MULTISTAGE STRUCTURAL EVOLUTION OF NORTHERN KARAKORAM (HUNZA REGION, PAKISTAN)

Detailed mapping and structural work in Upper Hunza Valley, Pakistan, have enlightened the tectonics and the structural evolution of the sed imentary cover of Northern Karakorum. This includes the Northern Sedim entary 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 unkn own age. In the Sost Unit a mid-Cretaceous deformed belt is sealed wit h a strong angular unconformity by the Late Cretaceous formations. Fol ds within the mid-Cretaceous belt possibly indicate north-vergent tran sport. Stacking of NE- to N-vergent thrusts sheets postdates the depos ition of Cretaceous sediments, which are largely included within tecto nic slices developed along the southern flank of the Sost stack. The s outhern part of the stack is in turn intruded by the Palaeogene Kuk pl uton belonging to the Batura Unit of the KAB. S- to SSE-vergent thrust ing was successively active, stacking steep north-dipping thrust sheet s along the northern side of the Sost Unit, forming a complex antiform al stack, well exposed around Sost. High angle pure dip-slip reverse a nd oblique dextral motions are recorded by fault-slip data and calc-my lonites along major faults, forming a transpressive fault zone close t o the contact between the Sost and Misgar Units. During this stage, th e Misgar Unit was thrusted southward above the Sost Unit along the Nor thern Fault. Prosecution of dextral motion was also active afterwards along the boundary between the two units. The importance of wrench tec tonics is also indicated by widespread activation of E-W sinistral str ike-slip faults in the whole study area, generally moving along pre-ex istent fault planes.