Tracing subducted crust in the oceanic mantle with siderophile elements and transition metal stable isotopes and implications for the sources of basaltic volcanism
Final Report Abstract
The present project had as main objective to improve our understanding of material fluxes in the mantle during interaction of recycled subducted material with the ambient oceanic mantle, using HSE, 187Os/188Os and stable isotopes of transition metals of the main HSE host phases (BMS, Fe, Cu, Cu, Zn). The main objectives of the project were largely achieved, leading to interesting results and future collaborations. During the course of the project we obtained a dataset coupling for the first time HSE concentrations and Os isotopes with ‘non-traditional’ stable isotopes on both the whole rock and the individual grain scale, leading to important results. The HSE trace element signatures confirm a melt origin for the pyroxenites, the source of which has previously been attributed to recycled oceanic crust. As with other pyroxenite-peridotite associations, this confirms that recycled crust is returned to the upper oceanic mantle, and supports the hypothesis of pyroxenitic, rather than purely peridotitic, material playing a significant role in the genesis of basaltic magmas derived from the oceanic mantle such as mid-ocean ridge basalts and ocean island basalts. Together with the radiogenic 187Os/188Os signatures, these results highlight the mechanisms of reintroduction of crustal signatures into the mantle, and the potential of overprinting of primary mantle signatures through melt-rock interaction. In terms of transition metal stable isotopes, this study highlights the variable usefulness of these systems in studying melt processes in the mantle. While Zn isotopes show little potential to be used as a mantle tracer, the pyroxenites with the strongest melt signatures in terms of HSE and 187Os/188Os show the highest fractionation in δ65/63Cu, with the presence of both negative and positive δ65/63Cu values possibly pointing to different sources of melt. For Fe isotopes, signatures between pyroxenites and peridotites overlap, but with a tendency for pyroxenites to record more extreme values. Notably, the values recorded by pyroxenites overlap with the global database for basalts.
Publications
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(2017) From crustal protoliths to mantle pyroxenites: a highly siderophile element and Os isotope perspective from the Ligurian mantle section (N. Apennine, Italy). 2017 AGU Fall Meeting, New Orleans, LA
Montanini A., Luguet A., van Acken D., and Tribuzio R.
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(2017) Multiple events of melt-rock interaction recorded by undeformed spinel pyroxenites from the External Ligurian ophiolites. 2017 Italian Geosciences Meeting, Pisa, Italy
Montanini A., Tribuzio R., van Acken D., and Luguet A.
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(2017) Pyroxenites as carriers of isotopic heterogeneity in the oceanic mantle. 2017 Goldschmidt Conference, Paris, France
van Acken D., Luguet A., Montanini A., Debaille V., Tribuzio R., Nowell G. M., and Daly J.S.
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(2018) An undeformed pyroxenite-peridotite sequence from the External Ligurian Ophiolites records multiple events of melt-rock interactions 3rd European Mantle Workshop, Pavia, Italy
Montanini A., Tribuzio R., van Acken D., and Luguet A.
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(2018) Highly siderophile elements and 187Os signatures in single grain Base Metal Sulfides of pyroxenites from the External Liguride Peridotite Massif, Italy. 2018 GeoBonn, Bonn, Germany
Meides, N., van Acken, D., Luguet, A., Montanini, A., and Tribuzio, R.
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(2018) Pyroxenites as tracers for melt-rock interaction and recycled material in the oceanic mantle. 2018 GeoBonn, Bonn, Germany
van Acken, D., Luguet, A., Montanini, A., Tribuzio, R., and Daly, J.S.
