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The northwestern Nanga Parbat–Haramosh Massif; Evidence for crustal uplift at the northwestern corner of the Indian Craton

By
I. P. Madin
I. P. Madin
Department of Geology, Oregon State University, Corvallis, Oregon 97331-5506
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R. D. Lawrence
R. D. Lawrence
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Shafiq Ur-Rehman
Shafiq Ur-Rehman
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Published:
January 01, 1989

The Nanga Parbat–Haramosh (NPHM) massif is a unique structural and topographic high in the northwestern corner of the Himalayan convergence zone. Previously, the NPHM was thought to be bounded by the Main Mantle Thrust (MMT), a fault along which the Kohistan-Ladakh island arc was obducted onto the northern margin of India. This study presents field evidence that the recently active dextral reverse Raikot fault truncates the MMT and forms the western boundary of the NPHM. The Raikot fault separates medium-grade, Mesozoic to middle Cenozoic mafic metasedimentary and intrusive rocks of the Kohistan island arc (Kohistan Sequence) from high-grade Proterozoic metasedimentary rocks (Nanga Parbat Group) and orthogneisses of the Indian craton. The Kohistan Sequence rocks have experienced one tight to isoclinal folding event, probably associated with obduction of the island arc, and a second folding event associated with movement on the Raikot fault. The Nanga Parbat Group rocks were transposed by an early (possibly Proterozoic) isoclinal folding event and have subsequently been folded around east-trending axes in the early Cenozoic by the obduction of Kohistan, then around north-trending axes in late Cenozoic time in association with the uplift of the NPHM and initiation of the Raikot fault. The Raikot fault consists of both mylonite zones and numerous major and minor faults. Slickensides and mylonitic lineations both indicate dextral reverse slip.

The Raikot fault and associated folds appear to have accommodated as much as 15 to 25 km of uplift during late Cenozoic time. The localization of the uplift and the involvement of the Moho suggest that the Raikot fault follows a major crustal structure, possibly a pre-collision Indian plate boundary. If this is the case, rotational underthrusting of greater India along the MMT would require dextral slip along the Raikot fault. It is proposed that the Raikot fault is a terminal tear fault on the MCT.

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GSA Special Papers

Tectonics of the western Himalayas

Lawrence L. Malinconico, Jr.
Lawrence L. Malinconico, Jr.
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Robert J. Lillie
Robert J. Lillie
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Geological Society of America
Volume
232
ISBN print:
9780813722320
Publication date:
January 01, 1989

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