Late Miocene to Early Pliocene tectonometamorphism and cooling in south-central Karakorum and Indus-Tsangpo suture, Chogo Lungma area (NE Pakistan)

Abstract

The Chogo Lungma glacier is located at the northeastern edge of the Nanga Parbat-Haramosh spur where the Ladakh-Kohistan arc formations are laminated between the Karakorum and High Himalaya units. In the Karakorum metamorphic complex, metamorphism of a pelitic and granitic protolith took place in two tectonometamorphic phases. Isoclinal folds (∼700°C, 1 GPa) were followed by doming (∼630–700°C, 400–750 MPa) in a compressional climax (Lemennicier et al., 1996). One hornblende and two biotites associated to syntectonic magmatism with mantle affinities, contemporaneous of doming, give cooling ages between 3.0 and 7.7 Ma. A muscovite from an orthogneiss in the Karakorum gives an age of 5 Ma. Fast cooling (70–110 KMa) has prevailed ever since. Two muscovites from a foliated intrusion emplaced on the thrust of the Ladakh-Kohistan arc over the High Himalaya Crystallines have ages of 8.2 and >9 Ma (despite being collected in the same locality), dating the thrust at just before 9 Ma. All this points to a coeval tectonometamorphism and thrusting in that area during the Tortonian.