Rutile Controls on Vanadium During Eclogite Partial Melting
Abstract
The trace element compositions of arc volcanoes are regulated by chemical fluxes from the subducting slab to the mantle wedge [e.g., 1-2]. These fluxes are in part controlled by the transfer of trace elements between residual slab minerals to melts or fluids during dehydration or melting reactions at depth. The partitioning behavior of redox-sensitive trace elements should reflect the oxygen fugacity (fO2) of the mineral-melt/fluid environment. Vanadium (V) is a multivalent trace element that transitions from V3+ to V4+ to V5+ over Earth-relevant fO2s and has attracted attention as a promising fO2 proxy for arc rocks. We present experiments that quantify V partitioning during ecologite melting in order to monitor how oxygen is cycled through the subduction system.
Rutile (TiO2) is a common accessory mineral in eclogites and other subduction-related metamorphic rocks that should incorporate V4+ on the Ti4+ site. To examine V partitioning between rutile and silicate melts in response to fO2, we executed eclogite partial melting experiments at 2 GPa and 1050-1200 °C at controlled, and measured, fO2. Our results show rutile/melt partition coefficients (DVrt/melt) decrease by an order of magnitude as fO2 increases from QFM-1 to QFM+3.5, while DVgarnet/melt and DVpyroxene/melt change modestly. Under reducing conditions, rutile will strongly retain V during partial melting of metabasalts, producing a silicate liquid strongly depleted in V. Only under oxidizing conditions will ecologite partial melts contain appreciable V. Our experiments indicate that despite its low modal abundance in ecologite, rutile may play a major role in controlling the flux of V from the slab to the overlying wedge. [1] Kelemen et al. (2003) Treatise on Geochemistry. [2] Turner and Langmuir (2015) Geochemistry, Geophysics, Geosystems.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V33C0247H
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGYDE: 3630 Experimental mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 3640 Igneous petrology;
- MINERALOGY AND PETROLOGYDE: 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY