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Oroclinal bending versus regional significant clockwise rotations in the Himalayan arc—Constraints from secondary pyrrhotite remanences

By
E Schill
E Schill
Institut für Geophysik, ETH Zürich, Hönggerberg HPP O14, 8093 Zürich, Switzerland
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E Appel
E Appel
Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, Germany
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C Crouzet
C Crouzet
Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, Germany
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P Gautam
P Gautam
Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal
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F Wehland
F Wehland
Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, Germany
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M Staiger
M Staiger
Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, 72076 Tübingen, Germany
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Published:
January 01, 2004

Late orogenic rotations and tilting along a N-S transect at ~84.5 °E crossing the Manaslu leucogranite, and earlier results from the western and central part of the Himalaya, are used to investigate the existence of oroclinal bending and ramping on the Main Central Thrust. Tectonic deformation is deduced from secondary remanent magnetization residing in pyrrhotite, which formed during metamorphism. Remanence acquisition is related to the last cooling event through 325 °C (Curie temperature of pyrrhotite). Local and regional thermo-chronological constraints suggest Oligocene to Pliocene acquisition ages.

In the south, similar inclinations of the Greater Himalayan Sequence and Lesser Himalayan Sequence across the Main Central Thrust result in a mean southward tilting of ~15°. This is in contradiction to the existing model of Main Central Thrust ramping; it favors the interpretation of duplex structures.

In the north of the transect significant clockwise rotations of 47° ± 8° with respect to the Indian plate are observed in the Tethyan metasediments north of the South Tibetan detachment system. This result coincides with earlier data from the Tethyan sedimentary series in the central Himalaya. Further to the south, in the Greater Himalayan sequence and Lesser Himalayan sequence, clockwise rotations are distinctly smaller (~10°) and rather consistent within these units. In contrast to the western Himalayas, where paleomagnetic results indicate oroclinal bending around the syntaxis, the large late-orogenic clockwise rotation in the hanging wall of the South Tibetan detachment system in the investigated area and the increasing clockwise rotations across the central Himalayas from west to east argue against oroclinal bending of the whole Himalayan arc. The rotation angle of ~10°, observed south of the South Tibetan detachment system, may be related to uniform rotational shortening at the northern margin of India, which must have occurred south of the Lesser Himalayan sequence. However, the large late-orogenic clockwise rotation observed in the Tethyan sedimentary series is more likely related to the eastward extrusion of the Tibetan plateau.

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GSA Special Papers

Orogenic curvature: Integrating paleomagnetic and structural analyses

Aviva J. Sussman
Aviva J. Sussman
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Arlo B. Weil
Arlo B. Weil
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Geological Society of America
Volume
383
ISBN print:
9780813723839
Publication date:
January 01, 2004

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