The pyroclastic breccias from Cabezo Negro de Tallante (SE Spain): Is there any relation with carbonatitic magmatism?

The small Plio-Quaternary volcanic centre of Cabezo Negro de Tallante in SE Spain includes a thick deposit ofpolymictic pyroclastic tuff-breccia, whose fragments are agglutinated by a carbonate-rich component. This feature is also observed in other monogenetic volcanic centres cropping out in the Tallante-Cartagena volcanic district. The carbonate fraction has been recently interpreted in literature as representing a mantle component,therefore pointing to the existence of a diffuse carbonatitic activity in the area.Based on detailed sedimentological (presence of pisoids and root remnants), petrographic (presence of plagioclase and absence of euhedral silicate minerals in the calcite plagues), mineral chemistry (Ba-Sr-poor calcite composition), whole-rock chemistry (overall low incompatible element content in the pure carbonate fraction and amonotonous trace element negative correlation with CaO) as well as isotopic constraints (perfect correlations between Sr-Nd-Pb isotopic ratios with CaO in the basaltic and carbonate fraction, as well as heavy delta18O and lightdelta13C isotopic composition of the carbonate fraction), we propose a secondary origin for the carbonate component,excluding any contribution of mantle carbonatite melts. The presence of carbonates infiltrating the abundantmantle and crustal xenolith fragments found in the pyroclastic breccia is not related to the presence ofcarbonatitic melts at mantle to lower crustal depths, but to in-situ fragmentation of the Strombolian tuff breccia deposit, followed by secondary carbonate infiltration. The pyroclastic breccia was indeed affected by analternation of carbonate precipitation and dissolution in a vadose zone, where the activity of bacteria, fungi,roots and meteoric water led to the formation of a calcrete (caliche)-type deposits.Basaltic rocks (hawaiites and basanites) occur in the area as scoria and lava fragments in the pyroclastic breccia aswell as small lava flows. They have been modelled with a low-degree partial melting of an amphibole-bearingperidotitic mantle close to the lithosphere-asthenosphere boundary. The origin of the mildly alkaline sodic basaltic activity in SE Spain post-dates the abundant and long-lasting subduction-related volcanic phase in the BeticChain. Its origin is explained without requiring the presence of any thermal anomaly, but simply as consequenceof the difference of lithospheric depths and edge-driven-type small-scale convection.