucosome and adjacent melanosome layering. In addition, the presence of zoned igneous plagioclase in leucosome and mesosome, leucocratic material in meter-long shear zones, and 2-3 cm wide dikes containing minerals in optical continuity with foliation parallel leucosomes (Fig. 3- 8), indicate that partial melting was responsible for the formation of the stromatic migmatite in the Chiwawa Mountain domain (Wenatchee Block). Evidence for partial melting elsewhere in the Swakane Gneiss is inferred by the presence of peraluminous dikes. Paterson et al. (2004) concur that these dikes represent local melts that have traveled only a short distance from the source rock. This conclusion is drawn based on inferred dike viscosity, dike widths, and inherited zircons (Ruhin, 1995; Matzel et al., 2002). Two factors that dictate how far magma will propagate from the source area 64 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. are viscosity and dike width. Studies conducted by Petford et al. (1993) and Rubin (1995) that calculate dike length based on viscosity, temperature gradient, and dike width are applicable for melt volumes greater than what is present in the Swakane Gneiss. Therefore their calculations estimate longer dike lengths than what would be expected in the Swakane Gneiss. The peraluminous composition of the Swakane dikes suggests a viscosity of 10'*-10^ Fa s (Holtz et al., 2001; Scaillet et al, 1997), similar to the viscosity of rhyolitic dikes. This estimation accoimts for the presence of free water, which acts to lower viscosity, and is therefore a minimum estimate. Thermal studies on rhyolitic dikes with a viscosity of 10“*-10^ have shown that the magma will freeze within 10s to 100s of meters after propagation from the source region into rocks that are below the magma solidus (Rubin, 1995). This estimate is for dikes 1 meter (Rubin, 1995) to 2-7 meters thick (Petford et al, 1993). The average thickness of the Swakane dikes is on the order of 10-20 cm, with some as thin as a 1-2 cm, therefore the length of a dike propagating past the source area is on the scale of 10s of meters. Since the majority of dikes in the Swakane Gneiss show only one pulse of magma (no zoning or cumulate texture), there was no sustained melt input that would have increased the distance melt could travel from the source area. These dikes are therefore locally derived. Zircons found in the Swakane Gneiss have an age distribution of 1600 Ma to 73 Ma, all of which have oscillatory igneous zoning with chaotic metamorpbic rims (Matzel et al., 2002). Primary igneous zircons are uncommon in the peraluminous dikes, and most zircons plucked form intrusive samples have an age distribution 65 R eproduced with perm ission o fth e copyright owner. Further reproduction prohibited without perm ission. similar to Swakane Gneiss zircons (Appendix 2), indicating that the zircons were inherited (Mattinson, 1972; Matzel et al, 2002). It is possible that zircons were incorporated into the dikes as they passed through the Swakane Gneiss, however, since the rheological evidence presented above suggests the dikes traveled only a short distance, the Swakane Gneiss is a likely source for melt. Melting and Regional Deformation Field evidence shows that melting in the Swakane Gneiss occurred in the biotite gneiss layers and not the amphibolite layers, therefore, pressure and temperature were greater than melting conditions for pelitic and psammitic rocks, hut less than the melting conditions required for amphibolite rocks. Pressure and temperature data obtained by Whitney et al. (1999) and Valley et al. (2003) reveal that peak metamorphism of the Swakane Gneiss in the Wenatchee block occurred at 8-9.7 khar and 650 °C, and 10-12 kbar and 650-725 °C in the Chelan block. These values are below the requisite pressures and temperatures for fluid-absent muscovite and biotite dehydration reactions as determined by Patino Douce and Harris (735- 800 °C at 6-10 khar for pelitic rocks; 1998), however, a study by Thompson (1982) revealed that the presence of H2O can lower the solidus temperature in a biotite gneiss to 650-700 °C, which means the Swakane Gneiss was above the solidus for fluid present melting. These pressures and temperatures were below amphibolite melting conditions as determined by Skjerlie and Johnston (850 °C at 6-10 kbar; 1996). Provided melting took place in the presence of fluids as suggested by the 66 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. abundance of pegmatitic dikes, the P-T data and field observations are in agreement with respect to SGB and amphibolite layers. In other areas of the Cascades core (i.e. Skagit gneiss; Whitney, 1992) and the Coast Plutonic Complex (i.e. Shuswap complex, southern British Columbia; Vanderhagae et al., 1999 and Norlander et al., 2002), decompression melting has been proposed as a viable cause of melting. For this to apply to the Swakane Gneiss, thermobarometric data must indicate sufficient peak metamorphic conditions for fluid absent melting, however, the arguments presented above preclude fluid absent melting. In addition, Matzel et al. (2002 & in review) has shown that burial and intrusion occurred within 5 Ma of protolith deposition. U-Pb dating of detrital zircons in the Swakane Gneiss indicates that the protolith was deposited after 73 Ma, the age of the yoimgest detrital zircons (Matzel et al., 2002). Based on two U-Pb zircon ages of 68 Ma obtained from pegmatites in the Chelan Block, the age of melting is 68 Ma, (Mattinson, 1972; Matzel et al., 2002). The calculated burial rate is 6-8 mm per year, and if decompression was the cause of melting, this rate would be higher. This argument does not rule out decompression as a cause of prograde and eventual retrograde metamorphism in the Swakane gneiss, however it is unlikely that it caused melting given the age data provided by Matzel et al (2002). Rapid burial alone does not account for melting of the Swakane gneiss in the time allotted (i.e. 5 Ma; Matzel et al., 2002). Therefore, the tectonic setting of the plate margin must be examined. Three mechanisms have been proposed to account for melting of a rapidly thickening crust. Jacobsen et al. (2000), Yin (2002), and 67 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Matzel et al. (2002) have suggested two of these models; 1) Over thickening of the crust due to forearc or backarc basin closure; and 2) underthrusting of the accretionary wedge during subduction (Jacobsen et al., 2000; Yin, 2002; and Matzel et al., 2002). These two models incorporate subduction as a mechanism to explain the rapid burial of the Swakane Gneiss, which can lead to partial melting. The third model, proposed by Gerdes et al. (2000), uses fmite element modeling to suggested that radiogenic heating of fertile sediments buried to mid- to deep-crustal depths is sufficient to produce mid-crustal migmatites without the influence of mafic magmas or lithospheric delamination. Since there is no evidence of a mantle influence in the Swakane Gneiss, radiogenic heating following rapid burial may be a viable hypothesis. Mechanical Controls on Melt Injection Melt injection in the Swakane Gneiss was scale dependent, with buoyancy and stress gradients dominating melt behavior. With small volumes at the source, melt migrates down the stress gradient, which is controlled by heterogeneous strain, and accumulates in lower stress/strain sites such as; folds, axial planes (Hand & Dirks, 1992; Vernon & Paterson, 2001), foliation, shear zones (Mogk, 1992), and houdin necks (Petford et al., 2000; Marchildon and Brown, 2001). In the case of the Swakane Gneiss, pervasive, shallow to flat-lying foliation, was the dominant anisotropy. Initial melt migration was parallel to this foliation, resulting in the formation of stromatic migmatites in the Chiwawa Mountain domain (see Fig. 2-4). 68 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 4-1. This is a photo of melt initially cutting across the dominant foliation as a meter long shear zone. The host rock is migmatitic quartz biotite gneiss, and the shear zone is filled with a fine to coarse grained leiicogranite. Width of the photo is 30 cm, Ultimately, buoyancy contrast between melt and host rock forced the melt to cut across anisotropy in order rise in the crust (Fig. 4-1). When this occurred, strain gradients due to local anisotropies were abandoned as a control on melt migration in favor of gravitational buoyancy effects, which eventually produced leucogranite dikes, sheets, and stocks. 69 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Of the Chelan Block leucogranite intrusions, fewer than 30 % (Fig. 3-22a & b) were injected parallel to the dominant foliation (e.g. sills along the Columbia River; sheets in Tamarack Creek), therefore an alternative control on injection needs to be examined. Statistically, dike orientations in the Chelan block plot in a conjugate pattern (e.g. Figs. 3-17 & Fig. 3-23), with an extrapolated maximum principle stress direction generally trending SW-NE when foliation is restored to subhorizontal. This extrapolation is consistent with the kinematics of plate motion at the time of burial of the Swakane Gneiss when motion along the Farallon/North American plate margin shifted from SW-NE contraction to dextral transpression (Umhoefer and Miller, 1996; Paterson et al., 2004; Matzel et ah, 2002). It is, therefore, reasonable to infer that regional stress exerted a significant influence on dike injection in the Chelan Block. Buoyancy is the third factor that influenced melt injection and. In the Tamarack Creek domain stocks intruded across foliation (Fig. 2-12) without leaving a structural or thermal aureole. In the Chiwawa Mountain domain, dike orientations appear to be random (e.g. Fig. 1-8, Fig. 1-9, & Fig. 3-23). They show no apparent pattems to injection, either as one group, or segregated by cross-cutting relationships and composition, and fewer than 5 % of dikes measured are parallel to the dominant foliation (Fig.3-22c). Assuming an initially subhorizontal foliation in both domains, buoyancy was the most effective mechanism in moving melt through the crust. 70 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Conclusions 1) Partial melting of the Swakane Gneiss was caused by rapid burial (6-8 mm/year) of the Swakane Gneiss under fluid-present conditions. 2) Partial melting occurred in the Swakane Gneiss and is preserved as in situ migmatite and locally-derived peraluminous dikes, sills, sheets, and stocks. Along with geochronology, the timing of melting and therefore peak metamorphism in the Swakane Gneiss is independently constrained to ca. 68 Ma. 3) Below small melt volumes (ca. 20 %) in the source region, melt migration is controlled by strain gradients and anisotropy. 4) With increasing melt volume, melt cross-cuts anisotropy and injection is controlled by buoyancy and/or regional stress. This is a requirement for efficient melt removal, particularly if anisotropies are subhorizontal, which has been inferred in the Swakane Gneiss. 5) The maximum principle stress extrapolated from stereonet projections of Chelan Block dikes is subhorizontal and trending SW-NE. This is consistent with previous authors assertions of Farallon/North American plate margin kinematics based on regional folds, lineations, and kinematic indicators. 71 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. REFERENCES Alsleben, H., 2000, Structural analysis of the Swakane Terrane, North Cascades core, Washington: [M. S. Thesis], San Jose State University, 168 p. Baldwin, J. A., Whitney, D. L., and Hurlow, H. A., 1997, Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen-parallel shear zone in the Cordillera of western North America: Tectonics, v. 16, p. 662-681. Barbey, P., Brouand, M., Le Fort, P., and Pecher, A., 1996, Granite-migmatite genetic link: the example of the Manaslu granite and Tibetan Slab migmatites in central Nepal: Lithos, v. 38, p. 63-79. Bevins, R. E., Kokelaar, B. P., and Dunkley, P. N., 1984, Petrology of lower to middle Ordovician igneous rocks in Wales: a volcanic arc to marginal basin transition,: Proceedings of the Geologists’ association, v. 95, p. 337-347. Boysun, M. A. and Paterson, S. R., 2001, Statistical distribution of leucocratic melts in the Swakane Terrane, North Cascades Crystalline Core, Washington: EOS Transactions of the American Geophysical Union: Abstract with Programs, vol. 82, p. F1352. Boysun, M. A. and Paterson, S. R., 2002, Melt injection in the Swakane biotite gneiss. North Cascades Core: Processes of melting and dike emplacement in deep crust: Geological Society of America, Abstracts with Programs, vol. 34, p. A374. Boysun, M., A., and Paterson, S. R., 2003, Partial melting, melt collection, and transportation in the Swakane Terrane, North Cascades crystalline core, Washington: Geological Society of America, Abstracts with Programs, v. 35, p. A223. Brown, E. H. and McClelland, W. C., 2000, Pluton emplacement by sheeting and vertical ballooning in part of the southeast Coast Plutonic Complex, British Columbia: Geological Society of America Bulletin, v. 112, no. 5, p. 708-719. Brown, E. H., and Walker, N. W., 1993, Magma -loading model for Barrovian metamorphism in the Southeast Coast Plutonic Complex, British Columbia and Washington: Geological Society of America Bulletin, v. 105, p. 479-500. Brown, M., 1994, The generation, segregation, ascent and emplacement of granite magma: the migmatite-to-crustally-derived granite connection in thickened orogens: Earth-Science Reviews, v. 36, p. 83-130. 72 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Cater, F. M., 1982, Intrusive rocks of the Holden and Lucerne quadrangles, Washington - the relation of depth zones, composition, textures, and emplacement of plutons: United States Geological Survey Professional Paper 1220, 108 p. Chamberlain, V. E., and Lambert, R. St. J., 1985, Cordillera, a newly defined Canadian microcontinent: Nature, v. 314, p. 707-713. Clemens, J. D., and Mawyer, C. K., 1992, Granitic magma transport by fracture propagation: Tectonophysics, v. 204, p. 339-360. Clemens, J. D., 1998, Observations on the origins and ascent mechanisms of granitic magmas: Journal of the Geological Society, London, v. 155, p. 843-851. Evans, B. W., and Davidson, G. F., 1999, Kinetic control of metamorphic imprint during synplutonic loading of batholiths: An example from Mount Stuart, Washington: Geology, v. 27, p. 415-418. Evansen N. M., Hamilton, P. J. and O’nions, R. K., 1978, Rare earth abundances in chondritic meteorites. Geochemica Cosmochimica Acta, v. 42, p. 1199-1212. Gerdes, A., Womer, G., and Henk, A., 2000, Post-collision granite generation and HT-LP metamorphism by radiogenic heating: the Variscan South Bohemian Batholith: Joumal of the Geological Society, London, v. 157, p. 577-587. Hand, M., and Dirks, P. H. G. M., 1992, The influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic Napperby Gneiss, central Australia: Joumal of Stractural Geology, v. 14, no. 5, p. 591-604. Holtz, F., Johannes, N., and Behrens, T. H., 2001, Maximum and minimum water contents of granitic melts generated in the cmst: a reevaluation and implications: Lithos, V . 56, p. 1-14. Irving, E., Woodsworth, G. J., Wynne, P. J. and Morrison, A., 1985, Paleomagnetic evidence for displacement from the south of the Coast Plutonic Complex, British Columbia: Canadian Joumal of Earth Sciences, v. 22, p. 584-598. Jacobson, C. E., Oyarzabal, F. R., and Haxel, G. G., 1996, Subduction and exhumation of the Pelona-Oracopia-Rand schists, southem California: Geology, v. 24, p. 547-550. Johannes, W., 1983, On the origin of layered migmatites: in M. A. Atherton and C. D. Gribble (editors), Migmatites, Melting and Metamorphism. Shiva Publishing Limited, p. 234-248. 73 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Laravie, J. A., 1976, Geologic field studies along the eastern border of the Chiwaukum Graben, Central Washington: [M.S. Thesis], University of Washington, 56 p. Marchildon, N., and Brown, M., 2002, Grain-scale melt distribution in two contact aureole rocks: implications for controls on melt localization and deformation: Joumal of Metamorphic Geology, v. 20, p. 381-396. Mattinson, J. M., 1972, Ages of zircons from the northem Cascade Mountains, Washington: Geological Society of America Bulletin, v. 83, p. 3769-3784. Matzel, J. P., Bowring, S. A., and Miller, R. B., 2002, U-Pb Geochronologic evidence of a late Cretaceous protolith age for the Swakane Gneiss, North Cascades, WA: Geological Society of America, Abstracts with Programs, v. 34, p. A510-511. Matzel, J. P., Bowring, S. A., and Miller, R. B., Reassessing tectonic models for the assembly of the North Cascades Arc, WA, in light of the late Cretaceous protolith age of the Swakane Gneiss: in review. McGroder, M. F., 1991, Reconciliation of two-sided thmsting, burial metamorphism, and diachronous uplift in the Cascades of Washington and British Columbia: Geological Society of America Bulletin, v. 103, p. 189-209. Miller, R. B., 1985, The ophiolitic Ingalls Complex, north-central Cascade Mountains, Washington: Geological Society of America Bulletin, v. 96, p. 27-42. Miller, R. B., and Bowring, S. A., 1990, Stracture and geochronology of the Oval Peak batholith and adjacent rocks: implications for the Ross Lake fault zone. North Cascades, Washington: Geological Society of America Bulletin, v. 102, p. 1361- 1377. Miller, R. B., Paterson, S. R., Debari, M. And Whitney, D. L., 2000, North Cascades cretaceous cmstal section kinematics, rheology, metamorphism, pluton emplacement and petrogenesis from 0 to 40 kilometers depth: in Woodsworth, G. J., Jackson, L. E. Jr., Nelson, J. L., and Ward, B.C. eds.. Guidebook for Geological Field Trips in Southwestem British Columbia and Northem Washington. Geological Association of Canada, p. 229-278. Miller, R. B., and Paterson, S. R., 2001, Construction of mid-crastal sheeted plutons: examples form the North Cascades, Washington: Geological Society of America Bulletin, v. 113, p. 1423-1442. Misch, P., 1966, Tectonic evolution of the Northem Cascades of Washington State, in Gunning, H. C., ed.. Tectonic History and Mineral Deposits of the Westem Cordillera, Canadian Institute of Mining and Metallurgy, v. 8, p. 101-148. 74 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Mogk, D. W., 1992, Ductile shearing and migmatization at mid-crustal levels in an archean high-grade gneiss belt, northem Gallatin Range, Montana, USA: Joumal of Metamorphic Geology, v. 10, p. 427-438. Monger, J. W. H., Price, R. A., and Tempelman-Kluit, D. J., 1982, Tectonic accretion and the origin or the two metamorphic and plutonic welts in the Canadian Cordillera: Geology, v. 10, p. 70-75. Norlander, B. H., Whitney, D. L., Teyssier, C., and Vanderhaeghe, O., 2002, Partial melting and decompression of the Thor-Odin dome, Shuswap metamorphic core complex, Canadian Cordillera: Lithos, v. 61, p. 103-126. Obata, M., Yoshimura, Y., Nagakawa, K., Odawara, S. And Osanai, Y., 1994, Cmstal anatexis and melt migrations in the Higo metamorphic terrane, west-central Kyushu, Kumamoto, Japan: Lithos, v. 32, p. 135-147. Patino Douce, A. E. and Harris, N., 1998, Experimental constraints on Himalayan anatexis: Joumal of Petrology, v. 39, p. 689-710. Paterson, S. R., and Vemon, R. H., 1995, Bursting the bubble of ballooning plutons: a return to nested diapers emplaced by multiple processes: Geological Society of America Bulletin, v. 39, p. 689-710. Paterson, S. R. and Miller, R. B., 1998, Mid-crastal magmatic sheets in the Cascades Mountains, Washington: implications for magma ascent: Joumal of Stractural Geology, v. 20, no. 9, p. 1345-1363. Paterson, S. R., Miller, R. B., Alsleben, H., Whitney, D. L., Valley, P. M., and Hurlow, H., 2004, Driving mechanisms for 40-60 km of exhumation during Late Cretaceous contraction and Paloegene arc-oblique extension. Cascades Core, Washington: Geological Society of America Bulletin, (in press). Pearce, J. A., 1983, Role of the suh-continental lithosphere in magma genesis at active continental margins, in Hawkesworth, C. J., and Norry, M. H., eds.. Continental basalts and mantle xenoliths, Shiva, Nantwich, p. 230-249. Petford, N., Kerr, R. C., and Lister, J. R., 1993, Dike transport of granitoid magmas: Geology, v. 21, p. 845-848. Petford, N., Craden, A. R., McCaffrey, K. J. W., and Vigneresse, J.-L., 2000, Granite magma formation, transport and emplacement in the Earth's crust: Nature, c. 408, p. 669-673. Rubin, A. M., 1993, Dikes vs. diapirs in viscoelastic rock: Earth and Planetary Science Letters, v. 119, p. 641-659. 75 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Rubin, A., 1995, Getting granite dikes out of the source region: Joumal of Geophysical Research, v. 100, p. 5911-5929. Rutter, M. J. and Wyllie, P. J., 1988, Melting of vapour-absent tonalite at 10 kbar to simulate dehydration-melting in the deep cmst: Nature, v. 331, p. 159-160. Sawyko, L., 1994, The geology and petrology of the Swakane Biotite Gneiss, North Cascades, Washington: [M. S. Thesis], University of Washington, 134 p. Scaillet, B., Holtz, F., Pichavant, M., and Schmidt, M., 1996, Viscosity of Himalayan leucogranites: implications for mechanisms of granitic magma ascent: Joumal of Geophysical Research, v. BlOl, p. 27,691-27,699. Skjerlie, K. P. and Johnston, A. D., 1996, Vapour-absent melting from 10 to 20 kbar of cmstal rocks that contain multiple hydrous phases: implications for anatexis in the deep to very deep continental cmst and active continental margins: Joumal of Petrology, v. 37, p. 661-691. Stein, E., and Stowell, H., 2002, Thermobarometric constraints on high-pressure exhumation history of the Dinkelman decollement. North Cascades, Washington: a record of decompression in amphibolite gamet coronas: Geological Society of America, Abstracts with Programs, vol. 34, p. A432. Tabor, R. W., Zartman, R. E., and Frizzell Jr., V. W., 1987a, Posssible tectonostratigraphic terranes in the North Cascades Crystalline Core, Washington, in Schuster, J. E. (Ed.), Selected papers on the geology of Washington: Washington Division of Geology and Earth Resources, Bulletin, v. 77, p.107-127. Tabor, R, W., Fritzell, V. A., Jr., Whetten, J. T., Waitt, R. B., Swanson, D. A., Byerly, G. R., Booth, D. B., Hetherington, M. J., and Zartman, R. E., 1987b, Geological map of the Chelan 30-minute by 60-minute quadrangle, Washington: United States Geological Survey, Map 1-1661, scale 1:100,000. Tabor, R. W., Haugemd, R. A., and Miller, R. B., 1989, Overview of the geology of the North Cascades: American Geophysical Union, International Geological Congress, Trip T307. Taylor, S. R., and McLennan, S. M., 1981, The composition and evolution of the continental cmst: rare earth element evidence from sedimentary rocks: Philosophical Transactions of the Royal Geological Society, v. A301, p. 381-399. Thompson, A. B., 1982, Dehydration melting of pelitic rocks and the generation of HaO-undersaturated granitic liquids: American Joumal of Science, v. 282, p. 1567- 1595. 76 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Umhoefer, P. J., 1987, Northward translation of "Baja British Columbia" along the late Cretaceous to Paleocene margin of westem North America: Tectonics, v. 6, p. 377-394. Umhoeffer, P. J., and Miller, R. B., 1996, Mid-Cretaceous thrusting in the southem Coast Belt, British Columbia and Washington, after strike-slip fault reconstmction: Tectonics, v. 15, p. 545-565. Valley, P. M., Whitney, D. L., Paterson, S. R., Miller, R. B., and Alsleben, H., 2003, Metamorphism of the deepest exposed arc rocks in the Cretaceous to Paleogene Cascades belt, Washington: evidence for large -scale vertical motion in a continental arc, Joumal of Metamorphic Geology, v. 21, p. 1-19. Van den Eeckhout, B., Grocott, J., and Vissers, R., 1986, On the role of diapirism in the segregation, ascent and final emplacement of granitoid magmas - Discussion: Tectonophysics, v. 127, p. 161-169. Vanderhaeghe, O., Teyssier, C. and Wysoczanski, R., 1999, Stractural and geochronological constraints on the role of partial melting during the formation of the Shuswap metamorphic core complex at the latitude of the Thor-Odin dome, British Columbia: Canadian Joumal of Earth Science, v. 36, p. 917-943. Vigneresse, J.-L., 1999, Should felsic magmas be considered at tectonic objects, just like faults or folds?: Journal of Stractural Geology, v. 21, p. 1125-1130. Vemon, R. H., and Paterson, 2001, Axial surface leucosomes in anatectic migmatites: Tectonophysics, v. 335, p. 183-192. Waters, A. C., 1932, A petrologic and stractural study of the Swakane gneiss, Entiat Mountains, Washington: Joumal of Geology, v. 40, no. 6, p. 604-633. Weinberg, R. F., 1999, Mesoscale pervasive felsic magma migration: altematives to dyking: Lithos, v. 46, p. 393-410. Wemicke, B., and Getty, S. R., 1997, Intracrastal subduction and gravity currents in the deep crust: Sm-Nd, Ar-Ar, and thermobarometric constraints from the Skagit Gneiss Complex, Washington: Geological Society of America, v. 109, p. 1149-1166. Whitney, D. L., 1992, High-pressure metamorphism in the Westem Cordillera of North America: an example from the Skagit Gneiss, North Cascades: Joumal of Metamorphic Geology, v. 10, p. 71-85. Whitney, D. L., Miller, R. B., and Paterson, S. R., 1999, P-T-t evidence for mechanisms of vertical tectonic motion in a contractional orogen: north-westem US and Canadian Cordillera: Joumal of Metamorphic Geology, v. 17, p. 75-90. 77 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Wickham, S. M., 1987, The segregation and emplacement of granitic magmas: Joumal of the Geological Society, London, v. 144, p. 281-297. Yin, A., 2002, Passive-roof thrust model for the emplacement of the PelonaOracopia Schist in southem Califomia, United States: Geology, v. 30, p. 183-186. 78 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CD ■ D OQ. C o CDQ. ■DCD C/) W o'o o o o ■D cq' o CD ■D OQ. C a o o ■O o CDQ. ■DCD (/)(/) Appendix 1. Foliation and Lineation data from the Columbia River domain (CR), the Tamarack Creek domain (TC), and the Chiwawa Mountain domain (CM). (*) denotes stations where detailed ourcrop mapping was completed and measurements of dike orientations were taken. Data is provided on the included CDROM. Foliation ® Lineation ^ Strike Dip Mineral Plunge Trend 01=2001 Station 02=2002 Rock 01=2001 Station 02=2002 Rock Foliation ® Lineation ^ Strike Dip Mineral Plunge Trend VO 1 TC-01 Swakane 384 29 biotite 01 150 2 TC-01 Swalcane 30 25 3a TC-01 Swakane 336 44 quartz 19 352 4 TC-01 Swakane no data 5 TC-01 Swakane 342 37 5 TC-01 Swakane 343 38 6 TC-01 Swakane 000 43 6 TC-01 Swakane 001 35 1 TC-01 Swakane 014 21 31 103 7 TC-01 Swakane 025 39 8 TC-01 Swakane 330 39 9 TC-01 Swakane 329 23 10 TC-01 Swakane 030 39 11 TC-01 Swakane 004 21 12 TC-01 Intrusive 042 16 quartz 15 160 12 TC-01 Swakane 307 15 13 TC-01 Swakane 341 21 14 TC-01 Intrusive 044 20 quartz 19 142 15 TC-01 Swakane 350 07 16 TC-01 Swakane 340 14 17 TC-01 Intrusive 357 10 18 TC-01 Mingled 340 39 19 TC-01 Swakane 006 25 quartz 17 154 20 TC-01 Swakane 001 31 21 TC-01 Mingled 085 24 22 TC-01 Swakane 345 34 chlorite 15 145 23 TC-01 Intrusive 347 37 chlorite 19 140 23 TC-01 Intrusive 337 29 qtz, bt 12 144 24 TC-01 Intrusive no data 25 TC-01 Mingled 005 35 15 145 26* TC-01 Swakane 308 29 27 TC-01 Mingled 355 52 28 TC-01 Intrusive 066 28 29 TC-01 Swakane 11 169 30 TC-01 Swakane 308 14 quartz 04 345 30 TC-01 Mingled 008 19 30 TC-01 Intrusive 307 38 31 TC-01 Intrusive 325 39 quartz 15 126 31 TC-01 Mingled 345 37 32 TC-01 Mingled 024 34 quartz 39 151 33 TC-01 Dike no data 34 TC-01 Intrusive 343 39 13 098 34 TC-01 Mingled 000 15 35 TC-01 Swakane 321 22 biotite 15 008 36 TC-01 Swakane 350 11 biotite 03 160 37 TC-01 Swakane 357 23 qtz, bt 13 159 38 TC-01 Intrusive 006 37 39 TC-01 Swakane 343 19 quartz 03 165 39 TC-01 Swakane biotite 07 140 40 TC-01 Swakane 350 20 41 TC-01 Mingled 330 13 42 TC-01 Swakane 332 19 biotite (w) 00 328 42 TC-01 Swakane chit (w) 21 330 43 TC-01 Swakane 003 21 CD ■ D OQ. C o CDQ. ■DCD C/) W o'o o Appendix 1 cont. OO■D c q ' O’ o CD ■D O Q . C a o Q ■o o CD Q . ■DCD (/)(/) 00 o 44 TC-01 Swakane 019 27 45 TC-01 Mingled 355 22 biotite 14 145 46 TC-01 Swakane 023 29 biotite (m) 21 059 46 TC-01 Intrusive 040 24 47 TC-01 Mingled 314 25 muse (w) 07 152 48 TC-01 Mingled 060 10 49 TC-01 Swakane 346 30 biotite (m) 15 140 50 TC-01 Swakane 355 33 quartz (w) 05 154 51 TC-01 Swakane 321 16 quartz (w) 12 341 52 TC-01 Swakane 007 10 biotite (m) 05 151 53 TC-01 Swalcane 311 19 quartz (s) 09 140 54a TC-01 Intrusive 009 11 54b TC-01 Swakane 326 16 quartz 06 143 55 TC-01 Intrusive no data 56 TC-01 Swakane 322 23 quartz (s) 01 150 56 TC-01 Swakane 320 29 qtz, bt (w) 05 134 57 TC-01 Swakane 316 20 quartz (s) 02 329 58 TC-01 Intrusive no data 59 TC-01 Swakane 335 25 60 TC-01 Swakane no data 61 TC-01 Swakane 349 13 62 TC-01 Swakane no data 63 TC-01 Swakane 355 17 64 TC-01 Swakane 210 11 64 TC-01 Intrusive 116 08 65 TC-01 Swakane 357 08 66 TC-01 Swakane 315 02 biotite (w) 00 142 67 TC-01 Swakane no data 68 TC-01 Swakane 356 05 quartz (w) 04 119 68 TC-01 Swakane 295 04 biotite (m) 03 336 70 TC-01 Mingled no data 71 TC-01 Mingled 229 12 quartz 15 331 72 TC-01 Swakane no data 73 TC-01 Swakane 320 21 chlorite 14 319 74 TC-01 Swakane no data 75 TC-01 Swakane 304 39 quartz 07 337 76 TC-01 Mingled 057 17 biotite 18 144 77 TC-01 Swakane 316 24 biotite 12 340 78 TC-01 Swakane 034 04 biotite (w) 05 170 79 TC-01 Swakane 035 14 80 TC-01 Intrusive no data 81 TC-01 Swakane 039 15 quartz 13 152 82 TC-01 Mingled 325 22 quartz 10 325 83 TC-01 Mingled 006 14 84 TC-01 Intrusive Oil 41 84 TC-01 Swakane 016 23 85 TC-01 Mingled 317 44 quartz (s) 07 131 86 TC-01 Swakane 03 42 86 TC-01 Intrusive 016 30 biotite 03 Oil 87 TC-01 Swakane 343 43 quartz 21 010 88 TC-01 Swakane no data 89 TC-01 Swakane 334 19 90 TC-01 Swakane 350 31 91 TC-01 Swakane 001 26 92 TC-01 Mingled 001 25 93 TC-01 Swakane 063 31 94 TC-01 amph 009 37 95 TC-01 Swakane no data 96 TC-01 Mingled 003 23 quartz (w) 13 145 97 TC-01 Swakane 338 39 98 TC-01 Swakane no data 99 TC-01 Swakane 342 29 quartz (w) 05 149 CD ■ D OQ. C o CDQ. ■DCD C/) W o'o o Appendix 1 cont. OO■D c q ' O’ o CD ■D O Q . C a o Q ■o o CD Q . ■DCD (/)(/) 100 TC-01 Swakane 349 38 101 TC-01 Dike no data 102 TC-01 Swakane 037 13 102 TC-01 Swakane 036 15 102 TC-01 Mingled 315 19 quartz (m) 13 356 103 TC-01 Swakane 335 20 quartz (w) 12 134 103 TC-01 Intrusive no data quartz (s) 02 148 104 TC-01 Intrusive no data 105 TC-01 Swakane 031 28 quartz (m) 21 26 106 TC-01 Swakane 328 40 quartz (w) 10 134 106 TC-01 Swakane 349 34 106 TC-01 Swakane 308 18 qtz (s) 03 129 106 TC-01 Swakane 315 18 107 TC-01 Mingled 307 17 108 TC-01 Intrusive no data 109 TC-01 Mingled 326 26 110 TC-01 Intrusive 327 29 111 TC-01 Intrusive no data 112 TC-01 Swakane 243 16 113 TC-01 Intrusive no data 114 TC-01 Intrusive 030 08 115 TC-01 Swakane 309 40 116 TC-01 Swakane 345 46 117 TC-01 Swakane no data 118 TC-01 Intrusive 014 52 119 TC-01 Swakane 350 42 120 TC-01 Swakane 335 21 121 TC-01 Swakane 349 32 qtz, bt (w) 04 157 122 TC-01 Swakane 005 18 biotite (w) 15 170 123 TC-01 Swakane 325 29 124 TC-01 Swakane 339 16 125 TC-01 Swakane 333 34 126 TC-01 Mingled 359 24 127 TC-01 Mingled 020 34 128 TC-01 Swakane 350 29 129 TC-01 Swakane 059 10 130 TC-01 Swakane 003 34 131 TC-01 Swakane 350 15 132 TC-01 Mingled 323 23 133 TC-01 Swakane 355 46 134 TC-01 Swakane 315 45 135 TC-01 Swakane 305 25 quartz (s) 12 325 136 TC-01 Swakane 346 25 137 TC-01 Mingled 078 49 138 TC-01 Swakane 316 25 138 TC-01 Intrusive 004 22 139 TC-01 Intrusive 045 17 139 TC-01 Swakane 330 60 biotite (w) 18 138 140* CR-01 141* CR-01 142n* CR-01 142s* CR-01 143e* CR-01 143w* CR-01 143s* CR-01 144 TC-01 Dike no data 145 TC-01 Swakane 129 17 quartz (w) 04 344 146 TC-01 Swakane 359 16 147 TC-01 Swakane 051 22 bt, qtz (m) 21 116 148 TC-01 Swakane 116 19 quartz (m) 18 156 149 TC-01 Intrusive no data 150 TC-01 Swakane 338 24 bt, qtz 10 349 CD ■ D OQ. C o CDQ. ■DCD C/) W o'o o Appendix 1 cont. OO■D c q ' O’ o CD ■D O Q . C a o Q ■o o CD Q . ■DCD (/)(/) ocN) 151 TC-01 Swakane 001 12 151 TC-01 Swakane 010 58 152 TC-01 Swakane 108 04 quartz (w) 10 141 153 TC-01 Swakane 151 11 biotite (w) 08 332 154 TC-01 Swalcane 347 18 155 TC-01 Swakane 347 47 qtz, bt (m) 19 140 156 TC-01 Swakane no data 157 TC-01 Swakane 358 26 158 TC-01 Swakane 324 20 158 TC-01 Intrusive 295 21 qtz, bt (m) 10 354 159 TC-01 Swakane 006 26 biotite (s) 17 145 159 TC-01 Intrusive 229 05 160 TC-01 Swakane 275 15 161 TC-01 Swakane 349 28 quartz (s) 26 072 162 TC-01 Swakane 293 17 bt, qtz (s) 10 332 163 TC-01 Swakane 354 30 bt, qtz (w) 09 157 164 TC-01 Swakane 350 26 quartz (s) 02 154 165 TC-01 Swakane 053 14 quartz 10 128 166 TC-01 Swakane no data 167 TC-01 Swakane 010 14 168 TC-01 Intrusive no data 169 TC-01 Intrusive 308 59 169 TC-01 Swakane 315 44 170 TC-01 Intrusive 115 30 171 TC-01 Swakane no data 172 TC-01 Swakane 336 41 173 TC-01 Swakane 321 33 174 TC-01 Swakane 300 43 175 TC-01 Swakane 324 43 biotite (w) 32 012 176 TC-01 Swakane 353 19 177 TC-01 Swakane 274 43 quartz (s) 31 077 2001 CM-02 Swakane 151 82 2001 CM-02 Intrusive no data 2002 CM-02 Swakane 315 16 2003 CM-02 Swakane 241 06 2003 CM-02 amph no data 2004 CM-02 amph 261 23 hbl 26 005 2005 CM-02 Swakane 351 02 2006 CM-02 Swakane 322 33 qtz 06 344 2007 CM-02 Swakane 008 20 qtz 06 165 2008 CM-02 Swakane 325 27 qtz 09 335 2009 CM-02 Swakane 169 77 qtz 68 314 2009 CM-02 Swakane 141 86 2009 CM-02 Swakane 133 81 05 316 2009 CM-02 Swakane 140 80 06 318 2009 CM-02 Swakane 318 10 75 136 2010 CM-02 Swakane 287 67 qtz 67 022 2011 CM-02 Swakane 281 67 qtz 65 356 2011 CM-02 Swakane 295 45 qtz 45 019 2012 CM-02 Swakane 060 60 2013* CM-02 Swakane 2014 CM-02 Swakane 128 53 bt 12 297 2015 CM-02 Swakane 165 34 bt 03 181 2015 CM-02 Swakane 161 31 2016* CM-02 Swakane 168 37 qtz 17 171 2016* CM-02 Swakane 190 40 qtz 05 168 2016* CM-02 Swakane 132 28 qtz 11 146 2017* CM-02 Swakane 161 65 2018* CM-02 Swakane 170 28 2018* CM-02 Swakane 163 39 bt 12 324 2018* CM-02 Swakane 070 41 2019* CM-02 Swakane 291 75 O ro o o N a- (N o C nI o fS o fo <N o c \ «N 0\ o Tf o o Ci o o t-' o o oo o oo o <ui I c/3 § § C/2 § GO C/3 ■rt GO <NO O fOo O O U U rsO O fOo U_ ■3« fS O CN o U O U r^POo fS (S0 1in o cs o MPO ■ o PS <N o M00 PO o PS fS o u _H PS o PS o PN PS mPS N x: o> m PS»T) o PS ooVO o PS o rPS Os Os Os PS so O s PS PS oo a o . a -d s u ftft < § $C/D <NO U o O S O _o 9 o u u 1GO _o ■a PS PS o PS PS o s •}C PS o PS CD I C/3 •5< PO PS o PS § GO ■}!'•y PS o 0> § G2 C/2 U _U So PS o PS CD 1CO O . _ 4 c c i a '1 ^ ------------- --------- -- 2 0 ? d v /2 0 6 ^ ■o Isotopic ages calculated using the decay constants o f Jaffey et al. (1971); A.(~ U) - 9.8485x10’ y f and X( U) ^ 1.55125x10’ yr“ ; error in Pb/ Pb date reported at the 2a confidence interval. Dates in bold are the best estimates o f the age o f the zircon. oo O s Plate 2b. Geologic map ofthe Tamarack Creek domain. Mapping was accomplished by M. A. Boysun, and the location ofthe Dinkelman decollement was taken from mapping by S. R. Paterson (Miller et al., 2000). Plate 2a. Station numbers. Structural data for each location is provided on Plate 2b and in Appendix 1. The locations ofsamples used for microstructural and/or geochemical analyses are shown in bold. R.AL kAL ' 33 20 Pld T. 10 S. Kal PLAYA LAKE CLAY DEPOSITS R5E R.6 E Indio) R 7E 33 25 T9 S. FAULT, EXPOSED FAULT, BURIED CONTACT 33°ZO approximate contact T. IOS. ILal Pld RECENT ALLUVIUM SAMO AHO GRAVEL OF valley flwr anp stream AREAL BEOLOBY 2491 2303 '523.... sss •: Clark. • /094 3315 Til S. T. 11 S. DAD LANDS DEPOSITS | Gil 33° 10' Gr,n GRANITE GNEISS Wells T. 12 S. Um Gt Pls BORE.GO VALLEY, CALIFORNIA is mean, sea level V. MAHDIEIZED LIMESTONE table mountain formation TERXACE DEPOSITS Bore Pea k UMI Ffelentiated metaM0R.PH1C SERIES, QNEI55, 5CHIST, xm. LIMESTONE rn Dry Lake 5^2 Lt>af GR.N R.7 E. Polyconic projection to place on North American datum move projection lines 640 feet south and 360 feet west. grahite and SRAMODIORJTE WITH D10RJTIC FACIES PALEOZOIC? JU R A 5 5 1C ? Q .U A T E R .N A R .Y 116° 30z 33° 25' 3 3° 15' 33 10 T. 12 S. 3 3 05 _ ___ 116° 30' Topography by Wm. R. B. Osterholt Surveyed ’ 19 3 5 -1934 R. 6 E 20 Scale Contour interval 500 feet CALIFORNIA (SAN DIEGO COUNTY) BOego vagley quadrangle iq' £ T9 s. go Um ___ 33° 05 TlfflO'

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Asset Metadata

Creator Boysun, Melissa Ann (author)

Core Title Partial melting, melt collection and transport in the Swakane Gneiss, North Cascades crystalline core, Washington

Degree Master of Science

Degree Program Geological Sciences

Degree Conferral Date 2004-05

Publication Date 05/14/2004

Defense Date 05/14/2004

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Format theses (aat)

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Paterson, Scott R. (committee chair), Anderson, James Lawford (committee member), Miller, Robert B. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-314276

Unique identifier UC11337257

Identifier 1421759.pdf (filename),usctheses-c16-314276 (legacy record id)

Legacy Identifier etd-Boysun

Dmrecord 314276

Document Type Thesis

Format theses (aat)

Rights Boysun, Melissa Ann

Internet Media Type application/pdf

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA