Carbon elemental and isotopic composition in mantle xenoliths from Spain: Insights on sources and petrogenetic processes
The carbon elemental concentration (C wt%) and isotopic (δ 13 C %%) composition of mantle xenoliths from the Tallante and Calatrava volcanic occurrences (in South-East and Central Spain, respectively) have been investigated to identify carbon sources and processes occurring in distinct geodynamic settings of the Iberian Peninsula. The peridotitic mantle xenoliths from Calatrava show elemental C ranging from 0.11 to 2.87wt% which is coupled with a continuous isotopic variation from very negative values (δ 13 C -26.1%%) to typical mantle values (δ 13 C -5.9%%). On the other hand, the Tallante mantle xenolith suite displays lower C contents (0.06-0.15wt%) showing a tighter variation with 13 C-depleted values ranging between -20.1 and -23.7%%; higher elemental C up to 0.41wt% displaying distinctly less negative isotopic values (δ 13 C between -13.8 and -11.9%%) have been recorded in veins crosscutting Tallante peridotites, plausibly representing the product of metasomatic reactions. The data from the two investigated xenolith suites invariably display a good correlation between elemental and isotopic composition, suggesting a mantle origin for carbon and Rayleigh-type fractionation as the process responsible for the observed C-δ 13 C variation. However, the correlation between the carbon isotopic data with other isotopic tracers (e.g. 87 Sr/ 86 Sr, 3 He/ 4 He) used to identify distinct mantle components and metasomatic reactions, indicates systematic differences between the two xenolith suites suggesting that beneath the Betic Cordillera (where Tallante is located) the deep C-cycle involves recycling, via subduction preceding/accompanying continental collision, of crustal components back in the mantle. Coherently, geochemical trends observed in the Tallante xenoliths seem to be influenced by metasomatic agents generated by melting of crustal lithologies that according to the analysis of a metasedimentary xenolith can contain C up to 1.2wt% having δ 13 C of ca. -18.0%%.
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