Cenozoic Climate-Tectonic Interactions in the Western Himalaya Recorded in the Indus Submarine Fan from IODP Expedition 355

Abstract:

The Indus Submarine Fan is the largest repository of clastic sediment eroded from the Western Himalayas since the start of India-Eurasia collision likely around 50 Ma. This sedimentary archiveis central to understanding how the climate and the tectonic evolution of the mountains have evolved together. A number of models now propose linkages between surface processes, controlled by climatic influences, and the tectonics of the solid Earth. In particular, exhumation of deeply-buried high-grade metamorphic rocks in the Greater Himalaya and the development of large-scale duplexes within the Lesser Himalaya are likely triggered by changes in the rate and location of erosion. Although some of these issues can be addressed by studies onshore, erosion has removed much of the older record from the crystalline basement itself. As a result the sediment record must be used to understand how fast erosion was occurring and whether that was linked to changes in tectonics and climate. A major unconformity in the foreland basin means that this work cannot be done fully using terrestrial records but rather the more complete records in the Arabian Sea and Bay of Bengal. Drilling by International Ocean Discovery Program Expedition 355 in the Eastern Arabian Sea has recovered two sections spanning the last ~11 Ma, which should allow us to reconstruct how the Western Himalaya have responded to climate change since the late Miocene, spanning the time when the Lesser Himalaya began to exhume. Autocyclic processes within the fan and a major mass transport deposit mean that the record is not continuous, but should nonetheless allow us to examine the impact of the important climatic transition at 7–8 Ma noted on the Oman margin and in the foreland basin. Initial results indicate that the Indus Fan was receiving material from Himalayan high-grade metamorphic rocks since at least ca. 14-17 Ma and that there was a direct connection with the suture, likely close to the western syntaxis, dating from the late Miocene.