Greenstone-altered rocks of rift zones in median ridges of Indian Ocean

Abstract

Recently sampled slopes of ridges and canyons in the mid-oceanic hyperbasitic belt yield typical greenstones, products of metamorphism of basic intrusive and effusive rocks, which are associated paragenetically with the more or less serpentinized ultrabasic rocks. Expressions of metamorphism indicate a wide range of stages and temperatures. Low-temperature metamorphism accompanied by intensive deformations is regionally common. Nearly every sample shows it as fissuring, slickensides, fragmentation, tectonic brecciation, and so on, and every new phase of mineralogenesis represents a tectonic movement. Secondary alterations of greenstones resemble a regressive regional metamorphism, as in ancient geosynclines; serpentinization of ultrabasic rocks is very much like it is in peridotites of the Alpine type. -- V.P. Sokoloff