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

蒙古中部下地壳包体的热年代学和地球化学：陆内环境中深部地壳的形成和演化

• 批准号: 1426857
• 负责人: Peter Zeitler
• 金额: $ 8.29万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1426857&HistoricalAwards=false
• 关键词: Thermochronology; Geochemistry; Lower; Crustal; Xenoliths

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.

关于地球，我们还不了解的一件事是，为什么以及如何在远离构造板块边界的地方形成高海拔。在一个这样的异常地形区域内，塔里亚特的年轻熔岩。蒙古携带着罕见的下地壳样本，以所谓的？捕虏体？这些捕虏体可以帮助回答下地壳的变化如何反过来控制地表地形的问题。高地地形的形成和破坏可控制生态系统和生物多样性的演变，并可改变气候模式。特别是，了解蒙古高原地形形成的时间对了解北半球的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地壳的时间、形成和热演化，Tariat的这一多学科项目，下地壳捕虏体将使用温压法，地质年代学、热年代学、常量元素、微量元素和同位素地球化学。热压法将用于约束捕虏体的平衡温度和压力。将通过U-Pb激光烧蚀ICP-MS和ID-TIMS对样品中观察到的丰富锆石进行定年，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支撑的情况下，限制根的年龄将有助于限制岩石隆起的时间，并通过推理和建模，限制地表隆起。全岩的主要和微量元素地球化学以及Sr、Nd、Hf和Pb同位素分析将有助于限制下地壳的形成过程。造山后，下地壳的长期热演化将使用U-Pb分析的一些微量相可能存在于这些样品中，包括独居石和磷灰石进行评估。结合正在进行的蒙古地球动力学研究，这项工作，这是博士学位的一部分。论文，将确定蒙古中部高地形的时间和演变，更广泛地说，推进我们对地球动力学过程的认识，可以在大陆内部产生高地形。