HR: 14:40h
AN: T13H-05    [Abstracts]
TI: Structural Observations From the Tangra Yum Co, Lunggar Shan, and Lopu-Kangri Rift Systems, Southern Tibet
AU: * Taylor, M
EM: mht@ku.edu
AF: University of Kansas Department of Geology, 1475 Jayhawk blvd. 114 Lindley Hall, Lawrence, KS 66045, United States
AU: Kapp, P
EM: pkapp@geo.arizona.edu
AF: University of Arizona Department of Geosciences, Gould-Simpson Bldg. #77, Tucson, AZ 85721-0077, United States
AU: Stockli, D
EM: stockli@ku.edu
AF: University of Kansas Department of Geology, 1475 Jayhawk blvd. 114 Lindley Hall, Lawrence, KS 66045, United States
AU: Murphy, M
EM: mmurphy@mail.uh.edu
AF: University of Houston Geosciences Department, 4800 Calhoun Rd., Houston, TX 77204, United States
AU: Dewane, T
EM: tjdewane@ku.edu
AF: University of Kansas Department of Geology, 1475 Jayhawk blvd. 114 Lindley Hall, Lawrence, KS 66045, United States
AU: Lin, D
EM: dinglin@mail.igcas.ac.cn
AF: Institute of Tibetan Plateau Research, CAS, P.O.Box2871, Beijing, 100085, China
AB: We suggest that boundary conditions exert more control over pre-existing structures in dictating the geometry for north-trending rifts in southern Tibet. We present geologic and neotectonic mapping, and observations made from satellite imagery along several north-trending rift systems in the Lhasa terrane, southern Tibet. From east to west, and to the south they include, 1) Tangra Yum Co, 2) Lunggar Shan, and 3) the Lopu-Kangri rift systems. Our observations bear new light on the geometry and kinematics of active extension in the hinterland of the Indo- Asian collision. Observations from the rift systems in southern Tibet indicate that they share a common trait; there is no obvious surface correlation with pre-existing structures. The architecture of the Lhasa terrane and its prior tectonic history illustrates this point as outlined by the following structural relationships. The Lhasa terrane is comprised of Pre-Ordovician gneiss overlain by Ordovician to Cretaceous strata. Pre-Mesozoic strata were intruded by Late Jurassic - Tertiary plutons and underwent significant shortening by the Cretaceous - early Eocene Gandese retroarc and northern Lhasa thrust belts. The plutons and the approximately E- trending contractional fabric of the Lhasa terrane are cut and offset by the active N-trending rift systems. Even though the southern Tibetan rifts share this first-order characteristic, they also vary markedly in structural style as a function of extension magnitude; most Tibet rifts are internally drained systems bounded by high-angle normal faults that have 10km or less extension, as reflected by the geometry of the Tangra Yum Co rift. However, rifts that have experienced large magnitude extension (>20 km) are bounded by low-angle normal faults (detachments) with mylonitic rocks and Miocene granites in the footwall, and intrabasinal topographic highs are actively developing near areas of inferred maximum extension. The Lopu-Kangri rift system in far southwestern Tibet is more enigmatic in that it trends NNW, yet it exhibits normal and oblique dextral shear indicators in the footwall rocks, and streams along the range front are dextrally offset. The fault system right-laterally separates the Gangdese batholith, Kailas conglomerate, Great Counter thrust, and the Tethyan fold-thrust belt. One explanation as to why boundary conditions appear to exert more control on determining the active rift geometry is that pre- existing structures are oriented at a high angle to the present orientation of the maximum principle stress direction, making them unfavorable to reactivation.
DE: 8012 High strain deformation zones
DE: 8107 Continental neotectonics (8002)
DE: 8110 Continental tectonics: general (0905)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting