Distribution of Ti and P in oceanic basalts as a test of origin

Abstract

A model is proposed to explain the distribution of titanium and phosphorus in oceanic basalts. This model is based on, the existence of titanium and phosphorus as primary components of specific mineral phases, the use of volumetric considerations to predict the stabilities of these phases and the existence of water as OH− in the mantle. If this model is correct then the distribution of titanium and phosphorus and their ratio may be used to test models for the origin of oceanic basalts. The amount of titanium and/or phosphorus is dependent on (in order of importance) the percent water in the original melt, amount of fractionation of silicate phases, and the depth. The ratio is largely dependent only on depth of partial melting, provided titanium and phosphorus are not depleted in the mantle by partial melting. A χ 2 analysis of the frequency distributions of these elements and their ratio is performed in order to test several models for the origin of basalts. From this analysis it is concluded that partial melting is the primary process for the generation of basalts but the degree of partial melting is relatively small and that the alkalinity of basalts increases with depth of partial melting.