Monsoon control over erosion patterns in the Western Himalaya: possible feed-back into the tectonic evolution

Abstract

The Indus Delta is constructed of sediment eroded from the western Himalaya and since 20 ka has been subjected to strong variations in monsoon intensity. Provenance changes rapidly at 12-8 ka, although bulk and heavy mineral content remains relatively unchanged. Bulk sediment analyses shows more negative 1 Nd and higher 87 Sr/ 86 Sr values, peaking around 8 -9 ka. Apatite fission track ages and biotite Ar-Ar ages show younger grains ages at 8-9 ka compared to at the Last Glacial Maximum (LGM). At the same time d 13 C climbs from -23 to -20‰, suggestive of a shift from terrestrial to more marine organic carbon as Early Holocene sea level rose. U-Pb zircon ages suggest enhanced erosion of the Lesser Himalaya and a relative reduction in erosion from the Transhimalaya and Karakoram since the LGM. The shift in erosion to the south correlates with those regions now affected by the heaviest summer monsoon rains. The focused erosion along the southern edge of Tibet required by current tectonic models for the Greater Himalaya would be impossible to achieve without a strong summer monsoon. Our work supports the idea that although long-term monsoon strengthening is caused by uplift of the Tibetan Plateau, monsoon-driven erosion controls Himalayan tectonic evolution.Supplementary material: A table of the population breakdown for zircons in sands and the predicted Nd isotope composition of sediments based on the zircons compared to the measured whole rock value is available at

Temporal variations in 87Sr/86Sr and ɛNd in sediments of the southeastern Arabian Sea: Impact of monsoon and surface water circulation

“…[32] The Sr and Nd isotopic composition of SS-3101G display variations similar to those reported for the Indus delta during the past ∼14 ka (" Nd ; Figure 5d) [Clift et al, 2008[Clift et al, , 2010 with both of them showing excursions in 87 Sr/ 86 Sr and " Nd during ∼9 ka. The similarity in the Sr and Nd isotopic composition and their temporal pattern hints at the possibility of supply of Indus delta sediments to the SS-3101G core site.…”

“…The more radiogenic 87 Sr/ 86 Sr and lesser " Nd during ∼9 ka in the core SS-3101G can be explained in terms of enhanced sediment supply through the Himalayan tributaries of the Indus. This can result from intensification of SW monsoon precipitation over the Himalaya during this period [Clift et al, 2008[Clift et al, , 2010. The intensification of SW monsoon during ∼9 ka resulted in stronger surface currents in the southeast direction from the Arabian Sea to the Bay of Bengal (Figure 1).…”

Geochemical record of Holocene to Recent sedimentation on the Western Indus continental shelf, Arabian Sea

“…Comparison of the temporal evolution in onshore and offshore records of Nd and Sr isotopes through time in the Indus Delta since 20 ka. Keti Bandar data from Clift et al [2008aClift et al [ , 2010. Note the major differences in ɛ Nd values between the marine cores and that taken at the coast at Keti Bandar, especially at 11-8 ka.…”

“…Here we explore this possibility using isotope data. Figure 11 compares temporal variations in ɛ Nd and 87 Sr/ 86 Sr values for both core sites with the river mouth record at Keti Bandar [Clift et al, 2010] in order to assess the whether the Indus Shelf can also record changes in Himalayan erosion. Most of the ɛ Nd values from Sites Indus-10 and -23 lie within the range of previously published values for Indus Canyon sediments [Clift et al, 2008a], but are typically shifted to slightly higher values compared to the synchronous values at the river mouth.…”

“…In the Ganga Basin ɛ Nd values and 87 Sr/ 86 Sr of river sediments are known to change on glacial time scales, changes that have been related to shifting Himalayan provenance and the large isotopic gradients known in the source regions [Rahaman et al, 2009]. Sediments deposited at the Indus River mouth since 15 ka also show changes in Nd and Sr isotope character that have been interpreted to reflect a shift in erosion from the Karakoram to the Lesser Himalaya following the Last Glacial Maximum [Clift et al, 2008a[Clift et al, , 2010. Curiously the direction of isotope change in the Indus delta (i.e., more negative ɛ Nd values) implies more Lesser Himalayas erosion while that on the Ganga floodplain indicates the opposite (more positive ɛ Nd values).…”