Motion of the Pacific plate relative to Eurasia and its potential relation to Cenozoic extension along the eastern margin of Eurasia

Abstract

Extension along the eastern margin of Eurasia has been regarded commonly as a far-field effect of the India-Eurasia collision. However, some aspects of the timing and location of this extension make a link between the collision and extension difficult. We suggest that some extensional features commonly interpreted as effects of the collision may be related more simply to changes in plate-convergence rates along the eastern plate boundary of Eurasia. An analysis of the motion of the Pacific plate relative to Eurasia suggests that the rate of Pacific-Eurasia convergence varied significantly during the Tertiary Period. From a Late Cretaceous convergence rate of ∼120–140 mm/yr, the rate declined substantially during early Tertiary time and reached a minimum in Eocene time of ∼30–40 mm/yr. In Oligocene to earliest Miocene time, the average convergence rate increased moderately to 70–95 mm/yr, then decreased again to 65–70 mm/yr during early to middle Miocene time. From late Miocene to the present, the rate of convergence increased to an average of 100–110 mm/yr. The Paleocene through middle Miocene episode of relatively slow convergence correlates with a period of widespread extension along the eastern margin of Eurasia. Decreased convergence may have been related to a net reduction in horizontal compressional stress transmitted between the Pacific and Eurasian plates, which resulted in widespread extension adjacent to the margin of Eurasia.