In:
Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 101, No. B12 ( 1996-12-10), p. 28149-28164
Abstract:
New 40 Ar/ 39 Ar and U‐Pb mineral ages from plutonic rocks help constrain the thermal and tectonic evolution of the Kohistan island arc terrane following its collision with India in early Tertiary time. Kohistan has experienced a prolonged tectonomagmatic history extending from the Early Cretaceous through the Tertiary. Thermal histories derived from multi diffusion domain analyses of K‐feldspar within the Kohistan batholith reveal rapid cooling events (70–140°C/m.y.) distributed through space and time. The cooling histories show a systematic variation along the length of the batholith suggesting that Kohistan experienced differential unroofing. An episode of rapid cooling in the middle Eocene is recognized in western Kohistan, whereas rapid cooling occurs substantially later, during the middle and late Miocene, in eastern Kohistan. Rapid cooling in western Kohistan might have been caused by postemplacement cooling of hot magma against cold country rocks at relatively shallow crustal levels. Within the NW region of eastern Kohistan, rapid cooling at 13–12 Ma is recorded in K‐feldspars ∼60 km from the contact with the Nanga Parbat‐Haramosh Massif (NPHM), whereas cooling does not occur until 11 Ma only 2.5 km from the contact. This temporal and spatial variation in cooling histories may record differential unroofing in response to the development and propagation of the NPHM structure beneath Kohistan. The NPHM has experienced rapid cooling and unroofing over the last 10 m.y., and our results are consistent with this mid–late Miocene event.
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1996
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