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Geological Society, London, Special Publications; 2002; v. 195; p. 97-116;
DOI: 10.1144/GSL.SP.2002.195.01.07
© 2002 Geological Society of London

Constraints on India-Eurasia collision in the Arabian Sea region taken from the Indus Group, Ladakh Himalaya, India

Peter D. Clift1, Andrew Carter2, Michael Krol3 & Eric Kirby4

1 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA pclift{at}whoi.edu
2 Department of Geological Sciences, University College, Gower Street, London WC1E 6BT, UK
3 Department of Earth Sciences and Geography, Bridgewater State College, Bridgewater, MA 02325, USA
4 Institute for Crustal Studies, University of California, Santa Barbara, CA 93106, USA

The Indus Group is a Paleogene, syntectonic sequence from the Indus Suture Zone of the Ladakh Himalaya, India. Overlying several pre-collisional tectonic units, it constrains the timing and nature of India’s collision with Eurasia in the western Himalaya. Field and petrographic data now allow Mesozoic-Paleocene deep-water sediments underlying the Indus Group to be assigned to three pre-collisional units: the Jurutze Formation (the forearc basin to the Cretaceous-Paleocene Eurasian active margin), the Khalsi Flysch (a Eurasian forearc sequence recording collapse of the Indian continental margin and ophiolite obduction), and the Lamayuru Group (the Mesozoic passive margin of India). Cobbles of neritic limestone, deep-water radiolarian chert and mafic igneous rocks, derived from the south (i.e. from India), are recognized within the upper Khalsi Flysch and the unconformably overlying fluvial sandstones of the Chogdo Formation, the base of the Indus Group. The Chogdo Formation is the first unit to overlie all three pre-collisional units and constrains the age of India-Eurasia collision to being no younger than latest Ypresian time (>49 Ma), consistent with marine magnetic data suggesting initial collision in the Arabian Sea region at c. 55 Ma. The cutting of equatorial Tethyan circulation north of India at that time may have been a trigger to the major changes in global palaeoceanography seen at the Paleocene-Eocene boundary. New 40Ar/39Ar, apatite fission-track and illite crystallinity data from the Ladakh Batholith and Indus Group show that the batholith, representing the old active margin of Eurasia, experienced rapid Eocene cooling after collision, but was not significantly reheated when the Indus Group basin was inverted during north-directed Miocene thrusting (23–20 Ma). Subsequent erosion has preferentially removed 5–6 km (c. 200°C) over much of the exposed Indus Group, but only c. 2 km from the Ladakh Batholith. Reworking of this material into the Indus fan may complicate efforts to interpret palaeo-erosion patterns from the deep-sea sedimentary record.





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P. D. Clift
A brief history of the Indus River
Geological Society, London, Special Publications, 2002; 195: 237 - 258.
[Abstract] [PDF]