A NEW GLOBAL DATABASE OF GEOCHEMICAL ANALYSES OF SEAFLOOR VOLCANIC GLASSES

Geochemical studies of magmas generated in a range of tectonic settings frequently use the compositions of magmas produced at non-convergent margin settings (i.e., mid-ocean ridges, MORB) as a reference to ‘typical’ mantle melts, for example, MORB normalised plots. Geochemical databases such as GEOROC (Geochemistry of Rocks of the Oceans and Continents; http://georoc.mpch-mainz.gwdg.de/georoc/) and GERM (Geochemical Earth Reference Model; http://earthref.org/GERM/index.html) are valuable tools for geochemists to use as a reference. However, few (if any) analyses of peer-reviewed data listed in these databases give comprehensive compositional data for MORB, including rare earth elements (REE), large ion lithophile elements (LILE), high field strength elements (HFSE) and less commonly analysed elements, such as W, Mo, As, Sb, Sn, Se, Ag, Cu, Tl, Cl, S, Bi, Cd and In, for individual samples and importantly, for a global range of MORB.

Submarine-quenched glasses provide the clearest record of magmatic evolution available, especially with respect to potentially volatile elements and compounds. Importantly, natural glasses are ideal samples for in situ analyses using LA-ICP-MS and EMPA techniques, circumventing analytical difficulties associated with whole rock analyses (e.g., sample contamination during preparation and sample dissolution) and inclusion of micro-phenocrysts. Furthermore, direct analysis of glasses avoid dilution effects associated with analysing mixtures of glass and phenocrysts during whole rock analysis. We present new analyses of major, S, Cl and ~60 trace elements in volcanic glasses from a global range of MORB, fracture zones and seamounts (340 samples) and compare them with data for >100 basaltic to andesitic glasses from back-arc basins and island arcs in the S.W Pacific.

Comparison of trace elements in volcanic glasses generated in non-convergent margins with convergent margin volcanic glasses from this comprehensive data base allows the systematic behaviour of ‘lesser-studied’ element pairs to be investigated (e.g., Mo/As, Sn/Be, P/Nd, Cu/Ag, Se/Ag, Cd/In, W/Th and S/Se) and constrained. Further, we use this dataset to characterise the behaviour of volatile elements such as As, Tl, In, Cd, Bi, Se and Sb during subduction-zone processes.