Characterization and correlation of megascopic tephras in Site 792 cores from the Izu-Ogasawara Forearc Basin (Japan) by trace elements and 87Sr/86Sr and 143Nd/144Nd isotopes

Abstract

Glass shards from 26 megascopic tephras (1-29 cm thick) were separated and analyzed for 26 elements and 87Sr/86Sr and 143Nd/144Nd isotope ratios. Correlation diagrams and mutivariate analyses have been used to characterize the glass shards in a tectonic setting and group the tephras according to their magmatic affinity. Four tholeiitic groups, two calc-alkaline groups, and one group with glass of shoshonitic affinity can be distinguished. The tephras have been correlated with volcanism along the Izu-Ogasawara and Ryukyu arcs by means of trace element distribution, 87Sr/86Sr ratios, and their magmatic affinity. -from Authors