Geochemistry of Andaman Ophiolite: Evidence for a Mid-Oceanic Ridge origin

Abstract:

 “Ophiolite conundrum” deals with the unresolved puzzle of the origin of ophiolite, whether they have primarily formed in mid-oceanic ridge (MOR) or supra subduction zone (SSZ) settings. This attracts considerable debate because most of the ophiolites are located along the present day suture zones. The Andaman Ophiolite is a Cretaceous complex that occurs on the Andaman accretionary prism of the Indian-Eurasian convergent plate boundary. Here, we present whole rock trace element and isotope (Sr-Nd) data from the crustal section of the ophiolite comprising of pillow basalt, basalt, dolerite and gabbro from Rutland Island, south and middle Andaman Islands. Trace element patterns for a majority of our samples show N-MORB affinity barring enrichments in Rb and Ba, which could be attributed to secondary alteration. Comparison of trace element patterns and isotopic compositions of these rocks (e_Nd (t = 95 Ma) = 7.5 to 9.4; ⁸⁷Sr/⁸⁶Sr_i = 0.703 to 0.704) with that of the 127- 64 Ma Indian Ocean MORB suggest strong similarities thus, implying that a large section of Andaman Ophiolite represents the subducting Indian Oceanic Plate. If so, then this ophiolite complex possibly represents an obducted Indian oceanic lithosphere that formed at the Indian Ocean MOR.