Morfología de circones vs. filiación geoquímica de rocas metavolcánicas en el Antiforme del Narcea (N de España)

Abstract

In the Narcea Antiform, both Ediacaran upper volcanic series and volcanic clasts in the overlying Cambrian micro-conglomerates, show geochemistry between those of calc-alkaline and alkaline series in the TAS diagram, and a mainly calc-alkaline trend in the Zr/TiO2-Nb/Y diagram. However, zircons reveal a common high temperature nature of the crystals and have overall characteristics typical of alkaline magmas. Such an apparent contradiction can be interpreted as a result of a change in the tectonic conditions. This would account for the mixed characteristics of rocks having a calc-alkaline geochemical signature but with an alkaline mineral assemblage. Moreover, zircon morphology has turned out to be an interesting clue to resolve the petrographical and geochemical discrimination in low-grade metamorphosed paleovolcanic rocks