EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

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A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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Unravelling the protracted U-Pb zircon geochronological record of high to ultrahigh temperature metamorphic rocks : Implications for provenance investigations.
(2023) Tedeschi, Mahyra; Vieira, Pedro Leonardo Rossi; Amaral, Matheus Henrique Kuchenbecker do; Ribeiro, Bruno Vieira; Barrote, Vitor Rodrigues; Reis, Humberto Luis Siqueira; Stutenbecker, Laura; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio
The assessment of detrital zircon age records is a key method in basin analysis, but it is prone to several biases that may compromise accurate sedimentary provenance investigations. High to ultrahigh temperature (HT-UHT) metamorphism (especially if T > 850 °C) is herein presented as a natural cause of bias in provenance studies based on U-Pb detrital zircon ages, since zircon from rocks submitted to these extreme and often prolonged conditions frequently yield protracted, apparently concordant, geochronological records. Such age spreading can result from disturbance of the primary U-Pb zircon system, likewise from (re)crystallization processes during multiple and/or prolonged metamorphic events. In this contribution, available geochronological data on Archean, Neoproterozoic and Palaeozoic HT-UHT metamorphic rocks, acquired by different techniques (SIMS and LA-ICP-MS) and showing distinct compositions, are reassessed to demonstrate HT-UHT metamorphism may result in modes and age distributions of unclear geological meaning. As a consequence, it may induce misinterpretations on U-Pb detrital zircon provenance analyses, particularly in sedimentary rocks metamorphosed under such extreme temperature conditions. To evaluate the presence of HT-UHT metamorphism-related bias in the detrital zircon record, we suggest a workflow for data acquisition and interpretation, combining a multi-proxy approach with: (i) in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources, and (ii) the integration of a petrochronological investigation to typify fingerprints of the HT-UHT metamorphic event. The proposed workflow is validated in the investigation of one theoretical and one natural example allowing a better characterization of the sedimentary sources, maximum depositional ages, and the tectonic setting of the basin. Our workflow allows to the appraisal of biases imposed by HT-UHT metamorphism and resulting disturbances in the U-Pb detrital zircon record, particularly for sedimentary rocks that underwent HT-UHT metamorphism and, finally, suggests ways to overcome these issues.
Magmatic diversity in continental rifts : a case study on the Early Tonian, plutono-volcanic Salto da Divisa Complex, Araçuaí Orogen, Eastern Brazil.
(2022) Victoria, Anderson Magalhães; Soares, Antônio Carlos Pedrosa; Cruz, Simone Cerqueira Pereira; Lana, Cristiano de Carvalho; Dantas, Elton Luiz; Dussin, Ivo Antonio; Borges, Ramon
Exposures from plutonic roots to volcanic roofs in deeply eroded regions may disclose the architecture and igneous processes in ancient metamagmatic edifices, like it is the Early Tonian Salto da Divisa Complex (SADICO) of Eastern Brazil. Field, petrographic, lithochemical and isotopic (in-zircon U-Pb and Lu-Hf, and whole-rock Sm-Nd) studies were conducted on the SADICO, an anorogenic plutono-volcanic complex located in the northeast Araçuaí orogen. The SADICO magmatic record comprises (with U-Pb crystallization ages, and isotopic Hf and Nd data): i) pyroxenite (εNd(t): +2.2 to −5.3; Nd TDM: 1.2–1.7 Ga); ii) mafic-intermediate dykes (εNd(t):+2.1 to −5.9; Nd TDM: 1.2–1.8 Ga) and enclaves with OIB-like signature; ii) ferroan, A-type granitoid with mafic-felsic mingling-mixing features (885 ± 9 Ma; εHf(t): −5 to −7, Hf TDM: 2.0–2.1 Ga; εNd(t): −3.2 to −4.3, Nd TDM: 1.5–1.7 Ga); iii) fluorite-bearing, metaluminous to peraluminous, ferroan A-type granites, including biotite-amphibole granite (915 to 875 Ma; εNd(t): −2.8 to −5.8, Nd TDM: 1.6–1.9 Ga), biotite granite (894 ± 10, εHf(t): −4 to −11, Hf TDM: 1.9–2.3 Ga; εNd(t): −1.6 to −8.0, Nd TDM: 1.4–2.2 Ga), and amazonite-bearing two-mica granite (εNd(t): −4.0; Nd TDM: 1.7 Ga); iv) rhyolite (905 ± 24 Ma; εHf(t): −1 to −8.7, Hf TDM: 1.8–2.2 Ga; εNd(t): +3.1, Nd TDM: 1.1 Ga) and subvolcanic silica-undersaturated trachyte (912 ± 13 Ma, εHf(t): −14 to −18, Hf TDM: 2.5–2.7 Ga; εNd(t): +0.3, Nd TDM: 1.2 Ga), also with ferroan A-type signature. Our integrated petrogenetic model envisages mantle-derived magmas (ultramafic and mafic rocks) evolved by assimilation-fractional crystallization to felsic subvolcanic and volcanic rocks, interacting with granitic magmas produced by crustal anatexis (biotite-amphibole granite) and subsequently fractionated (biotite granite) and highly fractionated (two-mica granite) with the involvement of F-rich fluids up to subvolcanic levels.
Implications for the refinement of the São Francisco Craton magmatic barcode and the North China link.
(2022) Mendes, Mônica de Cássia Oliveira; Lobato, Lydia Maria; Caxito, Fabrício de Andrade; Rosière, Carlos Alberto; Lana, Cristiano de Carvalho; Silva, Rosaline Cristina Figueiredo e
Late Archean to Paleoproterozoic dike swarms crosscut the basement and supracrustal sequences of the São Francisco Craton. Their spatial distribution and orientation patterns, as paleomagnetic signature, provide key evidence to the positioning of the cratonic area in ancient paleocontinental reconstructions through the refinement of the “magmatic barcode”. Zircon U–Pb data from dikes in the cratonic domain of the Quadrilátero Ferrífero Mineral Province, in the southern of São Francisco Craton, allowed the recognition of two magmatic stages: a Rhyacian-Orosirian pulse, belonging to the Paraopeba swarm, and a Statherian pulse that belongs to the Pará de Minas II swarm. The Ediacaran Brasiliano Orogeny later affected dikes from both swarms. The Paraopeba swarm consists of pulses related to the Rhyacian-Orosirian orogenic cycle, with dikes providing U–Pb zircon ages of 2019 + 23–11, 1944 ± 29 and 1918 ± 12 Ma. The zircon εHf values from these dikes are predominantly negative, suggesting reworking of preexisting crust, whereas the TDM ages vary from 4000 to 2500 Ma, which can be interpreted as a long period of crustal residence. The Statherian Pará de Minas II swarm, with a U–Pb zircon age of 1717 ± 9 Ma, is chronocorrelated to the lower stratigraphic sequence of the Espinhaço rift basin. Zircon grains from this dike have predominantly positive εHf values and TDM model ages between 3050 and 1950 Ma. Unlike the Paraopeba swarm, the Pará de Minas magmatism is marked by a striking input of juvenile mantle material with minor crustal contamination. The Ediacaran Brasiliano tectono-thermal event caused isotopic disturbance in both Paraopeba and Pará de Minas II swarms, resulting in lower intercepts at 595 ± 65 and 584 ± 27 Ma, respectively. Our data pinpoint dike emplacement related to tectonic events described in the southern of São Francisco. In the final stages of Rhyacian orogenic cycle, at ca. 2019–1918 Ma, data suggests an important crustal contamination. Thereafter, a crustal rifting event at ca. 1717 Ma involved dike swarm emplacement with magmatic source from a mantle plume. The Rhyacian-Orosirian ages obtained here are the first zircon U–Pb geochronological data presented for the Paraopeba dike swarm and allow for a refinement of the São Francisco Craton barcode, reinforcing previous suggestions of proximity with the North China Craton crosscut by the similarly aged Hengshan and Xiwangshan/Xuwujia dike swarms, whether or not those two cratonic pieces were part of the Columbia supercontinent.
Detrital zircon U–Pb analysis constrain the depositional age and provenance of Cryogenian glacial successions of the Macaúbas group in the northeastern Araçuaí orogen, eastern Brazil.
(2023) Pacheco, Fernando Estevao Rodrigues Crincoli; Caxito, Fabrício de Andrade; Souza, Maria Eugênia Silva de; Bento, Ciro Couto; Soares, Antônio Carlos Pedrosa; Lana, Cristiano de Carvalho
The precursor basin of the Araçuaí – West Congo Orogenic System (AWCO) formed a large gulf within the São Francisco – Congo Paleocontinent (SFCP), where the diamictite-bearing Macaúbas Group was deposited during the Neoproterozoic. However, the lack of robust age constraints on the Cryogenian glaciogenic successions prevents correlation to one or both of the Cryogenian Snowball Earth glaciations. The present study introduces new field data and new U–Pb detrital zircon data from diamictite-bearing units on the southern margin of the São Francisco Craton, in the northeastern Araçuaí Orogen. This region is much closer to possible EdiacaranCryogenian igneous rocks of the southern São Francisco craton than other regions previously studied for the Macaúbas Group, enhancing the probability of detecting detrital minerals from those rocks, if they were involved as source areas. In the studied region, the Macaúbas Group is composed of metadiamictite with sparse clasts and schistified metagraywacke with bulk mineralogy similar to the quartz-muscovite-feldspar matrix of the metadiamictites. U–Pb (LA-MC-ICP-MS) dating of 182 detrital zircon grains from the Lower Chapada Acauã Formation forming the syn-glacial sequence yielded main age peaks at 939 ± 3 Ma, 1409 ± 10 Ma, 1822 ± 8 Ma, 2044 ± 7 Ma, 2551 ± 9 Ma and 3103 ± 19 Ma. The youngest concordant zircon grain found in this study aged 753 ± 12 Ma. U–Pb (LA-MC-ICP-MS) dating of 104 zircon crystals from a granitic clast recovered from the diamictite exhibits highly discordant data plotting in distinct Discordia lines with upper intercept ages of 2.0 Ga, 2.5 Ga, 2.6 Ga and 3.2 Ga, indicating derivation from the adjacent cratonic basement. The U–Pb age spectra suggests important contribution from the Archean and Paleoproterozoic basement of the São Francisco – Congo paleocontinent and metamorphic complexes, from the Mesoproterozoic intrusive and volcanic rocks of São Francisco Craton, and from the Tonian Salto da Divisa Suite. Despite the relative abundance of Cryogenian zircon grains in the surrounding prospective source areas, the studied rocks lack this interval age. The glaciogenic events in the Macaúbas basin system probably did not sample rocks with these age intervals due to the general characteristics of this type of deposit or because the sources were not exposed. Thus, the lower diamictite-bearing units of the Macaúbas Group in the northeastern São Francisco craton were deposited after ca. 753 Ma, but their correlation to either the Sturtian or Marinoan global glaciations remain speculative.
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 Ramalho
The 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).
Detrital zircon U–Pb and Lu–Hf constraints on the age, provenance and tectonic setting of arc-related high-grade units of the transition zone of the Araçuaí and Ribeira orogens (SE Brazil).
(2022) Mendes, Raíssa Santiago; Caxito, Fabrício de Andrade; Soares, Antônio Carlos Pedrosa; Neves, Aparecida; Calegari, Salomão Silva; Lana, Cristiano de Carvalho
Sedimentary basins with epiclastic and volcanoclastic components are important geotectonic components for understanding the complex evolution of orogenic systems. The age, provenance and tectonic setting of ancient basins are, however, often hard to constrain, especially in the high-grade core of ancient mountain belts where original sedimentary and stratigraphic relations have been largely obliterated by deformation and metamorphism. In this case, analytical tools such as whole-rock geochemistry and U–Pb and Lu–Hf analyses on detrital zircon grains can be deployed to unravel the provenance and tectonic setting of high-grade metasedimentary and metavolcaniclastic units. Here, we apply these analytical tools on samples from gneissic paleosomes of migmatites found in the eastern transition zone between the Neoproterozoic–Eopaleozoic Araçuaí and Ribeira orogens (southeastern Brazil). The studied paleosomes comprise peraluminous paragneiss rich in biotite, garnet and sillimanite, metaluminous hornblende-bearing gneiss free of peraluminous silicates, and intermediate terms between these compositions, all of them with geochemical characteristics pointing to sources located in magmatic arc systems. Overall, U–Pb data from detrital zircon grains bracket a maximum sedimentation age for all samples between 600 and 627 Ma, while εHf(t): +5.7 to − 18.7 and Hf TDM model ages of 1.0–2.2 Ga suggest moderately juvenile to evolved sources for the gneiss protoliths. However, despite the similarity in age range, the analyzed samples show contrasting isotope data indicating significant variability in the source areas. Sample 7 only has grains with negative εHf (− 5.9 to − 18.7), most of them ranging in age from 708 Ma to 758 Ma, with very few older (1021–1143 Ma) and younger (642–651 Ma) zircons grains, indicating evolved crustal sources of distinct ages (e.g., the Late Tonian – Early Cryogenian South Bahia Alkaline Province, the Early Cryogenian magmatism found in the West Congo Belt, the Stenian to Early Tonian Espinhaço and Matadi-Noqui igneous rocks, and magmatic rocks of the early Rio Doce arc). Conversely, sample 13 has twenty grains with positive εHf values and ages between 602 and 758 Ma, suggesting sourcing from (meta)igneous rocks of the Rio Negro arc and their remelting products, and forty grains with negative εHf values with ages between 591 and 646 Ma suggesting magmatic sources in the Rio Doce arc. Additionally, the two youngest spot ages (553 Ma and 571 Ma) have highly negative εHf values (− 11.1 and − 16.4) suggesting their origin from collisional anatexis. Similarly, sample 12 shows detrital grains within the consistent time interval (ca. 596 Ma – 798 Ma) of the Rio Negro arc and Rio Doce arcs, reinforcing that the fragments of these arcs, or zircons that were inherited from these terranes, are potential sources to the sedimentary protoliths of the paragneisses. The regional scenario together with our field and analytical data, compared with data available in the literature, suggest the sedimentary protoliths of the studied samples filled orogenic basins related to the Rio Doce magmatic arc. Most detrital zircon ages are close to the maximum depositional age, a classical signature of orogenic basins related to magmatic arcs. The studied paragneiss unit correlates with the Nova Ven´ecia Complex, located on the intra-arc to back-arc zones of the Araçuaí orogen, and with the orogenic succession of the distal Andrelândia Group, shared by both the Araçuaí and Ribeira orogens. Furthermore, our data also suggest the juvenile Rio Negro - Serra da Prata arc system was either amalgamated with the Rio Doce arc or that fragments of these arcs were incorporated as unmelted xenoliths and xenocrystals within the Rio Doce arc rocks before ca. 614 Ma, providing key hints to unravel the evolution of the Araçuaí - Ribeira orogenic system (AROS) and its role in the Gondwana assembly.
Zircon petrochronology reveals the moderately juvenile signature of a diatexite from the boundary one between the Brasília and Ribeira orogens (SE Brazil) : relict of a Tonian arc?
(2022) Costa, Fernanda Moura; Penna, João Lucas Andrade; Martins, Lorena Cristina Dias; Tedesch, Mahyra; Novo, Tiago Amâncio; Araujo, Cristina Santos; Vieira, Pedro Leonardo Rossi; Lana, Cristiano de Carvalho; Soares, Antônio Carlos Pedrosa
Unraveling the tectonic evolution of Precambrian high-grade rocks is often challenging owing to widespread metamorphic overprint under high to ultra-high temperature conditions. In this scenario, isotopic systems-based investigations constitute an important tool to obtain the time constrains of formation and evolution of rocks.We present a petrochronological investigation using U–Pb and Lu–Hf data of zircon grains extracted from a biotitebearing granitic leucosome from a diatexite found in the boundary zone between the Brasília and Ribeira orogens, SE Brazil. Clusters of 176Hf/177Hf(t) ratio values characterize two distinct zircon data groups, suggesting at least two different crystallization stages. 176Hf/177Hf(t) ratios from group 1 range from 0.28230 to 0.28247 with εHf (t) between +7.54 and − 1.55, representing a moderately juvenile to evolved magma. This group constrains a time interval of ca. 890-540 Ma, and the ancient zircon core (890 Ma) could potentially record the minimum age for the magmatic crystallization of a moderately juvenile protolith, with ϵHf (890) ranging from +8.66 to +0.36. Excluding this ancient zircon (since it is the only date older than 800 Ma), the oldest grain provides a minimum crystallization age of ca. 797 Ma, with ϵHf (797) between +6.73 and -1.61. Group 2, exhibiting 176Hf/177Hf(t) ratios from 0.28214 to 0.28225and negative εHf(t) values (− 3.35 to − 7.53), represents xenocrysts of crustal origin from the protolith or an influx of allochthonous crustal melt during high-grade metamorphism. The age spreading from ca. 890 Ma to ca. 540 Ma along the concordia is consistent with a Pb-loss scenario, with cores locally providing younger ages than rims. This is also consistent with prolonged metamorphism, as newly crystallized domains also present a spread of ages. Our data indicate that the leucosome is the metamorphic product of a moderately juvenile rock. When placed in the regional context, the biotite-bearing granitic leucosome may represent the relic of a magmatic arc, now located in the boundary zone between the Brasília and Ribeira orogens. Its moderately juvenile signature suggests the following tectonic setting interpretations: (i) an intra-oceanic subduction setting similar to modern island arcs or an early stage of continental subduction, formed at ca. 890–800 Ma and, thus could be potentially correlated with juvenile magmatic arcs found in both Brasília (Mara Rosa – Arenopolis ´ arc system) and Ribeira (Serra da Prata – Rio Negro arc system) orogens, suggestive of a large ocean realm to the south of the Sao ˜ Francisco paleocontinental block in Tonian time; and (ii) the most primitive relic of an early stage of the continental magmatic arc installed on the active margin of the Paranapanema paleocontinent.
Implications for sedimentary transport processes in southwestern Africa : a combined zircon morphology and age study including extensive geochronology databases.
(2022) Gärtner, Andreas; Hofmann, Mandy; Zieger, Johannes; Sagawe, Anja; Krause, Rita; Stutzriemer, Marika; Gesang, Subani; Gerdes, Axel; Marko, Linda; Lana, Cristiano de Carvalho; Linnemann, Ulf
Extensive morphological and age studies on more than 4600 detrital zircon grains recovered from modern sands of Namibia reveal complex mechanisms of sediment transport. These data are further supplemented by a zircon age database containing more than 100,000 single grain analyses from the entire southern Africa and allow for hypothesising of a large Southern Namibian Sediment Vortex located between the Damara Orogen and the Orange River in southern Namibia. The results of this study also allow assuming a modifed model of the Orange River sand highway, whose origin is likely located further south than previously expected. Moreover, studied samples from other parts of Namibia give frst insights into sediment movements towards the interior of the continent and highlight the potential impact of very little spatial variations of erosion rates. Finally, this study points out the huge potential of detrital zircon morphology and large geo-databases as an easy-touse additional tool for provenance analysis.
Andean fingerprint on placer sands from the southern Brazilian coast.
(2022) Rizzi, Monique Aparecida Marchese; Dillenburg, Sérgio Rebello; Takehara, Lucy; Girelli, Tiago Jonatan; Wust, Cássia Fatima; Lana, Cristiano de Carvalho; Chemale Júnior, Farid
On the passive margin of southern Brazil, where the availability of sediments and coastal system conditions were adequate for forming a Ti–Zr-bearing placer in the Holocene, could there be a source of detrital contribution other than the Precambrian South American cratons? To answer that, detrital zircon U–Pb–Hf analyses were performed using the LA-ICP-MS method. The U–Pb age pattern distribution of 866 zircon grains showed that 35.3% of the grains belong to the Neoproterozoic, which covers the Brasiliano orogenic belts. However, 9.1% of the total zircons analyzed (up to 12% in some samples) correspond to grains younger than 50 Ma, restricted to the Andean orogeny in southern South America. The Hf signature of the zircons stands out by pointing to five significant and distinct groups interpreted as coming from the Andean (0–50 Ma), Gondwanides (230–380 Ma), Famatinian (380–500 Ma), Brasiliano (850–541 Ma), and Grenville (900–1300 Ma) orogens, confirming an Andean fingerprint as source rocks in addition to the sediments originating from the craton. This Andean source is related to the distal sediment contribution from the La Plata River system and Argentina rivers that discharge in the Atlantic Coast. Based on a statistical and Hf isotope approach, we defined that around 50% of the zircons grains were transported from the Argentina coast and La Plata River by the littoral drift for more than 1000 km to their final sink in the southern Brazilian coast.
Evidence for change in crust formation process during the Paleoarchean in the São Francisco Craton (Gavião Block) : coupled zircon Lu-Hf and U-Pb isotopic analyses and tectonic implications.
(2022) Santos, Cláudia dos; Zincone, Stéfano Albino; Queiroga, Gláucia Nascimento; Bersan, Samuel Moreira; Lana, Cristiano de Carvalho; Oliveira, Elson Paiva de
The continental crust growth/evolution processes and the tectonic regime through Eo- and Paleoarchean times are enigmatic due to the scarcity of preserved crust. The Gaviao ̃ Block, S ̃ ao Francisco Craton (Brazil), contains exposed and well-preserved Eo-Paleoarchean crust remnants, providing a rare opportunity to investigate these issues. Here, we describe new U-Pb ages and Hf isotope data of 3.51–3.4 Ga tonalites and diorites from the Gaviao ̃ Block and compare these with previously published Lu-Hf data from Hadean/Eo-Paleoarquean zircons from the Gavi ̃ ao Block and other primitive cratons. The Eo- to Paleoarchean evolution of the Gaviao ̃ Block is registered by ca. 360 Myr of continuous magmatic events from ca. 3.66 Ga to 3.30 Ga. From the available Hf data, we interpret that each of the events younger than 3.6 Ga registers a new juvenile addition that assimilated older crust, whereas the rocks older than 3.6 Ga are exclusively formed through the reworking of a Hadean, and to a less extent early Eoarchean crust. The shift in the crust generation process with the input of juvenile material into the Gavi ̃ ao Block has been documented within the ~ 3.8–3.5 Ga time in other primitive cratonic complexes including the Wyoming, Pilbara, Kaapvaal, Slave, Singhbhum, and Yilgarn. As documented in these other cra- tons, our data suggest that a shift in the Hf isotope record to rocks younger than 3.6 Ga reflects a transition from stagnant-lid to mobile-lid tectonics in the crust formation process of the S ̃ ao Francisco Craton. This change in the geodynamic regime appears to have been global at ca. ~ 3.8–3.5 Ga and facilitated the extraction of juvenile melts, crustal reworking, evolved magmatism, and the production of stabilizing melt-depleted lithospheric mantle.

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