Abstract

Obduction of an ophiolite complex onto the northwestern continental margin of the India plate occurred during the Late Cretaceous to early Paleocene, followed by collision of the ophiolitic complex of the India plate with the Eurasia plate in the Eocene. Lower Eocene marine strata overlie the ophiolitic complex suggesting that suturing was completed by early Eocene time.

The Quetta-Muslim Bagh-Sibi region is a structurally complex area within west-central Pakistan characterized by broad and tight folds, and reverse, thrust, and strike-slip faults. In order to understand this complex deformation, we have divided this region into five structural domains which are separated by four major boundary faults formed during four major periods of deformation related to oblique convergence of the India and Eurasia plates.

The five structural domains are (1) a foredeep, (2) a foreland fold-and-thrust belt, (3) a major deep trough that formed within the foreland fold-and-thrust belt and filled with collision molasse, (4) a thick flysch deposit, and (5) a subduction-obduction and related igneous rock terrane on the margin of the Eurasia plate (Afghan block).

The four major faults that bound the structural terrane are the Frontal (F), Ghazaband-Zhob (GZ), Gwal-Bagh (GB), and Chaman (C) faults. Four major periods of deformation are recognized: (1) emplacement of ophiolitic rocks onto the continental margin of the India plate; (2) convergence of the India-Eurasia plates; (3) deposition of Tertiary–Quaternary molasse units followed by major folding and thrusting, and formation of strike-slip faults; and (4) deposition of Pleistocene molasse units with subsequent folding, thrusting, and strike-slip motion that continues to the present.

First posted October 4, 2011