Cenozoic metamorphism along the Shan scarp (Myanmar): evidences for ductile shear along the Sagaing fault or the northward migration of the eastern Himalayan syntaxis?

The Mogok metamorphic belt, exposed along the NS trending Shan scarp and Sa gaing fault, in the eastern part of Myanmar, has been regarded as Paleozoic to Precambrian for a long time. New observations in the Shan scarp area, c lose to the Sagaing fault, from Thaton in the south to Mandalay in the nort h, allowed us to collect samples of high grade metamorphic and intrusive ro cks that have been analyzed by Ar-40/Ar-39 step heating method. The 13 samp les we analyzed provide Oligocene to Lower Miocene ages for this metamorphi sm. Oriented thin sections and field observations suggest that this metamor phism was caused by a NNW-SSE to N-S ductile extension. Therefore, we sugge st that this metamorphism is not directly related to the Sagaing fault, but could be instead related to the northward migration of the eastern Himalay an syntaxis, characterized by crustal thinning, resulting from the India-As ia oblique collision.