Structural geometry of the Himalayan Frontal Thrust Zone: Surghar Range, Pakistan
Abstract
Surghar Range of the outer Himalayas in Pakistan represents the active deformational front of Kohat fold and thrust belt. The range is migrating southward in response to the underthrusting of Indian craton underneath its sedimentary cover. The structural geometry of the range, in the vicinity of Chichali pass area is characterized by a south facing anticline i.e., Surghar anticline at the level of Jurassic. It is interpreted to be a fault bend fold above a major ramp detached within or at the base of Triassic rocks. The range front is thrust southwards over Punjab foreland along Surghar Fault, which is interpreted as south verging fore thrust. The thrust sheet above Surghar Fault displays contrasting structural geometries along strike. The Surghar Fault is believed to be a strongly emergent thrust in the west (north of Kutki village) having shallowly folded thrust sheet. Eastwards, the Surghar Fault translates into a tip-stick thrust front (north of Chapri and Tola Mangli village) with its thrust sheet being tightly folded and disrupted by several out of sequence thrust faults. The restored cross section along Kutki section reveals that 5.6 km shortening has taken place along Surghar Fault. The constraints upon the timing of deformation suggest that uplift along range front started about 2.3 Ma ago.
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