Petrogenesis and age of skarns associated with felsic and metamafic dykes from the Para?-ba do Sul Complex, southern Esp?-rito Santo State

摘要

This paper concerns the study of petrography, mineral chemistry and geochronology of skarns generated at the contact of marbles of the Para?-ba do Sul Complex with felsic and metamafic dykes in the southern Esp?-rito Santo State. The marbles were metamorphosed under P-T granulite facies conditions during the syn-collisional stage of the Neoproterozoic Ara?§ua?- orogen. ?-Metamafic bodies are composed of amphibolite and hornblende granofels, while felsic dykes consist of alkali-feldspar granite, monzogranite or syenogranite. From marble towards the dyke, skarns related to the metamafic bodies are composed of carbonate + olivine and diopside + hornblende zones. Skarn associated to the granitic dykes are composed of three different zones: carbonate + tremolite , diopside , scapolite + diopside . Variations in mineral chemical compositions along the metasomatic zones suggest introduction of Mg and Ca from the marbles, Fe from the metamafic dykes and Na from the granitoids. The presence of spinel in the metamafic dykes and their skarns indicates that both were metamorphosed under granulite facies conditions during the 580-560 Ma syn-collisional stage. U-Pb zircon geochronology (LA-ICP-MS) of an alkali-feldspar granite dyke resulted in a crystallization age of ca. 540 Ma, which suggests that its skarns are therefore younger than skarns associated with the syn-collisional metamafic dykes.