Abstract The Alfeu-I lamproite is one of the few alkaline rock occurrences in the South of Brazil that represents the alkaline event related to the South Atlantic opening and the enormous magmatic activity that formed the Paraná basalts. Alfeu-I lamproite is a diatreme facies and exhibits an inequigranular texture with macrocrysts of mica, spinel, garnet, and ilmenite and microcrysts of mica, pyroxene, and rare olivine, all immersed in a groundmass of pyroxene, spinel, perovskite, rutile, ilmenite, and, more rarely, olivine. Major element compositions of Alfeu-I pyroxene, garnet, ilmenite, mica, and olivine were determined by electron microprobe analyses, and trace element concentrations of clinopyroxene, garnet, ilmenite, and mica were measured using laser-ablation inductively coupled plasma mass spectrometry techniques. Temperature, pressure, and oxygen fugacity (fO2) conditions during the crystallization of Alfeu-I lamproite were calculated with the geothermobarometers and olivine, spinel, garnet, and orthopyroxene. The resulting mean equilibrium temperature ranges from 1375°C at 4 GPa to 1395°C at 5 GPa, whereas the fO2 points to ΔFMQ = +2.4 (at 4 GPa) and ΔFMQ = +2.2 (at 5 GPa). Rb-Sr and Sm-Nd isotopic data together with the trace element concentrations of minerals suggest that melting of a mantle source enriched in incompatible elements and volatiles due to previous subduction events occurred during the Gondwana breakup around 125 Ma ago. Fluids that may have originated from subducting slabs in the old subduction zone are probably the cause of the high fO2 conditions in Alfeu-I lamproite.

Abstract Trace elements provide crucial information about the origin and evolution of the Earth. One common issue regarding their analyses is the reduced analyte recovery during hot plate acid digestion for some geological samples. To overcome this, alkali fluxes (e.g., Lithium borate) have been used to produce an homogeneous synthetic glass that can be used then for both X-ray fluorescence (XRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In this sense, we developed a method for LA-ICP-MS whole rock trace element analyses in glasses prepared by mixing high-purity sodium tetraborate and rock powders at high-temperature. We selected six international reference materials including peridotite (JP-1), basalt (BRP-1), kimberlite (SARM-39), pyroxenite (NIM-P), diorite (DR-N) and andesite (JA-1). Glasses were produced in a fully automatic fusion machine with step heating. Run products analyses were carried out on a Thermo® Element2 SF-ICP-MS coupled to a New Wave Research® Nd:YAG (213 nm) laser ablation system and on a Thermo® Element XR ICP-MS coupled to an Analyte G2 (193 nm) LA system. Results show that glasses are homogeneous and there is good agreement (generally > 90%) between our data and literature values for most trace elements, including large ion lithophile elements (LILE), high-field strength elements (HFSE) and rare-earth elements (REE).