Magmatic evolution of the fresh basalts from the Ridge axis near Egaria Fracture Zone, Central Indian Ridge
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Fresh Mid-Ocean Ridge Basalts (MORBs) from the Central Indian Ridge (CIR) (20° 12'S; 66°53'E), located north of the Rodriguez Triple Junction (RTJ) are studied for their petrography and bulk composition along with mineral chemistry of plagioclase, olivine and spinels. Melt inclusions from plagioclases and olivines show post-entrapment depletion of oxides with the host mineral. Plagioclases and olivines show gradual changes in the anorthitic and forsteritic content (An = 89 to 78; Fo=90 to 85) from the basalts under study. These gradual changes in the olivines and plagioclase point to a simple evolution of the basaltic magma by differentiating mineral phases from the parental basalt The resorption features observed in high forsteritic olivines (~ 89,90) and zoning in the high anorthitic plagioclases (~ 90, 94) in fractionated host basalt indicate that these olivines and the plagioclases are xenocrystic to the host viz., evolved basalts. One basalt sample from a set of the basalts has a near primitive composition (MgO ~ 9.50%) and from this the remaining basalts seem to have fractionated. Major and trace element data reveal low-pressure crystal fractionation in a shallow level magma chamber within the crust. The chemical data of the basalts under study was run through a computer programme of the least square and mass balance calculations for understanding the evolutionary path by differentiating minerals present in these basalts. The results indicate that the basalts under study represent a set of basalts, with a parental basalt which is near primitive in its composition, and remaining have differentiated from this parental basalts. The chemical data of basalts under study has been compared with two published basalt data sets from the CIR for understanding the possible evolutionary sequences of basalts from CIR.
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