The India-Afghanistan collision zone exposed in Kurram-Waziristan area of NW Pakistan comprises a stack of thrust sheets derived from various parts of a continental shelf-ocean floor transition formerly located at the NW margin of the Indian plate (Beck et al., 1996). From SW to NE, these thrust sheets include Waziristan Ophiolite, Khaisora Nappe of outer shelf sediments, Shahur Tangi-Kahi Nappe of deep-marine olistostromal sequence and Isha Nappe of inner continental shelf. Late Palaeocene and younger shallow-marine and fluvial sediments unconformably overly the thrust stack and are involved in deformation. Four stages of tectonic evolution are recognized in the Waziristan-Kurram collision zone: Middle Cretaceous (∼ 90 Ma): An early phase of intraoceanic ophiolite obduction at ∼ 90 Ma gave rise to Shahur Tangi-Kahi Group of sediments in a fore-deep setting. This event conforms to a regional middle Cretaceous orogeny (Semail Ophiolites; Kohistan-Karakoram collision; Kamila shear zone, Kohistan). Early Palaeocene (∼ 65 Ma): A major thrust displaced the extensive nappe of Shahur Tangi-Kahi Group eastward on to the entire NW continental shelf of the Indian Plate during the Early Palaeocene, contemporaneous with and directly above the syndepositional breccia of Lokhart Formation. A closely following break-back thrusting event involved internal imbrication of the Waziristan Ophiolite, thrust emplacement of the Waziristan ophiolite stack eastward onto the outer shelf (Khaisora Group) and that of the Khaisora Nappe onto the Shahur Tangi-Kahi Nappe. This Palaeocene thrust stacking was complete prior to the deposition of Late Palaeocene Patala Formation onto the Shahur Tangi-Kahi Group (Thal area), that of the Datakhel Formation on the stacked Waziristan Ophiolite, and that of the Ghazij Formation and the younger sediments on the contact between the Isha and Shahur Tangi-Kahi groups (Khajuri Post area). Post Middle Eocene (∼ 45 Ma): Late Palaeocene-Middle Eocene shallow-marine transgression onto the thrust stack was followed by a major hiatus that marked onset of fluvial sedimentation at the expense of marine sedimentation. Late Miocene Kamlial Formation in the north (near ThaI) and the Pliocene Litra Formation (near Bannu) mark the earliest molasse sediments in this region. Quaternary (< 2 Ma): Molasse sediments in Waziritan-Kurram foreland are uplifted, tilted and folded. An extensive sequence of conglomerates overlying the Litra Formations is tilted to high angles in the foreland region near Bannu, suggesting Holocene (<1 Ma) age for this deformation event. A Quaternary transpressional upright fault brings base of the Shahur Tangi-Kahi Group in tectonic contact with Ghazij Formation near Shinki Post (Bannu-Miran Shah roadsection). In the hinterlands, the Quaternary deformation event may be responsible for large structures of Drasmand and Khadimak antiforms together with associated thrust faults. Whereas the Middle Cretaceous intraoceanic ophiolite obduction event correlates well with documented tectonic events in Kohistan and Oman, the Early Palaeocene thrust stacking is probably related with a second phase of ophiolite obduction similar to that of Spongtang, Ladakh (Searle, 1986), rather than with the India-Eurasia collision (Beck et al., 1996). The tectonic event related with Late Eocene termination of marine sedimentation could be the manifestation of India-Afghan collision in this region that continues into Quaternary due to an oblique collision and associated transpressional deformation.
|Number of pages||1|
|Journal||Journal of Asian Earth Sciences|
|Publication status||Published - 2001|
ASJC Scopus subject areas
- Earth-Surface Processes