Diachronous cooling along the Mogok Metamorphic Belt (Shan Scarp, Myanmar): the trace of the northward migration of the Indian syntaxis
Journal of Asian Earth Sciences, n. 19, pp. 649-659.
Keywords: Myanmar, Shan scarp, tectonics, radiochronology, India-Asia collision
Guillaume Bertrand – UMR 8538, Ecole Normale Supérieure, Laboratoire de Géologie, 24 rue Lhomond, F-75231, Paris cedex 05, France.
Claude Rangin – UMR 8538, Ecole Normale Supérieure, Laboratoire de Géologie, 24 rue Lhomond, F-75231, Paris cedex 05, France.
Henri Maluski - UMR 5567, Laboratoire de Géochronologie, Université Montpellier II, place Eugène Bataillon, F-34095, Montpellier, France.
Hervé Bellon - UMR 6538, Domaines océaniques, Université de Bretagne Occidentale, place Nicolas Copernic, F-29280, F-Plouzané, France.
The GIAC Scientific Party.
ABSTRACT
We present new observations and new mineral ages (eight by the 40Ar/39Ar and nine by the 40K-40Ar methods) from high grade metamorphic and foliated intrusive rocks collected along the Mogok Metamorphic Belt of central Myanmar, that complete preliminary results we previously published. All 30 ages presented here confirm the Oligocene to Middle Miocene age of the Mogok metamorphism. Moreover, the ages young from the Gulf of Martaban in the south to the China-Myanmar border in the north, showing a clear diachronism. These results confirm a northward migration of the tectonic event responsible for the cooling of our samples, at a velocity similar to the India relative to Indochina velocity at the same period.
In addition, intensive field work, along a 800 km long section of the Mogok Metamorphic belt, has revealed the numerous ductile structures that resulted from a strong NNW-SSE-trending extension. From the analogy between the present-day local extrusion around the eastern Indian syntaxis and the extension observed along the Mogok Metamorphic Belt, and from the diachronism we document, we suggest that the central part of Myanmar has "recorded" the northward passage of the eastern Indian syntaxis with respect to Indochina from Oligocene to Middle Miocene.
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