Rare earth and trace element geochemistry of a fragment of Jurassic seafloor, Point Sal, California

A suite of rocks from the Point Sal ophiolite, California, were analyzed for rare earth elements (REE (La, Ce, Sm, Eu, Tb, Yb, Lu)), Sc, Co, Na2O, Cr, Zn and FeO. The lavas all have either flat or slightly light REE (LREE) depleted profiles relative to chondrites. The lavas contain smectite of greenschist facies mineralogy and some have radiogenically enriched 87Sr/86Sr ratios. This is interpreted as evidence of basalt-seawater interaction. The smectite and zeolite bearing lavas that have been exposed to seawater for prolonged periods have anomalous Ce abundances. At higher grades of metamorphism, the lavas show no marked changes in light REE. The plutonic igneous rocks vary from early cumulus dunite to late stage, non cumulus diorite. All the plutonic rocks are light REE depleted with total REE abundance varying by a factor of 100 x between the dunites and diorites. Analyses of clinopyroxene and hornblende separates indicate that these two minerals strongly influence the REE characteristics of the early cumulates and late stage fractionates, respectively. (author)