Quade, Jay and Breecker, Daniel O. and Daëron, Mathieu and Eiler, John (2011) The paleoaltimetry of Tibet: An isotopic perspective. American Journal of Science, 311 (2). pp. 77-115. ISSN 0002-9599 http://resolver.caltech.edu/CaltechAUTHORS:20110607-113619763
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Stable isotopes provide a valuable perspective on the timing of elevation change of the Tibetan Plateau. We begin our paper by looking in depth at isotopic patterns in modern Tibet. We show that the δ^(18)O value of surface waters decreases systematically up the Himalayan front in central Nepal by about –2.8‰/km, in agreement with the patterns documented and modeled by previous research. On the Tibetan plateau itself there is no apparent correlation between elevation and the δ^(18)O value of flowing surface waters. Both surface waters and soil carbonates display a northward increase in δ^(18)O values, of about 1.5‰/° north of the Himalayan crest, even though elevation increases modestly. The isotopic increase with latitude reduces the isotope-elevation gradient for water in the northernmost plateau to –1 to –2‰/km. Carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau. Temperature estimates from clumped-isotope (Δ_(47)) analyses of modern soil carbonates significantly exceed mean annual air T and modeled maximum summer soil temperatures by 15.8±2.8° and 9.7±2.5 °C, respectively. Similarly elevated temperatures best account for the δ^(18)O values observed in modern soil and lake carbonates. We recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude-corrected isotopic values. With one notable exception, our revised model produces paleoelevation estimates very close to previous estimates. The exception is the reconstruction from late Eocene age deposits at Xoh Xil, for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed. Therefore, there is no evidence for northward progression through time of Tibetan elevation change. Instead, the available—but admittedly very scanty—evidence suggests that much of Tibet attained its modern elevation by the mid-Eocene. A truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across Tibet, especially in the center and north and for >15 Ma.
|Additional Information:||© 2011 American Journal of Science. JQ thanks Ding Lin, Paul Kapp and Pete DeCelles for involving him in their Tibetan research, and discussions and data from Dave Dettman and Andrew Leier, and acknowledges support from NSF-EAR-Tectonics 0438115. These colleagues in addition to Joel Saylor all helped collect modern water samples. We thank Alyson Cartwright for assembling the DEM in figure 1, and Hema Achyuthan, Chris Eastoe, Majie Fan, Adam Hudson for their help in the laboratory and field. DB thanks M. Jessup, D. Newell and J. Cottle for including him in their 2007 Tibetan research trip and Z. Sharp for the use of his stable isotope laboratory at the University of New Mexico, and acknowledges support form the Caswell Silver Foundation. JME acknowledges support from NSF-0843104. Michael Hren and Peter Molnar both provided very helpful reviews of the manuscript.|
|Subject Keywords:||Tibet; carbonates; paleoaltimetry; oxygen isotopes; uplift|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||08 Jun 2011 17:30|
|Last Modified:||08 Jun 2011 17:30|
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