Diffuse dyke swarms with intermediate to felsic composition and calcalkaline affinity crop out in the Serre Massif (Calabria, Southern Italy). These are part of the widespread late- to post-collisional magmatism affecting most southern European basements during the waning stages of the Hercynian orogeny. The dykes are andesitic and dacitic-rhyodacitic in composition, with medium- to high-K2O content, and show typical features of subduction-related magmas, such as LILE and LREE enrichment and HFSE depletion. Chondrite-normalized REE patterns are weakly to strongly fractionated (LaN/YbN = 8.5 to 14.0 for andesites and 2.3 to 16.3 for dacites-rhyodacites) with slightly negative to positive Eu anomaly for the andesites and markedly negative Eu anomaly for the dacites-rhyodacites. The petrogenesis of the late- to post-Hercynian calcalkaline rocks is usually linked to an extensional post-collisional setting involving thinning of the continental lithosphere and progressive upwelling of the asthenospheric mantle. In such a context, both pure mantle, crustal and hybrid melts are likely to be generated. The andesitic dykes show mineral and whole-rock major and trace element composition resembling boninitic rock associations (anomalously high MgO, Mg#, Cr and Ni, coupled with high SiO2, relatively low TiO2, high Mg# in clinopyroxene, high Al2O3/TiO2, high Zr/Hf, moderate LREE enrichment, low HREE and negative Nb-Ta troughs in primitive mantle-normalized diagrams). Petrological investigations suggest that they were probably produced by partial melting of an enriched mantle source metasomatized by crustal fluids/melts during former subduction of oceanic lithosphere and then suffered minor, if any, assimilation of lower crustal metapelites. Most dacite-rhyodacites were instead likely derived by hybridization in various proportions of crustal and mantle melts, whereas pure crustal metasedimentary sources, and more or less efficient restite unmixing processes, were involved in the generation of the most silica-rich rhyodacites.
|Titolo:||Genesis of intermediate-felsic calc-alkaline magmas at the end of the hercynian orogeny: the high-MgO andesite and dacite-rhyodacite dykes of the Serre Massif (southern Italy)|
|Data di pubblicazione:||2011|
|Appare nelle tipologie:||4.2 Abstract in Atti di convegno|