Relations of Cenozoic Tectonics of Central Rockies to Possible Movements of North American Plate: ABSTRACT

Abstract

Detailed studies of major uplifts in the central Rocky Mountains indicate that Cenozoic structures developed through predominantly vertical movements. This kinematic configuration in upper crustal levels is not necessarily incompatible with the concept of a laterally moving lithospheric plate, particularly if the plate overrides an oceanic rise or other undulation in the upper mantle. Lineaments are important tectonic elements in the movement plan. Some are well established, but others are only provisionally located or speculative. Much more work is needed to determine precisely the presence or absence of these large features and to define their characteristics. These lineaments could be entirely Cenozoic in age and represent crustal adjustments above transform faults, or could be reactivated zones of deformation along much older, even Precambrian lines of weakness. Evidence of intracontinental mobility through much of the Cenozoic suggests one possible sequence of events. In Early Cretaceous the west coast was east of the Pacific rise and bordered a subduction zone. By the Eocene, the plate had moved west over the subduction zone, the effects of which may have been Laramide deformation in the eastern Cordillera. Widespread erosion and gravel deposition beginning in the Oligocene may be related to a slowing or ceasing of drift 38 m.y. ago. A considerable change in patterns, rates, and relative motions of plates 20 to 10 m.y. ago and subsequent renewed westward drift coincides with the increased tectonic activity in western North America since the Pliocene. End_of_Article - Last_Page 629------------