HR: 0800h
AN: T31D-0674    [Abstracts]
TI: Does Tibetan lower crust flow? Preliminary constraints from a reconnaissance investigation of lacustrine shorelines around Siling Co, Tibet
AU: * Shi, X
EM: xzs104@psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802, United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802, United States
AU: Furlong, K
EM: kevin@geodyn.psu.edu
AF: Penn State University, Department of Geosciences, University Park, PA 16802, United States
AU: Wang, E
EM: erchie-wang@mail.iggcas.ac.cn
AF: Chinese Academy of Sciences, Institute of Geology and Geophysics, Beijing, 100029, China
AU: Asmerom, Y
EM: asmerom@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM 87131, United States
AU: Polyak, V
EM: polyak@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM 87131, United States
AB: Although rheology of crust and lithosphere is central to all models of lithospheric deformation during orogenesis, recent propositions that lateral flow of weak mid-to-lower crust is an active participant in the growth and evolution of the Tibetan Plateau demand close scrutiny of whether the appropriate conditions exist for such behavior. Unfortunately, determining crustal rheology from geologic and geophysical investigations remains challenging, and many lines of evidence are equivocal. One of the most definitive approaches to this problem exploits the flexural/isostatic response to changes in surface loads, often lacustrine in origin [Gilbert, 1890]. Here we present the results of a reconnaissance expedition to Siling Co, in east-central Tibet. With a present-day area of > 1800 km², Siling Co is the second-largest lake in Tibet, and the presence of high shorelines assumed to have formed during glacial lake highstands afford the opportunity to investigate deformation associated with isostatic adjustment to changes in lake levels. Shoreline features around Siling Co are remarkably well-preserved and consist of both erosional (wave-cut cliffs, notches) and constructional (beach ridges, spits, tombolos). The highest of these stands approximately 50m above the lake. Surveys of this shoreline, correlated by landscape position and geomorphic character, appear to be consistent with slight (several meter), but systematic, increases in elevation toward the center of the former lake. These results are preliminary, as they depend on correlations among undated shorelines. Early results from U-Th chronology of lacustrine tufas indicate the presence of a Stage 6 lake, but may not directly constrain the age of the shoreline. Future work with cosmogenic isotopes will allow us to both test shoreline correlations and also place age constraints on the timing of lake level fall . Our preliminary analysis indicates that length scales and the inferred magnitudes of shoreline deflection are appropriate to distinguish between models of middle/lower crustal flow or upper mantle (asthenospheric) flow in central Tibet.
DE: 1824 Geomorphology: general (1625)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting