Sinuous track of the flexural bulge in the eastern Himalayas and Bengal Basin from multiple loads on a variable rigidity plate, an explanation for the Barind and Madhupur Pleistocene uplands
Abstract
The load of the Himalayas creates the broad Ganges foreland basin and uplifted flexural bulge to the south, with the width being controlled by the rigidity of the Indian craton. However, in the eastern part of the range, the foreland tectonics increase in complexity. In West Bengal and Bangladesh, the Hinge Zone of the Early Cretaceous passive margin on the "backside" of India approaches the Himalaya. At the Shillong Massif, the Indian craton overthrusts the thinned crust of the passive margin at the Hinge Zone. This is the beginning of a forward jump of the Himalayas towards the weaker Bengal Basin. In addition, the IndoBurma foldbelt is obliquely advancing from the east. Both overthrust the Bengal Basin where sediment of the Ganges-Brahmaputra Delta (GBD) provides yet another flexural load. Within this region there are two areas of Pleistocene sediment exposure, the Barind Tract and the Madhupur Tract. Whether these slightly elevated areas represent tectonic uplift or bypassed interfluves between river valleys has been argued over for >50 years. Combining flexural models of loading due to the Himalayas, Shillong, the IndoBurma Ranges and the GBD over a variable rigidity plate, we are able show that the superposition of the flexural bulges associated with this complex loading can and provide an explanation for the observed geomorphic features. We find that the composite flexural bulge has a sinuous path across the region. It starts in the Central Indian Highlands over 500 km south of the Main Frontal Thrust (MFT) of the Himalayas. It then bends to the NE to the Barind Tract, 120-200 km south of the MFT where the Indian plate weakens near the Hinge Zone. Farther east, the superimposition of the additional loads associated with the growth of the Shillong overthrust (whose velocity and load increases eastward) and the progradation of the GBD, it bends back to the SE across the Madhupur Tract. The flexural bulge may continue eastwards across the maximum elevation arch of the IndoBurma foldbelt in Tripura, India about 150 km south of Shillong, on the other side of the Sylhet foreland basin. Additional collection of gravity data in the region is critically needed to improve our understanding of this exceptional case of multiple loading.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T23C0379S
- Keywords:
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- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS