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Fácies, elementos arquiteturais e análise de paleocorrentes da formação Tacaratu: sedimentação Ordovício-Siluriana da sub-bacia de Tucano Norte, Brasil

2025-04-24T13:56:51Z

Título: Fácies, elementos arquiteturais e análise de paleocorrentes da formação Tacaratu: sedimentação Ordovício-Siluriana da sub-bacia de Tucano Norte, Brasil Autor(es): Santana, Mateus do Nascimento Abstract: The Paleozoic sedimentary record of Northeastern Brazil includes the basal successions of the intracratonic basins of Parnaíba, Araripe, and Tucano-Jatobá, as well as smaller intracratonic basins. Sedimentation during this interval began in the Ordovician from continental-scale alluvial systems that drained the Neoproterozoic orogenic terrains of Gondwana. The Tacaratu Formation represents the basal Paleozoic interval in the Northern Tucano Sub-basin, Northeastern Brazil. This unit is predominantly composed of coarse-grained siliciclastic deposits associated with braided fluvial systems. This study investigates the sedimentary record of the Tacaratu Formation, focusing on facies, facies associations, and paleocurrents. Detailed fieldwork was conducted at 10 localities within the Tacaratu Formation, aiming to analyze facies, deposit geometry, bounding surfaces, and paleocurrents of the unit. Eleven facies were identified, allowing the distinction of four facies associations: FA1 - gravel and sandy bars, FA2 - sandy bars and bar tops, FA3 – coarse-grained middle channel bars, and FA4 - overbank fines. Paleocurrent analysis revealed a predominant northward paleoflow trend, consistent with previous studies, along with local variations suggesting low-sinuosity wandering channel morphologies, previously interpreted as braided. These findings refine the understanding of the sedimentary processes that controlled the deposition of the Tacaratu Formation, offering new insights into the depositional history of early fluvial systems of the Western Gondwana

Química mineral de cristais de biotita em enclaves sieníticos em granitos do Stock Granítico Glória Sul, Domínio Macururé, sul da Província Borborema

2025-04-15T15:02:39Z

Título: Química mineral de cristais de biotita em enclaves sieníticos em granitos do Stock Granítico Glória Sul, Domínio Macururé, sul da Província Borborema Autor(es): Menezes, Asayuki Rodrigues Abstract: Biotite is an important constituent in the syenitic microgranular enclaves hosted in granites of the Glória Sul Stock, located in the central region of the Sergipano Orogenic System. These enclaves are centimetric, rounded and ellipsoidal, have finer grain size than the surrounding granites and are composed of microcline, orthoclase, albite-oligoclase, diopside, quartz, hornblende, titanite, apatite, zircon, magnetite, ilmenite, and pyrite. The textures present in the enclaves imply to rapid cooling (fine-grained, acicular apatite and zircon and zonation in plagioclase). The chemical data allowed the brown mica from these enclaves to be classified as Mg-biotite and Fe-biotite. The compositional evolution of the investigated biotite crystals is essentially controlled by two substitutions (VIR2+ + 2 VIAl3+ ═ VI□ + 2 VISi4+ and VIR2+ + VITi ═ 2VIAl3+) that reflect aluminum and titanium decrease. The biotite chemistry of the enclaves indicates magma crystallization of the magnetite series of calcium-alkaline nature. The chemical signature of the crystals studied also indicates that the magma that formed it has a complex evolution and results from the mixture between mantle (trachytic) and crustal (rhyolitic) magma. Thermobarometry indicated that crystallization of biotite in the syenitic microgranular enclaves occurred at approximately 6.3 km between temperatures 788-975 °C. The similarity of the thermobarometric data of biotite from the enclaves and the surrounding granites suggests that these values correspond to that of the physical conditions of the interaction between trachytic (enclaves) and rhyolitic (granite) magmas. The petrogenesis established for the enclaves are coherent with the collisional environment established for the Sergipe Orogenic System.

Geologia e Geoquímica do Stock Serra das Intãs, Sistema Orogênico Sergipano, NE Brasil

2025-04-15T14:41:34Z

Título: Geologia e Geoquímica do Stock Serra das Intãs, Sistema Orogênico Sergipano, NE Brasil Autor(es): Teles, Danilo dos Santos Abstract: The Serra das Intãs Stock (SSI) is a 5 km2 stock with an ellipsoid shape, with a NW- SE orientation that occupies the axial region of a synform located between the municipalities of Gararu and Porto da Folha. This stock is intrusive in the metasediments of the Macururé Group of the Sergipano Orogenic System. The SSI is composed of muscovite biotite monzogranites, holeucocratic of whitish gray colors, medium to fine granulation, equigranular texture, locally with gneiss structure. Biotite is the mafic mineral in these rocks and the muscovite is associated with biotite, these micas include subhedral crystals of apatite, titanite and zircon. Chemical analysis of feldspar and biotite allowed to identify the composition of plagioclase crystals as having normal compositional zonation, varying from albite (An2-10%) to oligoclase (An10,1-15,4%) and alkali feldspar (Or91-94 , 5% Ab5.4- 9.7%). The chemical data of biotite crystals allowed to classify them as Fe-biotite, rebalanced primers associated with orogenic calciumalkaline magmas. The rocks are peraluminous to metalluminous, and have affinities with the calcium-alkaline series of high potassium and shoshonítica, that stand in the field of the cordilleran magnesian granites. They present enrichment of LILEs in relation to HFSE, with valleys pronounced in Nb, Ta, P and Ti; and have enrichment of the LREE in relation to the HREE, with weak negative anomalies in Eu. The geochemical signature of the SSI is compatible with syn-collisional granites of arc environment.

Petrografia e química mineral das rochas alcalinas do Batólito Sienítico Itabuna, província Alcalina do Sul do Estado da Bahia

2025-04-10T18:28:55Z

Título: Petrografia e química mineral das rochas alcalinas do Batólito Sienítico Itabuna, província Alcalina do Sul do Estado da Bahia Autor(es): Leandro, Marcel Vinicius Santos Abstract: The only occurrence of SiO2 subsaturated alkaline rocks in the São Francisco Craton is bounded by the Southern Bahia Alkaline Province (SBAP). A province formed by a neoproterozoic anorogenic alkaline magmatism intrusive in granulitic and gneissic-migmatitic rocks from the São Francisco Craton. Among the various plutons that make up SBAP rocks of the largest body, the Itabuna Sienitic Batholith (IBS), were studied in this work. It outcrops in the northern portion close to the cities of Itabuna, Itajuipe and Uruçuca. The Itabuna Sienitic Batholith consists of syenites, monzonites, foid syenites and in smaller volumes diorites and gabbros. Representative rocks from IBS were investigated with classical and electronic petrography. Chemical minerals analysis was obtained with a Wavelength Dispersive Spectrometer (WDS) coupled to an Electron Probe Microanalyzer (EPMA) and Dispersive Energy Spectrometer (EDS) coupled to a Scanning Electron Microscopy. The rocks have fine to coarse granulation. Essential minerals are alkali feldspar, plagioclase and nepheline, which together with biotite, amphibole and clinopyroxene are the most frequent phenocrysts. The matrix is composed mainly of alkaline feldspars, plagioclase and nepheline. Plagioclase Anorthite contents vary from albite to labradorite. Chemically biotite corresponds to siderophyllite, lepidomelane and Fe-biotite. Clinopyroxene was classified as diopside, hedenbergite and augite. The amphibole compositions have great chemical variations that define them as belonging to the groups of the Calcium, Fe-Mg-Mn-Li and Na-Ca amphibole. The accessory minerals present are apatite, sodalite, cancrinite, ilmenite, magnetite, pyrite, chalcopyrite, zirconolite, olivine, allanite, baddeleyite, zircon, calcite, monazite, barite, bastnasite and thorite. Primary crystal compositions were identified in biotite, amphibole, allanite and zirconolite. The coupled substitution ETR3++ Si4+= Ca2++P5+ was identified in the apatite crystals and can assist in the formation of monazite crystals. In the studied rocks, small crystals indicating the action of magmatic fluids such as carbonates, monazite and thorite are present. Magmatic temperatures (<989 o C), mean pressures for placing magma (<5.2 kbar) and high oxygen fugacity were inferred on clinopyroxene crystals. Temperatures <790 o C and pressures <2.2 kbar were obtained in the primary biotite crystals. And post-magmatic parameters based on the pairs of ilmenite and magnetite exsolution (maximum temperatures of 765 o C). Fractional crystallization was inferred as the main process responsible for the evolution of the rocks of the Itabuna Sienitic Batholith, a hypothesis also adopted for other SBPA plutons. The compilation and interpretation of the generated data was synthesized in the form of a scientific article.