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In this contribution we investigate the exhumation T-t path of a nappe system located in the southernmost edge of the Brasilia Orogen, southeast Brazil, developed during the West Gondwana assembly. The allochthons represent an inverted metamorphic pile of nappes and were deformed during the collision between the Paranapanema (active margin) and Sao Francisco (passive margin) paleocontinents. The nappe system comprises UHT rocks of a magmatic arc root (upper Socorro-Guaxupe Nappe), the accretionary wedge – foreland units metamorphosed under high-pressure conditions (intermediate Andrelândia Nappe System) and the lower passive margin metasedimentary sequences (the high-pressure Carrancas Nappes System and the Lima Duarte Nappe). New U-Th-PbT in monazite and 40Ar/39Ar in hornblende, biotite and muscovite ages combined with previously published data indicate different patterns of cooling for each allochthon. The upper nappes register a collision to exhumation/cooling path, from 630–625 Ma to 590–580 Ma, which indicates that the geological process active during the West Gondwana amalgamation involved fast exhumation tectonics. Cross-sections along the main transport direction of the nappes indicate a progressive decrease of metamorphic age peaks (630–625 Ma to 590–570 Ma) and 40Ar/39Ar cooling ages (600 Ma to 540 Ma) from the internal regions (SW) to the front (NE) of the nappe system, which indicate that the propagation of the nappe pile advanced progressively from the upper to the lower nappes.

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

The Paranapanema-Sao Francisco convergence is partially recorded in the arc-related high-K calc-alkaline intermediate magmatism of south-eastern Brazil (Southern Brasilia Orogen) during the West-Gondwana assembly. Similar geochemical affinities are widespread in the crustal fault-bounded slice, Sao Roque Domain, as in tectonic domains of the eastern Sao Francisco margin. The Sao Roque Domain comprises metavolcano-sedimentary sequences of Statherian maximum depositional age. Detrital zircon provenance points to a Rhyacian (2.17 Ga) proximal source belonging to the Socorro-Guaxupe Nappe basement. Unprecedented Tonian zircon U-Pb ages suggest a protracted evolution. The domain initiated magmatic activity at 680 Ma (Barro Branco orthogneiss) with weak Hf-Nd radiogenic signatures that agree with the arc evolution of the Socorro-Guaxupe Nappe. Granitoids grading from intermediate metaluminous to evolved peraluminous compositions intruded at 625 Ma (inequigranular orthogneiss) and 620 Ma (Moinho granodiorite). The most voluminous magmatism occurred within 610-590 Ma. Hf-Nd radiogenic compositions of the Ediacaran granitoids imply crustal participation. All granitoids have arc-related affinity with high Sr/Y and LREE, low Nb and Ti, and absence of Eu anomalies that indicate a lower crustal source with residual garnet (±amphibole ±rutile). The petrogenetic and geochronological characterizations favor a retro-arc setting for the Sao Roque Domain. Slab roll-back could have led to the northward migration of magmatism (Socorro-Guaxupe Nappe) producing a chronological gap in the retro-arc. The Ediacaran magmatism was probably triggered by the relaxation of the subducting angle. The last-longing subduction beneath the Paranapanema plate might have contributed to the high-K and radiogenic compositions through relamination. Monazite U-Pb ages from 630 to 600 Ma may be evidence of a thermal episode in the retro-arc, overlapping the syn-collisional metamorphism in the Southern Brasilia Orogen.

Whole rock elemental and Sr–Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810–580 Ma), and is dominated by crust-derived relatively low-T (850–750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative eNd t (−8 to −10) and highest mg# (30–40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96–1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595–580 Ma) plutons have a spread of compositions from biotite granites with SiO 2 as low as ∼65% (e.g., Itapeti, Maua, Sabauna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO 2 ). eNd T are characteristically negative (−12 to −18), with corresponding Nd T DM indicating sources with Paleoproterozoic mean crustal ages (2.0–2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative eNd t , highest 87 Sr/ 86 Sr t (0.714–0.717) and lowest 208 Pb/ 206 Pb and 207 Pb/ 206 Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd–Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Maua granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The Ediacaran granites are coeval with profuse granite magmatism attributed to continental arc magmatism in northern Ribeira and Aracuai belts. However, their evolved compositions with low mg# and dominantly peraluminous character are unlike those of magmatic arc granites, and they are more likely products of post-collisional magmatism or correspond to an inner belt of crust-derived granites.

New zircon U-Pb LA-ICP-MS data combined with Nd-Hf isotopes and whole-rock geochemistry provide constraints on timing and tectonic setting of Paleoproterozoic continental crust generation events in the basement of the Neoproterozoic southern Brasilia Orogen, SE Brazil. The Paleoproterozoic basement, designated as the Pouso Alegre Complex, comprises mainly metatexitic tonalitic to granodioritic orthogneisses with lenses and boudins of metamafic rocks. Minor porphyroclastic granite bodies also occur. Two well-defined crystallization ages groups were recognized at 2.14–2.15 Ga (6 samples; weighted average of 2146.7 ± 6.6 Ma) and 2.07–2.08 Ga (5 samples; weighted average of 2078.7 ± 6.7 Ma). Inheritance of older zircon grains is almost absent. Whole-rock Nd data show juvenile signatures with TDM ages between 2.16 and 2.37 Ga associated with positive ɛNd(t) values from +0.16 to +2.85. Zircon Hf LA-ICP-MS analysis yields positive ɛHf(t) values from +1.9 to +8.7. Whole-rock geochemical analyses show a wide range of SiO2 contents from 52 to 76 wt% with felsic types predominating over mafic ones. The analyzed samples show high concentrations of Rb, Ba, Th, U and low Nb/La ratios, which are characteristics of subduction zone magmas and most of the samples show continental arc affinities. The geochemical signatures associated with the predominance of felsic rocks suggest a continental arc margin or an evolved accreted oceanic arc as the favored tectonic setting for the Pouso Alegre Complex. The Pouso Alegre Complex is interpreted as the southernmost and youngest recognized part of an arc complex emplaced at the southern edge of the Sao Francisco paleo-continent during the Paleoproterozoic. This part of the arc complex was deeply reworked by the collisional events related to the Neoproterozoic southern Brasilia Orogen and its cratonic counterpart is the Mineiro Belt at the southern Sao Francisco craton. The Pouso Alegre Complex and the juvenile suites of the Mineiro Belt represent a major Paleoproterozoic continental crust generation event between 2.35 and 2.08 Ga. This time period has not been recognized for extensive continental crust generation and preservation globally. However, it appears to be a major period of continental crust generation and preservation at the southern edge of the Sao Francisco paleo-continent.

International audience; Sedimentary basins are, in many cases, the only preserved record of the geological processes active through geological time. These deposits preserve age, isotopic and geochemical signatures of the source rocks, providing insights into tectonic setting. In this context, we investigate the lithostratigraphy, provenance and tectonic environment of the Carrancas Group, a meta-sedimentary sequence characterised by a basal psammitic unit (Lower Unit) passing up into interbedded psammo-pelites (Intermediate Unit), which are overlain by a further psammitic unit (Upper Unit). This succession, along with the Canastra, Paranoá and Vazante groups (Brasília orogen), comprises a mature passive margin developed at the western-southern margin of the São Francisco craton during the Neoproterozoic. Detrital zircon U-Pb ages and Nd-Hf isotope data enable revised stratigraphic correlations across the basin, highlighting variations in the source of detritus. Deposition began after 0.92 Ga, with the sedimentation of the Lower Unit, with input of juvenile ∼2.1 Ga detritus (εNdt = −0.1 to +3.2) derived from the São Francisco craton. A marine transgression characterises the transition to the Intermediate Unit, which gradually covered over juvenile ∼2.1 Ga terrains and rendered them unavailable as possible source rocks for detrital zircons. Evolved Archaean-Palaeoproterozoic basement rocks, the Espinhaço Supergroup and evolved Neoproterozoic granitoids, all belonging to the São Francisco craton, acted as sources for the Intermediate and Upper units (U-Pb = 2.7 Ga to 0.9 Ga; εNdt = −10.4 to +7.1). The Goiás massif might also have acted as a source, providing juvenile Mesoproterozoic detritus. The sediments of the Upper Unit register a significant shift in source, with incoming of juvenile Mesoproterozoic and crustal 1.9 – 1.7 Ga detritus. This change in the ages of the detrital material may be related to exhumation of the Espinhaço Supergroup during the evolution of the passive continental margin basin. The whole-rock Nd TDM model ages become progressively younger from the base to the top of the sequence (Nd TDM = 2.6–1.8 Ga). The collisional events between Amazonian and São Francisco cratons and the Paranapanema block set the minimum age of deposition along this passive continental margin at around 0.67 Ga.

Combining U-Pb geochronology and trace element characteristics of accessory minerals more reactive during metamorphism and deformation than zircon, such as titanite (CaTiSiO5), is a powerful tool for elucidating pressure-temperature-time (P-T-t) evolution of orogenic basement complexes. This study reports in-situ titanite U-Pb and trace element data from upper-amphibolite facies metatexitic orthogneisses of the Pouso Alegre Complex in the basement of the Neoproterozoic southern Brasilia Orogen, SE Brazil. The titanite data is combined with thermodynamic modeling, major phase compositions and U-Pb zircon dating and used to constrain the P-T-t path of the complex during the Neoproterozoic orogenesis. The investigated garnet amphibole gneisses record peak metamorphic conditions of 750–775 °C and 10.5–12.5 kbar, associated with partial melting and dated at ca. 630–620 Ma based on U-Pb analyses of HREE+Y depleted titanite cores, inferred to have crystallized in the presence of garnet near the peak P-T conditions. Extensive melt crystallization at ca. 616 Ma is constrained by U-Pb dating of leucosome zircons. The exhumation of the complex and re-equilibration to ca. 550–625 °C at 6–9 kbar led to widespread generation of biotite + epidote/clinozoisite, partially replacing amphibole + garnet along the main foliation. Trace element signatures of these retrograde net-transfer reactions are recorded in the titanite rims which are HREE+Y enriched, strontium depleted and were dated at 605.7 ± 6.2 Ma. The average zirconium contents of the titanite rims are higher than cores suggesting disequilibrium partitioning of zirconium into titanite during the retrograde path resulting in overestimated Zr-in-titanite temperatures for the rims. The exhumation of the complex was concomitant with the intrusion of folded and recrystallized leucogranite dykes dated at 607.0 ± 5.7 Ma, attesting the persistence of deformation after their intrusion. Assuming that the Pouso Alegre Complex is part of the Sao Francisco paleocontinent reworked during the Brasilia orogeny, the data constrain the minimum age for the collision between the Sao Francisco paleocontinent and the Paranapanema block at ca. 620–630 Ma and agree with the idea of long-lived metamorphism and deformation in the southern Brasilia Orogen.

The Liberdade and Andrelândia nappes, SE Brazil, record the western Gondwana amalgamation in the Southern Brasilia Orogen during the Ediacaran. The Liberdade Shear Zone acted as the boundary between these two overlapping nappes. Quartz c-axis fabrics and strain data from quartzite samples and petrological data from hosting metapelite rocks were analyzed to investigate the tectonic processes involved in nappe development. Further constraints were achieved by conducting petrological modeling and geothermobarometry using P–T isochemical phase diagram approaches. Quartz axis plots show consistency with different kinematic criteria verified in the field in meso and macroscale. The fabrics are associated to both coaxial deformation and non-coaxial deformation. Quartz microstructures, metamorphic assemblages and c-axis concentrations primarily around Y and X structural directions suggest that deformation was accommodated by grain boundary migration recrystallization under temperature above 500 °C. Disregarding pressure effects the opening angles of quartz c-axis fabrics suggest temperatures between 480 and 640 °C (muscovite quartzite) and 650–720 °C (sillimanite quartzite). Considering pressure data, the opening angles indicate conditions of 550–650 °C and 7–10 kbar (muscovite quartzite) and 600–730 °C and 4–7 kbar (sillimanite quartzite), reflecting primarily distinct baric regimes. Sillimanite-bearing samples estimatives are supported by ubiquitous presence of chessboard subgrain patterns in quartz and by modeled isochemical phase diagrams that constrain conditions of 660–730 °C and 6–7 kbar for garnet-sillimanite-biotite schist samples. Altogether, these results indicate progressive tectonic evolution linked to oblique convergence between tectonic units represented by the Andrelândia and Liberdade nappes and the Paleoproterozoic basement. Besides recording distinct thermal and baric regimes, the nappes also present different structural styles, suggesting that pressure and temperature are important boundary conditions for the nappe structural style.

Closure of the southern Adamastor Ocean led to the development of the Neoproterozoic-Early Cambrian orogens on both margins of the present South Atlantic Ocean, which preserve a rich record of West Gondwana assembly and large-scale crustal evolution. Here we describe the distinct stages and tectonic regimes related to the evolution of the southern Adamastor Ocean as reconstructed from the geological record in southeastern Brazil, Uruguay and southwestern Africa. The welding of the Rio de la Plata/Paranapanema and African cratons was the result of a long history that generated the Dom Feliciano Belt in southeastern Brasil and Uruguay and its African counterparts, the Kaoko, Gariep and Saldania belts. Recent ideas and previous hypotheses are discussed and integrated into a tectonic model for the evolution of the southern Adamastor Ocean, largely based on comparison of the Neoproterozoic Kaoko and Dom Feliciano belts. The history of the southern Adamastor Ocean spans between 900 and 590 Ma, from the earliest records of magmatism related to Rodinia break-up (980–780 Ma), through the climax of the extensional phase that led to the opening of a vast ocean (780–640 Ma). Tectonic inversion led to subduction towards the east (in today’s coordinates), which generated an extensive magmatic arc on the western margin of the Congo and Kalahari cratons (640–600 Ma) and eventually the collision between the Congo and Rio de La Plata Cratons (600–590 Ma) juxtaposing the magmatic arc and the western South American schist belts. At around 530 Ma, still under the influence of plate convergence, a positive flower structure was generated causing the extrusion of the Granite Belt, the eroded remnant of the magmatic arc, and reactivation of the doubly verging thrusts that affected the supracrustal units of the Kaoko and Dom Feliciano belts. Only at that time did deformation reach the Itajai and Nama foreland basins.

The Veladero hill is a well-exposed upper crustal block located between the basement of Sierra de Umango (Western Sierras Pampeanas), and the Devonian - Carboniferous sedimentary sequence of Precordillera, at western Argentina. The hill is formed by schists, metaluminous granitoids and a subalkaline peraluminous andesite studied in this work. The country rocks are schists with mineralogy typically developed during a thermal event (e.g., cordierite, andalusite, biotite). The magmatic assemblage of the peraluminous andesite consists of K-feldspar + plagioclase + quartz + biotite + cordierite, with zircon, monazite, and oxides as accessory minerals. One representative sample from this rock was analyzed and has contents of SiO2 = 61%, Fe2O3 t + MgO = 9.03, Na2O + K2O = 6.6%, and aluminium saturation index = 1.5, consistent with the mineralogy. A U-Pb zircon Concordia age of 347 ± 4 Ma was acquired by LA-MC-ICP-MS from zircon hosted in the peraluminous andesite, which together with an age of 342 ± 2 Ma recently published for the metaluminous Veladero granitoid stock, indicate that these two ages overlap within error. Combined mineral assemblage and Al-in-hornblende geobarometric data from the Veladero granitoid stock reveal that the granitic magma passed through ∼10 km of continental crust before reaching its final emplacement level. Field evidence indicates that the Veladero granitoid stock was emplaced under dominantly brittle deformation mechanisms and that the peraluminous andesite magma was generated and subsequently intruded into a previously emplaced magma mush close to solidification, making space by the displacement of large blocks of the host granite. Documented mingling relationships between granite and peraluminous andesite also support emplacement while the granite remained partially crystallized so that the time interval between the two was relatively short, probably on the scale of hundreds of thousands of years. We propose that the peraluminous magma was generated during the ascent of the metaluminous Veladero granitoid stock magma and that the most of the zircon crystallized in high middle crust from the Veladero granitoid stock. These zircons were subsequently recycled and incorporated in the peraluminous andesite. Zircons in the Veladero granitoid stock and the peraluminous andesite have indistinguishable morphology and support this interpretation. In situ Hf isotope data were obtained from igneous zircons in the peraluminous andesite and reveal a dominantly continental source (average εHf,t = −8.0, excluding one just positive value). εHf,t and TDM values from zircon in the Veladero granitoid stock and hosted in the peraluminous andesite are indistinguishable, which is consistent with their original crystallization in the Veladero granitoid stock. TDM values mainly range from 1.5 to 1.9 Ga (average = 1.7 Ga) and reveal a continental Gondwana signature. Consistently, detrital zircon ages from schists in which the igneous rocks were emplaced indicate Ordovician depositional ages and original Gondwanan provenance. However, based on previous studies a Devonian depositional age cannot be ruled out. Fil: Dahlquist, Juan Andrés. Universidad Nacional de Córdoba (UNCA), Facultad de Ciencias Exactas, Físicas y Naturales; Argentina Fil: Alasino, Pablo Horacio. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR) - Prov. de La Rioja-UNLaR-SEGEMAR-UNCa-CONICET; Argentina. Universidad Nacional de La Rioja (UNLaR), Instituto de Geología y Recursos Naturales (INGeReN), Centro de Investigación e Innovación Tecnológica (CENIIT),; Argentina Fil: Basei, Miguel A.S.. Instituto de Geociências da Universidade de São Paulo; Brasil Fil: Morales Camera, Matías Martín. Universidad Nacional de Córdoba (UNC), Facultad de Ciencias Exactas, Físicas y Naturales; Argentina Fil: Macchioli Grande, Marcos Simón. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica La Rioja (CRILAR) - Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET; Argentina. Universidad Nacional de La Rioja (UNLaR), Instituto de Geología y Recursos Naturales (INGeReN), Centro de Investigación e Innovación Tecnológica (CENIIT),; Argentina Fil: da Costa Campos Neto, Mario(EXT). Universidade de São Paulo (UNSP), Instituto de Geociências; Brasil Fil: García Larrecharte, Matías. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de la Rioja; Argentina

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy., The authors acknowledge the Science Without Borders Programme, Process 075/2012, which supported this study and the São Paulo Research Foundation (FAPESP), Process 2011/17261-6. We also thanks C. Mazoca for his help with maps and figures., info:eu-repo/semantics/acceptedVersion

The petrogenetic nature of A-type granites is a controversial problem. The Vinquis batholith in the Sierras Pampeanas of Argentina contains unusual F-rich and strongly peraluminous A-type monzogranites. A new LA-MC-ICP-MS U–Pb zircon crystallization age of 355 ± 7 Ma indicates emplacement in latest Devonian or earliest Carboniferous time, overlapping with extensive metaluminous A-type magmatism in the area. The monzogranites have a restricted range of SiO2 content (71.5–74.8 %), they are poor in Ca (0.54–1.4% CaO) and rich in FeOt, with relatively high FeOt/(FeOt+MgO) values ranging from 0.77 to 0.86 (average = 0.80) Both [FeOt/ (FeOt+MgO)] vs. SiO2 and [(Na2O+K2O)−CaO] vs. SiO2 plots indicate ferroan and alkali-calcic signatures typical of A-type granitoids. The samples have MgO/TiO2 > 1.2 and are moderately enriched in total alkalis (average 8.18%), with high K2O/Na2O values of 1.40–2.24. The granites are strongly peraluminous, with ASI (molar Al2O3/[CaO + Na2O + K2O]) values of 1.2 to 1.3. The high P2O5 content (0.23–0.37%) is distinctive and close to values reported for other Paleozoic F-rich peraluminous A-type granites in the Sierras Pampeanas. They have moderate contents of high field strength elements (e.g., Zr, Nb, Th, Y, etc.) and moderately fractionated to flat REE patterns [(La/Yb)N in the range 4.8–19.6] showing significant negative Eu anomalies (Eu/Eu* = 0.41). Biotite has a distinctive composition, with relatively high Fe2 +/(Fe2 + + Mg) ratios (0.61–0.74) and high F (0.55–1.42 wt.%) content. Together with the whole-rock chemistry this may be useful in identifying strongly peraluminous A-type granites. In addition, the Rb/Sr vs. Th + Zr + Ce diagram may be an appropriate discriminant between metaluminous and peralkaline A-type granites, strongly peraluminous A-type granites and strongly peraluminous orogenic granites. The geochemical evidence indicates that differentiation of the granitic rocks occurred by mineral fractionation from a F-rich peraluminous parental magma, dominant of plagioclase, K-feldspar, biotite, and accessory minerals such as zircon, monazite, xenotime, and oxides. The peraluminous composition and isotope data (εHf,355 and εNd,355 ranging from − 9.5 to − 1.5 and − 6.1 to − 7.8, respectively), together with abundant inherited Ordovician and Cambrian zircon, strongly suggest a dominantly metasedimentary source. The whole-rock and biotite compositions indicate that the Vinquis batholith crystallized under mainly oxidizing conditions, whereas Early Carboniferous metaluminous to weakly peraluminous A-type granites of the Sierras Pampeanas crystallized under dominantly reduced conditions. Fil: Morales Camera, Matías Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Dahlquist, Juan Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Stipp Basei, Miguel Angelo. Universidade de Sao Paulo; Brasil Fil: Galindo, Carmen. Universidad Complutense de Madrid; España Fil: Campos Neto, Mario da Costa. Universidade de Sao Paulo; Brasil Fil: Facetti, Julio Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Jujuy. Universidad Nacional de Jujuy. Centro de Investigaciones y Transferencia de Jujuy; Argentina. Comision Nacional de Energia Atomica. Regional Noroeste; Argentina

The southern Brasilia Orogen occurs along the southernmost border of the Sao Francisco Craton. This Orogen is structured as a pile of Ediacaran syn-metamorphic thicked-skinned nappes that diachronically migrate toward the cratonic margin. A magmatic arc environment is represented by the Socorro-Guaxupe Nappe (SGN), which is a thick segment of partially molten lower to middle continental crust. The SGN comprises three main units: a lower granulitic, an intermediate diatexitic and an upper metatexitic. High-temperature metamorphic peak was reached at ∼625 Ma, when large volumes of high-K diatexitic rocks were formed. Charnockitic and mangeritic magmatic rocks (Sao Jose do Rio Pardo suite) and in situ leucosomes of mafic composition are inferred to have formed under hornblende-dehydration melting conditions (i.e. T ≥ 850 °C). Granitic diatexites (Pinhal-type) were also formed, and zircon thermometry indicates T ≥ 850 °C. Elemental and isotopic geochemistry indicate that these diatexites and in situ leucosomes derived from melting of lower to middle continental crust. TIMS zircon U–Pb ages are presented for the lower and middle units. U–Pb dating coupled to Lu–Hf analysis (LA-MC-ICP-MS) was performed on charno-enderbitic in situ leucosomes from metatexitic rocks that also resulted from hornblende-dehydration melting. Two different zircon typologies were recognized. The first comprises bipyramidal-prismatic grains with oscillatory zoning and high luminescence, sometimes preserving low-luminescence 670 Ma cores. The high-luminescence grains show 19 concordant ages at 621 ± 16 Ma. The second typology comprises isometric or soccer-ball-type grains. These grains show sector zoning and a concordia age of 608 ± 4 Ma. Th/U ratios from soccer-ball grains vary from 1.253 to 2.107, whereas prismatic grains vary from 0.118 to 1.774. Initial ɛHf signatures between −13 and −21 in both typologies provide evidence of a reworked crustal reservoir. The older prismatic grains may be related to the onset of metamorphic peak (∼625 Ma), whereas the isometric ones provide evidence of long-lived high-T conditions until ∼610 Ma.

A Nappe Lima Duarte está situada no sudeste do Orógeno Brasília. É constituída por paragnaisses migmatíticos com granada, sillimanita, biotita e muscovita, e ortoquartzitos grossos, com intercalações esparsas de gnaisses calciossilicáticos e de anfibolitos. O Complexo Mantiqueira, infraestrutura alóctone da nappe, ocorre na forma de lascas tectonicamente imbricadas na mesma. É constituído por ortognaisses migmatíticos e polimetamórficos, tipo TTG, com intercalações de rochas metabásicas granulíticas, na forma de enclaves máficos alongados e boudins, geralmente concordantes com a foliação principal. Também ocorrem rochas charnockíticas aparentemente intrusivas nos ortognaisses Mantiqueira, com rochas metabásicas associadas. A associação mineral observada nos paragnaisses (Grt + Bt + Sil + Pl + Rt +Ilm + Qtz ± Ms ± Kfs ± Ky) é relacionada a um metamorfismo progressivo de fácies anfibolito superior, caracterizado por reações de quebra de muscovita e geração de feldspato potássico. As condições de pico bárico obtidas no THERMOCALC para a associação com cianita são de 10 ± 0.6 kbar, a 807 ± 25ºC. O pico térmico de 827 ± 44ºC a 8.2 ± 1.8 kbar, no limite da curva de quebra da dumortierita, foi obtido no THERMOCALC com a associação mineral envolvendo sillimanita. As rochas metabásicas inseridas nos ortognaisses do Complexo Mantiqueira e rochas charnockíticas associadas apresentam a associação Grt-Cpx-Pl-Qtz±Opx+Hbl, que é diagnóstica do fácies granulito de alta pressão. São caracterizadas pela presença de texturas coroníticas progressivas de Grt-Cpx-Pl-Qtz nos contatos entre Opx, Pl e/ou opacos, aparentemente de origem ígnea, que marca a passagem do campo dos granulitos de pressão intermediária para o campo dos granulitos de alta pressão. As condições de pico registradas nos veios constituídos por Grt-Cpx-Pl nos metagabronoritos é de 831.8ºC, a 10 kbar. O granada granulito registra o pico metamórfico a 890 ± 41ºC, a 9.26 ± 1.93 kbar. Cálculos realizados no TWEEQU forneceram condições de equilíbrio de 801ºC, a 9.6 kbar para a associação de fácies granulito. As condições de pico bárico nas rochas charnockíticas são de 14.36 ± 1.9 kbar, a 680ºC, enquanto que as temperaturas máximas registradas são de 885.17ºC, a 10 kbar. Cálculos realizados no THERMOCALC forneceram temperatura de 771 ± 166ºC, a 11.8 ± 2.4 kbar. As rochas metabásicas relacionadas ao Complexo Mantiqueira apresentam baixas concentrações de elementos LILE, possivelmente devido ao empobrecimento destes elementos durante o metamorfismo através de perdas por reações de desidratação. Os dados geoquímicos apontam fontes do tipo E-MORB para grande parte das rochas metabásicas, embora sempre com enriquecimento em ETR maior, o que é sugestivo de fontes enriquecidas. O Grt-cpx anfibolito simplectítico apresenta assinaturas geoquímicas distintas, com enriquecimento maior em elementos LILE e ETRL, o que sugere uma origem a partir de fontes OIB. Os padrões de ETR e diagramas de variação multi-elementares de elementos traço sugerem que as rochas charnockíticas têm fontes relacionadas à ambientes de arco vulcânico. Os paragnaisses, em fácies anfibolito superior a granulito, registram uma trajetória inicial horária, descompressiva ao campo da sillimanita. É distinta da trajetória inicial anti-horária exibida pelas rochas metabásicas e charnockíticas, que registram nas coronas de Grt-Cpx-Pl o metamorfismo progressivo de fácies granulito de alta pressão. Sugere-se que esse relativo aumento de pressão tenha sido condicionado pela colocação dos metassedimentos da Nappe Lima Duarte sobre as rochas do Complexo Mantiqueira, porém no mesmo campo de temperatura. Assim, o avanço da nappe metassedimentar pode ter sido responsável pelo soterramento das rochas metabásicas e charnockíticas relacionadas com o Complexo Mantiqueira, o que justifica a pressão mais elevada nestes litotipos. A etapa de exumação foi compartilhada por ambas, o que é evidenciado nas semelhanças de condições metamórficas durante a trajetória de resfriamento quase isobárico, porém com os litotipos do Complexo Mantiqueira em nível crustal mais profundo. The Lima Duarte Nappe is located in southeastern Brasília Orogen and is composed by migmatitic paragneisses presenting garnet, sillimanite, biotite and muscovite, and coarse-grained orthoquartzites, with few amphibolite and calc-silicate interlayers. The Mantiqueira Complex occurs as tectonic imbricated lenses in the Lima Duarte Nappe, resembling an allochthon structure. It comprises TTG-type migmatitic and polymetamorphic orthogneisses, presenting granulitic metabasic interlayers, as mafic bands and lenses, as well as boudins, which are often concordant with the main foliation. Charnockitic rocks are apparently intrusive in the Mantiqueira orthogneisses, with associated metabasic rocks. The mineral assemblage observed in paragneisses (Grt + Bt + Sil + Pl + Rt + Ilm + Qtz ± Ms ± Kfs ± Ky) is related to an upper amphibolite facies progressive metamorphism characterized by muscovite breakdown reactions producing potassic feldspar. The peak baric conditions obtained in the THERMOCALC processing software for the assemblage involving kyanite are 10 ± 0.6 kbar and 807 ± 25ºC. The thermal peak of 827 ± 44ºC and 8.2 ± 1.8 kbar obtained in THERMOCALC for the assemblage envolving sillimanite, is placed in the boundary of breakdown curve for dumortierite. The metabasic rocks interlayered in Mantiqueira Complex orthogneisses show the Grt-Cpx-Pl-Qtz±Opx+Hbl assemblage, indicating high pressure granulite facies. They are characterized by the presence of Grt-Cpx-Pl progressive coronitic textures between Opx, Pl and/or opaques boundaries, apparently with an igneous origin, which marks the transitions from intermediate pressure granulites field to high pressure granulite field. The peak conditions recorded in Grt-Cpx-Pl veins in metagabbronorites is 831.8ºC, and 10 kbar. The garnet granulite records the metamorphic peak at 890 ± 41ºC, and 9.26 ± 1.93 kbar. Thermobarometric calculations performed at TWEEQU revealed equilibrium conditions at 801ºC, and 9.6 kbar based on granulite facies mineral assemblage. The peak baric conditions achieved by the charnockitic rocks are 14.36 ± 1.9 kbar, and 680ºC, while maximum temperatures recorded are 885.17ºC, and 10 kbar. Thermobarometric calculations performed at THERMOCALC revealed temperatures of 771 ± 166ºC, and 11.8 ± 2.4 kbar. The metabasic rocks related to Mantiqueira Complex show low concentrations of LILE elements, possibly due to the depletion of these elements during metamorphism in dehydrating reactions. Geochemical data point out to E-MORB type sources for the great majority of metabasic rocks, even though with an REE enrichment, suggesting more enriched sources. The symplectitic Grt-Cpx amphibolite show distinct geochemical signatures, characterized by a greater enrichment in LILE and light-REE elements, suggesting an OIB source for their origin. REE patterns and trace element spidergrams suggest that charnockitic rocks sources are related to a volcanic arc tectonic setting. Paragneisses, in upper amphibolite to granulite facies, recorded an initial clockwise path, decompressing to the sillimanite field. It differs from initial counterclockwise path exhibited by the metabasic and charnockitic rocks, which preserves the progressive high pressure granulite facies metamorphism in Grt-Cpx-Pl coronae. This pressure increase is probally related to the metassediments of the Lima Duarte Nappe, that thrusted over the Mantiqueira Complex rocks, although in the same temperature field. The buried character of metabasic and charnockitic rocks may be caused by the thrust of the metassedimentary nappe, justifying the higher pressure found in these lithotypes. The exhumation phase was shared by both of them, which is confirmed in the metamorphic similarities conditions, as they cooled out together in a near isobaric path, although the Mantiqueira Complex lithotypes were in a deeper crustal level.

O grande incentivo para realização deste trabalho, foi a complexidade geológica que envolve os terrenos Pré-Cambrianos da porção sul-oriental do Estado de São Paulo, tendo como cidades limites principais, Mongaguá, Sete Barras, Pariquera-Açu, Iguape e Peruíbe. Utilizando-se de diversas ferramentas como a petrologia, geologia estrutural, geoquímica, geocronologia e geologia isotópica, procurou-se melhor definir e caracterizar os terrenos que constituem a área de estudo, reconhecendo-se quatro importantes blocos tectônicos. O quadro tectônico atual observado na região estudada, estabeleceu-se no final do Neoproterozóico, como resultado de colagens associadas à formação do Gondwana Ocidental. O Bloco Embu, ocorre a norte da Zona de Cisalhamento Cubatão (ZCC), predominando, na área de estudo, rochas metassedimentares, localmente migmatíticas, e granitos peraluminosos intrusivos. Apresentam forte estruturação em torno de E-W, reflexo do Sistema de Cisalhamento Cubatão Itariri (SCCI). Os litotipos graníticos apresentaram idades de formação em torno de 600 Ma (U-Pb - monazitas), interpretadas como, relacionadas à fase tardi-colisional do Cinturão Ribeira, responsável pelo desenvolvimento do SCCI. O Bloco Mongaguá, é limitado a NW pela ZCC, a SW pela Zona de Cisalhamento Itariri (ZCI) e a leste pelo Oceano Atlântico. Predominam rochas gnáissico-migmatíticas, envolvendo termos graníticos e dioríticos. As rochas graníticas deste domínio foram subdivididas em três grupos principais: Granito Tipo Itariri, Areado e Ribeirão do Óleo. Apresentam estruturação geral E-NE, com exceção das rochas gnáissicas de Itanhaém, com estruturação NW e mergulhos sub-horizontais. Os termos graníticos apresentaram heranças isotópicas com idades U-Pb (zircões) no intercepto inferior entre 580 e 640 Ma. Os valores próximos a 600 Ma, foram interpretados como relacionados à época de mistura de magmas (mingle / mix), possivelmente em processos) distensionais. As análises isotópicas de Nd e Sr indicam que os precursores crustais destas rochas se diferenciaram do manto em épocas paleoproterozóicas distintas e tiveram origens a partir de fontes distintas com características de reservatórios crustais. O Bloco Registro é limitado a norte pelo SCCI e a sul pela Zona de Cisalhamento Serrinha (ZCS). É composto por rochas graníticas com feições migmatíticas, que mostram diferentes graus de assimilação com material máfico diorítico, e rochas metassedimentares, representadas pelos paragnaisses do Maciço da Juréia. Apresenta estruturação NW, e E-NE, quando influenciadas pela cinemática do SCCI. As rochas granito-migmatíticas sugerem associação com processos distensionais, com formação de diques sin-plutônicos e enclaves, relacionados a mingling e mixing de materiais distintos, ocorrido possivelmente em épocas paleoproterozóicas (idades U-Pb zircões entre 2.2 e 1.9 Ga). Adicionalmente, mostram-se intensamente afetadas pelo evento tectono-termal brasiliano, apresentando rochas gnáissicas com idades U-Pb (zircões) de 600 Ma, e idades intercepto inferior em torno de 580 Ma. As idades \'T IND. DM\' obtidas concentram-se principalmente entre 2.7 e 2.9 Ga. As rochas gnáissicas do Maciço da Juréia apresentaram idade U-Pb em monazitas de 750 Ma, interpretada como importante evento térmico gerador de metamorfismo do fácies anfibolito. O Granito Votupoca, intrusivo nas rochas gnáissico-migmatíticas, correlacionado à Suíte Granítica Serra do Mar, apresentou idade de 582 Ma. O SCCI, constitui-se por granitóides, e subordinadamente metassedimentos, miloníticos e protomiloníticos. Para facilidade de estudo, foram considerados domínios distintos, onde o ramo A-B apresenta direção preferencial em torno de E-W e o ramo C em torno de N60E. As rochas afetadas pelo SCCI registraram, pelo menos, 2 fases importantes distintas de deformação. Uma fase está relacionada a uma ) movimentação sinistral com componente de abatimento para NW, com idade máxima de 600 Ma, e outra associada a movimentações sinistrais e dextrais com componente compressiva para SW. Reativações posteriores em condições mais rúpteis são observadas. Os litotipos investigados do Bloco Iguape, limitado a norte pela ZCS e a S-SE pelo Oceano Atlântico, envolvem rochas graníticas e metassedimentares com estruturação principal NE. As rochas metassedimentares englobam principalmente metassedimentos de baixo grau metamórfico. As rochas graníticas foram subdivididas em três grupos principais. Granitos que ocorrem no Maciço de Iguape, normalmente protomiloníticos, com idades em torno de 600 Ma, com assinatura geoquímica sugestiva de granitos de arcos-vulcânicos ou sin-colisionais. Os granitos da Serra do Paratiú/Cordeiro e os Granitos da Serra de Itapitangui, apresentam características de rochas graníticas do tipo intra-placa e idades em torno de 580 Ma. Os três grupos graníticos apresentaram carecterísitcas geoquímicas e isotópicas distintasl A ZCS, apresenta direção principal em torno de E-W, com movimentação dextral e afeta rochas graníticas e metassedimentares. Apresenta importante ramificação com direção SE, e movimentação sinistral. Possivelmente, a justaposição entre estes blocos tectônicos ocorreu em épocas neoproterozóicas muito próximas. Neste trabalho sugere-se que a justaposição do Bloco Embu ao Bloco Registro, através de em zona de cisalhamento com direção aproximadamente E-W, deu-se em torno de 606 Ma. Granitos peraluminosos intrusivos no Bloco Embu, com cerca de 598 Ma, associados ao SCCI, podem estar relacionados à justaposição do Bloco Mongaguá, aos Blocos Registro e Embu. Esta justaposição se deu através de uma movimentação sinistral na ramificação B (direção E-W) e dextral na ramificação C (direção NE) do SCCI. A associação do regime distensivo, interpretado como responsável pela geração ) as rochas gnáissico-migmatíticas do Bloco Mongaguá (612 \'+ OU -\' Ma), à cinemática de justaposição do Bloco Mongaguá aos Blocos Embu e Registro (598 \'+ OU -\' 8 Ma) ainda é incerta, podendo representar um regime anterior à justaposição dos blocos, ou mesmo um regime distensional associado a esta justaposição. A época mais provável da justaposição do Bloco Iguape ao Registro, entre 570 e 580 Ma é sugerida através de datações U-Pb em monazitas de protomilonito granítico da ZCS. Datações K-Ar em biotitas em torno de 500 Ma, obtidas em rochas miloníticas do SCCI e da ZCS, são interpretadas como referentes à reativações posteriores ocorridas nestas zonas de cisalhamento. The main stimulus for the execution of this study was the geological complexity of the Precambrian terrains in the southeastern part of the state of São Paulo, between the cities of Mongaguá, Pariquera-Açu, Iguape and Peruíbe. An attempt was made to define the main features of the terrains in this area, using petrology, structural geology, geochemistry, geochronology and isotope geology. Four major tectonic blocks were separated. The present tectonic situation in the studied area is the product of collages related to the formation of West Gondwanaland, which ended in the Neoproterozoic. The Embu Block occurs north of the Cubatão shear zone (CSZ). In the studied area it is mainly composed os metasedimentary rocks, locally migmatized, and peraluminous granites. The structure is strongly E-W oriented as a result of the action of the Cubatão - Itariri shear system (CISS). U-Pb (monazite) ages of the granites of about 600Ma are interpreted as reflecting the late collisional stage of the Ribeira Belt which was responsible for the formation of the CISS. The NW limit of the Mongaguá block is the CSZ, while the western limit is the Itariri shear zone (ISZ), and th eastern limit is the Atlantic Ocean. The main rock type is gneiss-migmatite with granitic and dioritic compotions. Three main groups of granite, the Itariri, Areado and Ribeirão do óleo types, are encountered. The main structural direction in E to NE, with the exception of the Itanhaém gneisses which have a NW-SE structure and sub-horizontal dip. Analyses of zircon indicate crustal inheritance, and lower intercept U-Pb (zircon) ages fall between 580 and 640 Ma. Ages around 600Ma are believed to date a magma mixing/mingling event, which probably occurred during an extensional event. Sr and Nd isotopic compositions demonstrate that differentiation of the different crustal sources from the mantle occurred during defferent paleoproterozoic events. The Registro block, with the CISS as its northern limit and the Serrinha shear zone (SSZ) as its southern limit, is formed by granitic rocks with migmatitic aspect and showing different degrees of assimilation by dioritic material, and by the paragneisses of the Juréia massif. It has an NW-SE structure which swings to E or NE under the influence of the CISS. The migmatitic granites present evidence for the action of extensional processes in the form of Syn-plutonic dykes and enclave swarms. Mixing and mingling between the granitic and dioritic materials probably occurred between 2.2 and 1.9 Ga as shown by U-Pb (zircon) ages. The rocks were intensely affected by the Brasiliano tectono-thermal event, as shown by the lower intercept U-pb (zircon) ages of about 580Ma in gneisses which have model Nd Tdm ages concentrated in the 2.7 - 2.9 Ga interval. Gneiss from the Juréia massif gas a U-Pb (monazite) age of 750 Ma, believed to register the thermal event responsible for amphibolite-grade metamorphism. The Votupoca granite, a member of the Serra do Mar suite intruded into the gneiss-migmatites, has an age of 582+8Ma. The CISS cuts granitoids and subordinate metasediments, which are now protomylonites or mylonites. To simplify the study, the systems was divides into two different domains, in which the structure of the A-B domain in mainly E-W, while the structural direction of the C domain is N60ºE. At least two major deformation events affected the rocks. One of the phases, younger than 600Ma, was sinistral with northwestwards dip-slip. The other phase with southwestward compression involved both sinistral and dextral movements. Later reactivations under more brittle conditions also occurred. Rocks of the Iguape Block, limited northwards by the SSZ and south-southeastwards by the Atlantic Ocean, include granites and metasediments with a dominantly NE structural orientation. The metasediments are mostly in low metamorphic grade, while the granites comprise three separate geochronological and geochemical groups. Protomylonitic granites if the Iguape massif have ages around 600Ma, and have geochemical signatures of volcanic arc or syncollision granites. The granites of the Paratiú - Cordeiro and Itapitangui hills are 580 Ma intraplate granites. The SSZ has a dominantly E-W direction and dextral sense, but an important SE-oriented branch is sinistral. It is probable that the tectonic blocks were united during a short time interval in the Neoproterozoic. Here we suggest that the joining of the Embu Block to the Registro Block occurred at about 606Ma along an E-W shear zone. The 598Ma peraluminous granites intruded into the Embu Block may register the arrival of the Mongaguá Block against the newly formed Registro-Embu domain. This welding occurred along the sinistral, E-W oriented branch (B) and the NE-oriented dextral movement along branch C of the CISS. It is still uncertain whether there is an association between the tensional regime responsible for the formation of the gneiss-migmatites of the Mongaguá Block at about 612+3Ma, and the cinematic situation created by the union of the Mongaguá and Embu Registro blocks at 598+8Ma. The welding of the Iguape and Registro blocks probably occurred between 580 and 570Ma, as suggested by the U-Pb (monazite) age of the protomylonitic granites of the SSZ. Later reactivations of the CISS and SSZ at about 500 Ma are suggested by K-Ar ages of biotites.

The Camboriu Complex is the only gneissic-migmatitic inlier within the Neoproterozoic Brusque Group supracrustal rocks, in the northernmost part of the Dom Feliciano Belt, southern Brazil. It comprises the Morro do Boi migmatites and the diatexitic Ponta do Cabeco Granite. Zircon U-Pb dating of migmatites and associated granitic neosomes shows that crustal evolution started in the Paleo- Mesoarchean (3.3-3.0 Ga), continued with events through the Neoarchean and Paleoproterozoic and ended in the Neoproterozoic (0.64-0.61 Ga). Integration of zircon Hf isotopic data and U-Pb ages indicate that juvenile crustal accretion was restricted to the Archean and that afterwards intracrustal reworking predominated. The exception to this is the ca. 1.56 Ga xenoliths (basic dike remnants?), whose magmatic zircons have juvenile Hf isotopic signatures. This basic magmatism marks extension of the earlier Precambrian complex. Although the Camboriu Complex is dominated by early Precambrian crustal additions, it was so strongly reworked in the Neoproterozoic that melts derived from it intruded the adjacent Neoproterozoic Brusque Group supracrustal rocks. Because of this strong overprint, we regard the Camboriu Complex as a Neoproterozoic (Ediacaran) geotectonic unit. In terms of its history, the Camboriu Complex most closely matches the Atuba Complex, the basement of the Curitiba Microplate that occurs further to the north, close to the Ribeira Belt, another Neoproterozoic orogen of southern Brazil.

Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (< 2 kbar). One of these, the San Blas intrusive complex formed over millions of years (≤ 2–3 m.y.) through three periods of magma additions that are characterized by variations in magma sources and emplacement style. The main units, mostly felsic granitoids, have U-Pb zircon crystallization ages within the error range. From older to younger (based on cross-cutting relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by ~ WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNdt = − 5.8 and εHft in zircon = − 2.9 to − 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNdt = + 0.6 to − 4.8 and εHft in zircon = + 3 to − 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include older hot magma mush. The latter results in ductile downward flow of older, during rise of younger magma. Such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted., This work was supported by Argentine public grants FONCYT PICT 2013-0226, SECyT-UNC 2016 and SECyT-UNLaR 0599/2011.

High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasilia Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs ± Bt ± Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 °C and 900 °C. The GASP baric peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz ± Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelândia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelândia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC).

Two granitoid associations were emplaced during the development of the Major Gercino Shear Zone in eastern Santa Catarina, southern Brazil. The 614 Ma Fernandes Granitoid Association is composed mainly of hornblende syenogranites including A-type, and alkali-calcic and calc-alkaline types. Initial Sr isotope ratios are heterogeneous, but systematic isotopic and element variations suggest that different source rocks produced magmas which underwent mixing and fractional crystallization. The Rolador Granitoid Association of biotite-bearing granodiorite is less isotopically heterogeneous, but systematic isotopic and element variations are not obvious.

A. Westin and M.C. Campos Neto acknowledge support from São Paulo Research Foundation (FAPESP) through grants 2011/13311-9, 2013/13530-8 and 2013/19095-1. A. Westin is a grant holder at FAPESP and M. C. Campos Neto is a CNPq researcher. P. A. Cawood, C. J. Hawkesworth and H. Delavault acknowledge support from Natural Environment Research Council grant NE/J021822/1. Early Proterozoic sedimentary basins are an important record of crust generation processes and consequently a fundamental key to unravelling Earth's evolution through geological time. Sediments within the basins are typically deformed and metamorphosed by subsequent tectonothermal events, which can obliterate their links to source terranes. Nd-whole-rock and detrital zircon U-Pb and Lu-Hf isotopic analyses are among the most reliable tools to be used in provenance investigations, since zircon is a resilient mineral and the Sm-Nd system is not extensively modified during metamorphism. These methods have been applied to a study of the provenance and tectonic setting of the São Vicente Complex, preserved in a Neoproterozoic passive margin related allochthon within the Southern Brasilia Orogen. The complex consists of siliciclastic and calc-silicate gneisses with mafic and minor ultramafic rocks, which were deformed and metamorphosed during late Neoproterozoic collision between the Paranapanema Block and the São Francisco-Congo plate. Detrital zircons indicate derivation from a juvenile Paleoproterozoic source terrane (peaks of crystallisation ages of ca. 2130 Ma, 2140 Ma and 2170 Ma; ɛHft between +0.1 and +6.0; NdTDM = 2.31-2.21 Ga; ɛNdt = +1.6 to +2.8), with a minor contribution from older continental crust. Interlayered amphibolite rocks, with juvenile signatures (ɛHft = +5.8 to +8.2; NdTDM = 2.14 and 2.30 Ga; ɛNdt = +2.2 and +3.2), yielded similar ages of 2136 ± 17 and 2143 ± 14 Ma, suggesting syn-sedimentary magmatism. Thus, the maximum age of deposition at around 2130 Ma represents the best estimate of the depositional age of the complex. The dominance of detrital zircons ages close to the age of deposition, along with syn-sedimentary magmatism, imply a convergent margin basin tectonic environment for the São Vicente Complex, with similarities to fore arc basin and trench deposits. Amphibolite and meta-sedimentary rocks point to important juvenile magmatism around 2.14 Ga. Juvenile Rhyacian (ca. 2.1 Ga) granite-granodiorite-tonalite orthogneisses with arc-related geochemical signatures (Pouso Alegre Complex) that override the São Vicente Complex, are the probable main source of detritus within the complex. Both basin and source were part of the southern edge of the São Francisco plate during the assembly of West Gondwana, and served as sources for early Neoproterozoic passive margin related basins. The age of intrusive anorogenic A-type Taguar granite indicates that by 1.7 Ga the São Vicente Complex was in a stable tectonic environment. Postprint

An Early Cambrian pluton, known as the Guasayán pluton, has been identified in the central area of Sierra de Guasayán, northwestern Argentina. A U-Pb zircon Concordia age of 533±4 Ma was obtained by LA-MC-ICP-MS and represents the first report of robustly dated Early Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentary rocks and its magmatic assemblage consists of K-feldspar (phenocrysts)+plagioclase+quartz+biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessory minerals. Geochemically, the granitic rock is a metaluminous subalkaline felsic granodiorite with SiO2=69.24%, Na2O+K2O=7.08%, CaO=2.45%, Na2O/ K2O=0.71 and FeO/MgO=3.58%. Rare earth element patterns show moderate slope (LaN/YbN=8.05) with a slightly negative Eu anomalies (Eu/Eu*=0.76). We report the first in situ Hf isotopes data (εHft=-0.12 to-4.76) from crystallized zircons in the Early Cambrian granites of the Sierras Pampeanas, helping to constrain the magma source and enabling comparison with other Pampean granites. The Guasayán pluton might provide a link between Early Cambrian magmatism of the central Sierras Pampeanas and that of the Eastern Cordillera, contributing to define the western boundary of the Pampean paleo-arc., Un plutón de edad Cámbrica temprana, conocido como plutón Guasayán, ha sido identificado en el área central de la sierra de Guasayán, noroeste de Argentina. Una edad U-Pb en concordia de 533±4 Ma fue obtenida en circones mediante LA-MC-ICP-MS. Esta edad representa el primer reporte de magmatismo Cámbrico temprano para el noroeste de las Sierras Pampeanas. El mismo está emplazado en rocas metasedimentarias de bajo grado y se caracteriza por una asociación magmática de K-feldespato fenocristales)+plagioclasa+cuarzo+biotita, con circón, apatita, ilmenita, magnetita y monacita como minerales accesorios. Geoquímicamente, la roca granítica se clasifica como una granodiorita félsica metaluminosa subalcalina con contenidos de SiO2=69,24%, Na2O+K2O=7,08%, CaO=2,45% y relaciones de Na2O/K2O=0,71 y FeO/MgO=3,58%. Los patrones de elementos de tierras rara muestran una pendiente moderada (LaN/YbN=8,05) con una ligera anomalía negativa de Eu (Eu/Eu*=0,76). Nosotros reportamos los primeros datos in situ de isótopos de Hf (εHft=-0,12 a -4,76) para circones cristalizados en granitos del Cámbrico temprano de Sierras Pampeanas, lo que aporta información crítica sobre la fuente de los magmas, permitiendo la comparación con otros granitos pampeanos. El plutón Guasayán podría proveer el enlace entre el magmatismo del Cámbrico temprano del sector central de las Sierras Pampeanas y aquel de la cordillera Oriental, contribuyendio a definir el límite occidental del paleoarco Pampeano., Facultad de Ciencias Naturales y Museo, Centro de Investigaciones Geológicas

The late Archean was a period of important changes in geodynamic processes and magmatism style. This period seems to mark the time when crustal reworking processes start to predominate over new continental crust generation and is most likely related to the beginning of continental collision and “modern-style” plate tectonics. This study reports a new dataset of zircon U-Pb and Hf isotopes, whole-rock geochemistry and Nd isotopes from Meso- to Neoarchean complexes within the basement of the Neoproterozoic southern Brasilia Orogen, SE Brazil. The data provide important insights into the petrogenesis of Mesoarchean TTG suites and their implications for tectonic settings of Archean continental crust generation. Isotopic and geochemical data constrain the timing and nature of the Neoarchean transition from TTG-type to high-K granitic magmatism in the studied area and we discuss the involvement of these complexes in the southern Sao Francisco paleocontinent assembly. A well-defined period of TTG-type magmatism between 3.00 and 2.96 Ga is identified, with mostly suprachondritic eHf (t) values, between 0 and +5.1, associated with average two-stage model ages between 3.2 and 3.3 Ga. Whole-rock Nd analyses yield T DM ages between 3.2 and 3.4 Ga. These TTGs are interpreted as juvenile additions to the continental crust most likely generated by partial melting of a hydrous mafic crust. The variable trace element compositions of the analyzed TTG samples indicate partial melting at different depths at the same time. These results strongly support the idea of a non-unique tectonic setting of Archean continental crust generation. An additional period of Neoarchean high-K granitic magmatism at ca. 2.76 Ga is interpreted to record the transition from TTG-type to high-K granitoid magmatism in the studied area. This Neoarchean magmatism is associated with less radiogenic isotopic signatures with mostly negative eHf (t) values. The isotopic and geochemical signatures suggest that reworking of the Mesoarchean TTG crust, most likely in a collisional setting, was the main mechanism for the generation of the Neoarchean granitic suite. This supports the idea that the Neoarchean transition from TTGs to granites was most likely a result of the beginning of continental collision processes.

A Nappe system south to southwest of the Sao Francisco Craton represents the southern extension of the Brasilia belt and describes an inverted metamorphic pile of greenschist facies toward amphibolite facies. The Aiuruoca-Andrelândia nappe is one of the nappes of this system. The hind portion of the Aiuruoca-Andrelândia nappe , south of Caxambu and Aiuruoca (MG), consists of a structural-metamorphic domain transported toward the E-NE. There is a metamorphic transition, from the kyanite zone to kyanite and sillimanite coexistence, until the sillimanite zone. Metapelitic rocks preserve high-pressure parageneses (Rt–Ky–Grt–Ms–Bt–Pl–Qtz) and contain retrograde eclogitic rocks. Sil–Pl–Qtz coronitic intergrowths around garnets are common decompressive textures. Kyanite schists register the P max of 11 kbar at 660 °C and define a decompressive path until 6–7.5 kbar at 650 °C. These P – T conditions represent the equilibrium in S 2 schistosity (amphibolite facies) and the beginning of the cooling path in the Ky–Sil transition. The decompressive path suggests an extrusional process, immediately after burying at about 60 km. Exhumation controlled by convergent events, related to the Sao Francisco Plate subduction and tectonic erosion, took these units, isothermally, to higher levels (20–33 km). Later, the metamorphic path shifted toward near-isobaric cooling.

O Orógeno Tocantins Meridional representa a pilha colisional de nappes entre três ambientes tectônicos principais (de WSW para ENE): domínio de arco magmático desenvolvido na margem continental ativa da Placa Paranapanema (Nappe Socorro-Guaxupé), domínio continental subductado (Terreno Andrelândia) e domínios com afinidades de margem passiva e/ou relacionados à Placa Sanfranciscana (Sistema de Nappes Carrancas e Nappe Lima Duarte). O magmatismo relacionado ao período de subducção remonta a 670 Ma, com auge metamórfico (geoterma relaxada na margem ativa e perturbada no terreno subductado) há 625 Ma. A atividade de arco na margem ativa foi contemporânea à sedimentação tipo-flysch no Terreno Andrelândia. Os processos metamórficos e deformacionais da etapa orogênica controlada por colisão frontal migraram para ENE de ca. 620 a 580 Ma. A duração dos processos foi"instantânea" na nappe interna ocidental (ca. 7 Ma, com plutonismo pós-orogênico há 612 Ma) e perdurou por ca. de 20 Ma na nappe oriental de alta pressão. O terreno subductado registrou rápida velocidade de exumação (ca. 2,2 mm/ano). Atividades magmáticas superimpostas, controladas por regimes extensionais (Cinturão Itu) acompanharam a exumação do orógeno e precederam a instalação de bacias sucessoras continental-marinhas há 570 Ma. O Orógeno Araçuaí, relacionado à convergência entre a margem passiva oriental Sanfranciscana e o Terreno Juiz de Fora (microplaca em ambiente de margem ativa) registrou o auge metamórfico colisional no domínio interno há 563 Ma. A migração das nappes Araçuaí contra o domínio cratônico, com o pico térmico metamórfico há 530 Ma, reflete a superposição de eventos colisionais múltiplos no Sistema Orogênico Mantiqueira. O embasamento da borda cratônica foi regenerado no Cambriano e engajado ductilmente no orógeno. Cavalga o domínio de foreland, no Quadrilátero Ferrífero, caracterizado por sistema thin-skinned de cavalgamento segmentado por domos do embasamento e calhas sinformais das supra-crustais. A colisão oblíqua entre o Sistema Orogênico Mantiqueira e o protocontinente consolidado pelo Orógeno Tocantins Meridional foi responsável pelo metamorfismo facies xisto-verde baixo das bacias sucessoras e migrou para norte, de 555 a 500 Ma. A colagem orogênica brasiliana, no sul do Cráton do São Francisco, representou a interação entre etapas orogênicas curtas em um longo processo de convergência, consumo de placas e migração de orógenos até o limite Cambro-Ordoviciano. O último evento metamórfico pré-colagem no embasamento cratônico ocorreu entre 2,03 - 2,06 Ga provavelmente sob regime extensional.

O Sistema de Nappes Carrancas compõe um sistema de nappes que circunda ao sul o Cráton do São Francisco e é formado pela Unidade Biotita Xisto e pelas formações Campestre e São Tomé das Letras do Grupo Carrancas. A Unidade Biotita Xisto contém veios de quartzo e xistosidade anastomosada e é formada por quartzo, biotita, muscovita, clorita e, localmente plagioclásio, carbonato e granada. A Formação Campestre é formada por quartzitos intercalados a filitos/xistos que variam de cloritóide filitos grafitosos, com muscovita, quartzo e turmalina e, localmente, granada a xistos com granada, estaurolita e cianita. A investigação da Unidade Biotita Xisto como autóctone em relação ao Cráton do São Francisco, seu potencial agrupamento com o Grupo Carrancas em uma megassequência deposicional, bem como sua comparação com a unidadealóctone Xisto Santo Antônio (Nappe Andrelândia) constituem parte dos objetivos deste estudo. Para tal, foram feitas análises químicas e isotópicas (Sr e Nd) em rocha total e geocronologia U-Pb em cristais de zircão detríticos, tanto na Unidade Biotita Xisto como na Formação Campestre, com intuito de elucidar a relação entre as mesmas e compará-las com dados da literatura disponíveis para o Xisto Santo Antônio. A Unidade Biotita Xisto apresenta características químicas compatíveis com sedimentos que sofreram intemperismo químico de intensidade e período de tempo moderados, depositados em ambientes de colisão continental, com área-fontecomposta essencialmente por rochas félsicas. Assinaturas de elementos traço e isotópicas de Sr ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' entre 0,713 e 0,715) e Nd (\'\'épsilon\' IND.Nd\' entre -6 e -5) indicam contribuição de arco magmático e crosta continental e diferem, portanto, daquelas esperadas em ambientes de margempassiva. A mesma contribuição é observada para o Xisto Santo Antônio, cuja área fonte registra importante assinatura de material juvenil. As idades U-Pb LA-MC-ICP MS obtidas em cristais de zircão mostram contribuição principal de rochas do final do Criogeniano e contribuição secundária do Riaciano. A classe modal ao redor de 665 Ma é comparável com a idade cristais de zircão detrítico do Xisto Santo Antônio, o que aponta parauma mesma área-fonte principal para ambas unidades. A deposição dos sedimentos precursores da Unidade Biotita Xisto ocorreu entre 630-611 Ma, sendo as fontes principais os granulitos cálcio-alcalinos e rochas vulcânicas co-genéticas, além de granitos sin-colisionais da Nappe Socorro-Guaxupé. A pouca representatividade de idades paleoproterozóicas e a ausência de assinaturas químicas de margem passiva, inviabilizam as rochas do Cráton doSão Francisco como parte da área-fonte. Desta forma, a Unidade Biotita Xisto não é autóctone em relação ao Cráton do São Francisco, sendo, potencialmente, a unidade que compõe a frente da Nappe Andrelândia. Por outro lado, a Formação Campestre possui assinatura geoquímica de sedimentos que sofreram uma intensa reciclagem e alteração da composição do sedimento original. As assinaturas químicas de elementos traço e isotópicas Sr e Nd indicam contribuição de crosta continental superior, com componente de crosta antiga e sem afinidade com sedimentos depositados em margem passiva (\'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' entre 0,74 e 0,76; \'\'épsilon IND.Nd\' entre -18 e -15). Os zircões detríticos analisados forneceram idades U-Pb LA-MC-ICP-MS variadas, do Toniano ao Mesoarqueano, correlacionáveis com rochas vulcânicas e plutônicas do Cráton do São Francisco, com as faixas marginais do Cráton de Angola e/ou faixas orogênicas do Cráton Amazônico e com rochas dos arcos Mara Rosa e Goiás.A abrangência das idades U-Pb da Formação Campestre e das formações Chapada dos Pilões e Paracatu, permite a correlação, no Orógeno Brasília, entre os Grupos Carrancas e Canastra. A paleogeografia mais provável é a de um ambiente de rifte, antecessor à deriva e aoestabelecimento de uma margem continental passiva. The Carrancas Nappe System composes a system of nappes that surround the southern margin of the São Francisco Craton and is formed by the Biotite Schist Unit and by the Campestre and São Tomé das Letras formations of the CarrancasGroup. The Biotite Schist Unit encompass quartz veins and anastomosed schistosity and is formed by quartz, biotite, muscovite, chlorite and, locally plagioclase, carbonate and garnet. The Campestre Formation is composed by interleaved quartzites and phyllite/schist that varies from graphite-chloritoid phyllites, with muscovite, quartz, tourmaline and garnet, and locally garnet schists and schists with garnet, staurolite and kyanite. The investigation of the Biotite Schist Unit as authochtonous in relation to the São Francisco Craton, it´s potencial grouping with the Carrancas Group in a deposicional megassequence, as well as it´s comparison with the allochthonous Santo Antônio Schist (Andrelândia Nappe) is part of the goals of this study. For this purpose, chemical and isotopic (Sr and Nd) whole rock analysis were obtained, along with U-Pb detrital zircon data, in the Biotite Schist Unit and also in the Campestre Formation, in order to elucidate the relationship between these units and compare them with literature data available for theSanto Antônio Schist. The Biotite Schist Unit show chemical characteristics compatible with sediments that underwent chemical weathering of moderate intensityand time, deposited in continental collision setting, with source region composed essentially by felsic rocks. Trace elements and Sr isotopic signatures ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' between 0,713 and 0,715) and Nd (\'\'épsilon IND.Nd\' between -6 and -5) points to contribution from magmatic arc and continental crust, and are different from the expected for passive margin settings. The same contribution is observed in the Santo Antônio Schist, which source area registers an important juvenile material signature. The U-Pb LA-MC-ICP MS zircon data show major contribution from rocks of the later Cryogenian and minor contribution from the Ryacian. The modal class around 655 Ma is comparable with the U-Pb detrital zircon data from the Santo Antônio Schist, pointing to the same source area for both units. The deposition of the precursors sediment of the Biotite Schist Unit occurred between 630 - 611 Ma, and the main sources were the calk-alcaline granulites and co-genetic volcanic rocks, besides the Socorro-Guaxupé Nappe sin-collisional granites. The low representation of Paleoproterozoic ages and the absence of passive margin chemical signatures preclude the rocks of the São Francisco Craton as part of the source area. Thus, Biotite Schist Unit is not an autochthonous unit in relation to the São Francisco Craton, and is, potentially, the unit that composes the Andrelândia Nappe front. On the other hand, the Campestre Formation has geochemical signatures of sediments that underwent intense recycling and alteration of the original sediment. The trace element and Sr and Nd isotopic signatures indicates upper continental crust contribution, with older crust component and no affinity with passive margin sediments ( \'ANTPOT.87 Sr\'/\'ANTPOT. 86 Sr\' between 0,74 and 0,76; \'épsilon\' IND.Nd\' between -18 and -15). The U-Pb LA-MC-ICP MS detrital zircon data provide varied ages, from the Tonian to the Mesoarchean, correlated withvolcanic and plutonic rocks of the São Francisco Craton, with the marginal belts of the Angola Craton, and/or orogenic belts of the Amazonian Craton and with the Mara Rosa and Goiás magmatic arcs. The range of the U-Pb ages of the Campestre Formation and the Chapada dosPilões and Paracatu formations, allows the correlation, in the Brasília Orogen, of the Campestre and Canastra groups. The most likely paleogeography is that of a rift setting, before the continental drift and the establishment of a passive continental margin.

Oxygen isotope studies were carried out across units of a Neoproterozoic nappe system, south of Sao Francisco Craton. A temperature decrease toward the base of the system is found, consistent with a previously recognized inverted metamorphic pattern. The tectonic contact of the basal unit and the reworked southern Sao Francisco craton show a steep temperature gradient, suggesting that low temperature thrusting acted as the dominant tectonic process. The contrasts between the δ18O values of the Tres Pontas-Varginha and Carmo da Cachoeira nappes and the differences among the samples and minerals are consistent with the preservation of sedimentary isotopic composition during metamorphism. The small differences in the δ18O values between the undeformed and the deformed calc-silicate samples (∼1.6‰) suggest that the δ18O value of mylonitization fluids was close to that which equilibrated with the metamorphic assemblage. The distinct δ18O values of metapelitic and calc-silicate samples and the great temperature difference from one type to the other indicate that no large-scale fluid interaction processes occurred during metamorphism. Oxygen isotopic estimations of both Tres Pontas-Varginha undeformed rocks and Carmo da Cachoeira unaltered equivalents indicate δ18O values of up to 18‰. Comparison between these values and those from the ‘basement’ orthogneisses (8.3–8.5‰) indicates the latter are not sources for the metapelites.

Metamorphic conditions are described for three major tectonic entities on the basis of geothermobarometry in a huge Neoproterozoic nappe complex that verges toward the southern border of the Sao Francisco craton. The uppermost Socorro-Guaxupe Nappe, represented by its granulite facies basal portion, yields a maximum temperature and pressure of 890 °C and 11 kbar. Its metamorphic evolution is consistent with heating at the base of the crust as a result of an abnormally high geothermal gradient, probably due to underplating by the lithospheric mantle. The underlying Tres Pontas-Varginha Nappe yields two somewhat distinct P – T paths, both characterized by peak assemblages in the kyanite stability field. The basal kyanite-bearing granulites show higher peak pressure values (15 kbar at 840 °C) and a trajectory that continues in the kyanite stability field, whereas the upper sillimanite granulites show higher temperatures (880 °C at 13 kbar) and a steeper path toward the sillimanite stability field. Data for the Carmo da Cachoeira nappe reveal a steep trajectory, in which the elevated maximum pressure (18.5 kbar at 820 °C) was obtained from a garnet amphibolite that lies along its basal contact. The inverted metamorphic pattern previously observed across these sequences is confirmed by our thermobarometric data, which reveal that the highest temperatures were attained toward the top of the pile.

The Neoproterozoic giant nappe system exposed south of the Sao Francisco craton underwent a minimum of 150 km of near-horizontal northeastward displacement. This nappe system comprises an uppermost unit derived from a plutonic magmatic arc terrane with high-pressure, high-temperature intermediate to mafic granulites at its base (Socorro–Guaxupe nappe), underlain in sequence by a high-pressure kyanite granulite nappe, an amphibolite facies metapelite nappe, and finally by a quartzite nappe which forms the lowest part of the pile and rests on a parautochthonous unit related to the passive margin of the craton. The kyanite granulites crystallized ca 13 kbar, 750°C and have only at their top sillimanite related to T -increase overprinting ( T =890°C), a consequence of downward heat advection from the overlying Socorro–Guaxupe granulites equilibrated at 900°C. Pressures of 13–14 kbar are documented in the underlying metapelite nappe with temperatures of 640–670°C, in which lenses of eclogite indicate P max of ca 17.5 kbar. Phyllites of the parautochthonous unit are directly overlain by HP granulites in the north and record P =7 kbar and T =500°C. The distribution of metamorphic facies is reminiscent of inverted metamorphism with eclogites from subduction-related metamorphism and kyanite granulites from early extrusion of subducted continental crust. The metamorphic conditions of the parautochthon may represent a stage achieved during late metamorphic thinning of the nappe pile. The overall picture suggests that high-pressure units recrystallized in a subduction zone located to the WSW. The frontal thrusts of the nappe system show a late, north northeastward transported thin-skinned pattern.

The Embu Domain represents the central part of the Ribeira Fold Belt in Sao Paulo, Brazil. It hosts several granitic occurrences of varied composition ranging from small granitic bodies that outcrop in a domain bounded by the intersection of two major sutures (Taxaquara and Guararema Faults) and batholitic masses outcropping to the east. Understanding the evolution of such granites is of vital importance to better constrain evolutionary models for the Ribeira Belt. In the present study, a set of samples from eleven main granite occurrences from the east of Sao Paulo state was selected for geochronological investigation using laser ablation-multicollector-inductively coupled plasma spectrometry (LA-MC-ICP-MS) and thermal ionization mass spectrometry (TIMS) U–Pb dating of zircon and monazite crystals, respectively. The results indicate a remarkable cluster of ages around 590 Ma with older events of granite magmatism between 660 and 600 Ma registered for four plutons, indicating a long history of crustal reworking and magma generation. The ages of reworked sources were evaluated from inherited zircon cores. Although highly discordant these point to the predominance of Paleoproterozoic (2.4–2.1 Ga) sources, with minor contributions from Mesoproterozoic (1.1–0.9 Ga) and Archean sources (∼3.1 Ga). The new data bring important insights into the role played by the Embu Domain on the paleogeography and evolution of the Ribeira Belt.

Fil: Meira, Vinícius Tieppo. Instituto de Geociências, Universidade de São Paulo; Brasil. Fil: Campos Neto, Mario da Costa. Instituto de Geociências, Universidade de São Paulo; Brasil. Fil: González, Pablo Diego. CONICET - Centro de Investigaciones Geológicas, Universidad Nacional de La Plata; Argentina. Fil: Stipp Basei, Miguel Ângelo. Instituto de Geociências, Universidade de São Paulo; Brasil. Fil: Varela, Ricardo. CONICET - Centro de Investigaciones Geológicas, Universidad Nacional de La Plata; Argentina. The basement rock of the Pampean flat-slab (Sierras Pampeanas) in the Central Andes was uplifted and rotated in the Cenozoic era. The Western Sierras Pampeanas are characterised by meta-igneous rocks of Grenvillian Mesoproterozoic age and metasedimentary units metamorphosed in the Ordovician period. These rocks, known as the northern Cuyania composite terrane, were derived from Laurentia and accreted towardWestern Gondwana during the Early Paleozoic. The Sierra de Umango is the westernmost range of the Western Sierras Pampeanas. This range is bounded by the Devonian sedimentary rocks of the Precordillera on the western side and Tertiary rocks from the Sierra de Maz and Sierra del Espinal on the eastern side and contains igneous and sedimentary rocks outcroppings from the Famatina System on the far eastern side. The Sierra de Umango evolved during a period of polyphase tectonic activity, including an Ordovician collisional event, a Devonian compressional deformation, Late Paleozoic and Mesozoic extensional faulting and sedimentation (Paganzo and Ischigualasto basins) and compressional deformation of the Andean foreland during the Cenozoic. A Nappe System and an important shear zone, La PuntillaeLa Falda Shear Zone (PFSZ), characterise the Ordovician collisional event, which was related to the accretion of Cuyania Terrane to the proto-Andean margin of Gondwana. Three continuous deformational phases are recognised for this event: the D1 phase is distinguished by relics of S1 preserved as internal foliation within interkinematic staurolite porphyroblasts and likely represents the progressive metamorphic stage; the D2 phase exhibits P-T conditions close to the metamorphic peak that were recorded in an S2 transposition or a mylonitic foliation and determine the main structure of Umango; and the D3 phase is described as a set of tight to recumbent folds with S3 axial plane foliation, often related to thrust faults, indicating the retrogressive metamorphic stage. The Nappe System shows a top-to-the S/SW sense direction of movement, and the PFSZ served as a right lateral ramp in the exhumation process. This structural pattern is indicative of an oblique collision, with the Cuyania Terrane subducting under the proto-Andean margin of Gondwana in the NE direction. This continental subduction and exhumation lasted at least 30 million years, nearly the entire Ordovician period, and produced metamorphic conditions of upper amphibolite-to-granulite facies in medium- to high-pressure regimes. At least two later events deformed the earlier structures: D4 and D5 deformational phases. The D4 deformational phase corresponds to upright folding, with wavelengths of approximately 10 km and a general NeS orientation. These folds modified the S2 surface in an approximately cylindrical manner and are associated with exposed, discrete shear zones in the Silurian Guandacolinos Granite. The cylindrical pattern and subhorizontal axis of the D4 folds indicates that the S2 surface was originally flat-lying. The D4 folds are responsible for preserving the basement unit Juchi Orthogneiss synformal klippen. This deformation corresponds to the Chanica Tectonic during the interval between the Devonian and Carboniferous periods. The D5 deformational phase comprehends cuspate-lobate shaped open plunging folds with EeW high-angle axes (D5 folds) and sub-vertical spaced cleavage. The D5 folds and related spaced cleavage deformed the previous structures and could be associated with uplifting during the Andean Cycle

A comprehensive review of the geological, geochronological, and isotopic features of the Mesoproterozoic Grenvillian terranes attached to the southwest of the Rio de la Plata craton in Early Paleozoic times is presented in this paper. They are grouped into the northern (sierras de Umango, Maz and del Espinal and surroundings), central (Sierra de Pie de Palo, southern Precordillera and Frontal Cordillera), and southern (San Rafael and Las Matras Blocks) segments. The Mesoproterozoic basement consists mainly of arc related, intermediate to acidic and mafic–ultramafic rocks of 1,244–1,027 Ma, with juvenile, Laurentian affinity. Exception to it is the Maz Group, with a protracted history and reworked character. They are affected by 846–570 Ma, extensional magmatism in the northern and central segments, which represents the Neoproterozoic breakup of the Rodinia supercontinent. Successive passive margin sedimentation is registered in Late Neoproterozoic (~640–580 Ma) and Cambro-Ordovician (~550–470 Ma) times. The southern segment is noted for the younger sedimentation alone, and for showing the exclusive primary unconformable relationship between the Mesoproterozoic basement and Early Ordovician cover. The effects of Early Paleozoic Famatinian orogeny, associated with the collisions of Cuyania and Chilenia terranes, are recorded as main phase (480–450 Ma), late phase (440–420 Ma), and Chanic phase (400–360 Ma). Among them, the tectonothermal climax is the Ordovician main phase, to which klippe and nappe structures typical of collisional orogens are related in the northern and central segments. Preliminary data allow us to suggest a set of paired metamorphic belts, with an outboard high-P/T belt, and an inboard Barrowian P/T belt.

The southern Brasilia Orogen is organized in a pile of nappes that records the Neoproterozoic history of the subduction and collision between passive and active margins, respectively belonging to the Sao Francisco and Paranapanema Plates. The whole pile of allochthons comprises the rootless Andrelândia Nappe System (the upper kyanite-bearing granulite of Tres Pontas-Varginha Nappe, the intermediate high-pressure amphibolite-to eclogite facies of Liberdade Nappe and the lower Andrelândia Nappe) that is located below an Andean-type magmatic arc (Socorro-Guaxupe Nappe) and overrides the Lima Duarte Nappe and the Carrancas Nappe System. The tectonic units of the Andrelândia Nappe System seem to be exotic to the Sao Francisco Plate. The retroeclogite of the Liberdade Nappe yielded a 670 Ma SHRIMP U–Pb age in zircon, that is interpreted as the age of N-MORB-type basic magmatism. Detrital zircon grains of proximal flysh deposits of wackes in the Andrelândia Nappe present similar ages that reflect the crystallization in its source area. Both, rocks present Nd isotopic juvenile signatures with TDM in the range of 1.4 to 1.1 Ga. Rhyacian orthogneisses occur as slices in the Liberdade Nappe and have Nd isotope signature of juvenile source. The building of the collision pile of the whole system of nappes was diachronic and records a continuous outward migration of the orogen. The main structure is a middle crust-level duplex. The propagation of the structure and the metamorphism advanced progressively from the upper to the lower nappes, as is shown by U–Pb monazite ages in the range of 618–595 Ma for the Andrelândia Nappe System and 590–575 Ma for the Carrancas and Lima Duarte nappes.

High-pressure granulites are formed within the lowermost continental crust. If exhumation is driven only by erosion, these granulites will remain at their site of formation indefinitely. Their exposure, then, requires a complex process. In this study, the Andrelândia Nappe System is used to investigate the formation and exhumation of high-pressure granulites related to subduction–collision–extrusion processes. This nappe system is part of the southern portion of the Neoproterozoic Brasilia Orogen in Brazil, which comprises a pile of syn-metamorphic rootless nappes in which high-pressure granulites are an important constituent. The Andrelândia Nappe System is thrusted by a magmatic arc allochthon, and it overrides the allochthonous passive margin that is represented by rocks of the Carrancas Nappe System. Metamorphism within the Andrelândia Nappe System presents an inverted pattern that varies from top to bottom and from granulite to amphibolite facies conditions under a high-pressure regime. The Carvalhos Klippe is part of the uppermost nappe and is located 60 km ahead of its original allochthon. This klippe is composed of rutile–kyanite–garnet–K-feldspar granulites, and it displays ternary feldspars and associated mafic granulites that in turn contain garnet–clinopyroxene–plagioclase–quartz as a peak mineral assemblage. Both granulite types crystallized at a higher pressure than the rocks within the orthopyroxene stability field. The kyanite-bearing granulites show a clockwise P – T path, which is inferred from reaction textures and thermobarometry. Peak conditions were attained at 825 °C and 12 kbar at 617.7 ± 1.3 Ma, which is determined by an ID-TIMS analysis of monazite. The convergent kinematic flow of the klippe was directed eastward, then northeastward, and finally changed northward to northeastward, which is contemporaneous with extension and thinning under high-temperature conditions. Melt-filled dilation shear zones were observed and the melt worked as a lubricant within the shear zones, facilitating granulite exhumation-extrusion.

The Major Gercino Shear Zone is one of the NE–SW lineaments that separate the Neoproterozoic Dom Feliciano Belt, of Brazil and Uruguay, into two different domains: a northwestern supracrustal domain from a southeastern granitoid domain. The shear zone, striking NE, is composed of protomylonites to ultramylonites with mainly dextral kinematic indicators. In Santa Catarina State, southern Brazil, the shear zone is composed of two mylonite belts. The mylonites have mineral orientations produced under greenschist facies conditions at a high strain rate. Strong flattening and coaxial deformation indicate the transpressive character, while the role of pure shear is emphasized by the orientation of the mylonite belts in relation to the inferred stress field component. The quartz microstructures point out that different dynamic recrystallization regimes and crystal plasticity were the dominant mechanisms of deformation during the mylonitization process. Additionally, the fabrics suggest that the glide systems are activated for deformation conditions compatible with the metamorphism in the middle greenschist facies. Elongated granitoid intrusions belonging to two petrographically, geochemically and isotopically distinct rock associations occur between the two mylonite belts. The structures observed in the granites result from a deformation range from magmatic to solid-state conditions points to a continuum of magma straining during and just after its crystallization. Conventional U–Pb analysis of multi-crystal zircon fractions yielded essentially identical ages of 609 ± 16 Ma and 614 ± 2 Ma for the two granitic associations, and constrain the transpressive phase of the shear zone. K–Ar ages of biotites between 585 and 560 Ma record the slow cooling and uplift of the intrusions. Some K–Ar ages of micas in regional mylonites are similar, suggesting that thermo-tectonic activity was intense up to this time, probably related to the agglutination of the granite belt to the supracrustal belt NW of the MGSZ.

The 590–580 Ma Itu Granite Province (IGP) is a roughly linear belt of post-orogenic granite plutons ~ 60 km wide extending for some 350 km along the southern edge of the Apiai–Guaxupe Terrane in southeastern Brazil. Typical components are subalkaline A-type granites (some with rapakivi texture) that crystallized at varied, but mostly strongly oxidizing conditions, and contrast with a coeval association of also oxidized high-K calc-alkaline granites in terms of major ( e.g. , lower Ca/Fe) and trace elements (higher Nb, Y, Zr). Mantle-derived magmas (such as those forming the LILE-rich Piracaia Monzodiorite, with eNd (t) = −7 to −10, 87 Sr/ 86 Sr (t) = 0.7045–0.7055) are inferred to derive from enriched subcontinental lithosphere modified during previous subduction, and may have played a role in the generation of the A-type granites, adding melts or fluids or both to the lower crust from which the latter were generated. The IGP is interpreted as a reflection of crust uplift and increased heat flux during ascent of hot, less dense asthenosphere after continental collision, probably reflecting breakoff of an oceanic slab coeval to the right-lateral accretion of a terrane related to the Mantiqueira Orogenic System.

The high-grade crystalline nappes exposed southeast of the Sao Francisco craton comprise two distinct units of mainly granulite facies rocks that represent a composite section of Neoproterozoic deep continental crust: the Socorro-Guaxupe nappe above, derived from an arc terrane, and the Tres Pontas-Varginha nappe below. Metamorphism in the Tres Pontas-Varginha nappe is characterized by the exceptional preservation of kyanite granulites (700–750°C, 15 kbar), and followed by limited retrogression. Maximum temperatures around 900–950°C were reached toward the base of the overlying Socorro-Guaxupe nappe during the intrusion of charnockitic-mangeritic magmas. Lower-pressure metamorphism, accompanied by anatexis, prevailed at shallower crustal levels. Our petrological results document an inverted thermal structure with isobaric heating of the top of the high-pressure granulite nappe. Both granulite nappes were transported more than 200 km eastward above lower nappes involving reworked basement and passive margin units, both metamorphosed to high-pressure but lower-temperature conditions. Significant thinning and cooling of the two granulite nappes may have occurred before their emplacement onto the lower nappes. The proposed geodynamic scenario considers that continental subduction took place westward underneath Neoproterozoic oceanic lithosphere. The two granulite units crystallised at ∼ 45 km depths under distinct paleogeotherms within this subduction zone around 630 Ma. The kyanite granulites were rapidely exhumed through the mechanism of low-angle “forced” extrusion, whereas syncollisional collapse affected the soft, anatectic middle crust of the overlying arc terrane. The final emplacement of the thinned nappe pile onto the cold Sao Francisco craton and its platform cover, with at most, anchizonal to greenschist-facies metamorphism, occurred around 600 Ma.

The lithostratigraphic units of the Canastra and Paranoa groups, to the west of the Minas Gerais State, were affected by five folding phases of the Brazilian Cycle. In the Canastra Groups, a disposition of 1 1 -lineations shows a probable ante-schistosity structure. The first two phases, almost homoaxial, are related to the syntectonic stage of the orogenesis and contained an axial-plane schistosity (S 1 and S 2 ). Both have tectonic vergency towards the Sao Francisco Craton and were affected by a thrust structure overcoming the Canastra Group over the Paranoa Group. There are three postschlstosity late phases with a random distribution in the region. Generally, each of the five fold phases shows a cilindric pattern.