HR: 1340h
AN: T53A-0468    [Abstracts]
TI: Tertiary Shortening at the Northeastern Margin of the Tibetan Plateau
AU: * Angerman, C
EM: cangerma@geosc.psu.edu
AF: Penn State University, 311 Deike Building, University Park, PA 16802
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Penn State University, 218 Deike Building, University Park, PA 16802
AU: Harkins, N
EM: nharkins@geosc.psu.edu
AF: Penn State University, 311 Deike Building, University Park, PA 16802
AB: Although the Indo-Asian collision is the quintessential example of continental collision, the timing, extent, and distribution of Tertiary deformation around the current margins of the plateau are not well known. Two contrasting hypotheses for plateau growth exist: 1) shortening and crustal thickening occurred over a wide area during the Paleocene and Eocene, such that the plateau reached its present-day extent by Oligocene time, and 2) deformation progressively migrated north and east, such that the current margins of the plateau were not established until Late Miocene-Pliocene time. One means of testing between these two models is to establish estimates for the timing and magnitude of deformation at the edges of the plateau. At the northeast margin of the plateau, the Linxia basin experienced deposition of terrestrial sediments beginning in Oligocene time and continuing up into the Pliocene (Fang et al., 2003); however, little is known about the degree of deformation at the southern margin of the basin. Here we present new geologic mapping and preliminary stratigraphic observations along the southern margin of the Linxia basin. The basin margin is defined for nearly 90 km along strike by an E-W striking, north-vergent thrust system. Along the western section of the fault (near the Daxia river), Mesozoic and Paleozoic sediments are thrust over Tertiary basin sediments. A lack of cutoffs precludes a precise estimate of shortening. However, along the eastern segment (near the Tao river), Tertiary sediments are exposed both in the basin and in the hanging wall of the fault. Mapped relations indicate that the Tertiary conglomerates are folded over the basin-bounding structure and delineate significant deformation within the hanging-wall block. Stratal geometries exhibit up-section decreases in limb angle, indicative of progressive tilting during synchronous fold growth and sediment accumulation. We interpret geologic relations along this section of the Linxia Basin margin to reflect progressive deformation above a blind fault tip. Restoration of balanced cross-sections allows a preliminary estimate of the magnitude of Tertiary shortening along this margin of the Tibetan Plateau.
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting