MAGMATIC AMPHIBOLES AND MICAS IN OCEANIC PERIDOTITES AND SOME SPECIFIC FEATURES OF THE RELATED MAGMAS: 15 DEG 20'' N MAR FRACTURE ZONE

Abstract

The aim of this work was to study the petrography and mineralogy of mineral associations with magmatic high-Ti hornblendes and micas in MAR spinel harzburgite. The mineral compositions were examined using electron and ion microprobes. It was found that these mineral associations had been formed in a temperature range of 870-950° C as a result of the crystallization of a residual highly differentiated (96-98%) mantle magma and its interaction with the host peridotite. Based on the compositions of the pyroxenes and amphibole, the initial mantle magma was in equilibrium with the minerals of the restite harzburgite and based on its enrichment in LREE (La/SmN = 10-12) can be classified as intraplate OIB magma. The absence of a Sr anomaly in the model composition of the initial magma, evaluated for one of the two MAR areas concerned (Site 16ABP-68), and the negative Sr anomaly characteristic of the model composition of the magma, calculated for the other MOR area (Site 16ABP-62), can serve as an independent confirmation of the local rock heterogeneity in the region of intraplate magma generation, possibly associated with a crustal component recycling.