HR: 1340h
AN: T53A-0467    [Abstracts]
TI: Evidence of Cretaceous Foreland Basin Systems in the Lhasa Terrane and the Implications for the Tectonic Evolution of Southern Tibet
AU: * Leier, A L
EM: aleier@geo.arizona.edu
AF: The University of Arizona, Gould-Simpson Building, 1040 E. Fourth St., Tucson, AZ 85721 United States
AU: Eisenberg, D A
EM: danieladameisenberg@yahoo.com
AF: The University of Arizona, Gould-Simpson Building, 1040 E. Fourth St., Tucson, AZ 85721 United States
AU: Kapp, P A
EM: pkapp@geo.arizona.edu
AF: The University of Arizona, Gould-Simpson Building, 1040 E. Fourth St., Tucson, AZ 85721 United States
AU: DeCelles, P G
EM: decelles@geo.arizona.edu
AF: The University of Arizona, Gould-Simpson Building, 1040 E. Fourth St., Tucson, AZ 85721 United States
AB: Any model attempting to explain the relationship between the Indo-Asian collision and the uplift of the Tibetan plateau must first consider the tectonic circumstances in southern Asia immediately preceding the collision. Current hypotheses regarding Cretaceous tectonism in the Lhasa terrane of southern Tibet range between end-member models involving regional extension and regional contraction. We examined the Cretaceous sedimentary strata of the central Lhasa terrane in order to reconstruct the depositional history and basin evolution of the region, and from these findings, to determine the tectonic conditions during this period. Lower Cretaceous sediments consist of marginal marine and fluvial deposits with abundant quartzite- and granite-clast conglomerates in the northern part of the Lhasa terrane and finer-grained sediments interbedded with occasional quartzite-clast conglomerates in the south. Paleocurrents indicate south- to southwest-directed transport. Overlying these clastic units are widespread Aptian-Albian shallow marine limestones. The thickest limestones occur in the central portion of the Lhasa terrane while to the north and south the limestones are thinner and interbedded with clastic units. Upper Cretaceous strata are preserved primarily in the south and consist of arkosic fluvial red-beds with rare quartzite-clast conglomerates. Paleocurrents in the upper Cretaceous strata indicate north- to northwest-directed transport. We propose that the lower Cretaceous clastic sediments were deposited in a peripheral foreland basin that formed on the Lhasa terrane as it collided with the Qiangtang terrane during the Late Jurassic - Early Cretaceous. The upper Cretaceous sediments were deposited in a retro-arc foreland basin system that was created as the Gandese magmatic arc developed on the southern margin of the Lhasa terrane. The widespread Aptian-Albian limestones mark a significant transition from a peripheral foreland basin in the north to a retro-arc foreland basin in the south. The results of this study substantiate the idea that compressional deformation was occurring on the southern margin of Asia long before the Cenozoic collision with India. Although further study is needed to refine the extent of deformation, these tectonic events should be incorporated as initial conditions into any model addressing the evolution of the Tibetan plateau.
DE: 9320 Asia
DE: 9609 Mesozoic
DE: 8102 Continental contractional orogenic belts
DE: 8150 Plate boundary--general (3040)
DE: 3675 Sedimentary petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting