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