Chaman Fault Zone

The Chaman fault zone is part of the Eurasian-Indian plate boundary complex, with the Suleiman Ranges marking a jog to the east in the northern edge of the Indian continental plate. The Chaman zone has evolved from a thrust fault of the Arabian-Eurasian collisional complex to a strike-slip fault along the Eurasian-Indian transform boundary.The Arabian-Eurasian plate boundary, a subduction zone, is beneath the Indian Ocean to the south of the Makran region. Sedimentary rocks (turbidites) that were originally deposited on the seafloor have been scraped off as the Arabian plate is subducted beneath the Eurasian plate. They were then uplifted and folded into the Makran Ranges during that plate collision. As India moves northward, the east ends of the Makran folds (on the Eurasian plate) have been dragged to the north along the Chaman fault zone.


Structures at the junction of the Arabian, Eurasian, and Indian plates are visible in this northward view across the Indian Ocean into Iran, Pakistan, and Afganistan. The Makran ranges (M) result from collision of the Arabian and Eurasian plates; that plate boundary is beneath the sea. The Chaman fault zone (C) and Suleiman folded ranges (S) reflect Indian and Eurasian plate interaction.The flat basin of the Helmand block (H) occupies the upper center of the frame. The three prominent volcanoes (V) are discussed in the context of the volcano line.In the next two frames, structural details of the sweeping bend in the Makran ranges and the evolution of the Chaman fault zone are highlighted.

Chaman fault is a thrust fault at T in this view, along which layers of rock have been driven up and over those farther south.To the northeas it bends northward and becomes the strike-slip (S) fault of the transform zone - the block on the east is moving north (upward) relative to that on the west. 'Bending' of the beds south of Chaman fault is accomplished through small lateral displacements on a suite of closely spaced strike-slip faults -- much as each playing card in a deck slips a small distance past the next when the deck is flexed. In this view (a NE-ward continuation of STS051J-43-S), the Chaman (C) fault is dominantly a strike-slip zone that defines the Eurasian-Indian transform plate boundary for ~900 km northward almost to Kabul, Afghanistan. The Indian plate (IP) is moving north (upper right) relative to the Eurasian plate (EA); disrupted drainages across the fault indicate ongoing motion. The earlier, original plate boundary lies in the broad valley at lower right. Dark clots within the belt are remnants of oceanic basaltic crust mixed with sedimentary rock (O - ophiolite).
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