Identification of Zenikame-Menagawa Tephra Using Major Element Compositions of Amphibole Phenocrysts

Abstract

Petrochemistry of the mafic minerals played an important role in the identification and correlation of tephra layers that include few glass shards, due to chemical weathering and/or alteration. The analyses are applied to the correlation of the Zenikame-Menagawa tephra（Z-M）in the Tokachi district, eastern Hokkaido, with those erupted from Zenikame volcano, located about 200 km west of the district. By utilizing quantitative major element analysis of amphiboles, distal Z-M tephra layers are recognized to be interbedded with the eruptive deposits, derived from Kuttara volcano. Accordingly, the eruption age of the Z-M is estimated to be between 44.1 and ca. 54 ka.