Amphiboles and clinopyroxenes from Euganean (NE Italy) cumulus enclaves: evidence of subduction-related melts below Adria microplate

Abstract

Euganean Hills are a magmatic district belonging to the Veneto Volcanic Province, whose magmatism developed during an extensional tectonic regime within the Alpine orogenesis in an intra-plate setting (the Adria microplate). Mafic and ultramafic cumulus enclaves occur within the Euganean trachytes. We estimated the trace element composition of liquids in equilibrium with cumulus minerals, employing a set of partition coefficients. Parental melts of cumulus clinopyroxenes are characterized by a marked enrichment in LILE, Th and U relative to N-MORB. Conversely, HREE and HFSE concentrations resemble N-MORB contents. These geochemical signatures are typical of subduction-related magmas, and also characterized the parental melts of Adamello cumulates. Conversely, Veneto Volcanic Province mafic lavas show geochemical patterns typical of anorogenic magmas. Therefore, those rocks are not cogenetic with Euganean cumulates, which are interpreted as crystallized from Alpine subduction-related basaltic magmas. These cumulates were subsequently dismembered and transported to shallower levels by ascending lavas related to the Veneto Volcanic Province magmatism. Therefore, magmatic products related to Alpine subduction are more widespread beneath the Adria microplate than previously known