Geochemistry, trace elements and minerals at DSDP Holes 80-550B and 80-551

The basalts from the two holes are almost identical; most of their primary geochemical and mineralogical characteristics have been preserved, but they have undergone some low-temperature alteration by seawater, such as enrichment in K, Rb, and Cs and development of secondary potassic minerals of the "brownstone facies." K/Ar dating fail to give realistic emplacement ages; the apparent ages obtained become younger with alteration (causing an increase in K2O).

Hole 551 basalts are clearly different from the continental tholeiites emplaced on the margins of oceanizing domains during the prerift and synrift stages.