EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

Notícias

A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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A perspective on potassic and ultrapotassic rocks : constraints on the Paleoproterozoic late to post-collisional event in the São Francisco paleocontinent.
(2021) Bersan, Samuel Moreira; Danderfer Filho, André; Storey, Craig Darryl; Bruno, Henrique; Moreira, Hugo Souza; Abreu, Francisco Robério de; Lana, Cristiano de Carvalho; Gonçalves, Leonardo Eustáquio da Silva; Nahas, Isabela
The late- to post-collisional stage in orogenic systems is characterized by the coeval existence of bimodal potassic to ultrapotassic magmatic activity related to partial melting of an enriched lithospheric mantle together with crustal derived melts. In this paper, we present new whole rock geochemical analyses combined with zircon and titanite U–Pb and zircon Hf isotopic data from potassic to ultrapotassic rocks from six plutons that occur within the Archean Itacambira-Monte Azul block (BIMA), to discuss their petrogenesis and the tectonic implica- tions for the São Francisco paleocontinent. The new U–Pb ages range from ca. 2.06 Ga to 1.98 Ga and reveal long- lasting potassic magmatism within the BIMA, which is within the late- to- post-collisional stage of the São Francisco paleocontinent evolution. The ultrapotassic rocks are compatible with a fluid-related metasomatized mantle source enriched by previous subduction events, whereas the potassic rocks are bimodal and have a tran- sitional shoshonitic to A-type affinity. These rocks have a hybrid nature, possible related to the mixing between the mafic potassic/ultrapotassic rocks and high temperature crustal melts of the Archean continental crust. Our results also show an increase of within-plate signature towards the younger potassic magmas. The participation of an important Archean crustal component in the genesis of these rocks is highlighted by the common and oc- casionally abundant occurrence of Archean inherited zircons. The Hf isotopic record shows that most of the zircon inheritance has dominantly subchondritic εHf(t) values, which fits a crustal reworking derivation from a similar Eo- to Paleoarchean precursor crust. However, the presence of juvenile 2.36 Ga zircon inheritance in an ultrapotassic sample reveal the existence of a hidden reservoir that is somewhat similar to the described for the Mineiro Belt in southern São Francisco paleocontinent.
Drill core structural analysis and extensional-contractional controls on the sulfide mineralization at the Ambrosia Sul zinc deposit, Vazante group, Western São Francisco craton, Brazil.
(2022) Botura Neto, Basilio; Danderfer Filho, André
The Ambrósia Sul Zn-(Pb) sulfide deposit is located in the southern section of the Vazante Group, which is the border area between the Brasília belt and the southwestern edge of the São Francisco craton. This region is characterized by a typical karst environment in a tropical climate that is commonly represented by the intense development of thick and uneven soil cover, which hinders structural geologic mapping. A survey with oriented core samples allowed a full structural investigation and description of structures such as faults, fractures, veins, bedding, folds, foliations, and lineations. The structural analysis suggests an extensional phase with down block in the west, during which normal faults and high-angle veins were generated, followed by a contractional phase associated with the reactivation of bedding planes, the nucleation of reverse faults and low-angle veins, and east- vergent folding. The zinc sulfide ore bodies are preferentially hosted in high-angle veins and in cataclastic rocks generated during the extension. Low-angle veins, rarely mineralized with Zn, cut the high-angle veins, suggesting that the mineralization event lasted even during the tectonic inversion phase. The regional context indicates that the Ambrósia Sul deposit formed in the bulge region of the foreland basin and that it was affected first by an extensional phase during its nucleation and subsequently by a compressive phase with the advancement of thrusting in the Brasília belt to the east.
Stratigraphic, isotopic, and geochronological record of a superposed pro- foreland basin in the eastern São Francisco craton during west Gondwana amalgamation.
(2020) Rossi, Ariadne Verônica Andrade; Danderfer Filho, André; Bersan, Samuel Moreira; Kelmer, Luiza Rocha; Tavares, Túlio Delôgo; Lana, Cristiano de Carvalho
The Três Marias Formation, a siliciclastic succession that occurs at the top of the Bambuí Group, has recorded the filling of the Brasiliano foreland basin that developed on the São Francisco craton. At the eastern portion of this craton, the Três Marias Formation outcrops in Gorutuba ridge, north of Minas Gerais, which area was in- vestigated by using field work, stratigraphic analysis, and isotopic U–Pb and Lu–Hf analysis. In this area, the Três Marias Formation includes molasse deposits composed mainly of arkoses and hybrid conglomerates. The arkose sediments came into the basin through a fluvio–deltaic system located to the northeast and were reworked in a siliciclastic shelf under the influence of waves, tides and storm currents. The paleocurrents indicate a coastline around the NW and NE directions, with current flows reworking sediments parallel and transversal to the coast. The detrital zircon grains indicate a 555 ± 17 Ma maximum age of the deposition for this unit, and its main sources are related to granitoids from the pre-orogenic and pre-to syn-collisional stages of the Araçuaí orogen (ca. 630–560 Ma). The filling of the foreland basin system created in response to the Araçuaí fold–thrust belt is younger than the one existing in the occidental portion of Bambuí basin, which is related to the Brasília fold and thrust belt. Therefore, the final filling of the Bambuí basin would have been controlled by the development of these two-fold–thrust belts throughout the margins of the São Francisco craton during the assembly of West Gondwana.
Record of Early Tonian mafic magmatism in the central Espinhaço (Brazil) : new insights for break-up of the Neoproterozoic landmass ancestor of São Francisco-Congo paleocontinent.
(2020) Moreira, Helen Fonseca; Danderfer Filho, André; Costa, Alice Fernanda de Oliveira; Bersan, Samuel Moreira; Lana, Cristiano de Carvalho; Queiroga, Gláucia Nascimento
Petrological characterization, U–Pb geochronology, Lu–Hf analyses and major and trace element data from mafic intrusions in the Central Espinhaço (central portion of the Brazilian shield) are used here to investigate the geological significance of the Early Neoproterozoic magmatism in the context of the S~ao Francisco-Congo paleocontinent. These mafic bodies are represented by medium to coarse-grained metagabbros with plagioclase, amphibole and clinopyroxene. Zircon U–Pb isotopic data from two samples yielded weighted mean 206Pb/238U ages of 895 3.4 Ma (MSWD ¼ 1.7) and 896 2.4 Ma (MSWD ¼ 0.64), regarded as the best estimates for the crystallization age of these mafic rocks. Major and trace element data (including REEs) show that the gabbros originated from a subalkaline tholeiitic magma, typical of intraplate magmatism. Such rocks are slightly enriched in LREEs and LILEs and depleted in HFSEs. Our new isotope and geochemical data, along with regional knowledge, indicate that these metagabbros mark the beginning of an important Tonian-age extensional tectonic event of the landmass of which the S~ao Francisco-Congo paleocontinent was part (Rodinia supercontinent or Central African block?). We furthermore suggest that these rocks belong to a prominent suite of Tonian-age mafic rocks that mark a diachronic breakup attempt of this landmass which may have occurred from south to north along the Espinhaço mountain range.
Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent : insights from the shoshonitic high Ba–Sr Montezuma granitoids.
(2020) Bersan, Samuel Moreira; Costa, Alice Fernanda de Oliveira; Danderfer Filho, André; Abreu, Francisco Robério de; Lana, Cristiano de Carvalho; Queiroga, Gláucia Nascimento; Storey, Craig Darryl; Moreira, Hugo Souza
New, integrated petrographic, mineral chemistry, whole rock geochemical, zircon and titanite U–Pb geochronology, and zircon Hf isotopic data from the Montezuma granitoids, as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex, provides new insights into the late- to post-collisional evolution of the northeastern S~ao Francisco paleocontinent. U–Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca. 2.2 Ga to 1.8 Ga and comprise distinct groups. Group I have crystallization ages between ca. 2.15 Ga and 2.05 Ga and are interpreted as inherited grains. Group II zircon dates vary from 2.04 Ga to 1.9 Ga and corresponds to the crystallization of the Montezuma granitoids, which were constrained at ca. 2.03 Ga by the titanite U–Pb age. Inverse age zoning is common within the ca. 1.8 Ga Group III zircon ages, being related to fluid isotopic re-setting during the Espinhaco rifiting event. Zircon εHf(t) analysis show dominantly positive values for both Group I ( 4 to þ9) and II ( 3 to þ8) zircons and TDM2 model ages of 2.7–2.1 Ga and 2.5–1.95 Ga, respectively. Geochemically, the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids, enriched in LILES and LREE, with high to moderate Mg# and depleted in some of the HFSE. Their lithochemical signature, added to the juvenile signature of both inherited and crystallized zircons, allowed its classification as a shoshonitic high Ba–Sr granitoid related to a late- to post-collisional lithosphere delamination followed by asthenospheric upwelling. In this scenario, the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc, being these hybrid magma interpreted as the source of the Montezuma granitoids. The Corrego Tinguí Complex host rocks are akin to a syn- to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks. The results presented in this study have revealed the occurrence of juvenile rocks, probably related to an island arc environment, that are exotic in relation to the Paleo- to Neoarchean crust from the S~ao Francisco paleocontinent’s core.
Ferroan alkalic volcanism associated with Calymmian rifting in the Paramirim aulacogen, São Francisco craton, Brazil : new insights from lithofacies analysis and evidence of mantle-derived alkaline H2O-rich metasomatic fluids affecting ancient crustal materials.
(2020) Santos, Cláudia dos; Danderfer Filho, André; Queiroga, Gláucia Nascimento; Zincone, Stéfano Albino; Castro, Marco Paulo de; Lana, Cristiano de Carvalho
Rift-related volcanism is widely used in models of supercontinent reconstruction, while the associated metasomatic fluids provide information about the mantle-crust process during intracrustal melting events. The Paleoproterozoic/Mesoproterozoic Paramirim aulacogen corresponds to multiple intracratonic rift cycles that register many basin developing events. Intense volcanic activity is recorded in some rift events, but the volcanic lithofacies and their petrogenesis are poorly constrained. Herein, we present lithofaciological characterization, whole-rock and mineral chemistry, and U-Pb and Lu-Hf isotope data from the 1.58 Ga volcanic rocks. Trachytic and trachy-andesitic lava flows and primary to secondary volcaniclastic lithotypes characterize this volcanism. The primary volcaniclastic rocks resulted from direct volcanic activity and can be divided into pyroclastic and hydroclastic lithofacies associations. The pyroclastic lithotypes correspond to air-fall, density currents and blockand-ash flow deposits formed in explosive eruptions; hydroclastic lithotypes are represented by hyaloclastites and peperites, reflecting effusive eruptions and interactions between magma, water and sediments. The secondary volcaniclastic lithotypes resulted from late-stage reworking processes and consist of debris flows, ephemeral streams associated with high energy and gravitational flow deposits. The lava flows show well-preserved primary volcanic features, such as magma flow textures and euhedral phenocrysts. Based on petrographic and chemical characteristics, associated with negative ɛHf(t) values, we infer that high melt rate of an ancient crust, previously metasomatized by H2O-rich alkaline mantle-derived fluids, generated the alkalic ferroan lavas. These fluids promoted potassic and sodic metasomatism that affected all the volcanic rocks, modifying the chemistry of the feldspars to pure orthoclase (Or96-98) and albite (Ab98-100). In some lavas, a higher concentration of Na-rich fluids synthesized aegirine at a minimum temperature of 200 °C and promoted its peralkaline character. The potassic-sodic metasomatism influenced the volcano-sedimentary sequence of the Pajeú Group and the oldest rocks of the basement but did not affect the overlying sedimentary sequences, indicating that fluids ceased with the end of volcanism. We suggest that the H2O-rich alkaline fluids arose by focused degassing in response to a rising asthenospheric mantle during the Calymmian rift of the Paramirim aulacogen.
Stratigraphic, isotopic, and geochronological record of a superposed proforeland basin in the eastern São Francisco craton during west Gondwana amalgamation.
(2020) Rossi, Ariadne Verônica Andrade; Danderfer Filho, André; Bersan, Samuel Moreira; Kelmer, Luiza Rocha; Tavares, Túlio Delôgo; Lana, Cristiano de Carvalho
The Três Marias Formation, a siliciclastic succession that occurs at the top of the Bambuí Group, has recorded the filling of the Brasiliano foreland basin that developed on the São Francisco craton. At the eastern portion of this craton, the Três Marias Formation outcrops in Gorutuba ridge, north of Minas Gerais, which area was investigated by using field work, stratigraphic analysis, and isotopic U–Pb and Lu–Hf analysis. In this area, the Três Marias Formation includes molasse deposits composed mainly of arkoses and hybrid conglomerates. The arkose sediments came into the basin through a fluvio–deltaic system located to the northeast and were reworked in a siliciclastic shelf under the influence of waves, tides and storm currents. The paleocurrents indicate a coastline around the NW and NE directions, with current flows reworking sediments parallel and transversal to the coast. The detrital zircon grains indicate a 555 ± 17 Ma maximum age of the deposition for this unit, and its main sources are related to granitoids from the pre-orogenic and pre-to syn-collisional stages of the Araçuaí orogen (ca. 630–560 Ma). The filling of the foreland basin system created in response to the Araçuaí fold–thrust belt is younger than the one existing in the occidental portion of Bambuí basin, which is related to the Brasília fold and thrust belt. Therefore, the final filling of the Bambuí basin would have been controlled by the development of these two-fold–thrust belts throughout the margins of the São Francisco craton during the assembly of West Gondwana.
Basement controls on cover deformation in eastern Chapada Diamantina, northern São Francisco Craton, Brazil : insights from potential field data.
(2019) D'Angelo, Taynara; Barbosa, Maria Sílvia Carvalho; Danderfer Filho, André
The Proterozoic sedimentary cover in eastern Chapada Diamantina recorded positive inversion tectonics at the Paramirim aulacogen during Neoproterozoic times. Additionally, geological evidence suggests that although the basement was not involved in the contractional tectonics, it exerted control on cover deformation. The Euler deconvolution, based on aeromagnetic and gravimetric databases, integrated with geological framework, was used to delineate the structures and deep architecture of the crystalline basement and to understand their relationships with cover deformation. The 3D view of Euler deconvolution profiles show a graben and horst geometry in the basement architecture. Horsts and grabens are limited by NNW-SSE, N-S and E-W normal faults, which nucleated during two extensional events and favored for deep Archean-Paleoproterozoic discontinuities. The first event was related to the development of a half-graben that had a NNE-SSE-oriented eastern boundary and that was filled with rocks of the Chapada Diamantina Group. The second event gave rise to an asymmetrical graben that evolved from dextral strike-slip displacement and was filled by rocks of the Una Group in the Irecê domain. In the late Neoproterozoic, two contractional, thin-skinned cover deformations with ENE-WSW and N-S shortening directions affected the Chapada Diamantina and Irecê domains. Our geophysical models reveal a parallelism between the thin-skinned structures and N-S and E-W normal faults, interpreted in the crystalline basement, suggesting a control on strain and stress distribution during cover deformation. During the second contractional tectonic event, the NNW-SSE and N-S lineaments at the boundaries of the Irecê domain were reactivated, producing Ubiaí and Serra da Babilônia brittle shear zones in the sedimentary cover, respectively. In summary, the superposed intracratonic basin formation was controlled by older structures in the crystalline basement, while the inversion tectonics was controlled by the geometry of these basins.
Geoquímica e geocronologia da Suíte Paciência : implicações para o fim da evolução riaciana do Bloco Itacambira-Monte Azul.
(2018) Bersan, Samuel Moreira; Danderfer Filho, André; Abreu, Francisco Robério de; Lana, Cristiano de Carvalho
Diversos corpos plutônicos alcalinos de alto potássio paleoproterozoicos ocorrem no embasamento do cráton São Francisco, bem como no embasamento dos orógenos que o bordejam. Localizado no bordo oeste do cráton São Francisco, o bloco Itacambira- Monte Azul integra o embasamento do orógeno Araçuaí, em partes retrabalhado pelo evento tectonometamórfico Brasiliano. Nesse bloco, os plutonitos Paciência, Morro do Quilombo e Serra Branca, constituídos de rochas alcalinas, são englobados na Suíte Paciência. Os resultados petrográficos para a Suíte Paciência mostram o predomínio de monzonitos e sienitos, equigranulares a porfiríticos, com ocorrência de enclaves máficos. As análises químicas indicam altas concentrações de álcalis, bem como o enriquecimento de óxidos ferromagnesianos e alto Mg# (número de magnésio). Essas rochas são dominantemente metaluminosas, alcalinas a alcalino-cálcicas e magnesianas, enriquecidas em Ba, Sr e Rb e depletadas em Nb, P, Ti e em elementos incompatíveis. Mostram altos conteúdos em elementos terras raras (ETR) com fracionamento dos ETR leves sobre os pesados e anomalias de Eu que variam de negativas a fracamente positivas. As características geoquímicas dessas rochas são similares às de granitoides potássicos originados tardiamente em eventos orogênicos associados à subducção, com fonte mantélica metassomatizada e enriquecida em elementos incompatíveis e participação de crosta arqueana na geração desse magma. A idade de cristalização em 2053 ± 6.3 Ma indica que as rochas da Suíte Paciência se relacionam aos estágios tardios da orogênese Transamazônica, possivelmente associados com a evolução de um extenso arco magmático desenvolvido ao final do Riaciano. Dessa forma, a Suíte Paciência e também as demais suítes alcalinas paleoproterozoicas presentes no embasamento do orógeno Araçuaí registram um período de estabilização do paleocontinente São Francisco-Congo na transição Riaciano-Orosiriano.
Registro e análise de estruturas relacionadas com a tectônica extensional do rifteamento Macaúbas na Serra Central, norte de Minas Gerais.
(2017) Bersan, Samuel Moreira; Danderfer Filho, André
Na região norte da faixa Araçuaí, no domínio fisiográfico do Espinhaço Central, existem registros de bacias sedimentares superpostas instaladas sobre o embasamento do cráton São Francisco. Nesse contexto, a morfoestrutura da Serra Central, norte de Minas Gerais, é sustentada por uma sucessão siliciclástica do Supergrupo Espinhaço superposta a oeste por diamictitos da base do Grupo Macaúbas, representando os registros de rifteamento superpostos ao final do Esteniano e do Toniano Superior, respectivamente. No bordo oeste da Serra Central, são descritas estrias de média a alta obliquidade desenvolvidas sobre os planos de acamamento da sucessão do Grupo Sítio Novo, incompatíveis com a tectônica compressional Brasiliana, que afeta essas rochas. Essas estrias são associadas a degraus e definem vetores de deslizamento interestratais indicativos de movimentação normal a normal destral. Associados a essas lineações, ocorrem veios que também apontam para a atuação de um campo de esforço extensional, com componente destral associada. A análise cinemática e dinâmica dessas estruturas permitiu a interpretação de um regime tectônico distensivo de natureza transtrativa destral e, possivelmente, relacionado ao evento de rifteamento Macaúbas. Nesse cenário, o bloco de capa regional do rifte Macaúbas, representado pela sucessão esteniana do Grupo Sítio Novo, foi deformado sob a atuação de um cisalhamento antitético, com desenvolvimento de um rollover associado. No flanco frontal do rollover, as camadas experimentaram significativa magnitude de rotação, revelando elevado mergulho próximo à borda de falha e favorecendo o desenvolvimento do deslizamento interestratal.

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