The PI's will carry on a paleomagnetic research program on newly discovered volcanic rocks in central Qiangtang of northern Tibet, where Ar-Ar dates on lava flows, dykes, and volcanic cones have recently been obtained. As part of the intellectual merit of the proposed activity, they seek answers to the following two leading questions: (1) The first is the consistent pattern of disturbingly low paleolatitudes derived from a large number of high-quality paleomagnetic studies of Tertiary rocks from sites that reach all the way from eastern China to Kyrgyzstan, 3,000 km to the west. The difference between these paleolatitudes and those expected from paleomagnetic reference poles for Eurasia averages 18 degrees in western China and Kyrgystan, implying northward displacements relative to Siberia in the Tertiary that are much larger than geological estimates of shortening across intervening mountain belts. The reliability of these mainly sedimentary paleomagnetic data must be tested before we can evaluate how much of the discrepancy is tectonic, geomagnetic, and rock magnetic. (2) The second problem is the history of Indo-Asian convergence and terrane accretion in Tibet. The existing evidence concerning this subject is interpreted in a wide variety of ways, resulting in controversy over the timing and geometry of terrane accretion both within Tibet and between Tibet and Eurasia. In particular, the PI's seek answers to the solution of two important tectonic problems in the tectonic evolution of the region: namely, the apparent dilemma in paleolatitudes for Lhasa, west Qiangtang, Tarim, and Junggar blocks in late Cretaceous and early Tertiary, and terrane accretion history between east and west Qiangtang block.
Reliable paleomagnetic data are needed to answer these questions. The approach is framed by these debates. The PI's will concentrate their sampling in volcanic rocks wherever promising sections are available, to avoid the risk of our being misled by the spurious inclination shallowing that often affects sedimentary rocks. They will also make a representative sampling of red beds that are associated with the volcanics and with fold tests. In this way they will be able to assess the magnetic fidelity of redbeds. Successful completion of the paleomagnetic program proposed here will, for the first time, produce reliable paleomagnetic results from Cenozoic volcanic rocks and red beds in northern Tibet, which are directly involved in the debate over Cenozoic inclination shallowing in central Asia. The new paleomagnetic results will also provide pole positions and paleolatitudes to constrain the rate calculation for Indo-Asian convergence. The expertise in paleontology, geochronology, petrology, rock magnetism, and structural and field geology of Chinese colleagues, who hail from three universities in China, ensures the necessary support for this research and argues strongly for the chances of success. The PI's anticipate the following broader impacts of the proposed activity: (1) results will be presented at national meetings, reported to the NSF, and published in international peer- reviewed journals; (2) some of the results of the research will also be introduced into both undergraduate and graduate classrooms; (3) graduate and undergraduate student researchers will be directly involved in both field and laboratory work; and (4) findings on the extent of Indo- Asian convergence and the timing of Tibetan uplift may help lead to a better understanding of the effects of the Tibetan Plateau on global climate.
