Cenozoic metamorphism along the Shan scarp (Myanmar): evidences for ductile shear along the Sagaing fault or the northward migration of the eastern Himalayan syntaxis?
Geophysical Research Letters, V. 26, n. 7, pp. 915-918.
Keywords: Myanmar, tectonics, radiochronology, Sagaing fault, Shan scarp, Mogok metamorphic belt, continental extension
Guillaume Bertrand – UMR 8538, Ecole Normale Supérieure, Laboratoire de Géologie, 24 rue Lhomond, 75231, Paris cedex 05, France - téléphone: (33) 01 44 32 22 63 - fax: (33) 01 44 32 20 00 - email: bertrand@sphene.ens.fr
Claude Rangin – UMR 8538, Ecole Normale Supérieure, Laboratoire de Géologie, 24 rue Lhomond, 75231, Paris cedex 05, France.
Henri Maluski – CNRS UMR 5567, Laboratoire de Géochronologie, Université Montpellier II, Montpellier, France.
Tin Aung Han - Geology department, Dagon University, Yangon, Myanmar.
Myint Thein - Geology department, University of Mandalay, Mandalay, Myanmar.
Ohn Myint - Geology department, University of Yangon, Yangon, Myanmar
Win Maw - Myanmar Oil and Gas Enterprise, Yangon, Myanmar
San Lwin - Myanmar Oil and Gas Enterprise, Yangon, Myanmar
ABSTRACT
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 40Ar/39Ar 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.
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