The world system of underwater rift-type spreading zones is a long-lived, complex, evolving system. It includes various provinces differing in age and geodynamics. The igneous activity which accompanied the formation of the oceanic lithosphere can be used as an indicator of the processes which controlled the specific characters of different regions. The extreme western termination Shpiss Ridge of the extensive South-West Indian Ridge in the Atlantic Ocean is referred to in the Russian literature as the African-Antarctic Ridge of a relatively young age. Proceeding from the results of magnetic surveys, the onset of the spreading was dated less than 2million years. Of particular interest in this connection was to study the conditions of the formation and character of igneous activity under the newly formed and developing spreading zone. The Shpiss Ridge was formed under specific conditions, where the new rift zone originated in the oceanic crust which had been formed earlier in the MAR region. The complex dynamics of the Shpiss Ridge area evolution resulted in the formation of a new central-type volcanic rise with a relative height of about 2km and minimal depth of 320m, and a caldera amounting to 4km in diameter. The eastern and western slopes of the Shpiss Ridge are marked by a series of small secondary volcanic cones. The preliminary study of the igneous rocks of this ridge ranked them as tholeiites enriched in lithophile elements. The source of this enrichment was the rise of an enriched plume under the area of the Bouve Island. The aim of this study was to reconstruct the conditions of magma formation under the ridge, to verify the potential existence of an intermediate-depth magma chamber, and to estimate its potential size. This information is important for deriving a model for the evolution of the oceanic lithosphere in the region of the triple junction of its plates.
crystallization and geochemistry of tholeiite magmas, rift-type spreading zones, igneous activity.
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