Mannar Volcanics - Implications for Madagascar Breakup

Summary Mannar sub basin of Cauvery basin is the southern- most of the Mesozoic rift basins existing along eastern continental margin of India and lies between Indian coast and Sri Lanka. The volcanic activities within Turonian sediments so typical of Gulf of Mannar are seen in almost all the drilled wells but have not been reported from any of the other sub basins of Cauvery basin. This is also reported in Pearl-1 well of Mannar sub basin in Sri Lankan offshore. Taking clue from the pattern of reflectors corresponding to intrusions, seismic study has been extended to the deeper part of Gulf of Mannar and also in its western part (towards Comorin ridge side) and observed the spread of this igneous activity which covers quite a large area. Recent dating through 40 Ar- 39 Ar studies carried out on one core sample of drilled well GM-E-A is around 89.1+0.65 Ma (Rathore et al., 2007). This age of the intrusive matches excellently with radiometric age for the Madagascar flood basalt province, the felsic volcanics of St Mary’s Island (SMI), two late Cretaceous mafic dykes around Huliyardurga, Karnataka and two regional dykes from Kerala region of South-western India. Together, therefore, the volcanic activities around these places may be associated with the break up of Greater India (India plus Seychelles) and Madagascar, envisaged to have occurred in Upper Cretaceous at  88Ma.