TY - JOUR
T1 - Ancient depleted mantle as a source of boninites in the Izu-Bonin-Mariana arc
T2 - Evidence from Os isotopes in Cr-spinel and magnetite
AU - Senda, Ryoko
AU - Shimizu, Kenji
AU - Suzuki, Katsuhiko
N1 - Funding Information:
We thank Susumu Umino, Kyoko Kanayama, Takazo Shibuya, and Akira Ishikawa for their assistance in sampling and for providing geological information on the Bonin Islands and Guam. We are grateful to our editors and reviewers, Catherine Chauvel, Laurie Reisberg, Robert J. Stern, and Shoji Arai, for their thoughtful and constructive comments on this and an earlier version of this manuscript. We thank Hideo Yamamoto, Yukari Otsuki and Chie Yamauchi for their assistance in the analytical work. Jun-Ichi Kimura and Maria Luisa Tejada contributed to this work through continuous and constructive discussions. This work was supported by a JAMSTEC 7 th Award for Emergent Research and Development and by the Japan Society for the Promotion of Science through Grants-in-Aid to KS (no. 20340158 and 15H02142 ).
PY - 2016/11/7
Y1 - 2016/11/7
N2 - Boninite is a volcanic rock derived from shallow melting of highly depleted hydrous mantle, fluxed with water from subducted slabs. The eruption of boninite early in the history of the Izu-Bonin-Mariana (IBM) arc (~ 48–45 Ma), suggests generation by melting of upper mantle material that was relatively unmodified by subducted components. Thus, the boninite composition should largely reflect that of the sub-arc mantle. For better understanding of the mantle sources of nascent arc settings and the contributions of different components to arc melts, we analyzed Os isotope ratios (187Os/188Os) of bulk rocks and mineral separates (euhedral Cr-spinel from boninites and euhedral Cr-spinel/magnetite mixtures from tholeiites younger than 45 Ma that erupted after boninites) from the Bonin Islands and Guam. The age-corrected (initial) Os isotope ratios of the whole-rock samples (0.1179–0.2050) were more radiogenic and variable than those of the mineral separates, possibly because of contamination with crustal materials during magma ascent or alteration after emplacement. The age-corrected Os isotope ratios of euhedral Cr-spinel in boninite from the Bonin Islands (0.1187–0.1254) and from Guam (0.1220–0.1269) are unradiogenic relative to primitive mantle, and those of the Cr-spinel/magnetite mixtures from the tholeiites from the Bonin Islands are similar to or slightly more radiogenic (0.1224–0.1382). The most depleted Os isotope ratio of the Cr-spinel from boninite yielded a model Re depletion (TRD) age of 1.4 Ga, suggesting that the mantle source of the boninite experienced melt extraction prior to 1.4 Ga. The source of the boninites is interpreted to be mostly highly depleted mantle with a small contribution of slab flux arising from altered oceanic crust that has radiogenic Os components, with or without contributions from components with relatively unradiogenic Os such as volcaniclastics of oceanic island basalt affiliation or very young mid-ocean ridge basalt.
AB - Boninite is a volcanic rock derived from shallow melting of highly depleted hydrous mantle, fluxed with water from subducted slabs. The eruption of boninite early in the history of the Izu-Bonin-Mariana (IBM) arc (~ 48–45 Ma), suggests generation by melting of upper mantle material that was relatively unmodified by subducted components. Thus, the boninite composition should largely reflect that of the sub-arc mantle. For better understanding of the mantle sources of nascent arc settings and the contributions of different components to arc melts, we analyzed Os isotope ratios (187Os/188Os) of bulk rocks and mineral separates (euhedral Cr-spinel from boninites and euhedral Cr-spinel/magnetite mixtures from tholeiites younger than 45 Ma that erupted after boninites) from the Bonin Islands and Guam. The age-corrected (initial) Os isotope ratios of the whole-rock samples (0.1179–0.2050) were more radiogenic and variable than those of the mineral separates, possibly because of contamination with crustal materials during magma ascent or alteration after emplacement. The age-corrected Os isotope ratios of euhedral Cr-spinel in boninite from the Bonin Islands (0.1187–0.1254) and from Guam (0.1220–0.1269) are unradiogenic relative to primitive mantle, and those of the Cr-spinel/magnetite mixtures from the tholeiites from the Bonin Islands are similar to or slightly more radiogenic (0.1224–0.1382). The most depleted Os isotope ratio of the Cr-spinel from boninite yielded a model Re depletion (TRD) age of 1.4 Ga, suggesting that the mantle source of the boninite experienced melt extraction prior to 1.4 Ga. The source of the boninites is interpreted to be mostly highly depleted mantle with a small contribution of slab flux arising from altered oceanic crust that has radiogenic Os components, with or without contributions from components with relatively unradiogenic Os such as volcaniclastics of oceanic island basalt affiliation or very young mid-ocean ridge basalt.
UR - http://www.scopus.com/inward/record.url?scp=84976338464&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84976338464&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2016.06.018
DO - 10.1016/j.chemgeo.2016.06.018
M3 - Article
AN - SCOPUS:84976338464
SN - 0009-2541
VL - 439
SP - 110
EP - 119
JO - Chemical Geology
JF - Chemical Geology
ER -