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iv
free camping in the park, the odd life-saving hot shower, and rescued me more than
once during my Snake Range escapades!
Analytical work could not have been done without the assistance (and patience)
of Frank Kyte (UCLA, electron microprobe), Marty Grove and Kevin McKeegan
(UCLA, ion probe), Scott Bogue (Occidental College, cryogenic magnetometer),
George Rossman and Liz Miura Boyd (Caltech, Raman laser) and Gareth Seward
(UCSB, electron backscatter diffraction). Since the majority of this project revolved
around the electron microprobe I must especially thank Frank for spending so many
hours helping me, particularly when the probe broke over a weekend or late at night.
I am also grateful to Roger Powell, Boris Kaus, Thorsten Becker and Jim Connolly
for their helpful advice and guidance through my struggles with various computer
programs, notably Thermocalc, Matlab, and Perple_X!
Over the past five years I have made many good friends, both at UCL and USC.
Firstly my officemates: Ed Townend and Sam Tonkin at UCL, Geoffrey Pignotta, Helge
Alsleben, and Rita Economos in the strain lab at USC, and finally Geoffrey Pignotta
(again), Whitney Behr, and Lisa Alpert in the relative peace and quiet of room 309.
Without their friendship and support I probably would have cracked up years ago.
I have also made a number of good friends during my time at USC who I would
particularly like to mention. Catherine and Peter Powers supported me through the
ups and downs of my first few months in LA, for which I will be eternally grateful.
Lisa Collins was one of the first people I met at USC, and together we managed to get
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 4 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | iv free camping in the park, the odd life-saving hot shower, and rescued me more than once during my Snake Range escapades! Analytical work could not have been done without the assistance (and patience) of Frank Kyte (UCLA, electron microprobe), Marty Grove and Kevin McKeegan (UCLA, ion probe), Scott Bogue (Occidental College, cryogenic magnetometer), George Rossman and Liz Miura Boyd (Caltech, Raman laser) and Gareth Seward (UCSB, electron backscatter diffraction). Since the majority of this project revolved around the electron microprobe I must especially thank Frank for spending so many hours helping me, particularly when the probe broke over a weekend or late at night. I am also grateful to Roger Powell, Boris Kaus, Thorsten Becker and Jim Connolly for their helpful advice and guidance through my struggles with various computer programs, notably Thermocalc, Matlab, and Perple_X! Over the past five years I have made many good friends, both at UCL and USC. Firstly my officemates: Ed Townend and Sam Tonkin at UCL, Geoffrey Pignotta, Helge Alsleben, and Rita Economos in the strain lab at USC, and finally Geoffrey Pignotta (again), Whitney Behr, and Lisa Alpert in the relative peace and quiet of room 309. Without their friendship and support I probably would have cracked up years ago. I have also made a number of good friends during my time at USC who I would particularly like to mention. Catherine and Peter Powers supported me through the ups and downs of my first few months in LA, for which I will be eternally grateful. Lisa Collins was one of the first people I met at USC, and together we managed to get |
