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Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry

January 1, 1990

A bimodal volcanic suite with KAr ages of 0.05–1.40 Ma was collected from the Sumisu Rift using alvin. These rocks are contemporaneous with island arc tholeiite lavas of the Izu-Ogasawara arc 20 km to the east, and provide a present day example of volcanism associated with arc rifting and back-arc basin initiation. Major element geochemistry of the basalts is most similar to that of basalts found in other, more mature back-arc basins, which indicates that back-arc basins need not begin their magmatic evolution with lavas bearing strong arc signatures.

Volatile concentrations distinguish Sumisu Rift basalts from island arc basalts and MORB. H2O contents, which are at least four times greater than in MORB, suppress plagioclase crystallization. This suppression results in a more mafic fractionating assemblage, which prevents Al2O3 depletion and delays the initiation of Fe2O3(tot) and TiO2 enrichment. However, unlike arc basalts,Fe3+/ΣFe ratios are only slightly higher than in MORB and are insufficient to cause magnetite saturation early enough to suppress Fe2O3(tot) and TiO2 enrichment. Thus, major element trends are more similar to those of MORB than arcs.

H2O, CO2 and S are undersaturated relative to pure phase solubility curves, indicating exsolution of an H2O-rich mixed gas phase. HighH2O/S, highδD, and low (MORB-like)δ34S ratios are considered primary and distinctive of the back-arc basin setting.

Publication Year 1990
Title Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry
DOI 10.1016/0012-821X(90)90184-Y
Authors A.G. Hochstaedter, J.B. Gill, M. Kusakabe, S. Newman, M. Pringle, B. Taylor, P. Fryer
Publication Type Article
Publication Subtype Journal Article
Series Title Earth and Planetary Science Letters
Index ID 70015994
Record Source USGS Publications Warehouse