Navegando por Assunto "Granito tipo-A"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Estudo geoquímico e isotópico (U-Pb/Lu-Hf) de novas ocorrências de granitos tipo-A no Domínio Carajás.
(Universidade Federal do Pará, 2023-04-18) AFONSO, Jully Mylli Lopes; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Carajás Mineral Province was the setting of an extensive magmatic event, marked by anorogenic granitic intrusions and associated dykes. Geological mapping methods carried out in the central portion of the Canaã dos Carajás Domain allowed the individualization of two new anorogenic granitic stocks. These granites occur as isotropic, semicircular shaped stocks, which occur as intrusions in Archean granitic rocks of the Vila União and Cruzadão granite suites. And are classified as monzogranites and divided into biotite-monzogranite equigranular facies (BMzE) and biotite monzogranite porphyritic (BMzP) facies, where biotite is the main ferromagnesian mineral and are often associated with fluorite, in addition to allanite, zircon, apatite and epidote. They are meta- to peraluminous, with a high content of HSFE iron-related with a reduced to moderately oxidized character. When compared to others type-A granites of the Carajás Mineral Province, these granites display significant contrasts with the Jamon and Velho Guilherme suites and are similar to those observed in the Serra dos Carajás suite and, consequently, the Gogó da Onça Granite. Geochronological data of U-Pb in zircon revealed that crystallization age of these granites is ~1893 ± 13 Ma, and associated with isotopic data of Lu-Hf indicate crustal sources for these rocks, with strongly negative ƐHf values ranging from -14 at -17°C and TDM between 3.38 Ga to 3.57 Ga. Based on this informations, the geochemical modeling imply that these granites were generated from partial melting of tonalitic granites of similar composition to the Arco Verde Tonalite or Caracol Tonalite from the Rio Maria Domain. Such results are suitablewith the hypothesis that these granites were generated from a fusion of Archean granitoids and placed in a shallow crust between 1.88 and 1.86 Ga.
Acesso aberto (Open Access)
Petrogênese dos granitos Manda Saia e Marajoara: contribuições para a definição da natureza do magmatismo paleoproterozóico da Província Carajás.
(Universidade Federal do Pará, 2024-12-13) SANTOS, Rodrigo Fabiano Silva; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; https://orcid.org/0000-0001-7976-0472
The Marajoara (MJG) and Manda Saia (MSG) granites are located in southeastern Pará State, Brazil, and represent circular intrusions with stock dimensions embedded in Mesoarchean rocks of the Rio Maria Domain, in the central-southern portion of the Carajás Province. These rocks outcrop as extensive pavements, exhibiting no solid-state deformation features (isotropic aspect) and frequently containing angular enclaves of the surrounding host rocks. The MJG comprises equigranular biotite monzogranite (eBMzG) and heterogranular (hBMzG) varieties, as well as porphyritic (pME) and microgranular enclaves (ME) restricted to the hBMzG facies. Quartz content and plagioclase/microcline ratios vary significantly, allowing these rocks to be classified from syenogranitic to monzogranitic, and even granodioritic in the case of microgranular enclaves. They are peraluminous granites, similar to ferroan granites with high K2O+Na2O/CaO and FeOt/(FeOt+MgO) ratios, enriched in Rb, Zr, Y, Nb, F, and heavy REEs, with more evolved facies displaying low Sr and Ba contents. In REE patterns, negative Eu anomalies are prominent, and heavy REEs show a gradual increase with magmatic differentiation. These granites fall within the intraplate granite field and exhibit geochemical affinities with A-type granites. Their FeOt/(FeOt+MgO) ratios align with typical oxidized (hBMzG and pME) and reduced (eBMzG) A-type granites, while the MSG displays a moderately reduced character. The ME, however, show affinity with magnesian and calcalkaline series granites. According to biotite mineral chemistry, MSG and the hBMzG facies of MJG fall within the magnetite series field, while eBMzG rocks are similar to ilmenite series rocks. SHRIMP zircon U–Pb analyses provide crystallization ages of 1884 ± 11 Ma for MJG and 1866 ± 10 Ma for MSG (LA–SF–ICP–MS). Lu–Hf isotopic data indicate ƐHf(t) between - 11 and -18 and Hf-TDMC from 3.2 to 3.6 Ga for MJG; and ƐHf(t) between -13 and -19 and Hf-TDMC from 3.3 to 3.6 Ga for MSG. The compositional gaps among the various MJG varieties suggest that their magmas are not cogenetic. Geochemical modeling suggests that MJG and MSG were generated by partial melting of tonalitic rocks, with occasional metasedimentary contributions, at a melting rate ranging from 16 to 18%, with a residual assemblage of plagioclase, quartz, biotite, magnetite, and ilmenite. Felsic and mafic magma mixing played an important role in the emplacement. The enclaves represent enriched lithospheric mantle-derived magmatism injected into the magma chamber during the subduction process, interacting to varying degrees with the magma forming the Marajoara granite. This hypothesis may be reinforced by the occurrence of a 1.88 Ga diabase-porphyritic granite composite dyke in the Rio Maria region. The proposed model suggests that the granitic magma initially formed a magma chamber, followed by repeated mafic magma injections, resulting in small-scale convection. Subsequently, large volumes of hot mafic magma entered the chamber, leading to mixing processes. Microgranular and porphyritic enclaves were formed due to magma mixing in areas where there were temperature contrasts between felsic and mafic magmas. The results presented in this study highlight the importance of the Archean crust in the origin of Paleoproterozoic granites, which were emplaced in shallow crustal levels through a dyke feeder system as a result of extensional tectonics.
Acesso aberto (Open Access)
Petrografia e geoquímica do Granito Manda Saia, Província Carajás.
(Universidade Federal do Pará, 2020-09-09) SANTOS, Marcelo Reis; OLIVEIRA, Davis Carvalho de; http://lattes.cnpq.br/0294264745783506; 0294264745783506
The Manda Saia granite is located to southeast of the of Xinguara town and it is represented by two semicircular plutons separated by the Mesoarquean basement of the Rio Maria Domain. The bodies crosscut in the northern portion the Mesoarquean TTG granitoids and the Rio Maria Granodiorite, and in the south, eastern and western portions they are intrusive in the metabasalts of the sequence greenstone belt of the Babaçu Group. The Manda Saia pluton is formed by rocks of isotropic aspect, grayish pink in color and monotonous textural variation. They are hololeucocratic rocks of medium-to-coarse heterogranular texture, occasionally porphyritic, which are classified as monzo- and syenogranites. Biotite is the main ferromagnesian mineral and amphibole is rare and interstitial. Secondary minerals are clay minerals, sericite, muscovite, fluorite and chlorite. Manda Saia pluton is formed by peraluminous rocks that present a restricted and high SiO2 contents (74.80 and 77.70wt.%), and high Fe/(Fe+Mg) ratios. Their REE pattern is marked by enrichment in light and heavy REE and moderate negative Eu anomaly. The pluton can be classified as ferrous type-A granite and akin to the reduced types and those most evolved from the oxidized granites of the Carajás Province. The occurrence of interstitial amphibole identified in the Manda Saia granite also is observed in the plutons of the Velho Guilherme Suite. On the other hand, the frequent occurrence of magnetite combined with the compositional aspects of its rocks, also shows that the Manda Saia granite is akin to the leucogranitic facies of the oxidized granites from Jamon Suite. The emplacement of the Granite Manda Saia is linked to extensional tectonics and the transport of magma that resulted in the emplacement of the plutons in shallow crustal levels (~ 1.0 ± 0.5 kbar) through a dyke feeding system.