Avanzinelli, R.

Casalini, M.

Conticelli, S.

Elliott, T.

Tommasini, S.

English

Florence Research

Geophysical Research AbstractsVol. 21, EGU2019-10953, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.Ce/Mo and Molybdenum isotopes as tracers of sediment recycling into themantleMartina Casalini (1,2), Riccardo Avanzinelli (1,3), Simone Tommasini (1), Tim Elliott (2), Sandro Conticelli (1,3)(1) Università degli Studi di Firenze, Earth Sciences Department, Firenze, Italy (martina.casalini@unifi.it), (2) School of EarthSciences, University of Bristol, Bristol, United Kingdom, (3) Istituto di Geoscienze e Georisorse, Consiglio Nazionale delleRicerche, Firenze, ItalyThe geochemical composition of igneous rocks is strongly related to geodynamic settings in which they formed.Subduction zones have always been considered as one of the most intriguing environments: here the lithosphereis subducted and recycled into the Earth’s interior, modifies the geochemical budget of the mantle and, in the lastpart of the cycle, affects the geochemical signature of orogenic magmas. Trace element and isotope compositionsrepresent a unique tool to investigate the role played by the different components involved (i.e. crust vs. mantle),and the nature of the material (i.e. sediment melts vs. fluids) recycled into the mantle. Our contribution to thistopic consists in the application of Mo elemental and isotopic systematics, as a new tracer to subduction-relatedigneous rocks, to the Italian potassic and ultrapotassic magmas of Tuscany (lamproite-like rocks) and Mt. Vesuvius(leucite-bearing rocks). The mantle sources of these rocks are clearly dominated by recycling of sediments withdifferent lithologies (carbonate-poor vs. carbonate-rich), which is highlighted by the extreme enrichment in traceelements and peculiar radiogenic isotope compositions. The resulting Mo isotope compositions of these two rocksuites are similar, at odds with the significantly different trace element and radiogenic isotope signature, and arealso among the isotopically heaviest recorded so far in subduction-related magmas. This suggests the involvementof recycled sediment components with originally heavy Mo isotope composition. What is significantly differentis the elemental behaviour of Mo in the two suites, in particular when other trace elements, such as Ce and Nb,are considered. This can be explained by the role of different accessory phases (i.e. sulphides, rutile vs. epidote)occurring as residual phases to sediment melting, which are able to fractionate these elements in opposite ways(i.e. high and low Ce/Mo and Nb/Mo). To further investigate this process, we present a model to set constraintson the elemental fractionation able to reproduce the melt components responsible for mantle metasomatism ofthe studied rocks. This approach reveals that the direction of elemental fractionation depends on both the residualmineralogy (retaining/releasing Mo, Ce, Nb) and the lithology of the subducted sedimentary material undergoingmelting, which controls the stability of a residual phase over another.

Ce/Mo and Molybdenum isotopes as tracers of sediment recycling into the mantle

https://flore.unifi.it/bitstream/2158/1164617/1/EGU2019-10953.pdf

Ce/Mo and Molybdenum isotopes as tracers of sediment recycling into the mantle

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