Discussion
The typical record of the early crust of ultramafic high Fe-Mg rocks depicting upto 500°C hotter mantle are :
Answer: D
The rocks are komatiites.
Komatiites are ultramafic volcanic rocks with very high MgO (more than 18 per cent), mostly of Archaean age, often showing spinifex texture formed by rapid cooling of olivine. Their eruption required melting temperatures of about 1600 °C, which is taken as evidence that the Archaean mantle was up to several hundred degrees hotter than today's.
Eclogite is a high-pressure metamorphic rock, pegmatite is a coarse felsic igneous rock, and anorthosite is a plagioclase-rich rock; none is an ultramafic lava recording a hotter mantle.
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