Style of Fractional Crystallization in Basalts from the Paleoarchean Western Iron Ore Group of Singhbhum Craton, Eastern India: Implications from One Atmosphere Experimental Studies

Abstract

One atmosphere experimental study on fresh basaltic rocks of Paleoarchean western Iron Ore Group (IOG) basin of Singhbhum Craton, Eastern India gives insight of the crystallization behavior of the parent magma, liquid lines of descent and appearance of the different constituent phases. The natural starting material is sufficiently ferroan (FeO^t: 14.28 wt%) and corresponds to ‘ferro-basalt’. Regarding the experimental run products, clinopyroxene shows Al₂O₃ rich character (ranging from 2.23 – 6.94 wt%; formed due to fluctuating silica activities in the magma) while plagioclase reveals typical Fe-Mg enrichment (that corresponds to higher K_d ^Fe-Mg between plagioclase and the parent liquid caused due to immiscible silicate melt inclusion in plagioclase where Mg enters more readily in plagioclase than Fe). The run-product glass corresponds to both high and low iron contents suggesting liquid immiscibility in the parent magma at particular temperature-domains. This study suggests that the crystallization of the western Iron Ore Group basalts represents a broad ‘Skaergaard analogue’ involving depression/ shift of eutectic point in the diopside-anorthite system during crystallization.