Geochronological constraints on the evolution of the Nanga Parbat syntaxis, Pakistan Himalaya
Published:January 01, 2000
P. J. Treloar, D. C. Rex, P. G. Guise, J. Wheeler, A. J. Hurford, A. Carter, 2000. "Geochronological constraints on the evolution of the Nanga Parbat syntaxis, Pakistan Himalaya", Tectonics of the Nanga Parbat Syntaxis and the Western Himalaya, M. Asif Khan, Peter J. Treloar, Michael P. Searle, M. Qasim Jan
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New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission track data are presented from the western margin of the Nanga Parbat syntaxis as well as from the Indus and Astor valley sections which cross the syntaxis. Amphibole data date a regional cooling through 500 °C at 25 ± 5 Ma and are inconsistent with earlier suggestions that the peak of regional metamorphism was Neogene in age, although there is no doubt that some rocks were still at upper amphibolite facies temperatures as recently as 5 Ma. The data can be used to constrain structural models for syntaxial uplift. After an initial phase of crustal-scale buckling, bodily uplift of the syntaxis was along subvertical shear zones developed along its margins, although with a significantly higher time-averaged strain rate for shears developed along the western margin than along the eastern margin. The latter may be antithetic to the former. These shears were operative from 10 to < 1 Ma. In the southwestern part of the syntaxis, this subvertical uplift was superseded, since 6 Ma, by uplift along moderately SE-dipping NW-vergent shears on the hanging wall of which are located Neogene-aged migmatites.
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Tectonics of the Nanga Parbat Syntaxis and the Western Himalaya
The western syntaxis of the Himalaya is one of the most exciting frontiers of continental tectonis studies. The region around the mountain of Nanga Parbat has some of the highest peaks, deepest valleys and highest uplift, exhumation and erosion rates known on earth. Surrounding regions include the Hindu Kush and Karakoram mountains (Asian plate), the Kohistan island arc and the Ladakh and Zanskar ranges of the western Himalaya (Indian plate). This volume includes 24 papers on all these regions as well as five new fold-out maps of the eastern Hindu Kush, the Spontang Ophiolite region of Ladakh, part of the west margin of the Indian plate, the Indus syntaxis in Pakistan and the Bouguer gravity anomalies in Pakistan.