Anorthositic Magma

Proterozoic Anorthosite - Origins of Proterozoic Anorthosites
... The problem begins with the generation of magma, the necessary precursor of any igneous rock ... Magma generated by small amounts of partial melting of the mantle is generally of basaltic composition ... Under normal conditions, the composition of basaltic magma requires it to crystallize between 50 and 70% plagioclase, with the bulk of the remainder of the magma crystallizing as mafic minerals ...