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

利用藏北新发现的33~45 Ma火山岩研究印亚辐合与中亚浅倾角问题

• 批准号: 0310309
• 负责人: Xixi Zhao
• 金额: $ 28.68万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0310309&HistoricalAwards=false
• 关键词: Paleomagnetic; Study; Indo; Asian; Convergence

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.

Zhaothe Pi的将在西藏北部的Qiangtang中新发现的火山岩进行古磁研究计划，最近在那里获得了熔岩流，堤坝和火山锥的Ar-Ar日期。作为拟议活动的智力优点的一部分，他们寻求以下两个主要问题的答案：（1）第一个是始终如一的低较低的古呈较低的模式，这些模式来自大量高质量的古磁研究，从东部到达吉尔吉斯斯坦，3,000 km到吉尔吉斯斯坦，对来自东部中国东部的地点的三级岩石研究。这些古介质与古磁参考极点的差异在中国西部和吉尔吉斯坦平均为18度，这意味着相对于三级西伯利亚的北部位移，这些位移远大于间隔山皮带的缩短地质估计值。在我们评估多少差异是构造，地磁和岩石磁性之前，必须测试这些主要是沉积古磁数据的可靠性。 （2）第二个问题是西藏中印度 - 亚洲融合和地形积聚的历史。有关该主题的现有证据以多种方式解释，从而引起了关于西藏内部以及西藏和欧亚大陆之间地层积聚的时间和几何形状的争议。特别是，PI寻求解决该地区构造进化的两个重要构造问题的答案：即，拉萨（Lhasa），西Qiangtang，Tarim和Junggar街区的旧难题明显的困境在晚期和早期的第三阶段和地段历史上，以及对Qiangtang bloce的较早的问题。这些辩论构成了这种方法。 PI将其采样集中在有希望的部分的火山岩中，以避免我们被伪造的倾斜度误导的风险经常会影响沉积岩。他们还将对与火山和折叠测试相关的红床进行代表性抽样。通过这种方式，他们将能够评估红床的磁性保真度。成功完成此处提出的古磁计划将首次产生可靠的古磁性结果，该磁去成岩石岩石和西藏北部的红床直接参与了中亚中亚的新生代倾向的辩论。新的古磁结果还将提供极点位置和古介质，以限制印度 - 亚洲融合的速率计算。来自中国三所大学的中国同事的古生物学，年代学，岩石学，岩石学，岩石磁性以及结构和田地地质的专业知识确保了对这项研究的必要支持，并强烈争辩成功的机会。 PI预期拟议活动的以下更广泛的影响：（1）结果将在国家会议上提出，向NSF报告，并在国际同行评审期刊上发表； （2）研究的一些结果也将引入本科和研究生教室； （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）关于印度亚洲融合和藏族提升时间的发现，可能有助于更好地理解藏族高原对全球气候的影响。