New petrogenetic information of the Caspi Cuchuna basanites, Sierra Norte de Córdoba

Abstract

New mineralogical and geochemical data from the Caspi Cuchuna basic alkaline dykes located in the central-western region of the Sierra Norte-Ambargasta batholith are presented. The petrography and bulk rock chemistry classify these dikes as basanites. Mineral chemistry data for selected olivine and clinopyroxene phenocrysts suggest high temperature and high pressure conditions for initial crystallization; the system evolved towards lower pressure and temperature along with an increase of the oxygen fugacity, possibly approaching emplacement conditions. The Cr (333 ppm), Ni (183 ppm) and MgO (9.13 wt. %) contents indicate relatively primary characteristics for the rock, suggesting olivine, pyroxene and magnetite fractionation. The depletion of HREE is indicative of the presence of residual garnet in the source. The enrichment of incompatible elements (Cs, Rb, and Ba) suggests crustal contamination during ascent and emplacement of the melt. The geochemical signature is compatible with a within-plate setting (WPB) and the multielemental diagram is comparable with within-plate alkaline basalts like those representative of extensional regimes located east of the active volcanic Andean zone. The geochemical characteristics suggest derivation from partial melting of a subcontinental lithosphere possibly contaminated with a continental crust component.