Paper No. 134-1
Presentation Time: 8:00 AM-12:00 PM
UNDERGRADUATES MAP FORCEFULLY EMPLACED WESTERN NEVADA PLUTON AND ADJACENT REGIONAL STRUCTURES
SATTERFIELD, Joseph I., BARBER, Tyler, DO, Danny, and MILLER, Laurie J., Geology Department, San Jacinto College, 5800 Uvalde Rd, Houston, TX 77049, joe.satterfield@sjcd.edu

Well-exposed, 1.6 km-long pluton margins in Copper Mountain, in the S. Koegel Hills 100 km E of the Sierra Nevada batholith, contain map- and outcrop-scale regional structures as well as unrelated local structures produced by forceful intrusion of a 155-158 Ma granitic pluton. Three sophomores paid as research assistants accompanied the first author and spent 3 weeks mapping in western Nevada at 1:4000- to 1:24,000-scale. Students described rock types, measured S1, S0, and fold orientations, located contacts, discussed alternative hypotheses, and drafted figures. Field methods were taught during fieldwork. Units mapped include: a) Upper Triassic unmetamorphosed dark gray laminated limestone and sparse interstratified carbonate diamictite, b) gray foliated marble, c) Middle Jurassic granite, d) Jurassic amphibole-feldspar porphyry dikes, and e) 2 Tertiary igneous units. Laminated deep-marine limestone contains ammonites characteristic of Middle Norian Columbianus Zone (identifications by N.J. Silberling). Granite pluton has been dated at 158 and 155 Ma (K-Ar on biotite; Ekren and Byers, 1978). Several alternative sequences of events were tested: 1) pluton emplacement produced foliation in marble (S1) and spaced cleavage in limestone (S1), 2) pluton emplacement caused marble foliation (S2) that cross-cut earlier spaced cleavage in limestone (S1), and 3) foliation in marble (S1) and spaced cleavage in limestone (S1) define a strain gradient that predated pluton intrusion. Alternative 3 best fits the data and is part of this sequence of events: 1) Regional D1 deformation produced D1 folds and a strain gradient, 2) Granite pluton intruded, cross-cutting and reorienting S1, 3) Amphibole-feldspar porphyry dikes cross-cut the granitoid and S1, 4) NE- and NW-trending folds correlated to Luning-Fencemaker thrust belt deformation folded S1, 5) Cenozoic normal and strike-slip faults of the central Walker Lane cross-cut earlier structures. Thus at this location regional and pluton-caused deformation events are unrelated. Coupled with timing constraints from the nearby Sand Springs Range, Copper Mountain relations constrain the high-strain regional D1 event to have occurred between 202 and 158 Ma: no older than Sinemurian - Pliensbachian, age of the youngest map unit deformed by D1 in the Sand Springs Range, and before 158 Ma, age of the Copper Mountain granite.

2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 134--Booth# 150
Undergraduate Research in the Geosciences: Faculty and Student Perspectives (Posters)
Colorado Convention Center: Exhibit Hall
8:00 AM-12:00 PM, Tuesday, October 29, 2002
 

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