MOTION OF THE PACIFIC PLATE RELATIVE TO EURASIA AND ITS POTENTIAL RELATION TO CENOZOIC EXTENSION ALONG THE EASTERN MARGIN OF EURASIA

Extension along the eastern margin of Eurasia has been regarded common ly as a far-field effect of the India-Eurasia collision, However, some aspects of the timing and location of this extension make a link betw een the collision and extension difficult, We suggest that some extens ional features commonly interpreted as effects of the collision may be related more simply to changes in plate-convergence rates along the e astern plate boundary of Eurasia. An analysis of the motion of the Pac ific plate relative to Eurasia suggests that the rate of Pacific-Euras ia convergence varied significantly during the Tertiary Period. From a Late Cretaceous convergence rate of similar to 120-140 mm/yr, the rat e declined substantially during early Tertiary time and reached a mini mum in Eocene time of similar to 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 convergenc e increased to an average of 100-110 mm/yr, The Paleocene through midd le Miocene episode of relatively slow convergence correlates with a pe riod of widespread extension along the eastern margin of Eurasia. Decr eased convergence may have been related to a net reduction in horizont al compressional stress transmitted between the Pacific and Eurasian p lates, which resulted in widespread extension adjacent to the margin o f Eurasia.