PROVENANCE OF NEOGENE SANDSTONES IN SOUTHEASTERN PART OF BENGAL BASIN AND CENTRAL BASIN OF MYANMAR, IN RELATION TO THE INDIA-ASIA COLLISION AND UNROOFING OF EASTERN HIMALAYAS

Neogene clastic sequences preserved in the Baronga Islands, western part of Indo-Burman ranges and Pegu Yoma ranges, Central Myanmar provide detrital information from the on land part that documents an erosional unroofing history of the eastern Himalayas, and India-Asia collision. All of the sedimentology and provenance data link the syntectonic sedimentation and sequential evolution of eastern part of the Bengal basin, a remnant ocean basin south of the eastern Himalayas and, the formation of paleoincised valleys at the eastern trough of Central Tertiary basin bordered by the Mogok belt lie east of the Sagaing Fault, and the Asian Plate to the far east. Model analysis of the Lower Miocene sandstone of the Baronga Islands, and Pegu Yoma ranges documents that are rich in both monocrystalline and polycrystalline quartz, sub-angular to sub-rounded feldspar grains and lithic fragments including metamorphic rocks with minor basaltic rock fragments suggesting onset of uplift and erosional unroofing in the eastern Himalayas, and basement uplifting in the Mogok belt and Gangaw ranges of Upper Irrawaddy Basin in the western part of Asia Plate and initiation of river systems supplying orogenic detritus to the south since the early Miocene. Middle Miocene sandstones of the both areas are rich in subangular monocrystalline quartz grains, chert and argillite with little amount of feldspar and metamorphic lithic fragments relative suggesting low supply from the Himalayas and associated with the widespread marine transgression occurred in early Middle Miocene (about 16 Ma). Post-early Miocene dextral displacement along the western part of Asia Plate possibly contributed the subsidence led to subsequent relative sea-level rise and accumulation of middle Miocene thick mud units in these areas. Sandstones of the upper Miocene contain abundant metamorphic lithic fragments and feldspar (both orthoclase and plagioclase) grains with volcanic rock fragments suggesting continued orogenic unroofing in the northern parts and the younger granitic sources from the eastern Himalayas and the Mogok Belt along the eastern part of Sagaing Fault.