Subduction-related lamproitic signature in intraplate-like volcanic rocks: the case study of the Tallante alkali basalts, Betic Chain, South-Eastern Spain

Abstract

South-Eastern Spain is a key locality of the Western Mediterranean to unravel the origin of post-collisional magmatism and its relationships with the multi-stage evolution of the upper mantle in complex geodynamic settings. This study is focused on the Plio-Pleistocene post-collisional intraplate-like alkali basalts cropping out in the Tallante area (South-Eastern Spain) that are erupted in a region previously characterised by subduction-related calc-alkaline to ultrapotassic (i.e., lamproitic) volcanism. Tallante alkali basalts represent a volcanic episode similar to other contemporary small volume intraplate volcanism of Western-Central Europe and North Africa, which are believed to derive from a Common Mantle Reservoir characterising the entire Circum-Mediterranean asthenosphere.We report new major, trace element, and Sr-Nd-Pb isotope data on Tallante alkali basalts, showing compositions broadly similar to the other mafic volcanic rocks derived from the Common Mantle Reservoir and thus suggesting an asthenospheric component similar to other European within plate volcanic rocks. On the other hand, specific trace element ratios, such as Ce/Pb, Nb/U, Th/Yb, along with D207Pb/204Pb and 87Sr/86Sr, clearly indicate the involvement of an enriched, subduction-related component, with a lamproitic geochemical and isotopic flavour. The trace element ratios suggest that low melting degree magmas from the Common Mantle Reservoir infiltrated and triggered melting of the strongly metasomatised sub-continental lithospheric mantle, which produced the lamproitic magmas previously erupted in the same area.The proposed origin of Tallante alkali basalts, located along a large scale left-lateral strike-slip fault, is consistent with analytical, numerical and laboratory models indicating that narrow subduction zones such as the Gibraltar Arc are characterised by mantle inflow around the slab edges determining upwelling and adiabatic melting of the asthenospheric mantle through slab tears.