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

Hochstaedter, Alfred G. and Gill, James B. and Kusakabe, Minoru and Newman, Sally and Pringle, Malcolm and Taylor, Brian and Fryer, Patty (1990) Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry. Earth and Planetary Science Letters, 100 (1-3). pp. 179-194. ISSN 0012-821X. doi:10.1016/0012-821x(90)90184-y.

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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. H_2O 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 Al_2O_3 depletion and delays the initiation of Fe_2O_3_((tot)) and TiO_2 enrichment. However, unlike arc basalts,Fe^(3+)/ΣFe ratios are only slightly higher than in MORB and are insufficient to cause magnetite saturation early enough to suppress Fe_2O_3_(tot) and TiO_2 enrichment. Thus, major element trends are more similar to those of MORB than arcs. H_2O, CO_2 and S are undersaturated relative to pure phase solubility curves, indicating exsolution of an H_2O-rich mixed gas phase. High H_2O/S, high δD, and low (MORB-like) δ^(34)S ratios are considered primary and distinctive of the back-arc basin setting.

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Newman, Sally0000-0003-0710-995X
Additional Information:© 1990 Published by Elsevier. Received January 22, 1990; revised version accepted March 21, 1990. M. Yuasa provided us with preliminary petrological information on the Sumisu Rift and with dredge samples collected immediately after the dive program. S. Mayeda measured the volatile concentrations and isotopic ratios reported here. Jim Carolan prepared the samples for geochemical analysis. The manuscript was improved by conversations with Q. Williams and reviews by A. Ewart and R.S. Harmon. This work was supported by NSF grants OCE-8512829 to Gill, OCE8410605 to Taylor, and INT-8415165 to Taylor, Gill and Craig.
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Issue or Number:1-3
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Official Citation:Alfred G. Hochstaedter, James B. Gill, Minoru Kusakabe, Sally Newman, Malcolm Pringle, Brian Taylor, Patty Fryer, Volcanism in the Sumisu Rift, I. Major element, volatile, and stable isotope geochemistry, Earth and Planetary Science Letters, Volume 100, Issues 1–3, 1990, Pages 179-194, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90293
Deposited By: George Porter
Deposited On:22 Oct 2018 16:13
Last Modified:16 Nov 2021 03:31

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