This paper proposes to construct three-dimensional geological-geotechnical models using the geostatistical interpolation from geomechanics parameters of rocks as lithology and fracturing, plus Rock Designation Quality and Rock Mass Rating classification systems. Generally, the geostatistical interpolation is used to analyze the mining, but this project aims to optimize the prediction of the geological conditions during the initial assessment for infrastructure projects. In this way, the correct predictions of the geological conditions allow us to minimize the inherent risks of failures in the predictability of the structural and geometric patterns of the rocky mass in depth. The proposed procedure aims to ensure the safety of the workers during a complex enterprise. The control of the expenses, as well as the enterprise's durability after construction, promotes social, financial, and environmental security. This methodology has been applied using data from the construction of two different sites, located in Minas Gerais state (Brazil). It was used 44 drill data, 28 from site I and 15 from site II. The results of models showed that it is possible to predict the geological conditions using this geostatistical interpolation; it is possible to affirm that geostatistical interpolation has been effective in the evaluation of geomechanical parameters.

In this contribution, we report new P-T (pressure-temperature) and U-Pb zircon geochronological data from the Lima Duarte Nappe and basement rocks from the Mantiqueira Complex, Central Ribeira Orogen, southeastern Brazil, highlighting their relevance to the understanding of the West Gondwana assembly. The lower metasedimentary sequence of the Lima Duarte Nappe records a passive margin environment, with a majority of Paleoproterozoic detrital zircon grains, with probable main source rocks located in the Sao Francisco paleocontinent. The upper foreland sequence of the Lima Duarte Nappe has a prevalence of Tonian-Cryogenian detrital zircon grains, absent in the lower passive margin sequence and source rocks were most likely in a magmatic arc developed during the convergence between the Sao Francisco and the Paranapanema paleoplates. Zircon rims from the Lima Duarte passive margin and foreland sequences, and zircon grains from an amphibolite of the Lima Duarte Nappe record granulite facies metamorphism at ca. 560-590 Ma (Th/U ratio < 0.1). Similar ages are recorded by CL-dark zircon rims and overgrowths in orthogneisses of the Mantiqueira Complex and are interpreted to reflect basement reworking. Metapelitic metatexites from the foreland sequence record granulite facies peak metamorphism at - 780-800 C and 8-9.5 kbar in the sillimanite-rutile stability field, constrained by phase equilibrium modeling. Rutile inclusions in garnet record minimum peak temperatures of similar to 750 C-degrees. The retrograde mineral assemblage in the matrix is marked by the disappearance of rutile and the presence of ilmenite and mineral compositions re-equilibrated at upper amphibolite facies. Late Tonian (ca. 850-750 Ma) metamafic rocks within the Mantiqueira and Juiz de Fora complexes might record an extensional intraplate mafic magmatism episode that culminated with the establishment of the passive margin at the south of the Sao Francisco paleocontinent. The Lima Duarte metasedimentary sequence along with the Canastra and Carrancas groups (western and southern portions of the Brasilia Orogen, respectively) represent a Tonian proximal passive margin environment, developed at the margin of the Sao Francisco paleocontinent. The Lima Duarte Nappe metasedimentary units and the orthogneisses of the Mantiqueira Complex record Ediacaran syn-collisional metamorphism related to the Aracuai-Ribeira Orogenic System.

Featuring 3 000-km-long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (similar to 500 Ma) post-collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep-seated intrusions, ellipsoidal-shaped roots with gabbroic-to-hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE-trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith-size bodies of coarse-grained granite emplaced at the shallow to mid-crust, show general NS-trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice.

To optimize the prediction of structural geological conditions in the underground as of data collected at the surface, due to the usual great uncertainties involved, we discuss new perspectives for the construction of structural geological models, bearing in mind the common doubts involved and their implications in the safety of infrastructure works, mining, etc. This paper presents a statistical simulation applied to structural geological measures (dip-dip direction) obtained from schists during the design and construction of civil works through a correlation between surface data with different depth levels. Angular structural geological measures of joints and foliations converted in direction cosines were subjected to the PERMANOVA test to verify the amplitude of differences at different depth levels. The asymptotic results allowed to determine regions of confidence built around centroids through statistical simulation, allowable consistency was considered in regions where the differences in the simulated values were small enough from a practical point of view, considering that the difference between joint structures and foliation structures is smaller in the former. The foliation is a characteristic structure of rock deformation just like the joints.

The Neoproterozoic Araçuaí belt of eastern Brazil formed during the amalgamation of Western Gondwana and holds characteristics of a hot collisional belt, involving large amounts of magma, partial melting of the middle crust, and slow cooling rates. To improve our understanding of the mechanical behavior of the continental crust under these conditions we combined structural, magnetic, and geochronological studies to access information related to the flow of rocks, deformation history, and structural patterns associated with the behavior of this orogen. Anisotropy of magnetic susceptibility (AMS) coupled with rock magnetism investigations supports that the magnetic fabric is a good proxy of the structural fabric. Field and AMS measurements of syn-to late plutonic bodies hosted in metasedimentary rocks revealed four domains with contrasting fabric patterns. The structural patterns from W to E are characterized by westward thrusting orthogonal to the belt (region 1), orogen-parallel transpression induced strain partitioning (regions 2 and 3), and orogen-parallel flow and subsidiary eastward vergence magmatic flow (region 4). The use of AMS to determine the lineation was vital to unraveling the kinematics. The composite observed fabric results from the interplay of collision-driven and gravity-driven deformations, induced by the convergence between the São Francisco and Congo Cratons.

Large, hot orogens are characterized by an orogenic plateau supported by a zone of weak ductile flow. During the collision phase, the magnitude of the belt and the temperature increase as radioactive crustal material is accreted, buried and heated. After convergence ends, no material is added to the orogenic system and the orogen undergo gravitational (or extensional) collapse that results from the lateral flow of the hot orogenic infrastructure. In the Araçuaí-West Congo orogen (AWO), the high temperatures, slow cooling, and excessive amount of melt in the hinterland, in the northern part of the belt, imply that a high temperature was maintained for a long time. Geochronologic results suggest that this internal domain was hot for a long time, cooling at < 3°/Myr since 600 Ma until 500 Ma, and cooling through the Ar/Ar retention temperature for biotite occurred around 470 Ma. In the south the collapse of the orogen is marked by the widespread intrusion of bimodal, composite plutons at ~500 Ma. Here we use the magnetic fabric (i.e. low-field anisotropy of magnetic susceptibility) of intrusions in the north and south sectors to track the kinematics and rheological changes across the belt. In the northern part of the AWO we studied the Padre Paraíso Charnockite and the southern part of the AWO we studied the Conceição de Muqui and Santa Angélica plutons. The Padre Paraíso charnockite has a coherent magnetic fabric, with magnetic foliations trending N-S, following the general structure of the belt in that sector. In turn, Conceição de Muqui and Santa Angélica plutons show a concentric distribution of foliations and lineations, in starking contrast with the general NE-SW trend of the belt in the south. This contrasting structural pattern for coeaval plutons along the AWO belt reveal the strain partitioning at the scale of the orogenic belt during the cooling of the AWO. At 500 Ma the hot northern sector remains warm enough to allow a coherent deformation of intrusions and host rocks. At the same time, more material was being added to the margins of the hot orogen, which already cold, with the diapire-like plutons structure being dominantly controlled by the forces of magma ascent and emplacement.

The Aracuai Orogen (AO) has been interpreted as a Neoproterozoic example of a large, "hot" orogen, based on a broad zone (250 km) of midcrustal metamorphic assemblages with a long, 70-Myr history of crustal melting and episodic magmatism throughout the late Neoproterozoic and earliest Paleozoic. Here, we present results of U-Pb sensitive high-resoution ion microprobe (SHRIMP) zircon dating and detailed anisotropy of magnetic susceptibility (AMS) study on a late Cambrian, bimodal pluton related to final period of collapse of the AO. New U-Pb zircon ages constrain the crystallization age of different suites within the Santa Angelica Pluton, 506 +/- 3 Ma for the early felsic phase and 498 +/- 5 Ma for the mafic core. New AMS data indicate that the emplacement of the Santa Angelica Pluton corresponds to two coupled plutons with concentric structures arrayed about a twin, bull's eye pattern. During the final stages of intrusion, upward relative movement of the northeastern lobe exposed the deeper levels of the intrusion, relative to the more shallowly eroded southwestern lobe. These observations suggest that magma emplacement was controlled by magma buoyancy forces, with little influence of regional tectonic stress. This behavior contrasts with the well-defined, tectonic-controlled fabrics of coeval plutons occurring to the north which was still hot, therefore highlighting the contrasting thermal evolution between different sectors of the orogen during its final stages.

The Cristalandia do Piaui Block, located in the northwestern margin of the Sao Francisco Craton, represents the basement of the Rio Preto Fold Belt. It is composed of Archean orthogneisses of ca. 3.2 Ga reworked at 2.81 and 2.68 Ga with juvenile to moderately juvenile eHf values between -1.51 and -8.07, and high-K syenogranites dated at 2.65 Ga with crustal eHf values between -10.37 and -19.54, both with model ages (TDMc) varying from 3.57 to 4.33 Ga, indicating cryptic Paleo- to Eoarchean and even Hadean sources. Metamafic-ultramafic rocks, iron formations, metacherts, and graphite schists occur in association with the Archean orthogneiss. The whole set is intruded by Paleoproterozoic (ca. 2.2 Ga) metagranitoids with compositions varying from granodioritic with sanukitoid-type signatures tomonzogranitic, and alkali-feldspar graniticwith crustal signatures. They are related to the Rhyacian-Orosirian orogeny, responsible for the complex deformation patterns printed in the Archean basement. Orosirian metasedimentary rocks are represented by garnet-biotite paragneiss with maximum depositional age of ca. 1.95 Ga. Intrusive mafic dikes in the complex show ages of ca. 2.07 Ga and isotopic features of mantle-derived magmas. Considering the presented data, the Cristalandia do Piaui Block represents a metacratonic domain corresponding to part of the Guanambi-Correntina Paleoplate, wich had been involved in crustal accretion and reworking from the Archean to the Paleoproterozoic. Many of the elements of the evolutionary stageswich are present in the Sao Francisco-Congo Paleocontinent can be recognized, suggesting an evolution of this crustal segment amounts to the Eoarchean era and disclosing the existence of cryptic Paleoarchean or even Hadean nuclei, reworked in at least three metamorphic events during the Rhyacian-Orosirian orogeny. (C) 2020 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The Aracuai-Ribeira belt formed during the amalgamation of West Gondwana in the late Neoproterozoic. Its evolution encompasses a main tectono-metamorphic peak at 600-580 Ma and a minor one, associated with the final collision with the Western Congo at 540-530 Ma. This belt holds characteristics of a hot-orogen: high thermal gradient (>30 °C/km), pervasive partial melting of the middle crust, emplacement of huge volume of magmas resulting from partial melting of the lower crust and underlying mantle, and slow cooling after the peak of temperature. We report 21 new amphibole, biotite and muscovite 40Ar/39Ar ages, which complement data already published by our group. Altogether, these data support slow cooling (3-4 °C/Myr) during several tens of million years after the peak temperature (~800 °C at ~600 Ma), followed by faster cooling (>10 °C/Myr) after the final amalgamation of Western Gondwana. We estimate that ~30 Myr were needed to heat the middle crust to the peak of temperature and that anatectic and plutonic bodies remained in the magmatic state over at least 40 Myr. This protracted thermal evolution likely had major effects on the rheology of the middle crust and on the tectonic evolution of this orogen. For instance, correlation of U-Pb zircon crystallization ages and 40Ar/39Ar biotite cooling ages in the anatectic core of the orogen denotes a diachronic thermal evolution likely related to a 3D deformation characterized by successive upwelling of anatectic components, along a channel crosscutting pre-existent fabric (channel-flow type). This study also highlights that classical structural analysis techniques relying on changes in pressure or temperature conditions to identify the succession of deformation phases, cannot be used to decipher the tectonic evolution of hot, slowly cooling orogenic belts, where temperature varies weakly over tens of millipn years, allowing diachronic episodes of deformation to occur under almost similar pressure and temperature conditions.

The Aracuaf-Ribeira belt formed during the amalgamation of West Gondwana in the late Neoproterozoic. Its evolution included a main tectonometamorphic peak at 600-580 Ma and a minor peak associated with the final collision with the Western Congo at 540-530 Ma. This belt has the characteristics of a hot orogen, including a high thermal gradient ( > 30 degrees C/km), pervasive partial melting of the middle crust, emplacement of large volumes of magmas resulting from partial melting of the lower crust and underlying mantle, and slow cooling after the peak temperature. We report 21 new amphibole, biotite and muscovite 40Ar/39Ar ages that complement previously published data. These data suggest slow cooling (3-5 degrees C/Myr) over several tens of million years after the peak temperature (similar to 800 degrees C at similar to 600 Ma) followed by faster cooling ( > 10 degrees C/Myr) after the final amalgamation of West Gondwana. We estimate that -30 Myr was required to heat the middle crust to the peak temperature and that anatectic and plutonic bodies remained in the magmatic state for >= 40 Myr. This protracted thermal evolution likely had major effects on the rheology of the middle crust and on the tectonic evolution of this orogen. For example, the correlation of U-Pb zircon crystallization ages and 40Ar/39Ar biotite cooling ages in the anatectic core of the orogen denotes a diachronic thermal evolution likely related to 3D deformation involving successive upwelling of anatectic components within a thrust unit crosscutting the pre-existing fabric ("channel flow-like"). This study also highlights that classical structural analysis techniques relying on changes in pressure or temperature conditions to identify the succession of deformation phases are not efficient at deciphering the tectonic evolution of hot, slowly cooling orogenic belts, where the temperature varies slowly over tens of million years, allowing diachronic episodes of deformation to occur under nearly similar pressure and temperature conditions.

The parallelism between older collisional belts and younger rift systems is widely known and particularly well portrayed along the Atlantic Ocean. How tectonic inherited and new‐formed shear zones control rift nucleation and the final architecture of rifted conjugate passive margins is still poorly understood. Here we present lithospheric‐scale thermo‐mechanical numerical models that self‐consistently create extensional and contractional tectonic inheritance, where prior extension and contraction are systematically varied. Our results show that (1) initial reactivation occurs along the former lithospheric suture zones; (2) upper crustal thick‐skinned basement thrusts are partially or fully reactivated depending on the amount of prior contraction and size of the orogen; (3) with a small amount of contraction, thick‐skinned thrusts are efficiently reactivated in extension and provide the template for rifted margin formation; (4) with larger amounts of contraction, thick‐skinned thrusts distal to the lithospheric suture zone do not reactivate in extension; and (5) reactivation of prior contractional shear zones dominates during the early stages of rifting, while during the final stage of margin formation new‐formed extensional shear zones dominate. Force balance analysis predicts an inverse relation between midcrustal viscosity and the maximum offset for reactivation of weak upper crustal structures. Force balance also predicts that the degree of weakening or healing of the weak suture and the thermal thinning of the necking area control at which stage suture reactivation is deactivated and extension proceeds by mantle lithosphere thermal necking. Two rifted conjugate margins with orogenic inheritance in the North and South Atlantic are used for comparison.

Palinspastic reconstructions suggest that the late Proterozoic-Cambrian Brasiliano/Pan-African orogenic belt in southeast Brazil and west Congo terminated northwards into an embayment within the Sao Francisco-Congo cratonic unit. The orogenic shortening that created the Aracuai-West Congo orogen in this embayment has been explained by tightening of the horseshoe-shaped Sao Francisco-Congo craton in a fashion referred to as "nutcracker tectonics". We show that this model is incompatible with the general orogenic evolution proposed in recent literature, which involves (1) similar to 50 m.y. of subduction of oceanic crust and associated arc formation, followed by (2) collisional orogeny and crustal thickening. Quantitative considerations show that the original nutcracker model is too rigid to explain even the second, crustal thickening part, let alone any long pre-collisional history. To soften the model, we suggest that the so-called Sao Francisco - Congo bridge was broken by a similar to 150 km wide orogenic corridor along the current African Atlantic margin. This corridor adds sufficient mobility to the system to explain the orogenic thickening of the crust to 60-65 km. However, even with this additional softening the confined nature of this orogen is incompatible with prolonged arc development. We therefore suggest that oceanic crust was nonexistent or very limited in the Macaubas basin, and reject the widely published model involving similar to 50 m.y. of subduction of oceanic crust and related arc development. Instead, we find strong support for a hot intracontinental orogen model in the currently available P-T, geochronologic, petrographic and structural data. In this model, extensive melting and flow of the middle crust is likely to have caused spreading of the upper crust in an orogenic setting that was created by collisions along the N, W and S margins of the Sao Francisco craton from similar to 630 Ma.

Based on samples from the major high-temperature Tres Rios-Alem Parafba-Padua transpressive shear zone in the Ribeira orogenic belt, Brazil, we discuss the applicability of TitaniQ geothermometry to constrain peak temperature conditions during high-temperature mylonitization of quartzofeldspatic rocks, and explore the microfabrics formed at these conditions. We discuss various aspects of the TitaniQ method and conclude that deformation occurred at temperatures ranging from 612 to 740 +/- 20 degrees C in the studied segment of the shear zone. This high-temperature deformation resulted in relatively large grain size, quartz ribbons and abundant intracrystalline deformation. However, the CPO fabrics are weak, and microstructures suggest that quartz deformation was accommodated by dynamic recrystallization involving grain boundary migration with subsequent grain growth, and later some subgrain rotation during exhumation. We relate the weak fabrics to diffusion processes during or immediately after dynamic recrystallization and dislocation creep, and to the effect of competing slip systems during deformation. In terms of rheology, evidence for Dauphine twinning in our samples suggest strain softening during mylonitization, and we suggest that such twinning may add to the rheologically weak nature of quartzo-feldspatic portions of hot middle to lower crust.

Whether the Araçuaí and the Ribeira Neoproterozoic belts in southeast Brazil represent a continuous or two distinct orogenic belts is still a debated question. We compile existing geologic and geophysical data and argue that the two belts, in spite of differences in tectonic style and kinematics, should be considered as part of an orogenic continuity that formed during the mostly Late Proterozoic Brasiliano orogenic evolution. Structural mapping supported by Anisotropy of Magnetic Susceptibility data shows that the transition between the two belts is gradual, with a progressive change from a NE-trending subvertical foliation and subhorizontal stretching lineation in the Ribeira belt to gently dipping and less pronounced fabrics in the Araçuaí belt. The lineation progressively changes northward from NE to E-W, suggesting a transition from overall transcurrent to thrust kinematics, and the solid-state finite strain seems to get progressively higher into the Ribeira belt. Differences in tectonic style are explained by the southward termination of the rigid São Francisco craton, which caused oblique collision and lateral escape, as supported by numerical modeling. Shear-wave splitting measurements suggest that the transcurrent deformation in the Ribeira belt affected the entire lithosphere. In the transitional zone, the seismic anisotropy pattern is more complex and the delay time between the fast and slow shear-waves is smaller. These observations, together with a similar record of magmatism and timing of orogenic events and P-T conditions during peak metamorphism strongly support continuity between the Araçuaí and the Ribeira belts. This model is a "quasi-facsimile" of the Paleoproterozoic deformation that occurred in the Great Slave Lake area in Canada.

The Brazilian Paranurim belt divides the Sao Francisco Craton . At to the west and soulhwest occurs the Sao Francisco Craton (sensustrictu), and to the East is present lhe Salvador Craton, separated from lhe Congo-Zaire Craton by the opening of the Atlantic Ocean during Early Mesozoic time. The Archean-Early Proterozoic basement of lhe Paramirim belt was intruded by subalkaline granites approximately 1,700 Ma old. The Espinhaco Supergroup is the most important unit of the Paramirim belt. It's made up of detritic metasediments (quartzites, metaconglomerates, phyllites) with acid metamagmatic rocks (rhyolites-rhyodacites) in the lowerpart. The Espinhaco Supergroup was deposited in a continental rift during lhe interval 1,700 to 1,100 Ma. The Espinhaco Supergroup deformation is roughly dated at 600 Ma (Brazilian Tectonic Cycle). It is characterized by major ductile north-south low-angle shear zones and assymmetric folds wilh westward vergence. Astretching or/and minerallineation, transverse to the belt, indicates westward transport of materials. These ductile shear zones continue to the south, affecting the external units of de Aracuai fold belt and older (Early Proterozoic) units of the Quadrilatero Ferrifero (MG).

Together, the Rio Preto and Riacho do Pontal belts form a 600 km-long orogenic system developed along the northwestern and northern margins of the Sao Francisco craton during the Neoproterozoic Brasiliano orogeny. Involving the Paleoproterozoic (similar to 1.9 Ga) Formosa Formation (schist, quartzite, greenschist and amphibolite) and the Neoproterozoic (900-600 Ma) Canabravinha Formation (metadiamictite, metawacke, metaturbidite), the Rio Preto fold belt, exposed in Bahia and Piaui states, borders the craton to the northwest. Neoproterozoic deformation between 600 and 540 Ma originated a complex, asymmetrical and double-verging thrust wedge, whose southern branch propagated for over 100 km into the craton interior in form of a thin-skinned deformation front. The Rio Preto belt probably represents an inverted Neoproterozoic hemi-graben developed along the northern margin of the craton. The Riacho do Pontal fold belt occupies the northern margin of the craton. Its external zone is made up of a south-verging thin-skinned nappe system detached along the basement-cover contact. Ages of syn-to late-collisional granitic intrusions suggest that the main deformation phase in the Riacho do Pontal belt occurred between 667 and 555 Ma. The Barra Bonita Formation (quartzite, schist and marble), a correlative of the Una Group in craton interior (Paramirim aulacogen), represents a platformal unit, deposited on the northern Sao Francisco passive margin. The Monte Orebe metabasalts, exposed further north in the central sector of the belt, might represent remnants of a Neoproterozoic oceanic crust.

The presence of melt during deformation produces a drastic change in the rheological behavior of the continental crust; rock strength is decreased even for melt fractions as low as ∼7%. At pressure/temperature conditions typical of the middle to lower crust, melt-bearing systems may play a critical role in the process of strain localization and in the overall strength of the continental lithosphere. In this contribution we focus on the role and dynamics of melt flow in two different mid-crustal settings formed during the Brasiliano orogeny: (i) a large-scale anatectic layer in an orthogonal collision belt, represented by the Carlos Chagas anatexite in southeastern Brazil, and (ii) a strike-slip setting, in which the Espinho Branco anatexite in the Patos shear zone (northeast Brazil) serves as an analogue. Both settings, located in eastern Brazil, are part of the Neoproterozoic tectonics that resulted in widespread partial melting, shear zone development and the exhumation of middle to lower crustal layers. These layers consist of compositionally heterogeneous anatexites, with variable former melt fractions and leucosome structures. The leucosomes usually form thick interconnected networks of magma that reflect a high melt content (>30%) during deformation. From a comparison of previous work based on detailed petrostructural and AMS studies of the anatexites exposed in these areas, we discuss the rheological implications caused by the accumulation of a large volume of melt “trapped” in mid-crustal levels, and by the efficient melt extraction along steep shear zones. Our analyses suggest that rocks undergoing partial melting along shear settings exhibit layers with contrasting competence, implying successive periods of weakening and strengthening. In contrast, regions where a large amount of magma accumulates lack clear evidence of competence contrast between layers, indicating that they experienced only one major stage of dramatic strength drop. This comparative analysis also suggests that the middle part of both belts contained large volumes of migmatites, attesting that the orogenic root was partially molten and encompassed more than 30% of granitic melt at the time of deformation.