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

0309910Geissman夫妇提出了一项综合的物源、构造和古地磁研究，以确定印度东北角(在阿萨姆邦/孟加拉国)和印度支那之间早新生代板块边界的位置。这条边界的准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，目前人们对此知之甚少。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，存在两个截然不同的沉积序列。其中一处暴露在孟加拉盆地，从印度克拉通向西有成熟的沉积物来源。第二个是在印度阿萨姆邦发现的，据解释，它的造山源来自印度-缅甸山脉和/或最东端的喜马拉雅山脉，作为印度支那的一部分，在东部和北部。这两个层序之间的边界没有暴露，但PI的假设是它靠近卡拉丹断层，该断层具有年轻到活动的位移。关于这两个层序的两个可验证的假说与印度和亚洲之间的整个碰撞历史有关：(1)孟加拉盆地受到沉积运移障碍(如外围前隆起)的保护，不受造山碎屑的影响；或(2)两个层序在地体到达现在的位置之前相隔了相当长的距离。了解沉积时层序的古纬度对于检验这些假说至关重要。如果这两个层序沉积在不同的板块上，孟加拉盆地可能向南最远可达2500公里，在沉积的衰退期，它们之间的距离可能会减小。如果层序沉积在相似的纬度，因此可能在同一板块上，那么印度和印度支那之间的初始缝合可能发生在始新世/渐新世，容纳印度向北移动的主要板块边界将更向东。该项目的意义在于，在喜马拉雅东部前渊的陆地上可以获得大量未开发的地层记录，这为在一次受到很好限制的现代大陆碰撞中重建从西瓦利克和远距离孟加拉扇研究的地层之前的造山作用和地表过程提供了机会。厘清孟加拉盆地和阿萨姆邦层序的古纬度将为东南亚的重建提供宝贵的信息。对卡拉丹断裂两侧前中新世层序的详细物源研究，包括砂岩岩石学、重矿物分析、矿物化学、单颗粒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。拟议研究的影响：拟议的研究将涉及三个不同机构的三名研究生的培训。学生们将相互合作，相互互动，而PI将促进地质科学领域相当广泛的专业知识的发展。此外，至少有两名本科生将密切参与奥本和新墨西哥州的研究。除了与美国几个学术机构(奥本、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，这项建议还涉及与那些在地球科学研究方面没有得到很好支持的国家(孟加拉国和印度)的地球科学家合作。国际和平研究所计划以尽可能及时的方式在拥有广泛读者的地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.