Mechanism of rift flank uplift and escarpment formation evidenced by Western Ghats, India

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.

Mesozoic origin and ‘out-of-India’ radiation of ricefishes (Adrianichthyidae)

“…The divergence of O. setnai and its endemism to western India may be related to the formation of the Western Ghats mountain ranges. The western coast of India could have appeared as an abrupt cliff some 1000 m in elevation ca 65-90 Ma after the Indian subcontinent broke away from Madagascar [51], becoming the present-day Western Ghats. This long (1600 km) and high mountain range running parallel to the southwestern coast of the Indian subcontinent may have acted as a physical barrier preventing the migration of species between the western and eastern coasts.…”

Low geomagnetic field strength during End-Cretaceous Deccan volcanism and whole mantle convection

“…The lava pile represents the stratigraphic formations that constitute the Wai Group. The top ~350 m section belongs to the Mahabaleswar formation with normal polarity and thereafter, the section down to the basement is monotonously of reverse polarity that represents the Ambenali, upper Poladpur and lower Poladpur formations in succession downwards 33 . The drill hole section recovered at least seven red boles amounting to a thickness of more than 5 m and a few alteration zones indicating that smaller pulses of eruptions are separated by longer times of volcanic quiescence.…”