Resende lamprophyres: new petrological and structural interpretations for a regional Upper Cretaceous alkaline mafic dyke swarm

Abstract

New petrographic, lithogeochemical and structural analyses were performed on the Upper Cretaceous lamprophyres emplaced in the Proterozoic basement rocks of the Resende sedimentary basin in SE Brazil. Field characteristics and petrographic data confirm their identification as alkaline lamprophyres. Geochemical variations were mainly controlled by fractional crystallization of clinopyroxene and olivine. Liquid immiscibility, rapid cooling and crustal assimilation may have occurred subordinately during the evolution of the Resende lamprophyres. Mantle and chondrite-normalized diagrams point to an enriched mantle as the lamprophyre’s magma source. Th/Yb and Ta/Yb ratios confirm a within-plate enriched mantle source with residual carbonate and phlogopite/amphibole as suggested by LILE enrichment and the presence of carbonate and phlogopite/amphibole as primary phases. The predominance of an ENE-trend of the dykes is related to a prevalent NNW-SSW orientation of the minimum principal stress (σ₃) orientation in an extensional regime during the emplacement of the Resende lamprophyres’ dyke swarm. Frequent offsets produced by local dilation direction are parallel to the NNW-oriented extension of the main segments. WNW to NW secondary sets are controlled by previous discontinuities that were favored as pathways for the highly volatile lamprophyre magma. An NNW-SSE distension related to the Resende lamprophyre dyke swarm emplacement is consistent with the early stages of evolution of the Resende basin and uplift of its basement during the Late Cretaceous to the Paleocene.

Keywords:
lamprophyre dykes; Resende, fractional crystallization; Upper Cretaceous magmatism