Carbon budget in Calatrava and Tallante xenoliths: insights on sources and petrogenetic processes

We present elemental and isotopic analyses of carbon (C) carried out on mantle xenoliths from the Calatrava and Tallante volcanic districts (Spain). The C content of peridotite xenoliths from Calatrava, previously studied by Bianchini et al. (2010), generally range between 1100 and 5500 ppm, with up to 2.9 wt.% C in a single sample. The associated isotopic composition (delta 13C) of most samples varies between -26.1 to -15.2 ‰, whereas the carbon-rich outlier displays a distincly less negative C isotopic composition (-6.2‰) that conforms with a typical “mantle signature” (Deines, 2002). The C content of xenoliths from Tallante previously studied by Bianchini et al. (2011), varies from 600 to 1000 ppm in anhydrous peridotites, to 1500 ppm in an amphibole bearing peridotite; higher C content of 4000 ppm have been recorded in the felsic vein crosscutting a peridotite composite xenolith previously studied by Bianchini et al. (2015). The associated isotopic composition (delta13C) varies between -20.1 to -22.4 ‰ in peridotites, whereas the mentioned felsic vein displays the value of -11.9‰. In both xenolith suites a correlation is observed between the carbon contents and the respective delta13C values suggesting that analogous fractionation processes affected vast domains of the Iberian lithospheric mantle. Noteworthy, in the Tallante xenolith suite delta13C values approaching the notional “mantle signature” are never recorded. The less negative isotopic composition recorded by Tallante xenoliths approaches that of the carbonate matrix of the xenolith-bearing volcanoclasic deposit (-9.8‰). On the whole, the available data suggest that the carbon of the studied xenoliths, host lavas and cabonate volcanoclastic matrices is juvenile, mostly originated deep in the mantle, and influenced by multiple episodes of degassing, that ultimately led to extremely explosive volcanic eruptions. Differences between the two suites are possibly related to distinct geodynamic settings, as the Tallante mantle section was interested by supra-subduction metasomatic fluids/melts that didn’t occur at Calatrava.