Abstract:
The nephelinite occurs as a N-S trending plug (500 x 200 m.) intrusive into basalts. The rock is porphyritic and principally composed of complexly zoned phenocrysts of clinopyroxene, Fe-Ti oxide and olivine (less than 5 percent) in a fine grained groundmass dominated by clinopyroxene, nepheline and Fe-Ti oxides. Mineralogically and chemically the rocks vary between pyroxene melanephelinites and nephelinites.The mineral chemistry implies that the magma has undergone varying degrees of polybaric crystallisation in a subcrustal magma chamber with mixing of more fractionated magma with primitive pulses in which are incorporated disaggregated mantle xenolith phases.
