Post-collisional volcanism in a sinking slab setting - crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alboran volcanic province, southeastern Spain

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 letter rock formation may h ave developed through crystal fractionation of mainly plagioclase and pyrox enes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernandez formation is overlain by Bujo formation while Viuda formation is absent, and a southwes tern domain where Viuda formation forms the only fractionate after Hernande z formation. Hernandez parent magma is thought generated through crustal an atexis by dehydration melting of a predominantly amphibolitic source rock c omplex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositiona l variation within this protogenetic complex. Single crystal U-Pb ages of c . 500 Ma to 1800 Ma for inherited zircon support the presence of elastic ma terial of Proterozoic derivation within the original volcano-sedimentary co mplex. Regional study of syn-collisional rock formations (Alpine nappe comp lexes) indicate that the collisional tectonic stage in the Betic-Rif orogen ic belt took place rather early (25-30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500 degrees C/my) and extensio nal tectonics in the period 22-17 Ma. This later tectonic stage was set int o motion by slab break-off which set the stage for a high temperature regim e in the overlying lithosphere, providing the framework for the crustal mel ting and magma production responsible for the calc-alkaline rocks of Albora n volcanic province. Miocene zircon with ages ranging from c, 17 to 11 Ma i ndicate a rather protracted magmatic development prior to eruption at c. 11 Ma. Post-collisional character of Caldear Volcanic Group thus seems well e stablished. (C) 1998 Elsevier Science B.V. All rights reserved.