| Rocky Mountain Section - 57th Annual Meeting (May 23–25, 2005) | |
| Paper No. 4-12 | |
| Presentation Time: 8:00 AM-4:00 PM | ||
PRODUCTION OF MULTIPLE FOLIATIONS IN GARNET ZONE ROCKS: A RESPONSE TO SEVIER CRUSTAL THICKENING AND EXTENSION IN THE PEQUOP MOUNTAINS, NEVADA | ||
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DINKLAGE, William S., HEALEY, Adam R., and SAILER, Victoria A., Earth Science, Utah Valley State College, 800 West University Pkwy, Orem, UT 84058, dinklawi@uvsc.edu The Pequop Mountains of northeast Nevada present an ideal location for studying metamorphism and ductile deformation of sedimentary layers caused by thrust burial. Two phases of contraction in the region occurred by motion on the Windermere and Independence thrusts during the Cretaceous Sevier orogeny. Tertiary extension caused uplift and rotation of the rocks, exposing garnet through chlorite metamorphic zones. Most of the hanging walls of the thrust faults have been eroded away, leaving the metamorphosed footwall layers exposed at the surface. However, a sliver of the hanging wall of the smaller and younger Independence thrust still remains. We spent six days field mapping predominantly within the footwall of the Independence thrust in the Pequop Mountains. Outcrop and thin section analysis of 38 samples revealed that the dominant foliation in the region is S2, which dips moderately southeast, subparallel to compositional layering. Biotite porphyroblasts, which we interpret to be peak-metamorphic, predate S2. Locally, especially in the highest grade rocks, S2 is a high-strain, penetrative foliation that formed concurrently with a well developed east-trending mineral stretching lineation. In other cases S2 is a variably developed crenulation cleavage that overprints an S1 foliation still measurable in thin section. Inclusion trails in biotite porphyroblasts in rocks containing penetrative S2 dip more shallowly southeast than S2; we interpret these to be S1. If compositional layering was mostly subhorizontal throughout the formation of S1 and S2, then S1 would have formed with a shallow NW dip. We agree with Camilleri (1998, JSG) that the dominant foliation (the one we call S2) was produced by nearly coaxial vertical shortening of the crust following thrusting. This may have been an adjustment to the taper of the Sevier orogenic wedge as deformation propagated eastward. Our results indicate, however, that there was an earlier foliation (S1) that we interpret to have formed during southeast-directed Windemere thrusting. GIS analysis of our field data, combined with the thin section study, revealed no evidence of additional fabric development, metamorphism or even disruption of metamorphic isograds across the later Independence thrust.
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Rocky Mountain Section - 57th Annual Meeting (May 23–25, 2005)
General Information for this Meeting | ||
| Session No. 4--Booth# 12 General Geology (Posters) Mesa State College: Liff Auditorium 8:00 AM-4:00 PM, Monday, May 23, 2005 Geological Society of America Abstracts with Programs, Vol. 37, No. 6, p. 8 | ||
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