Petrology, geochemistry, and mineralogy of the early Cretaceous evolved N-MORB from Sites 765 and 766, eastern Indian Ocean

The Early Cretaceous basaltic rocks obtained from Sites 765 and 766 in the eastern Indian Ocean floor were mostly iron-rich normal mid-ocean ridge basalts (N-MORB) which were derived from a depleted mantle source having strongly light rare earth element (LREE)- depleted rare-earth patterns and a high Ti/Zr ratio. Basaltic rocks in the upper part of the Site 765 basement section include megacrysts and gabbroic fragments of widely varying mineral chemistry. This varying mineralogy indicates that a considerable degree of fractional crystallization took place in the magma chamber. Strontium isotope ratios of the basaltic rocks from both sites are comparable to those of mid-Indian Ocean ridge basalts (MIORB). The basalt pebbles encountered in the sedimentary section include basaltic compositions ranging from primitive N-MORBs to evolved enriched(E)-MORBs. Their mantle source was not as depleted as that of the basement basalts. These rocks may be the products of earlier volcanism that took place during the rifting of the Australian continent. -from Author