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[S1-P-03] Geochemical evolution of Izu-Oshima volcano: Constraints from analysis of melt inclusions in a submarine core
Keywords:Izu-Oshima volcano, melt inclusion
Background
Magmas erupting from Izu-Oshima volcano have been interacted with those from Izu-Tobu volcano (Ishizuka et al., 2015, EPSL). Ishizuka et al. (2015) clarified geochemical evolution of Izu-Oshima volcano based on whole-rock geochemical analysis of Izu-Oshima onland samples. In order to extend their previous study, we analyzed melt inclusions in a submarine core.
Samples and analytical methods
We recovered a 25-cm long submarine push core from the seafloor located as far as about 10 km east of Izu-Oshima volcano during the research cruise KR21-16. This core comprises of tephra layers deposited from 4,500 y.B.P. to 3,200 y.B.P., where ages were determined by 14C dating of foraminifera. The push core samples were divided into ten parts, each of which is 2.5 cm long. We then collected minerals (olivine, plagioclase and orthopyroxene) from each part and polished them until the surface of the melt inclusions were exposed. Volatile elements (H2O, CO2, S, F and Cl) and P2O5 were analyzed by SIMS, and major elements were analyzed by EPMA. For larger melt inclusions, we also analyzed trace elements by LA-ICP-MS.
Results and discussion
We finally analyzed 100 melt inclusions (51-55 wt% SiO2) in total. Geochemical data of melt inclusions can be separated into 3 groups. Group A melt inclusions are dominant at upper levels of the push core, which corresponds to Izu-Oshima melts (Ishizuka et al., 2015). Systematics of H2O and CO2 concentrations of Group A melt inclusions demonstrate that crystallization differentiation took place at P<100 MPa. Group C melt inclusions are dominant at lower levels, which is hybrid magma of Izu-Oshima and Izu-Tobu magmas. Systematics of H2O and CO2 concentrations of Group C melt inclusions demonstrate that crystallization differentiation took place at P>100 MPa. Group B melt inclusions are dominant at intermediate levels and show intermediate characteristics between Group A and Group C melt inclusions, suggesting that Group A and Group C mixed. We argue that melt composition of Izu-Oshima volcano evolved from Group C, Group B to Group A from 4,500 y.B.P. to 3,200 y.B.P.
Magmas erupting from Izu-Oshima volcano have been interacted with those from Izu-Tobu volcano (Ishizuka et al., 2015, EPSL). Ishizuka et al. (2015) clarified geochemical evolution of Izu-Oshima volcano based on whole-rock geochemical analysis of Izu-Oshima onland samples. In order to extend their previous study, we analyzed melt inclusions in a submarine core.
Samples and analytical methods
We recovered a 25-cm long submarine push core from the seafloor located as far as about 10 km east of Izu-Oshima volcano during the research cruise KR21-16. This core comprises of tephra layers deposited from 4,500 y.B.P. to 3,200 y.B.P., where ages were determined by 14C dating of foraminifera. The push core samples were divided into ten parts, each of which is 2.5 cm long. We then collected minerals (olivine, plagioclase and orthopyroxene) from each part and polished them until the surface of the melt inclusions were exposed. Volatile elements (H2O, CO2, S, F and Cl) and P2O5 were analyzed by SIMS, and major elements were analyzed by EPMA. For larger melt inclusions, we also analyzed trace elements by LA-ICP-MS.
Results and discussion
We finally analyzed 100 melt inclusions (51-55 wt% SiO2) in total. Geochemical data of melt inclusions can be separated into 3 groups. Group A melt inclusions are dominant at upper levels of the push core, which corresponds to Izu-Oshima melts (Ishizuka et al., 2015). Systematics of H2O and CO2 concentrations of Group A melt inclusions demonstrate that crystallization differentiation took place at P<100 MPa. Group C melt inclusions are dominant at lower levels, which is hybrid magma of Izu-Oshima and Izu-Tobu magmas. Systematics of H2O and CO2 concentrations of Group C melt inclusions demonstrate that crystallization differentiation took place at P>100 MPa. Group B melt inclusions are dominant at intermediate levels and show intermediate characteristics between Group A and Group C melt inclusions, suggesting that Group A and Group C mixed. We argue that melt composition of Izu-Oshima volcano evolved from Group C, Group B to Group A from 4,500 y.B.P. to 3,200 y.B.P.