Himalayan sedimentary pulses recorded by silicate detritus within a ferromanganese crust from the Central Indian Ocean

A Central Indian Ocean deep-water seamount hydrogenous ferromanganese crust (SS663-Crust) contains variable (7-23%) amounts of detrital material (silicate-detritus). Taking into account the growth rate of the authigenic component, the accumulation rate of the silicate-detritus has been calculated, which shows an overall decrease during the past 25+/-2 Ma growth history of the specimen. This silicate-detritus displays epsilonNd(0) between -7.7 and -12.7, and Sr-87/Sr-86 between 0.7083 and 0.7215. The Sr-Nd isotopic compositions record the variation in the mixture of two detrital end-members throughout the growth history of the SS663-Crust. While one end-member clearly appears to be Himalayan-derived material, the other component is less well defined, but could be related to the volcanogenic component from the Indonesian back-arc basin. We have unscrambled the proportion of these two components in the silicate-detritus of the SS663-Crust to quantify the variation in the accumulation rate of the Himalayan-derived silicate-detritus during the last 25 Ma. The result shows three periods of high accumulation rates (modern, around 10 Ma and prior to 16 Ma). These sedimentary pulses have already been recognised and described in the turbidites from the distal Bengal Fan, which is located more than 1000 km away from the SS663-Crust location, suggesting that these sedimentary pulses are of regional significance rather than of local importance. The timings of elevated contents of the Himalayan-derived silicate-detritus in the specimen during the Neogene closely superimpose the periods of the Himalayan uplift along the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust. This further emphasises the tectonic control of the sediment production by the erosion of an active orogenic range and its distribution over a vast area. Additionally, close superimposition of the Early Miocene detritus pulse in the SS663-Crust on the riverine Sr isotopic positive excursion suggests that the physical and chemical weathering of the Himalaya was strongly coupled during the Early Miocene, while the spatial decoupling appears to have taken place only around 12-14 Ma. (C) 2002 Elsevier Science B.V. All rights reserved.