Structural Evolution of the Quetta-Sibi Orocline at the juncture of western Sulaiman Lobe, Northern Kirthar Range and Muslim Bagh Ophiolite, Balochistan, west Pakistan: Insights for Hydrocarbon exploration and Traps

This study thoroughly investigates the structural evolution of the Quetta-Sibi orocline in west Pakistan through tectonostratigraphy, geological and geophysical data as well as highlights, its implications for hydrocarbon potential and subsurface trap geometries. The study area is marked by two major fold belts, the western Sulaiman Lobe to the north, Kirthar range to the south, intersected by WNW-ESE oriented Sibi trough and Zarghun depression. Its structural evolution of the orocline was initiated with the obduction of the Muslimbagh ophiolites onto the Indian subcontinent’s passive plate margin during the late Cretaceous to early Paleocene, followed by the oblique collision of the Indian plate with the Afghan block of Eurasian plate in Eocene, resulting in complex structural geometries. The structural evolution of the Quetta-Sibi orocline is attributed to the interaction of the south vergent Sulaiman lobe and east vergent Kirthar fold and thrust belt which creates an east-west jog, overlapping and interfering structural trends while to the west, the north south oriented Chaman transform fault system and Muslim Bagh ophiolites defines the tectonic plate boundary. Structural analysis through geological mapping, seismic interpretation, Geoseismic and tectonostratigraphic modelling reveals various structural styles are controlled by structural detachments within Jurassic, Eocene and Mio-Pliocene sedimentary layers, reflecting the influence of rock mechanical properties. It also explains that most of the structures and uplifts in the region are underlain by deep-seated thrust faults, extending into the Mesozoic to older strata, suggest significant geological activity with evidence of late Neogene to Pleistocene deformation and reactivation of the major fault which controls the structural grain. The presence of thick, mechanically incompetent Ghazij shales of Eocene age acts as a fold detachment surface, suggesting superimposed deformational events such as different structure styles in the Eocene’s Kirthar (carbonate) and Jurassic-Paleocene succession. Structural modelling depicts a sequence of compressional deformations in the region with post-collisional northeast-southwest directed compression superimposed on earlier east-west compression further complicates the structural geometry. It also depicts multi fault bounded structural highs along with petroleum system elements in the subsurface in the Quetta-Sibi orocline region. Geophysical and geological data indicates that the Siwalik’s filled Zarghun, Uzh Garh and Sibi depressions within the orocline region have buried the Paleogene, Cretaceous to older source rocks up to optimal depth, providing an optimal environment for the hydrocarbon generation. Despite the hydrocarbon (gas, condensate & heavy oil) discoveries from Paleocene, Cretaceous and Jurassic carbonates at Ziarat Zarghun south and Bolan, the Quetta-Sibi oroclinal region remains underexplored due to its intricate structural geometry which serves as global structural analogue. This research also explains the fold development mechanism and possible hydrocarbon kitchen in the region that could represent significant indigenous hydrocarbon resources, warranting further exploration.