QUATERNARY DEFORMATION IN THE EASTERN PAMIRS, TAJIKISTAN AND KYRGYZSTAN

Active deformation in the eastern Pamir of Central Asia is concentrate d 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 pedimen ts, now at > 500 m above the piedmont, Holocene fault scarps, and larg e earthquakes with N to NW oriented P axes. Seismicity in the interior of the orogen outlines a N-S belt that includes normal faulting event s with E-W oriented T axes. N-S striking, active normal faults in the interior Lake Karakul region are compatible with these earthquakes; th ey define an asymmetric graben with a master fault at the western basi n margin. In the southern Pamirs, dextral strike-slip faults root in t he dextral Karakorum Fault, which bounds the Pamirs to the east. A mix ture of dextral and reverse offsets totalling 135 m in Pleistocene ter races and 8 m in late Pleistocene/Holocene deposits demonstrates conte mporary transpression, indicating average displacement rates of < 1 mm /yr. The concentration of young thrusts along the Trans-Alai, the nort hward migration of thrusting, and the scarcity of other large-scale sh ortening features within the eastern Pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihila tion 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 t he Muji-Tashgorgan graben of the Chinese Pamirs are interpreted as loc alized space accommodation phenomena, formed during progressive transf er of compressional deformation along a dextral strike-slip deformatio n zone with extensional stepovers.