Quaternary deformation in the Eastern Pamirs, Tadzhikistan and Kyrgyzstan

Authors

  • M. R. Strecker,

  • W. Frisch,

  • M. W. Hamburger,

  • L. Ratschbacher,

  • S. Semiletkin,

  • A. Zamoruyev,

  • N. Sturchio


Abstract

Active deformation in the eastern Pamir of Central Asia is concentrated on the margins of the orogen with minor deformation within the high terrain. Along the Trans-Alai mountain front at the northern perimeter of the orogen, Quaternary thrusting is documented by uplifted pediments, now at >500 m above the piedmont, Holocene fault scarps, and large earthquakes with N to NW oriented P axes. Seismicity in the interior of the orogen outlines a N–S belt that includes normal faulting events with E–W oriented T axes. N–S striking, active normal faults in the interior Lake Karakul region are compatible with these earthquakes; they define an asymmetric graben with a master fault at the western basin margin. In the southern Pamirs, dextral strike-slip faults root in the dextral Karakorum Fault, which bounds the Pamirs to the east. A mixture of dextral and reverse offsets totalling 135 m in Pleistocene terraces and 8 m in late Pleistocene/Holocene deposits demonstrates contemporary transpression, indicating average displacement rates of <1 mm/yr. The concentration of young thrusts along the Trans-Alai, the northward migration of thrusting, and the scarcity of other large-scale shortening features within the eastern Pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihilation of the intermontane Alai Valley. Widespread dextral shear in the eastern Pamirs, both to the south and north of the extensional Karakul depression, and combined dextral strike-slip and normal faulting in the Muji-Tashgorgan graben of the Chinese Pamirs are interpreted as localized space accommodation phenomena, formed during progressive transfer of compressional deformation along a dextral strike-slip deformation zone with extensional stepovers.

Ancillary