Cooperative Institute for Research in Environmental Sciences

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Northeastern Tibet

Upward and Outward: Tibetan Plateau Growth and Climate Consequences

Supported by NSF’s Continental Dynamics Project

Collaborators (recent past and present)

• Jean-Daniel Champagnac, Swiss Federal Institute of Technology, Zurich, Switzerland
• Katherine Dayem, Ecos Consulting, Inc., Durango, Colorado
• Doug Burbank and Richard Lease, University of California, Santa Barbra
• Marin Clark and Alison Duval, University of Michigan
• Carmie Garzione and Brian Hough, University of Rochester
• Ken Farley, Caltech
• Eric Kirby, Penn State University
• Gerard Roe, University of Washington
• Yuan Daoyang and Ge Weiping, Institute of Seismology, Lanzhou, Gansu, China
• Zhang Huiping, Zhang Peizhen, Zheng Dewen, and Zheng Wenjun, Institute of Geology, China Seismology Administration, Beijing China

The Tibetan Plateau not only serves as the world’s best laboratory for studying intracontinental deformation, but also acts as the continents’ largest perturbation to atmospheric circulation. Accordingly, changes in the height or lateral extent of the plateau both should reflect deep-seated processes in the lithosphere and should affect climate. We are examining physical mechanisms that link geodynamic processes operating beneath the Tibetan Plateau since Late Miocene time to concurrent local and regional environmental changes, including a strengthening of the Indian Monsoon, the aridification of regions both south and northeast of Tibet, and an increase in aeolian deposition northeast of Tibet, and even to the North Pacific Ocean (Figure 1). For those who are interested, Molnar [2005] presents a summary of tectonic and paleo-environmental observations relevant to this topic. Mechanisms that can link the geodynamic and environmental changes include an increase in the mean elevation of the plateau [e.g., Molnar et al., 1993] and an outward growth of it by flow of lower crust that rapidly expands the area of high topography. The deformation of the region surrounding the plateau seems to have acclerated near 10-8 million years ago, and this suggests an outward, if not upward, growth of the plateau (Figure 2).

This research includes focused studies (1) to determine when deformation occurred along the northeastern margin of Tibet and how much crustal shortening has occurred, (2) to date the initiation of erosion and river incision into high terrain and (3) to decipher when particular regions of high terrain began shedding debris to both nearby and distant basins, both of which will address when relief was created, (4) to map spatial and temporal patterns of environmental change, (5) to exploit geophysical data to discriminate among possible processes occurring within the crust and mantle, and (6) to understand how high topography affects regional atmospheric circulation, dust transport, and heat transport within the atmosphere. Our goals are to create images of how northeastern Tibet has grown outward and of how that growth has affected regional climate.

Figure 1. Map of eastern Asia showing time series of environmental changes (Molnar [2005]). In all plots, time increases from the past on the left to present day on the right; red lines show 5 Ma intervals, the green line shows 7.5 Ma, and light shading for young parts of some show periods for which there are no data (no sediment, in most cases). Blue symbols indicate measurements of carbon (∞13C) and oxygen (∞18O) isotopes from pedogenic carbonates in Pakistan by Quade, Cerling, and colleagues, percentages of grass (Gramineae) pollen from the Siwalik sediment of Nepal from Hoorn et al., and percentages of conifer pollen from the Linxia Basin from Ma et al. Purple show fractions of microorganisms in Ocean Drilling Project cores: percentages of Globigerina bulloides in the Arabian Sea counted by Kroon et al. 1991 and of Neogloboquadrina dutertrei in the South China Sea from Wang et al. 2003. Brown indicates loess accumulation and terrigenous sediment at the southern edge of the Bengal Fan, both the accumulation rate, with tic marks at intervals of 50 m/Myr, and mean grain sizes, with tick marks at 200-micron intervals from France-Lanord et al.. Loess accumulation rates are shown for four regions, with all plotted at the same scale: Qinan from Guo et al., Lingtai from Ding et al., Xifeng from Sun et al., and Jiaxian from Qiang et al., who did not sample the top 3 Ma. Finally, aeolian deposition in the North Pacific from Rea et al. is plotted with tic marks at 0.2 kg/m2/kyr.

Figure 2. Map of eastern Asia showing loci of inferred tectonic developments that began within a few million years of 8 Ma, with types of observations color-coded (from Molnar [2005]). Yellow dots show three locations where Garzione et al., Rowley et al., and Spicer et al. reported elevations similar to those today at 11, 8, and 15 Ma, respectively. Dark blue dots show places where northerly trending normal faults have been dated: Shuang Hu graben by Blisniuk et al., Thakkhola graben by Coleman and Hodges and by Garzione et al., Nyainqentanghla graben by Harrison et al. and by Pan and Kidd, and two other normal faults assigned dates of 8 ± 1 and 9 ± 1 Ma by Harrison et al., and the light blue dot shows where north-south trending dikes were dated as old as 18 Ma by Williams et al. Red dots show places where folding, thrust faulting, and crustal shortening seem to have begun at in late Cenozoic time: Equatorial Indian Ocean (work of Cochran, Curray and Munasinghe, and Krishna et al., Tien Shan (work of Abdrakhmatov et al. and Bullen et al., Qilian Shan (from Métivier et al.), Gobi-Altay (from Kurushin et al.), Liupan Shan (from Zheng et al.), and the Min Shan and Longmen Shan (from Kirby et al.). The purple dot shows the location of the Linxia Basin, where Fang et al. inferred that progradation of a foreland fold-and-thrust belt and flexure ceased, and the locus of deformation moved far from this area. Brown dots show regions where Clark and her colleagues inferred late Cenozoic incision to result from a Late Miocene rise of the gentle surface of the southeastern Tibetan Plateau.

Recent field work by Champagnac, Yuan, Ge, and Molnar is desgined to assess rates of slip on both strike-slip and thrust faults in northeastern Tibet (Figure 3).

In addition to the research being carried out, CIRES's Outreach group has produced a short film for high school students entitled: "Upward and Outward: Scientific Inquiry on the Tibetan Plateau."

References

Champagnac, J.-D., D.-Y. Yuan, W.-P. Ge, P. Molnar, and W.-J. Zheng (2010), Slip rate at the northeastern front of the Qilian Shan, China, Terra Nova, 22, 180-187.

Dayem, K. E., P. Molnar, M. K. Clark, and G. A. Houseman (2009), Far-field lithospheric deformation in Tibet during continental collision, Tectonics, 28, TC6005, doi:10.1029/2008TC002344.

Dayem, K. E., G. A. Houseman, and P. Molnar (2009), Localization of shear along a lithospheric strength discontinuity: Application of a continuous deformation model to the boundary between Tibet and the Tarim Basin, Tectonics, 28, TC3002, doi:10.1029/2008TC002264.

Molnar, P (2005), Mio-pliocene growth of the Tibetan Plateau and evolution of East Asian climate.Palaeontologia Electronica, 8, 8.1.2A, 23p, 625KB; http://palaeo-electronica.org/paleo/2005_1/molnar2/issue1_05.htm.