Abstract
The Western Ghats is one of the largest escarpments on earth, containing Reunion plume derived Deccan Traps, it is an excellent example to probe epeirogenic uplift, extension and subsidence in volcanic continental margins. The most continuous unbiased stratigraphic section of basalt down to the basement within a 1250 m drill hole of the Continental Scientific Deep Drilling Project is a valuable resource to investigate the above aspects. The flows across the entire drill core are geologically subaerial in character with basement exposed ~300 m below the mean sea level; they clearly display more evolved compositions from primary melts of mantle in terms of petrology, and only a single geomagnetic polarity transition in palaeomagnetic data. These results, combined with existing geological and geophysical data, constitute a multi-method approach that demonstrates (a) igneous underplating caused uplift prior to frequently suggested flexural isostasy (b) plume impact and eruption are near-simultaneous and extension/rifting essentially followed soon after volcanism and (c) lithosphere beneath the continental margin, while returning to normal temperatures following the Seychelles-India breakup, experienced thermal collapse and subsidence causing slumping of basalt basement below sea level.
Highlights
The Western Ghat (WG) escarpment was developed from rifting and separation of India from the Seychelles and is closely linked with the late Cretaceous (~65–66 Ma) Deccan flood basalt eruption; it demarcates the low-lying seaward coastal plains in the west from the elevated plateau to the east (Fig. 1)
Deep Drilling at Koyna (Fig. 1) within the WG13 gives a unique opportunity to access every successive flow of the stratigraphic section of the Deccan eruption down to the basement
The KBH-7 core was drilled at an elevation of 949 m above mean sea level (MSL).The basalt sequence along the core is demarcated into 37 flows this number varies between different authors
Summary
The KBH-7 core was drilled at an elevation of 949 m above mean sea level (MSL).The basalt sequence along the core is demarcated into 37 flows this number varies between different authors. Mass balance studies and numerical modeling of flexural responses to onshore denudational unloading and offshore sediment loading infer that flexural isostasy alone is not adequate to explain the quantum of offshore sediment deposition[6,7] and requires a pre-existing elevated rift flank We propose here such elevated rift flank topography was formed by igneous underplating at the crust mantle interface and development of a low density depleted mantle layer on removal of melts at the time of up-rise of mantle and flood basalt eruption. An argument against such a mechanism prefers lithospheric necking for the uplift in the WG escarpment[36,37]. The on-going micro-seismic activity and erosion/denudation in the WG indicate that the epeirogenic movements of flexural isostasy are still active in the Western Ghats and the denudation/erosion is likely driven mainly by uplift rather than climate
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