Abstract
The Kapalagulu intrusion displays the following sequence of cumulus phase layering in a stratigraphic sequence of 1400 m: Basal Zone (BZ) olivine + or - chromite --> Intermediate Zone (IZ) olivine + plag + opx -->, olivine + plag + opx + cpx --> Main Zone (MZ) plag + opx + cpx --> plag + cpx + Fe/Ti oxide + apatite. The corresponding cryptic variation is olivine Fo (sub 83 - 77) (limited to BZ and IZ), orthopyroxene En (sub 82 - 56) , clinopyroxene Ca (sub 46) Mg (sub 45) Fe (sub 9) to Ca (sub 43) Mg (sub 37) Fe (sub 21) and plagioclase An (sub 88 - 80) . Reversals of the cryptic variation occur at the base of MZ (minor reversal) and in the middle of MZ (major reversal), and are attributed to the influx of relatively primitive magma. The major reversal indicates that progressive mixing of fresh and residual magmas occurred. Because of the major reversal, inverted pigeonite appears twice in the layered sequence, but at different compositions (En (sub 65) and En (sub 56) ). Unlike the cumulus olivine and pyroxene, cumulus plagioclase exhibits a wide range of composition (5-10% An) in individual rocks and even in single crystals.