COLLABORATIVE RESEARCH: Mesozoic Nonmarine Sedimentary Record of Transition from Contractile to Extensional Deformation, Southern Mongolia

9708207 Graham南蒙古中生代构造演化包括一个鲜为人知的从收缩构造到伸展构造的转变以及相关的沉积盆地发育。近年来，由于在邻近的中国中北部发现了一条主要的北缘早中生代褶皱冲断带，对蒙古南部同构造粗粒地层的勘查描述，以及蒙古南部晚中生代裂谷盆地有限的地球物理和地质文献，这种转变在最广泛的范围内才显现出来。与构造转变相关的构造和沉积体系的运动学、速率和样式的主要方面仍未解决，并构成本研究计划的基础。这些问题引出了一系列令人兴奋的问题：在非均质地壳上形成的沉积盆地系统如何响应构造变形风格的根本变化？是否出现了以前未被认识的盆地类型，如最近记录的中国西部在增生地体上形成的碰撞前陆盆地？在中国中北部边界有记录的变质核杂岩，在构造上明显连续，与拟建的野外区域类似，但未记录的构造，在从收缩构造到伸展构造的过渡中发挥了什么作用？这些问题只是这项建议要解决的许多问题中的几个。具体而言，本提案寻求三年的资金，以调查和记录沉积对从中生代早期挤压构造到中生代晚期伸展构造的快速和基本转变的反应。在回答上述每个问题时，我们建议首先记录收缩和伸展系统的基本地质，以填补目前在蒙古南部中生代地质认识中存在的巨大空白。我们建议采用的主要调查工具和方法包括综合构造和沉积地质学方法，其中构造数据和详细测绘将作为详细沉积系统和地层建筑分析、物源分析和热年代学研究的背景。重要的是，由于可以从目前正在开发的一个小油田获得重要的岩心材料，地下数据将被纳入调查。在完成了对每个构造体系及其沉积记录的基本记录之后，就可以解决上述重要的、更广泛的科学问题。除了其科学重要性外，拟议的研究还将使美国机构和蒙古科学院之间继续进行科学交流。该提案的一个重要的额外教育方面在于它支持一名博士后研究助理，一名博士研究生和两名硕士研究生。

9708207 Graham The Mesozoic tectonic evolution of southern Mongolia includes a poorly understood transition from contractile to extensional tectonism and associated sedimentary basin development. Only in its broadest outline has this transition become apparent in recent years, as a consequence of recognition of a major north-verging early Mesozoic fold-thrust belt in adjacent north-central China, reconnaissance description of syn-tectonic coarse-grained strata in southern Mongolia, and limited geophysical and geological documentation of late Mesozoic rift basins in southern Mongolia. Major aspects of the kinematics, rates, and styles of structural and sedimentary systems associated with the tectonic transition remain unresolved, and form the basis for this research proposal. From such issues stem a suite of exciting questions: How do sedimentary basin systems formed atop heterogeneous crust respond to fundamental changes in tectonic deformational style? Do previously unrecognized basin types occur, as recently documented for collisional foreland basins formed atop accreted terranes in western China? What role to metamorphic core complexes, documented across the border in north-central China and apparently structurally continuous with similar though undocumented structures in the proposed field area, play in the transition from a contractile to extensional tectonics? These questions are but several among many to be addressed by this proposal. Specifically, this proposal seeks three years of funding to investigate and document the sedimentary response to a rapid and fundamental transition from compressional tectonics of early Mesozoic age to extensional tectonism of late Mesozoic age. In answering each of the above questions, we propose first to document the fundamental geology of the contractile and extensional systems to fill the very large gaps which exist presently in the geologic understanding of Mesozoic southern Mongolia. The principal tools and means of investigation we propose to employ involve an integrated structural and sedimentary geologic approach in which structural data and detailed mapping will serve as backdrop for detailed depositional systems and stratigraphic architectural analysis, provenance analysis, and reconnaissance thermochronologic studies. Importantly, subsurface data will be incorporated into the investigation, thanks to access to vital core material from a small oil field currently in development. After fundamental documentation of each tectonic system and its sedimentary record has been completed, the important broader scientific questions posed above can be addressed. Beyond its scientific importance, the proposed research will enable continued scientific exchange between U.S. institutions and the Mongolian Academy of Sciences. An important additional educational dimension of the proposal lies in its support for one Post-doctoral Research Associate, one Ph.D. student, and two M.S. students.