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Sawakuchi A.O.,University of Sao Paulo | Blair M.W.,Los Alamos National Laboratory | DeWitt R.,Oklahoma State University | Faleiros F.M.,CPRM Servico Geologico do Brazil | And 2 more authors.
Quaternary Geochronology | Year: 2011

The optically stimulated luminescence (OSL) sensitivity of quartz has a significant influence on luminescence dating procedures. Furthermore, identifying the natural controls of quartz OSL sensitivity is an important step towards new applications of OSL in geology such as provenance tracing. We evaluate the OSL sensitivity (total and the proportion of the informally assigned fast, medium and slow components) of single grains of quartz extracted from 10 different igneous and metamorphic rocks with known formation conditions; and from fluvial and coastal sediments with different sedimentary histories and known source rocks. This sample suite allows assessment of the variability of the OSL sensitivity of single quartz grains with respect to their primary origin and sedimentary history. We observed significant variability in the OSL sensitivity of grains within all studied rock and sediment samples, with the brightest grains of each sample being those dominated by the fast component. Quartz from rocks formed under high temperature (>500 °C) conditions, such as rhyolites and metamorphic rocks from the amphibolite facies, display higher OSL sensitivity. The OSL sensitivity of fluvial sediments which have experienced only a short transport distance is relatively low. These sediments show a small increase in OSL sensitivity downstream, mainly due to a decreasing fraction of "dim" grains. The quartz grains from coastal sands present very high sensitivity and variability, which is consistent with their long sedimentary history. The high variability of the OSL sensitivity of quartz from coastal sands is attributed more to the mixture of grains with distinct sedimentary histories than to the provenance from many types of source rocks. The temperature of crystallization and the number of cycles of burial and solar exposure are suggested as the main natural factors controlling the OSL sensitivity of quartz grains. The increase in OSL sensitivity due to cycles of erosion and deposition surpasses the sensitivity inherited from the source rock, with this increase being mainly related to the sensitization of fast OSL components. The discrimination of grains with different sedimentary histories through their OSL sensitivities can allow the development of quantitative provenance methods based on quartz. © 2010 Elsevier B.V.

da Silva R.C.,CPRM Servico Geologico do Brazil | Sedor F.A.,Federal University of Paraná | Fernandes A.C.S.,Federal University of Rio de Janeiro
Journal of South American Earth Sciences | Year: 2012

Although Late Permian tetrapods are relatively common around the world, few taxa are known in rocks of this age in South America. So far, the study of the tetrapod paleofaunas in the Permian of Brazil has provided significant chronological data, though knowledge about them is still incipient. These studies generally take into account only body fossil records, but the ichnological record can provide new biostratigraphic elements for correlation. In Brazil, fossil tracks were first recorded in Rio do Rasto and Corumbataí Formations (Late Permian from Paraná Basin), but to date these tracks have not been studied in an ichnotaxonomic, morphofunctional, paleoenvironmental and chronological context. The study of these tracks became possible due to a considerable increase in the number of taxa from the Late Permian of Brazil, including Chelichnus isp. (Synapsida: Caseidae?), Procolophonichnium isp. (Procolophonoidea), Rhynchosauroides gangresci isp. nov. (basal Diapsida), Dicynodontipus penugnu isp. nov. (Dicynodontia) and Incertae sedis (Amphibia?). With the exception of Dicynodontia, the remaining recorded taxa are unknown through fossil skeletons, showing that the Brazilian Permian faunas were much more diverse than was previously reported and demonstrating the potential of South American fossil vertebrates for global correlations. © 2012 Elsevier Ltd.

De Brito Neves B.B.,University of Sao Paulo | Dos Santos R.A.,CPRM Servico Geologico do Brazil | Da Cruz Campanha G.A.,University of Sao Paulo
Geologia USP - Serie Cientifica | Year: 2012

The stratigraphic relationships between the Chapada Diamantina and Bambuí (or Una) groups were practically established with the papers of J. C. Branner, a century before. Sometimes that proposed lithostratigraphy was questioned, but we do know now that these arguments were based up incomplete or inadvertent field observations. At the sheet of Mirangaba, central-northern part of Bahia, both the angular and erosional unconformity between the above-mentioned groups are exposed of a conspicuous way, according to their three dimensions, what deserves the special mention here consigned. The quartzites and conglomerates of the Chapada Diamantina group are cropping out as folded and re-fold rock units (general strike ENE-WSW) and they present features of intense superposed erosional processes. Two paleosurfaces were formed and are being exhibited, with complementary features of erosional scarpments, as well as amphitheatres, suppression of some lithostratigraphic units, testimonies-hills (quartzitic islands), etc. The lower pediplan then formed (today with summits ≥ 500 m) was completely covered by the limestones (Salitre Fm.), where calcilutites are predominating, presenting many algalic edifications. We are not able to affrm that the proterozoic limestone progradation have covered the higher pediplan (today with summits ca. 1,000 m), but there are some testimonies-hills of limestone presenting tops up to 600 m, clearly above the present and predominating surface (Neogene, Velhas Surface), so reiterating that an intense erosional dissecation has occurred (Cenozoic in age) of the limestones. These limestones present monotonous subhorizontal structural attitudes, with the presence of some open folding (ondulations) when they are near of the contacts with the subjacent quartzites. Quite often these limestones were submitted to local ruptural displacements. The polyphasic deformation of the subjacent Chapada Diamantina group is being hypothetically attributed to the Brazilian cycle (as foreland domain of the Riacho do Pontal fold system), but this proposed condition needs to be better constrained, as well as the northern limit of the São Francisco Craton (to the north) demands to be reviewed. The basal diamictites of the Bambuí Group (Bebedouro Fm.) is only locally cropping out, at the southern and at the northwestern part of the area. The time interval between the deformation of the quartzites and the beginning of the limestones deposition was necessarily very long, some millions of years, and this is an obligatory target for future researches.

Santos L.C.M.D.L.,University of Brasilia | Santos L.C.M.D.L.,Federal University of Campina Grande | Dantas E.L.,University of Brasilia | Santos E.J.D.,CPRM Servico Geologico do Brazil | And 2 more authors.
Journal of South American Earth Sciences | Year: 2015

The Alto Moxotó Terrane is a Paleoproterozoic inlier within the Transversal Domain of the Neoproterozoic Borborema Province (NE Brazil). An isotopic and whole-rock geochemistry study has been performed in the Sucuru region (Paraiba State, NE Brazil) which revealed a long-lived evolution for this terrane. The first event is Siderian-aged, dated on 2.44Ga, being represented by granitic to granodioritic banded orthogneisses and migmatites of the basement. They correspond to meta to peraluminous high-K calc-alkaline series, where geochemical patterns besides zircon features and Nd isotopic data indicate that they were formed in a convergent tectonic environment with reworking of an older Archean continental crust. This basement was intruded by different magmatic suites through two distinct tectono-magmatic events. The older one is Rhyacian-aged recorded by emplacement of the Carmo mafic-ultramafic suite and Pedra d'Água granitic suite, with ages varying from 2.15 to 2.0Ga. The Carmo Suite shows compositions similar to tholeiitic and minor calc-alkaline series and geochemical patterns of a depleted source. These general chemical characteristics are compatible with an arc-related magmatism in early stages of subduction. The Pedra d'Água suite corresponds to middle to peraluminous high-K calc-alkaline magmatism which presents a typical magmatic arc geochemical signature. The negative εNd (. t) values suggest a strong continental component for genesis of these magmas. The last tectonomagmatic episode occurred in the Statherian-Calymmian boundary and is represented by bimodal magmatic association of the Serra da Barra Suite, dated around 1.6Ga. The dominant felsic rocks present an evolved composition and correspond to typical metaluminous sub-alkaline suite. The trace-element and REE patterns of both mafic and mainly felsic rocks suggest a within-plate setting. The attributed source is of crustal derivation, which is supported by the negative εNd (. t) values. A mantle plume can be invoked for mechanism of generation of the Serra da Barra magmatism. This polycyclic Paleoproterozoic evolution observed at Alto Moxotó terrane is also well documented in orogenic terranes worldwide, mainly those related to Atlantica supercontinent amalgamation. On the other hand, Statherian-Calymmian extensional event is also coherent with worldwide descriptions and are commonly referred to early break-up stage of the large Paleoproterozoic land masses. © 2014 Elsevier Ltd.

Do Nascimento M.A.L.,Federal University of Rio Grande do Norte | Galindo A.C.,Federal University of Rio Grande do Norte | de Medeiros V.C.,CPRM Servico Geologico do Brazil
Journal of South American Earth Sciences | Year: 2015

The Ediacaran-Cambrian plutonic activity is one of the most important geological features of the Rio Grande do Norte Domain (Borborema Province, NE Brazil). It is represented by several batholiths, stocks and dykes. Based on the petrographic, geochemical and geochronological characteristic of different rocks, this plutonic activity can be grouped in six separate suites: shoshonitic (Shos), porphyritic high-K calc-alkaline (PHKCalcAlk), equigranular high K calc-alkaline (EHKCalcAlk), calc-alkaline (CalcAlk), alkaline (Alk) and charnockitic alkaline (ChAlk). Geochemically, the Shos, CalcAlk and Alk suites are differentiated from the others, while ChAlc can be distinguished from the others in some diagrams. The greatest difficulty lies in distinguishing between the chemically similar PHKCalcAlk and EHKCalcAlk. To this end, existing geochronological data as well as related petrographic and textural field aspects may be used to distinguish the two mentioned suites (PHKCalcAlk and EHKCalcAlk).Petrographically, the Shos suite has composition between gabbro/diorite and quartz monzonite. Monzogranites (with subordinate granodiorites and quartz monzonites) predominate in both PHKCalcAlk and EHKCalcAlk. Calc is composed of granodiorites to tonalites. Alc is formed by alkali feldspar granites (with subordinate alkali feldspar quartz syenites and syenogranites), whereas ChAlc has quartz mangerites and charnockites.The suites were emplaced between the Ediacaran (635-541Ma) and Cambrian (541-485Ma), predominantly in the Ediacaran, based on 34 U-Pb datings (zircon, titanite, monazite and columbite-tantalite), 17 Rb-Sr (whole rock) and 1 Sm-Nd (total rock and mineral) internal isochrons. The Shos suite has U-Pb ages varying from 599±16 (Poço Verde pluton) to 579±7 (Acari and São João do Sabugi plutons), slightly older than those of the PHKCalcAlk suite, which ranges between 591±4Ma (Totoró pluton) and 544±7Ma (São José de Espinharas pluton). The CalcAlk Suite has only one dated body, aged 598±3Ma (Serra da Garganta pluton). The EHKCalcAlk suite U-Pb dating is younger than the aforementioned suites, ranging from 582±5Ma (dykes in Dona Inês pluton) and 527±8 (Cerro Corá pluton). The Alk suite was dated at 578±14Ma (Caxexa pluton, Sm-Nd internal isochron) and at 597±4Ma (Japi pluton, U-Pb zircon), while ChAlc U-Pb zircon ages of 601±10Ma and 593±5Ma (Umarizal pluton). The magmatism of Cambrian age in the Rio Grande do Norte Domain is represented by pegmatite dykes with U-Pb dating between 515 and 510Ma. A atividade plutÔnica ediacarana-cambriana constitui uma das mais importantes feiçoes geológicas encontrada no Domínio Rio Grande do Norte (Província Borborema, NE do Brasil). Ela é representada por diversos batólitos, stocks e diques. Com base em características petrográficos, geoquímicas e geocronológicas de diferentes rochas é possível agrupar esta atividade plutÔnica em seis suítes distintas, são elas: Shoshonítica (Shos), Cálcio-alcalina de alto K Porfirítica (CalcAlcAKP), Cálcio-alcalina de alto K Equigranular (CalcAlcAKE), Cálcio-alcalina (CalcAlc), Alcalina (Alc) e Alcalina Charnoquítica (AlcCh). Geoquimicamente, as suítes Shos, CalcAlc e Alc são individualizadas das demais, enquanto que a AlcCh pode ser distinguida das outras em alguns diagramas. A dificuldade maior está na distinção entre as CalcAlcAKP e CalcAlcAKE, sendo elas quimicamente similares. Os aspectos de campo aliados aos petrográficos e texturais podem ser utilizados para distinção entre as suítes CalcAlcAKP e CalcAlcAKE, bem como os dados geocronológicos existentes.Petrograficamente, a Suíte Shos possui composição entre gabros/dioritos e quartzo monzonitos. Na CalcAlcAKP predomina monzogranitos (com granodioritos e quartzo monzonitos, subordinados), semelhante a CalcAlcAKE. A CalcAlc é formada por granodioritos a tonalitos. A Alc é formada por álcali-feldspato granitos (com quartzo álcali-feldspato sienitos e sienogranitos, subordinados), enquanto que a AlcCh tem quartzo mangeritos e charnoquitos.As suítes foram alojadas entre o Ediacarano (635-541Ma) e o Cambriano (541-485Ma), predominando no Ediacarano, com base em 34 idades U-Pb (zircão, titanita, monazita e columbita-tantalita), 17 Rb-Sr (rocha total) e 1 isócrona interna Sm-Nd (rocha total e mineral). A Suíte Shos tem idades U-Pb variando de 599±16 (Plúton Poço Verde) a 579±7 (plútons Acari e São João do Sabugi). Esses valores são um pouco mais velhos do que as idades da Suíte CalcAlcAKP que possui valores entre 591±4Ma (Plúton Totoró) e 544±7Ma (Plúton São José de Espinharas). A Suíte CalcAlc possui apenas um corpo datado, com idade de 598±3Ma (Plúton Serra da Garganta). A Suíte CalcAlcAKE possui idades U-Pb mais jovens que as suítes anteriores, com valores entre 582±5Ma (diques no Plúton Dona Inês) e 527±8 (Plúton Cerro Corá). A Suíte Alc foi datada em 578±14Ma (Plúton Caxexa, isócrona interna Sm-Nd) e 597±4Ma (Plúton Japi, U-Pb em zircão), enquanto que a AlcCh foi datada, U-Pb em zircão, em 601±10Ma e 593±5Ma (Plúton Umarizal). O magmatismo de idade cambriana no Domínio Rio Grande do Norte está representado pelos diques de pegmatito com idades U-Pb variando entre 515 e 510Ma. © 2014 Elsevier Ltd.

Barreto C.J.S.,Federal University of Pará | Lafon J.M.,Federal University of Pará | da Rosa Costa L.T.,CPRM Servico Geologico do Brazil | Dantas E.L.,University of Brasilia
Journal of South American Earth Sciences | Year: 2013

Central Amapá, northern Brazil is located at the boundary between: (a) a northern Paleoproterozoic domain, consisting mainly of granite-greenstones terrains and (b) a southern Archean continental block(Amapá block), including an Archean basement reworked during the Transamazonian orogeny (2.26-1.95Ga). Field investigations, Pb-Pb zircon and Sm-Nd whole rock geochronology supported by geochemical data on granitoids brought further constraints on Paleoproterozoic crustal growth in the southeastern Guyana Shield. A first magmatic episode, dated at 2.26Ga, is marked by the crystallization of metaluminous low-K tholeiitic tonalites and quartz-diorites, which geochemical affinity with volcanic arc and association with T-MORB amphibolites suggest that they formed in a back-arc basin - island arc system. This event is coeval to the oceanic stage registered in French Guyana during the Eorhyacian (2.26-2.02Ga). A second magmatic episode is represented by peraluminous, medium- to high-K calc-alkaline tonalite and granodiorite, which revealed some similarities with Mesorhyacian TTG rocks of French Guyana. For granitoids of both episodes, TDM and εNd values indicate the contribution of some Archean crustal component, probably by assimilation or contamination. This second magmatic episode occurred at 2.10Ga, indicating that the period of successive calc-alkaline magmatic arcs formation may have extended until the Neorhyacian. Meanwhile, during this time, tectonic accretion by collision of the newly formed continental landmass was the prevailing process in French Guyana. The latter magmatic episode, even though poorly constrained, was registered around 2.08-2.02Ga in central Amapá. It corresponds to the emplacement and solidification of high-K collisional granitoids, produced by partial melting of the Archean continental crust, as testified by the Archean TDM, inherited Pb-Pb zircon ages and strongly negative εNd values. Our results point toward the existence of a protracted episode of crustal growth during the Neorhyacian in the southeastern Guyana Shield. This episode has been predominantly driven by magmatic arc accretion during, at least, 160 My, along the period of 2.26-2.10Ga. This cycle ended with diachronic closure of the oceanic basins and arc-continent collision. © 2013 Elsevier Ltd.

Simoes M.S.,CPRM Servico Geologico do Brazil | Almeida M.E.,CPRM Servico Geologico do Brazil | de Souza A.G.H.,CPRM Servico Geologico do Brazil | da Silva D.P.B.,CPRM Servico Geologico do Brazil | Rocha P.G.,CPRM Servico Geologico do Brazil
Journal of Volcanology and Geothermal Research | Year: 2014

The Iricoumé Group (1.897 to 1.875. Ma) is a widespread volcanic sequence in the Amazonian Craton, South American Platform. In the Pitinga region, it consists of acidic to intermediate ignimbrites with cogenetic surge and ash-fall deposits associated to hypabissal and effusive acidic rocks. In the Balbina Lake area it consists of acidic to intermediate effusive rocks, crystal-rich ignimbrites and pumice-rich ignimbrites. Detailed petrographic studies of phenocrysts and crystal fragments provided characterization and distinctive features of pyroclastic, effusive and hypabissal rocks. The phenocrysts of hypabissal rocks were affected by high temperature resorption and flow-related physical fragmentation, the effusive rocks can have a considerable content of crystal fragments due to intense dissolution and fragmentation of the phenocrysts and the pyroclastic rocks crystal fragments are generated mainly by decompression mechanic fragmentation. Dissolution and resorption of quartz and feldspar crystals may have acted at pressure conditions between 500. MPa and 100. MPa, in response to rapid decompression in the magma ascent. The viscosity values of 7,5-10 log η (Pa. s) for anhydrous conditions decrease exponentially with estimated water addition. The amount of phenocrysts and their intratelluric character in the volcanic units of Iricoumé Group can be related to a magma chamber with high content of crystals. We suggest that even with the addition of water in the magma, the viscosities had a drastic increase with progressive crystal growth due to the viscosity dependence on the solid fraction and the deposits were generated by the extrusion of viscous lava and pyroclastic flows. © 2014 Elsevier B.V.

Simas M.W.,CPRM Servico Geologico do Brazil | Guerra-Sommer M.,Federal University of Rio Grande do Sul | Cazzulo-Klepzig M.,Federal University of Rio Grande do Sul | Menegat R.,Federal University of Rio Grande do Sul | And 3 more authors.
Journal of South American Earth Sciences | Year: 2012

The radiometric age of 291 ± 1.2 Ma obtained through single-crystal zircon U-Pb ages (Sensitive High Resolution Ion MicroProbe - SHRIMP II) of tonsteins from the Leão-Butiá Coalfield, southern Paraná Basin (Rio Grande do Sul state), associated with previous SHRIMP II radiometric data obtained from tonsteins from the western (Candiota Coalfield) and eastern (Faxinal and Leão-Butiá coalfields) borders of the basin indicate that the mean age of the main peat-forming interval is 291.0 ± 1.3 Ma. In a regional context, the mean age represents a consistent geochronological correlation for the uppermost and more important coal seams in southern Brazilian coalfields, but this assumption does not establish an ash fall origin from a single volcanic event. According to the International Stratigraphic Chart, the interval is dated as middle Sakmarian. The coal palynofloras are included in the Protohaploxypinus goraiensis Subzone within the palynostratigraphic framework for the Brazilian Paraná Basin. Formal relationships are also established with the Glossopteris- Rhodeopteridium Zone within the phytostratigraphic chart for the Lower Permian of southern Brazilian Paraná Basin. © 2012.

Rodrigues J.B.,CPRM Servico Geologico do Brazil | Rodrigues J.B.,University of Brasilia | Pimentel M.M.,University of Brasilia | Pimentel M.M.,Federal University of Rio Grande do Sul | And 5 more authors.
Gondwana Research | Year: 2012

The Vazante Group show varied U-Pb provenance patterns along the basin. Zircon ages range from 936 to 3409Ma, but Paleo- and Mesoproterozoic terrains constitute the main sources of the original sediments. The youngest population (~930Ma) establishes the maximum depositional age of the group. Sm-Nd T DM data show the predominance of Paleoproterozoic ages (1.90-2.08Ga) and also indicate some input from younger sources in rocks of the Lapa Formation (1.67 to 2.0Ga) in the upper part of the group, whereas rocks of the Serra do Garrote Formation present the oldest model ages (2.03 to 2.76Ga). Hf isotopic compositions of the detrital zircons indicate that they were derived mainly from recycled Paleoproterozoic crust with a minor Mesoproteroic juvenile component. Terranes within the São Francisco Craton represent the main sources of detrital sediments of this group and reinforce the interpretation that it may be a passive margin sequence developed along the western margin of the original continent. However, the origin of Mesoproterozoic grains remains uncertain. Slightly younger Sm-Nd model ages in the Lapa Formation, however, are not entirely consistent with derivation solely from the craton and may indicate contribution from younger sources, such as the Neoproterozoic Goiás Magmatic Arc. © 2011 International Association for Gondwana Research.

de Oliveira R.G.,CPRM Servico Geologico do Brazil | de Medeiros W.E.,Federal University of Rio Grande do Norte | de Medeiros W.E.,Brazilian National Council for Scientific and Technological Development
Journal of South American Earth Sciences | Year: 2012

In the Borborema Province (BP) - northeastern Brazil - two important Cenozoic events occurred at the surface: the Macau magmatism and the Borborema Plateau epeirogenesis. To obtain appropriated-scale geophysical data to explain the deep origins of these two events, different gravimetric/elevation databases were integrated with new surveys. Bouguer admittance estimates reveal that isostatic condition of the BP, especially in the Borborema Plateau, can be explained using elastic models to the lithosphere only if surface and buried loadings are combined. If the buried load is applied in the base of the crust, the ratio between buried and surface weights is circa 15 for a lithosphere with effective elastic thickness around 15 km and crust thickness around 33 km. From an interpretative viewpoint of the buried load, it is assumed that the lower crust under the Borborema Plateau might have an anomalous high value of density. Magmatic underplating might explain this fact as well as the observed surface magmatism and epeirogenesis. Crustal thickening of about 4 km under the Borborema Plateau and intracrustal seismic velocity discontinuity with high V p/V s ratio are geophysical facts consistent with magmatic underplating. However, the surface magmatism presents low volume and mainly alkaline composition - facts that are not entirely consistent with the hypothesis of magmatic underplating. Regardless the validity of this hypothesis, Cenozoic-to-present events in BP might be somewhat associated with imbalances in lithosphere-asthenospheric mantle and/or crust-lithospheric mantle systems. The existence of free-air anomalies showing no null integral over area and of an expressive positive geoid anomaly are geophysical evidences of these imbalances. Possibly, the Borborema Plateau is still suffering epeirogenesis. Post-depositional deformation found in Barreiras Formation strata, Late Quaternay fault reactivations, and AFT thermochronology analysis suggesting the existence of a cooling stage between 20 and 0 Ma might be geologic evidences of the continued action of epeirogenesis until the present. In addition, the relatively high level of the present intraplate seismicity recorded in several regions of the BP is another unequivocal geophysical evidence that the crust of the province is still submitted to accommodation processes. © 2012 Elsevier Ltd.

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