Petrology of ultrabasic rocks from rift zones of the Mid-Indian Ocean Ridge

Abstract

Ultrabasic rocks from the Mid-Indian Ocean Ridge and peridotites of the alpine type have similar petrographic characteristics. A petrochemical comparison of these rocks shows that oceanic peridotites are enriched in SiO ₂ and normative hypersthene. The direction of the development of the composition of ultrabasic rocks after separation of different amounts of basalt from pyrolites of oceanic and alpine type ultrabasic rocks was obtained by calculation. Combination of these data with experimental melting diagrams shows that alpine type ultrabasic rocks melt at higher temperatures than oceanic ultrabasic rocks. On geological and petrochemical grounds we think that the ultrabasic rocks which outcrop in the rift zones of the Mid-Indian Ocean Ridge are a specific formation. This formation consists of slighty differentiated pyrolites of the oceanic type.