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122
Table 5.1 Preliminary RSCM results
Sample FMW76, carbonate, Marble Wash, northern Snake Range
Graphite
analysis D1 D2 G R2 Temperature
(°C)
1 30360 2161.2 54578 0.3486 486
2 22502 3146.4 51682 0.2910 512
3 162420 10462 143160 0.5139 412
4 64809 6410.8 212210 0.2287 539
5 101530 2518.9 79003 0.5547 394
6 24231 4285.2 69494 0.2472 531
7 98538 6030.3 58664 0.6037 372
8 21791 5539.9 58478 0.2539 528
9 22997 18450 33504 0.3068 504
10 110930 10389 137480 0.4286 450
Mean 473
St. Dev. 61
Sample FMC147, metapelite, McCoy Creek, Schell Creek Range
Graphite
analysis D1 D2 G R2 Temperature
(°C)
1 52554 2341.3 53748 0.4837 426
2 181950 21332 149950 0.5151 412
3 55207 8716.2 81252 0.3803 472
4 51552 8070.5 94545 0.3344 492
5 43008 6148.8 71394 0.3568 482
6 46325 8938.9 62724 0.3926 466
7 112550 33731 125370 0.4143 457
8 40811 9950.5 68157 0.3432 488
9 59640 6547.6 92245 0.3764 473
Mean 463
St. Dev. 28
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 137 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 122 Table 5.1 Preliminary RSCM results Sample FMW76, carbonate, Marble Wash, northern Snake Range Graphite analysis D1 D2 G R2 Temperature (°C) 1 30360 2161.2 54578 0.3486 486 2 22502 3146.4 51682 0.2910 512 3 162420 10462 143160 0.5139 412 4 64809 6410.8 212210 0.2287 539 5 101530 2518.9 79003 0.5547 394 6 24231 4285.2 69494 0.2472 531 7 98538 6030.3 58664 0.6037 372 8 21791 5539.9 58478 0.2539 528 9 22997 18450 33504 0.3068 504 10 110930 10389 137480 0.4286 450 Mean 473 St. Dev. 61 Sample FMC147, metapelite, McCoy Creek, Schell Creek Range Graphite analysis D1 D2 G R2 Temperature (°C) 1 52554 2341.3 53748 0.4837 426 2 181950 21332 149950 0.5151 412 3 55207 8716.2 81252 0.3803 472 4 51552 8070.5 94545 0.3344 492 5 43008 6148.8 71394 0.3568 482 6 46325 8938.9 62724 0.3926 466 7 112550 33731 125370 0.4143 457 8 40811 9950.5 68157 0.3432 488 9 59640 6547.6 92245 0.3764 473 Mean 463 St. Dev. 28 |
