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 N‐S trending Shan scarp and Sagaing 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, close to the Sagaing fault, from Thaton in the south to Mandalay in the north, allowed us to collect samples of high grade metamorphic and intrusive rocks that have been analyzed by 40 Ar/ 39 Ar step heating method. The 13 samples we analyzed provide Oligocene to Lower Miocene ages for this metamorphism. Oriented thin sections and field observations suggest that this metamorphism was caused by a NNW‐SSE to N‐S ductile extension. Therefore, we suggest that this metamorphism is not directly related to the Sagaing fault, but could be instead related to the northward migration of the eastern Himalayan syntaxis, characterized by crustal thinning, resulting from the India‐Asia oblique collision.