Kinematic Evolution and Exhumation History of the South Tibetan Detachment System, Everest Massif, Tibet

在喜马拉雅造山带的中东部，最高级的变质岩出露于高喜马拉雅板片中，这是一个20-30 km厚的向北倾斜的深地壳岩石楔，在35-15 Ma时在14-56 km深度变质。 板块的沿着底部以南向主中央冲断层（MCT）为界，沿着顶部以北向正断层的藏南拆离系（STDS）为界，这些正断层将喜马拉雅的变质和深熔核与青藏高原的未变质岩石分开。 早中新世以来，高喜马拉雅板块向南的挤压作用对喜马拉雅地质地貌的演化产生了深远的影响，其最高的地形和最深的侵蚀与挤压楔的上部相对应。 区域尺度的几何形状的逆冲断层和非最终的限制板，现在是相当众所周知的，并已做了大量的工作，记录剪切方向指标沿着的上，下表面的板和限制早期阶段的PTT路径内的岩石板。 然而，至关重要的差距仍然存在于我们的理解的运动学（涡度）的流动和流动之间的关系和挤压楔内的渐进折返。 确定沿楔状边界断层的位移沿着的时间和大小与演化中的楔状体内的流动运动学之间的时空关系，对于理解造山带的地壳增厚、折返和侵蚀历史至关重要。 例如，是内部的板为主的纯剪切变形和有界的拉伸故障建议在最近发表的挤压模型，或流整个板为主的简单剪切建议在其他模型。 纯剪切分量的识别是至关重要的，因为一个显着的纯剪切分量的操作将导致：1）薄化和倾向平行延伸板本身，2）相对于严格的简单剪切，在两个应变率和extr-explanation/折返率的增加。 挤压模型的测试需要的空间和时间分布的运动（涡）域被映射出整个板，还需要运动和PTT分析之间的紧密结合，以约束渐进变形和折返路径。 只有一个已发表的定量涡度分析已沿着高喜马拉雅板块的基底部分，并没有这样的研究存在的板块中上部。 PI建议沿着沿着横跨板的南北走向对高喜马拉雅板的运动学演化和剥露历史进行综合研究，并选择了珠峰地区进行这项研究。 在珠峰地区，横跨板块的南北样带长度约为60-80 km，鉴于研究所需的详细实地工作，在NSF资助的标准项目的2-3年内不可能完成横跨板块的整个样带。 因此，PI建议将样带分为两个单独的资助阶段，从样带的北方端开始，岩石位于STDS的下盘，暴露在Mt.的北部和东部的Rongbuk和Kangshung山谷。 珠峰。 对于该项目的涡量部分，他将采用一系列不同的分析技术，使他能够交叉检查结果。 利用三种不同的分析技术对绒布地区进行的勘测研究表明，平均运动学涡度数（Wm）在0.73-0.98之间。这些数据表明，尽管简单剪切分量通常占主导地位，特别是在邻近STDS的样品中，但在位于分离下方400-600 in处的样品中也存在纯剪切的主要分量（在Wk=0.75时，纯剪切和简单剪切对流动的贡献相等）。紧密间隔的采样点是必不可少的，但是，确定潜在的阶跃函数的运动涡数，可能存在的深度下的STDS。 该区域几乎连续的暴露非常适合这项工作，并将允许PI在STDS下方3-4000英寸的深度进行采样。 涡度的时间变化将与变形温度使用显微结构和岩石组构标准，这些将反过来被链接到折返路径确定的当时nobarometry和准分子激光4 OAr/39 Ar微探针分析。

Within the central-eastem sector of the Himalayan orogen the highest grade metamorphic rocks are exposed in the High Himalayan slab, a 20-30 km thick northward-dipping wedge of deep crustal rocks metamorphosed at 14-56 km depth at 35-15 Ma. The slab is bounded along the base by the south-vergent Main Central Thrust (MCT), and along the top by the South Tibetan Detachment System (STDS) of north-vergent normal faults which separate the metamorphic and anatectic core of the Himalaya from unmetamorphosed rocks of the Tibetan plateau. Beginning in Early Miocene time, southward extrusion of the High Himalayan slab has had a profound influence on the geologic and geomorphic evolution of the Himalaya, and the highest topography and deepest erosion corresponds with the upper part of the extruding wedge. The regional scale geometries of the thrust and non-nal faults bounding the slab are now reasonably well known, and much work has been done on documenting shear sense indicators along the upper and lower surfaces of the slab and constraining the early stage PTt paths of rocks within the slab. However, critically important gaps remain in our understanding of both the kinematics (vorticity) of flow and relationships between flow and progressive exhumation within the extruding wedge. Deten-nining the spatial and temporal relationships between timing and magnitude of displacement along the wedge-bounding faults and the kinematics of flow within the evolving wedge are crucial to understanding of the crustal thickening, exhumation, and erosional history of the orogen. For example, is the interior of the slab dominated by pure shear deformation and bounded by stretching faults as suggested in one recently published extrusion model, or is flow throughout the slab dominated by simple shear as suggested in other models. Identification of a pure shear component is critically important because operation of a significant pure shear component would result in: 1) thinning and dip-parallel extension of the slab itself, 2) relative to strict simple shear, an increase in both strain rates and extr-usion/exhumation rates. Testing of extrusion models requires that spatial and temporal distributions of kinematic (vorticity) domains be mapped out across the slab, and also requires a close integration between kinematic and PTt analyses in order to constrain progressive deformation and exhumation paths. Only one published quantitative vorticity analysis has been made along a basal section of the High Himalayan slab, and no such studies exist for the upper-middle sections of the slab. The PI proposes to undertake an integrated study of the kinematic evolution and exhumation history of the High Himalayan slab along a N-S traverse across the slab, and has chosen the Everest region for this study. In the Everest region the N-S transect across the slab is some 60-80 km in length and, given the detailed fieldwork required for the study, it would be impossible to complete the entire transect across the slab in the 2-3 years of a standard NSF-funded project. The PI therefore proposes to break the transect into two separately funded stages starting in this Proposal at the northern end of the transect with rocks lying in the immediate footwall to the STDS that are exposed in the Rongbuk and Kangshung valleys on the north and east sides of Mt. Everest respectively. For the vorticity part of the project he will employ a range of different analytical techniques allowing him to cross-check between results. The reconnaissance studies in the Rongbuk area, using three different analytical techniques, demonstrate that mean kinematic vorticity numbers (Wm) range between 0.73-0.98. These data indicate that although a simple shear component is generally dominant, particularly in samples adjacent to the STDS, there is also a major component of pure shear in samples located at 400-600 in beneath the detachment (pure and simple shear make equal contributions to flow at Wk=0.75). Closely spaced sampling sites are essential, however, for identifying potential step functions in the kinematic vorticity number that may exist with depth beneath the STDS. The almost continuous exposure in the region is ideally suited for this work, and will allow the PI to sample to depths of 3-4000 in beneath the STDS. Temporal variations in vorticity will be correlated with deformation temperatures using microstructural and petrofabric criteria, and these will in turn be linked to exhumation paths determined by then-nobarometry and excimer laser 4OAr/39Ar microprobe analyses.