Multidisciplinary study on petit-spot: Clarification about revelation of asthenosphere melting, and comprehensive understanding for magma process

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To define petit-spot geology, a comprehensive data set about geochemistry (major and trace elements, and Sr and Nd isotopic compositions) and Ar-Ar age of alkaline basaltic rocks and glasses from three petit-spot volcanic fields in the northwestern Pacific were analyzed. Then, melting experiments for three geochemical types of basalt groups were conducted, to define finally equilibrated solid phases, temperature, and pressure for petit-spot primary magma. The spatiotemporally change of eruption place for each magma group indicates that magma is originated from isolated melt ponds at the lithosphere-asthenosphere boundary (LAB). And, results of melting experiments show that magma from LAB were tapped in lower lithosphere in response to plate flexure, and were finally equilibrated with ambient lithosphere, followed by eruption.