HR: 1340h
AN: V23C-1562    [Abstracts]
TI: Early Mesozoic overprinting of Paleozoic protoliths during shear zone formation in the southeast Gobi, Mongolia
AU: * Semple, I L
EM: ilsemple@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Webb, L E
EM: lewebb@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Taylor, J P
EM: jtaylo03@syr.edu
AF: Dept. of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Heumann, M J
EM: Heumann@earth.utah.edu
AF: Dept. of Geology & Geophysics, University of Utah, 135 S. 1460 East, Salt Lake City, UT 84112, United States
AU: Johnson, C L
EM: cjohnson@earth.utah.edu
AF: Dept. of Geology & Geophysics, University of Utah, 135 S. 1460 East, Salt Lake City, UT 84112, United States
AU: Minjin, C
EM: c_minjin@yahoo.com
AF: School of Geology, Mongolian University of Science & Technology, Ulaanbaatar, 210646, Mongolia
AB: The geology of southeastern Mongolia records continental growth via accretion of Paleozoic volcanic arcs and possibly fragments of continental crust. Locally, geologic maps imply major outcrops of Precambrian basement within the southern and southeast Gobi, the basis of the hypothesized South Gobi Microcontinent. However, results of tectonic studies of the East Gobi Fault Zone (EGFZ) indicate that the presence of bonafide Precambrian basement is suspect. We present field, structural and petrographic evidence that the Precambrian basement rocks mapped in the Tsagan Subarga and Tavan Har blocks of the EGFZ instead comprise Paleozoic sedimentary and volcanic protoliths overprinted by early Mesozoic metamorphism and deformation. NW-SE transects across the structural grain of the EGFZ were completed at Tsagan Subarga and Tavan Har. The Tsagan Subarga transect reveals a progressive increase in metamorphic grade from incipiently metamorphosed Carboniferous sedimentary and volcanic rocks in the north into greenschist-facies and amphibolite-facies metasedimentary and metavolcanic lithologies to the south. Synkinematic intrusives were observed in southernmost Tsagan Subarga. Despite the fact that relationships are complicated due to subsequent brittle deformation events that include Cenozoic strike-slip faulting, the lithologies, ductile deformation and metamorphism observed at Tsagan Subarga appear to correlate with that observed at Tavan Har. We present comparative analyses of mineral assemblages observed in thin sections of the metamorphic tectonites at Tsagan Subarga and Tavan Har with those of the Paleozoic protoliths. Microstructural analyses investigate the relationship between metamorphism and deformation. The results of this research bear on the tectonic evolution of Asia as well as mechanisms related to formation, growth and subsequent modification of continental crust.
DE: 3625 Petrography, microstructures, and textures
DE: 8000 STRUCTURAL GEOLOGY
DE: 8110 Continental tectonics: general (0905)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 9320 Asia
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting