DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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12 resultados
Resultados da Pesquisa
Item U-Pb and Lu-Hf zircon data of the grenvilian arc-related Zâmbué, Fíngoè and Cazula supracrustal complexes, Southern Irumide Belt, NW Mozambique.(2022) Petry, Thales Sebben; Philipp, Ruy Paulo; Jamal, D. L.; Lana, Cristiano de Carvalho; Alkmim, Ana RamalhoThe supracrustal rocks from the Zˆ ambu`e and Fíngo`e Supergroups and the Cazula Group in the Mesoproterozoic Southern Irumide Belt (SIB) of NW Mozambique provides a sedimentation record associated with the Rodinia supercontinent. The Zˆ ambu`e Supergroup comprises a succession of thick massive orthoquartzites and meta-arkoses, with minor calc-silicatic schists, marble, and a basal complex of ortho- and paragneisses. The Fíngo`e Supergroup and Cazula Group are composed of metasandstones, calc-silicatic schists, and metapelites interlayered with felsic, mafic, and ultramafic metavolcanic rocks. U-Pb and Lu-Hf isotopic determinations of detrital zircon from five key samples show similar ages for the main source rocks. Detrital zircon from the Zambu ˆ `e Supergroup range between 1208 and 1086 Ma in age, with a restricted contribution of Paleoproterozoic source rocks. The maximum depositional age was established at 1110 ± 2 Ma. The Fíngo`e Supergroup shows zircon ages between 1233 and 1106 Ma, with a subordinate contribution of Paleoproterozoic and NeoArchean zircon grains. The calculated maximum depositional age of 1142 ± 6 Ma is similar to the crystallization age of 1094 ± 9 Ma obtained from a meta-andesite, and indicates the syn-orogenic nature of these volcanism. In the Cazula Group samples, the zircon ages range between 1164 and 1076 Ma, with minor Paleoproterozoic contributions. The maximum depositional ages were established at 1076 ± 1 Ma and 1139 ± 1 Ma. The Lu-Hf data show predominantly positive εHf(t) values (+2 and +10) and TDM 2 ages ranging between 1.75 and 1.50 Ga, indicating isotopic signatures of juvenile sources, with limited older continental crust contributions. The age results, the well-defined young age modes of the detrital zircon associated with the arc magmatism of the Southern Irumide Belt and the Hf isotopic composition demonstrate that the Zambu ˆ ´e and Fíngo`e Supergroups and Cazula Group represent arc-related basins. Structural data indicate a complex and polyphasic evolution, with the development of the metamorphic foliations associated with Mesoproterozoic transpressional oblique tectonics, related to accretionary and collisional phases of the Irumide Orogeny (1200–1000 Ma).Item Sedimentary provenance and role of tectonic inheritance on the control of the Macaúbas group, eastern margin of São Francisco Craton (SE Brazil).(2021) Oliveira, Rosana Gonçalves; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Souza, Maria Eugênia Silva de; Lana, Cristiano de Carvalho; Alkmim, Ana Ramalho; Silva, Marco Antônio Leandro da; Bueno, Cássio; Linhares, DavidsonThe Neoproterozoic Macaúbas Group represents the precursor basin system of the Araçuaí–West Congo orogen, located in the southern margin of Sao ̃ Francisco Craton, and records a Tonian volcano-sedimentary succession, at the base, overlain by a Cryogenian sequence related to the Neoproterozoic global glacial event. Detailed strat- igraphic surveys along the Tonian units allowed the identification of two lithofacies associations related to al- luvial fan and braided river environments, while the three Cryogenian lithofacies associations indicate a glaciomarine environment associated with extensive tectonics that has evolved into a marine environment. The results show that the age spectra of the Tonian and Cryogenian units are similar, differing mainly for an increased peak in the Cryogenian sample in ca. 1.0 Ga, where the primary source is probably related to those magmatic rocks associated with the Stenian-Tonian extensional breakup of the Sao ̃ Francisco-Congo paleocontinent. The KS-Test shows that not all the Tonian samples are similar to each other, as in all the Cryogenian samples. The detailed stratigraphic and structural surveys associated with the geochronological U–Pb data allow us to interpret that the Tonian and the basal Cryogenian sequences were deposited in two episodes of an active intracontinental tectonic context related to fault reactivations along the WNW-ESE Pirapora aulacogen structures in superimposed basin-cycles, the middle-to late-Cryogenian sequences extrapolated the WNW-ESE boundaries while the basin local depocenter and its surroundings expanded to a large depocenter during the basin evolution.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 New U-Pb (SHRIMP) and first Hf isotope constraints on the Tonian (1000-920 Ma) Cariris Velhos event, Borborema Province, NE Brazil.(2020) Caxito, Fabrício de Andrade; Santos, Lauro Cézar Montefalco de Lira; Uhlein, Alexandre; Dantas, Elton Luiz; Alkmim, Ana Ramalho; Lana, Cristiano de CarvalhoOrthogneisses associated with metavolcanosedimentary successions related to the 1000 – 920 Ma Cariris Velhos event occur mainly in a ca. 700 km-long sigmoidal-shaped belt that crosscuts the Transversal Zone of the Borborema Province and extends to the fold belts located in its southern or external zone (part of the Riacho do Pontal and Sergipano orogens). Despite its importance, the tectonic setting and the role of those rocks in the geological evolution of the Borborema Province are contentious and not yet well understood. New zircon U-Pb SHRIMP data on an augen-gneiss sill of the Afeição Suite intruding mica-schists mapped as part of the Santa Filomena Complex yielded a Concordia Age of 974 ± 11 Ma, indicating that at least part of the metasedimentary rocks in the internal zone of the Riacho do Pontal Orogen are Tonian or older and possibly related to the Cariris Velhos event. Hf-in-zircon isotope data are presented for the first time for Cariris Velhos-related ortho-derived rocks of the Afeição Suite. Analyzed samples yielded εHf(t) in a narrow range between -1.51 and +2.41, with associated TDMHf of 1.6-1.4 Ga, similar to previously obtained Nd isotope data with εNd(t) = -1.0 to +3.1 and TDMNd of 1.5-1.2 Ga. A possible scenario to explain both the geochemical features and the moderately juvenile to slightly evolved, near-chondritic Hf and Nd isotope signatures is a continental arc setting, where fractionated melts produced in the supra-subduction zone mantle wedge carrying a Tonian juvenile signature became contaminated with discrete amounts of Archean-Paleoproterozoic continental crust during ascent, producing Mesoproterozoic model ages which represent the mixture of those two end-members.Item Provenance shift through time in superposed basins : from early cryogenian glaciomarine to late ediacaran orogenic sedimentations (Araçuaí Orogen, SE Brazil).(2020) Castro, Marco Paulo de; Queiroga, Gláucia Nascimento; Martins, Maximiliano de Souza; Soares, Antônio Carlos Pedrosa; Oliveira, Leon Dias; Lana, Cristiano de Carvalho; Babinski, Marly; Alkmim, Ana Ramalho; Silva, Marco Antônio daRecords of Precambrian glaciation have been reported from southeastern Brazil for over a century. We present sedimentological, stratigraphic and isotopic (U-Pb and Lu-Hf on detrital zircons, C and O on carbonates) studies on diamictite-rich to diamictite-free successions of the Araçuaí Orogen, the Brazilian counterpart of the Araçuaí – West Congo Orogenic System (AWCO). From base to top, the Chapada Acauã Formation (Macaúbas Group) includes a diamictite-rich unit, with lenses of graded sandstone and clast-supported conglomerate, that gradually passes to graded sandstone, pelite with sparse oversized clasts and rare carbonate lenses on top, representing mass flow and turbidity current deposits of submarine fan, followed by finer-grained turbiditic sedimentation with iceberg discharges along fan fringes, from glaciomarine to post-glacial scenarios. The Salinas Formation comprises a deep-sea sand-mud sequence composed of pelites and pelitic wackes. The Chapada Acauã Formation was deposited in-between 750 and 667 Ma. It shows wide spectra of zircon ages (typical of continental rift to passive margin settings) that start around 3.2 Ga and display main age peaks indicating sediment provenance from the Rhyacian-Orosirian basement (εHf(t) = +14.6 to −18.5) and Early Tonian anorogenic rocks (950–880 Ma; εHf(t) = −3.2 to −23.2) for the diamictite-rich lower unit and, for the upper unit, also in Early Cryogenian anorogenic rocks (ca. 715 Ma, εHf(t) = −9.6). In contrast, the Salinas Formation shows most ages in-between 676 and 620 Ma and a maximum sedimentation age around 551 Ma, with εHf(t) from +6.9 to −18.2, unravelling an important shifting of sediment provenance to sources located in magmatic arcs and collisional granites of the Araçuaí and Ribeira orogens. The Early Cryogenian age and negative Hf signature for the glaciomarine Chapada Acauã Formation point to sediment sources in the 720–670 Ma anorogenic igneous rocks found in AWCO and adjacent Congo – São Francisco Craton, and suggest correlation with the Sturtian global glaciation.Item Neoproterozoic magmatic arc volcanism in the Borborema Province, NE Brazil : possible flare-ups and lulls and implications for western Gondwana assembly.(2020) Caxito, Fabrício de Andrade; Basto, Camila Franco; Santos, Lauro Cézar Montefalco de Lira; Dantas, Elton Luiz; Medeiros, Vladimir Cruz de; Dias, Tatiana Gonçalves; Barrote, Vitor Rodrigues; Hagemann, Steffen; Alkmim, Ana Ramalho; Lana, Cristiano de CarvalhoNew zircon U-Pb (SHRIMP and LA-ICPMS), elemental and Nd-Sr geochemistry data on rhyolitic metavolcanic and metavolcaniclastic rocks of NE Brazil characterize widespread arc-related phenomena during the Neoproterozoic, related to the Conceição-type or Stage I plutonic rocks. U-Pb zircon dating pinpoint the main phase of magmatic activity at ca. 635-600 Ma in the 700-km long sigmoidal Piancó-Alto Brígida domain, but other important flareups might have taken place at ca. 670-690, 730-760, 810-820 and 860-880 Ma. A comprehensive compilation of detrital zircon data from metavolcanosedimentary successions of the entire Borborema Province (n=5532) confirms the occurrence of a quasi-continuum Neoproterozoic spectra punctuated by peaks at those same age intervals separated by minor lulls. Low Th/U rims of zircon crystals dated at ca. 577 Ma provide an estimate of the age of regional transpressional metamorphism. Samples of all age ranges are mostly calc-alkaline, magnesian and peraluminous, with moderately to highly fractionated LREE enrichment, negative Nb-Ta anomalies akin to convergent settings, and plot mainly within the volcanic arc field in tectonic discrimination diagrams. Nd-Sr isotope systematics indicate the involvement of juvenile Neoproterozoic melts from the mantle wedge, which upon mixing with Archean-Paleoproterozoic basement and contamination with the host metasedimentary rocks yield Mesoproterozoic TDM mainly at 1.14-1.44 Ga, near-chondritic εNd(t) and 87Sr/86Sri 0.703-0.710.We put forward a model involving a major continental back-arc zone related to the development of the Conceição magmatic arc, akin to the modern-day Taupo volcanic zone of New Zealand, crosscutting NE Brazil and presumably continuing through the schist belts of Nigeria and Cameroon. The main magmatic flare ups might have been induced by extra-arc phenomena, such as collision of the West African paleocontinent with the northwestern Borborema edge due to closure of the exterior Goiás-Pharusian Ocean, force-speeding subduction in the interior V-shaped oceanic basins that constituted the Transnordestino-Central African Ocean and generating clockwise windshield-wiper-like rotation of the blocks back towards the São Francisco-Congo paleocontinent in a complete Wilson Cycle.Item A Neoproterozoic hyper-extended margin associated with Rodinia's demise and Gondwana's build-up : the Araguaia Belt, central Brazil.(2019) Hodel, F.; Trindade, Ricardo Ivan Ferreira da; Macouin, Melina; Meira, V.T.; Dantas, Elton Luiz; Paixão, Marco Antonio Pires; Rospabé, M.; Castro, Marco Paulo de; Queiroga, Gláucia Nascimento; Alkmim, Ana Ramalho; Lana, Cristiano de CarvalhoThe Araguaia Belt encloses a poorly constrained Pan-African (Brasiliano Cycle) continental suture marked by a series of (~750 Ma) ophiolitic units which, when properly characterized, could provide important informations on its geological history, closely linked with the Rodinia demise and further western Gondwana amalgamation. We present new bulk-rock and mineral major and trace element compositions for these ultramafic and mafic units. They mainly consist in fully serpentinized harzburgite, scarce dunite lenses and chromite pods, tectonically overlain by basaltic pillow lavas. Low Al2O3/SiO2 ratios (0.01 to 0.06), rather highMgO concentrations (42.28 to 45.29 wt%) and spinels' Cr# and Mg# ratios comprised between 0.36 and 0.51 and 0.59 and 0.72, respectively, indicate a depleted oceanic-like protolith. MORB-peridotite interactions are evidenced both by pyroxenite, olivine gabbro and diabase occurrences in the serpentinites and by high TiO2 (up to 0.42 wt%) contents in spinels from some Serra do Quatipuru serpentinites. These observations support that the Araguaia Belt ophiolitic bodies are the remnants of the upper mantle section of a MOR or subcontinental lithosphere. The serpentinites wholerock REE content can be modeled as resulting from a dry partial melting involving 14 to 24% of melt extraction, coupled with refertilization by fertile melts, generated deeper in the mantle. Such an oceanic-like setting is also supported by the N-MORB signature of Serra do Tapa and Morro do Agostinho pillow lavas basalts. All together, these results tend to infirm the supra-subduction zone (SSZ) setting previously proposed for these ophiolitic units. Important LILE, B and Li enrichments in the serpentinites likely result from a metasomatic event involving sediments-derived fluids that occurred during the obduction of the units on the Amazonian Craton. Our results combined with (1) the apparent scarcity of igneous crustal rocks, (2) the proximal nature of the metasedimentary rocks hosting the ophiolitic units, and (3) the occurrences of Amazonian Craton fragments eastward of the ophiolitic bodies, allow us to propose that the Araguaia Belt comprises a fossil ocean-continent transition (OCT) accreted on the eastern border of the Amazonian Craton.Item Two billion years of evolution enclosed in hydrothermal rutile : recycling of the São Francisco Craton Crust and constraints on gold remobilisation processes.(2019) Pereira, Inês; Storey, Craig Darryl; Darling, James; Lana, Cristiano de Carvalho; Alkmim, Ana RamalhoThe Quadrilátero Ferrífero in the São Francisco Craton, Brazil is known for itsworld-class gold deposits hosted by the Rio das Velhas greenstone belt (RdV). As in other greenstone belts, gold is also concentrated in late Archean/ early Paleoproterozoic supracrustal units; in this casewithin the Moeda Formation. This unit has been compared to theWitwatersrand basinwhere there has been a long-termdebate over the nature of the gold andwhether it is detrital (placer), hydrothermal or hybrid (modified placer). Presently, links between gold in the Moeda Formation and RdV are tenuous. To enlighten this area of ambiguity, a new approach using chemical, isotopic andmineral inclusion data from detrital rutile found in the gold-bearing horizons of the Moeda Formation is presented. Grain textures and mineral inclusions have contributed to establishing a primary hydrothermal origin for the rutile, related to As-Fe-Cu-Sb-Pb-Wrich mineralising fluids. Fe, Nb and V indicate that the likely source of the goldrelated rutiles is the Archean banded iron formations within the RdV, where most of the lode-gold occurs. Average Nb/Ta values of these rutiles are lower than average continental crust ratios which suggests fractionation driven by fluid precipitation and/or competing mineral phases. U-Pb data yield primary crystallization ages older than deposition ages (N2.58 Ga), supporting the detrital nature of these rutiles. Rutiles record either resetting or new growth at 2.1 Ga and at ca. 500 Ma, duringwhich goldwas remobilised. Hence, this study supports a modified placer model for the gold-bearing horizons of the Moeda Formation. These fluid-assisted gold remobilisation events can be found in other correlated Paleoproterozoic gold-bearing horizon units that represent intracratonic basins related to the rifting of the Kenorland Supercontinent. This study reinforces the suitability of rutile and mineral inclusions as a powerful tool to elucidate processes and provenance.Item Characterization of xenotime from datas (Brazil) as a potential reference material for in situ u-pb geochronology.(2018) Vasconcelos, A. D.; Gonçalves, Guilherme de Oliveira; Lana, Cláudio Eduardo; Buick, Ian S.; Corfu, Fernando; Cipriano, Ricardo Augusto Scholz; Alkmim, Ana Ramalho; Queiroga, Gláucia Nascimento; Nalini Júnior, Hermínio AriasThis study investigatesfive megacrysts of xenotime (XN01, XN02, XN03, XN04, and XN05) aspotential reference materials (RMs) for U-Pb geochronology. These crystals belong to a 300 g xenotimeassortment, collected from alluvial deposits in SE Brazil. Electron microprobe and Laser Ablation-InductivelyCoupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses show that the selected crystals are internallyhomogeneous for most rare earth element, (REE, except some light REE) but are relatively heterogeneous forU and Th. The xenotime REE patterns are consistent with an origin from hydrothermal quartz veins in theDatas area that cut greenschist-facies metasediments and that locally contain other accessory phases such asrutile and monazite. High-precision U-Pb Isotope Dilution-Thermal Ionization Mass Spectrometry (ID-TIMS)analyses showed slight age heterogeneity for the XN01 crystal not observed in the XN02 sample. The twocrystals have slightly different average206Pb/238U ages of 513.4 ± 0.5 Ma (2 s) and 515.4 ± 0.2 Ma (2 s),respectively. In situ U-Pb isotope data acquired via LA-(Q,SF,MC)-ICP-MS are within the uncertainty of theID-TIMS data, showing homogeneity at the 1% precision of the laser ablation (and probably ion microprobe)technique. U-Pb LA-(MC, SF)-ICP-MS analyses, using XN01 as a primary RM, reproduced the ages of otherestablished RMs within less than 1% deviation. Other Datas crystals (XN03-05) also display a reproducibility inPb/U dates better than 1% on LA-ICP-MS, making them good candidates for further testing by ID-TIMS.Item A new appraisal of sri lankan bb zircon as a reference material for LA-ICP-MS U-Pb geochronology and Lu-Hf isotope tracing.(2017) Santos, Maristella Moreira; Lana, Cristiano de Carvalho; Buick, Ian S.; Schmitz, Mark D.; Kamo, Sandra L.; Gerdes, Axel; Corfu, Fernando; Tapster, Simon; Lancaster, Penelope; Storey, Craig Darryl; Basei, Miguel Ângelo Stipp; Tohver, Eric; Alkmim, Ana Ramalho; Nalini Júnior, Hermínio Arias; Krambrock, Klaus Wilhelm Heinrich; Leite, Cristiano Fantini; Wiedenbeck, MichaelA potential zircon reference material (BB zircon) for laser abla tion-in ductively coupled plasma-mass spectrometry (LA-ICP-M S)U-Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from SriLanka was studied. Within-grain rare earth element (REE) compositions are largely homogeneous, albeit with somevariation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains,the variation in U content for all analysed crystals ranged from 227 to 368 lgg-1and the average Th/U ratios werebetween 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between thegrains – mean176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 3 1018g-1for a numberof BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the samecrystal (analysed by ID-TIMS in four different laboratories) gave consistent U-Pb ages with excellent measurementreproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA-ICP-MS) from individual crystals returned results that arewithin uncertainty equivalent to the TIMS ages. Finally, we report on within- and between-grain homogeneity of theoxygen isotope systematic of four BB crystals (13.16‰ VSMOW).