Collaborative Research: Cenozoic Tectonics and Surface Uplift in North-Central Tibet

印度和亚洲的碰撞有力地抬高了青藏高原，这是地球表面地形最高、地壳最厚的地区。高原的隆升也可能在Cenozic时期控制全球气候方面发挥了重要作用。了解青藏高原的隆升历史是当今地球科学面临的主要挑战之一。尽管进行了三十多年的积极研究，但对于高原抬升的时间和高原抬升的构造过程，几乎没有达成共识。在这项合作研究中，来自加州大学圣克鲁斯分校和印第安纳大学的研究人员在西藏中北部三个纬度分布的盆地中开展了一项综合研究计划，该计划结合了古地磁学(磁性地层学和构造学)、沉积学(相描述、古水流和物源研究)、同位素测年和古高度学(玄武岩气泡密度和氧同位素)。主要目标是重建西藏中北部的古近纪构造史，评估上地壳过程对高原生长和维持的相对贡献，并评估预测早期(例如，大约4000万年前)逐渐隆起的构造模型和预测较新(不到1500万年前)突然隆起的构造模型的相对作用。为了实现这些目标，正在使用标准的盆地分析技术对每个盆地的岩石地层和沉积环境进行比较，以确定沉积的构造背景。详细的新磁性地层学结果和辐射测量数据将澄清这些盆地的年龄和相互关系。新的古地磁结果还将提供极点位置和古纬度，以限制对印度支那-亚洲会聚速率的计算，以及该地区构造块体之间构造旋转的数量和时间。这些盆地的氧同位素时间序列将提供有关其地形发育和气候历史的定量信息。与气泡状古高程相比较，熔岩古高程测量可以提供对海拔的独立检查，并消除关于低氧同位素值是否表明盆地本身或沿蒸汽运输路径顺风向区域的古海拔高的模糊性。这项研究将加深对与印度-亚洲碰撞有关的陆内变形构造过程的理解。明确的藏北隆起史对理解新生代气候变化具有重要意义，并将从根本上制约高原形成机制(S)，这引起了广泛科学界的兴趣。该项目构成了两名研究生攻读博士学位的基础，部分项目适用于本科生的研究论文。

The collision between India and Asia has forcefully raised the Tibetan plateau, the most extensive region of elevated topography and thick crust on the Earth's surface. The uplift of the plateau may also have played a major role in controlling global climate during Cenozic time. Understanding the uplift history of the Tibetan plateau is one of the main challenges in earth sciences today. Despite more than three decades of active research, there is little consensus regarding the timing of plateau uplift and the tectonic processes by which the plateau was raised. In this collaborative study, researchers from the University of California at Santa Cruz and Indiana University are carrying out an integrated research program combining paleomagnetism (magnetostratigraphy and tectonics), sedimentology (facies descriptions, and paleocurrent and provenance studies), isotopoic dating, and paleoaltimetry (basalt vesicularity and oxygen isotopes) in a series of three latitudinally spaced basins in North-Central Tibet. The primary goals are to reconstruct the Paleogene tectonic history of north central Tibet, assess the relative contribution of upper crustal processes to plateau growth and maintenance, and assess the relative roles of tectonic models that predict early (e.g., approximately 40 million years ago) gradual uplift and those that predict more recent (less than 15 million years ago) abrupt uplift. To achieve these goals, lithostratigraphy and depositional environments in each basin are being compared using standard basin-analysis techniques to characterize the tectonic setting of sedimentation. The detailed new magnetostratigraphic results and radiometric dates will clarify the age of and correlation between these basins. The new paleomagnetic results will also provide pole positions and paleolatitudes to constrain the calculation for the Indo-Asian convergence rate and the amount and timing of tectonic rotation between tectonic blocks in the region. Times series of oxygen isotopes from these basins will provide quantitative information on their topographic development and climatic history. Comparison with vesicularity paleoaltimetry of the lavas may provide an independent check on elevation and remove ambiguity as to whether low oxygen-isotope values signal high paleoelevation of the basins themselves or of regions downwind along the vapor transport path. This research will improve understanding of the tectonic processes of intracontinental deformation related to the India-Asia collision. A definitive uplift history of northern Tibet is important for understanding climate change during Cenozoic time and will place fundamental constraints on the mechanism(s) of plateau formation, which interests a broad scientific community. This project forms the basis for two graduate students' PhD studies, and parts of the project are suitable for undergraduate research theses.