Abstract

Karoo picrite basalts from the Letaba Formation of SE Zimbabwe and the NE Transvaal contain rare but widespread multigrain aggregates of high-pressure orthopyroxene. These are of two types interpreted as (a) crystallization products of the host liquids, (b) restite fragments (refractory residue) from the zone of partial melting. The latter are characterized by strong lattice-preferred-orientation fabrics produced by simple flattening. It is speculated that such fabrics are generated either by the upward flow of magma through refractory residue or by earlier solid flow in the axial region of a diapir. Ultimately, magma segregation appears to be sufficiently vigorous to entrain restite fragments, and the apparent degree of partial melting may increase as restite is dissolved during ascent.

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