The Mascarene Ridge, on which the Saya de Malha and Nazareth Banks lie, is a 2,000-km long, arcuate, convex-eastward submarine uplift between the Central Indian Ridge on the east and Madagascar and Africa on the west. Upper Proterozoic granitic rocks underlie the Seychelles Islands at the northern end. We interpret the ridge to be a relict island arc similar in origin to those in the western Pacific Ocean.

Since early Paleozoic time, vertical tectonics--as opposed to island-arc tectonics--have characterized the Mascarene Ridge. A large Tertiary basin (minimum, 25,000 sq km) began to form on the central part of the ridge during middle Paleocene time. Regional geologic and local geophysical studies led to the drilling of two wildcat wells during 1975--the SM-1 (Saya de Malha) and the NB-1 (Nazareth Bank). The total depths are 3,264 and 1,716 m, respectively. The sedimentary section, upper Paleocene-Quaternary, consists of neritic to shallow-water carbonate rocks which are 2,432 m thick in the SM-1. The carbonates overlie a section of basaltic rocks 832 m thick. The results of the two wells do not offer much encouragement for the petroleum prospects on the Mascarene Ridge. However, final j dgment should be withheld because two wells cannot condemn an area of this size, or a sedimentary prism of this volume.