Unusual Composition from the Cumulate Section of Andaman Ophiolite

Mafic and acid cumulates from Andaman ophiolite contain hornblende and magnetite as primary cumulus phases. Four samples with higher SiO₂range, contain in addition apatite and quartz crystallised from intercumulus liquid. These have lower Ni, Cr and higher total REE abundances than ophiolitic gabbros and plot away from the field of ophiolitic cumulates in the AFM diagram. Strong negative Eu-anomaly is in striking contrast to ophiolitic cumulates.

No volcanic rocks are associated with these cumulates. Volcanic rocks occurring in a different thrust slice are similar to 'transitional' ridge basalts. It is suggested that the cumulates have crystallised from melts more evolved than ridge tholeiites and possibly from melts similar to basaltic andesites of Andaman ophiolite. in a shallow magma chamber.