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Did the Kohistan-Ladakh island arc collide first with India?

Shuhab D. Khan, Douglas J. Walker, Stuart A. Hall, Kevin C. Burke, Mohammad T. Shah and Lisa Stockli
Did the Kohistan-Ladakh island arc collide first with India?
Geological Society of America Bulletin (March 2009) 121 (3-4): 366-384

Abstract

The Kohistan-Ladakh block occupies the northwestern corner of the Himalayan mountains and has long been recognized to represent an island arc constructed on ocean floor during Jurassic and Cretaceous times. Because the Kohistan-Ladakh block now lies within the Asian continent, it is important to know how and when it became sandwiched between India and the rest of Asia. We have found from analysis of paleomagnetic data that in Late Cretaceous-early Paleocene times, the Kohistan-Ladakh island arc could not have been far from the equator. India was close to the equator, but the southern margin of Asia was more than 3000 km to the north. Our new U-Pb zircon age results from rocks of the Kohistan-Ladakh block show that calc-alkaline volcanic arc igneous activity ended in the Kohistan-Ladakh arc by 61 Ma. We interpret that cessation to date the collision of Kohistan with India. This new timing is confirmed by evidence that a Southern Hemisphere enriched DUPAL mantle source was involved in the generation of the latest Cretaceous Teru Volcanic Formation rocks of the Kohistan-Ladakh arc. Further confirmation of the collision of the Kohistan arc with India in early Paleocene times comes from evidence of the timing of obduction of ophiolites and from the unconformity of postcollisional sedimentary rocks onto the Indian continental margin in northwestern and western Pakistan. Final incorporation of India, now carrying the Kohistan-Ladakh block in its NW corner, into Asia took place at the Shyok suture. The best evidence for the timing of that suturing ca. 50 Ma comes from two postcollisional granites (ages 47 Ma and 41 Ma) in northern Kohistan, which show in their zircon isotopic compositions evidence of the involvement of ancient Asian continental crust that did not exist under Kohistan before the suture formed. The 50 Ma age for Shyok suturing against the then-active Karakoram Andean arc fits well with the extension of the suture beyond the eastern end of the Kohistan-Ladakh block to join the precisely dated ca. 51 Ma Yarlung-Tsang Po suture between India and the southern (Lhasa block) margin of Tibet, which at that time was also occupied by an Andean arc, the Gangdese arc.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 121
Serial Issue: 3-4
Title: Did the Kohistan-Ladakh island arc collide first with India?
Affiliation: University of Houston, Department of Earth and Atmospheric Sciences, Houston, TX, United States
Pages: 366-384
Published: 200903
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 101
Accession Number: 2009-028232
Categories: Solid-earth geophysicsIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch maps
N36°00'00" - N36°30'00", E72°10'00" - E73°00'00"
Secondary Affiliation: University of Kansas, USA, United StatesUniversity of Peshawar, PAK, Pakistan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200916
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