Paleomagnetic Study of Indo-Asian Convergence and the Central Asian Shallow-Inclination Problem Using 33-45 Ma Volcanic Rocks Newly Discovered in Northern Tibet

在西藏北方羌塘中部新发现的火山岩中，进行了古地磁研究，获得了熔岩流、岩墙和火山锥的Ar-Ar年龄。作为拟议活动的智力价值的一部分，他们寻求以下两个主要问题的答案：（1）第一个问题是从大量高质量的第三纪岩石古地磁研究中得出的令人不安的低古纬度的一致模式，这些岩石从中国东部一直延伸到吉尔吉斯斯坦，以西3,000公里。这些古纬度与欧亚大陆古地磁参考极之间的差异在中国西部和吉尔吉斯斯坦平均为18度，这意味着在第三纪相对于西伯利亚的北向位移远大于地质学估计的缩短。这些主要是沉积物的古地磁数据的可靠性必须进行测试，然后我们才能评估有多少差异是构造，地磁和岩石磁性。(2)第二个问题是印度-亚洲会聚和西藏的拉张增生的历史。关于这个问题的现有证据被解释在各种各样的方式，导致争议的时间和几何形状的加积在西藏和西藏和欧亚大陆之间。特别是，PI的研究试图解决该地区构造演化中的两个重要构造问题：拉萨、西羌塘、塔里木和准噶尔地块在晚白垩世和早第三纪的古纬度问题，以及东、西羌塘地块之间的古加积历史问题，这些问题都需要可靠的古地磁资料来回答。这种方法是在这些辩论的基础上形成的。PI将集中在火山岩中的采样，只要有可能的部分，以避免我们被误导的风险，虚假的倾斜变浅，往往影响沉积岩。他们还将对与火山岩和褶皱试验有关的红层进行代表性取样。通过这种方式，他们将能够评估红层的磁性保真度。本文提出的古地磁方案的成功完成，将首次对直接涉及中亚新生代倾斜变浅争论的西藏北方新生代火山岩和红层产生可靠的古地磁结果。新的古地磁结果还将提供极位置和古纬度，以限制印度-亚洲会聚速率的计算。来自中国三所大学的中国同事在古生物学、地质年代学、岩石学、岩石磁学以及构造和野外地质学方面的专业知识，确保了这项研究的必要支持，并为成功的机会提出了强有力的理由。 主要研究者预计拟议活动将产生以下更广泛的影响：（1）结果将在国家会议上提出，向国家科学基金会报告，并在国际同行评审的期刊上发表;（2）研究的一些结果也将介绍给本科生和研究生课堂;（3）研究生和本科生研究人员将直接参与实地和实验室工作;（4）关于印支-亚洲辐合的范围和青藏高原隆升的时间的研究有助于更好地理解青藏高原对全球气候的影响。

ZhaoThe 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.