Ordovician acidic metavolcanics of the Eastern Southalpine basement: subsolidus alkali elements mobility, magmatic affinity and geodynamic environment

Acidic metavolcanics from the Eastern Southalpine metamorphic basement were affected by relatively low rate of alkali elements mobilization. The most altered seems to be Levico area affected by K-metasomatism, Na- and Mg-alteration are scarce. The volcanics were probably (according to the model from Bergslagen ore province) a part of the low-T hydrothermal system in greater distance from the intrusion centre. The Th/Yb vs Zr/Y diagram shows calc-alkaline magmatic affinity with moderate variability in source material.The geodynamic environment was determined with the use of re-evaluated diagrams Ta/Yb vs Th/Yb and Yb vs Th/Ta respectively. They imply active continental margin origin of the volcanites, with the samples of Comelico showing certain similarity to the volcanics from Japan, the Cima d'Arzon samples resemble Chilean Andes. A part of the samples in the field of within-plate volcanic zone could be interpreted as a result of the back-arc basin spreading. (authors)