Abstract

The northernmost segment of the Karakoram fault is an active normal dextral wrench fault that bounds the Muji-Tashgurgan Pliocene-Quaternary basin (eastern Pamir). The Kongurshan (7719 m) and Mustaghata (7546 m) mountains are interpreted as twin crustal ramp anticlines formed en echelon on the eastern side of the Karakoram fault by subduction of the Tarim lithosphere under the Pamir. West-dipping S/C mylonitic gneisses that have downdip stretching lineations form the western flank of Kongur Mountain. Kinematic criteria consistently indicate a top-to-the-west sense of shear. The mylonitic foliation is cut by a steeper active normal fault, which is marked by prominent triangular facets on west-facing spurs. The ductile normal shearing deformation occurred during the interval 5-1 Ma. Therefore, like the Himalayas, the Pamir mountain range shows the coeval development of frontal thrusting and rear normal faulting. The Kongur fault thus appears to be an excellent example of synorogenic extension where normal faulting contributes to relief.

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