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Sanukitoid rocks make up a complete magmatic series with distinct geochemical characteristics of TTG suites and granitoids from modern magmatic arcs and are regarded as markers of the transition from typically Archean geodynamics to modern plate tectonics. Although most known sanukitoid suites formed during the Neoarchean and Mesoarchean, numerous papers have characterized Paleoproterozoic magmatic arc granitoid rocks showing affinity with the sanukitoid series. This work presents new data from field, lithogeochemistry, zircon U-Pb geochronology, and Sm-Nd and Sr isotopic studies on granodioritic granulites with sanukitoid signatures from the Juiz de Fora Complex (JFC), one of the Paleoproterozoic tectonic components of the Minas-Bahia Orogenic System (MBOS), southern São Francisco Paleocontinent (southeastern Brazil). These rocks crystallized at ~2175 Ma and present values of εNdt between −4.0 and +0.5, TDM between 2.57 and 2.12 Ga, and 87Sr/86Sri between 0.6937 and 0.7137. We interpret these rocks as the result of crystallization of magmas from a hybrid mantle source extensively contaminated by crustal material during protracted subduction. In southeastern São Francisco Paleocontinent, the association of sanukitoid rocks with other magmatic arc rocks points to a complex and prolonged Rhyacian accretionary system similar to modern plate tectonics.

The Minas-Bahia orogeny juxtaposed Archean crustal fragments and Paleoproterozoic magmatic arcs to form the Sao Francisco-Congo Paleocontinent by the Rhyacian (ca. 2.05 Ga). Unravelling the Minas segment of the Minas-Bahia Orogenic Belt (MBO) is an important key to understanding the role of the Sao Francisco-Congo Paleocontinent in the construction of the Columbia Supercontinent. The Orosirian (ca. 1.9 Ga) final amalgamation of Columbia was preceded by a complex history of accretion of Archean nuclei and Proterozoic magmatic arcs. We present new whole-rock element geochemistry and isotopic (Rb-Sr, Sm-Nd) data and U-Pb ages for granitoid rocks of the main basement complexes located in the southern part of the Sao Francisco cratonic tip, which displays varied degrees of Neoproterozoic reworking related to the Brasiliano orogeny. Published data for the Campo Belo Complex, the Mineiro Belt and the Piedade Block are combined with the new data set to propose an integrated model for the tectonic evolution of the Minas segment of the MBO. This evolutionary model documents a complete Paleoproterozoic orogenic cycle, from subduction with terrane accretion to collision, followed by late-orogenic collapse. Subduction started diachronously between ca. 2.4 Ga and 2.2 Ga involving various Archean nuclei and Paleoproterozoic magmatic arcs that were later amalgamated during two collisional events at ca. 2.10 and 2.05 Ga. The oldest tonalite-trondhjemite-granodiorite (TTG) to sanukitoid magmatic suites transition are of Neoarchean age in the Piedade block, and of Paleoproterozoic age in the Mineiro belt and Mantiqueira complex, apparently indicating a diachronous onset of plate tectonic processes in different crustal segments. The petrogenesis, geochronology and isotopic signatures of these granitoid rocks provide important evidence towards understanding the periodicity of tectonic processes associated with the supercontinent cycle throughout Earth history.

The Gurupi Belt, in north-northeastern Brazil, is a mobile belt developed in the south-southwestern margin of the Sao Luis cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover. Field, petrographic, geochemical, geochronological, and Nd isotopic information (new and published) constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed. The Rhyacian was the main period of magmatic activity, which can be grouped into two main stages. (1) ~2185–2130 ​Ma: pre-collisional, juvenile, calc-alkaline magnesian and calcic ferroan granitoid suites, and minor calc-alkaline and tholeiitic mafic plutonism (now amphibolites), formed in intra-oceanic to transitional/continental arcs; and intra- or back-arc volcano-sedimentary basin. (2) ~2125–2070 ​Ma: syn- (two-mica granites) to late-collisional (potassic to shoshonitic granites and quartz-syenite) plutonic suites produced after crustal thickening and melting, with localized migmatization, that intruded during the compressive D1 deformational phase and concomitantly with greenschist to amphibolite metamorphism. There is a zonation of the Rhyacian episodes, with intra-oceanic stages occurring to the northeast, and the continental arc and collisional phases occurring to the southwest, indicating the presence of an active continental margin to the southwest, and subduction from NE to SW (present-day configuration). This magmatic framework is a continuation to the south of what is described for the Sao Luis cratonic fragment to the north, and the orogenic scenario is identical to what is observed for the same period in the West African Craton (Eburnean/Birrimian orogen), which additionally supports previous geological correlations. In the Neoproterozoic, a few magmatic occurrences are recognized. An extensional event allowed the intrusion of an anorogenic, nepheline syenite at ca. 730 Ma, which was followed by the intrusion of a crustal, calc-alkaline microtonalite, of uncertain tectonic setting, at 624 ​Ma. Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 ​Ma. This metamorphic event is probably related to crustal thickening, which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 ​Ma. The absence of oceanic and arc-related assemblages, along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic–Early Cambrian evolution of the Gurupi Belt, with rifting and posterior closure of the basin, without oceanization. Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly, respectively, but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events, but, instead, as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time.

The global plate tectonic regime in early Paleoproterozoic times is highly debated. The interval 2.45–2.2 Ga is known for a minima in juvenile magmatism, but this is not a global phenomenon. New results of whole-rock geochemistry and U–Pb-Hf analysis in igneous and detrital zircons, allied with existing isotopic and geophysical data, allow to identify and constrain the duration of magmatic flare-up and quiescence events in the western Sao Francisco Paleoplate. Igneous samples yield ages indicating three accretionary magmatic events, an older with ages ca. 2476.4 ± 9 Ma to 2462 ± 13 Ma, an intermediate at 2390 ± 14 Ma, and a younger from 2235 ± 26 Ma to 2201 ± 5 Ma, all presenting magmatic arc geochemical signatures. Xenoliths of quartzite and volcanic tuff from the upper greenstone sequence (Morro do Carneiro Fm.) are hosted in the 2211 ± 9 Ma tonalite and the maximum depositional age of the Morro do Carneiro basin is dated 2234 ± 12 Ma, indicating a syn-orogenic setting for this basin. Detrital zircon U Pb age distribution for quartzites of the greenstone sequence shows peaks at 2.65, 2.47, 2.39, 2.27 and 2.23 Ga. Altogether, the studied rocks record an accretionary orogeny with four distinct episodes: Episode S1: 2.52–2.46 Ga, ɛHf(t) values from +0.57 to +6.36; Episode S2: 2.43–2.37 Ga, ɛHf(t) values from +0.10 to +4.30; Episode R1: 2.32–2.26 Ga, ɛHf(t) values from +1.61 to −7.23 (from detrital zircons); Episode R2: 2.24–2.20 Ga, ɛHf(t) values from +0.39 to −2.73. These early Paleoproterozoic accretionary orogenies mark the onset of amalgamation of the Sao Francisco continental paleoplate that surrounds the craton, with accretions of an exotic micro-block and continental magmatic arcs, indicating evolution from dominant Siderian juvenile magmatism to Rhyacian crustal magmatism. These patterns show striking similarities to the orogenies in the Mineiro Belt and North China Craton.

The southern portion of the Sao Francisco Palaeocontinent in Brazil is denoted by Archean nuclei and Paleoproterozoic magmatic arcs that were amalgamated during Siderian to Orosirian orogenic processes (ca. 2.4–2.1 ​Ga). New isotopic U–Pb in zircon and Sm–Nd whole rock combined with major and trace element composition analyses constrain the crystallization history of the Neoarchean Piedade block (at ca. 2.6 ​Ga) and the Paleoproterozoic Mantiqueira Complex (ca. 2.1–1.9 ​Ga). These therefore display quite different magmatic histories prior to their amalgamation at ca. 2.05 ​Ga. Sm–Nd and Rb–Sr isotopes imply a mixed mantle-crustal origin for the samples in both units. A complete Palaeoproterozoic orogenic cycle, from subduction to collision and collapse, is recorded in the Piedade Block and the Mantiqueira Complex. Rhyacian to Orosirian subduction processes (ca. 2.2–2.1 ​Ga) led to the generation of coeval (ca. 2.16 ​Ga) TTG suites and sanukitoids, followed by late (2.10–2.02 ​Ga) high-K granitoids that mark the collisional stage. The collisional accretion of the Mantiqueira Complex against the Piedade Block at 2.08–2.04 ​Ga is also recorded by granulite facies metamorphism in the latter terrane, along the Ponte Nova suture zone. The collisional stage was closely followed by the emplacement of within-plate tholeiites at ca. 2.04 ​Ga and by alkaline rocks (syenites and enriched basic rocks) at ca. 1.98 ​Ga, marking the transition to an extensional tectonic regime. The discovery of two episodes of TTG and sanukitoid magmatism, one during the Neoarchean in the Piedade Complex and another during the Rhyacian in the Mantiqueira Complex, indicates that the onset of subduction-related melting of metasomatized mantle was not restricted to Neoarchean times, as generally believed, but persisted much later into the Paleoproterozoic.

The southeastern Guyana Shield, northeast Amazonian Craton, in the north of Brazil, is part of a widespread orogenic belt developed during the Transamazonian orogenic cycle (2.26–1.95 Ga) that includes a large Archean continental landmass strongly reworked during the Transamazonian orogeny, named Amapá Block. It consists mainly of a high-grade metamorphic granulitic-migmatitic-gneiss complex, of Meso- to Neoarchean age and Rhyacian granitoids and supracrustal sequences. For the first time, coupled U-Pb and Lu-Hf isotope data were obtained on zircon by LA-ICP-MS from five tectono-stratigraphic units of the Archean basement and one Paleoproterozoic intrusive rock, in order to investigate the main episodes of crustal growth and reworking. Whole-rock Sm-Nd isotope data were compared to the zircon Lu-Hf data. Three main magmatic episodes were defined by U-Pb zircon dating, two in the Mesoarchean (∼3.19 Ga and 2.85 Ga) and one in the Neoarchean (∼2.69–2.65 Ga). Subchondritic ɛHf(t) values obtained for almost all investigated units indicate that crustal reworking processes were predominant during the formation of rocks that today make up the Amapá Block. Hf-TDMC model ages, ranging from 2.99 Ga to 3.97 Ga, indicate that at least two important periods of mantle extraction and continental crust formation occurred during the Archean in southeastern Guyana Shield, an older one in the Eoarchean (∼4.0 Ga) and a younger one in the Mesoarchean (∼3.0–3.1 Ga). The latter is recognized as an important period of crustal accretion worldwide. The recognition of an Eoarchean episode to the southeastern most part of the Guyana Shield is unprecedented and was not recorded by whole-rock Sm-Nd data, which were restricted to the Meso–Paleoarchean (2.83 Ga to 3.51 Ga). This finding reveals that continental crust generation in the Amazonian Craton began at least 500 Ma earlier than previously suggested by the Sm-Nd systematics. Keywords: U-Pb-Lu-Hf isotopes, Zircon, Archean crustal evolution, Southeastern Guyana Shield, Amazonian Craton

O Granito Coimbra representa parte do embasamento da região de Corumbá, Mato Grosso do Sul. Esse corpo é composto das fácies porfirítica rosa, média a grossa cinza e fina rosa. Uma fase de deformação de caráter compressivo (F1) gerou uma foliação expressiva N10-20E nesse corpo, com a formação de zonas de cisalhamento paralelas. Posterior à deposição das coberturas neoproterozoicas, uma fase de deformação rúptil (F2) gerou falhas e fraturas. O granito estudado apresenta composição intermediária a ácida, gerado em ambiente de arco magmático a partir de um magmatismo calcioalcalino, metaluminoso a peraluminoso de natureza magnesiana, sendo caracterizada, litoquimicamente, como tonalitos, granodioritos, granitos e álcali granitos. A idade de cristalização U-Pb/SHRIMP em zircão é de 1859 ± 4 Ma, e os dados isotópicos Sm/Nd em rocha total indicaram valores εNd(1,86Ga) de -1,35 e idade modelo TDM de 2,27 Ga, que sugere a participação de uma fonte riaciana na origem do magma. As similaridades petrográficas, litoquímicas, geocronológicas e isotópicas entre o Granito Coimbra, o Granito Taquaral e as intrusões abrigadas na Suíte Intrusiva Alumiador do Bloco Rio Apa, sugerem que o Granito Coimbra pertença ao magmatismo representado por essa suíte e, consequentemente, ao Arco Magmático Amoguijá do Bloco Rio Apa.

The Ouricuri do Ouro Formation represents sedimentary deposits of the Statherian period in Sao Francisco Craton. Previous works have focused just on the Formation mapping, interpreting the depositional system only in general aspects. However, this study focuses on detailed facies analysis and geochronological investigations of the Ouricuri do Ouro Formation in the central area of Sao Francisco Craton, Brazil. Four facies associations are recognized: i) Proximal deposits dominated by non-cohesive debris flow; ii) Proximal sheetfloods; iii) Intermediate sheetfloods; and iv) Sandy plains of distal floods. Paleocurrent directions derived from cross-bedding indicate a radial pattern to NE-N. The vertical stacking of distal deposits overlying the proximal facies association suggests a retrogradation of the alluvial fan system, indicating a change in the dynamic of the depositional system. Retrogradation might have been caused by a decrease in the regional gradient declining of the tectonic activity or the retreat of the basin's margin faults system. Furthermore, the presence of higher frequency fining-upward cycles also suggests a climatic control in those deposits. These cycles could be results of the progressive decrease in flow capacity and competence, associated with a decrease of superficial runoff over time. Allied with the dominant paleocurrent, the geochronological data of four tuffaceous sandstones reveal the contribution of Rhyacian to Mesoarchean zircons, suggesting that they came with sediments transported from SW and S of the studied area during the Statherian. The transported sediments came from the southern portion of Gaviao Paleoplate. The contribution of volcanic zircons recognized in the tuffaceous sandstones is related to syndepositional magmatism of Statherian Rift of Espinhaco Supergroup. The tuff layer at the base of drill hole (Sample FLV-61 A) contains a zircon age with dominant fraction represented by Statherian zircons defining the syn-sedimentary age of 1722 ± 13 Ma at the basal section of the Ouricuri do Ouro Formation. The present results and available geochronological data constraints the depositional interval of Lower Espinhaco Basin or Megasequence (in sense of Chemale et al., 2012; Guadagnin et al., 2015a, b) between 1.68 Ga in the Chapada Diamantina Region.

Made available in DSpace on 2019-10-06T16:57:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-03-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The Amparo Complex and Serra Negra orthogneisses consists largely of Archean and Paleoproterozoic domains, which represent the older tectonizied basement of Ribeira Belt, southeastern portion of the Brasília Neoproterozoic Orogenesis. This is the subject of U–Pb SHRIMP and Nd and Sr isotopic and geochemical investigations aiming to increase the knowledge of these juvenile crustal domains. In this region, older Meso and Neoarchean rocks occur in physical proximity to younger Paleoproterozoic rocks of Serra Negra Orthogneiss. Mesoarchean gneisses with U–Pb zircon ages of 2956 Ma have a composition of TTG suites with TDM of 3176 Ma and a ƐNd(t) of −0.14, suggesting derivation from the partial fusion of older mafic rocks. Mafic (amphibolite) and ultramafic rocks are associated with these domains. Neoarchean porphyritic granites are associated with the former rocks, occurring as intrusive high-K granites. They have a TDM value of 3404 Ma and a ƐNd (2.7Ga) of −4.29, which demonstrates their derivation from older Archean crust. Paleoproterozoic units occur throughout the belt represented by granodioritic or tonalitic orthogneiss with intercalations of amphibolites and ultramafic rocks. In the extension to the west the units crop out in the Campinas region, and to the east are denominated Pouso Alegre Complex. They constitute a TTG-type granite-tonalite suite, as verified by their geochemical signatures, REE and incompatible elements, high Na/Ca ratios, and negative anomalies of Ta, Nb, and Ti. SHRIMP U–Pb zircon ages are between 2.09 and 2.16 Ga (Rhyacian) with TDM between 2.11 and 2.36 Ga and ƐNd(2.1 Ga) between +0.88 and + 3.18, indicating juvenile nature. Low 87Sr/86Sri ratios disclose a possible contribution of mafic precursors in their origin. Neoproterozoic Ediacaran ages of Ribeira Belt event are seen in zircon crystals of all samples analyzed for this study. The effects of this Neoproterozoic orogenic event on basement rocks resulted in anatexis, banding and folding of the older rocks. As suggested for the Paleoproterozoic Pouso Alegre Complex, it is possibly an important period of juvenile continental growth that, in association with the Archean gneisses, may be related to the southern end of the São Francisco Craton. Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista UNESP Instituto Geológico Secretaria do Meio Ambiente Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista UNESP FAPESP: 2012/17540-5

The Mineiro belt corresponds to a sequence of Siderian to Rhyacian arcs added to the Archean continental margin of the Sao Francisco Craton by soft-collision episodes. The study of the Rio Grande and Brumado metadiorites constrains processes of crust generation during the Rhyacian evolution of the Mineiro belt. The plutons contain autoliths of hornblendites and decrease in MgO, Fe2O3total, and CaO contents with the increase of SiO2 that points to fractional crystallisation. Calc-alkaline signature along with negative Nb Ta, P, and Ti anomalies indicate a magmatic arc setting. The age of the Rio Grande metadiorite between 2128 ± 24 and 2102 ± 33 Ma and of the Brumado metadiorite as 2124 ± 6 Ma correlate these plutons to the Rhyacian Ritapolis arc. The Rio Grande metadiorite displays slightly negative eNd(2.1 Ga) values and low 87Sr/86Sr(2.1 Ga) ratios that point to a mantle-derived magma. The presence of inherited zircon with age 2348 ± 11 Ma in this pluton indicates the contribution of the Siderian Resende Costa arc (2.35–2.31 Ga). The Brumado sample shows higher values of eNd(2.1 Ga) and 87Sr/86Sr(2.1 Ga) that suggest crustal contribution. The model for the generation and evolution of these plutons involves a subduction setting with the hydrous melting of the overlying mantle from fluids of the slab and consequent generation of dioritic magma. This magma ascended into the Resende Costa arc and the Rio das Mortes metavolcanic-sedimentary sequence. Crystallisation started by the generation of cumulates of magnesio-hornblende followed by their destabilisation and assimilation by a second pulse of dioritic-tonalitic magma and continuous fractional crystallisation.

A systematic investigation of amphibolites and a metaultramafite granofels was carried out in the southernmost Brasilia Orogen, part of the reworked margin of the Sao Francisco paleocontinent. These rocks occur interleaved within Neoproterozoic metasediments and the Archean-Paleoproterozoic basement. The amphibolites from the Andrelândia, Liberdade and the Carrancas nappe system show an N-MORB signature, enriched to slightly depleted in LILE (Large Ion Lithophile Elements) and LREE (Light Rare Earth Elements) and depletion in the HFSE. They define a flat sub primitive mantle (PM) normalized curve with negative anomalies of Nb and Ce. The Lima Duarte nappe amphibolite has an andesitic basalt with an E-MORB signature and magmatic arc filiation. U-Pb (SHRIMP) zircon dating on the different samples yielded similar crystallization ages of ca. 2.15 Ga. Metamorphic conditions record amphibolitic facies for all the samples and can be linked to lower intercepts aged between 560 and 590 Ma. Whole rock Nd isotopic data suggest a juvenile source with TDM ages between 1.95 and 2.22 Ga. The associated metaultramafite, from Carrancas Klippe, highlights inherited cryptic layering and fractional crystallization processes from mineral and whole rock chemistry. It is enriched in LILE and shows negative anomalies of Th and Nb and positive anomalies of Sr and Zr. The Platinum group elements present a total PGE abundance of 16.5 and 30.8 ppb. The Iridium group defines a steep positive normalized curve while the Palladium group defines a gentle positive one, as expected for differentiated liquids. U-Pb zircon dating yielded three data clusters: i) the ca. 2.5 Ga, interpreted as inheritance, ii) the ca. 2.1 Ga, considered as the crystallization age and, iii) the youngest, being ca. 600 Ma, associated with the amphibolite facies metamorphic overprint. REE analyses on Rhyacian zircons suggest plagioclase crystallization under the influence of free-REE bearing minerals. A magmatic zircon grain containing a quartz inclusion, presents a distinctive REE pattern, with a positive normalized curve and a strong negative Eu anomaly. It suggests a hybridized crystallization under influence of plagioclase-rich and silica-saturated fluids prior or during the igneous crystallization, possibly due to the influence of slab derived materials. These data unravel new insights towards mafic-ultramafic rocks formation in different settings within a Rhyacian suprasubduction system in the southernmost part of the Sao Francisco paleocontinent, later reworked during the Gondwana amalgamation.

The Gurupi Belt (together with the Sao Luis cratonic fragment), in north-northeastern Brazil, has been described in previous studies that used extensive field geology, structural analysis, airborne geophysics, zircon U–Pb dating, and whole-rock Sm–Nd isotope and geochemical data as a polyphase orogenic belt, with the Rhyacian being the main period of crust formation. This was related to a 2240 Ma to 2140 Ma accretionary processes that produced juvenile crust, which has subsequently been reworked during a collisional event at 2100 ± 20 Ma, with little evidence of Archean crust. In this study, we use Lu–Hf isotopic data in zircon from granitoids (including gneiss) of variable magmatic series, and amphibolite to improve the knowledge of this scenario, and investigate additional evidence of recycling of Archean basement. Pre-collisional high Ba-Sr and ferroan granitoids and amphibolite formed in island arc (2180–2145 Ma), show only zircons with suprachondritic eHf values (ca. +1 to +8) indicating the large predominance of juvenile magmas. Only 10% of the data show slightly negative eHf values (0 to −4), which have been observed in granodiorite-gneiss formed in continental arc (2170–2140 Ma), and in strongly peraluminous collisional granites (2125–2070 Ma), indicating the rework of older Paleoproterozoic to Archean components (HfTDM = 2.11–3.69 Ga). A two-component mixing model using both Hf and published Nd isotope data are in line with this interpretation and indicate more than 90% of juvenile material, and less influence of Archean materials. Comparing with other Rhyacian terranes that are interpreted to have been close to Gurupi in a pre-Columbia configuration (ca. 2.0 Ga), our results differ from those of SE-Guiana Shield, which show strong influence of Archean protoliths, and are very similar to those of the central-eastern portion of the Baoule-Mossi Domain of the West African Craton, which has also been formed largely by juvenile magmas in an accretionary-collisional orogen.

The southern Sao Francisco Paleocontinent (SFP) comprises Archean nuclei and Paleoproterozoic complexes encompassing magmatic arcs juxtaposed during a Rhyacian to Orosirian orogenic event. The Juiz de Fora Complex (JFC) represents an imbricated thrust system that comprises orthogranulites with a wide compositional range formed in an intra-oceanic setting during the Siderian to the Orosirian and later accreted to the southeastern margin of the SFP. Here we report new petrological, geochemical, whole-rock Nd and Sr data, as well as zircon U–Pb ages from felsic and mafic orthogranulites from the JFC. The new data is combined with a regional compilation that enables an evaluation of the interaction between magmatism and orogenetic episodes in the context of the consolidation of Sao Francisco Paleocontinent during the Rhyacian–Orosirian. Pre collisional Island Arc tholeiites (IAT), Tonalites-Trondhjemites-Granodiorites (TTGs) and sanukitoid magmatism occurred from 2200 Ma to 2085 Ma. This was followed by post-collisional magmatism, which is represented by hybrid granitoids coeval with the emplacement of E-MORB basic rocks. Crustal signatures for the Rhyacian to Orosirian evolution are highlighted by the dominance of negative eNd(t) associated with Meso- to Neoarchean Nd TDM model ages as well as inherited zircon grains from the hybrid granitoids. The JFC is extensively highlighted in the literature as a primitive intra-oceanic arc, but here we propose the reworking or recycling of ancient crustal segments within the mature arc stage of the JFC, suggesting a Mesoarchean crustal source involved in the JFC evolution.

We document new U-Pb detrital zircon LA-MC-ICP-MS data for seven metavolcanic-sedimentary successions and metasedimentary sequences and reassess additional dates of five siliciclastic samples toward their tectonic significance in the context of the Mineiro belt, Southern Sao Francisco Craton. This belt represents a crustal segment of the 2.47–2.00 Ga Minas Orogen, classically known by its Siderian and Rhyacian juvenile rocks with important implications in the Earth's geodynamics. The new and compiled detrital provenance constraints unravel the long-lived magmatic and sedimentary history of the studied basins, lasting ca. 230–220 Myr. The maximum depositional dates around 2.1 Ga reflect the renewed sediment budget with the subsequent metamorphic episode ca. 2.0 Ga. Most of the unmixed relative probability diagrams are consistent with sourcing from the Siderian and Rhyacian arcs of the Mineiro belt, determining a detrital provenance change in time and space for the precursor basins. Alternative potential sources could be the youngest rocks of the Mantiqueira and Juiz de Fora terranes that constitute the other segments of the Minas Orogen, given the age match. The overall detrital fingerprints determine the study basins resumed mainly in Rhyacian fore-arc and/or back-arc settings, i.e., akin to a subduction-related system that evolved to a collisional (foreland) environment. Few samples show fingerprints of primary extensional settings, determined by major Archean detrital populations sourced from areas outside the Mineiro belt beside the Paleoproterozoic detritus. The working model considers the collage between the Mineiro belt and the ancient foreland around 2.10 Ga and eventual interaction with other crustal segments of the Minas Orogen, generating the ca. 2.0 Ga metamorphism over the metasedimentary samples. The more complete isotopic repository in detrital and igneous zircon grains for the studied supracrustal successions and the associated rocks allows new insights into the Rhyacian–Orosirian dynamics of the Minas orogeny. In a broader perspective, the juvenile nature of the Mineiro belt reinforces the paradigm of uninterrupted continental growth during the Paleoproterozoic Earth.

The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies. Publisher PDF

A U-Pb SHRIMP zircon geochronological study was carried out in the Nico Pérez Terrane in the central-eastern portion of Uruguay with the aim of constraining its geological evolution and its cratonic affinity. Nico Pérez Terrane is made up by a mosaic of tectonic blocks with diferente lithologies and sizes. This terrane is limited to the west by the Piedra Alta Terrane through the Sarandí del Yí shear zone, and to the east, is in tectonic contact through the Retamosa thrust with the Dom Feliciano Belt (Brasiliano orogenic cycle). Lithologically, the Nico Pérez Terrane is composed by medium to high grade metamorphic rock contained in three tectonic blocks (Pavas, Valentines and Rivera blocks) represented mainly by granitoids, as well as ortho and parametamorphic rocks, such as amphibolites, metapyroxenites, BIFs, schists, quartzites with fuchsite, among others. Archean inheritance, Rhyacian, Statherian, and Neoproterozoic magmatic ages are reported here. Similar ages, which show Archaean inheritance and Neoproterozoic imprint, reported in units of the Piedra Alta Terrane modify the idea that the Río de La Plata Craton only corresponds to a juvenile Paleoproterozoic tectonic unit. This, together with recently published geophysical information, supports the cratonic affinity of the Nico Pérez Terrane with the Río de La Plata Craton.

During the Paleoproterozoic Era, the Brazilian cratons experienced orogenic events that modified the archean basement and sedimentary successions. In the southern São Francisco Craton, it can be recognized evidence of an orogenic event that happened between Rhyacian and Orosirian periods. It is related to the closure of an oceanic basin at this time, which led to the collision between the Archean Divinópolis and Campo Belo metamorphic complexes. Graphite schist occurs close to the cities of Formiga and Itapecerica (Minas Gerais), located between these complexes. To contribute to the understanding of the origin and metamorphism of the graphite from Formiga, petrographic studies, X-ray diffraction (XRD) and Raman spectroscopy analyses have been done. XRD and Raman methods revealed that the temperatures recorded by graphite are around 460°C. However, Raman data showed that the crystallite sizes correspond to higher metamorphic grade conditions (amphibolite to granulite facies). Temperatures of 460°C are probably associated with hydrothermal processes along faults in post-collisional stage. The presence of todorokite, a mineral typical of deep-sea Mn nodules formed by microorganisms, in association with graphite from Formiga, suggests a biogenic origin for the graphite occurrence.

The Juiz de Fora Complex (JFC) is one of the basement units of the Occidental Terrane, Central Ribeira belt, in the Neoproterozoic framework of Western Gondwana, regarded as part of the reworked border of the Sao Francisco Paleocontinent. The JFC comprises Paleoproterozoic granitoid rocks with TTG, calc-alkaline, sanukitoid, and tholeiite-type geochemical compositions. They exhibit complex deformational fabrics associated with two episodes of granulite-facies metamorphism, occuring in the early Orosirian and the Ediacaran. The new U-Pb (SHRIMP) isotopic ages and Lu-Hf (LA-MC-ICPMS) data combined with available lithogeochemical, whole-rock Sm-Nd and Rb-Sr isotopic data constrain the tectonic evolution of the JFC to a Siderian-Rhyacian evolved arc system. Five samples were selected for U-Pb geochronology and Lu-Hf analysis on zircon grains: a low-K tholeiite, one TTG, two sanukitoids, and a mafic tholeiite. Combined whole-rock Sm-Nd, Rb-Sr isotopes, and zircon Lu-Hf isotopic data suggest the following evolution: an initial moderately juvenile (2445 Ma) low-K tholeiitic magmatism (eNd(t) of − 0.1; eHf(t) from − 8 to + 3), followed by a moderately juvenile to evolved (2200–2182 Ma) coeval TTG-sanukitoid pulse (eNd(t) from − 0.6 to − 4.8; eHf(t) from − 11.7 to + 2.5), and eventually by a moderately juvenile (2130 Ma) tholeiitic magmatism (eNd(t) = − 0.05). The integrated information provides preliminary petrogenetic insights for these magmatic episodes, such as interaction between mantle sources and supracrustal subducted material, melting of the oceanic slab, and crustal assimilation. A ca. 2035 Ma collisional granulite event recorded in metamorphic rims and neoformed zircon grains in leucosomes, possibly marks the amalgamation of the JFC onto the Mantiqueira Complex. Geochronological and isotopic correlations with coeval terranes of the Minas-Bahia Orogen in the Brazilian and African counterparts are addressed for tectonic implications at a broader scale.

In this paper new geochemical, geochronological and isotopic Lu–Hf data from the Siempre Amigos Hills (SA), western Tandilia, Argentina, is presented. Outcrops in this small area include representative lithologies of the basement Río de la Plata craton (RPC) known as Tandilia Terrane. The new geochemical data characterize a heterogeneous Paleoproterozoic crust with a similar U–Pb SIMS magmatic age (~2.1 Ga) represented by a suite of mafic (amphibolites, charnockitic granulites), intermediate and felsic compositions (diorites, granodiorites and granitic gneisses), as well as intrusive granitic rocks (with Neoproterozoic age of ~652 Ma in zircon). Geochemical features suggest processes of magmatic differentiation from a mafic igneous protolith associated with the ‘Camboriu orogeny’ of the Trans-Amazonian–Eburnean cycle. Some amphibolites may represent sanukitoid magmas similar to those formed at the Archean-Proterozoic transition. This paper examines the hypothesis of a sanukitoid precursor for RPC Rhyacian magmatism. The potassic and calc-alkaline character of magmatic series, together with negative Nb–Ta–Ti anomalies and REE patterns, are compatible with classical modern subduction-related magmas. Precise Lu–Hf analyses of zircons collected from a granodiorite and a gneiss indicate a predominantly juvenile source (+εHf), with minor crustal recycling (-εHf). An inheritance age is recorded in a single Neoarchaean zircon core from a granodiorite (2771 ± 15 Ma), similar to calculated maximum Hf T (2.8 Ga). Considering the new available data from this region of the RPC, a sustainable petrogenetic model is proposed to explain the presence of geochemical and isotopic evidence of sanukitoid magmatism which may have occurred after 2.7 Ga, which seems to constitute a magmatic series which is a precursor to the development of the Rhyacian magmatic arc in the Tandilia Terrane. Medium-to high-grade metamorphic conditions probably resulted from Paleoproterozoic subduction followed by the intrusion of huge volumes of Rhyacian calc-alkaline magmatism. This model is compatible with RPC configuration as a collage of terranes, and also consistent with Trans-Amazonian–Eburnean amalgamation of various microcontinents in the formation of Atlantica., This paper was funded by the following grants: PIP N° 11220150100269 CO and PICT 2012–0644 , for which we are grateful to the CONICET and the ANPCyT . The authors are also indebted to the UNS- PGI project (Cod. 24/H137 ) for the partial funding of field trips. Melisa Angeletti would like to thank the Universidad Nacional del Sur and the Asociación Universitaria Iberoamericana de Postgrado for providing funds for travel to Spain to work with her co-authors. This paper also received funding from the European Union Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 778045 . Martim Chichorro is grateful for the funding provided by the GeoBioTec (UIDB/04035/2020). The authors greatly acknowledged Dr. Sebastian Oriolo for the editorial work and Dr. Mathias Hueck and anonymous reviewer for their constructive suggestions and comments.

The Mantiqueira Complex together with the Mineiro Belt and Juiz de Fora Complex, characterize a long-lived system of oceanic and continental magmatic arcs. The proposed accretion of these terranes in the Rhyacian resulted in the closure of the Minas Basin, a fundamental turning point for the geology of this area. Understanding this event is critical for determining the evolution of the South American continent. Despite its importance, there is a paucity of zircon U-Pb and Lu-Hf data available for the Mantiqueira Complex and no data from two complexes within the later.U-Pb zircon data were obtained from interpreted metasediments of those two complexes, the granulite facies Acaiaca Complex and Pedra Dourada Granulite. Four targeted samples yield cores with ages between 3.5 and 2.2 Ga and a large proportion of metamorphic grains and rims at ca. 2.1–2.0 Ga. The similarity between the detrital zircon signatures of the Acaiaca Complex and Pedra Dourada Granulite, and the Archaean inheritance of the Mantiqueira Complex, indicates that these three units are related. Potentially the Acaiaca Complex and Pedra Dourada Granulite either sourced the Mantiqueira Complex or the Mantiqueira intrusive suites reworked the protoliths of the Acaiaca Complex and Pedra Dourada Granulite.Hf-in-zircon data indicate two discrete sources for both the Acaiaca Complex and Pedra Dourada Granulite. An Archaean source (model ages of 3.2–2.6 Ga), which is consistent with the suggested origin of the Mantiqueira Complex as recycled Archaean crust sourced from the São Francisco Craton and reworked during the ca. 2.1 Ga Transamazonian orogeny. A second more juvenile source (model ages of 2.4–2.2 Ga) recorded exclusively within the more mafic samples is identical in age and Hf to that found in the Juiz de Fora Complex. This could indicate a close link between the Mantiqueira and Juiz de Fora Complexes in the period 2.2 to 2.0 Ga. Alternatively, these juvenile zircons may represent an as yet unidentified juvenile portion of the Mantiqueira arc.The results of this study are consistent with the prevailing theories for formation of the Mantiqueira Complex as a continental arc with cumulative proportion curves indicating an active-margin type depositional setting.

U-Pb and Lu-Hf isotopic studies were performed in igneous zircon crystals from orthogneisses, metagranodiorites and a gabbro of the Tumucumaque Complex, in Vila Nova region, south of Amapa state, Brazil. The complex is located in the southeastern region of the Guyana Shield, northeastern portion of the Amazonian Craton. The Tumucumaque Complex is represented by tonalitic to granodioritic gneisses and amphibolites, with subordinate metagranites and intrusive gabbros, metamorphosed in conditions of middle to Upper Amphibolite facies. The complex represent the basement of the metavolcano-sedimentary associations of the Vila Nova and Serra do Navio regions, and occur as NW-SE elongated domes. The contact of infra- and supracrustal rocks is defined by N45°-55°W-trending high-angle ductile shear zones. In this contribution we provide U-Pb zircon ages by LA-MC-ICPMS which attest for the presence of a broad area of Archean rocks in the Guyana Shield. In addition, we present stratigraphic relationships and structural data between the Tumucumaque Complex and the Rhyacian Vila Nova Greenstone Belt. The orthogneisses yielded zircon igneous ages of 2.851 ± 37 Ma and 2.852 ± 32 Ma and the metagranodiorites of 2.822 ± 33 Ma and 2.812 ± 17 Ma. Intrusive gabbro present age of 2.671 ± 46 Ma. The Lu-Hf data suggest an enriched mantle source and reworking of Paleo-archean crustal rocks. The results obtained suggest a magmatic orogenic episode during the Meso-archean (2.85–2.81 Ga) and a later Neo-archean (2.67 Ga) event, probably anorogenic.

The origin and significance of the metavolcanic rocks of the Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of the Guyana Shield in Paleoproterozoic times. This work presents new LA-MC-ICPMS U-Pb zircon data and geochemical analyses carried out on metavolcanic rocks of the VNGB. This information was supplemented by petrography, stratigraphic and structural data acquired through geologic mapping and boreholes descriptions. In the Vila Nova region, the VNGB units rest on the Archean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB consists of metabasalts and andesitic metabasalts, covered by an upper metasedimentary domain with subordinate metavolcanic and exhalative chemical rocks. The metavolcanic rocks include metabasalts, meta-andesites, amphibolites and amphibole schists, deformed and elongated according to the regional NW-SE structure. U-Pb zircon data yielded an age of 2154 ± 6 Ma for a meta-andesite of the lower portion of VNGB. One orogenic metamorphism followed by three deformational events were recognized. The D1 and D2 events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation cleavage (S2) associated with the development of the oblique shear zones. Two distinct assemblages: 1) garnet, hornblende and biotite, and 2) hornblende, plagioclase and diopside define two distinct metamorphic peaks: M1 and M2 with temperatures of 450 and 650 °C, and lithostatic pressure between 4 and 6 kbar. The metabasites comprise geochemical compositions of Fe- and Mg-tholeiites with komatiitic affinity. The first group is enriched in LREE and HFSE. The second group shows MORB-like REE patterns in association with negative Nb, Ti and P anomalies. The observed features indicate that the metavolcanic rocks of the VNGB represent the evolution of back-arc basins and island arcs associated with the Trans-Amazonian Orogeny. These rocks characterize the Rhyacian evolution of the Maroni-Itacaiunas Province in the eastern portion of the Guyana Shield.

Assembled during the Rhyacian-Orosirian boundary, the Congo-Sao Francisco palaeocontinent remained linked by a continental bridge from ca. 2 Ga to the Atlantic Ocean opening in the Cretaceous. To the south of that bridge, precursor basins and orogenic outcomes encompassed by the Neoproterozoic-Cambrian Aracuai-Ribeira orogenic system (AROS) and its African counterparts, developed. The AROS discloses reworked basement units, like the Juiz de Fora, Pocrane and Quirino complexes, which are key units to retrieve the Palaeoproterozoic history of the Congo-Sao Francisco palaeocontinent. This paper presents new U-Pb ages, and the first Lu-Hf in zircon signatures from those complexes. All magmatic zircon grains show Rhyacian and Orosirian ages, ranging from c. 2250 Ma to c. 1850 Ma. The best Concordia ages range from 2184 ± 9 Ma to 2080 ± 19 Ma. Hf in zircon and whole-rock Sm-Nd data disclose mantle-related signatures for both, the Pocrane and Juiz de Fora complexes, suggesting igneous protoliths with no or very few involvement of continental crust, similarly to juvenile magmatic arcs. Conversely, Hf in zircon data for the Quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with Archaean components. Together with a thorough compilation on Rhyacian-Orosirian orogenic systems (ROOS), our data allow us to envisage links within the Congo-Sao Francisco palaeocontinent, comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance. They are grouped into the: (i) W-ROOS, including the Mantiqueira complex, the west segment of the Eastern Bahia belt, intrusions in the south Gaviao and Porteirinha blocks, and parts of the Mineiro belt; and (ii) E-ROOS, comprising the Quirino complex, basement rocks of the Cabo Frio tectonic domain, the coastal Eastern Bahia belt, and, in Africa, Eburnean and Kimezian complexes, as well as the western Angola shield. Assembled between the W-ROOS and E-ROOS, an orogenic system with prominent juvenile to moderately juvenile isotopic signature (JU-ROOS) includes the Juiz de Fora and Pocrane complexes, and the Buerarema complex at the central segment of the Eastern Bahia belt.

The granitic rocks of the Erepecuru-Trombetas Domain, southeastern Guyana Shield, are part of two extensive volcano-plutonic associations that marked the central portion of the Amazonian Craton during the Orosirian. The older episode (2.0–1.97 Ga) encompasses the Igarape Paboca volcanic Formation and Caxipacore Suite and the younger episode (1.90–1.87 Ga) comprises the Agua Branca and Mapuera plutonic suites and the pyroclastic/effusive rocks of the Iricoume Group. LA-ICP-MS U-Pb zircon dating of granitoids provided ages of 1991 ± 5.9 and 1989 ± 7 Ma for the Caxipacore Suite, 1887.5 ± 4.8 Ma for the Agua Branca Suite and 1881 ± 8.1 Ma for the Mapuera Suite, which reinforce the occurrence of two Orosirian magmatic episodes in the southeastern Guyana Shield. The geochemical characteristics of the Caxipacore granitoids suggest that they formed in an orogenic tectonic setting, related to a subduction environment, while the geochemical signatures of the Agua Branca and Mapuera granitoids betray the evolution from a convergent context to an extensional intracontinental environment. Nd-TDM (2.19–2.22 Ga) and Sr-TUR (1.95–1.96 Ga) model ages and slightly positive eNd (+0.26 to +0.66) for the Caxipacore granitoids point to an origin from melting of mantle-derived magmas with participation of Rhyacian sialic crust. The Agua Branca and Mapuera granitoids display Nd-TDM (1.95–2.30 Ga) and Sr-TUR (1.84–2.02 Ga) model ages and positive to negative eNd (+2.92 to −1.96) that indicate parental magmas derived from melting of dominantly Rhyacian crustal sources with minor mantle contribution. In addition, the Nd signature and the lack of Archean inherited zircon in the plutonic rocks do not favor the existence of an Archean basement in this part of the southern Guyana Shield. This assumption together with similarities with the adjacent Uatuma-Anaua Orosirian Domain, westward, led to suggest that the Erepecuru-Trombetas Domain should not be longer interpreted as belonging to the Central Amazon Province, as defined in the current geotectonic models of the Amazonian Craton.

Rhyacian (c. 2.30–2.05 Ga) subduction-accretion and collisional processes are thought to represent an important event of crustal growth and reworking, often reported in the so-called Tranzamazonian/Eburnean granite-greenstone terranes of N/NE Brazil and West African craton. In this work, we present whole-rock geochemistry and U–Pb–Hf zircon ages for Rhyacian plutonic rocks that intrude Paleoproterozoic granite-greenstone terranes and Archean basement rocks of the Troia Massif, Borborema Province, NE Brazil. U–Pb SHRIMP zircon age of 2185 ± 4 Ma was obtained for a metatonalite sample (Mirador metatonalites). The metatonalites show geochemical affinity similar to those of adakites-like rocks, with all “classic” (slab-derived) adakitic signature (e.g. high Sr/Y, La/Yb and low HREE), but more akin to those evolved from partial melting of the metasomatized mantle wedge, followed by fractional crystallization. Zircon Hf crustal model ages of the metatonalite sample range between 2800 and 2660 Ma, evidencing that Archean crustal components contributed to its magma genesis, probably via subduction of continental-derived sediments to the mantle wedge. For potassic plutons of the Troia Massif (Bananeira suite) we obtained U–Pb SHRIMP zircon age of 2079 ± 4 Ma for a deformed quartz-monzonite with geochemical affinities similar to those derived from low-pressure partial melting of a K-rich mafic protolith. For less-deformed equigranular granites, we obtained a U–Pb LA-ICPMS zircon age of 2068 ± 5 Ma. They are high-K calc-alkaline and slightly peraluminous granites that probably derived from low-pressure partial melting of tonalitic crustal sources (metatonalites) and/or metagraywackes. Zircon Hf crustal model ages of a granite sample range from 2713 to 2535 Ma, evidencing Archean crustal contribution to magma genesis. However, two analyzed c. 2307 Ma inherited zircon grains show eHf(t) values of c. +4.87, indicating that crustal reworking of less-radiogenic Paleoproterozoic sources also participated in its genesis. Regional correlations of our results with the Paleoproterozoic record of the Troia Massif, Borborema Province and surrounding cratonic domains, suggest that the studied plutons are related to the c. 2.2–2.0 Ga Transamazonian/Eburnean orogenic cycle. The c. 2185 Ma metatonalites are associated to pre-collisional setting, while the c. 2079–2068 Ma quartz monzonites and granites evolved during collisional setting.

The extensive Neoproterozoic Brasiliano belts that surround the Sao Francisco craton in southern Brazil are a consequence of tectonic processes that resulted in the formation of the supercontinent Gondwana in the Ediacaran to Cambrian. One of these Brasiliano-age orogens, the Aracuai belt, overprints an earlier orogen developed during the so-called Transamazonian event at the transition between the Rhyacian and Orosirian periods. Archean and Paleoproterozoic basement units in the southern Aracuai belt have been shown to have experienced both the Transamazonian and Brasiliano orogenies and have the potential to have preserved the P-T conditions of both events. This study investigates a series of granulite- and amphibolite-facies samples from the southern Aracuai belt. Granulite-facies samples from the Acaiaca Complex and Pedra Dourada Granulite give monazite U-Pb ages in the range: 2015–1960 Ma. Both the granulite samples preserve two metamorphic textures. Coarse-grained garnet + biotite + orthopyroxene + K-feldspar + plagioclase + quartz + ilmenite + inferred melt and later, fine-grained garnet + biotite + hornblende + quartz that grows at the expense of orthopyroxene. Peak conditions for the earlier event were c. 750–800 °C and 6 kbar, whereas those of the later event are poorly constrained. A garnet-bearing amphibolite-facies sample from the Mantiqueira Complex contains monazite included within garnet, which gives U-Pb ages of c. 1940 Ma, whereas matrix monazite grains give ages of c. 590–540 Ma. Garnet core compositional zonation indicates P-T conditions of 6 kbar and 700 °C for the c. 1940 Ma metamorphism, while the matrix assemblage records a P-T path culminating in peak conditions of 8–9 kbar at 650 °C. A second amphibolite-facies sample was obtained from the Dom Silverio Group, whose depositional age post-dates the Transamazonian event. This sample gives two monazite U-Pb age populations, 597 ± 3 Ma and 547 ± 5 Ma. Garnet core zonation indicates a prograde P-T evolution with peak conditions of c. 8–9 kbar and 650 °C, although it is uncertain at this time what age population this event corresponds to. The results of this study provide better constraints on the chronology and metamorphic regimes of both the Transamazonian and Brasiliano events in the southern Aracuai belt.

The late Neoproterozoic processes of western Gondwana assembly are well-preserved in most Brazilian orogens. In the southern edge of the Sao Francisco Craton, a syn-metamorphic pile of nappes is the result of the closure of the Goias-Pharusian Ocean through the collision between the Sao Francisco (passive margin) and Paranapanema (active margin) paleoplates. The inner segments of the orogen suggest active margin- to syn-collisional-type sedimentation and magmatism recorded by the Andrelândia and Liberdade Nappes, among others. The Liberdade Nappe metasedimentary rocks, which have a maximum depositional age of 760 Ma, suggest a source area in an evolved Tonian-Cryogenian continental magmatic arc located in the east-northeastern Paranapanema margin. The Santo Antonio Unit (maximum depositional age of 680 Ma) of the lower Andrelândia Nappe for the same age interval instead presents a source primarily in an island arc. The Serra da Boa Vista, the upper unit of the Andrelândia Nappe, seems to record the beginning of continental collision because of its Rhyacian source, recognized as being in the Sao Francisco Craton, and no important evidence for Neoproterozoic arc magmatism. Grenville- and Rondonian-San Ignacio-type source areas, as well as Statherian ages, are observed in all units. Metabasic rocks interlayered in the Liberdade Nappe metasedimentary rocks have chondritic to suprachondritic eNd(t) (−1.86 to 1.75) and 1.09–1.48 Ga Nd TDM model ages, suggesting juvenile magmatism. Retroeclogitic and metavolcaniclastic rocks of Calymmian age (1.46–1.48 Ga) occur as exotic blocks within the same metasedimentary rocks. The complete ocean closure and the beginning of continental collision must have occurred at approximately 670 Ma, which corresponds to the maximum depositional age of the syn-collisional unit (Serra da Boa Vista) and to the age of the eclogitic rocks. The Andrelândia Nappe System migration was probably restricted to the 635–600 Ma interval, followed by the thinning of the orogenic crust.

Aeromagnetic, petrographic and isotopic data coupled with information obtained from a deep stratigraphic hole (440 m), shallow drillings (

The Great Oxidation Event (GOE) and Lomagundi-Jatuli Event (LJE) during Paleoprterozoic Era represent significant global environmental changes in Earth’s history and their geological records have been identified from many ancient cratons. However, reliable records of GOE and LJE are rare in the North China Craton (NCC) due to high-grade metamorphism on Paleoproterozoic strata during Orosirian Period and poor age constraints. Weakly metamorphosed to unmetamorphosed Proterozoic strata termed as Fanhe Group of around 8 km thick are well preserved in Fanhe Basin in the Archean Longgang Block in northeastern NCC and the Guanmenshan Formation from the lower part of the Fanhe Group is characterized by positive δ13Ccarb excursion of around +5‰. Since the Fanhe Group was usually considered as Meso-Neoproterozoic in ages, the reasons for positive δ13Ccarb excursions in the lower Fanhe Group are unclear. Our new LA-(MC-)ICP-MS U-Pb dating on a dolerite sill intruding into the Guanmenshan Formation yields two upper intercept 207Pb/206Pb ages of 2065 ± 20 Ma (95% confidence, MSWD = 1.4, N = 26) and 2062 ± 22 Ma (95% confidence, MSWD = 1.05, N = 22), respectively. Combined with the weighted mean 207Pb/206Pb age of the youngest detrital zircon population of the Daposhan Formation (2199 ± 19 Ma, 95% confidence, N = 8, MSWD = 0.47) and their contact relations, the deposition ages of the Daposhan, Kangzhaungzi, Guanmenshan and Tongjiajie formations from the lower part of Fanhe Group were constrained to be Rhyacian Period from ca. 2200 Ma to ca. 2060 Ma, not Mesoproterozoic Era as previously regarded. These new age constraints provide solid evidence for the existence of weakly metamorphosed stratigraphic records of GOE and LJE in lower part of Fanhe Group in the NCC. Stratigraphic correlations with other ancient cratons show that the Guanmenshan Formation in Fanhe Basin in the northeastern NCC can be correlated with the Dashiling Formation of the Hutuo Group in the central NCC, the Lucknow Formation in West Australia, the Upper Pretoria Formation in South Africa, the Gordon Lake Formation in North America and the Tulomozero and Kuetsjarvi formations in Fennoscandia, and therefore the Fanhe Group provides excellent stratigraphic records to study GOE and LJE in the NCC.

The Tartarugal Grande Complex (TGC) is an association of high-grade metamorphic rocks with Archean and Paleoproterozoic protoliths, located at the border of the Archean Amapa and Rhyacian Lourenco domains, in southeastern Guiana Shield, northeast of the Amazonian Craton. It consists of felsic granulites, and aluminous leucogneisses and rare mafic granulites. Both granulites and gneisses are affected by thrust and transcurrent shear zones along NW-SE trend. Migmatization with quartz-feldspathic neosomes, with or without orthopyroxene, and garnet-rich neosomes are present in felsic granulites and leucogneisses, respectively. The gneisses have high silica contents and are peraluminous due to the presence of biotite, garnet, and cordierite, indicating the derivation from metasedimentary sequences. The felsic granulites have medium to high silica content and geochemical signature of calc-alkaline magmatic arc series. The mafic granulites are small bodies embedded in the felsic granulites and leucogneisses. They display geochemical affinities with tholeiitic series and represent ancient diabase dykes. The metamorphic paragenesis in the granulite facies is represented by Pl-antiperhtite + Qtz + Mc-mesoperthite + Opx + Cpx + Bt ± Hbl (enderbitic granulite), Pl-antiperhtite + Qtz + Mc-mesoperthite + Opx ± Bt (charnoenderbitic granulite); Mc-mesoperthite + Qtz + Pl + Opx + Bt (charnockitic granulite), Pl (An60)+Opx + Cpx ± Hbl ± Grt (mafic granulite), and Qtz + Mc + Pl ± Bt ± Grt ± Crd (leucogneiss). The presence of orthopyroxene, clinopyroxene and hornblende in equilibrium in the granulites allows estimating temperatures at 800° ± 20 °C. In addition, non-extensive anatexis under anhydrous conditions produced charnockitic neosomes in the granulites and garnet-bearing leucogranite neossomes in the paragneisses. The presence of cordierite in leucogneisses indicates low-medium pressure conditions around 6–7 kbar. The partial or total replacement of pyroxenes by hornblende and/or biotite, garnet by biotite, clinopyroxene by titanite, and myrmekite intergrowths, indicate retrometamorphism and cooling during exhumation to higher crustal levels. The U–Pb LA-ICP-MS dating on zircon from a charnoenderbitic granulite yielded an age of 2082 ± 5 Ma for the crystallization of the igneous protolith of the granulites. Metamorphic zircons from an enderbitic granulite yielded a U–Pb LA-ICP-MS age of 2045 ± 14 Ma, which corresponds to the high-grade metamorphic episode that has affected the region at the end of the Rhyacian. The age of the protoliths is not constrained but 207Pb/206Pb dates at 2.57–2.70 Ga indicated inherited crystals and/or xenocrystals from Archean source. In agreement with previous works, we conclude that the TGC consists of calcium-alkaline magmatic rocks and pelitic sedimentary sequences formed during the development of a Rhyacian magmatic arc at the edge of the Archean Amapa Block. This was followed by a thermo-tectonic event at the end of Rhyacian, around 2.05 Ga, under high-grade conditions reaching the granulite facies, with restricted anatexis. Records of the tectonic exhumation of these terranes were defined by partial disequilibrium of some mineral phases in amphibolite facies. This Late-Rhyacian thermo-tectonic event is contemporaneous to the ultra-high temperature metamorphism (2.09–2.03 Ga) of the Bakhuis Granulite Belt in Suriname. The thermal differences between these two high-grade metamorphic terrenes may be related to the different crustal levels where they settled. Late-Rhyacian asthenospheric upwelling by crustal stretching during oblique continental collision seems to be the more plausible scenario as previously proposed, even if a slab break-off scenario cannot be ruled out.

The Archean-Paleoproterozoic Crixas greenstone belt is one of the most important components of the Crixas-Goias Domain, the oldest crustal segment of the Central Brazil Goias Massif. This gold-bearing greenstone comprises amphibolite facies ultramafic-mafic metavolcanic rocks overlaid by a low-grade metasedimentary succession associated with rocks of intermediate composition. We present new integrated geochemical and isotopic data of the metaigneous rocks to characterize the stages of magmatism and delineate the petrogenetic processes and tectonic environment of the different units. The data give important insights into the geological evolution of the Crixas greenstone belt during the Archean and Paleoproterozoic, including that the Crixas greenstone belt consists of genetically and temporal unrelated rocks that are spatially associated in a structural framework marked by stacking and imbrication. Two lithological assemblies were described: i) a Mesoarchean komatiite-tholeiite association formed by heterogeneous mantle plume melting in an oceanic plateau setting, and ii) a Rhyacian intraoceanic arc association. These units are allochthonous and override an Archean crustal basement dominated by granites and gneisses of mostly TTG composition. Chemical composition of the komatiites is similar to the Barberton-type Al-depleted komatiites, whilst the basalts consist of high-Mg tholeiites with flat chondrite-normalized REE patterns and immobile trace element systematics that resemble Phanerozoic oceanic plateau lavas. Eruption age of the ultramafic and mafic lavas is roughly estimated at ~3.0 Ga, based on previously published Sm Nd and Pb Pb isotopic studies, whereas whole-rock Re Os isotopic data of samples of komatiite and basalt presented here yielded a 2609 ± 65 Ma isochron age. This younger age may reflect a Neoarchean overprinting event associated with metasomatic Re-addition recorded in the lower ultramafic-mafic metavolcanic rocks, possibly related to the late stages of the cratonization of the Crixas-Goias Domain during the emplacement of the youngest Archean granites of the region (~2.70 Ga). Newly described andesites and diorites possess a subduction zone fingerprint. LA-ICP-MS U Pb zircon dating of an andesite sample provided an upper intercept Concordia age of 2172.2 ± 12.7 Ma, constraining the age of the intermediate magmatism. Therefore, these rocks are correlated with the Rhyacian syn-orogenic poorly-sorted graywackes and carbonaceous phyllites of the greenstone's upper stratigraphy. Andesites and diorites have homogeneous Paleoproterozoic two-stage Nd model ages of 2.28 to 2.26 Ga and positive initial eNd values of +2.34 to +2.69, indicating a juvenile nature for the arc magmatism. Re Os geochronology of gold-related arsenopyrite from a metasedimentary rock-hosted massive sulfide provided an age of 2137 ± 11 Ma, suggesting that the mineralization is also coeval to the Rhyacian collisional stage.

The Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Carajas domain with the Paleoproterozoic Bacaja domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Lomagundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox-sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (−2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn-oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO32− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi-like δ13C allows to correlate the Buritirama Formation with the Aguas Claras Formation within the Carajas domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton.

The age and stratigraphic position of Paleoproterozoic to Mesoproterozoic covers that occur along the western border of the Sao Francisco Craton (SFC) are still uncertain. Based on detailed sedimentological and stratigraphic survey, combined with U-Pb and Lu-Hf zircon dating, we present a new proposal for the stratigraphy and correlation with similar sequences, situated in other regions of the SFC, the Chapada Diamantina and Northern Espinhaco. Our study demonstrates that the so-called Trairas Formation (Arai Group) has a maximum depositional age of 1543 ± 31 Ma. The zircon distribution pattern shows a dominant Rhyacian source and minor contribution of Statherian, Calymmian, Neoarchean and Paleoarchean sources. The Rhyacian zircon grains have dominant positive eHf (t) signature, suggesting a large contribution from the juvenile Paleoproterozoic terranes, most probably from the Goias Massif, located west of the study area. The Calymmian maximum depositional age, calculated for the upper Arai Group (Trairas Formation), leads to the conclusion that the Serra da Mesa Group (ca. 1.55 Ga maximum depositional age) and the Trairas Formation have coexisted in time, possibly forming a larger sag basin, although laterally heterogeneous. The data presented also allow a new geotectonic interpretation for the Goias Massif, since it necessarily had to be connected to the Sao Francisco Craton during the Mesoproterozoic. This excludes the possibility that this massif was accreted to the Sao Francisco Craton in the Brasiliano Collage, as previously believed. The study also sheds light to the always debated tectonic relationship between the Serra da Mesa Granite (intrusive or basement) and Serra da Mesa Group (ca. 1.57 crystallization age and 1.55 Ga maximum depositional age, respectively). Furthermore, based on the new data, we present a stratigraphic revision for the actual Arai and Paranoa groups, proposing to raise the Trairas Formation to group status and its former members to formation status, representing an individual sag-type basin, different from the Arai rift-type basin. We also propose to combine the three Proterozoic intracontinental extensional pulses (which generated the Arai, Trairas and Paranoa groups) as the Veadeiros Supergroup, respectively chronocorrelated to the lower, middle and upper Espinhaco Supergroup, located at the SFC eastern margin.

The Paleoproterozoic Arai continental rift, Central Brazil, hosts metabasaltic lava flows interbedded with a thick transgressive metasedimentary sequence at the basal portion of the Arai Group (Arraias Formation). The lava flows have basalt to basaltic andesite compositions, subalkaline, tholeiitic and within-plate geochemical signatures. These rocks still have low to moderate REEs content, negative Ta, Ti, Nb anomalies, higher La/Nb (2.69–5.06) and lower La/Ba (0.03–0.23) ratios, suggesting some degree of contamination. Isotopic geology data presented in this paper revealed zircon U–Pb crystallization age of 1783 ± 17 Ma, with a significant frequency of inherited zircon from Rhyacian (2221 ± 14 Ma), negative eNd (t) = −4.46 to −6.58, Nd TDM model age from 2.49 to 2.72 Ga and 87Sr/86Sr(i) = 0.702400–0.708293. The eNd(t) vs Nb/La and eNd(t) vs 87Sr/86Sr diagrams suggest low to moderate contamination rate, linked to interactions of the plume-derived magmas with the subcontinental lithospheric mantle and the Archean-Paleoproterozoic continental old-crust, during to ascent and intrusion episodes, respectively. These new data are nicely correlated with the available isotopic data (U–Pb, Sm–Nd, Sr–Sr) on the acid volcanic and A-type granites from the basal portion of the Arai rift, indicating an important bimodal magmatic event, with volcano-plutonic characteristics, occurred during the continental syn-rift stage.

The Borborema Province is a complex orogenic system in northeast Brazil, whose current structural configuration is associated with the late Neoproterozoic-early Phanerozoic Brasiliano/Pan-African Orogeny. Magnetotelluric (MT) data were collected along four linear profiles across the northeastern corner of the province to assess the regional deep electrical resistivity structure. The site distribution is non-ideal for 3-D modeling, but dimensionality analysis showed that the data are dominated by 3-D effects. The model resulting from the 3-D inversion was critically evaluated for robustness and was found to provide a coherent view of the regional structure. A major crustal conductivity anomaly was modeled beneath Neoproterozoic supracrustal rocks of the Serido belt and this anomaly deepens to upper mantle depths in the northwest direction. Considering independent geophysical information and the geometry and location of the conductor, it likely reflects remnants of a northwest-directed subduction zone with enhanced conductivity associated with interconnected magnetite along the suture/shear zone. Constrained by geochemical data, it is proposed that subduction occurred during the Rhyacian orogenic event and since then became a key pre-existing intra-basement mechanical weakness, prone to concentrate tectonomagmatic events. Its reactivation during several episodes of extension and compression in the Borborema Province was linked to the nucleation of the original Serido rift basin (pre-Brasiliano), emplacement of mineralized bodies and crustal deformation in the Serido belt (Brasiliano), and tectonic control for volcanics erupted during the Cenozoic (post-Brasiliano). All these processes after the Rhyacian collision in this sector of the province took place in an intracontinental setting.

This paper aims to summarize the current knowledge of the Serrinha Nucleus and add new U–Pb geochronological data for this area. New ages were obtained for granitoids and a metadacite belonging to the Felsic Volcanic Unit of the Rio Itapicuru Greenstone Belt (RIGB). The age of 3185 ± 9 Ma obtained at the Pedra Alta granodiorite-tonalite pluton corresponds to the interval of emplacement (2.9–3.2 Ga) of the TTG granites in the Serrinha Nucleus during the Archean. As expected for granites belonging to the Paleoproterozoic TTG/calc-alkaline group, Barrocas and Lagoa dos Bois plutons yielded U–Pb zircon ages of 2168 ± 12 Ma and 2158 ± 13 Ma, respectively. These 2.15–2.17 Ga ages are attributed to a syn-orogenic evolution of the calc-alkaline felsic volcanism of the RIGB during the Rhyacian period, which is related to the closure of the Itapicuru basin. A sample of a biotite-granite dyke collected at the Araci TTG Pluton, which also is part of the Archean TTGs group of granites, yields an age related to the post-orogenic Morro do Lopes magmatism. Its age of 2076 ± 6 Ma also coincides with those attributed to the hydrothermal event that resulted in the gold mineralization at the RIGB and reinforces the widespread efects of this thermal post-orogenic alkaline magmatic event. The metadacite age of 2147 ± 38 Ma is considered the minimum crystallization age for the felsic volcanic arc of the RIGB, being compatible with regional ages obtained for other metavolcanic rocks and granitoids from this area. The ages obtained in the present work, added to the geochronological database of Serrinha Nucleus, show that the closure of the Itapicuru basin occurred between approximately 2.15 and 2.17 Ga, period corresponding to the first deformation phase that affected the orogen. The age obtained for the intrusive Barrocas Pluton (2168 ± 12 Ma), which outcrops at the southern tip of the greenstone, suggests that the volcanic-sedimentary rocks of Itapicuru should be older and highlights a new model for the evolution of Serrinha Nucleus and the concept of the “Rio Itapicuru Greenstone Belt”.

A review of the current knowledge of lithostratigraphy, geochronology, mineralogy, alteration, fluid chemistry and structural data is provided in order to discuss the main controls on mineralization in the Crixás gold deposit and the existing structural framework and evolution. Gold mineralization at Crixás represents orogenic upper mesothermal to lower hypothermal types developed within the overturned Paleoproterozoic (Rhyacian) stratigraphic sequence. The structural data indicates that upright folding of the stratigraphy and formation of a distinct S1 foliation characterizes D1 deformation. This controls the formation of laminated quartz veins, precipitation of Au-rich sulfides, and the development of NW trending orebodies. Localized F2 folding of D1 structures and strong L2 stretching lineations characterizes the D2 event. This localized F2 folding created oreshoots trending W-WNW within distinct orebodies. The D2 deformation is associated with the precipitation of native Au. The ‘bulk plunge’ of these orebodies is a combination of both plunges defined by D1 and D2 deformation events. A critical assessment of lithostratigraphic and structural data reveal two possible tectonic scenarios operating during the Paleoproterozoic. The first possible tectonic scenario considers sagduction and the development of a regional-scale synclinorium, followed by tilting and localized folding of D1 structures. The second scenario, which is similar to the current model, considers accretion producing a synclinorium, followed by thrusting. Based on the current knowledge, both models are considered to be permissible and a series of focused research studies are proposed to test both the current and the new tectonic models.

The Guanhaes block is one of the basement units present in the context of the Neoproterozoic West Gondwana assembly. It was reworked as a basement inlier within the Aracuai orogen, in the margins of the Sao Francisco-Congo (SF-C) paleocontinent. The Guanhaes block’s Rhyacian-Orosirian record is revealed for the first time by the Felicio and the Merces granitic plutons. Geophysical, petrographic, lithogeochemical and U-Pb (LA-ICPMS) analyses define and characterize these plutons, and link their genesis to the major Paleoproterozoic orogenic event that is thought to have amalgamated the SF-C paleocontinent. The Felicio pluton is composed of mesocratic fine-grained epidote-biotite-granodiorite, the Merces pluton comprises biotite-monzogranite and hornblende-syenogranite. These two plutons show different geochemical features; the Felicio rocks are low-K, magnesian, calcic to calc-alkalic, metaluminous, and the Merces rocks are rich in K, ferroan, alkali-calcic to alkalic, peraluminous, their shared common features are enrichment in LILE, LREE and HFSE and negative anomalies of Ti, Ta, Nb and P. Zircons collected from the Felicio pluton granodiorite yielded a U-Pb concordia age of 2151 ± 12 Ma, interpreted as the pluton’s crystallization age. The Merces pluton monzogranite yielded a discordia with upper intercept at 2014 ± 11 Ma and lower intercept at 539 ± 13 Ma, interpreted as the Merces pluton’s cristallization age and the Brasiliano metamorphic overprint, respectively. Trace elements and REE signatures suggest that the magma that originated both plutons shares a common source, compatible with the metasomatization of a mantle wedge by dehydration of a subducted slab. Based on the petrographic, geochemical and geochronological data, the following tectonic scenario is suggested: subduction and accretion of the Mantiqueira arc and emplacement of the Felicio pluton at c. 2.15 Ga, followed by collision, gravitational collapse of the orogen, post-collisional magmatism and emplacement of the Merces pluton at c. 2.01 Ga. This scenario is reinforced by the regional geochemical correlations among the many coeval terranes in the eastern margin of the Sao Francisco craton, along the Minas-Bahia orogen. At a broader scale, these correlations can be expanded to the African counterpart, giving insights into the SF-C paleocontinent framework in the Precambrian.

The Carajas Basin, situated in the southeastern Amazonian Craton in northern Brazil, hosts a > 6 km thick pile of volcano-sedimentary rocks deposited from the Neoarchean to the early Paleoproterozoic eras (ca. 2.75–2.06 Ga). It is claimed that this basin started as a rift configuration in which volcanic and banded iron formation strata were deposited during the Neoarchean Era. However, the tectono-sedimentary evolution of this basin through the Paleoproterozoic Era remains unexplored. Based on a sedimentological, stratigraphic, and U–Pb detrital zircon geochronological investigation of a marine to a fluvial succession of this basin, this study suggests that the Carajas Basin evolved in a foreland setting during the early Paleoproterozoic Era. Probably, the Carajas Foreland Basin was sedimented in the underfilled stage (ca. 2.5–2.3 Ga) by deep-marine strata (i.e., glaciogenic submarine fan deposits), likely from the Siderian–Rhyacian Serra Sul Formation. Subsequently, shallow-marine deposits of the Azul Formation were deposited in the filled stage (ca. 2.3–2.1 Ga), followed by deposition of the fluvial to alluvial deposits of the Aguas Claras and Gorotire formations during the overfilled stage (ca. 2.1–1.9 Ga). The Azul and Aguas Claras formations were supplied mainly by Meso- to Neoarchean source rocks, whereas Paleoproterozoic and Paleoarchean rocks played the role of a subordinate source of sediments. The youngest U–Pb age cluster, at ca. 2.27 Ga, is interpreted as its maximum depositional age. In terms of paleogeography, the occurrence of Rhyacian zircon grains in the Azul Formation deposits suggests, at least partially, a connection between the Carajas Protocontinent with the Bacaja Domain during that period. The integrated data corroborate the hypothesis that the foreland basin was formed in a scenario of collision between the Bacaja Domain and the Carajas Protocontinent during the Transamazonian Cycle. These dramatic upheavals are directly related to the configuration of the Columbia Supercontinent, which initially led to the emergence of the Carajas Foreland Basin, and soon after, the cratonization of proto-Amazonia

The Río de la Plata Craton is one of the three major cratons of South America. The craton is largely covered by sedimentary basins where its most exposed area is Buenos Aires-Piedra Alta Province (Chernicoff et al., 2014). This province includes the Martín García Island in the confluence of Uruguay River and the Río de la Plata estuary. Despite to be a reference area for the craton the Martín García Island lacks modern geological investigation. We present U-Pb SIMS (secondary ion mass spectrometer) geochronological data on zircon and titanite, as well as Hf isotope determinations on zircon, from rocks of Martín García Island (Argentina), Sola and Dos Hermanas Islands (Uruguay) and from Paso Severino Formation (Uruguay). We investigated: 1) Rhyacian intermediate-to acidic plutonic, arc-type rocks of the Florida Belt dated between 2090 Ma and 2115 Ma, derived from juvenile Neoarchean crust (TDMHf: 2.52 Ga; average εHf: +3.62); 2) Rhyacian metadacite (San José metamorphic belt) of 2127 Ma; 3) Statherian metagabbros of 1724–1734 Ma, with Transplatense inheritance; 4) Early Ectasian metagabbro of 1392 Ma, with Rhyacian inheritance; and 5) Stenian metagabbros of 1193 Ma (TDMHf: 2.00 Ga, εHf: 0.1). Most of the dated orthogneisses show Brasilian-age (from 778 to 550 Ma) Pb loss in the zircons, interpreted to be caused by shearing or uplifting during Neoproterozoic. The results show that the area is not exclusively Rhyacian in age but encompasses Statherian, Ectasian, and Stenian gabbros. The last two are interpreted as distal intrusions associated to the Sunsás Orogen. All post-Transplatense metagabbros have geochemical signature of island arc basalt derived from primitive mantle with enrichment of LILE and depletion of HFSE. These characteristics point to the recurrence of magma chambers intermittently active during the Rhyacian, Statherian, Ectasian, and Stenian, all with a similar source. The term “Transplatense” is used to replace “Trans-Amazonian” events that occurred within the craton. Fil: Santos, João O. S.. University of Western Australia; Australia Fil: Chernicoff, Carlos Jorge. Curtin University; Australia. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Zappettini, Eduardo Osvaldo. Curtin University; Australia Fil: McNaughton, Neal J.. Macquarie University; Australia Fil: Gréau, Yoann. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

This paper presents new isotopic Sm-Nd ID-TIMS data and applies the Zr saturation thermometry on orthogneisses of the Quirino Complex to address the mechanisms of magma genesis, evolution and tectonic setting. Quirino Complex is considered a Paleoproterozoic basement inlier within a Neoproterozoic belt, comprised of two distinct calcalkaline magmatic suites: a Siderian to Rhyacian high-K suite (2.30–2.19 Ga); and a Rhyacian medium-K suite (2.17–2.16 Ga). High zircon solubility and eNd (t) values (+2.7 to −5.8) indicate that the protoliths of the high-K suite gneisses can be related to high-temperature (TZr = ca. 810 °C) I-type granites. The gneisses of the medium-K suite display isotopic signature for crustal residence (eNd (t) = −17.9 and −8.1). Their protoliths, rich in inherited zircons (ca. 3.0 Ga) and other restitic/refractory components (hornblende clots and mafic enclaves), were derived from partial melting of Archean crust at relatively low temperature (TZr = ca. 750 °C) within a collisional tectonic setting.

The Ticunzal Formation is exposed in the northern portion basement of the external zone of the Brasilia Fold Belt and corresponds to a sequence of biotite-garnet paragneisses and mica-graphite schists with mineral assemblages indicating retrograde metamorphism under greenschist facies conditions. The formation displays local mylonitic structures and is intruded syn-to post-tectonically by 2.11–2.16 Ga peraluminous plutons of the Aurumina Suite. Detrital zircon U-Pb ages, Nd model ages between 2.23 and 2.88 Ga and geochemical data reflect a provenance probably represented by the 2.20 and 2.46 Ga tonalitic/granodioritic rocks of the Almas-Dianopolis terrane, exposed northwards of the study area. Zircon U-Pb geochronology and field observations suggest an age interval for the deposition of the precursor sediments of the Ticunzal Formation between 2.16 and 2.19 Ga. Raman spectroscopy analyses on graphite indicate high-crystallinity internal structures consistent with peak metamorphic temperatures between 620 and 630 °C. Trace element geochemical data of Ticunzal Formation samples suggest that precursor sediments were deposited in a continental arc-related basin, defining a setting consistent with an active mobile belt at the western margin of the Sao Francisco Craton during Rhyacian times, as inferred also from the characteristics of rocks from the Almas-Dianopolis terrane and the Aurumina Suite.