Petrology of Basalt Fragments Recovered with Manganese Nodules in Marquesas Fracture Zone, South Central Pacific

Abstract

A suite of 12basalt samples recovered at 9 sites vary from volcanic glass, vesicular glassy basalt to fine grained basalt, and show gJomeroprophyritic texture. They consist of plagioclase (An_68-70) in varying propOrtion, augite (2V_z 53°-56°), palagonite, and opaques. The anorthite content in plagioclase phenocrysts is higher (An_{73 <i>-</i>75})than that of the tiny phenocryst needles in the groundmass (An_{60 -70}) Glassy groundmass contains several round to sub-round globules, probably representing immiscible liquid drops and devitrified glass. Chemically, the basalts are Fe and Ti enriched tholeiites. There is also a remarkable positive correlation between the oxide pairs TiO₂ to P₂O₅, K₂O, MgO, and A1₂O₃. These rocks represent undifferentiated nature and appear to represent the original composition of the magma.