Search

This work is based on the unprecedented Tectonic-Geochronological Map of Bahia (TGMBA): metallogenic implications. In the TGMBA, sixteen tectonic domains were identified, and the main mineral occurrences and deposits in each were recorded. Of the Palaeo-Mesoarchean blocks, the Gavião (GB), Serrinha (SB) and Uauá (UB) blocks were highlighted. The southern GB was formed by plate tectonics, in two stages, at ca. 3403–3378 and 3259–3240 Ma. These rocks served as basement for the Umburanas Greenstone Belt, which comprises felsic metavolcanic rocks (3147 Ma) interspersed with ocean floor mafic metavolcanics and could have been the source of the recently found orogenic gold. This crust could also have formed the basal section of the Brumado metavolcanic-sedimentary sequence, which hosts one of the most important magnesite mines in the world. The northern part of the GB hosts TTGs with ages of ca. 3642–3520 Ma, the oldest known rocks in the whole São Francisco Craton. This region served as a passive margin for the Jacobina-Umburanas Sea, where quartzites and conglomerates (3305 Ma) with detrital gold were deposited and, in the deeper portions of this sea, Mesoarchean ocean floor or Island-arc basalts (3200 Ma) with pillow-lava structures were formed. On the platform of this basin, Mn deposits were formed in association with pelites and sandstones [ABSTRACT FROM AUTHOR]

Coeval Neoproterozoic mafic dykes with a well‐constrained isotopic age of 925 Ma are distributed in the North China Craton (NCC) of China and São Francisco Craton (SFC) of Brazil. Several recent studies favor the hypothesis that these two cratons were connected during 925 Ma and constituted building cratons for the supercontinent Rodinia. However, the paleo‐positions of the two cratons in Rodinia have not yet been paleomagnetically resolved. This paper presents the paleomagnetic results of these dykes in both NCC and SFC. Detailed thermal and alternating‐field demagnetization revealed that these dykes record stable components of magnetization with unblocking temperatures below the Curie temperature of magnetite. Rock magnetic results and scanning electron microscope analysis further confirm that the major magnetic minerals in dyke samples are pseudo‐single domain titanomagnetites. The mean directions of the characteristic remanent magnetization (ChRM) of the dykes are distinct from those of rocks of different ages in the sampling localities, and are supported by positive baked contact tests, indicating primary remanent magnetization. The ChRM of the SFC dykes also exhibits dual polarity. Our results suggest that the NCC and SFC were in the moderate to high paleolatitudes of the Southern Hemisphere during approximately 925 Ma, suggesting a possible paleogeographic connection between the two cratons. A new paleogeographic reconstruction of both cratons during 925 Ma is proposed, which is supported by other geological evidence. Plain Language Summary: The formation and breakup of the supercontinent Rodinia have played crucial roles in the global tectonic evolution and paleoclimate changes during the Neoproterozoic which lasted from 1.0 billion to 541 million years ago. The exact configuration of the Rodinia remains debatable, including whether the North China Craton (NCC) and São Francisco Craton (SFC) were integral components of the Rodinia. In this paper, we present new results of an integrated investigation, including paleomagnetic and rock magnetic studies and scanning electron microscope analysis, on the well dated coeval 925 Ma mafic dykes in both NCC and SFC. The results of scanning electron microscope and magnetic measurements confirm the major magnetic minerals and the stability of characteristic remanence directions. The results imply that both NCC and SFC were located at moderate to high paleolatitudes of the Southern Hemisphere during approximately 925 Ma, suggesting the possibility of a paleogeographic connection between the two cratons in the Rodinia. The findings of this study help gain improved understanding of paleogeography of the early Earth. Key Points: Characteristic remanence for the 925 Ma dykes in North China Craton and São Francisco Craton is interpreted as primaryBoth cratons were located at moderate–high paleolatitudes, southwest of Rodinia's core at 925 Ma, suggesting a paleogeographic connectionThe possible paleogeographic connection between the two cratons is supported by new paleomagnetic and geological evidence [ABSTRACT FROM AUTHOR]

This work reports on the first identification of sapphirine‐bearing ultrahigh‐temperature (UHT) metamorphic rocks within the Borborema Province, in NE Brazil. The investigated UHT diatexites outcrop in the Arapiraca Complex, a high‐grade Palaeoproterozoic block embedded within the Neoproterozoic metavolcano‐sedimentary sequence of the Sergipano fold‐and‐thrust belt. A sapphirine‐bearing diatexite sample preserves two distinct residual mineral associations as inclusions in cordierite poikiloblasts: a volumetrically dominant silica‐saturated, garnet–sillimanite–orthopyroxene–quartz domain, and a restricted silica‐undersaturated, sapphirine–magnetite–spinel–corundum domain. Phase equilibrium modelling for the whole‐rock bulk composition constrains the reactions preserved in the silica‐saturated domain, which, coupled with reintegrated ternary feldspar thermometry and Al‐in‐orthopyroxene thermobarometry, indicates peak UHT metamorphism occurring at ~970°C/8.5 kbar followed by a clockwise near isobaric cooling stage crossing the H2O‐undersaturated solidus at ~910°C/7.7 kbar. The T–MSiO2 and P–T phase equilibrium models reveal that the stabilization of magnetite‐spinel in the silica‐undersaturated domain can be a product of domanial SiO2‐depletion ascribed to inherited compositional banding and progressive melt‐loss episodes. The appearance of sapphirine as thin coronae around previously formed magnetite‐spinel cores requires an increase in the bulk silica content during retrograde metamorphism. This was driven by variable degrees of chemical interaction between the silica‐undersaturated domain and trapped silica‐rich leucosomes. U–Pb dating of zircon coupled with trace element behaviour records the timing of melt crystallization between ca. 2.03 and 1.96 Ga, after peak UHT metamorphism and supporting a protracted, ca. 70 My period of melt presence in the crust. The UHT metamorphism in the Arapiraca Complex is related to a contemporaneous UHT event recorded within the São Francisco Craton and more broadly coincides with high geothermal gradients at ca. 2.0 Ga linked to the formation of the Columbia supercontinent. The integration of new petrological and geochronological data indicates that the Arapiraca Complex is a continental ribbon pulled away from the São Francisco–Congo palaeocontinent possibly during the early Neoproterozoic intermittent rifting events and opening of the Sergipano oceanic basin between ca. 0.98–0.74 Ga. During the late Neoproterozoic at ca. 0.63–0.57 Ga, the Arapiraca Complex continental ribbon was thrusted back onto the northern margin of the São Francisco Craton as an inlier of the Sergipano fold‐and‐thrust belt. [ABSTRACT FROM AUTHOR]

Copyright of Geologia USP: Série Científica is the property of Geologia USP and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated TZr<800 °C for most samples. Its mineralogy is dominated by quartz and feldspar (77% to 95%), biotite is the only mafic mineral present (2% to 18%) and, titanite, zircon, apatite, allanite are important accessory phases. These rocks range from metaluminous to weakly peraluminous, and have large variation in major and trace elements, and high alkali contents (>6 wt.%). Zircon analyses by LA-ICP-MS and SHRIMP yielded a concordia age of 2 119±10 Ma for the porphyritic facies and an upper intercept age of 2 111±15 Ma for the equigranular facies. The whole-rock Sm-Nd TDM ages vary from 2.4 to 2.8 Ga with εNd(2.1) values between −0.7 and −5.3, indicating crustal derivation from distinct and/or heterogeneous protoliths. Field observations indicate that the Gentio metagranitoid was formed through different pulses of magma. Individual batches were subject to little or even no fractionation process after its emplacement. Although the Gentio metagranitoid crosscuts metamafic and metaultramafic rocks akin to an oceanic arc setting, this pluton is likely originated by partial melting of a more evolved quartz-feldspathic crustal igneous rock in a post-collisional environment, after the accretion of the arcs from the Mineiro belt and rocks of the Mantiqueira Complex. [ABSTRACT FROM AUTHOR]

The Jacobina Basin has a well-preserved sedimentary record, including continental and marine deposits, and hosts Au-(U)-Py mineralization in metaconglomerate beds similar to the Witwatersrand gold province. Based on petrographic observations, in situ trace-elements, and multiple sulfur isotope analyses (32S, 33S, 34S, and 36S) on pyrite from alluvial and marine facies, several types of pyrite were recognized. The pyrite grains identified in the alluvial metaconglomerates resemble those found in several pre-GOE gold-bearing metaconglomerates, including detrital and epigenetic varieties. Detrital inclusion-bearing pyrite is enriched in several redox-sensitive trace-metals as well as Au, which indicate an association with carbonaceous shales. On the other hand, the sources of detrital massive pyrite are more variable and include igneous, metamorphic, and hydrothermal sources from the Paleoarchean hinterland of Jacobina Basin. Epigenetic pyrite in metaconglomerates formed during metamorphism by the recrystallization of detrital pyrite with negligible contributions from external hydrothermal fluids to the basin. Diagenetic and epigenetic pyrite are found in marine lithologies. In a metapelite sample, the pyrite grains formed near the sediment-water column interface, with S sourced from the photolytic sulfate (SO 4 2−, Δ33S < 0) dissolved in the water column. A quartzite sample, in turn, has detrital pyrite grains that were likely reworked from continental deposits, as well as pyrite formed by the assimilation of elemental sulfur (S 8 , Δ33S > 0) that accumulated in sediment pore water during diagenesis. Significantly, the pyrite associated with terrestrial metasediments shows a wide range in δ34S values but quite restricted ranges in Δ33S and Δ36S values, whereas pyrite associated with the marine metasedimentary rocks exhibits limited δ34S values but has a wide range in Δ33S values and correlated Δ36S values close to the Archean array. These data suggest distinct preservation routes for MIF-S from atmospheric SO 4 2− and S 8 in terrestrial and marine environments. Conditions on the terrestrial surface resulted in re-equilibration of distinct S sources, diminishing the amplitude of the Archean atmospheric signal. In contrast, SO 4 2− dissolved in shallow marine settings while S 8 settled to the floor, favoring the preservation of MIF-S isotopic signatures. Such processes may also explain the apparent differences in interpretations of atmospheric conditions derived from uncharacterized pyrites from Archean sources. Our data suggest that the Earth's atmosphere remained anoxic, and terrestrial conditions were such as to allow the syngenetic accumulation of gold, as recently proposed for the Witwatersrand gold deposits. [ABSTRACT FROM AUTHOR]

The Itareru tonalite is one of the Paleoproterozoic plutonic rock units that intruded the Serrinha block, an Archean-Paleoproterozoic crustal fragment of the São Francisco Craton (Bahia, Brazil). It is characterized by a ca. 80 km long, NW-SE elongated leaf-shaped body, mainly comprised of tonalite-diorite to granodiorite rocks with numerous dioritic enclaves. Magnetic studies were performed on 26 sites of the Itareru pluton (including country rocks). Anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) are coaxial, indicating that all minerals have the same orientation, partially controlled by regional strain. Rock-magnetism measurements reveal that paramagnetic–matrix minerals contributed significantly to the magnetic susceptibility and AMS while magnetite grains in the range of 2–5 μm are responsible for AARM. Magnetic fabrics in the central region of the pluton are probably primary (magmatic), which was acquired when the rocks were crystallized, reflecting magma flow linked to a magma feeder zone (magma chamber). The moderated magnetic lineation plunges in the northern part of the pluton suggest that this region was close to the feeder zone. In contrast, the southern region should be far from it, since the magnetic lineations are horizontal to sub-horizontal. The Itareru tonalite emplacement was also controlled by regional strains related to the collision of the Paleoproterozoic Rio Itapicuru greenstone Belt with the Archean basement. • AMS and AARM are coaxial indicating that all minerals have the same orientation. • Magnetic fabrics in the central region of the pluton are probably magmatic acquired when the rocks were crystallized. • Magnetic fabrics in the central region of the pluton are related to magma flow. • The emplacement of the pluton was controlled by regional strains. • Itareru emplacement is related to the collision of the RIGB with the Archean basement. [ABSTRACT FROM AUTHOR]

• Characteristic remanence recorded by the Uauá tholeiitic dykes, Brazil, is primary. • A new ∼2.62 Ga paleomagnetic pole for the northern São Francisco craton is obtained. • The northern São Francisco craton was part of the Supervaalbara supercraton. The original connections of Archean cratons are becoming traceable due to an increasing amount of paleomagnetic data and refined magmatic barcodes. The Uauá block of the northern São Francisco craton may represent a fragment of a major Archean craton. Here, we report new paleomagnetic data from the 2.62 Ga Uauá tholeiitic mafic dyke swarm of the Uauá block in the northern São Francisco craton, Eastern Brazil. Our paleomagnetic results confirm the earlier results for these units, but our interpretation differs. We suggest that the obtained characteristic remanent magnetization for the 2.62 Ga swarm is of primary origin, supported by a provisionally-positive baked contact test. The corresponding paleomagnetic pole (25.2°N, 330.5°E, A 95 = 8.1°, N = 20) takes the present northern part of the São Francisco craton to moderate latitudes. Based on the comparison of the paleolatitudes of cratons with high-quality paleomagnetic data and magmatic barcodes, we suggest that the northern part of the São Francisco craton could have been part of the proposed Supervaalbara supercraton during the Archean. Supervaalbara is proposed as including (but not limited to) the part of the São Francisco craton as well as the Superior, Wyoming, Kola + Karelia, Zimbabwe, Kaapvaal, Tanzania, Yilgarn, and Pilbara cratons. [ABSTRACT FROM AUTHOR]

We present the first data on the geochemistry and isotopic age of zircons from rocks of the Roseta (lherzolite and olivine orthopyroxenite) and Córrego da Areia (olivine orthopyroxenite) ultramafic massifs localized among Archean-Proterozoic metamorphic strata in the southern folded framing of the São Francisco Craton. The examined zircons differ in crystal morphology, the intensity and type of cathodoluminescence, oscillatory zoning, the distribution of trace elements, and U-Pb isotopic age. Zircon crystals from the Roseta lherzolite have an age of 800-728 Ma and show negligible cathodoluminescence. Some of them have reaction rims with an age of 663-619 Ma. The crystal cores are enriched in rare earth elements (REE) but are often depleted in U as compared with the reaction rims. The age of zircons from the Roseta olivine orthopyroxenite showing moderate cathodoluminescence is within 622.6-596.9 Ma. Zircons from the Córrego da Areia olivine orthopyroxenite show moderate to intense cathodoluminescence and often have a rhythmic oscillatory zoning. They are characterized by an uneven distribution of REE and other trace elements and have high contents of U and Th. Most of these zircons have an ancient isotopic age (2558-2100 Ma). The examined zircons are of several types: relict, xenogenic, syngenetic, and epigenetic. The Roseta and Córrego da Areia massifs are considered to be protrusive outliers of a deep-seated Precambrian mafic-ultramafic complex, which were tectonically transferred along faults into the intensely metamorphosed Archean-Proterozoic strata in the southern folded framing of the São Francisco Craton. [ABSTRACT FROM AUTHOR]

Field gravimetric and stratigraphic surveys were conducted with the aim to constraint the mechanisms responsible for the initiation of the Stenian-Tonian Paranoá basin, central Brazil, a subject not yet studied in detail. The Paranoá Group crops out in the external zone of the Brasília Belt, a Neoproterozoic orogen in the western margin of the São Francisco Craton. Detailed geological mapping confirmed the existence of a regional scale fault that controlled sedimentation of the Paranoá Group during the deposition of its basal formations, revealing important details about basin initiation and early evolution. Gravimetric modeling indicates the existence of paleorift structures beneath the Paranoá sequence in the study area. Results from both stratigraphic and gravimetric surveys show strong evidence of mechanical subsidence by faulting during basin initiation. Unsorted, angular, clasts cut by quartz veins and brecciated boulders present in the basal conglomerate, support this hypothesis. Basin initiation faults coincide with deeper paleorift faults and are thus interpreted as reactivations of the older Statherian Araí Rift. The reactivations favored an initial regime of mechanical subsidence, dominated by the development of epirogenic arches subsiding at different rates. Apart from faulting activity, the post-basal sequence presents no evidence of rift environment in the strict sense. Besides, the great lateral continuity and relatively constant thickness of facies, indicate that an initial mechanic subsidence rapidly gave way to flexural subsidence during subsequent stages of basin evolution. The Paranoá Group do not present reliable characteristics that would allow its strict classification as a passive margin. Its main stratigraphic characteristics, tectonic location and basement architecture, indicate that the Paranoá Group was deposited in a cratonic margin basin, and may have been either connected to a passive margin basin at times of sea level rise, or evolved to a passive margin later in time. [ABSTRACT FROM AUTHOR]

The metasedimentary succession of the Minas Supergroup in the Quadrilátero Ferrífero (QFe) region, eastern Brazil, contains important, up to 400 m thick Lake Superior-type Banded Iron Formation (BIF) of the Cauê Formation. These are superposed by dolomitic carbonates of the Gandarela Formation, deposited ca. 2.4 Ga ago and thus probably registering the Great Oxygenation Event (GOE) of the Paleoproterozoic. The Segredo BIF deposit is located in the SW part of the QFe. The structural complexity and the discontinuity of layers challenge local studies on the sedimentary evolution of the Minas Basin. In the Segredo deposit, the stratigraphic sequence of the Minas Supergroup is exposed in the overturned limb of Fábrica Synform, that refold the Dom Bosco Synform. Based on the geological mapping and the study of a 480-m deep drill core, a lithostratigraphic review of the area is proposed, with stacking of the Itabira, Piracicaba, Sabará and Itacolomi groups, from the bottom up. The Itabira Group comprises BIF, intraformational metaconglomerate and dolostone with lateral and vertical interlayering. The chemical and isotopic data from the Cauê and Gandarela formations are defined by variations of the trace element and C-isotopic signatures. The intraformational metaconglomerate is interpreted as gravity flow products at the edges of the carbonate platform. Dolomitic BIFs show positive Eu anomalies and low terrigenous content, thus confirming the contribution of seawater hydrothermal fluids during the precipitation of BIF and carbonates. Negative Ce anomalies reflect a locally oxygenated ocean during precipitation of the Gandarela Formation carbonates. The carbon isotope stratigraphy is marked by δ13C values from around −1.5‰ in the Cauê BIF and around 0‰ in the Gandarela dolomites, indicating normal seawater conditions and deposition probably before the global Lomagundi event. The negatively fractionated values obtained for the Cauê BIF are consistent with previous studies suggesting the operation of microbial Dissimilatory Iron Reduction as an important process in BIF formation. Above the Gandarela carbonates, the occurrence of the Sabará Group through an angular unconformity is for the first time confirmed in the region by the occurrence of detrital sedimentary facies and by U–Pb geochronological data (younger detrital zircon at ca. 2.1 Ga). • Lithostratigraphy review of Itabira and Sabará groups at the Segredo Deposits. • Trace elements and C–O isotopes of the Paleoproterozoic BIF and carbonates (Itabira Group). • U–Pb geochronological data for Sabará Group (younger detrital zircon at ca. 2.1 Ga). • Discussion about the paleoproterozoic BIF and GOE effects at the Minas Basin, Quadrilátero Ferrífero province. [ABSTRACT FROM AUTHOR]

A suite of kimberlite-hosted mantle xenoliths from the Catalão region, southwestern margin of the São Francisco Craton (SFC), Brazil, consists of spinel lherzolites (type I and II) and garnet-phlogopite wehrlites. The chemical composition of these xenoliths provides evidence of enrichment and refertilization of the SFC lithosphere which were caused by distinct metasomatic agents. Garnet-phlogopite wehrlites have porphyroclastic textures and were equilibrated between 1005 and 1010 °C and 2.9–3.0 GPa (∼99 km). They record metasomatism caused by carbonatite and proto-kimberlite melts. Type I spinel lherzolite contains spinel-pyroxene symplectites indicating garnet destabilization due to variations of the P-T conditions. The minerals in this rock were equilibrated between 975 and 990 °C and their chemical compositions contain evidence for carbonatite metasomatism. High-Cr and low-Al clinopyroxene of garnet-phlogopite wehrlites and type I spinel lherzolite have high Mg#, Ca/Al, La/Yb N, Zr/Hf ratios, and high Sr contents, coupled with low to intermediate Ti/Eu and Ti/Nb, which also suggests that they were formed by carbonatite melt. These geochemical features, together with the presence of carbonate inclusions in the olivines, corroborate the interaction with carbonatite melt. The low-Ti-Cr phlogopite (Phl1), which is restricted to only the garnet-phlogopite wehrlites, was probably produced through the release of volatiles components from the carbonatite melt that reacted with garnet porphyroclasts. Furthermore, metasomatic reactions involving garnet-phlogopite wehrlites and a proto-kimberlite melt formed high-Ti-Cr phlogopite (Phl2), consuming the original phlogopite (Phl1). Phl2 occurs as rims around Phl1, as isolated flakes around garnets, and in the matrix of wehrlites. Therefore, we assume that the proto-kimberlite metasomatism responsible for generation of Phl2 occurred prior to the eruption of the host kimberlite magma. Conversely, type II spinel lherzolites (876–915 °C; ∼1.5 GPa) contain evidence of metasomatic reactions with silicate melts. These samples have high cpx/opx ratios (1.10–2.93) with low-Cr and high-Al clinopyroxene, and depleted incompatible trace element compositions. Some clinopyroxene crystals, however, show some enrichment in light rare earth elements (LREE), large ion lithophile elements (LILE), and Ti. Their low Ca/Al, La/Yb N , and Zr/Hf, low Sr contents, high Ti/Eu and Ti/Nb, and a strong positive correlation of Ti with the other high field strength elements (HFSE) and LREE, may indicate that these clinopyroxene crystals were formed by refertilization caused by a silicate melt that was depleted in incompatible elements. Overall, these metasomatic processes suggest a pervasive refertilization of the cratonic lithosphere where the typically depleted peridotites of cratonic regions were replaced by a pyroxene-rich lithology. • Mantle xenoliths from the SW margin of the SFC record pervasive metasomatism. • Wehrlites was formed by reaction of carbonatite melts with peridotite. • Low-Ti-Cr phlogopite records carbonatite metasomatism. • High-Ti-Cr phlogopite indicates proto-kimberlite melt metasomatism. • The shallow mantle (∼50 km) records refertilization caused by silicate melts. [ABSTRACT FROM AUTHOR]

In this study we present U–Pb and Hf isotope data combined with O isotopes in zircon from Neoarchean granitoids and gneisses of the southern São Francisco craton in Brazil. The basement rocks record three distinct magmatic events: Rio das Velhas I (2920–2850 Ma), Rio das Velhas II (2800–2760 Ma) and Mamona (2750–2680 Ma). The three sampled metamorphic complexes (Bação, Bonfim and Belo Horizonte) have distinct ε Hf vs. time arrays, indicating that they grew as separate terranes. Paleoarchean crust is identified as a source which has been incorporated into younger magmatic rocks via melting and mixing with younger juvenile material, assimilation and/or source contamination processes. The continental crust in the southern São Francisco craton underwent a change in magmatic composition from medium- to high-K granitoids in the latest stages, indicating a progressive HFSE enrichment of the sources that underwent anatexis in the different stages and possibly shallowing of the melting depth. Oxygen isotope data shows a secular trend towards high δ 18 O (up to 7.79‰) indicating the involvement of metasediments in the petrogenesis of the high potassium granitoids during the Mamona event. In addition, low δ 18 O values (down to 2.50‰) throughout the Meso- and Neoarchean emphasize the importance of meteoritic fluids in intra-crustal magmatism. We used hafnium isotope modelling from a compilation of detrital zircon compositions to constrain crustal growth rates and geodynamics from 3.50 to 2.65 Ga. The modelling points to a change in geodynamic process in the southern São Francisco craton at 2.9 Ga, from a regime dominated by net crustal growth in the Paleoarchean to a Neoarchean regime marked by crustal reworking. The reworking processes account for the wide variety of granitoid magmatism and are attributed to the onset of continental collision. [ABSTRACT FROM AUTHOR]

High-silica rhyolites having U–Pb zircon ages of 3303 ± 11 Ma occur along the eastern border of the Gavião Block (Brazil) associated with the Contendas-Mirante and Mundo Novo supracrustal belts. Unlike many Archean greenstone sequences, they are not interlayered with mafic to intermediate units. Instead, they belong to an inter-related plutonic–volcanic system, together with granitic massifs having similar zircon crystallization ages of ca. 3293 ± 3 Ma and 3328 ± 3 Ma and plotting along the same geochemical trends as the rhyolites. The rhyolites show well-preserved primary volcanic features such as magma flow textures and euhedral phenocrysts. High emplacement temperatures are indicated by petrographic evidence (β-quartz phenocrysts), zircon saturation temperatures (915–820 °C) and geochemical data, especially high SiO 2 (74–79 wt.%) together with elevated Fe 2 O 3(T) (~ 3 wt.%), MgO (0.5–1.5 wt.%) and low Al 2 O 3 (< 11 wt.%). The rhyolites show homogeneous trace element ratios (La/Yb N 4.8 ± 1.8; Eu N /Eu* ~ 0.55; Sr/Y ~ 0.7) and negative ԐHf (3.3 Ga) from 0 to − 7, indicating derivation from a single crustal source for both occurrences. Specifically, the rhyolites would have derived from extraction and eruption of highly silicic residual liquid formed by crystallization of granitic magma in a relatively shallow (< 10 km) reservoir, now represented by the granite massifs. The granite magma was formed by melting or differentiation of material similar to the diorite gneiss that occurs regionally. The 3.30 Ga volcanic–plutonic systems formed after a period of crustal growth and stabilization of a thick continental lithosphere, represented by massive 3.40–3.33 Ga TTG and medium to high-K calk-alkaline magmatism in the Gavião Block. The 3.30 Ga-old rhyolites and granites would therefore have formed in an intracontinental tectonic setting after the formation and stabilization of new continental crust, and accordingly would represent the first stages of rifting and continental break-up. Intraplate magmatism and intracrustal differentiation processes took place on Earth at 3.3 Ga and produced magmas that were distinct from Archean TTGs, questioning the reliability (or at least the uniqueness) of “intraplate models” to explain the origin of the latter. [ABSTRACT FROM AUTHOR]

The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ 13 C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ 13 C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ 13 C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ 13 C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin. [ABSTRACT FROM AUTHOR]

The southern portion of the Gavião Paleoplate is composed by Archean orthogneisses, Archean-Paleoproterozoic metavolcano-sedimentary rocks and Siderian-Rhyacian-Orosirian granitoids. Petrographic, geochemical, U–Pb (Laser Ablation, ICPMS) and Sm-Nd data are presented for five Paleoproterozoic granitoids that were recently mapped: Jussiape II, Lagoa das Almas, Humaitá, Belo Campo and Broco granitoids. These granitoids present U–Pb zircon (LA-ICPMS) ages of 2052 ± 43, 2114 ± 24, 2140 ± 9, 2049 ± 23 and 2038 ± 8 Ma, respectively. In addition to these granitoids, another twenty-five ones were identified and studied by several authors, resulting in a total of twenty-nine plutons. Despite the previous petrography, geochemistry and geochronology studies that have been performed, no model had been proposed to explain the tectonic setting of this extensive granitogenesis. Integration of the new data and the literature has been done and corresponds to the second part of the article. Based on U–Pb dating and geochemical data, Siderian-Rhyacian-Orosirian granitoids of the southern Gavião Paleoplate were classified into five groups, or five suites: 1 (2324 ± 6 to 2091 ± 6.6 Ma), 2a (2054 −6/+8 to 2041 ± 23 Ma), 2b (2066 ± 37 to 2019 ± 32 Ma), 2c (2058 ± 8 to 1852 ± 50 Ma) and 2d (2049 ± 12 to 1929 ± 16 Ma). The granitoids of Group 1 present heterogeneous deformation, while the granitoids of groups 2a to 2d are generally not deformed. Usually the rocks are potassic, but sodic granitic rocks can be found in samples of groups 1, 2c and 2d. Several chemical classification parameters are presented and discussed herein, but it is noteworthy that the granitoids of Group 1 are mainly classified as calcic to calc-alkalic, while the rocks of the second group are mostly classified as alkalic ones. In the remaining groups, the samples vary between calc-alkalic and alkali-calcic. The ε Nd values range between 4.0 and −15.4 and suggest an important and varied share of the continental crust in the formation of these rocks. The Humaitá granitoid probably presents the lowest contribution from the continental crust in its genesis. The rocks from Group 1 were generated as the product of an active continental margin arc situated eastwards from the southern portion of the Gavião Paleoplate. The spatial distribution between the granitoids of groups 1 and 2a suggests westwards subduction and led to a cordilleran model for the Western Bahia Magmatic Arc. Continental collision between the Gavião and Jequié paleoplates occurred around 2.09 Ga and was followed by the setting of late-collision granitoids of groups 2a to 2d. The comparison between the tectonic model presented in this study and other existing models that explain the Siderian-Rhyacian-Orosirian granitogenesis of the Mineiro Belt and Mantiqueira Complex suggests a continuation of the Western Bahia Magmatic Arc and of the collisional orogen that followed, towards the south. The Western Bahia Magmatic Arc emplacement occurred before the Paleoproterozoic granitogenesis of the Serrinha (Bahia-Brazil) and Congo (Africa) paleoplates. [ABSTRACT FROM AUTHOR]

The Quadrilátero Ferrífero is a metallogenic district (Au, Fe, Mn) located at the southernmost end of the São Francisco craton in eastern Brazil. In this region, a supracrustal assemblage composed of Archean greenstone and overlying Neoarchean–Paleoproterozoic sedimentary rocks occur in elongated keels bordering domal bodies of Archean gneisses and granites. The tectonomagmatic evolution of the Quadrilàtero Ferrífero began in the Paleoarchean with the formation of continental crust between 3500 and 3200 Ma. Although this crust is today poorly preserved, its existence is attested to by the occurrence of detrital zircon crystals with Paleoarchean age in the supracrustal rocks. Most of the crystalline basement, which is composed of banded gneisses intruded by leucogranitic dikes and weakly foliated granites, formed during three major magmatic events: Rio das Velhas I (2920–2850 Ma), Rio das Velhas II (2800–2760 Ma) and Mamona (2760–2680 Ma). The Rio das Velhas II and Mamona events represent a subduction-collision cycle, probably marking the appearance of a modern-style plate tectonic regime in the Quadrilátero Ferrífero. Granitic rocks emplaced during the Rio das Velhas I and II events formed by mixing between a magma generated by partial melting of metamafic rocks with an end member derived by recycling gneissic rocks of older continental crust. After deformation and regional metamorphism at ca. 2770 Ma, a change in the composition of the granitic magmas occurred and large volumes of high-K granitoids were generated. The ca. 6000 m-thick Minas Supergroup tracks the opening and closure of a basin during the Neoarchean–Paleoproterozoic, between 2600 and 2000 Ma. The basal sequence involves continental to marine sediments deposited in a passive margin basin and contain as a marker bed the Lake Superior-type Cauê Banded Iron Formation. The overlying sediments of the Sabará Group mark the inversion of the basin during the Rhyacian Minas accretionary orogeny. This orogeny results from the collision between the nuclei of the present-day São Francisco and Congo cratons, generated the fold-and thrust belt structure of the Quadrilátero Ferrífero. Afterwards, the post- orogenic collapse resulted in the deposition of the Itacolomi Group and in the genesis of the dome-and-keel structure. In this paper, we review current knowledge about the 1500 Ma long-lasting tectonomagmatic and structural evolution of the Quadrilátero Ferrífero identifying the most compelling open questions and future challenges. [ABSTRACT FROM AUTHOR]

Detrital zircon ages are an important tool to study the provenance and evolution of sedimentary rocks, and currently there is a general lack of such studies in greenstone belt basins. In this paper, we combine field observations and in situ U–Pb/Lu–Hf detrital zircon analyses to constrain the evolution of a large, ancient convergent basin in SE Brazil. The Maquiné Group (the uppermost clastic sequence of the Rio das Velhas Greenstone Belt) was deposited during a fundamental shift in the evolution of the southern São Francisco Craton that ended with closure of the greenstone belt basin and the stabilization of the continental crust at ca. 2730–2700 Ma. We show that detritus accumulated in the Maquiné basin derived from uplifted nearby source rocks and that sedimentation was marked by drastic upward lithological changes (from flysch to molasse-type sedimentation). The restricted distributary provenance (marked by a strong uni-modal age spectra at 2770–2780 Ma) requires that sedimentation was concomitant with exhumation of a proximal 2770–2780 Ma TTG magmatic arc. The entire detrital zircon spectra show that maximum deposition ages are very close to the timing of deposition, and confirm that deposition occurred during or immediately after tectonic convergence. Variations in ɛHf (t) values support the idea that the Archaean crystalline crust of the craton was built by crust–mantle mixing processes with a successive decrease of values in zircons crystallized after 3100 Ma. In a regional context, our dataset supports previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession of magmatic arcs and Archaean convergent basins. [ABSTRACT FROM AUTHOR]

This study is focused on speleogenesis of the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR), the longest caves in South America occurring in the Neoproterozoic Salitre Formation in the São Francisco Craton, NE Brazil. We employ a multidisciplinary approach integrating detailed speleomorphogenetic, lithostratigraphic and geological structure studies in order to reveal the origin of the caves, their functional organization and geologic controls on their development. The caves developed in deep-seated confined conditions by rising flow. The overall fields of passages of TBV and TBR caves represent a speleogenetically exploited large NE–SW-trending fracture corridor associated with a major thrust. This corridor vertically extends across the Salitre Formation allowing the rise of deep fluids. In the overall ascending flow system, the formation of the cave pattern was controlled by a system of sub-parallel anticlines and troughs with NNE–SSW dominant orientation, and by vertical and lateral heterogeneities in fracture distribution. Three cave-stratigraphic stories reflect the actual hydrostratigraphy during the main phase of speleogenesis. Cavities at different stories are distinct in morphology and functioning. The gross tree-dimensional pattern of the system is effectively organized to conduct rising flow in deep-seated confined conditions. Cavities in the lower story developed as recharge components to the system. A laterally extensive conduit network in the middle story formed because the vertical flow from numerous recharge points has been redirected laterally along the highly conductive unit, occurring below the major seal — a scarcely fractured unit. Rift-like and shaft-like conduits in the upper story developed along fracture-controlled outflow paths, breaching the integrity of the major seal, and served as outlets for the cave system. The cave system represents a series of vertically organized, functionally largely independent clusters of cavities developed within individual ascending flow cells. Lateral integration of clusters occurred due to hydrodynamic interaction between the flow cells in course of speleogenetic evolution and change of boundary conditions. The main speleogenetic phase, during which the gross cave pattern has been established and the caves acquired most of their volume, was likely related to rise of deep fluids at about 520 Ma or associated with rifting and the Pangea break-up in Triassic–Cretaceous. This study highlights the importance of speleogenetic studies for interpreting porosity and permeability features in carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Geologic information supported by in situ U-Pb zircon ages, and geochemistry coupled with zircon Hf and Nd-Sr isotopic analyses on orthogneisses, metagranitoids and metadiorites unravel the nature and tectonic significance of a calc-alkaline continental arc in the Mineiro belt – southern portion of the São Francisco Craton. The zircon U-Pb ages defined two plutonic episodes: 2174–2149 Ma (metaquartz-diorite, metagranitoids and orthogneisses) and 2145–2100 Ma (metadiorites, metagranitoids and orthogneisses) whereas several samples contain inherited zircons with concordant 207 Pb/ 206 Pb ages as old as 2785 Ma. Our rocks show variable SiO 2 contents (54.8–77.1 wt.%), are metaluminous to peraluminous and mostly magnesian and variably enriched in LREE. The older rocks have La/Yb N = 2.24 to 11.87 whereas the metadiorites have La/Yb N = 9.60–13.82 and the youngest rocks in the range 7.79–91.27. Most samples show Nb and Ti negative anomalies that can be attributed to a subducted source whereas some yield marked Pb positive anomalies that highlight the important role of crustal contamination/assimilation. Dy/Dy* and coupled Dy/Yb values (from 0.7 to 0.5 and 1.4 to 2.0, respectively) indicate the metaigneous rocks derived from a LREE enriched MORB source in a subduction zone with mixed Paleoproterozoic and Archean material. This scenario is consistent with the U/Pb data from inherited nuclei and xenocrysts, the range of the zircon ɛ Hf(t) (from +8 to −10) and ɛ Nd(t) (from −7 to +0.3) values, as well as with the Lu-Hf T DM ages that vary between 2.3 and 3.2 Ga. Our data and regional geologic–tectonic correlations are consistent with the onset of an ultimate collisional event in the Mineiro belt that followed a long-lived accretionary regime active in Proterozoic times, outboard the Archean core of the São Francisco Craton. [ABSTRACT FROM AUTHOR]

The Campinorte Arc is a poorly exposed 2.19-2.07 Ga Paleoproterozoic terrane in contact with the Neoproterozoic Goiás Magmatic Arc by the Rio dos Bois Fault in the northern Brasília Belt, Central Brazil. The Campinorte Arc is divided into Pau de Mel Suite metatonalites to metamonzogranites and the Campinorte volcano-sedimentary Sequence. Pau de Mel Suite whole rock geochemistry indicates at least three separate coeval parental magmas compatible with arc signatures. U--Pb geochronology data of paragranulite and mafic granulite exposed in the region as part of the Campinorte Arc provide additional information on this Paleoproterozoic orogenic cycle. The formation and preservation of these granulites was due to tectonic switching of the back arc basin and consequent lithospheric thinning from 2.14 to 2.09 Ga with metamorphic peak from 2.11 to 2.08 Ga. A Pau de Mel Suite granodiorite sample dated at ca. 2.08 Ga indicates post-peak magmatism. The arc was thereafter rapidly contracted preserving Paleoproterozoic high metamorphic grade mineral assemblages. Additionally, the Campinorte Arc and the neighboring Crixás/Guarinos/Faina greenstone belts may have shared the same source of sediments as attested by geographic proximity, coeval maximum sedimentation, felsic volcanism and the occurrence of similar rock types. Gravimetric and seismic data also support a common basin hypothesis. The formation of the Campinorte Arc is contemporaneous to other northern Brasília Belt basement terranes and, along with similar arcs within and at the São Francisco Craton edges, indicate a continental crust formation event that eventually led to the assemblage of Columbia. [ABSTRACT FROM AUTHOR]

Geophysical techniques can improve knowledge about the deep structures of collisional orogens. Therefore, magnetotelluric and gravimetric data were combined in this study to enhance the poorly understood subsurface structure of the transition zone from the São Francisco Craton to the Neoproterozoic Sergipano Orogen in northeastern Brazil. The results along a 240-km-long, NE–SW trending geophysical transect revealed two main geoelectric domains beneath the Cretaceous Tucano Basin, which can be linked to two distinct tectonic blocks on the surface. The less resistive SW domain corresponds to the rocks of the Serrinha Block within the São Francisco Craton. In contrast, the more resistive NE domain matches the basement rocks of the northernmost units of the Sergipano Orogen. The results are discussed considering Paleoproterozoic and Neoproterozoic scenarios with different interpretations of the NE domain. Based on the surface geology and additional gravimetric and magnetotelluric data, the best scenario is to consider the NE domain as representing the geoelectric signature of the three northernmost geological domains of the Sergipano Orogen (Macururé, Poço Redondo–Marancó, and Canindé) and that of the Pernambuco–Alagoas Block (PEAL). PEAL collided with the São Francisco paleolithosphere forming the Sergipano Orogen. The NE geoelectric domain can be interpreted as an indenter of the tectonically intruded PEAL beneath the São Francisco paleolithosphere. The new data properly define the northern limit of the São Francisco Craton and explain both indentation structures and contrasting sediment provenance observed in the Sergipano Orogen. [Display omitted] • Geophysical data for the basement of the Cretaceous Tucano Basin, Brazil. • Basement comprises the São Francisco Craton–Sergipano Orogen transition zone. • Magnetotelluric data characterize two blocks: Northeast (NE) and Southwest (SW). • SW Block is the Craton, NE Block is the Sergipano Orogen and Pernambuco-Alagoas block. • Contact between SW and NE blocks dips to SW and was formed by indentation. [ABSTRACT FROM AUTHOR]

The São Francisco Craton (SFC) is an Archaean craton that hosts a significant number of mafic intrusions. Previous attempts to date the igneous emplacement of these rocks are limited to a few dates of poor precision. Here, two dyke swarms from the Uauá Block in the northeastern portion of the craton were dated using U–Pb on baddeleyite (ID-TIMS) and zircon (SIMS). The older dyke swarm trends mainly N–S to NW–SE (but also NE) and comprises norite dykes, whereas the younger dykes are tholeiite and trend NE–SW. The ages of 2726.2±3.2 and 2623.8±7.0Ma date dykes of noritic and tholeiitic compositions, respectively. The older age matches the ages of several Archaean-Large Igneous Provinces (tholeiitic-komatiite greenstone belts and continental flood basalts) worldwide and represents part of a feeder system, but the younger age is similar to Andean style continental margin magmatism in the São Francisco and Zimbabwe cratons. The two dyke swarms are tholeiitic in composition but the noritic dykes are more enriched in both compatible and incompatible elements and have higher (La/Yb)N ratios than the tholeiite dykes. The norite dykes are interpreted as low degrees of melting from enriched refractory mantle sources, whereas the tholeiite dykes represent high degrees of partial melting of more depleted mantle sources; the two mafic dyke swarms may be related to each other by progressive extension of the continental lithosphere. It is suggested that the Uauá Block with its dyke swarms is a small piece of Archaean crust dispersed after the break-up of a major Archaean supercraton. [ABSTRACT FROM AUTHOR]

Abstract: New U–Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68Ga to 1.80Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa–Brumadinho Formation) with a younger zircon peak at 1192Ma, which is the maximum age for deposition of the upper units. The obtained U–Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8Ga to 0.91Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian–Tonian ages of the Upper Espinhaço Basin units (906Ma to 1192Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas. [Copyright &y& Elsevier]

Abstract: The São Francisco craton in eastern Brazil hosts sedimentary sequences deposited between the Paleoarchean (∼3300 Ma) and Late Neoproterozoic (∼580 Ma). Proterozoic successions occurring in this region comprise five 1st-order sedimentary sequences, which besides episodes of global significance record major basin-forming events. The ca. 8000 m-thick Minas-Itacolomi 1st-order sequence, exposed in the Brazilian mining district of the Quadrilátero Ferrífero and containing as marker bed the Lake Superior-type Cauê Banded Iron Formation, tracks the operation of a Wilson cycle in the Paleoproterozoic Era. The quartz-arenite dominated Espinhaço I and II sequences record at least two major rift-sag basin-forming events, which affected the host continent of the São Francisco craton at around 1.75 Ga and 1.57 Ga. The Macaúbas sequence and its correlatives in the extracratonic domains witness the individualization of a São Francisco-Congo plate in synchronicity with the break-up of Rodinia in the Cryogenian period. The São Francisco-Congo plate together with various fragments derived from Rodinia reassembled to form Gondwana in the Ediacaran period. In the course of the Gondwana amalgamation, orogenic belts developed along the margins of the craton; its interior, converted into foreland basins, received the shallow water carbonates and pelites of the Bambuí 1st-order sequence and its correlatives. [Copyright &y& Elsevier]

Abstract: Remnants of a Neoproterozoic glaciation in east central Brazil are represented by thin diamictite layers (Jequitaí Formation and correlative units), locally overlying striated pavements on the São Francisco craton. The diamictites are covered by the Sete Lagoas Formation of the basal Bambuí Group, which is generally accepted to be a typical cap carbonate sequence. Although most authors have preferred a mid-Cryogenian (post-Sturtian) age for it, based mainly on Pb-Pb whole rock data, the Sete Lagoas Formation bears lithostratigraphic and isotopic characteristics that are identical to early Ediacaran cap carbonates worldwide, including a basal thin (0–10m) pale and flinty cap dolostone, preserving a drop in δ13C values from around −3.2‰ to −4.5‰ with associated δ18O around −5‰, and crystal-fan facies interpreted as aragonite pseudomorphs. Ediacaran zircons have been recovered from the middle of the Sete Lagoas Formation, constraining the deposition of its upper half to be younger than 610Ma (). Although there is an unconformity below the point where the zircons were collected, it is short-lived, as suggested by the identical, typically Ediacaran 87Sr/86Sr values above and below (0.7074–0.7076). Carbonate clasts from the Jequitaí Formation and correlative diamictite-bearing units in the fold belts that surround the São Francisco craton (Canabravinha and Serra do Catuni formations) display similar ranges in δ13C (−6.7 to +2.6‰), suggesting the erosion of a pre-glacial carbonate platform with negative δ13C values (i.e. the Islay and/or Trezona anomalies). The cratonic Carrancas Formation, on the other hand, yielded pale dolostone clasts with δ13C in a small range between −4.2 and −3.4‰, and δ18O values around −6.5‰. These clasts could be derived from the cap dolostone unit itself, in which case the Carrancas Formation would represent resedimented basal Sete Lagoas Formation and imply that sections of the Sete Lagoas Formation sitting atop the Carrancas Formation are incomplete. The base-truncated sections have confused previous attempts to correlate the Sete Lagoas Formation with other cap carbonate successions. In light of the available lithostratigraphic, isotopic and U-Pb zircon data, we propose that the Sete Lagoas Formation represents a basal Ediacaran cap carbonate sequence (∼635–610Ma) deposited after the Marinoan glaciation in east central Brazil. [Copyright &y& Elsevier]

Abstract: The Paleoproterozoic is considered the main period of crustal growth in the South American continent, with voluminous production of granitoid suites emplaced during the onset of the ca. 2.2–2.1Ga Trans-Amazonian orogeny. This work documents and interprets mineral chemistry, whole rock geochemistry, Nd isotopes and U–Pb geochronology data for the high-aluminium Lagoa Dourada TTG suite. This suite constitutes a hitherto unknown episode of Paleoproterozoic (ca. 2350Ma) juvenile felsic plutonism in the southern São Francisco craton, Minas Gerais, Brazil. It is also a rare example of juvenile continental crust production in the global crustal age-gap between 2.45 and 2.2Ga. The suite is composed of metaluminous to slightly peraluminous, low-Mg#, low-K and high-Ca, biotite-hornblende to hornblende-biotite (± garnet-magnetite) tonalites and biotite trondhjemites, varying from ∼62 to 73wt.% SiO2. The trace element geochemistry of the suite is characterized by mildly depleted Nd isotope compositions [ɛ Nd(t)=+1.0 to +2.1], low large-ion-lithophile element (LILE, i.e., Rb, Ba, and including the highly incompatible Th) and heavy Rare Earth element (REE, Yb<1.00ppm) contents. The suite is also characterized by high Sr/Y ratios (≥41 up to 81), high (La/Yb)N ratios (≥12 up to 46), and positive Eu/Eu* anomalies. These data are consistent with the derivation of the suite from a tholeiitic metabasaltic source, which had a short crustal residence time prior to melting. The chemical diversity of the suite is attributed mainly to the fractional crystallization of hornblende and accessory minerals, coupled with plagioclase accumulation in the tonalitic parental melt. Emplacement of new batches of magma could explain samples which diverge from the proposed liquid line of descent of the suite. The composition and age of the Lagoa Dourada suite suggest a link with the accretion of greenstone belt packages in an intra-oceanic tectonic setting. [Copyright &y& Elsevier]

Abstract: The collision of oceanic arcs with continents is a common plate tectonic process in the Phanerozoic, but its recognition in the Precambrian is hampered by deformation and metamorphism. The Rio Capim volcanic–plutonic–sedimentary belt lies in sharp tectonic contact with Archaean rocks of the Uauá block in the northern part of the São Francisco craton. Field relationships and high-precision geochronology indicated that the Rio Capim basalts, gabbros, diorites, and dacites were emplaced approximately at 2148–2143Ma, and later intruded by 2128Ma-old diorite to tonalite plutons. All rocks were metamorphosed under amphibolite to granulite facies conditions mainly between 2080Ma and 2070Ma, but deformation may have lasted until about 2040Ma as estimated from syn-deformation zircon and titanite grains. The association of basalt, andesite, dacite, and their plutonic counterparts, combined with their positive ε Nd(t) values and incompatible trace element geochemical signatures similar to island arc magmas, support the proposition that the Rio Capim belt was a Palaeoproteorozoic intra-oceanic arc sequence that collided with a continent, of which the Mesoarchaean Uauá block is a remnant. The implications for the regional evolution and metallogenesis are also discussed. [Copyright &y& Elsevier]

Abstract: The studied tonalitic and trondhjemitic granulites are located in the SSE granulitic domain of the São Francisco craton, Bahia, Brazil, where they represent most of the southern part of the Archean and Paleoproterozoic Itabuna-Salvador-Curaçá Block (ISCB). Chemically, the tonalitic and trondhjemitic granulites belong to a low-K calc-alkaline suite; their REE patterns are steep with strong LREE/HREE fractionation and no significant Eu anomaly. Garnet-bearing mafic granulites that occur as enclaves in the tonalitic and trondhjemitic granulites were derived from basalts and/or gabbros of tholeiitic affinity. Geochemical modelling showed that the tonalitic and trondhjemitic granulites were produced by moderate fractional crystallization of an assemblage of hornblende and plagioclase, with subordinate amounts of magnetite, apatite, allanite and zircon. The garnet-bearing mafic granulites would be the source of the magmas that generated these rocks. Partial melting left a residue made up of plagioclase, garnet, orthopyroxene and hornblende. [Copyright &y& Elsevier]

Abstract: Paleomagnetic, magnetic anisotropy data and 40Ar/39Ar ages are presented for high-grade metamorphic rocks of the Jequié block, São Francisco Craton. Jequié charnockites and enderbites gneisses from the eastern border of the block present northern and steep-downward directions, carried by Ti-poor titanomagnetite with high unblocking temperatures (550–600°C). A mean direction for 12 sites of enderbites from the eastern sector yielded a magnetic component A (D m =47.0°, I m =75.7°, α 95 =6.3°, K =48.8) with a corresponding paleomagnetic pole at 339.6°E, 5.4°N (A 95 =11.2°). Sites sampled on other metamorphic rocks including granulite-facies, tonalites and dacites yield different magnetic components. Anisotropy of magnetic susceptibility measured for all sampling sites shows a high degree of anisotropy (P =1.121–1.881), with NE- or NW-trending magnetic lineations and vertical magnetic foliations. These data were used to correct the mean site directions for all components. While the other components presented larger scatter after anisotropy correction, the component A shows a slightly tighter clustering of magnetic directions (D m =61.2°, I m =76.5°, α 95 =5.4°, K =66.2) giving a new, anisotropy corrected paleomagnetic pole at 342.1°E, −0.5°N (A 95 =9.6°). 40Ar–39Ar plateau ages of 2035±4Ma (hornblende) and 1876±4Ma (biotite) obtained for one of the samples with component A imply a very low cooling-rate of 1.4°C/Ma for these rocks. Based on these ages and corrected unblocking temperatures of the magnetic component A, we argue that the characteristic magnetization of the Jequié metamorphic rocks was acquired by high temperature thermo-chemical processes during regional cooling of the adjacent Itabuna–Salvador–Curaçá belt between 2089 and 1985Ma (pole age likely at 1.99Ga). Comparison of this pole with available paleomagnetic poles from South America and Africa suggests that neither Atlantica nor Ur have ever existed, and dispersed continental fragments dominated the paleogeography at ca. 2.0Ga ago. [Copyright &y& Elsevier]

Abstract: This paper aims at establishing a tectonic and temporal framework to characterize the metallogenic processes that contributed to the origin of the mineral provinces in the northern São Francisco Craton. Many Archean mineralizations (eg. massive sulfide zinc, lead, zinc and copper, besides magnesite–talc, iron–titanium–vanadium, iron, chromite and manganese) were generated before the assembly of the Craton. Deposits of chromite, nickel, gold and emerald were produced during the Paleoproterozoic orogenic cycle, when the Craton was amalgamated into the Atlantica paleocontinent. An extension event is recorded in the Neoproterozoic, during the breakup of Rodinia, associated with deposits of phosphorite and uranium. Kimberlite diamond and gold mineralization were generated during the Brasiliano orogenic cycle, coeval with the amalgamation of West Gondwana. A long-lasting and rather uniform crustal stress is recorded in the area during the Cambrian period. Resetting of the isotopic and magnetic systems that affected the Neoproterozoic sediments of the Irecê Basin at about 520 Ma was attributed to the regional-scale fluid migration and mineralization in the aftermath of the Brasiliano orogenic cycle. [ABSTRACT FROM AUTHOR]

Abstract: On December 9, 2007, a 4.9 m b earthquake occurred in the middle of the São Francisco Craton, in a region with no known previous activity larger than 4 m b. This event reached intensity VII MM (Modified Mercalli) causing the first fatal victim in Brazil. The activity had started in May 25, 2007 with a 3.5 magnitude event and continued for several months, motivating the deployment of a local 6-station network. A three week seismic quiescence was observed before the mainshock. Initial absolute hypocenters were calculated with best fitting velocity models and then relative locations were determined with hypoDD. The aftershock distribution indicates a 3km long rupture for the mainshock. The fault plane solution, based on P-wave polarities and hypocentral trend, indicates a reverse faulting mechanism on a N30°Ε striking plane dipping about 40° to the SE. The rupture depth extends from about 0.3 to 1.2km only. Despite the shallow depth of the mainshock, no surface feature could be correlated with the fault plane. Aeromagnetic data in the epicentral area show short-wavelength lineaments trending NNE–SSW to NE–SW which we interpret as faults and fractures in the craton basement beneath the surface limestone layer. We propose that the Caraíbas–Itacarambi seismicity is probably associated with reactivation of these basement fractures and faults under the present E–W compressional stress field in this region of the South American Plate. [Copyright &y& Elsevier]

Abstract: U–Pb single zircon crystallization ages were determined using TIMS and sensitive high resolution ion microprobe (SHRIMP) on samples of granitoid rocks exposed in the Serrinha nucleus granite–greenstone terrane, in NE Brazil. Our data show that the granitoid plutons can be divided into three distinct groups. Group 1 consists of Mesoarchaean (3.2–2.9Ga) gneisses and N-S elongated TTG (Tonalite-Trondhjemite-Granodiorite) plutons with gneissic borders. Group 2 is represented by ca. 2.15Ga pretectonic calc-alkaline plutons that are less deformed than group 1. Group 3 is ca. 2.11–2.07Ga, late to post-tectonic plutons (shoshonite, syenite, K-rich granite and lamprophyre). Groups 2 and 3 are associated with the Transamazonian orogeny. Xenocryst ages of 3.6Ga, the oldest zircon yet recorded within the São Francisco craton, are found in the group 3 Euclides shoshonite within the Uauá complex and in the group 2 Quijingue trondhjemite, indicating the presence of Paleoarchaean sialic basement. Group 1 gneiss-migmatitic rocks (ca. 3200Ma) of the Uauá complex constitute the oldest known unit. Shortly afterwards, partial melting of mafic material produced a medium-K calc-alkaline melt, the younger Santa Luz complex (ca. 3100Ma) to the south. Subsequent TTG melts intruded in different phases now exposed as N-S elongated plutons such as Ambrósio (3162±26Ma), Araci (3072±2Ma), Requeijão (2989±11Ma) and others, which together form a major part of the Archaean nucleus. Some of these plutons have what appear to be intrusive, but are probably remobilized, contacts with the Transamazonian Itapicuru greenstone belt. The older gneissic rocks occur as enclaves within younger Archaean plutons. Thus, serial additions of juvenile material over a period of several hundred m.y. led to the formation of a stable micro-continent by 2.9Ga. Evidence for Neoarchaean activity is found in the inheritance pattern of only one sample, the group 2 Euclides pluton. Group 2 granitoid plutons were emplaced at 2.16–2.13Ga in a continental arc environment floored by Mesoarchaean crust. These plutons were subsequently deformed and intruded by late to post-tectonic group 3 alkaline plutons. This period of Transamazonian orogeny can be explained as a consequence of ocean closure followed by collision and slab break-off. The only subsequent magmatism was kimberlitic, probably emplaced during the Neoproterozoic Braziliano event, which sampled older zircon from the basement. [Copyright &y& Elsevier]

Abstract: The São Francisco Craton, in the central-eastern region of Brazil, is a cratonic fragment stabilized after the Rhyacian tectono-metamorphic event (2.25–2.05Ga). Volcanic and sedimentary rocks of the Espinhaço (Paleo- to Mesoproterozoic) and São Francisco (Neoproterozoic) basins crop out on this craton. In the northern sector of the craton, the Espinhaço basin crops out in two domains: the Northern Espinhaço Range and the Chapada Diamantina, that are separated by the Paramirim Corridor, a Brasiliano/Pan African (650–500Ma) deformation zone, which crosses the craton in NNW–SSE direction. The stratigraphic framework of the Northern Espinhaço is characterized by eight synthems that comprise units bound by unconformities, or stratigraphic discontinuities with regional extent over the Espinhaço basin. These synthems are: Algodão, São Simão, Sapiranga, Pajeú and Bom Retiro (lower interval), São Marcos and Sítio Novo (intermediate interval) and Santo Onofre (upper interval). For each interval the sedimentary processes, the depositional systems, the filling style of the basin and the tectonic settings were evaluated, based mainly on the facies association characteristics and their lateral/vertical changes. Zircon U–Pb SHRIMP and basin analysis studies carried out along the eastern border of the Northern Espinhaço Range provide a few new or improved anchors upon which the tectonic evolution of the Espinhaco basin can be pinned. We identified Statherian rifting in the São Simão Synthem, by dating volcanic rocks at 1.73Ga. This is followed by a previously unknown, minor intracratonic rift phase within the São Francisco Craton, dated at circa 1.57Ga through a volcanic unit within the Pajeú Synthem. The entire lower interval is cut by mafic intrusive dykes of which we dated one at 850Ma, which we correlate with a Tonian rifting phase affecting the eastern part of the São Francisco craton, and related to the break-up of the Rodinia Supercontinent. Our data show that the development of the Northern Espinhaço Range spans a large time interval, and comprises a discontinuous series of tectonic events that gave rise to the formation of the various synthems and are punctuated by the extrusion of minor volcanic units and emplacement of dykes within the eastern part of the São Francisco Craton. [Copyright &y& Elsevier]

Abstract: First-order regional unconformities separate Proterozoic supracrustal rocks of the gas-bearing São Francisco craton and surrounding thrust-and-fold belts (eastern Brazil) into four genetic stratigraphic units, which constitute 1st-order basin-fill sequences (Espinhaço, Canastra–Paranoá–Vazante, Macaúbas and Bambuí sequences). The Espinhaço 1st-order sequence (ca. 1.73–1.50Ga) records a stage of aborted lithospheric stretching of the São Francisco-Congo continental mass. The Espinhaço basin displays a “steer''s-head” geometry, where four 2nd-order sequences are recognized (prerift, rift, transitional and flexural). Third-order rift-propagation unconformities allowed the definition of three 3rd-order synrift sequences within the rift 2nd-order sequence. The 2nd-order flexural sequence of the Espinhaço basin can be subdivided into three 3rd-order transgressive–regressive sequences. The Canastra–Paranoá–Vazante and Macaúbas 1st-order sequences (ca. 1200–630Ma) comprise rift to drift successions deposited during the breakup of the supercontinent Rodinia and the opening of the Brazilide and Adamastor oceans, respectively, to the west and east of the São Francisco paleocontinent. According to seismic data, the passive-margin Canastra–Paranoá–Vazante 1st-order sequence can be divided into two 2nd-order sequences: rift and passive margin. The passive-margin 2nd-order sequence can be further subdivided into three 3rd-order sequences. The outcropping Canastra–Paranoá–Vazante sequence consists mainly of shallow-marine deposits, which contain black shales/marls with intervals showing high total organic carbon (TOC) contents, comprising one of the highest potential hydrocarbon source rocks of the São Francisco basin. The Bambuí foreland 1st-order sequence (ca. 750–550Ma) formed as a consequence of thrust loading related to shortening in the Brasília fold belt on the western flank of the São Francisco craton, during the closing of the Brazilide ocean and the assembly of the West Gondwana supercontinent. The Bambuí sequence shows two distinct successions, which reflect the main basin paleogeographic settings: foredeep and flexural ramp. Three transgressive–progradational 2nd-order sequences can be recognized in the ramp succession of the Bambuí basin. [Copyright &y& Elsevier]

Paleomagnetic results from unmetamorphosed Mesoproterozoic mafic dikes of Salvador, northern São Francisco craton, yield either an easterly direction with high upward inclination (Dm=110.8°, Im=-79.3°, α95=8.4°, N=8, paleopole at 122.7°E, 6.4°N), or a westerly direction with high downward inclination (Dm=290.7°, Im=64.7°, α95=7.5°, N=7, paleopole at 282.6°E, 5.6°N). Additional paleomagnetic analyses on country rocks (granulites and amphibolitic dikes) yield paleomagnetic poles similar to those obtained in other metamorphic rocks from the São Francisco craton affected by the Transamazonian orogeny (2200–1900 Ma). Positive baked contact tests in two dikes, together with rock magnetic studies, supported by petrographic and radiometric analyses, indicate that the remanent directions isolated for the unmetamorphosed dikes are primary TRM’s. 40Ar/39Ar step-heating analyses on biotite from a granulite sampled ∼90 cm away from the dike’s contact yield an integrated age of 1021±8 Ma, whereas the plagioclase from the dike itself yields an integrated age of 1003±33 Ma, interpreted to be the time of the emplacement. Our data in conjunction with the available late Mesoproterozoic poles from the São Francisco craton allow to best constrain its APW path between 1080 and 1010 Ma. [Copyright &y& Elsevier]

• We study hydrothermal fluid flow along a strike-slip fault and host carbonate rocks. • Hydrothermal fluids precipitated along faults breccias and veins. • Dilational jogs are sites for hydrothermal fluid precipitation in the fault zone. • Meteoric fluid formed calcite veins in host units at temperature 40 and 70 °C. • Base metals and silica-rich deeper fluids precipitate in the fault as breccia bodies. This study combines multiscale analyses of geological, fault, fracture, and stable isotope data to investigate strike-slip deformation and channeling of hydrothermal fluids along the Cafarnaum fault and calcite veins at different distances from the fault, which is a structure in the São Francisco Craton, northeastern Brazil. Meteoric fluids with δD values near −45‰ and δ18O values near −6.5‰ and temperatures at 40–70 °C precipitated as calcite veins in the host carbonate units. The Cafarnaum fault, a N-S-striking vertical, ~170 km long fault zone, juxtaposes Neoproterozoic carbonate rocks in the western block and Mesoproterozoic siliciclastic rocks in the eastern block. A zone of restraining bends occurs at the central part of the fault, whereas termination zones of horsetail geometry occur at both ends of the Cafarnaum fault. These zones are marked by NW-SE-striking extensional faults that are oblique to the main N-S-striking fault zone, where hydrothermal deposits occur. The zone of influence of the Cafarnaum fault is ~ 20 km wide around the main fault. The fault formed during the Brasiliano orogeny (740–560 Ma) after Neoproterozoic carbonate platform deposition. In contrast with the host units, fluids along the fault zone originated in deeper levels of the crust and show much lower δ18O values, indicating higher crystallization temperatures. These fluids caused brecciation in the Neoproterozoic carbonate host rocks, whereas a subsequent decrease in fluid pressure and cooling near the surface resulted in the precipitation of a hydrothermal paragenesis in veins, also affecting the host rock. [ABSTRACT FROM AUTHOR]

• The Gavião Complex has TTGs, high-K granites, and minor diorites. • Melting of low-K mafic crust at the base of an oceanic plateau produced the TTGs. • One of the first registers of potassic magmatism at 3.35 Ga in the Gavião Complex. • The oldest metamorphic age for the São Francisco Craton was dated at c. 3.27 Ga. • The Archean felsic crust of Gavião Block was formed by crustal reworking. Origin of early Earth's felsic crust is a matter of growing debate in which the rock record from old cratons plays a key role. In northeast Brazil, the São Francisco Craton preserves the oldest felsic rocks of South America and understanding its Archean evolution is an important piece of this debate. Here we present new SHRIMP U-Pb zircon ages and whole-rock geochemistry, as well as a large, compiled dataset to discuss the evolution of the south Gavião Block (GB), a major component of this craton. The GB contains Paleo- to Mesoarchean (3.36–3.18 Ga) TTGs, high-K granites, and minor diorites of the Gavião Complex followed by renewed magmatism, reworking and anatexis between 3.27 and 3.22 Ga. The TTG rocks of Gavião Complex can be divided into high-Sr (high pressure) and low-Sr (low- to medium pressure), evidencing that the sodic magmatism likely occurred at different depths diachronically between 3.36 and 3.20 Ga. We report a crystallization age of a ca. 3.35 Ga for an Archean unusual high-K calc-alkaline meta -granite which marks the first potassic magmatism of the Gavião Complex, suggesting reworking of preexisting TTGs. Zircon U-Pb dates from a TTG migmatite constrained an age of ca. 3.27 Ga, interpreted as a metamorphic event within the basement of the GB, stretching back in ca. 120 My the oldest metamorphic age known so far for the whole São Francisco Craton. Additionally, at ca. 2.7 Ga, the GB was intruded by the intraplate, alkaline magmatism of the Caraguataí Suite, marking thus the stability of this Block during Neoarchean. We argue that crustal reworking was the main mechanism responsible for the formation of the GB during the Paleo- to Mesoarchean. The data suggest the GB rocks share an old source possibly including Hadean components. We propose that the formation of the TTGs of GB is a result of the melting of low-K mafic crust at the base of a progressively thicker oceanic plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Lavra Velha deposit represents a new gold-rich IOCG mineralization at the São Francisco Craton. • The gold mineralization is associated with a hydrothermal breccia system with co-existing iron oxides and sulfides. • IOCG mineralization is related to the Rhyacian period of the northern São Francisco Craton. • Mineralization is marked by decreasing temperatures from the bottom to the top of the deposit. Lavra Velha is a newly discovered Rhyacian IOCG deposit in the northern portion of the São Francisco Craton, in the Bahia state of NE Brazil. Gold and copper mineralization is hosted by epigenetic hydrothermal breccia with large amounts of iron oxide. Multiple phases of breccia formation and hydrothermal alteration caused zoning from the base to the top of the deposit. The alteration is mainly characterized by hydrothermal calcite-epidote-magnetite, tourmaline-chlorite-magnetite, and sericite-hematite hydrothermal alteration styles. Tourmaline and chlorite chemistry indicates that low temperature alkaline fluids had variable Fe2+, Mg, Al, and Na contents throughout the evolution of the breccia complex. Magnetite and hematite display low vanadium content (≤0.24 wt%) and very low titanium content (≤0.06 wt%). The sulfide minerals are pyrite (with up to ~ 3 wt% Co), chalcopyrite, bornite, arsenopyrite, and covellite, in decreasing order of abundance. Coarse muscovite that is related to the latest stages of breccia displays a high barium content with an average of ≥ 1.27 wt%. Isotopic compositions of carbon and oxygen in calcite from the calcic breccia indicate that early mineralizing fluids were derived from a mixed magmatic/non-magmatic reservoir (δ13C ~ −2‰ and δ18O from 9.95 to 13.09‰ in calcite). The sulfur isotopic compositions of chalcopyrite and pyrite demonstrate that sulfur in the mineralized breccia was derived from cooling magmas that underwent weak contamination from oxidized fluids or host rocks (δ34S from 2.22 to 3.89‰). New U-Pb zircon ages indicate that mineralization occurred at approximately 2100 Ma, coeval with tourmaline-bearing porphyritic granite dikes that yield ages of 2098 ± 8 and 2112 ± 12 Ma respectively. Despite being considered a small deposit in relation to known reserves, Lavra Velha may be the first IOCG deposit recognized in the São Francisco Craton, particularly in the Gavião Block. Thus, it represents an important indicator for future precious and base metal exploration in the São Francisco Craton. [ABSTRACT FROM AUTHOR]

Greenstone belts and volcano-sedimentary sequences are essential features to understand the tectonic framework of Precambrian terranes worldwide. The São Francisco Craton, eastern Brazil, hosts several of these supracrustal belts related to its Archean-Paleoproterozoic evolution. The Rio Salitre Complex (RSC) is a Paleoproterozoic greenschist-metamorphosed volcano-sedimentary sequence deposited over Archean orthogneisses of the northern São Francisco Craton. Here, we present a tectonic model for the Rio Salitre Complex, integrated with regional and global contexts, based on geology, structures, whole-rock geochemistry, U–Pb zircon geochronology, and Lu–Hf isotopes. The RSC comprises the Baixo Vale do Rio Salitre (BVRS), formed by Lower and Upper Subunits, and the Sobradinho Unit. The BVRS Lower Subunit is composed of ultramafic, mafic, and felsic metavolcanic rocks, chemical, and minor clastic metasedimentary rocks. The BVRS Upper Subunit comprises clastic metasedimentary rocks, while the Sobradinho Unit consists of chemical and clastic metasedimentary rocks. The RSC units display evidence of shallow to deep marine platformal deposition in an intra-cratonic rift (abundance of pelitic facies, presence of phosphorites, iron formations, graywackes, arkoses, and cross-bedded quartzites). RSC phosphorites are a register of a global Paleoproterozoic phosphogenic event. The volcanics of the Rio Salitre Complex compose a bimodal suite. The mafic and ultramafic metavolcanics exhibit komatiitic, tholeiitic, and alkaline affinities. Enriched REE, trace elements patterns, and incompatible element ratios indicate a continental rift environment for the mafic and ultramafic metavolcanic rocks. These features also suggest enriched mantle-derived melts, with a variable crustal contribution. The porphyritic rhyolites and aphyric high-silica rhyolites have subalkaline to alkaline features, with enriched REE and trace element profiles and negative Eu, Nb, and Ti anomalies. U–Pb SHRIMP dating of porphyritic rhyolite resulted in a concordia age of 2161.1 ± 4 Ma (MSWD: 1.1). Archean Lu–Hf T DM ages with negative εHf (t) values (from −8.90 to −2.70), and an isolated Paleoproterozoic T DM age (2440 Ma) with positive εHf (t) value (+3.96), related to the geochemical features, indicate that RSC felsic metavolcanics were originated from melting of multiple Archean crustal sources (continental and slab), with minor contributions of Paleoproterozoic juvenile material, and emplaced in a continental rift environment. 2.0 Ga foliated metagranites and metagranodiorites (locally augen) intrude the RSC rocks, resulting in local hornblende-hornfels metamorphism. The RSC supracrustal lithotypes register D 1 ', D 1 ″, and D 2 structures. D1′ structures are mainly represented by N–S high-dip angle schistosity, N and SSE plunge folds, and high-rake mineral stretching lineation (Lx'); while D 1 ″ corresponds to NE-SW transpressional shear zones, NE-SW low-dip angle crenulation cleavage, and medium to low-rake mineral stretching lineation (Lx 1 ″). The D2 structures are related to, locally quartz-filled, fractures, in addition to NE-SW and ENE-WSW oriented faults. The structural framework reflects a two-phase deformation, with a ductile to ductile-brittle, W-E frontal to NW-SE oblique D 1 phase, and a late brittle, NE-SW D 2 phase. Late hydrothermal activity resulted in quartz veins and pyrite-pyrrhotite-(chalcopyrite) concentrations. The documented aspects of the Rio Salitre Complex are consistent with evolution in a Rhyacian-Orosirian continental rift basin, inverted by the influence of orogenic belts, approaching from northwest and southeast. [Display omitted] • A tectonic model for the Rio Salitre Complex, in the global context, is proposed. • This work brings unprecedented U–Pb age and Lu–Hf for the Rio Salitre Complex. • The petrogenesis of the bimodal volcanic suite is discussed. • The data show that the sequence was deposited in a Paleoproterozoic rift basin. [ABSTRACT FROM AUTHOR]

Precambrian terrane boundaries are sites of diverse rock associations and structural complexity. Motions along the boundary zones are commonly related to the construction of ancient large continental masses. This seems to be the case in the São Francisco Craton, Brazil, where three major blocks (Gavião, Jequié and Serrinha) collided in the Paleoproterozoic to form the northern part of the craton. This manuscript presents zircon U-Pb ages and whole-rock geochemistry for rock associations on the western border of the Jequié Block, which is defined by the north-trending left-lateral 600-km long Contendas-Jacobina fault zone. The studied rocks are granulite to amphibolite facies Neoarchean orthopyroxene-hornblende granite gneisses of the Jequié block, which also occur tectonically imbricated within Paleoproterozoic metavolcanosedimentary rocks of the Contendas-Mirante belt. The rocks are 2.65-2.63 Ga high-K ferroan, metaluminous to slightly peraluminous syeno-monzogranite in composition, with negative ƐNd (2650) and Nd model ages of 3.05-2.88 Ga. They are depleted in Sr and Ti, enriched in Th, Ba and Pb enrichment, and have marked negative Eu/Eu*. This geochemical signature coupled with the Nd-isotope data indicate that the parental granitic magma was generated by crustal reworking of felsic Mesoarchean crust distinct from the western-sitting >3.3 Ga Gavião Block. The investigated granitic gneisses are similar to other potassic granitoids that occur in the São Francisco Craton, which mark the thermal stabilization of the Archean lithosphere. The westward thrusting of the Neoarchean hornblende granitic gneiss and associated high-Mg tremolitite (meta-basalts) onto Paleoproterozoic volcano-sedimentary sequences establishes field evidence of Paleoproterozoic nappe stacking before lateral displacement during block collision. The crustal amalgamation is related to the assembly of the São Francisco-Congo Craton, a major landmass established before the Columbia supercontinent. • 2.65–2.63 Ga high-K granitic gneisses related to crustal reworking and cratonization • Transitions from granulite to amphibolite metamorphic facies at Jequié Block border • Strike-slip fault zone delimits the tectonic contact between distinct Archean terranes [ABSTRACT FROM AUTHOR]

The Quadrilátero Ferrífero region is located in the extreme southeast of the Brasiliano São Francisco craton, Minas Gerais state, Brazil. It is composed of (i) Archean TTG granite-gneaissic terranes; (ii) the Archean Rio das Velhas greenstone belt; (iii) the Proterozoic metasedimentary and metavolcano-sedimentary covers. The Rio das Velhas rocks were deposited in the synformal NW–SE-directed Nova Lima basin. The Archean deformation converted the Nova Lima basin into an ample synclinorium with an eastern inverted flank. Archean orogenic gold mineralization within the Rio das Velhas greenstone belt rocks is controlled by NNW–SSE-directed, Archean regional shear zones subparallel to the strata of the Nova Lima synclinorium borders. Transamazonian and Brasiliano orogenies are superposed onto the Archean structures that control gold mineralization. In the eastern domain, Brasiliano fold-and-fault belts prevail, whereas in the western domain Archean and Transamazonian structures abound. The present study focus mainly is the western domain where the Cuiabá, Morro Velho, Raposos, Lamego and Faria deposits are located. Gold orebodies plunge to the E–NE and are tectonically controlled by the Archean D1–D2 deformation. The D3 Transamazonian compression—Which had a SE–NW vector sub-parallel to the regional mineralized Archean foliation/bedding—Buckled these structures, resulting in commonly open, synformal and antiformal regional folds. These are well documented near the gold deposits, with NE–SW axial traces and fold axes plunging to E–NE. Such folds are normal to inverted, NW-verging, with an axial planar foliation dipping moderately to the SE. The Transamazonian compression has only been responsible for the reorientation of the mineralized Archean gold ores, due to coaxial refolding characterized by an opposite tectonic transport. It has therefore not caused any other significant changes. Thrust shear zones, sub-parallel to the strong Transamazonian foliation, have given rise to localized metric segmentation and to the dislocation of gold orebodies. Throughout the region, along the towns of Nova Lima to Sabará, structures pertaining to the Brasiliano Araçuaí orogeny are represented only by gentle folding and by a discrete, non-pervasive crenulation cleavage. Thrust-shear zones and small-scale normal faults have caused, at most, metric dislocations along N–S-oriented planes. [ABSTRACT FROM AUTHOR]

Isotopic Lu–Hf and geochronological studies on the zircon grains of the Paleoproterozoic Borrachudos Suite provide constrains of the evolution of the tectonomagmatic events that affected the southern border of the São Francisco Craton and leaded to the formation of the associated iron and emerald deposits. The granite records magmatic crystallization in the 1740-1688 Ma time range, and A2-type geochemical signature. Zircon grains present hydrothermal and anatectic areas with Cambrian age that are related to the gravitational collapse of the final stages of the Brasiliano orogen. During this event the granite was deformed and metamorphosed in the amphibolite facies, leading to anatexis and the formation of large amount of pegmatite bodies. The Hf isotope data on the hydrothermal/anatectic areas indicate partial melting were accompanied by hydrothermal fluids enriched in radiogenic Hf. These fluids contributed to the formation of large volume of hydrous melts (pegmatites), the formation of the emerald deposits and the high-grade iron orebodies. • New Hf isotope data for the Borrachudos Suite and associated deposits. • Evidences on the hydrothermal and anatectic zircon growth. • Isotopic signatures imply a mixture of juvenile material and old crust. • Isotopic constraints on the evolution and genesis of iron and emerald mineralization. [ABSTRACT FROM AUTHOR]

• 1.58 Ga rift-related ferroan alkalic volcanism of the Paramirin aulacogen. • We provide detailed analyses of the primary and secondary volcaniclastic deposits. • Magma source from high melt rate of ancient crust metasomatized by mantle fluids. • Mantle fluids provided K and Na metasomatism and modified the feldspars chemistry. • Na-rich fluids synthesized aegirine and promoted its peralkaline signature. Rift-related volcanism is widely used in models of supercontinent reconstruction, while the associated metasomatic fluids provide information about the mantle-crust process during intracrustal melting events. The Paleoproterozoic/Mesoproterozoic Paramirim aulacogen corresponds to multiple intracratonic rift cycles that register many basin developing events. Intense volcanic activity is recorded in some rift events, but the volcanic lithofacies and their petrogenesis are poorly constrained. Herein, we present lithofaciological characterization, whole-rock and mineral chemistry, and U-Pb and Lu-Hf isotope data from the 1.58 Ga volcanic rocks. Trachytic and trachy-andesitic lava flows and primary to secondary volcaniclastic lithotypes characterize this volcanism. The primary volcaniclastic rocks resulted from direct volcanic activity and can be divided into pyroclastic and hydroclastic lithofacies associations. The pyroclastic lithotypes correspond to air-fall, density currents and block-and-ash flow deposits formed in explosive eruptions; hydroclastic lithotypes are represented by hyaloclastites and peperites, reflecting effusive eruptions and interactions between magma, water and sediments. The secondary volcaniclastic lithotypes resulted from late-stage reworking processes and consist of debris flows, ephemeral streams associated with high energy and gravitational flow deposits. The lava flows show well-preserved primary volcanic features, such as magma flow textures and euhedral phenocrysts. Based on petrographic and chemical characteristics, associated with negative ɛHf(t) values, we infer that high melt rate of an ancient crust, previously metasomatized by H 2 O-rich alkaline mantle-derived fluids, generated the alkalic ferroan lavas. These fluids promoted potassic and sodic metasomatism that affected all the volcanic rocks, modifying the chemistry of the feldspars to pure orthoclase (Or 96-98) and albite (Ab 98-100). In some lavas, a higher concentration of Na-rich fluids synthesized aegirine at a minimum temperature of 200 °C and promoted its peralkaline character. The potassic-sodic metasomatism influenced the volcano-sedimentary sequence of the Pajeú Group and the oldest rocks of the basement but did not affect the overlying sedimentary sequences, indicating that fluids ceased with the end of volcanism. We suggest that the H 2 O-rich alkaline fluids arose by focused degassing in response to a rising asthenospheric mantle during the Calymmian rift of the Paramirim aulacogen. [ABSTRACT FROM AUTHOR]

• 3.4–3.3 Ga TTGs were products of partial melting of E-MORB and minor crustal sources. • 3.1–2.7 Ga successive magma addition denotes the first continental arc in the GCB. • Archean crust was intensely reworked in episodic tectono-thermal events (2.7/2.1 Ga). • 2.0 Ga crust represents the collisional event and further cratonization of GCB. The north-central part of the São Francisco Craton (SFC) is one of the oldest terranes in the South American platform and experienced three regional magmatic events at 3.4–3.3, 3.1–2.7, and 2.1 Ga. Our new SHRIMP U-Pb data place the origin of Guanambi-Correntina block (GCB) in the Paleoarchean, contemporaneous with the Gavião block in central north SFC. Lithological, geochemical, and isotopic evidence indicate that the 3.4–3.3 Ga rocks of the Favelândia complex are derived from partial melting of E-MORB sources during flat subduction. The 3.1–2.7 Ga K-granitoids in the Santa Izabel complex are derived from a mixture of crustal and mafic sources, as evidenced by the slightly negative to positive Ɛ Nd(T) and Sr/Sr i between 0.700 and 0.706. The 3.1–2.7 Ga event is responsible for the recycling of the Paleoarchean TTG crust, generation of low- to high-K evolved crust, and juxtaposition of the Favelândia and Santa Izabel complexes. The youngest magmatic event at ca. 2.1 Ga produced felsic plutons, derived from anatexis of Archean felsic rocks and mantle components. The collisional process tectonically juxtaposed the Riacho de Santana greenstone belt and Archean felsic rocks at 2.1–2.0 Ga, determining the region's current configuration. Based on the data reported in this study and previously published data, we suggest that the Guanambi-Correntina block was formed as an independent unit in the northern SFC. [ABSTRACT FROM AUTHOR]

• 3D view of Euler solutions allowed delineating the basement paleorelief. • Structures at basement paleorelief suggest 2 extensional events to basin evolution. • Geophysical and geological data suggest that older structures had control on basin evolution. • The lineaments relations in the Irecê basin suggest its evolution as a part of a transtensional zone. • The structures imprinted on cover suggest that basin paleo-relief control deformation during inversion tectonics. The Proterozoic sedimentary cover in eastern Chapada Diamantina recorded positive inversion tectonics at the Paramirim aulacogen during Neoproterozoic times. Additionally, geological evidence suggests that although the basement was not involved in the contractional tectonics, it exerted control on cover deformation. The Euler deconvolution, based on aeromagnetic and gravimetric databases, integrated with geological framework, was used to delineate the structures and deep architecture of the crystalline basement and to understand their relationships with cover deformation. The 3D view of Euler deconvolution profiles show a graben and horst geometry in the basement architecture. Horsts and grabens are limited by NNW-SSE, N-S and E-W normal faults, which nucleated during two extensional events and favored for deep Archean-Paleoproterozoic discontinuities. The first event was related to the development of a half-graben that had a NNE-SSE-oriented eastern boundary and that was filled with rocks of the Chapada Diamantina Group. The second event gave rise to an asymmetrical graben that evolved from dextral strike-slip displacement and was filled by rocks of the Una Group in the Irecê domain. In the late Neoproterozoic, two contractional, thin-skinned cover deformations with ENE-WSW and N-S shortening directions affected the Chapada Diamantina and Irecê domains. Our geophysical models reveal a parallelism between the thin-skinned structures and N-S and E-W normal faults, interpreted in the crystalline basement, suggesting a control on strain and stress distribution during cover deformation. During the second contractional tectonic event, the NNW-SSE and N-S lineaments at the boundaries of the Irecê domain were reactivated, producing Ubiaí and Serra da Babilônia brittle shear zones in the sedimentary cover, respectively. In summary, the superposed intracratonic basin formation was controlled by older structures in the crystalline basement, while the inversion tectonics was controlled by the geometry of these basins. [ABSTRACT FROM AUTHOR]

The study area is located in the central portion of the São Francisco Craton (SFC), between two of the main blocks that compose this feature: the Jequié and the Itabuna-Salvador-Curaçá blocks. The main objective of this study was to reevaluate the transition zone between both blocks, employing airborne geophysical, geologic and structural data. The geophysical data are represented by gamma-ray spectrometry and magnetic surveys, which showed the structure of the lithotypes mapped and helped in the identification of their limits. The analysis of these images established five radiometric domains and six magnetic zones. The geophysical data interpreted along with mapping survey, with macroscopic description and structural data, allowed better identification of the suture zone between the referred blocks. The structural analysis identified four deformation phases, characteristic of a transpressional zone, uplifting the ISCB onto JB. The present study proposes the modification of the limits between these blocks to a more southern location and updates the regional geotectonic understanding of the central region of the state of Bahia. • Macroscopic description has its reliability enhanced by geophysical data. • Airborne geophysical maps are an important tool to the interpretation of suture zones. • Radiometric and magnetic maps allow the observation of predominant structures. • The central portion of SFC is clearly characteristic of a transpressional environment. [ABSTRACT FROM AUTHOR]

Minor altered intrusions and drab retrogressed schists can easily be overlooked in geological studies but this contribution explores these rocks within the Archaean and Palaeoproterozoic southern São Francisco Craton (SSFC), Brazil using geological relationships and accessory mineral in situ analyses in the context of cratonic assembly. Three magmatic pulses are documented: i) Archaean and ii) Palaeoproterozoic felsic intrusions, both hosted by Archaean protoliths, and iii) Palaeoproterozoic felsic intrusions in Palaeoproterozoic supracrustal sequences. Archaean felsic intrusions confirm the Palaeoarchaean age of the mafic/ultramafic sequence of the Rio das Velhas Greenstone Belt and Rhyacian intrusions mark the collisional stage of the Mineiro Belt with the SFC at c. 2130 Ma. Greenstone belt schists show a wide distribution of rounded 'soccer ball' Archaean detrital and metamorphic zircon grains ranging in age from 3200 to 2750 Ma with an interpreted overprinting high-grade metamorphic event at c. 2700 to 2680 Ma. Most high-grade metamorphic rims have Th/U > 0.1, negative εHf (t) values and REE pattern consistent with eclogite/granulite metamorphic facies, reinforcing the hypothesis of a dehydrated-refractory crust formed during the stabilization of the SSFC, even though no such protoliths are preserved. This event links crustal thickening and partial melting of Archaean lower crust. Archaean rutile crystals from the greenstone belt schist were reset during the Palaeoproterozoic event but still preserve the early Archaean high-grade metamorphic signature. The presence of unstable ilmenite replaced by rutile in the schist, associated to felsic intrusions with the same age at c. 2130 Ma suggest high pressure, low temperature prograde metamorphism during the collisional stage of the Palaeoproterozoic orogen. Elongate and prismatic zircon grains from the Rhyacian intrusions have low εHf (t) signature and crystallised from partial melting of sedimentary protoliths. Accretionary events produced thicker and more differentiated crust by the end of Rhyacian time. Easily overlooked rocks in this study, when studied, have revealed a rich multi-event history of cratonic evolution. • Archaean felsic intrusions constrain the Rio das Velhas Greenstone Belt evolution in at least 200 Myr; • High-grade soccer ball metamorphic zircon grains depict conditions of Archaean crustal amalgamation; • First report of Rhyacian felsic intrusions in the Minas and Rio das Velhas supergroups of the Quadrilátero Ferrífero; • Rhyacian felsic intrusions in the supracrustal sequences derive from reworked crust; • Rhyacian felsic magmatism around the margins of the SSFC depicts the collisional stage of the Minas accretionary orogeny. [ABSTRACT FROM AUTHOR]

Field, petrographic, lithogeochemical, LA-ICP-MS in situ U-Pb zircon geochronology, and Nd and Sr isotopic data were used to determine the geologic evolution, timing of volcanism and tectonic setting of the Mundo Novo greenstone belt (MNGB) including nearby units, such as the basement and younger granitic rocks in the eastern São Francisco Craton (NE Brazil). The basement of the greenstone belt corresponds to the Gavião Block, which comprises tonalite-trondhjemite-granodiorite orthogneisses, migmatites and subordinate metarhyolites and metagranites. The MNGB is divided into three lithological sequences: (i) the lowermost unit is composed of metakomatiites; (ii) the middle unit is composed mainly of metabasalts, metadacites and metasedimentary chemical rocks; and (iii) the uppermost unit is composed of metasedimentary siliciclastic rocks. Additionally, two Rhyacian-Orosirian granitic plutons occur in the area, the Areia Branca and Jequitibá metagranites. U-Pb zircon data from the Miguel Calmon and Fazenda Coqueiro metagranites in the Gavião Block yield crystallization ages of 3355 ± 16 Ma and 3227 ± 23 Ma, respectively, and both metagranites were derived from the lower continental crust based on low 87Sr/86Sr i values (0.699 and 0.705, respectively) and negative values of Ɛ Nd(t) (−3.7 and −3.6, respectively). The 2595 ± 21 Ma U-Pb zircon crystallization age of the metadacites allowed the determination of the timing of volcanism in the middle sequence of the MNGB. The 2106 ± 71 Ma and 1975 ± 36 Ma U-Pb zircon crystallization ages for the Areia Branca and Jequitibá metagranites, respectively, which are both interpreted as derived from crustal protoliths based on high 87Sr/86Sr i values (0.744 and 0.730, respectively) and negative values of Ɛ Nd(t) (−7.7 and −6.5, respectively), record a Rhyacian-Orosirian tectonothermal event that affected the MNGB and the adjoining region. The whole-rock geochemical data in tectonic discrimination and multielement diagrams show that the volcanic rocks of the MNGB formed in island arc and back-arc basin settings related to the oceanic crust. Therefore, the following five stages are proposed for the tectonic evolution of the study region: stages (i) and (ii) were characterized by the establishment of the TTG basement by 3.35 Ga, when the Miguel Calmon granite was consolidated, followed by a rifting that formed the rhyolites, and subsequent granite formations occurred at 3.22 Ga (Fazenda Coqueiro granite formation), followed by the abort of the rift and a closure event. The volcanism during stage (iii) at 2.59 Ga in the MNGB occurred in island arc and back-arc basins in the oceanic crust between Archean cratonic blocks, and stages (iv) and (v) between 2.10 Ga and 1.97 Ga represent two stages of a progressive collision event in which the oceanic crust was compressed between the Gavião, Mairi, Jequié and Serrinha blocks and the Itabuna-Salvador-Curaçá Belt from the eastern part of the São Francisco Craton. The collisional event of stages (iv) and (v) was coeval with the Rhyacian-Orosirian formation of granites and basins such as that where the uppermost siliciclastic sequence of the MNGB was deposited. • The Paleoarchean metagranites were derived from the lower continental crust. • The Mundo Novo greenstone belt formed in island arc and back-arc basin settings. • The volcanism in the Mundo Novo greenstone belt occurred at 2595 ± 21 Ma. • The Rhyacian-Orosirian granitic bodies were derived from crustal protoliths. • The oceanic crust was compressed between cratonic blocks during the Paleoproterozoic. [ABSTRACT FROM AUTHOR]