Ediacaran to Cambrian magmatic suites in the Rio Grande do Norte ...

Journal of South American Earth Sciences 58 (2015) 281e299

Contents lists available at ScienceDirect

Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames

Ediacaran to Cambrian magmatic suites in the Rio Grande do Norte domain, extreme Northeastern Borborema Province (NE of Brazil): Current knowledge ticas Ediacaranas a Cambrianas no domínio Rio Grande Suítes magma do Norte, extremo Nordeste da Província Borborema (NE do Brasil): Conhecimento atual Marcos Antonio Leite do Nascimento a, *, Antonio Carlos Galindo a, Vladimir Cruz de Medeiros b a b

~o em Geodina ^mica e Geofísica, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil s-Graduaça Departamento de Geologia, Programa de Po gico do Brasil, Núcleo de Apoio de Natal (NANA/CPRM), Caixa Postal, CEP 59.078-970 Natal, RN, Brazil CPRM e Serviço Geolo

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 March 2014 Accepted 2 September 2014 Available online 19 September 2014

The EdiacaraneCambrian plutonic activity is one of the most important geological features of the Rio Grande do Norte Domain (Borborema Province, NE Brazil). It is represented by several batholiths, stocks and dykes. Based on the petrographic, geochemical and geochronological characteristic of different rocks, this plutonic activity can be grouped in six separate suites: shoshonitic (Shos), porphyritic high-K calcalkaline (PHKCalcAlk), equigranular high K calc-alkaline (EHKCalcAlk), calc-alkaline (CalcAlk), alkaline (Alk) and charnockitic alkaline (ChAlk). Geochemically, the Shos, CalcAlk and Alk suites are differentiated from the others, while ChAlc can be distinguished from the others in some diagrams. The greatest difficulty lies in distinguishing between the chemically similar PHKCalcAlk and EHKCalcAlk. To this end, existing geochronological data as well as related petrographic and textural field aspects may be used to distinguish the two mentioned suites (PHKCalcAlk and EHKCalcAlk). Petrographically, the Shos suite has composition between gabbro/diorite and quartz monzonite. Monzogranites (with subordinate granodiorites and quartz monzonites) predominate in both PHKCalcAlk and EHKCalcAlk. Calc is composed of granodiorites to tonalites. Alc is formed by alkali feldspar granites (with subordinate alkali feldspar quartz syenites and syenogranites), whereas ChAlc has quartz mangerites and charnockites. The suites were emplaced between the Ediacaran (635e541 Ma) and Cambrian (541e485 Ma), predominantly in the Ediacaran, based on 34 UePb datings (zircon, titanite, monazite and columbite etantalite), 17 RbeSr (whole rock) and 1 SmeNd (total rock and mineral) internal isochrons. The Shos ~o Joa ~o do Sabugi suite has UePb ages varying from 599 ± 16 (Poço Verde pluton) to 579 ± 7 (Acari and Sa plutons), slightly older than those of the PHKCalcAlk suite, which ranges between 591 ± 4 Ma (Totoro de Espinharas pluton). The CalcAlk Suite has only one dated body, aged pluton) and 544 ± 7 Ma (S~ ao Jose 598 ± 3 Ma (Serra da Garganta pluton). The EHKCalcAlk suite UePb dating is younger than the afore^s pluton) and 527 ± 8 (Cerro Cor mentioned suites, ranging from 582 ± 5 Ma (dykes in Dona Ine a pluton). The Alk suite was dated at 578 ± 14 Ma (Caxexa pluton, SmeNd internal isochron) and at 597 ± 4 Ma (Japi pluton, UePb zircon), while ChAlc UePb zircon ages of 601 ± 10 Ma and 593 ± 5 Ma (Umarizal pluton). The magmatism of Cambrian age in the Rio Grande do Norte Domain is represented by pegmatite dykes with UePb dating between 515 and 510 Ma. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Brasiliano Rio Grande do Norte Domain Borborema Province Granitoid magmatism Palavra-chave: Brasiliano Domínio Rio Grande do Norte Província Borborema Magmatismo Granitoide

s-Graduaça ~o em Geodina ^mica e Geofísica, Universidade Federal do Rio Grande do Norte, Campus * Corresponding author. Departamento de Geologia, Programa de Po rio S/N, Lagoa Nova, Caixa Postal 1678, CEP: 59078-970 Natal, RN, Brazil. Universita E-mail addresses: [email protected], [email protected] (M.A.L. do Nascimento), [email protected] (A.C. Galindo), [email protected] (V.C. de Medeiros). http://dx.doi.org/10.1016/j.jsames.2014.09.008 0895-9811/© 2014 Elsevier Ltd. All rights reserved.

282

M.A.L. do Nascimento et al. / Journal of South American Earth Sciences 58 (2015) 281e299

r e s u m o ^ nica ediacaranaecambriana constitui uma das mais importantes feiço ~ es geolo gicas A atividade pluto representada por encontrada no Domínio Rio Grande do Norte (Província Borborema, NE do Brasil). Ela e litos, stocks e diques. Com base em características petrogra ficos, geoquímicas e geodiversos bato gicas de diferentes rochas e possível agrupar esta atividade pluto ^ nica em seis suítes distintas, sa ~o cronolo lcio-alcalina de alto K elas: Shoshonítica (Shos), C alcio-alcalina de alto K Porfirítica (CalcAlcAKP), Ca lcio-alcalina (CalcAlc), Alcalina (Alc) e Alcalina Charnoquítica (AlcCh). Equigranular (CalcAlcAKE), Ca ~o individualizadas das demais, enquanto que a AlcCh Geoquimicamente, as suítes Shos, CalcAlc e Alc sa pode ser distinguida das outras em alguns diagramas. A dificuldade maior est a na distinç~ ao entre as CalcAlcAKP e CalcAlcAKE, sendo elas quimicamente similares. Os aspectos de campo aliados aos petficos e texturais podem ser utilizados para distinç~ rogra ao entre as suítes CalcAlcAKP e CalcAlcAKE, bem gicos existentes. como os dados geocronolo ~o entre gabros/dioritos e quartzo monzonitos. Na Petrograficamente, a Suíte Shos possui composiça CalcAlcAKP predomina monzogranitos (com granodioritos e quartzo monzonitos, subordinados), formada por granodioritos a tonalitos. A Alc e formada por semelhante a CalcAlcAKE. A CalcAlc e alcalilcali-feldspato sienitos e sienogranitos, subordinados), enquanto que a feldspato granitos (com quartzo a AlcCh tem quartzo mangeritos e charnoquitos. As suítes foram alojadas entre o Ediacarano (635e541 Ma) e o Cambriano (541e485 Ma), predom~o, titanita, monazita e columbitaetantalita), 17 inando no Ediacarano, com base em 34 idades UePb (zirca crona interna SmeNd (rocha total e mineral). A Suíte Shos tem idades UePb RbeSr (rocha total) e 1 iso ~o do Sabugi). Esses valores ao Joa variando de 599 ± 16 (Plúton Poço Verde) a 579 ± 7 (plútons Acari e S~ s~ ao um pouco mais velhos do que as idades da Suíte CalcAlcAKP que possui valores entre 591 ± 4 Ma ) e 544 ± 7 Ma (Plúton Sa ~o Jose de Espinharas). A Suíte CalcAlc possui apenas um corpo (Plúton Totoro datado, com idade de 598 ± 3 Ma (Plúton Serra da Garganta). A Suíte CalcAlcAKE possui idades UePb ^s) e mais jovens que as suítes anteriores, com valores entre 582 ± 5 Ma (diques no Plúton Dona Ine crona interna Sm 527 ± 8 (Plúton Cerro Cor a). A Suíte Alc foi datada em 578 ± 14 Ma (Plúton Caxexa, iso ~o), enquanto que a AlcCh foi datada, UePb em zirca ~o, em eNd) e 597 ± 4 Ma (Plúton Japi, UePb em zirca 601 ± 10 Ma e 593 ± 5 Ma (Plúton Umarizal). O magmatismo de idade cambriana no Domínio Rio Grande do Norte est a representado pelos diques de pegmatito com idades UePb variando entre 515 e 510 Ma. © 2014 Elsevier Ltd. All rights reserved.

1. Introduction The Ediacaran to Cambrian plutonic activity is one of the most important geological features of Rio Grande do Norte Domain and the entire Borborema Province. It is represented throughout the domain by several batholiths, stocks and dykes (Fig. 1), showing distinct petrographic, geochemical and geochronological characteristics. Almeida et al. (1967) made one of the first attempts to classify the plutonic rocks of Borborema Province with respect to the Brasiliano Cycle, based his classification in their tectonic relatioship: i) syntectonic granitoids, subdivided into Itaporanga (porphyritic) ~o (equigranular) types and ii) tardi-tectonic granitoids, and Conceiça comprising the Catingueira and Itapetim types (Table 1). Subsequently, Brito Neves and Pessoa (1974) and Santos and Melo (1978), also working in the Borborema Province, more specifically in the Transverse Zone Domain, added an assortment of petrographic data et al. (1981), to the study by Almeida et al. (1967). Jardim de Sa ), using focusing on the Rio Grande do Norte Domain (Faixa Serido structural parameters divided the Brasiliano granitoids in three subtypes: Gx (basic to intermediate rocks), G3 (porphyritic or equigranular granites and granodiorites) and G4 (late leucogranite). In the Borborema Province, Sial (1987) classified four major groups of granitoids using geochemical data: Potassic Calc-alkaline, Calc (1994) alkaline, Trondhjemitic and Peralkaline. Jardim de Sa distinguished the suites basic to intermediate, porphyritic and leucogranitic, to which were also added shoshonitic (Galindo et al., 1997a) and alkaline (Galindo, 1993; Araújo et al., 1993; Hollanda, 1998; Nascimento, 1998, 2000). Ferreira et al. (1998) using petrographic and geochemical data divided the Brasiliano granitoids of the Borborema Province into nine groups, called High-K calc-alkalic magmatic epidote-free granitoids, High-K calc-alkalic magmatic

epidote-bearing granitoids, Calc-alkalic magmatic epidote-bearing granitoids, Shoshonitic granitoids, Peraluminous calc-alkalic granitoids, Trondhjemitic granitoids, Peralkalic granitoids, High-K metaluminous syenitoids and Ultrapotassic peralkalic syenitoids, five of which described in the Rio Grande do Norte domain (see details Table 1). Finally, the Brazilian Geological Survey (Angelim et al., 2006) using data from the literature, introduced new suites to the previous classification of Almeida et al. (1967). Angelim et al. (2006) grouped the granitic rocks found in the state of Rio ~o Joa ~o do Sabugi, Grande do Norte in five intrusive suites, called Sa Itaporanga, Dona In^ es, Catingueira and Umarizal. This article unifies the petrographic, geochemical (461 analyses of major and trace elements and 217 of rare-earth elements-REE), and geochronology (56 analyses: 38 UePb, 17 RbeSr and 1 SmeNd) data of several Ediacaran to Cambrian plutonic bodies found along the Rio Grande do Norte Domain (list shown in Table 2 and in the references). 2. Geochemical (and petrographic) characteristics The data used for classification were initially selected through analysis of geochemical data from the literature (list shown in Table 2 and in the references). Data processing excluded those with anomalous values and samples of doubtful origin. The results of the geochemical analysis plotted in variation and/ or discriminant geochemical diagrams are significantly different. There is a group of rocks whose mafic nature varies from basic to intermediate (rocks predominantly dioritic) that stand out from the other rocks, which are essentially felsic/acid (rocks predominantly granitic). The Harker type variation diagrams show that the first group is characterized by rocks that contain low to intermediate SiO2 (46.7e61.5%), are rich in Al2O3, Fe2O3t, MgO, CaO and TiO2, and


283

Fig. 1. Geological framework of the Rio Grande do Norte domain, NE Borborema Province, with emphasis on the Ediacaran to Cambrian magmatism (modified from Nascimento et al., 2000, Nascimento et al., 2008). Legend: a e Meso-Cenozoic covers; b e Shoshonitic suite; c e Porphyritic high-K calc-alkaline suite; d e Equigranular high-K calc-alkaline suite, and calc-alkaline suite; f e Alkaline suite; g e Charnockitic alkaline suite; h e Archean gneissicemigmatitic basement; i e Paleoproterozoic gneissicemigmatitic basement; j e group; k e Neoproterozoic transcurrent shear zones; l e Neoproterozoic contractionetranspression shear zones; m e Neoproterozoic extensional shear zones; n e cities; o e Serido state capital.

poor in K2O and Rb, while Zr and Nb content vary widely especially with respect to the second group (Figs. 2 and 3). This group shows affinity with rocks of shoshonitic series in discriminant diagrams of the magmatic series (Fig. 4). The second group of rocks may be divided into five different groups; however, not always in all diagrams used. Aegirine-augite and garnet bearing leuco-microgranites (primarily represented by ~o, Serra do Boqueira ~o and Olho the plutons Caxexa, Serra do Algoda D'Agua, in Fig. 1) are usually distinguished from other granitic rocks due to high Na2O content (average > 4%) and very low CaO (600 ppm), with low values of Y (70%) of these granitoids are calcic-alkalic, what is the case for PHKCalcAlk Suite. Their character is mainly determined by the high potassium (K2O from 3.6 to 6.8%) and low calcium (CaO usually less than 3.0%) levels. They comprise rocks of mostly ferroan, or ferrous to magnesian nature (Fig. 11d).

2.3. Equigranular high-K calc-alkaline suite (EHKCalcAlk) The rocks of this suite occur as dyke swarms (Fig. 13a) and sills or with isolated bodies, exemplified by the plutons of Capuxu, Santa Luzia, Angicos, Flores, Picuí, Macaíba and Dona Inez and in the context of massive polidiapirs (of the PHKCalcAlk suite) in Acari, de Espinharas and Catole do Rocha, for example. S~ ao Jose They essentially consist of medium-to fine-grained monzogranites (Fig. 13b). Plagioclase (oligoclase), microcline and quartz are the essential minerals. The accessory mineralogy is composed of biotite (±amphibole), titanite, epidote, apatite, zircon, allanite, tourmaline and opaques. Some facies of Picuí (Silva, 1993) and Dona Inez plutons (McMurry et al., 1987a; Borges, 1996) contain garnet. These rocks show SiO2 contents of 66.7e76.5%, with high K2O/ Na2O ratios (0.8e4.4%) (Table 5). Harker variation diagrams (Fig. 2) show a negative correlation for Al2O3, Fe2O3t, MgO, CaO, TiO2 and Na2O (the latter with some dispersion) similar to PHKCalcAlk suite, while K2O is positively correlated, although with some dispersion. The negative correlation of these elements is possibly due to the fractionation of plagioclase, titanite, opaque minerals, biotite and allanite, also seen in the PHKCalcAlk suite. Ba, Sr, and Zr, are compatible; Rb tends to be incompatible (Fig. 3) while Nb and Y appear dispersed. REE patterns displays a pronounced negative Eu anomaly (Eu/Eu* ¼ 0.2e0.9) (Fig. 10c), sometimes standing out from preceding suites. The heavy rare earth elements (HREE) are comparatively lower than in other suites (except for Alc), in addition to having the highest LaN/YbN values (0.4e588.2). Geochemically, this suite includes mostly peraluminous and also metaluminous rocks with A/CNK ratios ranging from 0.9 to 1.4, usually larger than in the other surveyed suites. The geochemical


289

Table 3 Representative analyses of major, trace and rare earth elements, some geochemical parameters and minimum and maximum values of 122 (major and trace elements) and 68 (rare earth elements) analyses for shoshonitic suite in Rio Grande do Norte domain. Elements

RC-7A

ED113

ED109

SiO2 (wt%) Al2O3 Fe2O3t MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Total

46.70 15.60 13.20 0.20 7.70 9.60 3.30 1.80 1.60 0.22 0.95 100.87

48.27 15.78 13.08 0.17 5.23 8.83 3.52 1.45 2.08 0.50 0.74 99.65

49.23 16.11 12.67 0.14 5.10 8.75 3.45 1.08 1.87 0.55 0.72 99.67

Ba (ppm) Rb Sr Nb Y Zr

115 27 180 8 15 23

868 32 604 24 43 271

733 22 698 16 27 155

Na2O þ K2O K2O/Na2O FeOt/(FeOt þ MgO)

5.10 0.55 0.61

4.97 0.41 0.69

4.53 0.31 0.69

La (ppm) Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu SREE

19.60 37.80 e 12.83 2.37 1.00 2.44 e 1.99 e 0.63 e 0.55 0.06 79.27

54.81 130.00 e 54.47 11.76 3.06 9.85 e 7.26 e 3.58 e 2.91 0.40 278.10

45.35 98.84 e 40.85 8.16 2.50 6.69 e 4.86 e 2.45 e 2.00 0.27 211.97

VC-639 52.21 15.85 11.11 0.14 3.28 5.55 3.42 4.08 2.16 1.55 0.30 99.65 2015 148 697 29 47 329 7.50 1.19 0.75 94.20 207.30 23.48 92.10 15.90 3.99 11.92 1.78 8.94 1.68 4.21 0.61 3.76 0.56 470.43

RS3-53

AC4B

MS-19A

Q-270

F3C

RS3-62

MineMax

54.44 15.41 9.75 0.16 4.34 5.62 3.24 3.96 1.69 0.53 1.42 100.56

55.77 17.96 6.46 0.08 2.25 4.19 3.90 5.89 1.23 0.59 0.97 99.29

56.44 17.96 7.69 0.08 1.70 4.30 4.10 4.84 1.29 0.48 0.38 99.26

57.75 15.41 9.75 0.16 1.26 4.27 3.83 4.30 1.10 0.52 1.17 99.52

60.00 16.60 6.58 0.08 2.37 4.41 3.87 3.27 1.20 0.43 0.57 99.38

61.46 13.52 5.77 0.14 4.68 4.37 2.90 5.32 0.75 0.59 0.84 100.34

46.7e61.5 13.5e19.8 4.9e14.9