Discussion
Magma undering extensive differentiation in \(F_{e}^{tot}/(F_{e}^{tot} + MgO)\) ratio coincide with a miminal change in silica content resulting in crystallization of olivine and pyroxene without Fe-Ti oxides leads to formation of .................. .
Answer: C
Such differentiation leads to ferrobasalt.
In tholeiitic magmas at mid-ocean ridges, fractional crystallisation of olivine, plagioclase and clinopyroxene without Fe-Ti oxides removes magnesium faster than iron. The FeO(total)/(FeO(total) + MgO) ratio of the residual liquid therefore rises sharply while silica barely changes (the 'Fenner' or tholeiitic trend). Basalts that have gone far along this trend, with FeO(total) above about 12 per cent, are called ferrobasalts, as found on the Galapagos spreading centre.
N-MORB and E-MORB are distinguished by their trace-element enrichment, not by iron enrichment. 'Fast-spreading EPR' names a tectonic setting, not a rock type.
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