GEOCHEMICAL AND ISOTOPIC FEATURES OF BASALTS IN THE AXIAL MID-ATLANTIC RIDGE NEAR THE MARTIN VAZ FRACTURE ZONE, SOUTH ATLANTIC (19°-20° S)

Abstract

One of the essential problems of oceanic tectonics is estimation of the influence of plumes of the deep hot mantle on processes in the axial spreading zone. Areas of two giant (St. Helena and Tristan da Cunha) plumes in the Mid-Atlantic Ridge (MAR) rift zone (South Atlantic) are characterized by the effusion of basalts that differ from typical depleted riftogenic tholeiites by anomalously high contents of lithophile components and specific isotopic compositions. Moreover, the rift valley floor with basalt effusion is significantly uplifted above the adjacent sectors of the rift.