| Abstract: | The Denali fault system forms an arc, convex to the north, across southern Alaska. In the central Alaska Range, the system consists of a northern Hines Creek strand and a southern McKinley strand, up to 30 km apart. The Hines Creek fault may preserve a record of the early history of the fault system. Strong contrasts between juxtaposed lower Paleozoic rocks appear to require large dextral strike-slip or a combination of dipslip and strike-slip displacements along this fault. Thus the fault system may mark a reactivated suture zone between continental rocks to the north and a late Paleozoic island arc to the south, as suggested by Richter and Jones (1973). Major movements on the Hines Creek fault ceased by the Late Cretaceous, but local dip-slip movements continued into the Cenozoic.The McKinley fault is an active dextral strike-slip fault with a mean Holocene displacement rate of 1–2 cm/y. Post-Late Cretaceous dextral offset on this fault is probably at least 30 km and possibly as great as 400 km. Patterns of early Tertiary folding and reverse faulting indicate that the McKinley fault was active at that time and suggest that this fault developed shortly after strike-slip activity ceased on the Hines Creek fault. Oligocene — middle Miocene tectonic stability and late Miocene—Pliocene uplift of crustal blocks may reflect periods of quiescence and activity, on the McKinley fault.The two strands of the Denali fault divide the central Alaska Range into northern, central, and southern terranes. During the Paleozoic—Mesozoic there is evidence for at least two episodes of compressive deformation in the northern terrane, four in the central terrane, and two in the southern. During each, the axis of maximum compressive strain was subhorizontal and about north—south. This pattern suggests a Paleozoic and Mesozoic setting dominated by plate convergence, despite the possible large pre-Late Cretaceous lateral movement on the Hines Creek fault.The Cenozoic pattern of faulting and folding appears compatible with a plate tectonic model of (1) rapid northward movement of the Pacific plate relative to Alaska during the early Tertiary; (2) slow northwestward movement of the Pacific plate during the Oligicene and (3) rapid northwestward movement of the Pacific plate from the end of the Oligocene to the present. |
