Mathematics – Logic
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....9918175y&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. B9, p. 18,175-18,201
Mathematics
Logic
77
Earth Movements, Earth Planetary Structure, Geochronology, Geological Faults, Tibet, Paleoclimatology, Planetary Evolution, Plateaus, Tectonics
Scientific paper
Structural and thermochronological investigations of southern Tibet (Xizang) suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost Tibetan plateau since late Oligocene. Two thrust systems are documented in this study: the north dipping Gangdese system (GTS) and the younger south dipping Renbu-Zedong (RZT). West of Lhasa, the Gangdese thrust juxtaposes the Late Cretaceous forearc basin deposits of the Lhasa Block (the Xigaze Group) over the Tethyan sedimentary rocks of the Indian plate, whereas east of Lhasa, the fault juxtaposes the Late Cretaceous-Eocene, Andean-type arc (the Gangdese batholith) over Tethyan sedimentary rocks. Near Zedong, 150 km southeast of Lhasa, the Gangdese thrust is marked by a greater than 200-m-thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks. A major south dipping backthrust in the hanging wall of the Gangdese thrust puts the Xigaze Group over Tertiary conglomerates and the Gangdese plutonics north of Xigaze and west of Lhasa. A lower age bound for the Gangdese thrust of 18.3 +/- 0.5 Ma is given by crosscutting relationships. The timing of slip on the Gangdese thrust is estimated to be 27-23 Ma from Ar-40/Ar-39 thermochronology, and a displacement of at least 46 +/- 9 km is indicated near Zedong. The age of the Gangdese thrust (GT) is consistent with an upper age limit of approximately 24 Ma for the initiation of movement on the Main Central thrust. In places, the younger Renbu-Zedong fault is thrust over the trace of the GT, obscuring its exposure. The RZT appears to have been active at circa 18 Ma but had ceased movement by 8 +/- 1 Ma. The suture between India and Asia has been complexly modified by development of the GTS, RZT, and locally, strike-slip and normal fault systems.
Copeland Peter
Harrison Mark T.
Kidd William S. F.
Ryerson Frederick J.
Wenji Chen
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