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51
Table 2.4 Results of GARB and GMBP P-T calculations.
Sample Location UTM coordinates P-T results Burial depth
Long. (m) Lat. (m) P (kbar) T (°C) (km)
8.4 ± 2.0 666 ± 136 31.7 ± 7.6
8.4 ± 1.9 645 ± 131 31.7 ± 7.2
8.3 ± 1.9 653 ± 133 31.3 ± 7.2
7.9 ± 1.9 650 ± 132 29.8 ± 7.2
8.1 ± 2.0 658 ±136 30.6 ± 7.6
FDC62 Deadman Creek 739909 4354292
Av. 8.2 ± 0.9 654 ± 60 31.0 ± 3.3
8.1 ± 2.0 658 ± 135 30.6 ± 7.6
8.4 ± 2.0 647 ± 132 31.7 ± 7.6
8.1 ± 2.0 637 ± 130 30.6 ± 7.6
8.2 ± 2.0 656 ± 135 31.0 ± 7.6
FDe178 Deep Canyon 746484 4356252
Av. 8.2 ± 1.0 650 ± 67 31.0 ± 3.8
8.0 ± 1.9 582 ± 115 30.2 ± 7.2
7.9 ± 1.8 568 ± 113 29.8 ± 6.8
7.9 ± 1.9 586 ± 118 29.8 ± 6.8
7.8 ± 1.8 577 ± 116 29.5 ± 7.2
FHa49 Hampton Creek 748213 4348265
Av. 7.9 ± 0.9 578 ± 58 29.8 ± 3.5
7.9 ± 1.8 564 ± 115 29.8 ± 6.8
7.7 ± 1.8 565 ± 113 29.1 ± 6.8
7.6 ± 1.8 566 ± 113 28.7 ± 6.8
7.7 ± 1.8 576 ± 116 29.1 ± 6.8
FHa270 Hampton Creek 749609 4347966
Av. 7.7 ± 0.9 568 ± 57 29.2 ± 3.4
5.8 ± 1.6 506 ± 102 21.9 ± 6.0
5.7 ± 1.6 513 ± 104 21.5 ± 6.0
5.7 ± 1.6 507 ± 103 21.5 ± 6.0
FHe9 Hendry’s Creek 752223 4343911
Av. 5.7 ± 0.9 509 ± 59 21.7 ± 3.5
6.2 ± 1.6 496 ± 101 23.4 ± 6.0
6.0 ± 1.6 520 ± 107 22.7 ± 6.0
6.2 ± 1.6 505 ± 103 23.4 ± 6.0
6.0 ± 1.6 504 ± 103 22.7 ± 6.0
6.3 ± 1.6 501 ± 102 23.8 ± 6.0
FHe269 Hendry’s Creek 744316 4346774
Av. 6.1 ± 0.7 505 ± 46 23.2 ± 2.7
6.0 ± 1.7 548 ± 120 22.7 ± 6.4
6.1 ± 1.7 553 ± 119 23.0 ± 6.4
6.0 ± 1.7 543 ± 117 22.7 ± 6.4
FSi18 Silver Creek 739400 4340999
Av. 6.0 ± 1.0 548 ± 69 22.8 ± 3.7
Individual P-T determinations are given at the 2 confidence level. Average (Av.)
P-T results are given with the standard error of the mean ( x ), where x = / n is
the mean standard deviation for n thermobarometric calculations.
Burial depth = P/g, where = 2.7g/cm3 and g = 9.81ms-1.
Object Description
| Title | Structural and thermobarometric constraints on the exhumation of the northern Snake Range metamorphic core complex, Nevada |
| Author | Cooper, Frances Jacqueline |
| Author email | fcooper@usc.edu; fcooper@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2008-08-27 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-22 |
| Advisor (committee chair) | Platt, John P. |
| Advisor (committee member) |
Davis, Gregory A. Morrison, Jean Platzman, Ellen Thompson, Mark E. |
| Abstract | Observations from areas of large-scale continental extension, including the Basin and Range Province in western North America, have revealed the presence of regionally subhorizontal normal faults that appear to have exhumed rocks from mid- to lower-crustal levels. These detachment faults separate upper plate rocks extended on arrays of high-angle brittle normal faults from lower plate rocks exhibiting ductile mylonitic stretching and medium- to high-grade metamorphism. The origin and evolution of these detachments has been a matter of debate for decades, and yet a number of issues remain unresolved: (1) the dip of the faults when they were initiated and were active; (2) their penetration depth into the crust; (3) their role in exhuming high-grade metamorphic rocks; and (4) the origin and significance of the mylonitic deformation in their footwalls.; I explored these issues in the footwall to a classic detachment fault -- the northern Snake Range décollement (NSRD) in eastern Nevada -- using a combination of structural geology, geothermobarometry, paleomagnetism, isotope geochronology, and electron backscatter diffraction (EBSD) analysis. Garnet-biotite-muscovite-plagioclase thermobarometry suggests that the footwall to the NSRD experienced late Cretaceous peak metamorphic conditions of 6–8 kbar and 500–650°C, equivalent to a burial depth of ≤ 30 km. Calcite-dolomite thermometry indicates that Tertiary mylonitic deformation occurred under lower temperature conditions of 350–430°C, equivalent to mid-crustal levels. Structural, paleomagnetic, and EBSD data demonstrate that mylonites experienced two phases of shear (top-east and top-west), inconsistent with movement along a single throughgoing normal fault.; I conclude that exhumation of the northern Snake Range footwall was a two-step process. Initial ductile stretching and thinning of the crust exhumed footwall rocks to the middle crust beneath a discontinuity, referred to as the localized-distributed transition (LDT), that separated extension along brittle normal faults above from localized ductile shear zones below. Mylonites formed along the LDT were subsequently captured by a moderately-dipping NSRD that soled into the middle crust. The NSRD, therefore, appears to be a late-stage brittle normal fault that was responsible for only about half the total exhumation of the footwall, and is not directly related to the mylonitic deformation. |
| Keyword | continental extension; extensional tectonics; Basin and Range province; Cordillera; metamorphism; mylonite zone |
| Geographic subject | tectonic features: Snake Range décollement |
| Geographic subject (state) | Nevada |
| Geographic subject (country) | USA |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1695 |
| Contributing entity | University of Southern California |
| Rights | Cooper, Frances Jacqueline |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Cooper-2458 |
| Archival file | uscthesesreloadpub_Volume40/etd-Cooper-2458.pdf |
Description
| Title | Page 66 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 51 Table 2.4 Results of GARB and GMBP P-T calculations. Sample Location UTM coordinates P-T results Burial depth Long. (m) Lat. (m) P (kbar) T (°C) (km) 8.4 ± 2.0 666 ± 136 31.7 ± 7.6 8.4 ± 1.9 645 ± 131 31.7 ± 7.2 8.3 ± 1.9 653 ± 133 31.3 ± 7.2 7.9 ± 1.9 650 ± 132 29.8 ± 7.2 8.1 ± 2.0 658 ±136 30.6 ± 7.6 FDC62 Deadman Creek 739909 4354292 Av. 8.2 ± 0.9 654 ± 60 31.0 ± 3.3 8.1 ± 2.0 658 ± 135 30.6 ± 7.6 8.4 ± 2.0 647 ± 132 31.7 ± 7.6 8.1 ± 2.0 637 ± 130 30.6 ± 7.6 8.2 ± 2.0 656 ± 135 31.0 ± 7.6 FDe178 Deep Canyon 746484 4356252 Av. 8.2 ± 1.0 650 ± 67 31.0 ± 3.8 8.0 ± 1.9 582 ± 115 30.2 ± 7.2 7.9 ± 1.8 568 ± 113 29.8 ± 6.8 7.9 ± 1.9 586 ± 118 29.8 ± 6.8 7.8 ± 1.8 577 ± 116 29.5 ± 7.2 FHa49 Hampton Creek 748213 4348265 Av. 7.9 ± 0.9 578 ± 58 29.8 ± 3.5 7.9 ± 1.8 564 ± 115 29.8 ± 6.8 7.7 ± 1.8 565 ± 113 29.1 ± 6.8 7.6 ± 1.8 566 ± 113 28.7 ± 6.8 7.7 ± 1.8 576 ± 116 29.1 ± 6.8 FHa270 Hampton Creek 749609 4347966 Av. 7.7 ± 0.9 568 ± 57 29.2 ± 3.4 5.8 ± 1.6 506 ± 102 21.9 ± 6.0 5.7 ± 1.6 513 ± 104 21.5 ± 6.0 5.7 ± 1.6 507 ± 103 21.5 ± 6.0 FHe9 Hendry’s Creek 752223 4343911 Av. 5.7 ± 0.9 509 ± 59 21.7 ± 3.5 6.2 ± 1.6 496 ± 101 23.4 ± 6.0 6.0 ± 1.6 520 ± 107 22.7 ± 6.0 6.2 ± 1.6 505 ± 103 23.4 ± 6.0 6.0 ± 1.6 504 ± 103 22.7 ± 6.0 6.3 ± 1.6 501 ± 102 23.8 ± 6.0 FHe269 Hendry’s Creek 744316 4346774 Av. 6.1 ± 0.7 505 ± 46 23.2 ± 2.7 6.0 ± 1.7 548 ± 120 22.7 ± 6.4 6.1 ± 1.7 553 ± 119 23.0 ± 6.4 6.0 ± 1.7 543 ± 117 22.7 ± 6.4 FSi18 Silver Creek 739400 4340999 Av. 6.0 ± 1.0 548 ± 69 22.8 ± 3.7 Individual P-T determinations are given at the 2 confidence level. Average (Av.) P-T results are given with the standard error of the mean ( x ), where x = / n is the mean standard deviation for n thermobarometric calculations. Burial depth = P/g, where = 2.7g/cm3 and g = 9.81ms-1. |
