Petrology of Gameleira potassic lamprophyres, São Francisco Craton

Abstract

Gameleira lamprophyres are dykes and mafic microgranular enclaves associated with the shoshonitic Gameleira monzonite. This association belongs to the Paleoproterozoic alkaline magmatism from Serrinha nucleus, northeast Brazil. The liquidus paragenesis is diopside, pargasite, apatite and mica. Reverse zoning was identified in the groundmass alkali feldspar and was related to the undercooling of lamprophyric magma during the emplacement, with high growth rate of pargasite/edenite inducing disequilibrium between feldspars and liquid. Chemical data indicate that the lamprophyres are basic rocks (SiO 2 < 48 wt%), with alkaline character (Na 2 O + K 2 O > 3 wt%) and potassic signature (K 2 O/Na 2 O ≈ 2). High contents of MgO and Cr are consistent with a signature of a primary liquid, and such concentrations, as well as Al, K, P, Ba, Ni-and light rare earth elements, are consistent with an olivine-free metasomatic mantle source enriched in amphibole, clinopyroxene and apatite. By contrast, the ultrapotassic lamprophyres from Morro do Afonso, contemporaneous alkaline ultrapotassic magmatism in Serrinha nucleus, were probably produced by melting of a clinopyroxene-phlogopite-apatite enriched-source. The identification of different mineral paragenesis in the source of potassic and ultrapotassic lamprophyres from Serrinha nucleus can contribute to the understanding of the mantle heterogeneities and tectonic evolution of this region.

Petrologic features of mesoproterozoic lamprophyric dykes from Montevideo (Piedra Alta terrane, South Uruguay)

“…Alkaline magmatism is frequent in within-plate environments, related to extensional processes (Whalen et al 1987) and is characterized by high concentrations of HFSE and low values of LILE. Alkaline rocks showing strong enrichment in LILE and LREE are commonly associated with anorogenic or post-orogenic settings (Plá et al, 2011).…”

Shoshonitic Magmatic Series and the High Ba-Sr Granitoids: A Review with Emphasis on Examples from the Neoproterozoic Dom Feliciano Belt of Southern Brazil and Uruguay

“…Therefore, the genetic association of syenites with shoshonitic series can be explained by two alternative models: (i) potassic and ultrapotassic magmas, including lamprophyric ones, are generated by partial melting of phlogopite-or K-rich, amphibole-bearing mantle (Carvalho et al, 2014;Weaver et al, 2013;Plá Cid et al, 2012, 2003Prelević et al, 2012;Nardi et al, 2008Nardi et al, , 2007Green, 2004, 2000;Williams et al, 2004;Ferreira and Sial, 1993;Peccerillo, 1992), and (ii) syenitic and monzonitic magmas represent liquids derived from lamprophyric or trachyandesitic potassic magmas by fractional crystallization (e.g., Rios et al, 2007;Paim et al, 2002;Melzer and Foley, 2000;Zhao et al, 1995;Janasi et al, 1993;Guimarães and Silva Filho, 1992;Leat et al, 1988). Mixing of mantle-derived magmas, sometimes of alkaline affinity, such as lamproite or tephrite, with crustal melts is frequently proposed as a model, particularly when acidic rocks are abundant (Ferreira et al, 2015;Silva Filho et al, 1993;Thompson and Fowler, 1986).…”

“…Liquids of such compositions, including granitoids, could also be derived from lamprophyric or intermediate magmas through fractional crystallization, sometimes with concurrent assimilation of crustal materials. Fractional crystallization of lamprophyric magmas leading to the generation of syenitic rocks has been admitted by many authors (e.g., Rios et al, 2007;Melzer and Foley, 2000;Janasi et al, 1993;Leat et al, 1988), whilst others assume that syenitic and monzonitic magmas would be directly extracted from metasomatised mantle regions (e.g., Carvalho et al, 2014;Weaver et al, 2013;Plá Cid et al, 2012, 2003Nardi et al, 2008Nardi et al, , 2007Peccerillo, 1992;Venturelli et al, 1984). The association of both ultrapotassic and shoshonitic magmatism has been recognized by several authors (e.g., Prelević et al, 2012;Guo et al, 2006;Miller et al, 1999;Silva Filho et al, 1993;Rogers, 1992;Thompson and Fowler, 1986;Venturelli et al, 1984;Civetta et al, 1981), sometimes including lamproitic rocks (Conticelli et al, 2009) when the influence of subduction is less evident (Avanzinelli et al, 2009).…”

Minettes do Stock Monzonítico Glória Norte: evidência de magmatismo ultrapotássico pós-orogênico, com assinatura de subducção, no Sistema Orogênico Sergipano

“…Lamprófiros calcioalcalinos são rochas que ocorrem como corpos de pequenas dimensões (e.g., diques, pipes, sills) ou como enclaves em granitos (e.g., Conceição et al, 2016), sienitos (Conceição et al, 1995;Paim et al, 2002); monzonitos (Plá Cid et al, 2012;Lisboa, 2014) ou dioritos (e.g., Prelevic et al, 2004). Essas rochas são caracterizadas por apresentarem texturas porfirítica e panidiomórfica, com abundantes fenocristais de mica ou anfibólio e feldspatos limitados à matriz (e.g., Rock, 1987Rock, , 1991Woolley et al, 1996;Le Maître et al, 1989).…”