Brasiliano Orogeny Research Articles

Fault damage zones width: Implications for the tectonic evolution of the northern border of the Araripe Basin, Brazil, NE Brazil

Fault zones commonly have spatially variable fault rocks and brittle structures. Differing fault-rock attributes may retard or increase cross- and along-fault permeability. Our work analyzed brittle deformation of a segment of the Patos shear zone, Triunfo Fault, which is located in the northern border of the Araripe Basin, NE Brazil. We investigated the structural evolution and tectonic implications of the Triunfo Fault by mapping damage zone width patterns and the types and distributions of breccia and brittle structure arrays within the fault zone using scanline fracture analysis techniques and topographic and aeromagnetometric data. Fractured rocks of the damage zone mainly comprise: mylonitic orthogneiss (footwall); and sandstone and carbonate rocks (hangingwall). The fault core is composed of tectonic breccia and cataclasites occurring as lenses, with calcite-filled veins. Due to fault sinuosity and rheology heterogeneities, the width of the damage zone ranges from 240 to 290m (footwall), and 372–610m (hangingwall). Our analysis obtained from the topographic and gravimetric data combined with field data indicate the following sequential deformation phases: a) Dn, Brasiliano Orogeny, dextral shear zone; b) Dn+1, Paleozoic time, brittle-ductile deformation; and c) Dn+2, Lower Cretaceous time, brittle deformation.

Metamorphic evolution of metasedimentary rocks of the Feira Nova region: Tectonic implications for the Brasiliano Orogeny in eastern Borborema Province, Northeast Brazil

Thermobarometric estimations and X-ray maps were combined to evaluate the metamorphic evolution of metasedimentary rocks (Surubim Complex) in the Feira Nova region, eastern Borborema Province (NE Brazil). Sillimanite-bearing biotite schists, garnet-biotite schists and gneisses were studied. X-ray maps show different growing phases and retrograde zoning patterns for biotite and garnet. High Ca and Mg contents in garnet cores along with high Ti in biotite are interpreted as equilibrium compositions at peak metamorphism. Lower contents of Ca and Mg at garnet rims and of Ti in biotite rims suggest cooling and decompression. Garnet-biotite geothermometer and garnet-Al2SiO5-quartz-plagioclase (GASP) geobarometer constrain high temperature (∼650–760 °C) and medium pressure (∼0.6–0.9 GPa; burial to ∼23–34 km) conditions for the metamorphic peak, which was synchronous to development of a flat-lying foliation and local anatexis. Garnet rims indicate exhumation to ∼19-11 km (∼0.4–0.3 GPa) at ∼590-520 °C, probably during a transpressional regime. The data points to low exhumation and cooling rates. The lack of extensional fabrics in the region right after the Brasiliano Orogeny supports erosional unroofing rather than extensional collapse. Based on kyanite occurrences nearby, we infer a clockwise P-T path related to thickening in a predominant intracontinental setting, followed by exhumation with low erosional and cooling rates.

High-pressure metamorphic rocks in the Borborema Province, Northeast Brazil: Reworking of Archean oceanic crust during proterozoic orogenies

We present the first evidence of Archean oceanic crust submitted to Proterozoic high-pressure (HP) metamorphism in the South American Platform. Sm–Nd and Lu–Hf isotopic data combined with U–Pb geochronological data from the Campo Grande area, Rio Grande do Norte domain, in the Northern Borborema Province, reflect a complex Archean (2.9 ​Ga and 2.6 ​Ga) and Paleoproterozoic (2.0 ​Ga) evolution, culminating in the Neoproterozoic Brasiliano/Pan-African orogeny (ca. 600 Ma). The preserved mafic rocks contain massive poikiloblastic garnet and granoblastic amphibole with variable proportions of plagioclase ​+ ​diopside in symplectitic texture, typical of high-pressure rocks. These clinopyroxene-garnet amphibolites and the more common garnet amphibolites from the Campo Grande area are exposed as rare lenses within an Archean migmatite complex. The amphibolite lenses represent 2.65 ​Ga juvenile tholeiitic magmatism derived from depleted mantle sources (positive εHf(t) values of +3.81 to +30.66) later enriched by mantle metasomatism (negative εNd(t) values of –7.97). Chondrite and Primitive Mantle-normalized REE of analyzed samples and discriminant diagrams define two different oceanic affinities, with E-MORB and OIB signature. Negative Eu anomalies (Eu/Eu∗ ​= ​0.75–0.95) indicate depletion of plagioclase in the source. Inherited zircon cores of 3.0–2.9 ​Ga in analyzed samples indicate that the Neoarchean tholeiitic magmatism was emplaced into 2923 ​± ​14 ​Ma old Mesoarchean crust (εNd(t) ​= ​–2.58 and Nd TDM ​= ​3.2 ​Ga) of the Rio Grande do Norte domain. The age of retro-eclogite facies metamorphism is not yet completely understood. We suggest that two high-grade metamorphic events are recognized in the mafic rocks: the first at 2.0 ​Ga, recorded in some samples, and the second, at ca. 600 Ma, stronger and more pervasive and recorded in several of the mafic rock samples. The Neoproterozoic zircon grains are found in symplectite texture as inclusions in the garnet grains and represent the age of HP conditions in the area. These zircon grains show a younger cluster of concordant analyses between 623 ​± ​3 ​Ma and 592 ​± ​5 ​Ma with εHf(t) values of +0.74 to –65.88. Thus, the Campo Grande rock assemblage is composed of Archean units that were amalgamated to West Gondwana during Neoproterozoic Brasiliano orogeny continent-continent collision and crustal reworking.

Provenance of the Late Ediacaran Rocha Formation, Cuchilla Dionisio Terrane, Uruguay: Tectonic implications on the assembly of Gondwana

A provenance study on the Rocha Formation (Cuchilla Dionisio Terrane, Uruguay) based on elemental and isotope geochemistry and geochronology revealed characteristics typical of turbidites linked to orogenic arcs: textural and mineralogical immaturity, and low weathering and sedimentary recycling indicated by low CIA values, Th/U and Zr/Sc ratios. We separate data into two groups, namely northern and southern sectors. Even though the whole unit shows a provenance of upper continental crust denoted by Th/Sc, Zr/Sc, Th/U ratios around UCC averages, REE patterns parallel to PAAS and negative Eu-anomalies, a more depleted component was detected mainly in the northern sector (NS) showing lower Th/Sc and Th/U ratios, negative Eu- anomalies of up to 0.9, high abundances of compatible elements, and lower εNd (t) and 87Sr/86Sr ratios than the southern sector (SS). U-Pb detrital zircon ages indicate 569 ± 10 Ma as the maximum sedimentation age. The most prominent age peak is Neoproterozoic, and while the NS shows dominance of Tonian and a broad data spread for Paleoproterozoic ages, the southern sector comprises both the youngest and oldest zircon and displays a pattern with a more pronounced Stenian population whereas Paleoproterozoic ages are restrained to Orosirian. A K-S test indicates that the change in provenance shown by detrital zircon patterns is reflecting variations of the sediment supply linked to basinal geomorphic heterogeneities within an active margin. Given detailed whole-rock lithogeochemistry, Nd, Pb and Sr isotopic analyses as well as detrital zircon age patterns, correlations with the Oranjemund Group of the Marmora Terrane and with the Tygerberg Formation and associated units of the Malmesbury Terrane (Western Saldania Belt), raised from previous interpretations, are reassessed. Source areas were most likely located within the Cuchilla Dionisio Terrane and Kalahari Craton, and therefore deposition within a foredeep basin occurred before tangential accretion to the Río de la Plata Craton along the Sierra Ballena Shear Zone.

Integrated ophiolite and arc evolution, southern Brasiliano Orogen

Integrated study of Tonian ophiolite mélanges and intra-oceanic arc of the São Gabriel juvenile terrane exposes a key geotectonic unit in the evolutionary history of Gondwana during Brasiliano Orogeny. LA-ICP-MS U-Pb geochronology in rutile and zircon were combined with Lu-Hf and rare earth elements in zircon. We report the first rutile dating of ultramafic rock in the Brazilian Shield of 787.6 ± 2.6 Ma for the Cambaizinho ophiolite magnesian schist. Dating of rutile corresponds to the metamorphic age of the mantle section of the ophiolite. São Gabriel arc infrastructure is represented by the Cambaí Complex, including the Vila Nova Suite metatonalite with zircon U-Pb age of 724.6 ± 3.2 Ma and late Sanga do Jobim Suite monzogranite intrusions with two main pulses at 698.9 ± 4.2 Ma and 673.9 ± 6.8 Ma. Zircon εHf(t) values are positive for both rocks and range between +10.1 and +7.4 in metatonalite and +9.2 to +2.5 in monzogranite. Detrital zircon from metasedimentary rocks support superstructure arc investigation. Ages range from 817 to 650 Ma, with strong concentration between 750 and 730 Ma. Positive εHf(t) values and Rare Earth Elements (REE) signature point to main source of metasedimentary rocks in the arc, with ophiolitic contribution. Therefore, geotectonic processes in the Brasiliano Orogeny include the construction of São Gabriel terrane with Tonian oceanic crust evolving to intra-oceanic subduction until 650 Ma to final development along the margin of continental crust. Overthrusting of the São Gabriel terrane onto the Rio de La Plata Craton occurred at 650–620 Ma. Our data correlate with Tonian intra-oceanic arcs from Brasilia belt (Goiás arc ca. 862–630 Ma) and Ribeira belt (Serra da Prata arc – 856–838 Ma; Rio Negro arc – 790–620 Ma). Oceanic crust generation combined with subduction to form Tonian arcs along the Brasiliano Orogen were most significant for construction of West Gondwana.

Proterozoic to Ordovician geology and tectonic evolution of Rio de Janeiro State, SE-Brazil: insights on the central Ribeira Orogen from the new 1:400,000 scale geologic map

Abstract A comprehensive tectonic evolution of Proterozoic to Cambrian rocks that integrate the crystalline basement of Rio de Janeiro State, based on the new geological map, is presented. The map combines detailed geological data integrated to a 1:400.000 scale and new geochemical and geochronology data to characterize the distinct terranes amalgamated during three pulses of the Brasiliano orogeny. The Occidental terrane comprises the Tonian to Late Cryogenean passive margin of the Sao Francisco paleocontinent, including reworked cratonic basement. At the same period, two magmatic arc systems were developed outboard: The Continental Inner arc system represented by the dismembered terranes (Paraiba do Sul, Embu, and Cambuci domain) integrated now in the Central Superterrane: and the Intra-oceanic Outer Arc System, the Oriental Terrane, developed from 860 to 620 Ma. Related active basins were detected in association with the two arc systems that collided at ca. 620 - 595 and 605 - 550 Ma against the Sao Francisco passive margin. A later collision episode at ca. 535 to 510 Ma brought the Cabo Frio Terrane (Angola tip) and closed the Buzios back-arc basin. Finally, the collapse of the orogenic belt, probably related to slab detachment and asthenosphere upwelling marks transition to Gondwana stabilization.

Rapid magma ascent and formation of the Águas Belas-Canindé granitic batholith, NE Brazil: evidence of epidote dissolution and thermobarometry

Abstract Mineral chemistry and intensive parameter estimates for the Major Isidoro (626 Ma) and Monteiropolis (627 Ma) magmatic epidote-bearing granitic plutons, emplaced along the Jacare dos Homens transpressional shear zone (JHSZ), Borborema Province, are focused in this study. These plutons consist of medium-to-coarse grained equigranular to porphyritic tonalite to granite that show abundant dioritic enclaves. These granites contain biotite (Fe# 0.44 to 0.55), Fe-edenite (Major Isidoro), hastingsite (Monteiropolis), titanite, and epidote that often show allanite core as key mafic mineral phases. Pistacite molecular content in epidote is in the interval of 27 to 31 mol%, presenting TiO2 < 0.30%, typical for magmatic epidote. Estimated intensive parameters reveal crystallization at 6.5 ± 1 (Major Isidoro) and 4.7 ± 0.6 kbar (Monteiropolis), temperatures from ~940°C (near-liquidus) to 675 ± 35°C (near-solidus) and oxidizing conditions. Partial corrosion of epidote took place during 15.6 to 32 (Major Isidoro) and 27-49 years (Monteiropolis), corresponding to rather high magma ascension rates of 365 to 750 and 395 to 635 m.years-1, respectively. The JHSZ likely favored upward magma transport at the Sergipano and Pernambuco-Alagoas domains boundary, during the onset of the Brasiliano orogeny (650-620 Ma).

Petrogenesis of the Riacho do Icó Stock: evidence for Neoproterozoic slab melting during accretion tectonics in the Borborema Province?

Abstract One of the main characteristics of the Borborema Province in northeastern Brazil is the abundance of granitic domains. The Lagoa das Pedras plutonic-volcanic Complex record remnants of early to late Neoproterozoic primitive to highly evolved magmas. U-Pb SHRIMP determinations and whole-rock geochemistry on the granitic to granodioritic Riacho do Ico Stock, which is the largest plutonic body of this complex, were conducted. Zircon dating reveals that this body was intruded in the crust at 607 ± 3 Ma, whereas metamorphic overgrowths are coeval within uncertainty (600 ± 8 Ma). Geochemical characteristics of this stock suggest that it corresponds to Cordilleran-type magmas injected in the lithosphere above a subduction zone. Sr and Y contents in addition to MgO and SiO2 values are compatible with high-silica adakite-like magmas, interpreted as the result of slab melting in deep-seated regions. Based on the integration of this study and literature data, we suggest that the Riacho do Ico intrusion might be a dismembered part of a major continental magmatic arc described in the Central Subprovince of the Borborema Province, marking the onset of the accretionary stage of the Brasiliano orogeny.

Geochemistry and provenance of siliciclastic rocks from the Mesoproterozoic Upper Vazante Sequence, Brazil: Insights on the evolution of the southwestern margin of the São Francisco Craton and the Columbia Supercontinent

Studies of provenance and tectonic settings of Proterozoic sedimentary basins on the margins of the São Francisco Craton (SFC) can enhance understanding of its evolution. The Mesoproterozoic Upper Vazante Sequence is made up of siliciclastic and carbonate rocks (mainly dolomites) that were deposited on the southwestern margin of the SFC between 1300 and 1100 Ma and then thrust eastward on top of the SFC during the Neoproterozoic Brasiliano Orogeny (650–550 Ma). The Serra do Garrote Formation, stratigraphically below the main carbonate sequence, is made up of phyllites, carbonaceous phyllites (>1% TOC), as well as minor meta-arenitic rocks. Serra do Poço Verde Formation meta-siliciclastic rocks, which occur interbedded with dolomitic carbonates, are made up of phyllites, carbonaceous phyllites, dolomitic phyllites, carbonaceous dolomitic phyllites, minor meta-arenitic rocks and silty dolomites. Preserved sedimentary features in the meta-siliciclastic rocks include cross-bedding, ripples and mud drapes that are consistent with a shallow, tidally-influenced marine depositional setting. Three subunits (SG1, SG2 and SG3) were identified within the Serra do Garrote Formation based on molar Al/Ti ratios. Samples from the Serra do Poço Verde Formation have Al/Ti ratios similar to Serra do Garrote samples, indicating they shared similar sediment sources. Geochemical indicators of source rock composition and tectonic discrimination plots (Zr/Sc versus Th/Sc, Th – Sc – Zr/10, Hf versus La/Th, and rare earth element) revealed that andesitic to felsic continental arc rocks were the major source of detritus.The majority of concordant detrital zircons are Paleoproterozoic in age, with 207Pb/206Pb dates between 2350 and 1850 Ma, which overlap with the early and late stages of the Trans-Amazonian orogeny (≈2.3–1.9 Ga) and are coeval with construction of the Paleo-Mesoproterozoic Columbia Supercontinent. Detrital zircon provenance patterns suggest a rift-related tectonic setting during deposition. The youngest concordant U – Pb zircon 207Pb/206Pb dates (≈1340 Ma) are coeval with the formation of regional bimodal volcano – sedimentary sequences and layered that are interpreted to have formed during continental rifting. These events are synchronous with increased tectonic and magmatic activity (Mackenzie dyke swarm, North America; mafic dyke swarms, North China Craton) related to the break-up of the Columbia Supercontinent.

Coeval high Ba-Sr arc-related and OIB Neoproterozoic rocks linking pre-collisional magmatism of the Ribeira and Araçuaí orogenic belts, SE-Brazil

Two arc systems have been described within the Neoproterozoic Ribeira Belt: the inner continental magmatic arc and the outer intra-ocean magmatic arc. New geochemical and U-Pb and Lu-Hf (LA-ICPMS) data from zircons of the Marceleza-Leopoldina stocks, belonging to the inner magmatic arc system, in the boundary region between the Ribeira and Araçuaí orogenic belts are presented. The intermediate to felsic magmatic rocks have high Ba, Sr, K/Rb, LILE and LREE contents. Low Rb, Th, U, Nb, and very low Y and HREE contents point to their generation in a supra-subduction tectonic scenario, from melting of the asthenospheric wedge above a subducting oceanic plate. Zircon U-Pb (LA-ICPMS) data indicates crystallization ages between ca. 650 and 600 Ma, with high-grade metamorphic overprint at ca. 582 Ma. Tonian inherited zircons were found in the older rocks, suggesting that the development of the continental magmatic arc might have begun earlier. Associated basic (gabbros and monzogabbros) to intermediate (diorites and monzodiorites) rocks are geochemically heterogeneous. Some represent less evolved calc-alkaline basaltic magmas, while relatively more enriched varieties are intraplate basalts with OIB components. Together with lithogeochemical data, Lu-Hf signatures showing TDM model ages between ca. 1.7 to 1.3 Ga, with initial ɛHf values ranging from slightly negative values (−0.9 to −3.75) to strongly negative (up to −10.4) indicate a magmatic arc developed on continental margin environment (i.e., continental-type arc). The studied rocks represent the Rio Doce arc in the studied region and are correlated with other arc segments located from the north, in the Araçuaí Orogen, to the southernmost Ribeira Orogen, defining a c. 1000 km long continental-type magmatic arc. This inner arc system first collided against the São Francisco craton during the Neoproterozoic Brasiliano orogeny around 580 Ma. The geochemical diversity of coeval intermediate to felsic rocks and the variability of associated basic rocks are suggestive of a complex evolution of the subduction zone system. Possible mechanisms for the enrichment in incompatible elements of magmatic products may have involved slab roll-back and subduction of fore-arc rocks, and the influx of ascending asthenosphere associated with slab windows (slab break off, ridge subduction) prior to collision.

Siliciclastic-hosted zinc mineralization in the Proterozoic Vazante – Paracatu District, Brazil: Implications for metallogeny and sources of metals in sediment-hosted base metal systems

The Mesoproterozoic Upper Vazante Sequence is a mixed carbonate – siliciclastic marine succession, deposited between 1300 and 1100 Ma, which contains a variety of carbonate-hosted Zn silicate and Zn – Pb sulfide deposits in central Brazil. Carbonate-hosted Zn ± Pb mineralization is interpreted to have formed in two stages: one prior to the major deformation event and a second stage during the Brasiliano Orogeny (850 to 550 Ma). All known carbonate-hosted Zn-deposits and occurrences in the 250 km – long Vazante – Paracatu District are underlain by the Serra do Garrote Formation, a 500 + m-thick package made up mostly of phyllites and carbonaceous phyllites (>1% Total organic carbon) with minor interlayered meta-arenitic rocks. Our study revealed that siliciclastic rocks from the Serra do Garrote Formation contain horizons enriched in Zn (up to 0.46%).Siliciclastic-hosted zinc mineralization in the Serra do Garrote Formation is associated with pre-orogenic hydrothermal sulfide – quartz – chlorite layers and veinlets, which preferentially formed in carbonaceous and pyritic phyllites belonging to two subunits. The siliciclastic-hosted mineralization in these layers and veinlets is folded and crenulated (pre-orogenic). The geochemical signature of zinc-enrichment includes Cd, Cu, Hg, In, V ± Sb, Se, Mo, Re. Based on textural relationships and chemical U – Th – Total Pb dates of pre-orogenic and syn-orogenic monazite, sulfide mineralization in the Serra do Garrote Formation formed between 1200 and 650 Ma. Textural features indicate that base metals were locally remobilized within the Serra do Garrote Formation during the Brasiliano Orogeny, precipitating new generations of syn-orogenic sphalerite, chalcopyrite and pyrite. Mineralized zones in the Serra do Garrote Formation are distributed throughout the basin and have a similar geochemical signature as the overlying syn-orogenic carbonate-hosted base metal mineralization. However, there is no compelling evidence of depletion in the Serra do Garrote Formation, at the scale of this study, to suggest the ore-related metals have been leached from these siliciclastic rocks to be concentrated in the carbonate-hosted base metal deposits during the Brasiliano Orogeny. The findings of this study suggest that the Serra do Garrote Formation can be a potential target for siliciclastic-hosted base metal mineralization, similar to other Proterozoic sediment-hosted massive sulfide deposits.

Depicting the 3D geometry of ore bodies using implicit lithological modeling: An example from the Horto-Baratinha iron deposit, Guanhães block, MG

Abstract The definition of geological domains is essential for mineral exploration and is traditionally done manually, section by section, in a laborious, time consuming and subjective process, to construct a 3D model. The technique referred to as implicit modeling is an option to model deposits in a fast and practical manner. This article presents the lithological model of the Horto-Baratinha iron deposit, located in the Antonio Dias municipality, central-eastern part of Minas Gerais state, constructed using the Leapfrog Geo® software. The deposit is situated at the Guanhaes tectonic block that is a basement domain of the Neoproterozoic Aracuai Orogenic Belt. The deposit is comprised of itabirite-hosted high-grade iron bodies (>60 wt.% Fe) associated with polydeformed mica schists, amphibole schist with a Statherian maximum deposition age, enclosed by Statherian granitoids of the Borrachudos Suite and crosscut by undeformed pegmatite dikes crystallized during Late Ediacaran-Cambrian. The sequence was affected by progressive multiple deformation phases, associated with the collisional stage of the Brasiliano Orogeny (630-560 Ma), generating a dome and basin mesoscale refolding shape. The model points the proximity between high-grade bodies and pegmatite indicating the possibility that the intrusions contribute to the iron mineralization.

Carbonate chemostratigraphy of the Vazante Group, Brazil: A probable Tonian age

The thick carbonate-siliciclastic succession of the Vazante Group was deposited on the western border of the São Francisco craton, central Brazil, which was deformed during the Brasiliano Orogeny that ended at 540 Ma. In this research, we studied five drill cores and outcrops to obtain integrated isotope data (δ13Ccarb, δ18Ocarb, and 87Sr/86Sr) as well as U-Pb ages of detrital zircons to understand the chronostratigraphic relationships between the Tonian and Cryogenian periods. The Vazante Group forms a succession of more than 3 km thick of limestones, dolostones, shales and rare sandstones. These rocks were deposited on a marine shelf that shows distinct δ13C variations throughout the stratigraphic succession. The lower limestone of this group (Lagamar Formation) has low positive δ13C values (0.3–1.0‰) and 87Sr/86Sr ratios of 0.70646–0.70692 (with 423–1,719 ppm Sr), and possible vase-shaped microfossils (VSMs) that may be equivalent to those found in Huaibei Group in northern China (lower Tonian) or has stratigraphic correlations to the VSMs-bearing units of the upper Tonian. The Serra do Poço Verde Formation has a plateau of moderate δ13C positive values (0.0–4‰) followed by dolostones of the Morro do Calcário Formation, which is a 50-m-thick interval with negative values (as low as −4‰). The upper unit of the Vazante Group (Serra da Lapa Formation) begins with a sharp negative δ13C excursion locally overlying a few layers of diamictite, which may be the equivalent of the Sturtian glacial age. Restrictions on establishing the depositional age of the Vazante Group continue; however, the combination of biostratigraphic and chemostratigraphic data and the detrital zircons spectra suggest a Tonian age for the Vazante Group.

Using the receiver function for studying earth deep structure in the Southern Borborema Province

The Borborema Province is characterized by a succession of tectonic events, including compressive periods associated with amalgamation of lithospheric blocks during the Brasiliano orogeny in the Neoproterozoic, superimposed by extension events related to the breaking of the continents and the South Atlantic formation in the Cretaceous. Ten seismographic broadband stations belonging to the Geoterm Network were installed in the Transversal Zone and South Domains to collect the data used in this work in the southern Borborema Province, northeastern Brazil. Thus, this study aims to determine the thickness of the Moho and Mid-Crustal (“Conrad”) discontinuities and estimate the Vp/Vs ratios to define rock composition using the receiver function over a time window, using the HK-stacking method. The station in the Alto Moxotó Terrain determined a crustal thickness of 35.4 km. The two stations in the Pernambuco-Alagoas Terrain estimated thickness of approximately 37 km and no thinning trend in the geotectonic context. The four stations in the Sergipano Folding Belt indicated thickness ranging between 34.6 and 37.2 km, and a South-North crustal thickening. Mid-crustal discontinuity depth estimates ranged between 10 and 19 km, indicating a WNW-ESE thinning of the upper crust in the middle of the area. The P and S wave velocity ratios appeared to have no geological or tectonic correlation and ranged between 1.68 and 1.77, indicating that the crustal composition is predominantly felsic.

Geochemical and isotope evidence for mantle-derived source rock of high-K calc-alkaline I-type granites, Pernambuco–Alagoas Domain, northeastern Brazil

We report whole-rock major, trace, mineral, and isotope chemistries of the Jacare dos Homens, and Santo Antonio granitic rocks from the Aguas Belas–Caninde batholith, Pernambuco–Alagoas Domain of the Borborema Province, northeastern Brazil. These rocks exhibit low-angle foliation, suggesting emplacement under a regional strain field, associated with transpressive deformation tied to the onset of the Brasiliano orogeny. Both rocks are dominantly made up of K-feldspar, quartz, and plagioclase with biotite as the main mafic phase and minor hornblende. The Jacare dos Homens orthogneiss displays magnesian, slightly peraluminous, and alkali-calcic character, while the Santo Antonio granite is magnesian, metaluminous to slightly moderately peraluminous and alkali-calcic to alkalic. These granitic rocks are enriched in alkalis (up to 10.28 wt%), mg#, Rb, Ba, Sr, Th, and LREE, and depleted in HREE and HFSE, with distinct Nb, Ta, and Ti depletion. Decreasing MgO, CaO, TiO2, Na2O, Fe2O3T, P2O5, Al2O3, Sr, Zr, and Hf with increasing SiO2 are consistent with fractional crystallization of biotite, amphibole, plagioclase, apatite, zircon, titanite, and Fe–Ti oxides. U–Pb zircon dating of the Jacare dos Homens and Santo Antonio rocks yielded concordia ages of 642.4 ± 3 Ma and 636 ± 4 Ma, respectively. The isotope data for the Jacare dos Homens orthogneiss yielded an Nd-model age of 1.21 Ga with slightly negative eNd(642 Ma) of − 1.58, initial 87Sr/86Sr ratios of 0.7068, and δ18O (zircon) value of + 7.0‰ VSMOW. The isotope data for Santo Antonio pluton yielded Nd-model ages between 0.96 and 1.07 Ga, with eNd(636 Ma) from + 1.17 to − 0.67, initial 87Sr/86Sr ratios from 0.7048 to 0.7056, and δ18O (zircon) value of + 5.0 to 5.9‰ VSMOW. Altogether, the petrological, geochemical, and isotopic data are typical of I-type granites. We propose that the studied granitic rocks were derived from mantle-derived medium- to high-K basaltic lower crust of Stenian/Tonian (Jacare dos Homens) or Tonian (Santo Antonio) ages and that partial melting was triggered by the uplift of asthenosphere and underplating of lithospheric mantle. The migration and buoyancy-driven ascent of the magma to their present level were probably favored by the Jacare dos Homens shear zone.

Post‐Great Oxidation Event Orosirian–Statherian iron formations on the São Francisco craton: Geotectonic implications

AbstractThe protocratonic core of the São Francisco craton assembled during the 2.1–2.0 Ga Transamazonian orogeny. Orosirian Fe‐rich sequences that extend from the northwestern border of the São Francisco protocraton (Colomi Group) to the southeast under the Espinhaço Belt (the &lt; 1.99 Ga Serra da Serpentina Group) record the opening of an intracratonic basin with the episodically developed ferruginous waters prior to the initiation of the Espinhaço rift at 1.8 Ga. Ferruginous conditions developed again during deposition of the Canjica Iron Formation of the &lt; 1.7 Ga Serra de São José Group in the Espinhaço rift (contemporaneously with felsic magmatism; Conceição do Mato Dentro Rhyolite and Borrachudos Granitic Suite) and extensive sandstones of the &lt; (1666 ±32) Ma Itapanhoacanga and &lt; (1683 ±11) Ma São João da Chapada Formations. In the upper São João da Chapada Formation, banded hematitic phyllite also records input of Fe‐rich fluids. The young age of these iron formations with respect to the conventionally accepted 1.88 Ga age for the youngest shallow‐marine Paleoproterozoic iron formations, the apparent absence of granular facies (granular iron formations), and yet shallow‐water (above fair‐weather base) depositional environment indicate that an unusual setting developed in a large basin after the Great Oxidation Event, in the aftermath of the Transamazonian orogeny. We propose that mantle plumes led to the opening of a previously unrecognized rift system, that could have caused the magmatism, supplied hydrothermal Fe and led to the opening of the Espinhaço, Pirapora, and Paramirim rifts, later obliterated by the Araçuaí orogenic belt during the Neoproterozoic to Early Paleozoic Brasiliano orogeny. The rift system did not develop into an open continental margin but probably evolved into a broad sag basin, stretching across the São Francisco and Congo cratons.

The complex tale of Mantiqueira and Juiz de Fora: A comment on “Eoarchean to Neoproterozoic crustal evolution of the Mantiqueira and the Juiz de Fora Complexes, SE Brazil: Petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes”

In a recent volume of Precambrian Research (vol. 323, pp. 82–101), Kuribara et al. (2019) published a paper on the Eoarchean to Neoproterozoic evolution of the Mantiqueira and Juiz de Fora Complexes of SE Brazil. In this work, Kuribara et al. (2019) suggest that the complexes were previously indicated to be part of the Neoproterozoic to Cambrian Brasiliano Orogeny and that the results of their work instead show that these complexes are fragments of Archaean crust that accreted during the 590–560 Ma Brasiliano orogeny. Kuribara et al. (2019) also present conventional thermobarometry for both complexes that they interpret represents the single metamorphic event that they obtain zircon U-Pb age data for from the Juiz de Fora complex. No metamorphic ages were obtained from the Mantiqueira Complex, instead they have used the metamorphic ages that many workers have obtained from the Mantiqueira Province. In this comment we show that the Archaean crustal input in the Mantiqueira complex has long been known, and the Juiz de Fora Complex has long been considered a Palaeoproterozoic ocean arc. The Mantiqueira Complex records a polymetamorphic history with high-grade metamorphism occurring at ca. 2020–1940 Ma and a later amphibolite facies Brasiliano overprint at 580–540 Ma. The Mantiqueira Province and Mantiqueira Complex are different geological entities, and while the Mantiqueira Complex is affected by the Brasiliano event and occurs within the Mantiqueira Province, the use of metamorphic ages from the Mantiqueira Province is not appropriate for the Mantiqueira Complex. Finally we show that the data presented by Kuribara et al. (2019) actually fits in with the most recent version of the model for the formation of the two complexes.

Eoarchean to Neoproterozoic crustal evolution of the Mantiqueira and the Juiz de Fora Complexes, SE Brazil: Petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

The Mantiqueira and the Juiz de Fora Complexes (MQC and JFC) in the Araçuaí-Ribeira orogenic system, southeastern Brazil, have been regarded as parts of the Neoproterozoic to Cambrian Brasiliano Orogeny formed by a series of collisions of the São Francisco and the Congo Cratons. Here we report new petrological, geochemical, and zircon U-Pb and Lu-Hf isotopic data on felsic to mafic orthogneisses from the complexes with a view to evaluate the timing and P-T conditions of the collisional event as well as protolith formation. Metamorphic P-T estimates for orthogneisses indicate amphibolite-facies conditions of 650–730 °C and 5.8–9.1 kbar from the MQC, whereas slightly higher (upper amphibolite- to lower granulite-facies) conditions of 680–770 °C and 6.0–7.7 kbar were obtained from the JFC. Geochemical, zircon U-Pb geochronological, and Lu-Hf isotopic data of felsic orthogneisses indicate that the MQC was formed by a series of Neoarchean (ca. 2.67 and 2.61 Ga) volcanic arc magmatisms with magma sourced from Eoarchean to Paleoarchean (ca. 3.82–3.42 Ga) crustal components. In contrast, slightly younger U-Pb ages of ca. 2380 Ma and ca. 2050–1960 Ma were obtained from the JFC marking the timing of volcanic arc magmatism as Early to Middle Paleoproterozoic, with magma sourced from Paleoarchean (∼3.45 Ga) crust with addition of juvenile crustal components. The recycled ancient crustal components were also supplied for late Neoproterozoic (ca. 600 Ma) continental arc magmatism of the JFC. The high-grade metamorphism is possibly related to the final collision of the Congo and São Francisco Cratons at 590–560 Ma, which broadly compares with the formation of the Kuunga Orogen.

Lithogeochemical and Nd-Sr isotope data of the orthogranulites of the Juiz de Fora complex, SE-Brazil: insights from a hidden Rhyacian Orogen within the Ribeira belt

Abstract New petrography, geochemistry and Sm-Nd and Sr data from the orthogranulites of the Juiz de Fora complex in southern Rio de Janeiro State and compiled information provide insights on the petrogenetic and tectonic evolution. The complex comprises several geochemical groups including mafic orthogranulites (three tholeiitic and one alkaline) and felsic orthogranulites (three calc-alkaline and one tholeiitic/low K calc-alkaline). New geochemical and isotope data, combined with available U-Pb data suggest a long evolutionary history from the Paleoproterozoic to the Neoproterozoic. The oldest magmatic episode produced juvenile to slightly contaminated arc-type Rhyacian rocks, as well as granitic rocks related to collision or post-collision episodes. Altogether these rocks integrate part of a dismembered Rhyacian orogen within the Ribeira belt. Few TDM Nd model ages yielded 2.75 to 2.58 Ga, suggesting minor Archean contribution for magma genesis. Some of the basic granulites’ bodies yield Meso- to Neoproterozoic TDM Nd model ages, which may refer to an extensional magmatism. Orthogranulites present granulite facies paragenesis, related to the youngest tectonic episode in the Juiz de Fora Complex (Brasiliano Orogeny). The new data are potentially important for Paleoproterozoic reconstruction models, due to the predominantly juvenile character of the Juiz de Fora complex, as similarly worldwide.

Pseudosection modeling and U-Pb geochronology on Piranga schists: role of Brasiliano Orogeny in the Southeastern Quadrilátero Ferrífero, Minas Gerais, Brazil

ABSTRACT In the Southeastern Quadrilatero Ferrifero, a package of metapelitic rocks previously attributed to the Archean Rio das Velhas Supergroup crops out in Piranga locality. This study presents the mineral chemistry and U-Pb-Hf zircon geochronology on foliated staurolite-garnet mica schists. Garnet and staurolite index minerals are syn- to post-kinematic towards the main schistosity. Garnet porphyroblasts display well-developed compositional zoning of Mg-Fe-Mn-Ca, with increase of almandine and pyrope and decrease of spessartine towards the rim, implying in prograde metamorphic pattern. Estimates of P-T values for the metamorphic peak resulted in temperatures between 630 to 650oC and pressure around 7 kbar. Pseudosections show well-defined stability fields in amphibolite facies, with a metamorphic path displaying progressive increase in P-T conditions. Maximum depositional age of 1,875 ± 51 Ma is established for the Piranga mica schists pointing to a depositional history that is younger than those previously described. Metamorphic Cambrian ages characterize the strong influence of deformational processes related to the final stages of Brasiliano Orogeny in the Southeastern Quadrilatero Ferrifero.