The 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.
