Role of Chaman transform boundary fault in the deformation of Eastern Kharan Fore–Arc Basin

Abstract

The eastern part of Kharan Fore-Arc Basin has been evaluated for its subsurface structural style and its relation to plate boundary conditions. This part of Kharan Fore-Arc Basin resides on the eastern margin of Eurasian Plate south of Raskoh Range where the Indo-Pakistani Plate to the east has a transpressional boundary relation along Chaman Fault. A local area was the subject of an integrated 2D seismic, gravity, magnetic and remote sensing data evaluation, primarily for the purposes of hydrocarbon exploration. Conclusions on the tectonic character of the local area near the Chaman Fault have been extended into the broader region. The Raskoh Range and the North Makran Range confine the area to the north and south respectively. Jurassic to Oligocene igneous and sedimentary rocks have been documented in the outcrops along Raskoh Range. The sedimentary fill in the Fore Arc south of Raskoh ranges from 5000-7000 m in thickness based on gravity and magnetic data sets. The seismic reflection data also reveal a similar sedimentary fill. The Chaman Fault Zone is characterized by sinistral strike-slip movement with a minimum offset of 15 km (Lawrence and Yeats, 1979). Seismic reflection data suggest that the structural style in the eastern Kharan Fore- Arc Basin is dominantly associated with a transpressional regime. The structural features that appear on seismic data are dominantly positive flowers, bounded by high angle reverse faults that branch-off upward from steep fault zones at depth. A few of these steep fault zones at depth seem to link with the Chaman Fault and its splays such as Usman-Chaman Fault which dips steeply to the north and changes its motion from strike-slip to transpressional in the southwest direction, away from the Chaman Fault. The Cretaceous to Eocene sedimentary package is considered to contain a potential petroleum system. Potential reservoir targets include the carbonates of the Eocene Kharan Formation and the sandstone of the Cretaceous to Paleocene Rakhshani Formation. An effective sealing mechanism is likely to have been provided by thick shale sequences ranging in age from Cretaceous to Paleocene.