Abstract The Tapes Complex crops out in the southeastern Nico Perez Terrane (NPT) of the Rio de l... more Abstract The Tapes Complex crops out in the southeastern Nico Perez Terrane (NPT) of the Rio de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48–1.43 Ga) Parque UTE and Mina Verdun groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U–Pb SIMS age of 1360 ± 12 Ma for the youngest detrital zircon, (ii) the K–Ar age of 1253 ± 32 Ma for synkinematic muscovite of the Zapican thrust, which affects the unit, and (iii) an Sm–Nd isochronic age of 1403 ± 150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U–Pb SIMS age of 601 ± 5 Ma, associated with Brasiliano-Pan African tectonism, negative eHf values (mean = −31), δ18O zircon ratios ranging between 5.45 and 6.68‰ V-SMOW and inherited zircons dated at 1774-1756 Ma. The best preserved mafic and ultramafic samples yielded Nd model ages (TDM) between 1.55 and 1.68 Ga, close to the assumed crystallization age, and positive eNd(t). Nd model ages of metasedimentary rocks vary between 1.8 and 3.1 Ga, which is interpreted as reflecting two contrasting sources: Archean units of the NPT and Mesoproterozoic mafic and ultramafic rocks, including fragments of oceanic crust. Chondrite-normalized REE patterns of metasedimentary rocks are characterized by LREE enrichment and lack of an Eu anomaly, similar to REE patterns of co-occurring metabasalts. High MgO concentrations, high Cr/V and low Y/Ni and Th/Sc ratios imply the involvement of ultramafic rocks in the source area, which is also supported by whole-rock Pb isotope data. A geodynamic evolution is envisaged, from an extensional tectonic setting between 1.48–1.43 Ga (rift or retroarc basin) into a compressional, retroarc foreland basin at ca. 1.25–1.20 Ga, the latter being probably related to the Kibaran Orogeny in the Namaqua-Natal Belt. It is proposed that the corresponding arc granites and high-grade metamorphic rocks are likely to be found in one of the several terranes in the Namaqua sector of the belt. The Apiai Terrane (Ribeira Belt, Brazil) shows a similar geological record and evolution as the NPT, and maybe a fragment of the latter displaced to the NW by the Ibare Shear Zone. The Tapes Complex is a key unit for understanding the assembly of the Rio de la Plata and Kalahari cratons, and their incorporation into the Rodinia supercontinent.
New U-Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup ... more New U-Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68 Ga to 1.80 Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa-Brumadinho Formation) with a younger zircon peak at 1192 Ma, which is the maximum age for deposition of the upper units. The obtained U-Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8 Ga to 0.91 Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian-Tonian ages of the Upper Espinhaço Basin units (906 Ma to 1192 Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas.
Triassic continental sedimentation in Southern South America is related to the Gondwanides orogen... more Triassic continental sedimentation in Southern South America is related to the Gondwanides orogenesis directly. There were two distinct phases of sedimentation, (1) the wide alluvial basins during Early Triassic and (2) the restricted extensional basins during Middle and Late Triassic. The main Early Triassic deposits are the Sanga do Cabral Supersequence (Southernmost Brazil and Uruguay) and the Talampaya and Tarjados sequences (Western Argentina). These deposits represent poorly channelized braided rivers with source-areas in the Gondwanides units under compressional tectonic setting. The main Middle and Late Triassic strata are rifts in the back-arc setting such as the Ischigualasto and Cuyo basins (Western Argentina) and in the intracontinental setting (Santa Maria Supersequence, Southernmost Brazil). These basins are mainly composed of alluvial, lacustrine and deltaic deposits with a great pyroclastic contribution in the case of the basins of Argentina. Two rift sequences were identified in the Western Argentina basins composed of syn-rift alluvial deposition followed by lake transgression. The sag phase is marked by the progradation of deltaic and high sinuosity rivers. The Southernmost Brazil deposits were divided into three rift sequences composed of low sinuosity rivers followed by lake transgression. The progradation of deltaic and fluvial systems marks the sag phase. The accommodation space generation within the back-arc rifts was high if compared to the intracontinental coeval basin due to higher base level and higher tectonic subsidence rates. The development of deep organic matter-rich lakes suggests a more humid palaeoclimate in the back-arc region than in the intracontinental setting where playa lakes dominated. The back-arc rifts are related to sinistral transtensional stresses in the western branch of Gondwanides region. The intracontinental rifts (the Southernmost Brazil deposits and coeval rift basins of Southern Africa) were generated by transtensional stresses within a dextral shear zone. The shear is related to stress transmission from the southern branch of the Gonwanides where oblique compression occurred.
ABSTRACT The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous pa... more ABSTRACT The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous part of the Tocantins Province, a large Brasiliano/Pan-African orogen of the South American Platform formed during the Brasiliano orogeny. The terrane amalgamated to the province during the late stages of the orogeny as a crustal segment consisting of six Archean orthogneiss complexes and five low-grade metamorphic, in part Paleoproterozoic (Rhyacian) greenstone belts. The Uvá complex is the southernmost orthogneiss association of the Archean-Paleoproterozoic terrane of central Brazil. New U–Pb LA-ICP-MS data from zircon crystals show that the complex formed at least during two magmatic stages. The older consists of polydeformed tonalite and granodiorite batholitic and diorite stock protoliths with igneous age of 3040 Ma to 2930 Ma. The youngest comprises tonalite, monzogranite and granodiorite tabular bodies formed between 2876 and 2846 Ma. As compared to the orthogneisses of the northern portion of the terrane, both the oldest and youngest granitogenesis stages of the Uvá complex are, in average, about 150 Ma older. This suggests that the northern and southern orthogneisses formed during different times as independent crustal segments, but when and why they amalgamated is still under investigation.
Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating pri... more Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-MultiCollector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3±4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using 235U-205Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7±1.8 Ma (error 0.43 %) based on four successful...
The Tapes Complex crops out in the southeastern Nico Pérez Terrane (NPT) of the Río de la Plata C... more The Tapes Complex crops out in the southeastern Nico Pérez Terrane (NPT) of the Río de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48-1.43 Ga) Parque UTE and Mina Verdún groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U-Pb SIMS age of 1360±12 Ma for the youngest detrital zircon, (ii) the K-Ar age of 1253±32 Ma for synkinematic muscovite of the Zapicán thrust, which affects the unit, and (iii) a Sm-Nd isochronic age of 1403±150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U-Pb SIMS age of 601±5 Ma, associated with Brasiliano-Pan African tectonism, negative Hf values (mean=-31), 18O zircon ratios ranging between 5.45 and 6.6...
Este trabalho faz parte do projeto Correlação Brasil-África que tem como objetivo primordial esta... more Este trabalho faz parte do projeto Correlação Brasil-África que tem como objetivo primordial estabelecer a correlação entre as unidades estratigráficas e as feições tectônicas dos cinturões Brasilianos e Pan-Africanos, no sul do Brasil e na África do Sul, formados durante o Proterozóico Superior e o Eo-Paleozóico. Dentro do escopo do projeto estão sendo realizados estudos de correlação geológica entre as zonas de cisalhamento Major Gercino (SC-Brasil) e Purros (leste da Namíbia), as quais estiveram provavelmente conectadas ao final do Ciclo Brasiliano/Pan-Africano (aproximadamente 540 Ma.) pré-deriva continental. Através da análise detalhada de ambas zonas de cisalhamento poder-se-á estabelecer definitivamente se a presente hipótese de trabalho está correta. Para alcançar os objetivos propostos, foram coletadas amostras de rochas e minerais de ambas as áreas e preparadas com finalidade futura de investigar os aspectos petrográficos, microestruturais, geoquímicos e isotópicos (em especial, os sistemas: U-Pb, Rb-Sr, Sm-Nd e Ar-Ar). Os trabalhos desenvolvidos até o momento foram de cominuição de amostras de rocha e separação de minerais. (CNPq-PI/UFRGS).
O minério de ferro é uma das matérias-primas de uso mais antigo e, desde a sua descoberta, durant... more O minério de ferro é uma das matérias-primas de uso mais antigo e, desde a sua descoberta, durante o Período Neolítico, tem ampliado o seu leque de aplicação. Hoje, é um produto essencial para a indústria moderna, visto que a indústria do aço continua a ser a espinha dorsal do desenvolvimento industrial de um país. O Brasil possui 6,4% (21,0 bilhões de toneladas) das reservas mundiais e está em 5º lugar entre os países detentores de maiores quantidades de minério. Porém, os altos teores de ferro em seus minérios (60 a 67% nas hematitas e 50 a 60% nos itabiritos e jaspilitos, em termos de ferro contido no minério) levam o Brasil a ocupar um lugar de destaque no cenário mundial. A produção mundial de minério de ferro tem ao longo das últimas décadas crescido sensivelmente, quando já em 2002 a produção era de 1,1 bilhões de toneladas/ano; enquanto em 2008 a produção anual atingiu mais de 2,0 bilhões de toneladas. Destaca-se que a participação da produção brasileira representou em torno...
RESUMO O presente trabalho é parte de um estudo mais amplo de caracterização do minério de ferro ... more RESUMO O presente trabalho é parte de um estudo mais amplo de caracterização do minério de ferro brasileiro, com a utilização de diferentes técnicas analíticas e microanalíticas. A microscopia ótica é utilizada para revelar microtexturas que levam a identificação de fases baseadas em critérios morfológicos. Tendo em vista que esses critérios são, geralmente, subjetivos. Será apresentado um exemplo de utilização da técnica de Espectroscopia µ-Raman para obter uma identificação inequívoca das fases minerais presentes, bem como sua distribuição espacial. ABSTRACT The present work is part of major study for Brazilian iron ore characterization using different analytical and microanalytical experimental techniques. The optical microscopy is herein used to reveal microstructures for identification of phases based on morphological criteria. Since these criteria are usually subjectives, we present an example of use of µ-Raman Spectroscopy in order to unequivocally identify the occurrence of ...
The evolution of the Triassic-Cretaceous Cuyo Basin, located in the Andean Precordillera (NW Arge... more The evolution of the Triassic-Cretaceous Cuyo Basin, located in the Andean Precordillera (NW Argentina), was mainly controlled by extensional-transtensional tectonics along NW-trending structures inherited from Paleozoic sutures. Stratigraphic and isotopic studies are herein presented in order to constrain the sedimentary infi lling and source areas, as well as the age of Triassic strata related to the active faulted margin of the Cacheuta subbasin. The whole stratigraphic package of the Cuyo Basin is interpreted as a second-order depositional sequence, comprising lowstand (alluvial fan deposits), transgressive (fl uvialdeltaic and lacustrine deposits), and highstand (oxidized lacustrine and high-sinuosity fl uvial deposits) systems tracts. This stacking pattern was mainly controlled by the interplay between sedimentary infl ux and accommodation space, with important volcaniclastic contribution, especially during the early stages of basin development. Sm-Nd depleted-mantle model ages (T DM ) for both basement and volcano-sedimentary samples range from 867 to 1345 Ma. All samples have negative ε Nd (t) values (−0.33 to −5.02). Basal deposits present older T DM model ages compared to intermediate-positioned deposits, and upper deposits present a wider range of model ages. This time-integrated factor correlates with paleocurrent data, which indicate changes in the source areas through time. The Nd isotopic signature also suggests that sources of sediments for the Cacheuta sub-basin during the Triassic were restricted to units of Mesoproterozoic (Grenvillian) age, probably related to the Cuyania terrane. The U-Pb sensitive highresolution ion microprobe (SHRIMP) zircon age of 243 ± 5 Ma, obtained in juvenile magmatic zircons from a lithoclast-free ignimbrite interlayered within the basal alluvial fan facies of the Cacheuta sub-basin, places the lowstand deposits in the Olenekian and establishes a potential chronostratigraphic horizon for future correlations.
Abstract The Tapes Complex crops out in the southeastern Nico Perez Terrane (NPT) of the Rio de l... more Abstract The Tapes Complex crops out in the southeastern Nico Perez Terrane (NPT) of the Rio de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48–1.43 Ga) Parque UTE and Mina Verdun groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U–Pb SIMS age of 1360 ± 12 Ma for the youngest detrital zircon, (ii) the K–Ar age of 1253 ± 32 Ma for synkinematic muscovite of the Zapican thrust, which affects the unit, and (iii) an Sm–Nd isochronic age of 1403 ± 150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U–Pb SIMS age of 601 ± 5 Ma, associated with Brasiliano-Pan African tectonism, negative eHf values (mean = −31), δ18O zircon ratios ranging between 5.45 and 6.68‰ V-SMOW and inherited zircons dated at 1774-1756 Ma. The best preserved mafic and ultramafic samples yielded Nd model ages (TDM) between 1.55 and 1.68 Ga, close to the assumed crystallization age, and positive eNd(t). Nd model ages of metasedimentary rocks vary between 1.8 and 3.1 Ga, which is interpreted as reflecting two contrasting sources: Archean units of the NPT and Mesoproterozoic mafic and ultramafic rocks, including fragments of oceanic crust. Chondrite-normalized REE patterns of metasedimentary rocks are characterized by LREE enrichment and lack of an Eu anomaly, similar to REE patterns of co-occurring metabasalts. High MgO concentrations, high Cr/V and low Y/Ni and Th/Sc ratios imply the involvement of ultramafic rocks in the source area, which is also supported by whole-rock Pb isotope data. A geodynamic evolution is envisaged, from an extensional tectonic setting between 1.48–1.43 Ga (rift or retroarc basin) into a compressional, retroarc foreland basin at ca. 1.25–1.20 Ga, the latter being probably related to the Kibaran Orogeny in the Namaqua-Natal Belt. It is proposed that the corresponding arc granites and high-grade metamorphic rocks are likely to be found in one of the several terranes in the Namaqua sector of the belt. The Apiai Terrane (Ribeira Belt, Brazil) shows a similar geological record and evolution as the NPT, and maybe a fragment of the latter displaced to the NW by the Ibare Shear Zone. The Tapes Complex is a key unit for understanding the assembly of the Rio de la Plata and Kalahari cratons, and their incorporation into the Rodinia supercontinent.
New U-Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup ... more New U-Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68 Ga to 1.80 Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa-Brumadinho Formation) with a younger zircon peak at 1192 Ma, which is the maximum age for deposition of the upper units. The obtained U-Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8 Ga to 0.91 Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian-Tonian ages of the Upper Espinhaço Basin units (906 Ma to 1192 Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas.
Triassic continental sedimentation in Southern South America is related to the Gondwanides orogen... more Triassic continental sedimentation in Southern South America is related to the Gondwanides orogenesis directly. There were two distinct phases of sedimentation, (1) the wide alluvial basins during Early Triassic and (2) the restricted extensional basins during Middle and Late Triassic. The main Early Triassic deposits are the Sanga do Cabral Supersequence (Southernmost Brazil and Uruguay) and the Talampaya and Tarjados sequences (Western Argentina). These deposits represent poorly channelized braided rivers with source-areas in the Gondwanides units under compressional tectonic setting. The main Middle and Late Triassic strata are rifts in the back-arc setting such as the Ischigualasto and Cuyo basins (Western Argentina) and in the intracontinental setting (Santa Maria Supersequence, Southernmost Brazil). These basins are mainly composed of alluvial, lacustrine and deltaic deposits with a great pyroclastic contribution in the case of the basins of Argentina. Two rift sequences were identified in the Western Argentina basins composed of syn-rift alluvial deposition followed by lake transgression. The sag phase is marked by the progradation of deltaic and high sinuosity rivers. The Southernmost Brazil deposits were divided into three rift sequences composed of low sinuosity rivers followed by lake transgression. The progradation of deltaic and fluvial systems marks the sag phase. The accommodation space generation within the back-arc rifts was high if compared to the intracontinental coeval basin due to higher base level and higher tectonic subsidence rates. The development of deep organic matter-rich lakes suggests a more humid palaeoclimate in the back-arc region than in the intracontinental setting where playa lakes dominated. The back-arc rifts are related to sinistral transtensional stresses in the western branch of Gondwanides region. The intracontinental rifts (the Southernmost Brazil deposits and coeval rift basins of Southern Africa) were generated by transtensional stresses within a dextral shear zone. The shear is related to stress transmission from the southern branch of the Gonwanides where oblique compression occurred.
ABSTRACT The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous pa... more ABSTRACT The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous part of the Tocantins Province, a large Brasiliano/Pan-African orogen of the South American Platform formed during the Brasiliano orogeny. The terrane amalgamated to the province during the late stages of the orogeny as a crustal segment consisting of six Archean orthogneiss complexes and five low-grade metamorphic, in part Paleoproterozoic (Rhyacian) greenstone belts. The Uvá complex is the southernmost orthogneiss association of the Archean-Paleoproterozoic terrane of central Brazil. New U–Pb LA-ICP-MS data from zircon crystals show that the complex formed at least during two magmatic stages. The older consists of polydeformed tonalite and granodiorite batholitic and diorite stock protoliths with igneous age of 3040 Ma to 2930 Ma. The youngest comprises tonalite, monzogranite and granodiorite tabular bodies formed between 2876 and 2846 Ma. As compared to the orthogneisses of the northern portion of the terrane, both the oldest and youngest granitogenesis stages of the Uvá complex are, in average, about 150 Ma older. This suggests that the northern and southern orthogneisses formed during different times as independent crustal segments, but when and why they amalgamated is still under investigation.
Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating pri... more Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-MultiCollector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3±4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using 235U-205Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7±1.8 Ma (error 0.43 %) based on four successful...
The Tapes Complex crops out in the southeastern Nico Pérez Terrane (NPT) of the Río de la Plata C... more The Tapes Complex crops out in the southeastern Nico Pérez Terrane (NPT) of the Río de la Plata Craton and forms part of a NE-trending Mesoproterozoic belt together with the Calymmian (1.48-1.43 Ga) Parque UTE and Mina Verdún groups. The complex is characterized by interbedded/tectonically interleaved metasedimentary (mainly siliciclastic) and metaultramafic rocks, with subordinate intercalations of metabasites, carbonate and chert, all metamorphosed in the greenschist facies. The age of the Tapes Complex is constrained by: (i) a U-Pb SIMS age of 1360±12 Ma for the youngest detrital zircon, (ii) the K-Ar age of 1253±32 Ma for synkinematic muscovite of the Zapicán thrust, which affects the unit, and (iii) a Sm-Nd isochronic age of 1403±150 Ma for ultramafic and mafic rocks. The intruding Tapes Chico Syenite yielded a much younger U-Pb SIMS age of 601±5 Ma, associated with Brasiliano-Pan African tectonism, negative Hf values (mean=-31), 18O zircon ratios ranging between 5.45 and 6.6...
Este trabalho faz parte do projeto Correlação Brasil-África que tem como objetivo primordial esta... more Este trabalho faz parte do projeto Correlação Brasil-África que tem como objetivo primordial estabelecer a correlação entre as unidades estratigráficas e as feições tectônicas dos cinturões Brasilianos e Pan-Africanos, no sul do Brasil e na África do Sul, formados durante o Proterozóico Superior e o Eo-Paleozóico. Dentro do escopo do projeto estão sendo realizados estudos de correlação geológica entre as zonas de cisalhamento Major Gercino (SC-Brasil) e Purros (leste da Namíbia), as quais estiveram provavelmente conectadas ao final do Ciclo Brasiliano/Pan-Africano (aproximadamente 540 Ma.) pré-deriva continental. Através da análise detalhada de ambas zonas de cisalhamento poder-se-á estabelecer definitivamente se a presente hipótese de trabalho está correta. Para alcançar os objetivos propostos, foram coletadas amostras de rochas e minerais de ambas as áreas e preparadas com finalidade futura de investigar os aspectos petrográficos, microestruturais, geoquímicos e isotópicos (em especial, os sistemas: U-Pb, Rb-Sr, Sm-Nd e Ar-Ar). Os trabalhos desenvolvidos até o momento foram de cominuição de amostras de rocha e separação de minerais. (CNPq-PI/UFRGS).
O minério de ferro é uma das matérias-primas de uso mais antigo e, desde a sua descoberta, durant... more O minério de ferro é uma das matérias-primas de uso mais antigo e, desde a sua descoberta, durante o Período Neolítico, tem ampliado o seu leque de aplicação. Hoje, é um produto essencial para a indústria moderna, visto que a indústria do aço continua a ser a espinha dorsal do desenvolvimento industrial de um país. O Brasil possui 6,4% (21,0 bilhões de toneladas) das reservas mundiais e está em 5º lugar entre os países detentores de maiores quantidades de minério. Porém, os altos teores de ferro em seus minérios (60 a 67% nas hematitas e 50 a 60% nos itabiritos e jaspilitos, em termos de ferro contido no minério) levam o Brasil a ocupar um lugar de destaque no cenário mundial. A produção mundial de minério de ferro tem ao longo das últimas décadas crescido sensivelmente, quando já em 2002 a produção era de 1,1 bilhões de toneladas/ano; enquanto em 2008 a produção anual atingiu mais de 2,0 bilhões de toneladas. Destaca-se que a participação da produção brasileira representou em torno...
RESUMO O presente trabalho é parte de um estudo mais amplo de caracterização do minério de ferro ... more RESUMO O presente trabalho é parte de um estudo mais amplo de caracterização do minério de ferro brasileiro, com a utilização de diferentes técnicas analíticas e microanalíticas. A microscopia ótica é utilizada para revelar microtexturas que levam a identificação de fases baseadas em critérios morfológicos. Tendo em vista que esses critérios são, geralmente, subjetivos. Será apresentado um exemplo de utilização da técnica de Espectroscopia µ-Raman para obter uma identificação inequívoca das fases minerais presentes, bem como sua distribuição espacial. ABSTRACT The present work is part of major study for Brazilian iron ore characterization using different analytical and microanalytical experimental techniques. The optical microscopy is herein used to reveal microstructures for identification of phases based on morphological criteria. Since these criteria are usually subjectives, we present an example of use of µ-Raman Spectroscopy in order to unequivocally identify the occurrence of ...
The evolution of the Triassic-Cretaceous Cuyo Basin, located in the Andean Precordillera (NW Arge... more The evolution of the Triassic-Cretaceous Cuyo Basin, located in the Andean Precordillera (NW Argentina), was mainly controlled by extensional-transtensional tectonics along NW-trending structures inherited from Paleozoic sutures. Stratigraphic and isotopic studies are herein presented in order to constrain the sedimentary infi lling and source areas, as well as the age of Triassic strata related to the active faulted margin of the Cacheuta subbasin. The whole stratigraphic package of the Cuyo Basin is interpreted as a second-order depositional sequence, comprising lowstand (alluvial fan deposits), transgressive (fl uvialdeltaic and lacustrine deposits), and highstand (oxidized lacustrine and high-sinuosity fl uvial deposits) systems tracts. This stacking pattern was mainly controlled by the interplay between sedimentary infl ux and accommodation space, with important volcaniclastic contribution, especially during the early stages of basin development. Sm-Nd depleted-mantle model ages (T DM ) for both basement and volcano-sedimentary samples range from 867 to 1345 Ma. All samples have negative ε Nd (t) values (−0.33 to −5.02). Basal deposits present older T DM model ages compared to intermediate-positioned deposits, and upper deposits present a wider range of model ages. This time-integrated factor correlates with paleocurrent data, which indicate changes in the source areas through time. The Nd isotopic signature also suggests that sources of sediments for the Cacheuta sub-basin during the Triassic were restricted to units of Mesoproterozoic (Grenvillian) age, probably related to the Cuyania terrane. The U-Pb sensitive highresolution ion microprobe (SHRIMP) zircon age of 243 ± 5 Ma, obtained in juvenile magmatic zircons from a lithoclast-free ignimbrite interlayered within the basal alluvial fan facies of the Cacheuta sub-basin, places the lowstand deposits in the Olenekian and establishes a potential chronostratigraphic horizon for future correlations.
Uploads
Papers by Farid Junior