First constraints on the timing of structural evolution of the north Sulaiman Fold-thrust belt, Pakistan

The Sulaiman and Kirthar fold-and-thrust belts constitute the western boundary of the India-Asia collision zone. The Sulaiman fold-thrust belt is composed of a passive margin sedimentary sequence of Mesozoic to Cenozoic platform carbonates and clastic sedimentary rocks overlain by younger Himalayan foreland basin molasse sediments. This study uses newly acquired zircon (U‐Th)/He (ZHe) data and surface geology observations to document the structural evolution of the north Sulaiman fold-thrust belt. The hinterland zone includes the Zhob Valley Suture thrust, emplaced ophiolites, and folded Mesozoic strata, while the foreland is characterized by folded Eocene to Pliocene strata and hinterland-verging back thrusts. The initial deformation of the North Sulaiman Fold-thrust belt was driven by an east-west compressional event, giving rise to structures oriented in a north-south direction. The formation of fault propagation folds such as the Drazinda Syncline and Domanda Anticline in the foreland region resulted from east-vergent deformational events. Following this eastward deformation, the west-verging East Domanda Fault was activated, forming a roof thrust within the tectonic wedge beneath the Domanda Anticline.

ZHe dates were obtained from Jurassic to Pliocene sandstone samples collected along the Drazinda-Zhob transect, crossing the Sulaiman Fold-thrust belt. ZHe ages from the Middle Jurassic (Chiltan Formation) and late Jurassic to early Cretaceous (Sembar Formation) samples are completely reset. ZHe ages from the late Cretaceous (Mughal Kot and Pab formations) to early Paleocene (Ranikot Formation) samples are partially reset to unreset; Eocene to Pliocene sample ages are unreset. ZHe ages for the Chiltan Formation range from 3.9-16.2 Ma with an average of 7.6 Ma. The ZHe ages for the Sembar Formation range from 5.5-41.4 Ma with an average of 15.2 Ma. The fully to partially reset ZHe ages for the Mughal Kot Formation range from 4.5 to 64.2 Ma with an average of 31.6 Ma. The ZHe ages of the Pab Formation samples range in age from 25.1-58.6 with an average of 44.9 Ma. A single partially reset ZHe age from the Ranikot Formation is 38.5 Ma. Thick and rapid sedimentation in the Late Cretaceous, Early Eocene and Miocene-Pliocene in the region resulted in sufficient burial of the Chiltan and Sembar formations to reset the ZHe system. Most of the reset ages from the Chiltan and Sembar formations range between 3.9-7.5 Ma, indicating rapid late Miocene to Early Pliocene uplift of the north Sulaiman Fold-thrust belt. This uplift is associated with development of the Sulaiman anticline and the associated Dhana Sar backthrust. Located along the western boundary of the Indian Plate, this area exhibits transpressional tectonics. The dominant east-west compression component coupled with left-lateral wrenching plays a key role in this rapid and young uplift in the north Sulaiman Fold-thrust belt.