Inherited and magmatic zircon from Neogene Hoyazo cordierite dacite, SE Spain - anatectic source rock provenance and magmatic evolution

Abstract

Almandine-graphite-bearing biotite-cordierite dacite from Cerro del Hoyazo, southern Spain, represents erupted magma produced by Late Alpine anatexis of high-grade pelitic/quartzo-feldspathic paragneisses. U-Th-Pb ion microprobe analysis of inherited/detrital zircon cores from the dacite reveals five principal age groups, 2·8-2·5 Ga, 2·1-1·9 Ga, 1·1-0·9 Ga, 650-550 Ma and 350-320 Ma, indicating a Gondwana domain provenance. Some of the cores are surrounded by a thin euhedral overgrowth which has the same age as a suite of sharply euhedral new-grown zircons in the dacite, 6·33 ± 0·15 (tσ) Ma. This zircon precipitated from the melt during or just before eruption of the magma. A foliated graphite-bearing cordierite-plagioclase-almandine-sillimanite- biolite restite rock inclusion contains inherited zircon cores similar in age to those in the dacite, consistent with the syngenetic melt-restite relationship between the magmatic melt and its Al-rich rock inclusions. Over growths on the enclave zircon cores have an age of 8·34 ± 0·45(tσ) Ma, which probably records an early stage of the ultra- metamorphism leading to the generation of the anatectic magma body. The inheritance age patterns of both dacite and restitic enclave, and zircon ages from the basement below the Cerro del Hoyazo, suggest that the anatectic source complex was probably a high-grade amphibolite facies equivalent of either the Palaeozoic schist complex of the basal nappe section or, more likely, its Permo-Triassic cover section. Show more