LATEST CRETACEOUS-TERTIARY TECTONIC EVOLUTION OF NORTHERN YUKON AND ADJACENT ARCTIC ALASKA

Regional crustal shortening in northern Yukon and northeastern Alaska occurred episodically from the latest Cretaceous to the late Miocene, with a major culmination occurring in the Paleocene to middle Eocene, and a secondary culmination in the late Miocene. Structural trends are predominantly north to northeastward in northern Yukon and adjacent e ast-central Alaska, and generally east-west along the Brooks Range. Th e early Tertiary trend is strongly arcuate in the Beaufort fold belt a nd adjacent onshore areas. The continuity of structures southward from the Beaufort Sea region through northern Yukon and east-central Alask a supports the interpretation that the structures north of 65 degrees N form a single orogenic entity. The Beaufort Sea region is 1000 km fr om the nearest plate margin. Northward shortening across Arctic Alaska and the northern Canadian cordillera reflects the convergent componen t of Kula (later, Pacific)-North America interactions throughout the T ertiary. North- to northeast-trending structures of latest Cretaceous to early Tertiary age in northern Yukon and east-central Alaska accomm odate shortening of 180-240 km, and reflect Eurasia-North America conv ergence. The strongly arcuate offshore Beaufort fold belt and similar structures in adjacent northernmost Yukon and northeast Alaska were fo rmed by the complex interplay of three factors: shortening of northern Yukon between Arctic Alaska and the craton to produce a north-trendin g orogenic welt; northward displacements propagated from the Kula plat e margin; and local boundary conditions imposed by lithology and crust al structure, which aided lateral escape of the deforming supracrustal succession northward into the Beaufort Sea. In central Alaska, any ki nematic linkage between the Kaltag fault in the west and the Tintina f ault of the northern cordillera is more complex than was previously as sumed. A new regional tectonic reconstruction of northern Yukon-Alaska quantifies the tectonic shortening in central Alaska south of the Kal tag and Tintina faults in an area where tectonic shortening is difficu lt to quantify due to complex geology. Complex deformation accommodate d by folding, thrust and strike-slip faulting, and/or tectonic rotatio ns accounts for an estimated 460 km of crustal shortening, approximate ly equivalent in magnitude to the total Tintina fault displacement of at least 450 km. The foreland of the Brooks Range, the Beaufort fold b elt, and the northern cordillera contain proven petroleum basins. This regional synthesis validates a model of orogenic shortening for the B eaufort fold belt and provides a unifying tectonic setting for oil and gas plays throughout the region. The latest Cretaceous-Tertiary struc tural evolution of the Brooks Range, Beaufort, and northern Yukon fold belts is a case study of the temporally and kinematically complex far -field deformation arising from the convergence Of four major tectonic plates.