S.H. JAFRI, D. SRINIVASA SARMA*, TAVHEED KHAN and D. K. SINGH
The ophiolites of the Andaman-Nicobar Islands are well exposed in Andamans as dismembered units, and are considered as accreted and uplifted oceanic basement rocks, and mainly consists of ultramafics (harzburgite, wherlite, pyroxenite and dunite), gabbro, East Coast Volcanics (basalts and andesites), lower and upper pillow basalts, plagiogranites, dacites, basic dykes and radiolarian cherts. The radiolarian cherts are present as minor constituents in the eastern part of north Andamans in small exposures, belonging to Upper Cretaceous–early Eocene or Late Cretaceous to Middle Eocene age. Elemental abundances and their element relationship suggest that Type-I and Type-II cherts were derived from the terrigenous and volcanogenic (basaltic) source. LaN/CeN ratios and Ce/Ce* anomaly of these radiolarian cherts also suggest that they are deposited in continental margin environment. It has been suggested that the cherts deposited at different places, were scrapped off the subducting plate and obducted onto the leading edge of the Eurasian continent during the Late Cretaceous prior to the currently active Andaman–Java subduction, that was probably initiated during the Late Miocene.
J. Earth Syst. Sci. (2020) 129:103 Indian Academy of Sciences