Chapter 5 Arakan Coastal Ranges in western Myanmar, geology and provenance of Neogene siliciclastic sequences: implications for the tectonic evolution of the Himalaya–Bengal System

Abstract

Supplementary material : Preparation and analysis of samples with appendices are available at https://doi.org/10.6084/m9.figshare.c.3860926 Neogene clastic sequences preserved in the western part of Indo-Myanmar Ranges provide detrital information that document the erosional and unroofing history of the eastern Himalayas and the Burmese Arc during the Indian–Asian collision. All of the sedimentological and provenance data link the syntectonic sedimentation and sequential evolution of the Bengal Basin, a remnant ocean basin south of the eastern Himalayas and, at the time of formation, a palaeo-incised valley in the eastern trough of the Central Myanmar Tertiary Basin. To the east lies the Sagaing Fault and the Mogok Belt, and further east the Shan–Thai Block. Modal analysis of the Lower Miocene sandstones of the Baronga Islands, Arakan Coastal Ranges shows that they are rich in both monocrystalline and polycrystalline quartz, sub-angular to subrounded feldspars and lithic fragments including metamorphic rock fragments with minor basaltic fragments, suggesting the onset of uplift, erosion and unroofing of the eastern Himalayas and Indo-Myanmar Ranges. Since the Early Miocene, sediments were deposited in twin gulfs separated by the uplifted Indo-Myanmar Ranges. In the Middle Miocene there was a major change in the provenance of the Neogene sediments of the Arakan Basin and the Central Tertiary Basin of Myanmar. Since the Early Miocene, basement uplift of the Mogok Belt in the east and the Gangaw Ranges of the upper Irrawaddy Basin in the western part of the Asian Plate, as well as the initiation of river systems, supplied orogenic detritus to the south (Allen et al. 2008; Kyi Khin et al. 2014; Robinson et al. 2014; Licht et al. 2015). Middle Miocene sandstones from both areas are rich in sub-angular monocrystalline quartz, chert and argillites with small amounts of feldspar and metamorphic lithic fragments, suggesting a relatively low …