Browsing by Author "Aranda, Ramon de Oliveira"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Metallogenetic Mn-model of the Rhyacian-aged Buritirama Formation, Carajás domain (Amazon Craton).
    (2021) Salgado, Silas Santos; Caxito, Fabrício de Andrade; Silva, Rosaline Cristina Figueiredo e; Uhlein, Gabriel Jubé; Nogueira, Leonardo Brandão; Nalini Júnior, Hermínio Arias; Aranda, Ramon de Oliveira
    The Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Caraj ́ as domain with the Paleoproterozoic Bacaj ́ a domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Loma- gundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox- sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (− 2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn- oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO3 2− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi- like δ13C allows to correlate the Buritirama Formation with the Aguas ́ Claras Formation within the Caraj ́ as domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton.
  • No Thumbnail Available
    Item
    Petrology of the Afonso Cláudio intrusive complex : new insights for the Cambro-Ordovician post-collisional magmatism in the Araçuaí-West Congo Orogen, Southeast Brazil.
    (2020) Aranda, Ramon de Oliveira; Chaves, Alexandre de Oliveira; Medeiros Junior, Edgar Batista de; Venturini Junior, R.
    The Afonso Cláudio Intrusive Complex (ACIC) is an igneous body located in the Espírito Santo state, Southeastern Brazil. It is inserted in the geological setting of the post-collisional G5 plutonic Supersuite, related to the extensional collapse stage of the Araçuaí-West Congo Orogen (AWCO). This study presents integrated data of field relationships, petrography, whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes that contributed to understand ACIC petrology. The ACIC intruded in pre-collisional orthogneisses and Nova Venécia Complex paragneisses of the AWCO. It is constituted by two monzogabbro/monzodiorite off-centered mafic cores surrounded by quartz monzonite. Mingling and mixing zones were mapped between these rocks, where jotunite and quartz mangerite occur. Host rock enclaves are observed enclosed by monzogabbro, monzodiorite and quartz monzonite, as well as monzogabbro/monzodiorite enclaves in the quartz monzonite. The ACIC rocks are enriched in LILE and LREE, showing alkali-calcic post-collisional geochemical signature. Zircon U-Pb dating revealed crystallization ages of 480.9 ± 3.2 Ma related to quartz monzonite and 496.5 ± 3.6 Ma to monzogabbro. Both rocks show negative zircon εHf (t) values (with average values of −11.78 and −10.41, respectively) and TDM ages of 1.79 Ga to quartz monzonite and 1.72 Ga to monzogabbro. Supported by presented data, two models can be proposed to the ACIC evolution during the collapse stage of the AWCO and both considering crustal contamination, mixing/mingling and assimilation associated to fractional crystallization. One is based on coeval mantle and crustal melting, with magmas interaction to generate an alkali-calcic magma, whose crystallization produced the monzogabbro and monzodiorite. With the continuity of the orogeny collapse, these mafic rocks would have melted and contributed to generate felsic magmas that crystalized as quartz monzonite. The second one argues in favor to mantle magma intrusion in a magmatic chamber where the nearby crustal rocks melted and the different magmas interacted between them. Monzogabbro and monzodiorite would have been generated by fractional crystallization of the mafic magmas and the quartz monzonite by crystallization of the felsic magmas. Due to the similarities among the post-collisional plutons in the AWCO, the proposed models may explain the petrogenesis of other similar plutons in this orogenic system.