Thermochronology and Geochemistry of Lower Crustal Xenoliths, Central Mongolia: Formation and Evolution of the Deep Crust in an Intracontinental Setting

关于地球，我们还不了解的一件事是，为什么会在远离构造板块边界的地方形成高海拔，以及高度有多高。在这样一个异常地形的区域内，来自塔里岛的年轻熔岩。蒙古携带着稀有的下地壳样品，以所谓的捕虏体形式存在。这些捕捉体可以帮助回答有关下地壳的变化如何反过来控制地表地形的问题。高地形的形成和破坏可以控制生态系统和生物多样性的演变，并可以改变气候模式。特别是，了解蒙古形成高地形的时间对于了解北半球古气候演化具有重要意义，因为蒙古中部的高海拔地区目前对北太平洋风暴的成核非常重要。为了了解蒙古中部下大陆地壳的时间、形成和热演化，这一多学科的研究项目将利用热压法、年代学、热年代学和常量元素、微量元素和同位素地球化学。热压法将被用来限制捕捉体的平衡温度和压力。在样品中观察到的丰富的锆石将用U-铅激光烧蚀、电感耦合等离子体质谱和ID-TIMS测年，以确定下地壳形成和任何变质作用的时间。在汉盖地区由地壳根部支撑的程度上，限制根部的年龄将有助于限制岩石隆起的时间，并通过推断和模拟，限制地表隆起。全岩主量元素和微量元素地球化学以及锶、钕、氢、铅同位素分析将有助于限制形成下地壳的过程。将通过对这些样品中可能存在的一些痕量相(包括独居石和磷灰石)的U-Pb分析来评估造山后下地壳的长期热演化。与正在进行的蒙古地球动力学研究一起，这项作为博士论文一部分的工作将确定蒙古中部高地形的时间和演化，更广泛地说，将增进我们对地球动力学过程的了解，这些过程可以在大陆内部产生高地形。

One thing we do not yet understand about Earth is why and how high elevations can form far from the boundaries of the tectonic plates. Within one such region of anomalous topography, young lavas from Tariat. Mongolia carry in them rare samples of the lower crust in the form of what are called ?xenoliths?. These xenoliths can help answer questions about how changes in the lower crust might in turn control surface topography. The formation and destruction of high topography can serve as a control on the evolution of ecosystems and biodiversity, and can alter climate patterns. In particular, understanding when high topography formed in Mongolia has significant ramifications for understanding northern-hemisphere paleoclimate evolution because high-elevation regions in central Mongolia are currently important for the nucleation of northern-Pacific storms.To understand the timing, formation and thermal evolution of the lower continental crust in central Mongolia this multidisciplinary project of Tariat, lower-crustal xenoliths will use thermobarometry, geochronology, thermochronology, and major-element, trace-element, and isotope geochemistry. Thermobarometry will be used to constrain the equilibration temperatures pressures of the xenoliths. Abundant zircon observed in the samples will be dated by U-Pb laser ablation ICP-MS and ID-TIMS to determine the timing of lower-crustal formation and any metamorphism. To the extent that the Hangay region is supported by a crustal root, constraining the age of the root will help place constraints on the timing of rock uplift and, by inference and by modeling, surface uplift. Whole-rock major- and trace-element geochemistry as well as Sr, Nd, Hf, and Pb isotope analyses will help constrain what processes formed the lower-crust. The post-orogenic, long term thermal evolution of the lower crust will be assessed using U-Pb analyses of a number of trace phases likely to be present in these samples, including monazite and apatite. Together with ongoing studies of Mongolian geodynamics, this work, which is part of a Ph.D. dissertation, will determine the timing and evolution of the high topography in central Mongolia, and more broadly, advance our knowledge about geodynamic processes that can produce high topography in continental interiors.