O Stock Flores: Exemplo de magmatismo granítico tipo-A no Domínio Rio Piranhas-Seridó, NE da Província Borborema

Abstract

Resumo -O Stock granítico Flores intrude gnaisses paleoproterozoicos, relacionados ao ComplexoCaicó, no Domínio Rio Piranha-Seridó, porção setentrional da Província Borborema, NE do Brasil. Este trabalho tem como objetivo a caracterização petrológica e geoquímica de seu monzogranitos. O Stock Flores compreende duas fácies petrográficas de monzogranitos equigranulares, leucocrá-ticos: i) monzogranitos rosados de granulação media; e ii) monzogranitos cinza rosados de granulação fina. Localmente ocorrem no Fácies Tipo II, enclaves máficos exibindo feições de coexistência de magmas (mixing e mingling), e schlieren elipsoidais, interpretados como estruturas formadas por convecção magmática. Biotita é o máfico principal; titanita, allanita, apatita, zircão e opacos ocorrem como minerais acessórios; fluorita, clorita e saussurita ocorrem como minerais tardios relacionados a fluídos em estágio subsolidus. As análises geoquímicas evidenciam a natureza evoluída do Stock e afinidade alcalina com teores de SiO 2 > 71,0%, e Na 2 O+K 2 O ~ 9,0%. Os diagramas discriminantes de ambiente tectônico demonstram a tipologia de granito Tipo-A. Tais dados são coerentes com a idade U-Pb 553±4 Ma encontrada para o Stock, o colocando dentro do contexto tardi-a pós-tectônico em relação à Orogênese Brasiliana/Pan-Africana na Província Borborema. Palavras-chave: Granito alcalino, Tardi a Pós-tectônico, Província Borborema.Abstract -The Flores Stock: An example of A-type granitic magmatism on Rio Piranhas-Seridó Domain, NE Borborema Province.The Flores granitic stock intrudes paleoproterozoic gneissic related to Caicó Complex, in Rio Piranhas-Seridó Domain, North part of the Borborema Province, NE Brazil. This work focused on the petrological and geochemical characterization of its monzogranites. The Flores Stock comprises equigranular, leucocratic monzogranites, which are divide in two petrografic facies: i) medium grained, pink monzogranites; and ii) fine grained, gray to pink monzogranites. Locally we can find in this type dioritic enclaves displaying magmas coexistence features (mixing and migling), and ellipsoidal schlieren formed by magmatic convection. Mineralogically, the Stock is constitued by biotite as its main mafic; titanite, allanite, apatite, zircon, opaque, and as late minerals, fluorite, chlorite and saussurite, these late ones are interpreted as related to fluids in subsolidus stage. The studied monzogranites show high SiO 2 contents (> 71% wt%) and alkaline affinity with Na 2 O + K 2 O ~ 9,0%. Tectonic discriminant diagrams of tectonic environment suggest a typology of A-type granite related to a post-collisional environment, which is corroborated by U-Pb zircon crystallization age of 553±4 Ma. Thus, the Flores Stock is interpreted as emplaced in a late to post-tectonic stage of the Brasiliana / Pan-African Orogeny in the Borborema Province

O Batólito Catolé do Rocha (RN-PB): Um magmatismo granítico do tipo-A2 reduzido no Domínio Rio Piranhas-Seridó, Província Borborema, Nordeste do Brasil

“…signature, the CRB has a notable ferroan composition and next to the alkalic and alkali-calcic series (besides the relative HFSE enrichment; Table 1; Figures 4 and 5), similar to the ALK suite of Nascimento et al (2015; see also update in Dalan et al, 2019;Figures 6A and 6B). Some of these bodies are intrusive into the PSD, such as the Serra Negra do Norte pluton (Campos et al, 2000) and the Flores stock (Souza et al, 2017). Likewise, these rocks show alkaline signatures in several geochemical diagrams that are more typical of A-type granites (e.g., Whalen et al, 1987;King et al, 1997;Bonin, 2007).…”

“…(F) Discriminant diagram (Al 2 O 3 + CaO)/ (FeOt + Na 2 O + K 2 O) versus 100*(MgO + FeOt + TiO 2 )/SiO 2 for post-collisional granites with SiO 2 > 68 wt.% of Sylvester (1989). Data for granites from the Porphyritic High-K Calc-Alkaline and Alkaline suites of the ediacaran-cambrian magmatism in the Rio Piranhas-Seridó and São José do Campestre Domains were compiled from Campos et al (2000), Nascimento et al (2015) and Souza et al (2017). more evolved members of the calc-alkaline (= magnesian, I-type) series are prone to show the typical ferroan composition of the A-type granites (Frost et al, 2001;Frost and Frost, 2011;Castro, 2019).…”

“…Nevertheless, the CRB chondrite-normalized REE patterns are distinct from most granite bodies in the ALK suite that show lower REE contents (especially the HREE) and positive Eu anomalies (cf. Nascimento et al, 2015 and references therein), except for the Flores stock (Souza et al, 2017) which is chemically very similar to the CRB.…”

“…Qz: quartz; Kf: potassic feldspar; Pl: plagioclase; Bt: biotite; Hbl: hornblende; Ttn: titanite; Opc: opaque minerals; Mgt: titanomagnetite; Ilm: ilmenite; Mim: myrmekite. Table 1 presents the compositional ranges (major and trace elements) for the CRB, and the compositions of the ALK and CALCKP Ediacaran-Cambrian magmatic suites within the Rio Piranhas-Seridó and São José do Campestre Domains (data compiled from Campos et al, 2000;Nascimento et al, 2015;Souza et al, 2017). A detailed lithochemical discussion for CRB felsic and basic-intermediate rocks can be found in Medeiros et al (2008b).…”

“…Overall, the batholith has SiO 2 ranging from 62.4 to 75.1 wt.%, enrichment in alkalis (Na 2 O + K 2 O = 8.3 -10.6%) relative to CaO (0.8 -2.8%), high K 2 O/Na 2 O ratios (1.6 -2.0%) Table 1. Major and trace element compositional ranges for granites of the Catolé do Rocha Batholith (compiled from Medeiros et al, 2008a, along with our unpublished data) compared to the compositions of the Alkaline and Porphyritic High-K Calc-Alkaline Suites of the Edicaran-Cambrian plutonism in the Rio Piranhas-Seridó and São José do Campestre Domains (data compiled from Campos et al, 2000;Nascimento et al, 2015 andSouza et al, 2017).…”