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.

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