Characteristics of silicon and oxygen isotopic compositions of basalts near East Pacific Rise 13°N

Abstract

In this study, 13 groups of silicon and oxygen isotopes and major elements of the basalts near the East Pacific Rise 13°N are used to study the fractionation of silicon and oxygen isotopes. Among these data, Δ30Si values of basalts vary from −0.4‰ to 0.2‰ with a mean value of Δ30Si of (−0.18±0.22)‰. The δ18O values range from 4.1‰ to 6.4‰ with a mean Δ18O value of (+5.35±0.73)‰. Since the δ30Si values increase in the series of basalt-basaltic andesite-andesite, and δ18O values display a positive correlation with the SiO2 content, we propose that the fractionation of silicon and oxygen isotopes is influenced by the SiO2 content in igneous rocks. Compared with the igneous rocks from Manus Basin with clinopyroxene as their dominant mineral phase, MORBs in this study containing olivine and plagioclase as primary minerals have lower Δ18O and Δ30Si values, indicating that the fractionation of silicon and oxygen isotopes is also affected by different Si-O bridges in silicate minerals. Furthermore, our samples from the EPR are defined as E-MORB based on K/Ti ratios. Probably, the difference in Δ30Si and Δ18O between our samples and a normal MORB are cause by the enriched components in E-MORBs.