Inherited Palaeozoic and Mesozoic Rb-Sr isotopic signatures in Neogene calc-alkaline volcanics, Alboran volcanic province, SE Spain

A pyroxene andesite unit within the post-Alpine Alboran volcanic province h as a Neogene extrusion age; however, its Rb-Sr isotopic relations define a regression lille of 509 +/- 62(2 sigma) Ma (Early Palaeozoic). There are tw o concordant data point clusters on the regression line, one of which is we ll constrained, defining a secondary regression line of 202 +/- 30(2 sigma) Ma (Early Mesozoic). Considering the mineralogy of the andesites-plagiocla se, Ca-poor and Ca-rich pyroxene, and Ti-magnetite-and the presence of rest itic aggregates comprising these same four minerals, recent dehydration mel ting experiments suggest an origin by anatexis of an amphibolite-dominated source rock complex. Inherited zircon ion-microprobe ages in the range of 5 00-1800 Ma, an Sm-Nd isochron age of 1.5 +/- 0.4(2 sigma) Ga, T-CHUR(Nd) cr ustal derivation ages from similar to 0.75 to 1.05 Ga and epsilon(Nd)(0) va lues of -4 to -7 support a complex petrogenesis, involving large-scale rewo rking of older material. Sr-87/Sr-86 vs 1/Sr and Nd-143/Nd-144 vs 1/Nd indi cate a heterogeneous source rock complex showing two-component mixing. The data favour volcano-sedimentary source rock complex parent material which a t similar to 500 Ma underwent a diagenetic or hydrothermal event, which reg ionally reset Rb-Sr isotope systematics. Subsequently, at similar to 200 Ma the complex went through local diagenetic or hydrothermal re-equilibration , which created domains with slightly different Sr-87/Sr-86 ratios. before undergoing Alpine high-grade metamorphism and subsequent anatexis. Roughly coeval, restite-rich cordierite dacites show similar, similar to 200 Ma, hi gh-age Rb-Sr isotopic relations, which are interpreted as the age of diagen esis of its sedimentary parent material. This is supported by inherited zir con ion-microprobe ages of 300-400 Ma upwards. Also Sor these rocks Sr-87/S r-86 vs 1/Sr shows linear trends, which are explained analogically by sedim entary component mixing in the parent material of the anatectic source rock complex rather than by magmatic stage mixing or contamination. A sinking s lab model is suggested for the regional setting of the crustal anatectic re gime, melting being supported by fast uplift (of isotherms) and diapiric un derplating by high-temperature asthenospheric mantle.