Programa de Pós-Graduação em Geodinâmica e Geofísica
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Doctoral Thesis Cartografia dos enxames de diques máficos da Província Borborema com base em dados aerogeofísicos e mapas auto-organizáveis(Universidade Federal do Rio Grande do Norte, 2021-04-30) Melo, Alanny Christiny Costa de; ; http://lattes.cnpq.br/8279954644750743; ; http://lattes.cnpq.br/6542699550245691; Medeiros, Walter Eugênio de; ; http://lattes.cnpq.br/2170299963939072; Souza, Zorano Sérgio de; ; http://lattes.cnpq.br/1259445348649589; Carneiro, Cleyton de Carvalho; ; http://lattes.cnpq.br/2853220869923540; Archanjo, Carlos José; ; http://lattes.cnpq.br/0302090618069167Mapping widespread dyke swarms shed light on the tectonic processes that culminate in continental fragmentation, especially in the early phases of the crustal extension and magma emplacement. Airborne magnetic data are an effective geophysical tool to clarify the extent of dyke swarms in continental-scale areas due to the expressive magnetic contrast between magmatic bodies and host rocks. However, many geological features display similar magnetic patterns, making the qualitative interpretation of magnetic anomalies quite subjective and ambiguous. To improve and optimize the predictive mapping of dyke swarms, this research presents a multivariate analysis of airborne geophysical surveys, applying a Self-Organizing Maps (SOM) approach using two magnetic and three gamma-spectrometric variables. The SOM method was applied to investigate a set of mafic dyke swarms that intruded in the Neoproterozoic Borborema Province (BP), Parnaíba Basin (PB) and the São Francisco Craton (SFC) in NE Brazil. These dykes are part of a large magmatic event associated with the supercontinent Pangea breakup, which formed the Equatorial Atlantic Ocean in the Early Cretaceous, denominated EQUAMP. First, the SOM hyperparameters were defined by running the algorithm in a representative area in the central part of the BP. This training area worked as a SOM template, through which all data from the study area were processed. The SOM analysis identified seven different populations, according to responses found in the five geophysical input variables. Two of these populations were associated with the mafic dykes, reducing the subjectivity of the magnetic anomaly interpretation. These populations represent high SOM quantization error, which means that these groups are the most anomalous values, evidenced in airborne magnetic data. These results was checked during fieldwork, revealing that dyke swarms occur more widely than was previously known, throughout the BP, intruding the SFC, and showing some occurrences intro in the Paleozoic sedimentary infill of the eastern border of the PB. We also apply anomaly enhancement techniques to magnetic data to obtain the spatial distribution and depth estimate of the causative sources. A structural analysis was carried out, integrating magnetic patterns, field data and a compilation of previous geological maps to describe the detailed distribution of the dyke swarms in BP. Our analyses demonstrated that the dyke swarms extend over 6.8 x106 km2. The 1388 mapped mafic dykes are grouped in three distinct swarms: 1135 – Rio Ceará-Mirim (RCM); 168 – Canindé (CD); and 86 – Riacho do Cordeiro – RC. The dyke swarms show three preferential trends to E-W, NW-SE and NE-SW. The swarms intrude both the Precambrian basement units and the Cretaceous sedimentary basins. The geometry and structural analysis of the dykes allowed interpreting the paleostress field active at the intrusion time. To the RCM, the paleostress trajectories represent a N-S extension, rotating to NW-SE in the western portion of the swarm. While for CD, the paleostress orientation shows a NW-SE extension rotating to NE-SW. As for the RC, the trajectories were similar to those traced for the RCM, showing a predominant NW-SE extent.Doctoral Thesis Efeito térmico provocado pelo pluton ediacarano Umarizal em rochas do Grupo Seridó (RN): implicações estruturais, mineralógicas e petrofísicas(Universidade Federal do Rio Grande do Norte, 2020-12-17) Valcácio, Samir do Nascimento; Souza, Zorano Sérgio de; ; http://lattes.cnpq.br/1259445348649589; ; http://lattes.cnpq.br/0427498123851341; Vilalva, Frederico Castro Jobim; ; http://lattes.cnpq.br/6227637633613443; Moreira, José Antônio de Morais; ; Trindade, Ricardo Ivan Ferreira da; ; http://lattes.cnpq.br/3934334115083849; Neves, Sérgio Pacheco; ; http://lattes.cnpq.br/7440413221171078The northeastern portion of the Borborema Province (PB), in northeastern Brazil, is marked by a voluminous Ediacaran magmatism that intrudes the paleoproterozoic gneiss-migmatitic basement (the Caicó Complex) and neoproterozoic metasupracrustal rocks (the Seridó Group). In this context, the Umarizal pluton, the focus of this work, is classified among the magmatic Ediacaran types as the Charnockite Alkaline suite (ChAlk). The main objective of this research is the reevaluation of previous interpretations through new field and geochemical data, emplacement mechanism reevaluation, dating of plutonic rocks and neosome of thermally affected hosting units, and thermal modeling of magma cooling. The obtained results showed that the magmatic suite is composed of three distinct petrographic facies, where the Umarizal and Ação facies are restricted to the Umarizal pluton and the Lagoa facies is found as minor bodies intruding the Tourão pluton and satellites bodies. Usually, the ChAlk Suite is composed of quartz-syenite and quartz-monzonite and their charnockitic equivalents. Structurally, the main pluton is emplaced between the NE-SW Portalegre (PaSZ) and NE-SW Frutuoso Gomes (FGSZ) shear zones. Field criteria suggest that these lineaments had progressive movements, beginning with synistral strike-slip kinematic for the PaSZ and extension for the FGSZ that favoured the emplacement of the Umarizal magma, and finished with dextral transcurrence for the PaSZ and thrusting for the FGSZ. Synchronously with magma emplacement, a thermal aureole of up to 2 km thickness was formed in Formação Jucurutu country rocks, with Buchan-type metamorphic associations registered in andaluzite + sillimanite in paragnaisse, scapolite in calciosilicatic gneiss and flogopite in marble. Zircon U-Pb age of 583 ± 1.8 Ma of a neosome is similar, within error, to the zircon U-Pb ages of the Tourão (589.3 ± 4.4 Ma) and Umarizal (587,2 ± 2,3 and 563,7 ± 6,2 Ma) plutons. Modal and lithogeochemical compositions configure two suites for the AlkCh association, one of probable mantle-derived (gabbro-norites, anorthosites) and another crustal-derived (granites and charnoquites), thus characterizing an anorthosite - mangerite - rapakivi-granite – granite magmatic association. Mineralogical variation from the least differentiated to the most evolved facies suggests the dominance of anhydrous conditions (fayalite, hyperstene, diopside-hedenbergite) at the beginning of crystallization to water subsaturated at the end of evolution and then favouring the formation of hornblende and biotite. Initial crystallization conditions of the charnockite suite indicate control by the fayalite-magnetite-quartz buffer, with pressures of ~9 kbar and temperatures in the order of 900-1100 ° C. On the other hand, geothermobarometric data using Al-in hornblende allowed to calculate approximate conditions of 4.5 ± 0.6 kbar and 755 ± 32 ° C for the final crystallization stage and emplacement. The integration of mineralogical and petrophysical data of the plutonic units and the thermal aureole permitted the thermal modeling of the cooling magma, being coherent with conditions of high geothermal gradient (40 °C/km), thermal metamorphic peak about 15,000 - 80,000 years after emplacement, and thermal conditions extending to 2 km away from the contact. Considering the existence of countless other batholithic bodies of the same age in this part of the PB, it is proposed that the Ediacaran was a period of extensive crustal heating under conditions of high geothermal gradient, possibly due to the heating driven by underplating of mantelic (gabbro-norite) magmas.Master Thesis Tomografia de ruído sísmico de ambiente na Província Borborema com estações de período curto(Universidade Federal do Rio Grande do Norte, 2020-08-27) Silva, Cícero Costa da; Casas, Jordi Julia; ; ; Nascimento, Aderson Farias do; ; Rocha, Marcelo Peres;Analysis of ambient seismic noise has proved to be a viable alternative to earthquake-generated seismic wave analysis. Although for a long time it was commonly discarded from earthquake recordings, it has been shown that the cross correlation of ambient seismic noise allows the recovery of the Green’s function between receivers. Moreover, seismic noise has the property of propagating uninterruptedly and independently of the occurrence of earthquakes, allowing for high resolution tomographic studies in low seismicity regions. Over the past two decades, the correlation of seismic noise between pairs of seismographic stations has been widely utilized in surface-wave tomography studies. In particular, for the northeast Brazil region, tomography studies used temporary and permanent broadband stations to investigate the deep structure (upper crust) of the Borborema Province; however, in addition to the broadband stations mentioned above, there is a large volume of data collected by 22 short-period stations that could improve the resolution of these tomographic studies. Thus, the goal of this MSc dissertation is to investigate whether short-period data: (i) can be used in surface-wave tomography studies, and (ii) can be combined with broadband data in a single tomographic inversion. Through the cross correlation of the recorded ambient seismic noise between short-period stations and subsequent stacking, the emergence of the dispersive, fundamental-mode Rayleigh waves was verified. It was also found that the dispersion curves (group and phase) could be satisfactorily obtained for periods of up to 10 s (after removal of the instrumental response), using standard surface-wave analysis techniques, and that it was indeed feasible to invert them together with dispersion curves from broadband recordings. The results obtained in the Borborema Province show that, for the 5 to 10 s period range, it was possible to define structures such as the Sergipe-Alagoas basin and the Borborema Plateau, which were not well delineated in previous tomographic studies.Master Thesis O Batólito Catolé do Rocha (RN-PB): reavaliação de um magmatismo granítico de tipo-A no Domínio Rio Piranhas Seridó, Província Borborema, NE do Brasil(2020-01-31) Oliveira, Robson Rafael de; Vilalva, Frederico Castro Jobim; ; ; Florisbal, Luana Moreira; ; Souza, Zorano Sérgio de;The Catolé do Rocha Batolith (CRB) belongs to the geological context of the northerncentral portion of Borborema Province (NE Brazil), to the west of the Rio Piranhas Seridó Domain, and is an important example of the tectono-magmatic event that affected this geotectonic unit during the Brasiliano Cycle (ca. 571 ±3 Ma). The CRB is composed of metaluminous to slightly peraluminous syenogranites to quartz syenites (granitic facies), basic-intermediate rocks and subordinate microgranitic dykes and / or pockets. These rocks intrude paleoproterozoic rocks of the Caicó Complex and Poço da Cruz Suite. The CRB has been considered a member of the porphyritic high-K calc-alkaline granitic suite in this part of the Borborema Province, that encompasses rocks with chemical affinities akin to the Itype granites. This work presents a review of the geology, petrography, mineralogy and chemistry (whole-rock and mineral chemistry) of the CRB, in order to better define its chemical and typological classification. The CRB granites present alkali-calcic to alkaline affinities, given by relatively high alkali contents relative to CaO. They also have ferroan character, with high Fe/Mg ratios, as well as significant concentrations of LIL and HFS elements, and relative enrichment of light over heavy rare earth elements. Their mafic minerals are Fe-enriched, including annitic biotite and ferro-edenite and hastingsite. Based on the geochemical characteristics, the CRB granites classify as post-collisional A2-type granites. Geothermobarometric calculations point to crystallization temperatures at ~750– 950oC and pressures between 4.6–6.3 kbar. Oxygen fugacity estimates, obtained from the amphiboles, biotite and zircon chemical compositions, indicate that CRB was formed under reduced conditions (-4 < ΔQFM < -1). Therefore, the CRB can also be interpreted as a reduced A2-type granite batholith. Chemical evidences and contrasting redox crystallization conditions for the CRB granites and basic-intermediate rocks suggest they represent distinct magma batches, with local mixing and mingling. An inferred petrogenetic model involve partial melting of a enriched (metasomatized) source and magmatic differentiation driven mainly by fractional crystallization processes (FC). The predominance of FC processes for the CRB granites is supported by petrographic evidences (e.g. concentrically zoned plagioclase) and by multielement diagrams showing pronounced troughs for Ti, P, and Sr, which suggest ilmenite, apatite, and plagioclase and/or hornblende fractionation.Master Thesis Geoquímica, evolução magmática e condições de cristalização do pluton São João do Sabugi, RN(2020-01-30) Paiva, Dayvison Bruno Cordeiro de; Vilalva, Frederico Castro Jobim; ; ; Bertotti, Anelise Losangela; ; Nascimento, Marcos Antonio Leite do;The São João do Sabugi pluton, nearby the homonymous city in the Rio Grande do Norte state, is one of the most expressive individual occurrences of shoshonitic rocks within the Rio Piranhas-Seridó Domain of the Borborema Province. Therefore, a detailed study of these rocks allows a better understanding of the genetic and evolutive processes of the shoshonitic suite in the northern Borborema Province. The pluton was object of petrographic and litochemical studies, including geochemical modelling, in order to characterize their magmatic differentiation processes and intensive crystallization parameters. The identified lithotypes were grouped into three petrographic facies: (1) gabbro-dioritic facies (more mafic rocks), of restrict occurrence, made of dioritic and gabbroic rocks with andesine-labradorite (An45-63%) and the mafic paragenesis clinopyroxene ± orthopyroxene + amphibole ± biotite; (2) monzodioritic, composed of mafic to intermediate rocks, from diorites and monzodiorites to quartz-monzonites, with the mafic paragenesis amphibole + biotite (as well as pyroxenes in the more mafic varieties) and oligoclase-andesine (An22-45%); and (3) granodioritic, with the most felsic lithotypes within the pluton, varying from quartz monzonites to granodiorites, with biotite as the main mafic, as well as higher contents of orthoclase. Mafic and intermediate enclaves and xenoliths of the Jucurutu Formation (calc-silicate rocks and paragneisses) are common in the monzodioritic facies. The studied rocks are metaluminous, alcali-calcic and magnesian, and have shoshonitic affinity. They show relatively high contents of Ba, Rb, Th, K, and light rareearth elements, and pronounced negative Nb anomaly in primitive mantle-normalized diagrams. The clinopyroxenes and amphiboles in the monzodiorites are chemically classified as augite and ferro- and magnesium-hornblende, respectively, whereas the biotite is a relatively Mg-enriched (0.44 < Mg/(Mg+Fe) < 0.65) variety. Available geochemical data suggest the studied rocks are cogenetic. Major and trace element modeling reveal that the least evolved compositions of the gabbro-dioritic facies can be generated through ~12% of partial melting of a metasomatized mantle source. From these precursor magmas, the monzodioritic and granodioritic facies can be derived after ~60 to 80% of fractional crystallization associated to the assimilation of ~15% of country-rock materials from the Jucurutu Formation. The São João do Sabugi pluton crystallized at temperatures between 788 816oC, and pressures of 5 6 kbar, under relatively oxidizing conditions (1.2<NNO<1.4).Master Thesis Evidências geofísicas de domeamento na estruturação profunda da porção central da Faixa Seridó (NE-Brasil)(2020-01-08) Domingos, Nitzschia Regina Rodrigues; Medeiros, Walter Eugênio de; ; ; Archanjo, Carlos José; ; Medeiros, Vladimir Cruz de;The Seridó Belt (SB) is a Neoproterozoic schist belt in Borborema Province, northeast Brazil. It was deformed and metamorphosed in the context of the Pan-African/Brasiliano orogeny. During this tectonic event, the crust was partially melted, particularly at the connection between the Patos shear zone and SB, thus altering its rheological properties and, consequently, influencing its deformation. Among the occurrences of rocks associated with partial melting, the Santa Luzia anatetic dome (c. 575 Ma) is particularly noteworthy. The aeromagnetic map of SB shows an expressive long-wavelength (˃25 km) regional anomaly in the south-central part of the area. This anomaly is sigmoidal in shape and its central axis rotates from NNE-SSW to E-W near the Patos shear zone. Local anomalies with small wavelengths (<25 km) and large amplitudes (up to 2200 nT) overlap this regional anomaly. The limits of the magnetic anomalies often coincide with regional shear zones, thus revealing that the shear zones exert important tectono-structural control on the anomaly sources. Comparison with gravity data shows that both types of anomalies share the same common anomalous sources, being more magnetic and less dense than the surrounding crust. On the other hand, correlation with surface geology shows that the geophysical anomalies often occur in association within homogeneous magnetite-bearing migmatites and granites. We adopted two modelling approaches to analyse the available geophysical datasets. First, a three-dimensional (3D) automatic constrained inversion of the magnetic data was performed and, second, a two-and-a-half-dimensional (2.5D) interpreter-guided joint model was constructed based on magnetic and gravity datasets from three profiles. Through this work, we show the existence of a regional domical structure in the south-central part of SB. This large-scale gneiss dome is composed of four elongated internal structures, geophysically modelled as four anomalous bodies, besides the surrounding material. Together, these form a crustal structure with a long axis in the NE-SW direction that rotates to the E-W direction following the Patos shear zone. The Santa Luzia dome is a local small-scale example of this crustal-scale structure. The metasediments of the Seridó Group occur along synforms surrounding the internal structures that form the regional dome. In particular, because of the remarkable role of the Patos shear zone in shaping this crustal dome, the conception that the Patos shear zone was a very important tectonic constraint during the Pan-African/Brasiliano orogeny.Master Thesis Análise da sequência sísmica de 2017 no Noroeste da Bacia Potiguar(2019-12-05) Fonsêca, José Augusto Silva da; Ferreira, Joaquim Mendes; ; ; Santana, Flávio Lemos de; ; Borges, Sérgio Vieira Freire;The understanding of earthquake occurrence in intraplate areas has been one of the most difficult tasks in Seismology. Attenuation of seismic waves in these areas is lower compared to border plate regions. As a consequence, even moderate magnitude earthquakes can represent great hazard. In this case, assessing the stress field in intraplate regions is important to better understanding the earthquake generating mechanisms. We analyzed 241 earthquakes of the 2017 seismic sequence in NW Potiguar Basin and estimated the stress regime. Seismically defined faults were determined for 4 high-precision relocated NWSE- and NE-SW-trending clusters. Faulting intersection acting in one of this clusters was representative for suggest Intersection model for intraplate earthquakes as possible explanation about why moderate size earthquake occur in the study region. Another cluster presented an en echelon fault with a clear spatiotemporal evolution and occurrence of almost entire activity in very short period, which suggests energy build-up and rapidly release between this fault segment. We were be able to calculate composite focal mechanism for three clusters, with predominant sinistral strike-slip faulting. The inversion of focal mechanisms reinforce evidence for a superposition of local and regional stresses, with major compressional axis subparallel to continental equatorial margin.Master Thesis Estilo estrutural e contexto tectonoestratigráfico do Grupo Ubajara no NW do Ceará(2018-09-03) Souza, Roanny Assis de; Jardim, Emanuel Ferraz; ; ; Medeiros, Vladimir Cruz de; ; Souza, Zorano Sérgio de;The Ubajara Group is a neoproterozoic (of ediacaran age) low grade metassedimentary unit (ediacaran) that occurs adjacent to the TransbrasilianoKandi Lineament, in NW Ceará. This lineament corresponds to a NE-trending dextral strike-slip mega-shear zone related to the Brasiliano orogenic cycle. The Ubajara Group is part of the Middle Coreaú Domain, being completely surrounded by medium to low temperature shear zones that define its contact either with the Martinópole Group (also of neoproterozoic, tonian age, deformed at a higher strain and metamorphic grade) and gneissic-migmatitic terrains (paleoproterozoic to archaean). In its SE border, the Ubajara Group is in contact, through a NE-trending dextral transcurrent fault, with the ediacaran-cambrian Jaibaras Group, that fills the homonimous graben. The essentially tectonic contacts make it difficult to interpret the stratigraphic-structural context of the Ubajara Group and the metamorphic-structural contrast with the Martinópole Group and the gneissic-migmatitic terrains is evident. In addition, the absence of a nonconformity at the base of the Ubajara Group poses the hypothesis of expressive alloctony of this unit, preceeding the deposition of the Jaibaras Group. The Ubajara Group is involved in a complex deformation pattern with conytractional ans transcurrent structures related to the Brasiliano Cycle. The present work focuses on the structural style and tectonostratigraphic relations of the Ubajara Group with other adjacent units, through the interpretation of remote sensing imagery, field and microscale structural data. The second phase (D2) comprises ductile, transcurrent structures with dextral kinematics, including NEtrending steep-dipping shear zones, low-rake stretching lineations and open to tight folds with (S2) foliation trends varying from NS to NNE. The horn shape of the Mucambo Granite denotes the control of this phase during its emplacement. Finally, a late stage evolution to ductile-brittle or brittle structures also shares the same dextral transcurrent kinematics that characterizes the D2 phase (being thus referred as D2t). It is expressed by NE-trending normal dextral faults and E-W to ENE normal faults and extensional joints, being correlated to the transtensional tectonics that controls the Jaibaras pull-apart graben. In some mylonitic bands it is observed the raising of metamorphic grade. The main belt produced mylonitization in originally E-W trending subvolcanic granite dikes that filled extensional joints related to a transtensional termination site close to the Meruoca Pluton. The outstanding metamorphic-structural contrast of the Ubajara Group, as regards to the older units, as well as the lack of a non conformity in its base, point to an expressive alloctony, combining (D1) tangential transport and (D2) dextral transcurrent displacements, the latter associated with LTB. Finally, the final site of occurrence of the Ubajara Group was shaped by (D2t) transtensional structures correlated to those that shaped the jaibaras Graben.Master Thesis Granitos de afinidade alcalina nos domínios rio Piranhas Seridó e São José do Campestre (Província Borborema, NE do Brasil): estudo comparativo e reavaliação das condições de cristalização(2018-09-03) Dalan, Clarissa de Aguiar; Vilalva, Frederico Castro Jobim; Nascimento, Marcos Antonio Leite do; ; ; ; Galindo, Antonio Carlos; ; Florisbal, Luana Moreira;The ediacaran granitic magmatism of alkaline affinity (A-type) within the São José do Campestre (SJC) and Rio Piranhas-Seridó (RPS) Domains, in northeastern part of the Borborema Province, is represented by the Japi, Caxexa, Serra do Boqueirão, Serra do Algodão, Olho D’Água and Serra Negra do Norte plutons, and by the Flores stock. This work presents an integrated and comparative petrographic and chemical (whole-rock and mineral chemistry) study among these plutons, with the main focus on the revaluation of the intensive crystallization parameters (P, T, ƒO2), in light of new geothermobarometric calibrations and crystallization modelling with the rhyolite-MELTS software. In order to provide a regional understanding of this magmatism, the results are compared with available data for chronocorrelated A-type granites within the Transversal Zone (TZ) Domain of the Borborema Province. Based on petrographic data, the plutons are divided in two groups: (1) plutons intrusive into the SJC Domain (Japi, Caxexa, Serra do Algodão, Serra do Boqueirão and Olho D’Água) that are made mainly of alkali-feldspar granites, syenites and syenogranites, with calcic amphibole and/or calcic and sodic-calcic clinopyroxene. (2) plutons that crop out in the RPS Domain (Serra Negra do Norte and Flores), comprising syeno- and monzogranites with biotite ± calcic amphibole and clinopyroxene (Serra Negra do Norte). Titanite, apatite, zircon and opaque minerals are the main accessories. Andradite is found in the Caxexa and Serra do Algodão plutons, and primary epidote in the Serra Negra do Norte. Overall, the studied rocks show well-defined alkaline to alkali-calcic affinities in lithochemical diagrams. They are iron-rich (ferroan) and have meta- to peraluminous character. The Serra Negra do Norte pluton differs by showing more magnesian compositions that approach those typical of calc-alkaline granites (cordilleran I-type). The mafic minerals follow the chemical signatures of their hostrocks. Clinopyroxenes vay from diopside and augite (Serra Negra do Norte and Japi) to hedenbergite and aegirine-augite (Caxexa, Serra do Algodão); amphiboles are mainly Mgferri-horblende, and the biotite is annite, with more magnesian compositions in the Serra Negra do Norte granites. The Caxexa, Serra do Algodão, Serra do Boqueirão and Olho D’Água plutons share petrographic and chemical similarities with peralkaline granites of the TZ Domain, whereas the Flores stock are akin to meta- to peraluminous A-type granites of the Alto Moxotó and Alto Pajeú terrains inside the ZT Domain. The Japi, and mainly the Serra Negra do Norte plutons are transitional, with chemical similarities sometimes with one group, sometimes with another. The revaluated thermobarometry reveals that the studied granites crystallized under pressures of 3.0–3.7 kbar (~11–14 km at depth), except for those of the Japi pluton, with average pressures of 5.3 kbar (~20 km) that are akin to those found for the A-type granites in the Alto Moxotó and Alto Pajeú terrains. Crystallization modelling yielded liquidus temperatures in the range 885–917 oC, and 818 oC for the Flores stock, and solidus between 660–700 oC. When they are present, clinopyroxenes, amphiboles and biotite formed between 813–822 oC, 728–751 oC, and 750–789 oC, respectively. Among the accessories, the geothermometer Zr-in-titanite gave temperatures of about 780 oC (maximum of 830 oC). Crystallization took place under essentially oxidizing conditions for most of the plutons (+1.0 < ΔQFM < +2.1; +0.4 < ΔNNO < +1.5), except for the Flores stock formed under slightly more reduced conditions (ΔQFM ≈ 0.0; ΔNNO ≈ -0.6).Doctoral Thesis Estrutura do manto superior sob a Província Borborema através de tomografia telessísmica de onda P: implicações para o soerguimento, vulcanismo intraplaca e abertura do atlântico equatorial(2018-02-28) Simões Neto, Flodoaldo de Lima; Casas, Jordi Julia; ; ; Bezerra, Francisco Hilário Rego; ; Rocha, Marcelo Peres; ; Sacek, Victor; ; Medeiros, Walter Eugênio de;The Borborema Province is a geological and structural domain located in the Brazilian Northeast, which is limited to the South by the São Francisco craton, to the West by the Parna´ıba basin, and to the North and East by a number of marginal basins. Its basement consists of Paleoproterozoic rocks and Archean nuclei underlaying metamorphic supracrustal rocks with ages that span the entire Proterozoic eon. Its structuration occurred during the Brasiliano/Pan African orogeny, at the end of the Neoproterozoic, resulting in a complex orogenic system affected by ductile, metamorphic, and magmatic deformational processes. During the Mesozoic, the evolution of the Borborema Province was marked by extensional events that eventually led to continental breakup and the opening of the Atlantic Ocean. The separation formed a rift system in the Brazilian Northeast that was ultimately responsible for the formation of the marginal and interior basins that pervade the Province. After continental breakup, the evolution of the Province was characterized by episodes of intraplate volcanism along the Macau Queimadas Alignment (MQA) and tectonic uplift in the Borborema Plateau, which displays an elliptic topography and is located in the western half of the Borborema Province with maximum elevations of approximately 1200 m. In order to understand the origin of the intraplate volcanism and uplift after the opening of the Atlantic Ocean, P-wave (and PKPdf) relative residuals from teleseismic earthquakes were utilized to develop tomographic images of the upper mantle under the Borborema Province. About 120 events with magnitudes 5.5 and above, totaling over 1900 relative residuals, were mapped in three dimensions as P-wave velocity perturbations in the upper mantle under the recording seismic stations, through tomographic inversion. Among the main features displayed by the tomographic images are: (i) a relatively shallow low-velocity anomaly (< 150 km), located under the northeastern most corner of the continent and close to the Cenozoic volcanism, and (ii) a high-velocity lithospheric mantle (< 250 km) South of the Patos Lineament – approximately coinciding with the Southern half of the Borborema Plateau – when compared with the lithospheric mantle to the North. These results suggest that the origin of the Cenozoic volcanism might be related to a relatively shallow thermal anomaly at the corner of the continent, and that the Patos Lineament is a lithospheric-scale suture zone that separates contrasting mantle rheologies. The more rigid rheolgy to the South of the Patos Lineament is consistent with an independent tectonic model that explains the topographic elevation of the Borborema Plateau. The images also reveals a low-velocity channel bordering the Borborema Plateau at asthenospheric (250- 400 km) depths. The lithospheric velocity contrast is interpreted as arising from a colder, stronger lithosphere south of the lineament, while the asthenospheric low-velocity channel is interpreted as resulting from lateral flow from a distant mantle plume (located in SE Brazil). The rigid lithosphere South of the Patos Lineament might have also affected the stress regime during the opening of the Equatorial Atlantic. The equatorial region marked the last phase of continental breakup, and displayed a stress regime that contrasted with that in other segments of the Atlantic rift. A cold and rigid lithosphere at the Earth’s equator was independently postulated by other authors to explain the anomalous opening of the Atlantic Ocean in the equatorial region. However, theoretical calculations for the equatorial stress field developed in this work demonstrate that a cold and rigid equatorial lithosphere would have resulted in a stress rotation opposite to that inferred from geological observations. Additionally, the presence of a cold and rigid lithosphere contrasts with the tomographic results developed for the Borborema Province. Thus, a new tectonic model for the opening of the Atlantic Ocean in the equatorial region is proposed, in which Precambrian structures and lithospheric delamination – assisted by the St. Helena mantle plume – would have been responsible for stress transfer and rotation during the various rifting stages across the Equatorial region.