Constraining the links between the Himalayan belt and the Central Myanmar Basins during the Cenozoic: An integrated multi-proxy detrital geochronology and trace-element geochemistry study

Abstract

Geological and tectonic analysis of the Eastern Himalayan basins has given rise to a decade-long debate on the geodynamic evolution of the Burmese terrane and on the extent of reorganization of the main SE Asia drainage systems. However, the influence of the Himalayan belt on the Central Myanmar Basin (CMB) system remains poorly documented, although it is key to providing more accurate models for the evolution of the Himalayan-Burmese orogen. In this contribution, we present geochronological, isotopic and geochemical analysis from 2500 zircon, 1700 titanite, 700 rutile and 850 apatite detrital grains from fifteen Cenozoic siliciclastic samples and one Cretaceous igneous rock. The samples were collected within the fore- and back-arc basins of the Central Myanmar Basin domain (CMB) to constrain the provenance, maximum depositional ages, and depositional environments of the west Burma terrane. Nine key lithological units, the Sadwingyi, Ketpanda, Wabo Chaung, Gwegon, Minwun, Padaung, Okmintaung and Irrawaddy formations have detrital age spectra spanning from the Miocene to Paleoarchean. The entire data set has common age peaks at ca. 20, 40, 60, 90, 100 ​Ma, with about 80% of the U–Pb ages younger than ca. 140 Ma and only ca. 1% of the grains predating ca. 3.0 ​Ga.Our results shed light on the current ambiguities on the transport pathways of Himalayan detritus in the CMB. They show that the fore-arc basin was open to the trench and fed by the unroofing of both the Wuntho Popa volcanic arc to the east and possibly from the Burmese basement and/or from Himalayan-derived Bengal Fan detritus to the west during the Eocene, from at least ca. 44 Ma to before ca. 39 Ma. We show that the west Burma Terrane was partitioned into pull-apart basins such as the Minwun Basin, which during the Oligocene recorded the first evidence of a new source contribution into the CMB at ca. 27 Ma. This new source is characterized by detritus highly compatible with the SE Asia basement rocks, which we suggest corresponds to the initiation of the palaeo–Irrawaddy River. This geodynamic evolution does not require any Yarlung Tsangpo-Irrawaddy-Brahmaputra paleodrainage reorganization, since from the Oligocene to the Early Miocene, the Irrawaddy River fed an internally drained basin, and from the Late Miocene onwards, the Yarlung drained into the Brahmaputra in the Bengal Basin.