Arquitetura deposicional e evolução tectono-estratigráfica das sequências pré-rifte e rifte, na porção central do Vale do Cariri, Bacia do Araripe, NE do Brasil

A complex depositional history, related to Atlantic rifting, demonstrates the geological evolution during the late Jurassic and early Neocomian periods in the Araripe Basin NE Brazil. Based on outcrop, seismic and remote sensing data, a new model of the tectono-stratigraphic evolution of the section that covers the stages Dom João, Rio da Serra and Aratu (Brejo Santo, Missão Velha and Abaiara formations) is presented in this paper. In the stratigraphic section studied, ten sedimentary facies genetically linked to nine architectural elements were described, representing depositional systems associated with fluvial, aeolian and deltaic environments. Based on the relationship between the rates of creation of accommodation space and sediment influx (A / S) it was possible to associate these depositional systems with High and Low accommodation system tracks. These system tracks represent two tectono-sequences, separated by regional unconformities. The Tectono-sequence I, which includes lithotypes from the Brejo Santo Formation and is related to the pre-rift stage, is bounded at the base by the Paleozoic unconformity. This unit represents only a High Accommodation System Track, composed by a succession of pelitic levels interbedded with sandstones and limestones, from a large fluvial floodplain origin, developed under arid climatic conditions. The Tectono-sequence II, separated from the underlying unit by an erosional unconformity, is related to the rift stage, and is composed by the Missão Velha and Abaiara Formation lithotypes. Changes in depositional style that reflect variations in the A / S ratio, and the presence of hydroplastic deformation bands, make it possible to divide this tectonosequence into two internal sequences. Sequence IIA, which includes the lower portion of the Missão Velha Formation and sequence IIB, is composed by the upper section of the Missão Velha and Abaiara Formations The Sequence IIA below, composed only by the Low Accommodation System Track, includes crossbedding sandstones interbedded with massive mudstones, which are interpreted as deposits of sandy gravel beds wandering rivers. Sequence IIB, above, is more complex, showing a basal Low Accommodation System Track and a High Accommodation System Track at the top, separated by an expansion surface. The lower System Track, related to the upper portion of the Missão Velha Formation, is composed by a series of amalgamated channels, separated by erosion surfaces, interpreted as deposits of a belt of braided channels. The High Accommodation System Track, correlated with the Abaiara Unit, is marked by a significant increase in the A / S, resulting in the progradation of a system of braided river deltas with aeolic influence. Regarding tectonic evolution, the stratigraphic study indicates that the Tectonosequence Rift in the Araripe basin was developed in two phases: first characterized by a beginning of rifting, related to Sequence IIA, followed by a phase of syndepositional deformation, represented by sequence IIB. The first phase was not influenced by the development of large faults, but was influenced by a sharp and continuous decrease of accommodation space that permitted a change in depositional patterns, establishing a new depositional architecture. In turn, the stage of syndepositional deformation allowed for the generation of enough accommodation space for the preservation of fluvial-lacustrine deposits and conditioned the progradation of a braided river-dominated delta system.

Interpretação de dados de GPR com base na hierarquização de superfícies limitantes e na adaptação de critérios sismoestratigráficos

Due to its high resolution, Ground Penetrating Radar (GPR) has been used to image subsurface sedimentary deposits. Because GPR and Seismic methods share some principles of image construction, the classic seismostratigraphic interpretation method has been also applied as an attempt to interpret GPR data. Nonetheless some advances in few particular contexts, the adaptations from seismic to GPR of seismostratigraphic tools and concepts unsuitable because the meaning given to the termination criteria in seismic stratigraphy do not represent the adequate geologic record in the GPR scale. Essentially, the open question relies in proposing a interpretation method for GPR data which allow not only relating product and sedimentary process in the GPR scale but also identifying or proposing depositional environments and correlating these results with the well known Sequence Stratigraphy cornerstones. The goal of this dissertation is to propose an interpretation methodology of GPR data able to perform this task at least for siliciclastic deposits. In order to do so, the proposed GPR interpretation method is based both on seismostratigraphic concepts and on the bounding surface hierarchy tool from Miall (1988). As consequence of this joint use, the results of GPR interpretation can be associated to the sedimentary facies in a genetic context, so that it is possible to: (i) individualize radar facies and correlate them to the sedimentary facies by using depositional models; (ii) characterize a given depositional system, and (iii) determine its stratigraphic framework highligthing how it evolved through geologic time. To illustrate its use the proposed methodology was applied in a GPR data set from Galos area which is part of the Galinhos spit, located in Rio Grande do Norte state, Northeastern Brazil. This spit presents high lateral sedimentary facies variation, containing in its sedimentary record from 4th to 6th cicles caused by high frequency sea level oscillation. The interpretation process was done throughout the following phases: (i) identification of a vertical facies succession, (ii) characterization of radar facies and its associated sedimentary products, (iii) recognition of the associated sedimentary process in a genetic context, and finally (iv) proposal of an evolutionay model for the Galinhos spit. This model proposes that the Galinhos spit is a barrier island constituted, from base to top, of the following sedimentary facies: tidal channel facies, tidal flat facies, shore facies, and aeolic facies (dunes). The tidal channel facies, in the base, is constituted of lateral accretion bars and filling deposits of the channels. The base facies is laterally truncated by the tidal flat facies. In the foreshore zone, the tidal flat facies is covered by the shore facies which is the register of a sea transgression. Finally, on the top of the stratigraphic column, aeolic dunes are deposited due to areal exposition caused by a sea regression

Caracterização morfológica e sedimentar do talude continental (foz do Amazonas)

Created on 3 december 1997, the REMPLAC (Program for Assessment of Mineral Potencial of the Continental Shelf), this porgram aimed to make the basic survey, systematic geological and geophysical continental shelf, detail, at an appropriate scale, sites geo-economic, and perform the analysis and evaluation of mineral deposits. The REMPLAC should continue the efforts of Global Recognition Program of the Brazilian Continental Margin REMAC closed in 1978, the operations Geophysical Sea (GEOMAR) developed by the Directorate of Hydrography and Navigation and the various initiatives of the Program of Marine Geology and Geophysics (PGGM). Despite the high interest on the Amazon platform, there is little information o their morphology and sediment characterization, and in order to fill this gap, the present work samples sedimentological point followed by seismic acquisition. And the studies were to characterize the possible area of interest as being directly influence by tides, which sediments are reworked throughout the platform featuring grain angle with sharp corners, and the carbonate content increases as it approaches the breakdown the platform, and the bodies found outside the foraminifera and mollusks. However, diverging with organic matter that reduces its concentration as it moves away from the coast. The seismic profiles do not get satisfactory results because of low visibility, however, to correlate with the spot samples, of sediment were possible morphological characterization of the area.

Caracterização geológica tridimensional e monitoramento de dunas no litoral oriental do Rio Grande do Norte

This work presents geophysical and geological results obtained in a dunefield located in the east coast of Rio Grande do Norte State, with the aim to recognize the aeolian body depositional geometries to a future geologic modeling of the aeolian petroliferous reservoirs. The research, which was done in blowouts region situated at Nisia Floresta Municipally, included the characterization of external geometries with GPS and internal geometry analysis by GPR. Data was integrated in GoCAD software, where it was possible the three-dimensional characterization and interpretation of the studied deposits. The interpretation of GPR profiling allowed identifying: First-order bounding surfaces that separated the aeolian deposits of the Barreiras Formation rocks; Second-order bounding surfaces, which limit dune generations and Third-order bounding surfaces, a reactivation surface. This classification was based and adapted by the Brookfield (1977) and Kocurek (1996) propose. Four radarfacies was recognized: Radarfacies 1, progradational reflectors correlated to foresets of the dunes, Radarfacies 2, plain parallels reflectors related to sand sheets, Radarfacies 3, plain parallels reflectors associated to reworking of the blowout dune crest and Radarfacies 4, mounded reflectors associated to vegetated mound of sand or objects buried in subsurface. The GPR and GPS methods was also employed to the monitoring of dunefields susceptible to human activities in Buzios Beach, where the constructions along the blowout region and the tourism are changing the natural evolution of the deposits. This fact possibly to cause negative impacts to the coastal zone. Data obtained in Dunas Park, a unit environmental conservation, was compared with information of the Buzios Beach. There is a major tendency of erosion in Buzios, specifically in blowout corridor and blowout dune

As praças e a parceria público-privada em Natal/RN

Defined as public space or space open of common use, the square is a fundamental space for the urban life. Its function depends so much of the historical context, as of its location in the city, but general way, it is associated to leisure activities. In spite of its importance, many Brazilian squares are abandoned and degraded, some are used improperly, other they never left the paper and they are wastelands, most of the time, transformed in garbage deposits. The lack of appropriate equipments in the squares or to the precariousness of the same ones, such as banks, illumination and places for the different age groups; the lack of the "nature", in other words, of green; and the maintenance lack is some of the problems observed at the squares of Natal/RN. The maintenance is essential factor for the own existence of the square, so much in relation to the physical quality of the space, as in relation to the presence, or no, of users. In that work, we studied the squares of Natal/RN and the partnership public-private as form of shared administration of the public space. Our objective is to understand as it feels that partnership in the production and maintenance of squares in Natal/RN and which the benefits for the involved parts. For so much, we rescued the production of squares historically in the city of Natal/RN; We analyzed the legislation that regularizes the adoption of squares in some Brazilian municipal districts and the Bill of Adoption of Public Squares and of Sports and Green Areas in Natal/RN; and, last we analyzed three natalenses squares that had private investment in the construction, it reforms and/or maintenance. The "partnerships" involved exchange for land, environmental and social compensations, always assisting to the private interests, and nothing was registered or documented in the competent public organs. With that dissertation we wanted to contribute for the valorization of the squares and the relevance of the construction, renewal and maintenance of those public spaces in the city of Natal/RN, as life spaces, of encounters, of leisure

Comportamento geotécnico de misturas de solo e resíduos de perfuração onshore

The drilling of wells for petroleum extraction generates rocks and soils fragments, among other residues. These fragments are denominated petroleum drilling gravel or simply petroleum drilling residue. On the sites of onshore exploration are formed big deposits of drilling gravel, an expensive final destination material. This work aims at evaluating the addition of drilling residue to a lateritic soil, as composite material, for construction of compacted fills for earth work projects. Soil and residue were evaluated by X-ray diffraction (XRD) and X-ray fluorescence (XRF) and by laboratory tests traditionally used in soil mechanics, as particle-size analysis of soils, determination of liquid and plasticity indexes and compaction test. After soil and residue characterization, soil-residue mixtures were studied, using dosages of 2,5%, 5%, 10%, and 15% of residue in relation to the dry soil mass. These mixtures were submitted to compaction test, CBR, direct shear test and consolidation test. The test results were compared to the current legislation of DNIT for compacted fill construction. The results showed that the mixtures presented the minimal necessary parameters, allowing, from the point of view of geotechnical analysis, the use of these mixtures for construction of compacted fills

Análise da dinâmica deposicional das praias de Cacimbinha e do Madeiro, Tibau do Sul-RN, Brasil

The Cacimbinha and Madeiro beaches are located in the eastern coast of Rio Grande do Norte state, in the municipality of Tibau do Sul. Given the indicative of erosion in the coast of this district and the coastal processes acting on the beaches, the global aim of this project is comprehend the evolution of depositional environment on the Cacimbinha beach, moreover, the project seeks to characterize deposits from the Cacimbinha and Madeiro beaches, according to the geomorphologic compartments identified on these beaches; distinguish the coastal features which possibly interact with the Cacimbinha beach; identify the potential relationship between the sediments from the coastal features and the deposits from Cacimbinha beach; understand which depositional processes that prevail at each facies deposited on the beach; and identify the probable sedimentary environments and its energy of deposition through of the materials recorded on the Cacimbinha beach. This study was based on previous bibliographic and field research, both guided by academic works, laws, concepts and theories concerning the physical geography, geomorphology of the quaternary, sedimentary geology and stratigraphy. Thus, the methodology was divided in three steps: Prefield step: office work was performed; Field step: Sampling of facies of sedimentation; PosField step: analysis and integration of data obtained during the research period. Thus, the results showed deposicional facies with distinguished energy in the relief compartments, beach and terrace. After the sedimentary analysis and its interpretation linked to the architecture of the mounted sections based on drilling, it became possible to trace the evolutionary history of this stretch of beach. Therefore, it can be stated that studies performed on coastal areas are of great importance, as long as, around the world, the most part of urban zones are seated on deposits of quaternary age and, then this work improve the knowledge regarding the sedimentary dynamics of this beach, becoming scientific support for management and planning of this area which focus on, mainly, the foreign tourism

Indicadores do nível relativo do mar e evolução costeira durante o holoceno tardio no litoral oeste do Ceará, NE do Brasil

In the coastal region of Ceará, between the municipalities of Acaraú and Itapipoca, thirteen sites were identified containing indicators of relative sea level, six of these being dated by optically stimulated luminescence (OSL) and radiocarbon. Ages obtained supports that were formed prograding beaches in the study area. In the eastern portion, beaches in coastal plain deposits occur while a system lagoon/barrier paleomangrove occurs in the western portion of the study area. In both cases the coastal deposits prograde from east to west. Higher sea levels were identified between the current: (a) 3.110-2.830 cal. yr. BP; (b) 1.830 yr. BP (OSL) - 1.490 cal. yr. BP; (c) between 1.240-1.060 cal. yr. BP; (d) 845-715 yr. BP (OSL). Since then the sea level suffered by lowering the current level. Variations in sea level are interpreted as responses to changes in the pattern of marine circulation and do not exclude possible tectonic disturbances in the basin of the continental margin. The indicators of relative sea level west coast of Ceará present differently from other curves constructed in the coastal northeast, suggesting that local factors mentioned above contributed to sea level fluctuations.

Caracterização morfológica-sedimentar do vale inciso Apodi-Mossoró e plataforma continental adjacente - Bacia Potiguar Offshore

Systems of incised valleys have been studied in different continental shelves, including the Brazilian continental margin. The interest to characterize this feature is given by the information that it can provide variations on sea level, as well as the ability to host economically significant quantities of hydrocarbons in reservoirs located in deposits filling of the incised valleys. This thesis has the overall objective to characterize the morphology and sedimentary cover of the incised valley Apodi-Mossoró, located in the Northern Continental shelf of Rio Grande do Norte state, adjacent to Areia Branca city. The methodology included the integration of satellite imagery, bathymetric data, sedimentological data, shallow seismic, and the identification of foraminifera. The results indicate that the ApodiMossró incised valley is currently formed by two channels, shallow channel and deep channel, which have distinct morphological and sedimentological characteristics. The deep channel has connection with one of the heads of the Apodi Canyon, located in the slope area. The acquisition, processing and interpretation of shallow seismic data allowed the recognition of the depositional surface, erosional surface, discordance, and sismofaceis. The erosional surface mapped from shallow seismic sections is possibly a indicative of an ancient surface of valley incision, where it would probably be associated with the limit Pleistocene/Holocene. Different sismofaceis were identified and reflect the rise in sea level with standards sometimes agradacional, sometimes progradational. The thickness of sediments on this surface was estimated at a maximum of 22m thick in the central portion of the incised valley. Statistically, there are differences between the adjacent continental shelf and channels, and between these channels, for the content of calcium carbonate, organic matter, sand and mud perceptual, except for the gravel grain size. The analysis of living and dead foraminifera showed the presence of fifty species distributed in regards to morphology, depth and type of sediment. Four type of seismic echocharacteres were identified and mapped, as well as their bedforms, indicating different sedimentary processes along the incised valley. The integration of results suggests an activation of the Apodi-Mossoró incised valley in the Late Pleistocene.

“Acham que brotamos das fontes dessa cidade?”: uma etnografia sobre o cotidiano de sobrevivência de pessoas em situação de rua em Nata/RN

Through participant observation, held in the administrative region east of Natal / RN, this research aimed to understand about the daily life of men and women living on the streets in the city. How they relate to the space where they live? In this relationship, which uses and survival strategies triggered by this social segment? These were some of the questions that guided this research, in order to highlight the specificities of this way of life and the possible consequences that such a situation could reverberate. In this sense, there was an effort to keep up with people on the streets, their itineraries and seize their narratives. Along the search path - which took place intermittently between the years 2011-2015 - attended spaces of occupation and traffic of this population group in the street, as well as insert me and got involved in events, forums, seminars, meetings and subject of joints on the streets as a political movement (MNPR / RN). They are considered in this study as people on the street to those who occupy the street as their main space of survival and ordering of daily life: in the streets sleep, feed themselves, meet the physiological and hygienic needs, and is where draw sustenance. The street is taken in this research in its broadest sense, including all possible places relatively protected from the cold, rain and exposure to violence, thus includes both open and public spaces: as squares and parks; but also closed and private places: hostels, abandoned warehouses, prisons, etc. It was observed that in none of these spaces guys on the street are established in a fixed manner, in contrast, they experience the roaming, which in part is due to urban systems - which tends to stigmatize them and delete them places - and the very need to survive, because while living in the street differentiated practices are triggered, and these differ from the dominant mode of sedentary life.

“Acham que brotamos das fontes dessa cidade?”: uma etnografia sobre o cotidiano de sobrevivência de pessoas em situação de rua em Nata/RN

Through participant observation, held in the administrative region east of Natal / RN, this research aimed to understand about the daily life of men and women living on the streets in the city. How they relate to the space where they live? In this relationship, which uses and survival strategies triggered by this social segment? These were some of the questions that guided this research, in order to highlight the specificities of this way of life and the possible consequences that such a situation could reverberate. In this sense, there was an effort to keep up with people on the streets, their itineraries and seize their narratives. Along the search path - which took place intermittently between the years 2011-2015 - attended spaces of occupation and traffic of this population group in the street, as well as insert me and got involved in events, forums, seminars, meetings and subject of joints on the streets as a political movement (MNPR / RN). They are considered in this study as people on the street to those who occupy the street as their main space of survival and ordering of daily life: in the streets sleep, feed themselves, meet the physiological and hygienic needs, and is where draw sustenance. The street is taken in this research in its broadest sense, including all possible places relatively protected from the cold, rain and exposure to violence, thus includes both open and public spaces: as squares and parks; but also closed and private places: hostels, abandoned warehouses, prisons, etc. It was observed that in none of these spaces guys on the street are established in a fixed manner, in contrast, they experience the roaming, which in part is due to urban systems - which tends to stigmatize them and delete them places - and the very need to survive, because while living in the street differentiated practices are triggered, and these differ from the dominant mode of sedentary life.

Pirometamorfismo em calcários da formação Jandaíra, bacia potiguar, nordeste do Brasil

The present study aims the characterization of thermally affected carbonate rocks from Jandaíra Formation in contact with Paleogene and Neogene basic intrusions in the region of the Pedro Avelino and Jandaíra municipalities (RN), northeastern Brazil. For this study, field, petrographic, x-ray diffraction, electron microprobe, and whole rock litogeochemistry data of carbonates were undertaken. The thermally unaffected limestones are classified like wackstones, grainstones and packstones. They may constitute carbonates grains of benthic foraminifera, echinoderm spines, ostracods, algae, corals, bivalves, gastropods, peloids and intraclasts. The porosities are classified like vug, intraparticle, interparticle, intercrystal and moldic types. The major minerals are calcite, ankerite and dolomite; the detrital are montmorillonite, pyrite, limonite, quartz and microcline. The thermally affected limestones are very coarse to very fine-grained and light to dark gray color. The fossiliferous components totally disappear, and the porosity tends to disappear. With the data obtained, it can be inferred that the carbonate protoliths would be calciferous to dolomitic limestones, both with small amount of clay minerals. Crystalline carbonates from dolomitic protolith have rhombohedral calcite and iron oxides / hydroxides, making the rocks much darker. The carbonates from calciferous protolith have a wide variation of grain size according to the recrystallization degree, increasing toward contact with the basic bodies. In this group, it was identified the minerals lizardite and spinel in weakly to moderately affected samples, and spinel and spurrite in strongly affected rocks, as well as calcite, that occur everywhere. The geological context (shallow level diabase intrusions), the crystallization of the pyrometamorphic minerals spurrite and olivine, and comparison with diagrams from the literature allow estimating temperatures and pressures around 1050-1200 °C and 0.5-1.0 kbar, respectively, for PTOTAL=PCO2. The post-intrusion cooling would have afforded the releasing of metasomatic / hydrothermal fluids, allowing the opening of the metamorphic system, with possible contribution of chemical elements from host units (sandstones, shales) and from basic intrusions. This would induce hydration of previous phases, allowing the formation of serpentine, chlorite and brucite. The results discussed here reveal the strong influence of the heat from basic intrusions within the sedimentary pile. Whereas in the offshore portion of the basin occur sills with up to 1000 m thickness, the understanding of pyrometamorphism might be useful for understanding and measuring the thermally affected rocks.

Pirometamorfismo em calcários da formação Jandaíra, bacia potiguar, nordeste do Brasil

The present study aims the characterization of thermally affected carbonate rocks from Jandaíra Formation in contact with Paleogene and Neogene basic intrusions in the region of the Pedro Avelino and Jandaíra municipalities (RN), northeastern Brazil. For this study, field, petrographic, x-ray diffraction, electron microprobe, and whole rock litogeochemistry data of carbonates were undertaken. The thermally unaffected limestones are classified like wackstones, grainstones and packstones. They may constitute carbonates grains of benthic foraminifera, echinoderm spines, ostracods, algae, corals, bivalves, gastropods, peloids and intraclasts. The porosities are classified like vug, intraparticle, interparticle, intercrystal and moldic types. The major minerals are calcite, ankerite and dolomite; the detrital are montmorillonite, pyrite, limonite, quartz and microcline. The thermally affected limestones are very coarse to very fine-grained and light to dark gray color. The fossiliferous components totally disappear, and the porosity tends to disappear. With the data obtained, it can be inferred that the carbonate protoliths would be calciferous to dolomitic limestones, both with small amount of clay minerals. Crystalline carbonates from dolomitic protolith have rhombohedral calcite and iron oxides / hydroxides, making the rocks much darker. The carbonates from calciferous protolith have a wide variation of grain size according to the recrystallization degree, increasing toward contact with the basic bodies. In this group, it was identified the minerals lizardite and spinel in weakly to moderately affected samples, and spinel and spurrite in strongly affected rocks, as well as calcite, that occur everywhere. The geological context (shallow level diabase intrusions), the crystallization of the pyrometamorphic minerals spurrite and olivine, and comparison with diagrams from the literature allow estimating temperatures and pressures around 1050-1200 °C and 0.5-1.0 kbar, respectively, for PTOTAL=PCO2. The post-intrusion cooling would have afforded the releasing of metasomatic / hydrothermal fluids, allowing the opening of the metamorphic system, with possible contribution of chemical elements from host units (sandstones, shales) and from basic intrusions. This would induce hydration of previous phases, allowing the formation of serpentine, chlorite and brucite. The results discussed here reveal the strong influence of the heat from basic intrusions within the sedimentary pile. Whereas in the offshore portion of the basin occur sills with up to 1000 m thickness, the understanding of pyrometamorphism might be useful for understanding and measuring the thermally affected rocks.

Petrologia e geocronologia U-Pb do plúton granítico Serra da Rajada, porção central do domínio Rio Piranhas - Seridó, Província Borborema, NE do Brasil

The ediacaran plutonic activity related to the Brasilian/Pan-African orogeny is one of the most important geological features in the Borborema Province, represented along its extension by numerous batholiths, stocks, and dikes.The object of this study, the Serra Rajada Granitic Pluton (SRGP), located in the central portion of the Piranhas-Seridó River Domain is an example of this activity. This pluton has been the subject of cartographic, petrographic, geochronological and lithogeochemical studies and its rocks were characterized by two facies. First, the granitic facies were described as monzogranites consisting of K-feldspar, plagioclase (oligoclase - An23-24%), quartz and biotite (main mafic) and opaque minerals such as titanite, allanite, apatite, and zircon as accessories. Alteration minerals are chlorite, white mica and carbonate. Second, the dioritic facies consist of rocks formed by quartz diorite containing plagioclase (dominant mineral phase), quartz and K-feldspar. Biotite and amphibole are the dominant mafic minerals; and titanite, opaque minerals, allanite, zircon and apatite are the accessories. However, previous geological mapping work in the region also identified the presence of other lithostratigraphic units. These were described as gneisses and migmatites with undifferentiated amphibolite lenses related to the Caicó Complex (Paleoproterozoic) and metasedimentary rocks of the Seridó Group (Neoproterozoic) composed of paragneiss with calc-silicate lenses, muscovite quartzite and biotite schist (respectively, the Jucurutu formations, Equador and Seridó), the host rocks for the SRGP rocks. Leucomicrogranite and pegmatite dikes have also been identified, both related to the end of the Ediacaran magmatism and colluvial- eluvial and alluvial deposits related to Neogene and Quaternary, respectively. Lithogeochemical data on the SRGP granite facies, highlighted quite evolved rocks (SiO2 69% to 75%), rich in alkalis (Na2O+K2O ≥ 8.0%), depleted of MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO2 (≤ 0.36%) and moderate levels of Fe2O3t (2.16 to 3.53%). They display transitional nature between metaluminous and peraluminous (predominance of the latter) with sub-alkaline/monzonitic (High K calcium-alkali) affinity. Harker diagrams show negative correlations for Fe2O3t, MgO, and CaO, indicating mafic and plagioclase fractionation. REE spectrum shows enrichment of LREE relative to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in the Eu (Eu/Eu* = 0.70 to 0.23), suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows to correlate the SRGP rocks with those described as Calcium-Alkaline Suite of equigranular High K. The crystallization conditions of the SRGP rocks were determined from the integration of petrographic and lithogeochemical data. These data indicated intermediate to high conditions of ƒO2 (mineral paragenesis titanite + magnetite + quartz), parent magma saturated in H2O (early biotite crystallization), tardi-magmatic processes of fluids rich in ƒCO2, H2O and O2 causing part of the mineral assembly to change (plagioclase carbonation and saussuritization, biotite chloritization and opaques Sphenitization). Thermobarometrical conditions were estimated based on geochemical parameters (Zr and P2O5) and CIPW normative minerals, with results showing the liquidus minimum temperature of about800°C and the solidus temperature of approximately 700°C. The final/minimum crystallization pressure are suggested to be between 3 and 5 Kbar. The presence of zoned minerals (plagioclase and allanite) associated with lithogeochemical data in bi-log diagrams for Rb vs. Ba and Rb vs. Sr suggest the role of fractional crystallization as the dominant process in the magmatic evolution of SRGP. U-Pb Geochronological and Sm-Nd isotope studies indicated, respectively, the crystallization age of biotite monzogranite as 557 ± 13 Ma, with TDM model age of 2.36 Ga, and εNd value of -20.10 to the crystallization age, allowing to infer paleoproterozoic crustal source for the magma.

Petrologia e geocronologia U-Pb do plúton granítico Serra da Rajada, porção central do domínio Rio Piranhas - Seridó, Província Borborema, NE do Brasil

The ediacaran plutonic activity related to the Brasilian/Pan-African orogeny is one of the most important geological features in the Borborema Province, represented along its extension by numerous batholiths, stocks, and dikes.The object of this study, the Serra Rajada Granitic Pluton (SRGP), located in the central portion of the Piranhas-Seridó River Domain is an example of this activity. This pluton has been the subject of cartographic, petrographic, geochronological and lithogeochemical studies and its rocks were characterized by two facies. First, the granitic facies were described as monzogranites consisting of K-feldspar, plagioclase (oligoclase - An23-24%), quartz and biotite (main mafic) and opaque minerals such as titanite, allanite, apatite, and zircon as accessories. Alteration minerals are chlorite, white mica and carbonate. Second, the dioritic facies consist of rocks formed by quartz diorite containing plagioclase (dominant mineral phase), quartz and K-feldspar. Biotite and amphibole are the dominant mafic minerals; and titanite, opaque minerals, allanite, zircon and apatite are the accessories. However, previous geological mapping work in the region also identified the presence of other lithostratigraphic units. These were described as gneisses and migmatites with undifferentiated amphibolite lenses related to the Caicó Complex (Paleoproterozoic) and metasedimentary rocks of the Seridó Group (Neoproterozoic) composed of paragneiss with calc-silicate lenses, muscovite quartzite and biotite schist (respectively, the Jucurutu formations, Equador and Seridó), the host rocks for the SRGP rocks. Leucomicrogranite and pegmatite dikes have also been identified, both related to the end of the Ediacaran magmatism and colluvial- eluvial and alluvial deposits related to Neogene and Quaternary, respectively. Lithogeochemical data on the SRGP granite facies, highlighted quite evolved rocks (SiO2 69% to 75%), rich in alkalis (Na2O+K2O ≥ 8.0%), depleted of MgO (≤ 0.45%), CaO (≤ 1.42%) and TiO2 (≤ 0.36%) and moderate levels of Fe2O3t (2.16 to 3.53%). They display transitional nature between metaluminous and peraluminous (predominance of the latter) with sub-alkaline/monzonitic (High K calcium-alkali) affinity. Harker diagrams show negative correlations for Fe2O3t, MgO, and CaO, indicating mafic and plagioclase fractionation. REE spectrum shows enrichment of LREE relative to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in the Eu (Eu/Eu* = 0.70 to 0.23), suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows to correlate the SRGP rocks with those described as Calcium-Alkaline Suite of equigranular High K. The crystallization conditions of the SRGP rocks were determined from the integration of petrographic and lithogeochemical data. These data indicated intermediate to high conditions of ƒO2 (mineral paragenesis titanite + magnetite + quartz), parent magma saturated in H2O (early biotite crystallization), tardi-magmatic processes of fluids rich in ƒCO2, H2O and O2 causing part of the mineral assembly to change (plagioclase carbonation and saussuritization, biotite chloritization and opaques Sphenitization). Thermobarometrical conditions were estimated based on geochemical parameters (Zr and P2O5) and CIPW normative minerals, with results showing the liquidus minimum temperature of about800°C and the solidus temperature of approximately 700°C. The final/minimum crystallization pressure are suggested to be between 3 and 5 Kbar. The presence of zoned minerals (plagioclase and allanite) associated with lithogeochemical data in bi-log diagrams for Rb vs. Ba and Rb vs. Sr suggest the role of fractional crystallization as the dominant process in the magmatic evolution of SRGP. U-Pb Geochronological and Sm-Nd isotope studies indicated, respectively, the crystallization age of biotite monzogranite as 557 ± 13 Ma, with TDM model age of 2.36 Ga, and εNd value of -20.10 to the crystallization age, allowing to infer paleoproterozoic crustal source for the magma.