Post-collisional volcanism in a sinking slab setting - crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alboran volcanic province, southeastern Spain (vol 45, pg 499, 1998)

Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkali ne rock complex within S-a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernandez p yroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hor nblende-bearing pyroxene dacites-rhyolites. The latter two rock formations may have developed through crystal fractionation of mainly plagioclase and pyroxenes; however, there is no direct relation between them. CVG has a dom ainal structure with a northeastern domain where Hernandez formation is ove rlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernandez fo rmation. Hernandez parent magma is thought generated through crustal anatex is by dehydration melting of a predominantly amphibolitic source rock compl ex which was formed by metamorphism from c. 500 Ma volcano-sedimentary pare nt material. The domainal structure of CVG is explained by compositional va riation within this protogenetic complex, Single crystal U-Pb ages of c. 50 0 Ma to 1800 Ma for inherited zircon support the presence of elastic materi al of Proterozoic derivation within the original volcano-sedimentary comple x. Regional study of syn-collisional rock formations (Alpine nappe complexe s) indicate that the collisional tectonic stage in the Betic-Rif orogenic b elt took place rather early (?50-30 Ma?) and was followed by a stage of rap id regional rock uplift, fast cooling (c. 500 degrees/my) and extensional t ectonics in the period 22-17 Ma. This later tectonic stage was set into mot ion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alboran vol canic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indica te a rather protracted magmatic development prior to eruption at c. 11 Ma. Post-collisional character of Caldear Volcanic Group thus seems well establ ished.