UNIVERSIDADE DE BRASÍLIA - INSTITUTO DE GEOCIÊNCIAS
UNIVERSIDADE DE BRASÍLIA -
INSTITUTO DE GEOCIÊNCIAS
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ANO 2006
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Hercynite–quartz-bearing granulites from Brejões Dome area, Jequié Block, Bahia, Brazil: Influence of charnockite intrusion on granulite facies metamorphism
Johildo Barbosa
Christian Nicollet
Carlson Leite
Jean-Robert Kienast
Reinhardt A. Fuck
Eron Pires Macedo
Lithos(2006): 92(3-4):537-556
Keywords: Granulite; Jequié Block; Paleoproterozoic; São Francisco Craton;
Spinel + quartz; Ultrahigh-temperature
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ABSTRACT
In the present study, we describe and discuss the geology of aluminous–magnesian granulites and associated garnet-bearing charnockitic granulite from the Brejões Dome area, located in the Jequié Block, part of the São Francisco Craton in Bahia, Brazil. Investigation of metamorphic mineral assemblages allows the evaluation of P–T conditions for the formation of these rocks, and therefore to obtain constraints for the better understanding of the geological evolution of the area. We conclude that the rocks from the Brejões Dome area were formed under granulite facies conditions of low to intermediate pressure (5–8 kbar). Temperatures determined in samples of aluminous–magnesian granulites collected away from the dome are in the order of 850 °C, similar to those determined elsewhere in the southern part of the Itabuna–Salvador–Curaçá Orogen. However, samples of the same rock type collected close to the Brejões Dome are hercynite + quartz-bearing and record higher temperatures of about 900–1000 °C. It is suggested that the intrusion of the Brejões charnockite diapir was responsible for a local increase in temperature above the peak temperature of regional granulite metamorphism.
Kalungaite, PdAsSe, a new platinum-group mineral from the Buraco do Ouro gold mine, Cavalcante, Goiás State, Brazil. Mineralogical Magazine(2006), 70(1):123-130)
Botelho,N.F.; Moura,M.A.; Peterson,R.C; Stanley,C.J.;Silva,D.V.G.
Mineralogical Magazine(2006), 70(1):123-130)
Key words: Kalungaite; PdAsSe; New Mineral Species; Brazil; Buraco do Ouro; Gold Deposit
ABSTRACT
Kalungaite, PdAsSe, is a new mineral discovered in the Buraco do Ouro gold mine, Cavalcante town, Goiás State, Brazil. It occurs in a quartz-muscovite mylonite, related to a peraluminous granite, in platy anhedral aggregates along foliation planes. Associated ore minerals are gold, chalcopyrite, bohdanowiczite, an unnamed Pb-Bi-Se-S mineral, clausthalite, guanajuatite, stibiopalladinite, sperrylite and padmaite. Gangue minerals are muscovite, quartz and rare tourmaline and magnetite. Kalungaite is lead-grey, has a metallic lustre, a black streak and is brittle with uneven fracture. No cleavage was observed. The mineral has a micro-indentation hardness of VHN25 = 438 (range of 429–455 kg/mm2 from five indentations). Under reflected light, kalungaite is cream, or creamy grey adjacent to gold grains, has no internal reflections and is isotropic. Reflectance values in air (and in oil) are: 47.5 (33.3) at 470 nm, 46.9 (32.6) at 546 nm, 46.8 (32.6) at 589 nm and 48.0 (34.0) at 650 nm. The average of eight electron-microprobe analyses gives: Pd 41.32, As 27.49, Bi 0.35, Sb 1.59, Se 27.67 and S 1.22, total 99.64 wt. %, corresponding to Pd1.006(As0.950Sb0.034Bi0.004)Σ1.007. Kalungaite is cubic, space group Pa3, a = 6.089(4) Å, V = 225.78 Å3, Z = 4. Dcalc is 7.59 g/cm3. The strongest seven X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 3.027(75)(002), 1.838(100)(113), 1.172(95)(115, 333), 1.077(80)(044, 144, 334), 0.988(70)(116, 235, 253), 0.929(90)(335) and 0.918(70)(226). Kalungaite is interpreted as having formed from hydrothermal fluids of granitic origin, during synemplacement shearing and alteration, producing an unusual gold-platinum-group element deposit.
Sources of anthropogenic lead in sediments from an artificial lake in Brasília–central Brazil
S.M.C.L. Gioia, M.M. Pimentel, M. Tessler, E.L. Dantas, J.E.G. Campos, E.M. Guimarães, M.T.S. Maruoka, E.L.C. Nascimento
Science of The Total Environment; Volume 356, Issues 1-3 , 1 March 2006, Pages 125-142
Keywords: Pb isotopes; Urban lake sediments; Atmospheric deposition; Pollution; Brazilian Lake
Pb concentration and Pb isotopic composition are known to represent powerful tools to investigate the history of Pb pollution in water and sediments. In this paper, we present and discuss the results of a detailed study of sediments deposited in the Paranoá Lake, a 44-year-old artificial reservoir in Brasília, central Brazil. Pb concentration and isotopic composition of the sediments were obtained by ID-TIMS, on three different sample fractions: leachate, residue, and bulk sample. The leachate phase has proven to be most efficient to distinguish between anthropogenic and natural Pb inputs. In the Paranoá lake, important sources of contamination were recognized, producing higher Pb concentrations (max. 37.68 ppm) and significant variations in Pb isotopic composition, relative to the regional geogenic background. Contamination of the sediments due to anthropogenic activity produced less radiogenic Pb isotopic compositions (206Pb/207Pb = 1.15–1.17), compared with the regional natural composition (206Pb/207Pb = 1.19–1.25). 210Pb analyses along one bore hole which sampled the entire sediment section indicated a sedimentation rate of 8.2 ± 1.8 mm/year. The combined use of the 210Pb ages and Pb isotopic compositions of these samples revealed three distinct periods in the lake history: (1) the period of the time formation of the lake in 1959 until ca. 1970 was characterized by the deposition of sediments displaying more radiogenic Pb isotopic signature, (2) the time interval from the start of the process of eutrophication at 1970, until 1995, was characterized by the deposition of sediments having less radiogenic average compositions, and (3) from 1995 until the present represents a period of recovery of water quality, after two sewage treatment stations started to operate.
Lithosphere–asthenosphere interaction and the origin of Cretaceous tholeiitic magmatism in Northeastern Brazil: Sr–Nd–Pb isotopic evidence
Maria Helena Bezerra Maia Hollanda
Márcio Martins Pimentel
Diógenes Custódio Oliveira
Emanuel Ferraz Jardim de Sá
Lithos(2006), 86(1-2):34-49
Key words: Continental tholeiitic magmatism; South and Equatorial
Atlantic opening; EM and HIMU end-members; Northeastern Brazil
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ABSTRACT
Rio Ceará-Mirim Swarm forms a 400 km long, mainly E–W trending dykes which have been emplaced in Northeastern Brazil during the opening of South and Equatorial Atlantic oceans at Early Cretaceous. This swarm is dominated by high- and low-Ti tholeiitic dykes showing EM-type chemical characteristics, such as: (i) strong to moderate enrichment in large-ion lithophile and high-field strength elements, and (ii) radiogenic Sr (0.70713 to 0.70473) and non-radiogenic Nd (0.512494 to 0.512) and Pb (206Pb/204Pb 18.77 to 18.34) isotopic compositions. They are compatible with the melting of an old (TDM ages ca. 1.0 Ga) enriched lithospheric mantle source, indicating that both Proterozoic- and Mesozoic-related mantle processes accounted for the genesis of continental tholeiitic magmatism. Conversely, a distinct chemical component, comparable to HIMU-type, has been identified in local alkaline sub-swarm. Such dykes have depleted Sr (0.70367–0.7031) and Nd (0.5129-0.512772), and strongly radiogenic 206Pb/204Pb (19.95) ratios. The source of the Rio Ceará-Mirim basalts appears to be related to melting of an enriched lithospheric mantle triggered by a long-lived thermal anomaly. It could be related either to deep (St. Helena) mantle plumes or convective cells induced by lithospheric discontinuities.
Low- and high-alumina komatiites of Goiás, Central Brazil
Raul Minas Kuyumjian
Hardy Jost
Journal of South American Earth Sciences
Volume 20, Issue 4 , March 2006, Pages 315-326
Keywords: Komatiites; Lithogeochemistry; Goiás; Central Brazil
Archean komatiites of Goiás, central Brazil, have experienced deformation and low-grade metamorphism, but several outcrops preserve primary volcanic features. Samples from less deformed komatiites of four out of five greenstone belts (Crixás, Guarinos, Pilar de Goiás, and Santa Rita) have been investigated for their geochemical properties. Komatiites from the Crixás greenstone belt have very low Al2O3/TiO2, high CaO/Al2O3, and a hump-shaped rare earth element (REE) pattern. Those from the Guarinos and Pilar de Goiás belts have similar REE patterns, characterized by a slight enrichment in LREE coupled with almost flat HREE, but differ in their inter-incompatible element ratios. Compared with those from Pilar de Goiás and Guarinos, samples from the Santa Rita belt have fractionated REE patterns with LREE enrichment, as well as high Al2O3 contents, corresponding to Al-undepleted komatiites. Komatiites from Crixás have the lowest (La/Sm)N, (La/Yb)N, and Zr/Zr* ratios compared with their equivalents from the other belts, which suggests their source was relatively depleted in LREE and high field strength elements (HFSE), probably due to the retention of garnet in the residue. Komatiites from the Guarinos, Pilar de Goiás, and Santa Rita greenstone belts are enriched in incompatible elements, which can be attributed to either low-degree partial melting at high pressures or a source previously enriched in incompatible elements. Some of the studied komatiites belong to Al- and HREE-depleted and others to the Al- and HREE-undepleted types. The depleted komatiites probably derived by melting at depths greater than 200 km, the undepleted at less than 200 km. Therefore, the komatiites of the four belts may have been derived from either one single mantle plume with different melting depths or sources from distinct plumes.
Komatiitos de baixa e alta alumina de Goiás, Brasil Central
Palavras-chave: Litogeoquímica; Goiás; Brasil Central
Embora submetidos a deformação e metamorfismo, vários afloramentos de komatiitos arqueanos de Goiás ainda possuem feições vulcânicas primárias. Amostras de komatiitos menos deformados de quatro greenstone belts (Crixás, Guarinos, Pilar de Goiás e Santa Rita) foram analisados para conhecer suas características geoquímicas. Os de Crixás possuem razões Al2O3/TiO2 e CaO/Al2O3 respectivamente muito alta e muito baixa e padrão de ETR convexo. Os de Guarinos e Pilar de Goiás possuem padrões de ETR semelhantes, caracterizados por discreto enriquecimento em ETRL acoplados com ERTP praticamente plano, mas diferem nas razões entre elementos inter-incompatíveis. Comparativamente às amostras de Pilar de Goiás e Guarinos, as de Santa Rita possuem padrão de ETR fracionado com enriquecimento em ETRL e altos teores de Al2O3 correspondentes a komatiitos não exauridos. Komatiitos de Crixás possuem as menores razões (La/Sm)N, (La/Yb)N e Zr/Zr* comparativamente aos equivalentes dos demais greenstone belts, o que sugere que a fonte foi relativamente empobrecida em ETRL e HFSE, provavelmente devido à retenção de granada no resíduo. Os de Guarinos, Pilar de Goiás e Santa Rita são enriquecidos em elementos incompatíveis, o que pode ser atribuído a uma fusão parcial pouco avançada sob alta pressão ou a uma fonte previamente enriquecida nesses elementos. Alguns dos komatiitos estudados pertencem aos tipos empobrecidos em Al- e ETRP, enquanto outros aos não empobrecidos. Os empobrecidos provavelmente derivaram de fusões a profundidades superiores a 200 km e os não-empobrecidos a inferiores a 200 km. Isto significa que komatiitos dos quatro greenstone belts derivaram de uma mesma pluma mantélica mas de profundidades distintas, ou de diferentes plumas.
The bimodal rift-related Juscelândia volcanosedimentary sequence in central Brazil: Mesoproterozoic extension and Neoproterozoic metamorphism
Renato Moraes, Reinhardt A. Fuck, Márcio Martins Pimentel, Simone M.C.L. Gioia, Maria H.B.M. de Hollanda, Richard Armstrong
Journal of South American Earth Sciences(2006); 20(3):287-301
Keywords: Barro Alto Complex; Juscelândia sequence; Mesoproterozoic; SHRIMP U–Pb; Brasília belt
The Barro Alto Complex and Juscelândia volcanosedimentary sequence are exposed in the central part of the Neoproterozoic Brasília belt of central Brazil. The former is a large (approximately 150 km long), boomerang-shaped, mafic-ultramafic, layered complex formed by two different intrusions metamorphosed under granulite facies. These rocks are tectonically overlain by rocks of the Juscelândia volcanosedimentary sequence, represented mainly by biotite-gneiss and amphibolite, or amphibolite facies metamorphic equivalents of rhyolite and basalt, respectively. New SIMS U–Pb zircon data and Sm–Nd isochron data presented herein help clarify the igneous and metamorphic evolution of the Juscelândia volcanosedimentary sequence, as well as its relationship with the Barro Alto Complex. Zircon grains from two biotite gneisses were analyzed by SIMS (SHRIMP) and indicate Mesoproterozoic dates, approximately 1.28 Ga, interpreted as the time of bimodal volcanism in a tectonic setting transitional between a continental rift and an ocean basin. Metamorphism is constrained by Sm–Nd garnet-whole-rock isochrons for garnet amphibolite and pelitic schists of the Juscelândia sequence, as well as for clinopyroxene-garnet amphibolite and garnet granulite of the Barro Alto Complex, which give ages between 0.74 and 0.76 Ga, in agreement with SIMS dates for metamorphic zircon rims. These new data are significant, because they establish that a single metamorphic event affected both the Barro Alto Complex and the Juscelândia sequence. Based on these new data, we present a modified tectonic model for the Brasília belt.
Geochronological and isotopical review of pre-Devonian crustal basement of the Colombian Andes
Oswaldo Ordóñez-Carmona
Jorge Julián Restrepo Álvarez
Márcio Martins Pimentel
Journal of South American Earth Sciences
Volume 21, Issue 4 , September 2006, Pages 372-382
Keywords: Colombian Andes; Grenville orogeny; Quetame event
Under the flatlands east of the Andes, the crustal basement is exposed in a few places, composed mainly of the Mitú migmatitic complex and the Parguaza granite, whose ages range between 1.78 and 1.45 Ga. Extensive outcrops of high-grade metamorphic rocks are found in several places. Two metamorphisms are dated between 1.2–1.1 and 1.0–0.9 Ga. They are considered blocks that formed during the Grenville orogeny and have Sm–Nd TDM model ages of 1.87–1.47. The Andaquí terrane is formed mainly by the Garzón Massif, composed of granulites, migmatites, and granites, and the metamorphic rocks of the Sierra de la Macarena, which are covered by undeformed Cambrian sediments. It is believed that after the Grenville orogeny, this unit remained attached to the Amazonic Craton. All the other areas grouped in the Chibcha terrane, though they formed during the Grenville orogeny, are believed to have remained either as part of another continental block or dispersed islands to be amalgamated to the Amazonic Craton during the Lower Paleozoic orogeny, which in the Quetame Massif is dated between the Silurian and Devonian and is named the Quetame orogenic event.
Trace amounts of rare earth elements in high purity samarium oxide by sector field inductively coupled plasma mass spectrometry after separation by HPLC
W.R. Pedreira, C.A. Queiroz, A. Abrão, S.M. Rocha, M.E. de Vasconcellos, G.R. Boaventura, M.M. Pimentel
Journal of Alloys and Compounds, Volume 418, Issues 1-2 , 20 July 2006, Pages 247-250
Keywords: Rare earth elements; Inductively coupled plasma mass spectrometry; Samarium oxide
Today there is an increasing need for high purity rare earth compounds in various fields, the optical, the electronics, the ceramic, the nuclear and geochemistry. Samarium oxide has special uses in glass, phosphors, lasers and thermoelectric devices. Calcium chloride crystals treated with samarium have been employed in lasers, which produce light beams intense enough to burn metal. In general, the inductively coupled plasma mass spectrometry (ICP-MS) presents some advantages for trace element analysis, due to high sensitivity and resolution, when compared with other analytical techniques such as ICP optical emission spectrometry (ICP-OES). In this work, sector field inductively coupled plasma mass spectrometry was used. Sixteen elements (Sc, Y and 14 lanthanides) were determined selectively with the ICP-MS system using a concentration gradient method. The detection limits with the ICP-MS system were about 0.2 (La) pg mL−1 to 8 (Gd) pg mL−1. The %R.S.D. of the methods varying between 0.9 and 1.5% for a set of five (n = 5) replicates was found for the IPEN's material and for the certificate reference sample. Determination of trace REEs in two high pure samarium oxides samples (IPEN and JMC) was performed. IPEN's material is highly pure (>99.99%) and was successfully analyzed without spectral interference (MO+ and MOH+).
Neoproterozoic age of the Niquelândia Complex, central Brazil: Further ID-TIMS U–Pb and Sm–Nd isotopic evidence
Márcio M. Pimentel
César Fonseca Ferreira Filho
Alan Armele
Journal of South American Earth Sciences
Volume 21, Issue 3 , July 2006, Pages 228-238
Keywords: Niquelândia; Layered complex; Zircon U–Pb; Sm–Nd; Neoproterozoic rift
The age and tectonic significance of the Barro Alto, Niquelândia, and Cana Brava layered mafic–ultramafic complexes in Goiás have been a matter of debate and controversy. In many models, they have been considered representative of Paleoproterozoic intrusions metamorphosed in the Neoproterozoic, at approximately 0.79–0.76 Ga. Recent SHRIMP U–Pb data for dioritic rocks of the Niquelândia Complex, however, suggest that they crystallized around 0.80 Ga. Petrologic and field data suggest that these dioritic rocks are late-stage crystallization phases representing intense contamination with sialic country rocks rather than much younger intrusions into the lower layered series of the complex. In this study, igneous zircon grains from a cumulate websterite belonging to the upper part of the lower series of the Niquelândia Complex are investigated by the ID-TIMS U–Pb method and yield an age of 799±6 Ma. Sm–Nd isotopic data for the same sample reveal strong contamination with older crust (εNd(T) of −6.5 and TDM of 1.88 Ga). Additional Sm–Nd data for dioritic and late-stage granitic rocks of the complex have produced a whole-rock isochron with an age of 759±65 Ma and εNd(T) of −8.8. The data confirm that the upper mafic unit of the lower series of the Niquelândia Complex is Neoproterozoic and that the original magma is contaminated with Meso- to Paleoproterozoic crust. The layered complex may have been intruded into a continental rift developed at the western limb of the São Francisco-Congo continent, coeval with the development of the Goiás Magmatic Arc to the west.
Palavras-chave: Niquelândia; Complexo acamadado; Zircão; U–Pb; Sm–Nd; Rift Neoproterozóico
A idade dos complexos acamadados de Barro Alto, Niquelândia e Cana Brava, em Goiás, tem sido matéria de discussão e controvérsia. Nos modelos tradicionais eles têm sido considerados como intrusões paleoproterozóicas metamorfizadas no Neoproterozóico, há ca. 0.79–0.76 Ga. Dados geocronológicos U–Pb SHRIMP recentes em rochas dioríticas do complexo, entretanto, demonstram que essas rochas cristalizaram-se há ca. 0.80 Ga. Muito embora dados petrológicos e de campo têm sugerido que essas rochas dioríticas representam cristalizações de fases magmáticas tardias do complexo, as quais demonstram intensa contaminação com rochas encaixantes, elas também poderiam ser interpretadas como intrusões que cortam a série acamadada inferior do complexo. No presente estudo, portanto, cristais de zircão ígneo separados de uma amostra de websterito com textura cumulada pertencente à unidade máfica superior da série acamadada inferior do Complexo de Niquelândia, foram investigados pelo método ID-TIMS o qual indicou a idade de cristalização de 799±6 Ma. Dados Sm–Nd da mesma rocha sugerem forte contaminação com crosta continental mais antiga (εNd(T) de −6.5 and TDM de 1.88 Ga). Dados Sm–Nd adicionais em rochas dioríticas e graníticas tardias do complexo de Niquelândia produziram isócrona indicando a idade de 759±65 Ma e εNd(T) of −8,8.Os novos resultados confirmam, assim, que a série acamadada inferior do complexo cristalizou no Neoproterozóico e foi contaminada fortemente com rochas encaixantes meso- ou paleoproterozóicas. Assim, a intrusão pode ser interpretada como integrante de um rift continental desenvolvido no borda ocidental do continente São Francisco-Congo, contemporâneo, portanto, com o desenvolvimento do Arco Magmático de Goiás a oeste.
Shrimp U–Pb zircon dating and palynology of bentonitic layers from the Permian Irati Formation, Paraná Basin, Brazil
Roberto Ventura Santos, Paulo A. Souza, Carlos José Souza de Alvarenga, Elton Luiz Dantas, Marcio Martins Pimentel, Claudinei Gouveia de Oliveira,Laury Medeiros de Araújo
Gondwana Research(2006),9:459-463
Keywords: U–Pb dating; SHRIMP; Palynology; Permian; Irati formation; Paraná Basin; Brazil
This paper presents the first SHRIMP zircon age data from bentonitic ash fall layers intercalated with the Irati sedimentary rocks, as well as palynofossils retrieved from the PETROBRAS-Six mine, Paraná State, southern Brazil. The Permian Irati Formation is one the most important oil source horizons within the Paraná Basin, and consists mainly of siltstones, gray claystones, as well as organic-rich claystones intercalated with limestones. Zircon morphology based on cathodoluminescence images includes two different populations: a dominant population of euhedral, prismatic, elongate to acicular grains which are most likely related to an ash fall volcanism; and a population of rounded to large prismatic grains, that were interpreted as detrital grains. SHRIMP analysis performed on the euhedral and prismatic grains revealed an age of ca. 278.4 ± 2.2 Ma (7 points with 95% confidence) interpreted as the crystallization age of the volcanic eruption. Based on this new dating, the Irati Formation should be placed on the Lower Permian (Cisuralian), Artinskian in age, modifying substantially the traditional ages previously attributed to this unit. The palynofossils from this level include key species of the Lueckisporites virkkiae Zone (such as L. virkkiae, L. densicorpus, L. stenotaeniatus, Weylandites lucifer, Alisporites splendens). Typical species of this zone also occur in African and other South American (Argentina) Permian strata, allowing stratigraphical correlations. The origin of the ash falls is not clearly defined. It may be related either to calc-alkaline arc magmatism associated to the Sanrafaelica Orogeny (275 and 250 Ma) or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern Gondwana at ca. 278 My. The dating of this unit is significative to calibrate biostratigraphic schemes along the Paraná Basin, as well as equivalent zones in Gondwana areas, mainly in its Occidental portion.
Electron microprobe dating of monazite from high-T shear zones in the São José de Campestre Massif, NE Brazil
Zorano Sérgio de Souza, Jean-Marc Montel, Simone Maria Lima Costa Gioia, Maria Helena Bezerra Maia de Hollanda, Marcos Antonio Leite do Nascimento, Emanuel Ferraz Jardim de Sá, Venerando Eustáquio Amaro, Márcio Martins Pimentel, Jean-Marc Lardeaux,Michelle Veschambre
Gondwana Research, Volume 9, Issue 4 , June 2006, Pages 441-455
Keywords: Neoproterozoic; NE Brazil; Shear zones; Electron probe; Monazite dating
The easternmost domain of the Borborema Province, northeastern Brazil, presents widespread, extensional-related high-temperature metamorphism during the Brasiliano (=Pan-African) orogeny. This event reached the upper amphibolite to granulite facies and provoked generalized migmatization of Proterozoic metapelitic rocks of the Seridó Group and tonalitic to granodioritic orthogneisses of the Archean to Paleoproterozoic basement. We report new geochronological data based on electron microprobe dating of monazite from metapelitic migmatite and leuconorite within the high-T shear zones that make up the eastern continuation of the huge E–W Patos shear belt. These data were also constrained by using the Sm–Nd isotopic systematic on garnet from a syntectonic alkaline granite and two garnet-bearing leucosomes. The results suggest an age of about 578 to 574 Ma for the peak of the widespread high-T metamorphism. This event is best recorded by Sm–Nd garnet-whole rock ages. The U–Th–Pb isotopes on monazite of the metapelitic migmatite show a younger thermal event at 553 ± 10 Ma. When compared to the Sm–Nd garnet-whole rock ages, the U–Th–Pb electron probe monazite ages seem to record an event of slightly lower temperatures after the peak of the high-T metamorphism. This may reflect the difference in the isotopic behavior of the geochronological methods employed. Otherwise, the U–Th–Pb ages on monazites could indicate an event not yet very well defined. In anyway, this paper reveals the partial or even complete re-opening and resetting of the U–Th–Pb isotopic system produced by the action of low-T Ca-rich fluid.