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अमूर्त

Petrology and Geochemistry of Gabbros from the Andaman Ophiolite: Implications for their Petrogenesis and Tectonic Setting

Rasool QA, Ramanujam N, Biswas SK

The Andaman ophiolite has almost a complete preservation of ophiolite sequence with mantle section and comparatively less well-developed crustal section. The crustal part of the ophiolite comprises both ultramafic cumulates; dunite, wherlite and pyroxenite and mafic cumulates or gabbros. The gabbros are olivine gabbro, and pyroxene gabbro. They are distinguished into cumulates and non-cumulates. Geochemical features indicate that they are tholeiitic, fractionated and are formed in an arc-related tectonic setting. The large- ion lithophile (LIL) elements (Rb, Ba, Th, Sr) are relatively more enriched than Normal-mid-ocean ridge basalts (N-MORB). The enrichment of Large-ion lithophile (LIL) elements over the High-field strength (HFS) elements and the depletion of Nb relative to other High-field strength (HFS) - elements suggest involvement of subduction component in the depleted mantle source, and suggest that they are formed in a supra-subduction zone tectonic setting