Multistage structural evolution of Northern Karakorum (Hunza region, Pakistan)

Detailed mapping and structural work in Upper Hunza Valley, Pakistan, have enlightened the tectonics and the structural evolution of the sedimentary cover of Northern Karakorum. This includes the Northern Sedimentary Belt (NSB) with the Guhjal and Sost Units (Permian-Cretaceous), cropping out north of the Karakorum Axial Batholith (KAB); the NSB is bounded to the north by the Misgar Unit, consisting of slates of unknown age. In the Sost Unit a mid-Cretaceous deformed belt is sealed with a strong angular unconformity by the Late Cretaceous formations. Folds within the mid-Cretaceous belt possibly indicate north-vergent transport. Stacking of NE- to N-vergent thrusts sheets postdates the deposition of Cretaceous sediments, which are largely included within tectonic slices developed along the southern flank of the Sost stack. The southern part of the stack is in turn intruded by the Palaeogene Kuk pluton belonging to the Batura Unit of the KAB. S- to SSE-vergent thrusting was successively active, stacking steep north-dipping thrust sheets along the northern side of the Sost Unit, forming a complex antiformal stack, well exposed around Sost. High angle pure dip-slip reverse and oblique dextral motions are recorded by fault-slip data and calc-mylonites along major faults, forming a transpressive fault zone close to the contact between the Sost and Misgar Units. During this stage, the Misgar Unit was thrusted southward above the Sost Unit along the Northern Fault. Prosecution of dextral motion was also active afterwards along the boundary between the two units. The importance of wrench tectonics is also indicated by widespread activation of E-W sinistral strike-slip faults in the whole study area, generally moving along pre-existent fault planes