High-K andesites as witnesses of a continental arc system in the Western Alps, Italy: constraints from HFSE and Hf–Nd–Sr–Pb–O isotope systematics

Abstract Geochemical and isotopic data are presented for ~ 32 Ma-old high-K andesites dacites from the Alpine Chain. The samples consist of plagioclase, amphibole, titanomagnetite rare biotite quartz. isotope indicate that slab-derived fluids, sediment melts presumably AFC processes involving continental crust played a key role in petrogenesis rocks. A contribution fluids is suggested based on overall enrichment large-ion lithophile elements related high Ba/La, Ba/Zr, Ba/Th, Ba/Nb Pb/Nd, sometimes distinctively higher than average crust. Positively correlated Ba/Nb–Th/Nb relationships, low Ce/Pb, Nb/U negative correlation Pb isotopes with Ce/Pb positive ∆ 7/4 8/4 values similar to GLOSS imply additional involvement sediment-derived melt. Negatively Nb/Ta–Zr/Hf ratios at Nb/Ta (13–7.5) best explained by parental magma differentiation amphibole arc system. have moderately unradiogenic Nd (εNd: – 2.0 6.7) radiogenic 87 Sr/ 86 Sr compositions (0.7085–0.7113), ( 206 Pb/ 204 Pb: 18.50–18.72; 207 15.59–15.65; 208 38.30–38.67), elevated δ 18 O (+ 6.5 + 9.1 ‰). Epsilon Hf range 2.5 4.0. Negative εHf( t ) εNd( K 2 abundances processes. offset εHf given εNd points aged garnet-bearing crustal lithologies. latter feature qualitatively consistent modification unexposed primary basaltic deep material. In conclusion, an context, inferred primitive andesitic generated mantle wedge through fluid infiltration descending slab where may caused also partial melting sedimentary rocks mixed evolving andesite–dacite towards shallow-level intrusive extrusive High-K trace element features thus result combination already participation probably