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ii
ACKNOWLEDGEMENTS
Little did I know in March 2003, when I was offered a three-year fellowship to
study for my Ph.D. at University College London (UCL), that five years later I would
be completing it half way around the world at the University of Southern California
(USC). For this, and many other things, I must start by thanking my advisor John
Platt. As John’s only graduate student for the majority of my Ph.D., I have been lucky
enough to benefit from a close working relationship, from which I have learnt a huge
amount. John is an amazing structural geologist, field geologist, and of course, wine
connoisseur. He is really inspirational in the field (although we have managed to get
into a few intellectual tangles on the odd outcrop in 100°F heat), and a pleasure to work
with. I really hope that we will continue to collaborate in the future.
My dissertation committee members have also been invaluable to me over the
years. Greg Davis is a constant source of inspiration with his immense knowledge of
Cordilleran tectonics and metamorphic core complexes. Jean Morrison has been readily
available to offer advice and thoughts on thermobarometry, even though she’s always
swamped with her work at the Graduate school. Ellen Platzman’s paleomagnetism
expertise have been invaluable to this project, and I have really enjoyed this aspect of
my work, even though the drilling didn’t always go according to plan! I would also like
to thank my external committee member, Mark Thompson, for taking on the challenge
of learning about Snake Range rocks!
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 2 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | ii ACKNOWLEDGEMENTS Little did I know in March 2003, when I was offered a three-year fellowship to study for my Ph.D. at University College London (UCL), that five years later I would be completing it half way around the world at the University of Southern California (USC). For this, and many other things, I must start by thanking my advisor John Platt. As John’s only graduate student for the majority of my Ph.D., I have been lucky enough to benefit from a close working relationship, from which I have learnt a huge amount. John is an amazing structural geologist, field geologist, and of course, wine connoisseur. He is really inspirational in the field (although we have managed to get into a few intellectual tangles on the odd outcrop in 100°F heat), and a pleasure to work with. I really hope that we will continue to collaborate in the future. My dissertation committee members have also been invaluable to me over the years. Greg Davis is a constant source of inspiration with his immense knowledge of Cordilleran tectonics and metamorphic core complexes. Jean Morrison has been readily available to offer advice and thoughts on thermobarometry, even though she’s always swamped with her work at the Graduate school. Ellen Platzman’s paleomagnetism expertise have been invaluable to this project, and I have really enjoyed this aspect of my work, even though the drilling didn’t always go according to plan! I would also like to thank my external committee member, Mark Thompson, for taking on the challenge of learning about Snake Range rocks! |
