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Himalayan Geology, Vol. 32
(2), 2011, pp. 95-111, Printed in India
Neotectonic inversion of the Hindu Kush-Pamir Mountain Region
C.A. RULEMAN
U.S. Geological Survey, P.O. Box 25046, Denver Federal Center, MS 980,
Denver, CO 80225
Email: cruleman@usgs.gov
Abstract: The Hindu Kush-Pamir region of southern Asia is one of
Earth’s most rapidly deforming regions and it is poorly understood. This
study develops a kinematic model based on active faulting in this part of
the Trans-Himalayan orogenic belt. Previous studies have described
north-verging thrust faults and some strike-slip faults, reflected in the
northward-convex geomorphologic and structural grain of the Pamir Mountains.
However, this structural analysis suggests that contemporary tectonics are
changing the style of deformation from north-verging thrusts formed during
the initial contraction of the Himalayan orogeny to south-verging thrusts
and a series of northwest-trending, dextral strike-slip faults in the modern
transpressional regime. These northwest-trending fault zones are linked to
the major right-lateral Karakoram fault, located to the east, as synthetic,
conjugate shears that form a right-stepping en echelon pattern.
Northwest-trending lineaments with dextral displacements extend continuously
westward across the Hindu Kush-Pamir region indicating a pattern of
systematic shearing of multiple blocks to the northwest as the deformation
effects from Indian plate collision expands to the north-northwest. Locally,
east-northeast- and northwest-trending faults display sinistral and dextral
displacement, respectively, yielding conjugate shear pairs developed in a
northwest-southeast compressional stress field. Geodetic measurements and
focal mechanisms from historical seismicity support these surficial,
tectono-morphic observations. The conjugate shear pairs may be structurally
linked subsidiary faults and co-seismically slip during single large
magnitude (> M7) earthquakes that occur on major south-verging thrust
faults. This kinematic model provides a potential context for prehistoric,
historic, and future patterns of faulting and earthquakes.
Keywords: Hindu Kush, Pamir Mountains, Neotectonics, Afghanistan,
Pakistan, Himalaya, active tectonics
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