Petrography and geochemistry of late- to post-Variscan vaugnerite series rocks and calc-alkaline lamprophyres within a cordierite-bearing monzogranite (Sierra Bermeja Pluton, southern Iberian Massif)

Abstract

The Sierra Bermeja Pluton (southern Central Iberian Zone, Iberian Massif) is a late-Variscan intrusive constituted by cordierite-bearing peraluminous monzogranites. Detailed field mapping has allowed to disclose the presence of several NE–SW trending longitudinal composite bodies, formed by either aphanitic or phaneritic mesocratic rocks. According to their petrography and geochemistry these rocks are categorized as calc-alkaline lamprophyres and vaugnerite series rocks. Their primary mineralogy is characterized by variable amounts of plagioclase, amphibole, clinopyroxene, biotite, K-feldspar, quartz and apatite. Broadly, they show low SiO₂ content (49–56wt.%), and high MgO+FeO_t (10–17wt.%), K₂O (3–5wt.%), Ba (963–2095ppm), Sr (401–1149ppm) and Cr (87–330ppm) contents. Field scale observations suggest that vaugneritic rocks and lamprophyres would constitute two independent magma pulses. Vaugneritic dioritoids intruded as syn-plutonic dykes, whereas lamprophyres were emplaced after the almost complete consolidation of the host monzogranites. In this way, vaugnerite series rocks would be an evidence for the contemporaneity of crustal- and mantle-melting processes during a late-Variscan stage, while lamprophyres would represent the ending of this stage.