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Slowing rates of regional exhumation in the western Himalaya: fission track evidence from the Indus Fan

Published online by Cambridge University Press:  03 October 2019

Peng Zhou
Affiliation:
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA, 70803, USA
Andrew Carter
Affiliation:
Department of Earth and Planetary Sciences, Birkbeck College, University of London, London WC1E 7HX, UK
Yuting Li
Affiliation:
Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, 47907, USA
Peter D. Clift*
Affiliation:
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA, 70803, USA Research Center for Earth System Science, Yunnan University, Kunming, Yunnan Province, 650091, China
*
Author for correspondence: Peter D. Clift, Email: pclift@lsu.edu

Abstract

We use apatite fission track ages from sediments recovered by the International Ocean Discovery Program in the Laxmi Basin, Arabian Sea, to constrain exhumation rates in the western Himalaya and Karakoram since 15.5 Ma. With the exception of a Triassic population in the youngest 0.93 Ma samples supplied from western Peninsular India, apatite fission track ages are overwhelmingly Cenozoic, largely <25 Ma, consistent with both a Himalaya–Karakoram source and rapid erosion. Comparison of the minimum cooling age of each sample with depositional age (lag time) indicates an acceleration in exhumation between 7.8 and 7.0 Ma, with lag times shortening from ∼6.0 Myr at 8.5–7.8 Ma to being within error of zero between 7.0 and 5.7 Ma. Sediment supply at 7.0–5.7 Ma was largely from the Karakoram, and to a lesser extent the Himalaya, based on U–Pb zircon ages from the same samples. This time coincides with a period of drying in the Himalayan foreland caused by weaker summer monsoons and Westerly winds. It also correlates with a shift of erosion away from the Karakoram, Kohistan and the Tethyan Himalaya towards more erosion of the Lesser and Greater Himalaya and Nanga Parbat, as shown by zircon U–Pb provenance data, and especially after 5.7 Ma based on Nd isotope data. Samples younger than 5.7 Ma have lag times of ∼4.5 Myr, similar to Holocene Indus delta sediments.

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Type
Original Article
Copyright
© Cambridge University Press 2019

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