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.
Navegar
6 resultados
Resultados da Pesquisa
Item Assessing the U-Pb, Sm-Nd and Sr-Sr isotopic compositions of the sume apatite as a reference material for LA-ICP-MS analysis.(2022) Lana, Cristiano de Carvalho; Gonçalves, Guilherme de Oliveira; Mazoz, Ariela Oliveira; Buick, Ian S.; Kamo, Sandra L.; Cipriano, Ricardo Augusto Scholz; Wang, Hao; Moreira, Hugo Souza; Babinski, Marly; Queiroga, Gláucia NascimentoThis study has determined the trace element and the U-Pb, Sm-Nd and Sr-Sr isotope composition of the Sume apatite (from NE Brazil) to assess its suitability as a primary/secondary reference material for LA-ICP-MS. Reproducibility tests demonstrate that one batch (~ 100 g) of the Sume apatite (Sum e-570) is uniform in terms of Nd-Nd and U-Pb isotope compositions. Bulk isotope dilution TIMS/ICP-MS and LA-MC-ICP-MS analyses confirm that the apatite is well suited for use as quality control material for Nd isotopes and U-Pb geochronology. U-Pb ID-TIMS analyses yield weighted mean ratios of 0.09211 0.00053 (2s; 206Pb*/238U) and 0.06120 0.00063 (2s; 207Pb*/206Pb*) and a weighted mean 206Pb*/238U date of 568 3 Ma (95% c.l.). U-Pb LA-(SF/MC)-ICP-MS runs using Sume-570 as a primary RM and reproduces the dates of other established RMs within 1% deviation (except for Durango 2–4%). Major and trace element abundances show that Sume-570 is a fluorapatite derived from a syenitic source. It also strongly shows LREE-enriched chondrite-normalised REE patterns with significant negative Eu anomalies, due to crystallisation of plagioclase in the residue.Item Depositional setting and U-Pb detrital record of rift‐related deposits in the Moeda Formation (Minas Supergroup) at the Gandarela and Ouro Fino synclines, Quadrilátero Ferrífero, Brazil.(2021) Madureira, Rafael da Silva; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Lana, Cristiano de Carvalho; Dutra, Luiz Fernandes; Alkmim, Ana RamalhoThe Moeda Formation (Caraça Group, base of Minas Supergroup) registers the initial rift stages of the Minas Basin in the Quadrilátero Fer- rífero, Southern São Francisco craton, SE-Brazil. We present stratigraphic and U-Pb detrital zircon dating analyses of the Moeda Formation that contribute to the comprehension of its sedimentary evolution in the southernmost Gandarela and Ouro Fino synclines (Central-Eastern Quadrilátero Ferrifero). The Moeda Formation sequence consists of a basal proximal alluvial fan with clast-supported conglomerates, grading upward into an alluvial floodplain with quartz arenites, and upper massive sandstones from distal fluvial fans. Because the Moeda Formation is normally limited by similar lithologies at both its base (Nova Lima Group, Rio das Velhas Supergroup) and top (Batatal Formation, upper- most Caraça Group) and stratigraphic inversion has occurred in the study area, U-Pb detrital zircon dating was also extended to these units to differentiate them stratigraphically. The youngest clusters of detrital zircon ages in the Nova Lima Group and Moeda and Batatal formations were 2716, 2777 and 2786 Ma, respectively. Based on our data and relevant literature, the depositional age of the Moeda Formation was interpreted as between 2716 and 2520 Ma with the Mesoarchean continental crust, the Rio das Velhas Supergroup and the Archean TTG complexes as its main source areas.Item A-type Medina batholith and post-collisional anatexis in the Araçuaí orogen (SE Brazil).(2018) Serrano, Paula; Soares, Antônio Carlos Pedrosa; Medeiros Júnior, Edgar Batista de; Boa, Tobias Fonte; Araujo, Cristina Santos; Dussin, Ivo Antonio; Queiroga, Gláucia Nascimento; Lana, Cristiano de CarvalhoThe Medina batholith and its host granitic migmatites record intriguing plutonic processes in the northern Araçuaí orogen (SE Brazil). This orogen shows a long lasting (630–480 Ma) succession of granite production events from the earliest pre-collisional plutons to the latest post-collisional intrusions. The Medina batholith includes granite intrusions ascribed to the post-collisional stage. They show high alkali and halogen contents, low CaO (at SiO2=71%:Na2O+K2O=7 to 9%; CaO=1.6%), and high FeOt/(FeOt+MgO) ratios (0.78 to 0.92). The Medina granites are metaluminous to weakly peraluminous, with ASI (molecular ratio Al/(Ca-1.67P+Na_K)) values of 1.76 to 2.07, and have high concentrations of high field strength elements (Zr+Nb+Ce+Y N 700 ppm), as well as high Ga/Al ratios. Accordingly, the Medina intrusions are typical ferroan A-type granites. U\\Pb ages fromzircon (501±2 Ma) and monazite (497±2 Ma) constrain the emplacement timing of theMedina batholith. Surprisingly, all monazite ages from host rocks also cluster around 500Ma, despite their nature and distance from the batholith, suggesting that they would have shared a same thermal process. The studied host rocks are granitic migmatites varying from patch metatexite to nebulitic diatexite, comprising paleosome of foliated sillimanite-garnet-biotite metagranite to gneiss, and non-foliated garnet-cordierite neosome poor to free of biotite. A metatexite (R14) located relatively far from the Medina batholith, and a diatexite (M26) found at the batholith contact were sampled for detailed studies. The paleosome of foliated metagranite (R14A) only shows zircon grains with igneous features and Th/U ratio from1.64 to 0.26. Although the spreading of zircon spots, themain cluster yields a Concordia age at 556±6 Ma, constraining the protolithmagmatic crystallization. A minor cluster furnishes a Concordia age at 499±7 Ma, in agreement with the U\\Pb monazite age at 501±2Ma. Extracted from the same metatexite sample, the non-foliated garnet-cordierite neosome (R14B) shows both igneous and metamorphic zircon domains with Th/U ratios ranging from 1.47 to 0.00. Again, the U\\Pb spots cluster at two distinct Concordia ages (562±3Ma and 499±3Ma). The youngest of them, fitting with themonazite age (495±3Ma), constrains melt crystallization,while the oldest age suggests paleosome inheritance. The nebulitic diatexite (M26) showsmonazite (497±2Ma) and zircon (Th/U=1.7 to 0.0; Concordia ages at 564±2Ma and 507±3Ma) populations similar to themetatexite neosome, alsowith the youngest ages bracketing themelt crystallization process around 500 Ma. Accordingly, all those ages at around 500Ma disclose a partial melting episode coeval with the Medina batholith emplacement. Phase equilibrium modeling on a garnet-cordierite neosome furnished P-T conditions of 750–840 °C at 2.4–3.5 kbar for that post-collisional anatexis. Evidence for such a late thermal event are common in the Araçuaí orogen, even far from the post-collisional batholiths. Thus, a possible major heat source can be envisaged, like a mantle plume triggering crustal anatexis and regional fluid circulation during the gravitational collapse of the Araçuaí orogen.Item Petrography and geochronology of the Furquim Quartzite, an eastern extension of the Itacolomi Group (Quadrilátero Ferrífero, Minas Gerais).(2015) Evangelista, Hanna Jordt; Alvarenga, João Paulo Mantovani; Lana, Cristiano de CarvalhoThis paper presents the results of a petrographic and geochronological inves¬tigation of the Furquim Quartzite (FQ) to establish its stratigraphic correlation to quartzitic units of the Quadrilátero Ferrífero (QF) province. The Quartzite comprises a ca. 20km long and 1-6km wide ridge overlying discordantly the Archean to Paleo¬proterozoic gneissic basement and rocks of the Archean Rio das Velhas Supergroup between the city Mariana and the town Furquim, southeast of the QF. Despite the discordant contacts, previous field-based stratigraphic studies considered the Furquim Quartzite as part of the Archean Maquiné Group – top unit of the Rio das Velhas Supergroup. U-Pb zircon geochronology via LA-ICP-MS identified several detrital populations ranging from Paleoproterozoic to Archean age. The youngest popula¬tion of 2087±19 Ma defines the maximum age for the sedimentation of the precursor sandstone. This age can be correlated to be the age of the youngest zircon population of the Itacolomi Group quartzites in the QF. Thus, in contrast to previous studies, the results indicate that the FQ is an eastern extension of the Itacolomi Group, the young¬est unit of the Paleoproterozoic Minas Supergroup.Item Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent : new stratigraphic and geochronology record from the eastern São Francisco craton.(2014) Danderfer Filho, André; Lana, Cristiano de Carvalho; Nalini Júnior, Hermínio Arias; Costa, Alice Fernanda de OliveiraAn integrated approach of stratigraphic analysis and U–Pb age dating reveals some information on the tectonosedimentary evolution of the Statherian cover of the São Francisco craton in the so-called Espinhaço basin (Atlantic shield in eastern Brazil). Here, continental sedimentation patterns, such as alluvial fan, braided-plain and lacustrine facies associations, with associated volcanic rocks are documented in two superposed basin fill-successions, which are defined as the Algodão and Sapiranga Synthems and grouped in the Botuporã Supersynthem. Both studied units consist mainly of conglomerates and cross-bedded sandstones and minor amounts of mudstones, sedimentary breccias, volcanic lava beds and volcaniclastic rocks, whichwere deposited in a rift basin – the Botuporã rift – during two syn-rifting phases. The Algodão Synthem represents the first rifting phase. The basal synsedimentary conglomerates of this unit were depositedmainly by subaerial debris flows, most likely along and near a rift border fault. The framework of this rock consists of only crystalline rock clasts from the basement and no fragments of volcanic rocks. Detrital zircon grains that were extracted from this facies show ages older than 2.05 Ga. The remainder of the section is dominated by fluvial sandy lithofacies with minor conglomerate lenses and sandstone–mudstone heterolithic lithofacies, which represent distal, waning-flood deposits in a lacustrine environment. The upper section also contains hummocky cross-stratified sandstone lithofacies, which are related to a storm-influenced deposition. On top of the Algodão succession, the volcanic rockswere dated at 1775±7 Ma,which was interpreted as the near final age of the first rift-phase. Representing the second rift-phase, the Sapiranga Synthem shows similar sedimentation patterns to the Algodão Synthem. The Sapiranga Synthem rests directly on the volcanic rocks of the Algodão Synthem, and its basal conglomerates (which are most likely also related to a master fault) contain voluminous clasts of volcanic rocks, sandstones and crystalline rocks. The detrital zircon grains thatwere extracted from this facies show ages of 1741 ± 14 and 1766 Ma as well older than 2.05 Ga. The volcanic rocks on the upper succession of the Sapiranga Synthem record ages of 1740 ± 10 Ma, which finalized the Botuporã rift evolution. A preliminary geochemical study of volcanic rocks from the Botuporã Supersynthemshowed that these rocks are alkaline rocks with high K2O/Na2O ratios, which belong to an ultrapotassic suite. The low concentrations of MgO wt.% suggest a felsic ultrapotassic character. The Botuporã Supersynthem is unconformably covered by a volcanosedimentary rift-succession of EoCalymmian age — the Pajeú Synthem, which represents the second rifting stage of the Espinhaço basin. Several Statherian-related volcano-sedimentary sequences and anorogenic granitoids occur dispersed in the São Francisco block, which requires a regional geologic model to explain the extensional and magmatism process during this time.We used the last Columbia paleocontinental reconstruction to constrain these processes by relating them to far-field continental extensional and magmatic record as part of a silicic LIP, which was triggered by the convection-driven tectonic-plate motion on the western border of the Atlantica block inside of the Columbia supercontinent.Item 3230-3200 Ma post-orogenic extension and mid-crustal magmatism along the southeastern margin of the Barberton Greenstone Belt, South Africa.(2011) Lana, Cristiano de Carvalho; Buick, Ian S.; Stevens, Gary; Rossouw, Riana; Wet, Willem deThe Barberton Granitoid-Greenstone Terrain (SouthAfrica) preserves a complex and protracted evolution involving several events of magmatism and terrain accretion along convergent tectonic boundaries. Recent studies propose that the main period of tectonic accretion and arc-related magmatism is linked to a system of divergent subduction zones above which voluminous TTG magmas were emplaced between ca. 3236 and 3227 Ma. Our structural and LA-ICP-MS U–Pb geochronology study along the southeasternmargin of the BarbertonGreenstoneBelt (BGB) ties the waning stages of this TTG magmatism to a short (ca. <30 Ma) period of mid-crustalextension, between 3228 and 3205 Ma. We document a major NE-trending detachment that juxtaposed upper sequences (Moodies Group clastic sediments) against mid-crustal 3418 ± 10 Ma amphibolite-facies rocks of the base of the greenstonebelt (Onverwacht Group rocks). Several granodiorite bodies - intruded along this detachment - contain well-preserved (syn- and post-magmatic) fabrics that are demonstrably related to extensional shearing and exhumation. Field observations and U–Pb zircon data from these granitoids are consistent with the deformation taking place at 3228 ± 10 Ma – contemporaneous with the voluminous (3236–3227 Ma) TTG magmatism in the northwestern margin of the BGB. The timing of the granodiorite emplacement also constrains a minimum age for the deposition of the Moodies Group clastic sediments, which for much of the southern and southeastern parts of the BGB must have happened before ca. 3228 Ma. 3205 ± 9 Ma subvolcanic dykes intruded into the granodiorite complex indicate that the period of exhumation and cooling of the crystalline rocks along the extensional detachment was relatively short (<30 Ma), between 3228 and 3205 Ma. Our observations combined with previously published structural data from the northwestern and southern margin of the belt suggest that the main mechanism of large-scale infolding of the supracrustal strata was shortly followed by the extension-related magmatism and subsequent, solid-state diapiric movement of the arc-related plutons.