Waziristan Ophiolite: A back-arc basin caught in continental collision, Waziristan, NW Pakistan

The western margin of the Indian plate is a classical example of continent-continent collision. The Afghanistan-Kabul-India continental blocks are here welded to each other by a network of sutures defined by the occurrence of ophiolites. The Waziristan Ophiolite (WO) is one of a series of ophiolites sandwiched between the western margin of the Indian plate and Afghanistan block. It is highly dismembered, but contains all the segments of an ideal ophiolite suite. It can be internally divided into three nappes which, from east to west, are: Vezhda Sar nappe, comprising entirely of pillow basalts; Boya nappe, a tectonic melange with an intact ophiolite section in the basal part at Mami Rogha; and Datta Khel nappe, consisting of sheeted dykes with variable proportions of other components. The intact ophiolite section consists of 1) basal ultramafics followed upward by 2) isotropic gabbros, and 3) pillow basalts, intercalated with and capped by pelagic sediments (chert, shale, limestone) (Figure 1). Isolated mafic dykes (doleritic), characterised by chilled margins, intrude all types of ophiolitic rocks, except the pillow basalts of Vezhda Sar nappe. Trondhjemites mostly intrude the ultramafics and rarely gabbroic rocks. Layered gabbros, missing in the ophiolite section, are sporadically distributed as fault-bounded blocks in the two western nappes.