Esmeralda Submarine Volcano, Southern Mariana Island Arc: Geochemistry and Petrogenesis of Igneous Rocks

The paper presents data on the mineralogy and petrochemistry of basaltoids, dacite, and gabbro dredged from Esmeralda submarine volcano, southern Mariana island arc, during Cruises 4 and 5 of the R/V Vulkanolog. The basaltoids and gabbros of the tholeiitic series are highly fractionated rocks, in contrast to most of the studied rocks from submarine volcanoes and basins in the southern Mariana island-arc system. The rocks contain elevated iron concentrations. The elevated Fe# is consistent with the high Fe content of the pyroxenes and plagioclase, which classes most of the dredged rocks with the association of arc ferrotholeiites. Similar to the basaltoids, the dacite sample contains both an elevated Fe content and a high Fe2O3 concentration in plagioclase, suggesting that the dacite may be genetically related to the dredged basaltoids. The lower concentrations of high-field strength (HFSE) and heavy rare earth (LREE) elements in the rocks than in N-MORB suggest that their parental melts were derived from a depleted mantle source at a spinel-facies depth level. The high FeOtotal/MnO values and discriminant petrochemical characteristics suggest that the deep source contained pyroxenite. The enrichment of the basaltoids and gabbro in large-ion lithophile elements (LILE) and the correlations between some elemental ratios (Th/Nb, Ba/Nd, Ba/Yb, Th/Yb, etc.) indicate that the magma was generated in the presence not only of a low-temperature fluid component but also of a high-temperature magmatic melt, produced by the melting of sedimentary rocks.