Stable (C, O, S) isotopes and whole-rock geochemistry of carbonatites from Alto Paranaíba Igneous Province, SE Brazil

Abstract

ABSTRACT:The present work investigates the relationship between whole-rock geochemistry and stable isotope composition from carbonatites belonging to the Tapira, Araxá, Salitre, Serra Negra, Catalão I, and Catalão II alkaline-carbonatite complexes of the Alto Paranaiba Igneous Province (APIP), central Brazil and from the Jacupiranga Complex, of the Ponta Grossa Province, southeast Brazil. The APIP complexes are ultrapotassic, comprising bebedourites, phoscorites, nelsonites, and carbonatites, whereas Jacupiranga is a sodic complex composed of ijolite-series rocks, syenites, carbonatites, and alkaline gabbros. The geochemistry data allied to mineralogical constraints allowed us to classify the carbonatites into five groups, and to devise a chemical index (BaO/(BaO+SrO)) to gauge the magmatic evolution of the studied carbonatites.The APIP carbonatites evolve from apatite-rich calciocarbonatites toward Ba-, Sr-, and rare earth element (REE)-rich magnesiocarbonatites. This evolution is mostly driven by apatite, phlogopite, dolomite, and calcite fractionation and consequent enrichment in monazite, norsethite, and strontianite. Stable isotope data show a wide diversity of petrogenetic processes in play at the APIP, relatively to the Jacupiranga Complex, which is interpreted as a result of the shallower intrusion levels of the APIP complexes. Such shallower emplacement, at low lithostatic pressure, allowed for a complex interplay of fractional crystallization, liquid immiscibility, degassing, and interaction with hydrothermal and carbohydrothermal systems. KEYWORDS: INTRODUCTIONBrazilian alkaline provinces have been studied by a range of techniques such as whole-rock geochemistry, mineral chemistry, stable and radiogenic isotope geochemistry, with a range of petrogenetic aplications (Gomide et al. 2013, Barbosa 2009, Cordeiro et al. 2011, Grasso 2010, Ribeiro 2008, CominChiaramonti et al. 2001, Traversa 2001, Andrade et al. 2002, Huang et al. 1995, Santos & Clayton 1995, Ulbrich & Gomes 1981. We aim to contribute to the knowledge of carbonatite petrogenetic evolution, investigating the relationships between whole-rock geochemistry and stable isotope geochemistry data, reporting geochemical and isotopic data from carbonatites of the Late-Cretaceous Alto Paranaíba Igneous Province (APIP), and discuss their implications for magma evolution, both at single-complex and Province-wide scales. The results obtained are compared with the Early-Cretaceous Jacupiranga carbonatite complex, in the Ponta Grossa Province.Alkaline rocks and alkaline-carbonatite associations include highly variable petrographic types and correspondingly extensive nomenclature. We adopt the nomenclature proposed by Le Maitre et al. The APIP alkaline-carbonatite complexes are multistage intrusions formed by rocks derived from the bebedourite, carbonatite, and phoscorite series, which are related to each other by a complex interplay of fractional crystallization, liquid immiscibility, and degassing (Brod et al. 2004, Ribeiro 2008, Barbosa 2009, Cordeir...

Cretaceous carbonatites of the southeastern Brazilian Platform: a review

“…Additional multielement diagrams are also found for other areas: the Ponta Grossa Arch (Gomes et al 2011a, Azzone et al 2013, Beccaluva et al 2017, Chmyz et al 2017, Amambay (Gomes et al 2011b, Comin-Chiaramonti et al 2014, and the Alto Paranaíba province (Gomide et al 2016).…”

“…However, it is important to consider that in some complexes like Barra do Itapirapuã, Jacupiranga and Juquiá, the evolution of carbonatite magmas resulted in rocks of wide variation in chemical composition representing different stages of intrusion. Thus, early stage carbonatites of the Jacupiranga and Alto Paranaíba complexes tend to show a more calcic composition, that evolved to more magnesian in latter stages of crystallization (Gomide et al 2016). This calciocarbonatites→magnesiocarbonatites evolution trend, reaching up to ferrocarbonatites in a few cases, has been described in Barra do Itapirapuã (Ruberti et al 2002), Cerro Chiriguelo (Censi et al 1989) and Juquiá (Walter et al 1995) complexes.…”

“…However, association of these different petrographic types in a same complex is rare (e.g., Araxá, Barra do Itapirapuã, Juquiá). Plottings of whole-rock chemistry data in CaO-MgO-(FeO + MnO) classification diagrams (Woolley & Kempe 1989) are discussed in various papers (e.g., Comin-Chiaramonti et al 2001, 2005c, 2007a, Gomide et al 2016. They usually stress the large chemical variation of carbonatites, analyses covering the three, Ca, Mg and Fe compositional fields.…”

“…REE fluorocarbonates are relatively abundant in late stage carbonatites (e.g., Barra do Itapirapuã, Cerro Manomó). Chondrite-normalized (Thompson 1982, Boynton 1984, McDonough & Sun 1995 REE distribution diagrams for various carbonatite complexes are discussed in several papers (e.g., Comin-Chiaramonti et al 2005c, 2007a, 2014, Gomes et al 2011a, 2011b, Azzone et al 2013, Gomide et al 2016, Beccaluva et al 2017, Chmyz et al 2017. Patterns are in general marked by high REE concentration and variable LREE/ HREE fractionation degrees.…”

“…A strong increase from Lu to La is observed in Cerro Chiriguelo, Jacupiranga, Lages (both early and late carbonatites) and Mato Preto complexes, and also Alto Paranaíba occurrences that characterizes different stages of fractional crystallization (C1 to C5, cf. Gomide et al 2016). Flat REE or patterns with a smooth decrease from La to Lu are characteristic of Anitápolis, Barra do Itapirapuã (late calciocarbonatites), Ipanema, Jacupiranga (calciocarbonatites) and Juquiá (magnesio-and calciocarbonatites) rocks.…”