Collaborative Research: Identification of the Plate Boundary Between India and Indochina Through Integrated Petrologic, Structural, and Paleomagnetic Analyses

PI提出了一项综合物源、构造和古地磁研究，以确定早期新生代印度东北角（在阿萨姆邦/孟加拉国）和印度支那之间的板块边界位置。这条边界的精确位置将有助于确定印度和印度支那之间的接触（碰撞）年龄，目前人们对这一点知之甚少。对喜马拉雅东部始新世—渐新世（约43 ~ 23 Ma）前陆地层的初步成分研究表明，该地区存在两种截然不同的沉积序列。其中一个暴露在孟加拉盆地，有来自印度克拉通以西的成熟沉积物源。第二个，暴露在印度阿萨姆邦，被解释为有一个造山源来自印度-缅甸山脉和/或最东部的喜马拉雅山脉，作为印度支那的一部分，向东和向北。这两个层序之间的边界没有暴露出来，但PI的假设是它靠近卡拉丹断层，该断层有年轻到活跃的位移。关于这两种序列，有两个可检验的假设与印度和亚洲碰撞的整个历史有关：(1)孟加拉盆地受到沉积物运输障碍的保护，例如外围前隆起；或者，(2)这两个序列在地质体到达它们现在的位置之前被分开了相当长的距离。了解沉积时期序列的古纬度对于验证这些假设至关重要。如果这两个层序沉积在不同的板块上，那么孟加拉盆地可能远在南部约2500公里，在沉积的减弱阶段，它们之间的距离可能会减小。如果这些序列沉积在相似的纬度，因此可能在同一个板块上，那么印度和印度支那之间的最初缝合将发生在始新世/渐新世时期，而容纳印度向北运动的主要板块边界将更向东。这个项目的意义在于，在喜马拉雅东部前深的陆地上可以获得大量未开发的地层记录，这为在一个约束良好的现代大陆碰撞中重建造山作用和地表过程提供了机会，这些造山作用和地表过程是在siwalik和远孟加拉扇研究的地层之前进行的。澄清孟加拉盆地和阿萨姆邦序列的古纬度将为东南亚的重建提供宝贵的信息。对卡拉丹断层两侧前中新世序列的详细物源研究，包括砂岩岩石学、重矿物分析、矿物化学、单粒地质年代学和选定矿物相的同位素分析，将确定两个地体的沉积物来源，并与古地磁和构造研究相结合，将有助于重建早第三纪碰撞的主要元素。拟议研究的更广泛影响：拟议的研究将涉及三个独立机构的三名研究生的培训。学生们将相互合作，相互交流，PI将促进地质科学专业知识的广泛发展。此外，至少有两名本科生将密切参与奥本大学和新墨西哥州的研究。除了与来自美国几个学术机构（奥本大学、佛罗里达州立大学、麻省理工学院、新墨西哥州）的科学家合作外，该提案还涉及与来自没有得到很好支持从事地球科学研究的国家（孟加拉国和印度）的地球科学家合作。PI计划尽可能及时地在具有广泛读者群的地球科学期刊上传播我们的工作成果。

0309910GeissmanThe PI's propose an integrated provenance, structural, and paleomagnetic study to determine the location of the plate boundary between the NE corner of India (in Assam/Bangladesh) and Indochina during early Cenozoic time. Precise location of this boundary will contribute to the age of contact (collision) between India and Indochina, which is presently very poorly known. Preliminary compositional studies on Eocene-Oligocene (ca. 43 to 23 Ma) foreland strata of the eastern Himalaya indicate that two dramatically different sedimentary sequences are present. One, exposed in the Bengal basin, has a mature sediment source from the Indian craton to the west. The second, exposed in Assam, India is interpreted to have an orogenic source from the Indo-Burman ranges and/or easternmost Himalayas, as part of Indochina, to the east and north. The boundary between these two sequences is not exposed, but the PI's hypothesize that it is near the Kaladan fault, which has young to active displacement. Two testable hypotheses regarding these two sequences bear on the overall history of collision between India and Asia: (1) the Bengal basin was protected from orogenic detritus by a barrier to sediment transport, such as a peripheral forebulge; or, (2) the two sequences were separated by a considerable distance before the terranes reached their present positions. Understanding the paleolatitudes of the sequences at the time of deposition is critical to testing these hypotheses. If the two sequences were deposited on different plates, the Bengal Basin could have been as far to the south as ~2500 km, with the distance between them probably decreasing during the waning stages of deposition. If the sequences were deposited at similar latitudes, and thus perhaps on the same plate, then the initial suturing between India and Indochina would have occurred during Eocene/Oligocene time and the major plate boundary that accommodated the northward movement of India would be farther to the east. The significance of this project lies in the largely unexploited stratigraphic record accessible on land in the eastern Himalayan foredeep, which provides the opportunity, in a well-constrained modern continental collision, to reconstruct orogenesis and surface processes that pre-date strata studied from the Siwaliks and the distal Bengal fan. Clarification of the paleolatitudes of the Bengal basin and Assam sequences will provide invaluable information for Southeast Asia reconstructions. Detailed provenance studies of the pre-Miocene sequences on both sides of the Kaladan fault, including sandstone petrology, heavy-mineral analysis, mineral chemistry, single- grain geochronology, and isotopic analyses of selected mineral phases, will define the sediment sources of the two terranes and, in concert with paleomagnetic and structural studies, will aid in reconstructing major elements of the early Tertiary collision.Broader impacts of the proposed research: The proposed research will involve the training of three graduate students at three separate institutions. The students will collaborate with one another and their interactions with each other and the PI's will foster the development of considerable breadth of expertise in the geological sciences. In addition, at least two undergraduate students will be intimately involved in aspects of the research at Auburn and New Mexico. In addition to collaboration with scientists from several academic institutions (Auburn, Florida State, MIT, New Mexico) in the United States, this proposal also involves collaboration with geoscientists from countries (Bangladesh and India) that are not well supported to do geoscience. The PI's plan to disseminate the results of our work in as timely a fashion as possible in geoscience journals with a broad readership.