Geochemistry and minerals at DSDP Leg 81 Holes

The basalts from the four holes are almost similar. Most of their primary characteristics have been preserved, although they have suffered alteration by seawater.

From the petrological and mineralogical points of view, they resemble deep-ocean-floor basalts but show some peculiarities (occurrence of pigeonite and ilmenite as normal components of the groundmass differentiation sequences toward ferrobasalts). Their geochemical characteristics are dominated by their extreme depletion in the most hygromagmaphile elements (Th, Ta, La, and Nb), the concentrations of which are sometimes lower than the corresponding chondritic values.