Rb-Sr dating of the Kohistan arc-batholith in the Trans-Himalaya of North Pakistan, and tectonic implications

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doi: 10.1016/0012-821X(85)90165-7
Authors:Petterson, Michael G.; Windley, Brian F.
Author Affiliations:Primary:
The Univ., Dep. Geol., Leicester, United Kingdom
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 74(1), p.45-57. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1985
Note:In English. 39 refs.; illus. incl. 3 tables, geol. sketch maps
Summary:This arc-batholith is situated between the Indus suture and the Northern suture, in the Trans-Himalayan belt which continues E as the Ladakh arc-batholith in India and the Kangdese batholith in Tibet. In Kohistan the arc consists of a stratiform complex of norites, noritic gabbros and Cr-bearing layered dunites which formed the sub-arc magma chamber, and plutons of tonalite and diorite, one of which has a Rb/Sr age of 102 + or - 12 m.y. These are followed by basaltic tholeiites, andesites, rhyolites and sediments formed in overlying intra-arc basins, containing Albian-Aptian fauna. All these rocks were deformed by major folds correlated with formation of the Northern suture. NE-SW-trending basic dykes cross-cut all these structures and have a 39Ar/40Ar hornblende age of 75 m.y.; thus the Northern suture must have formed between 102 + or - 12 m.y. and 75 m.y. B.P. Further northward subduction of the Tethyan plate gave rise to an Andean-type batholith, two plutons of which have Rb/Sr ages of 54 + or - 4 m.y. and 40 + or - 6 m.y. The Dir-Utror group of calc-alkaline lavas (and sediments with Eocene fossils) are remnants of the volcanic cover of the Andean-type batholith. It is suggested that late Cretaceous blueschists formed during subduction under the active continental margin, and that continental collision and formation of the Indus suture occurred in the Eocene. The batholith was intruded by layered aplite-pegmatite sheets at 34 + or - 14 m.y. and 29 + or - 8 m.y. (Rb/Sr ages) in post-collisional times. The 87Sr/86Sr initial ratios of all the dated rocks range 0.7039-0.7052. Whole-rock Rb/Sr data for five rock units from the Kohistan arc-batholith, with average chemical and modal compositions, are presented. [P.Br.]
Subjects:Absolute age; Alkaline earth metals; Ar/Ar; Argon; Batholiths; Cenozoic; Cretaceous; Dates; Geochronology; Igneous rocks; Intrusions; Island arcs; Isotopes; Mesozoic; Metals; Methods; Noble gases; Petrology; Rb/Sr; Spectroscopy; Sr-87/Sr-86; Stable isotopes; Strontium; Upper Cretaceous; Asia; Himalayas; India; Indian Peninsula; Pakistan; Chilas Complex; Indus Suture; Kamila Belt; Kangdese Batholith; Kohistan Batholith; Ladakha Batholith; Northern Pakistan; Northern Suture; Northwest India; Ratios; Southern Tibet; Tibet; Trans-Himalayan Belt; Yasin Group
Abstract Numbers:86M/0028
Record ID:1985072098
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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