Similar V/Sc Systematics in MORB and Arc Basalts: Implications for the Oxygen Fugacities of their Mantle Source Regions |
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| Authors: | AEOLUS LEE CIN-TY; LEEMAN WILLIAM P; CANIL DANTE; LI ZHENG-XUE A |
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| Institution: | 1 DEPARTMENT OF EARTH SCIENCES, MS-126, RICE UNIVERSITY, 6100 MAIN STREET, HOUSTON, TX 77005, USA
2 SCHOOL OF EARTH AND OCEAN SCIENCES, UNIVERSITY OF VICTORIA, PETCH BUILDING, ROOM 280, 3800 FINNERTY ROAD, VICTORIA, BC, CANADA V8W 3P6 |
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| Abstract: | V/Sc systematics in peridotites, mid-ocean ridge basalts andarc basalts are investigated to constrain the variation of fO2in the asthenospheric mantle. V/Sc ratios are used here to ‘seethrough’ those processes that can modify barometric fO2determinations in mantle rocks and/or magmas: early fractionalcrystallization, degassing, crustal assimilation and mantlemetasomatism. Melting models are combined here with a literaturedatabase on peridotites, arc lavas and mid-ocean ridge basalts,along with new, more precise data on peridotites and selectedarc lavas. V/Sc ratios in primitive arc lavas from the Cascadesmagmatic arc are correlated with fluid-mobile elements (e.g.Ba and K), indicating that fluids may subtly influence fO2 duringmelting. However, for the most part, the average V/Sc-inferredfO2s of arc basalts, MORB and peridotites are remarkably similar(–1·25 to +0·5 log units from the FMQ buffer)and disagree with the observation that the barometric fO2s ofarc lavas are several orders of magnitude higher. These observationssuggest that the upper part of the Earth's mantle may be stronglybuffered in terms of fO2. The higher barometric fO2s of arclavas and some arc-related xenoliths may be due respectivelyto magmatic differentiation processes and to exposure to large,time-integrated fluid fluxes incurred during the long-term stabilityof the lithospheric mantle. KEY WORDS: vanadium; scandium; oxygen fugacity; mantle; arcs |
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| Keywords: | : vanadium scandium oxygen fugacity mantle arcs |
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