The enigmatic Indo-Burma convergent margin at the Ganges-Meghna-Brahmaputra delta
Abstract
At active convergent margins, sedimentation, sediment recycling and sediment accretion can broadly affect the thermal structure and the hydrogeology at the plate boundary, and in turn, bear on fault behavior and seismogenesis. On the eastern flank of the India-Eurasia collision, the Indian plate is obliquely colliding beneath southeast Asia. While typical oceanic subduction occurs beneath the Sumatra-Andaman subduction zone, the continuation of this plate boundary to the north encounters the heavily sedimented passive margin of India, today occupied by the world's largest delta, the Ganges-Brahmaputra-Meghna Delta (GBMD). While the GBMD is overthrust by the IndoBurma foldbelt from the east and the Shillong Plateau from the north, it also receives an enormous influx of Himalayan sediments since, likely, more than 10 Ma. This context makes the GBMD an unparalleled opportunity to explore the potential effect of sediment on active margin dynamics. In this study, we have integrated all the recent observations from fieldwork and published seismic, gravity and borehole data to build up a regional history of sedimentation, subsidence and uplift that we are using to constrain a first set of thermo-mechanical models in this region. We are exploring, in these preliminary models, the blanketing effect of sediments (warming beneath sediments with a low thermal conductivity), the downward thermal advection potentially associated with rapid deposition of cold sediments, the fluid generation and upward migration, and the development of overpressure. We are also using the modelling results to revisit the estimation of exhumation rates from thermochronology data in the foldbelt, and to refine our understanding of the tectonics in the Indo Burma Ranges. In all the models explored, the present thermal gradient at the surface is very low (<15°C/km) and significant overpressure develops in the buried marine units as well as in Miocene sandy reservoir units. In addition, the pressure and temperature at the sediment-crust interface meet the conditions of low-grade metamorphism. Such extreme thermo-mechanical conditions for the incoming crust, covered by a thick pile (more than 10 km) of sediment at the GBMD, challenge most of the classical models of active margins.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT047...08G
- Keywords:
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- 7240 Subduction zones;
- SEISMOLOGY;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS