The volcanic-plutonic connection unveiled

Are upper crustal plutons solidified magma bodies or residues from extracted and erupted liquids? This remains one of the key questions to address to understand the construction and eruption of upper crustal magmatic systems. We have investigated the Takidani Pluton and contemporaneous volcanic deposits (Nyukawa PFD, Chayano Tuff and Ebisutoge PD) distributed around this crustal intrusion to understand whether they were sourced from this pluton. The Takidani Pluton is a good candidate because it contains petrographic and geochemical evidences for residual melt extraction, and pressure quenching associated with eruptive activity (Hartung et al., 2017). We analysed major and trace element concentrations of 18 plagioclase phenocrysts (core to rim) from the Takidani Pluton and Nyukawa-Chayano-Ebisutoge eruptions. Major elements were first analysed using an electron microprobe and trace elements were subsequently determined by laser ablation inductively coupled mass spectrometry in the same spot. Plagioclase chemistry shows that the Chayano and Ebisutoge rhyolitic deposits are not petrogenetically related to either the Takidani Pluton or the Nyukawa PFD. However, plagioclase of the Nyukawa PDF and the Takidani Pluton show indistinguishable REE patterns suggesting a common source domain for plagioclase from the two units. Ebisutoge plagioclase grains commonly contain xenocrystic cores that have major and trace element compositions comparable to the plagioclase grains observed in the Takidani Pluton and Nyukawa PFD. Our data show that the Nyukawa and Takidani plagioclase are geochemically indistinguishable, suggesting that the Takidani pluton was the magma reservoir that fed this large eruptive unit (400 km3, Oikawa, 2003). The Ebisutoge magma was not extracted directly from the pluton, but interacted with Takidani-Nyukawa when it was still molten. We have no evidence to suggest that the Takidani Pluton was the source of either the Chayano Tuff or the Ebisutoge PD.