The Salitre intrusion, which is subdivided into Salitre I and Salitre II. It was dated to ~86-82 Ma by Sonoki and Garda (1988). It is part of the Alto Paranaíba Igneous Province (APIP, Fig. 1) in Brazil. The APIP is one of the largest ultrapotassic/carbonatitic/kimberlitic provinces in the world. The intrusion consists of lamproites, carbonatites, and one lamprophyre, as well as various intrusive cumulitic rocks. These rocks include perovskite-phlogopite dunites, phlogopite-perovskite clinopyroxenites (salitrites, s.l.), phlogopitites, phoscorites, and perovskitites. These rocks are characterized by variable enrichment of olivine, clinopyroxene, phlogopite, perovskite, oxides, apatite, and carbonate, as well as several accessory phases, such as baddeleyite and calzirtite. Their geochemical and petrological features are related to the variable amounts of these minerals.
For this part of the project, we have analyzed the concentrations of trace elements in the primary minerals (clinopyroxene, phlogopite, garnet, perovskite, apatite and olivine) identified in three phlogopite-perovskite clinopyroxenites and one perovskite-phlogopite dunite.
Analyzing the trace elements in these minerals helped us to better understand the differential settling of minerals within the Salitre magma chamber, and their possible genetic relationship with carbonatitic and lamprophyric rocks. These analyses also provided important information about the minerals' enrichment in rare earth elements (REEs) and high field strength elements (HFSEs).
This publication results from work conducted under the transnational access/national open access action at Mass spectrometry la-icp laboratory (IGG-CNR, Italy) supported by WP3 ILGE - MEET project, PNRR - EU Next Generation Europe program, MUR grant number D53C22001400005.
Mantle xenoliths are hosted in lavas localized in the Nemby area (25°24' S, 57°32' W; Asunciòn-Sapucai-Villarrica graben, ASV, central Paraguay: Fig.1), where a small melanephelinitite plug (Cerro Nemby), with elliptical topography (800 x 500 m, about 100 m above the plain), contains very abundant mantle xenoliths (10-15% by volume of the plug) together with crustal xenoliths (Comin-Chiaramonti et al., 2001).
According to Le Bas (1987), lavas consist of nephelinite and subordinately of ankaratrite (CIPW Ab < 5 wt% e Ne > 20 wt%).
The average size of the mantle xenoliths (10-12 cm, max 45 cm, i.e. the largest observed in ASV) and the compositional range (lherzolite to dunite to pyroxenite) make these xenoliths particularly suitable for a study regarding metasomatic processe(s) affecting the Sub-Continental Lithospheric Mantle of central Paraguay.
The dunite results to be the most abundant xenolith type in such lavas. In-situ geochemical characterization was performed on silicates and glasses from very fresh xenoliths, which document a large variety of rock types. Five samples were investigated, namely: i) dunite 3209; ii) spinel harzburgite 3284; iii) spinel lherzolite 3293; iv) olivine websterite 3253 and v) olivine clinopyroxenite 3270. The analyses were directly carried out on thin petrographic sections (30 µm thick) of the selected samples.
Global geochemistry database for cratonic / anorogenic lamproites and related potassic rocks (compiled and screened from GEOROC in April 2020).
Related key publication: Ngwenya, Ntando S.; Tappe, Sebastian (2021): Diamondiferous lamproites of the Luangwa Rift in central Africa and links to remobilized cratonic lithosphere. Chemical Geology. https://doi.org/10.1016/j.chemgeo.2020.120019