The transition from continental collision to oceanic subduction in Myanmar

The geology at the margins of continental collision zones is characterized by a pronounced three-dimensionality, whereby crustal thickening, lateral material flow, and crust-mantle interaction are acting processes. The region of the eastern syntaxis of the Himalayas, parts of which are located in Myanmar, China, and India, is an ideal natural laboratory for studying the processes at the transition from continental collision to oceanic subduction. We report an investigation of the location of the continental collision‒oceanic subduction transition in the upper plate (see Min et al., 2022 for a study on the lower plate), the Mogok metamorphic belt, an equivalent to the Lhasa Terrane and the Gangdese magmatic arc in Tibet. Our working hypothesis is that crustal thickening by shortening, Barrovian metamorphism, anatectic melting characterize the continental collision section and arc magmatism, Buchanan metamorphism, and lack of major shortening characterize the oceanic subduction section. Therefore, we reconstruct the pressure-temperature-deformation time (P-T-d-t) history along several transects along-strike of the Mogok metamorphic belt from Yunnan in the north to the Mergui archipelago of southern Myanmar in the south. Transition zones from continental collision to oceanic subduction may also trigger the initiation and subsequent sideway propagation of slab break-off (e.g., Webb et al., 2017). Such a location may be characterized by advective heat input, manifested by ultra-high temperature metamorphism and a flare-up of magmatism. We present first results from several traverses concerning this research questions from petrology, and Lu/Hf garnet, U-Th-Pb zircon, monazite, titanite, Ar/Ar amphibole, mica, feldspar, fission-track zircon, titanite, and apatite, and (U-Th)/He apatite geochronology.