Understanding the resurgence of traditional authorities in post-apartheid South Africa

Drawing their power not from the ballot box but from a supposedly ancient wellspring of power, hereditary traditional authorities in postcolonial Africa have frequently posed challenges for incoming ‘democratic’ governments. The situation in post-apartheid South Africa is no different. However contentious their role under the colonial and apartheid systems of government was, the Constitution of the new South Africa (1996) recognised traditional authorities and afforded them opportunities for a political resurgence. This paper reviews the changing status of traditional authorities in the Eastern Cape Province over the twenty years since 1994. It explores the resurgence of the chiefs in relation to the consolidation of both democratic processes and of emergent, neo-patrimonial modes of government. It briefly considers the role of traditional authorities in three key and closely related spheres, namely the institution of the Eastern Cape House of Traditional Leaders, the question of how gender is handled by and within traditional institutions, and the continuing challenges of land administration and development in rural areas. In all these spheres, and in the face of real opposition, the voice and influence traditional authorities have emerged stronger than ever. We conclude by suggesting that as they are drawn deeper into governance and have to play a formal role in addressing the myriad institutional challenges, new questions will and should be asked about the status and influence of traditional authorities, and their substantive contribution to democracy in South Africa.

UV optical absorption spectra analysis of beryl crystals from Brazil

The spectral decomposition analysis was applied to the optical absorption spectra of green and colorless beryl crystals from the Brazilian Eastern Pegmatitic province in the natural state, Submitted to heat treatment and irradiated with UV light The attributions of the lines were made taking into account highly accurate quantum mechanical calculations The deconvolution of the green beryl spectra revealed four lines, two of them around 12,000 cm(-1) (1 5eV) and two of them around 34,000 cm(-1) (4.2 eV) attributed to Fe(2+) and Fe(3+), respectively The deconvolution of the colorless beryl spectra without any treatment, after heating and for the same heat treatment followed by UV light irradiation revealed five lines The analysis of ratio relations showed that the lines at 36,400 cm(-1) (4.5 eV) and 41,400 cm(-1) (5 1 eV) belongs to a single defect attributed to a silicon dangling bond defect (=Si). Discussions and comparison with reported defects in quartz have supported the allocation of the lines at 61,000 cm(-1) (7.6 eV) and 43,800 cm(-1) (5 4 eV) to diamagnetic oxygen vacancy defect ( Si-Si ) and unrelaxed ( Si Si ) defect, respectively Finally, the line at 39.100 cm(-1) (4.8 eV), quite polarized along the c-axis, was attributed to a (Fe(2+) OH(-)) defect in the structural channels (C) 2009 Elsevier B V All rights reserved

The Cariris Velhos tectonic event in Northeast Brazil

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the Sao Luis-West Africa craton to the north and the Sao Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Medio Coreau, Ceara Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000-920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province. Within the Transversal Zone, the Alto Pajeu terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeu terrane, the Riacho Gravata subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found. In both the Alto Pajeu and Riacho Gravata terranes, TIMS and SHRIMP U-Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Polo Redondo-Maranco terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U-Pb ages (SHRIMP data) around 0.98-0.97 Ga. For all these domains, Sm-Nd data exhibit Tom model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive epsilon(Nd)(t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7-0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events. Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent. (C) 2009 Elsevier Ltd. All rights reserved.

Condicionamento estrutural das zonasa de cisalhamento da região de Forquilha, domínio Ceará Central: uma abordagem integrada de sensoriamento remoto e geologia estrutural

The studied region, named Forquilha and localized in northwestern Central Ceará domain (northern portion of Borborema Province), presents a lithostratigraphic framework constituted by paleoproterozoic metaplutonics, metasedimentary sequences and neoproterozoic granitoids. The metasedimentary rocks of Ceará group occupy most part of the area. This group is subdivided in two distinct units: Canindé and Independência. Canindé unit is represented basically by biotite paragneisses and muscovite paragneisses, with minor metabasic rocks (amphibolite lens). Independência sequence is composed by garnetiferous paragneisses, sillimanite-garnet-quartz-muscovite schists and quartz-muscovite schists, pure or muscovite quartzites and rare marbles. At least three ductile deformation events were recognized in both units of Ceará group, named D1, D2 and D3. The former one is interpreted as related to a low angle tangential tectonics which mass transport is southward. D2 event is marked by the development of close/isoclinal folds with a N-S oriented axis. Refolding patterns generated by F1 and F2 superposition are found in several places. The latest event (D3) corresponds to a transcurrent tectonics, which led to development of mega-folds and several shear zones, under a transpressional regime. The mapped shear zones are Humberto Monte (ZCHM), Poço Cercado (ZCPC) and Forquilha (ZCF). Digital image processing of enhanced Landsat 7-ETM+ satellite images, combined with field data, demonstrate that these penetrative structures are associated with positive and negative geomorphologic patterns, distributed in linear and curvilinear arrangements with tonal banding, corresponding to the ductile fabric and to crests. Diverse color composites were tested and RGB-531 and RGB-752 provided the best results for lineament analysis of the most prominent shear zones. Spatial filtering techniques (3x3 and 5x5 filters) were also used and the application of Prewitt filters generated the best products. The integrated analysis of morphological and textural aspects from filtered images, variation of tonalities related to the distribution of geologic units in color composites and the superposition over a digital elevation model, contributed to a characterization of the structural framework of the study area. Kinematic compatibility of ZCHM, ZCPC, ZCF shear zones, as well as Sobral-Pedro II (ZCSPII) shear zone, situated to the west of the study area, was one of the goal of this work. Two of these shear zones (ZCHM, ZCPC) display sinistral movements, while the others (ZCSPII, ZCF) exhibit dextral kinematics. 40Ar/39Ar ages obtained in this thesis for ZCSPII and ZCPC, associated with other 40Ar/39Ar data of adjacent areas, indicate that all these shear zones are related to Brasiliano orogeny. The trend of the structures, the opposite shear senses and the similar metamorphic conditions are fitted in a model based on the development of conjugate shear zones in an unconfined transpression area. A WNW-ESE bulk shortening direction is infered. The geometry and kinematic of the studied structures suggest that shortening was largely accommodated by lateral extrusion, with only minor amounts of vertical stretch

Evolução geodinâmica e condicionamento estrutural dos terrenos Piancó-Alto Brígida e Alto Pajeú, domínio da zona transversal, NE do Brasil

This thesis aims to advance in the geological knowledge of the region comprising the Piancó-Alto Brígida (TPAB) and Alto pajeú (TAP) terranes, in the Transversal Zone Domain (Borborema Province, NE Brazil), with the main objective of understanding the geodynamic evolution and the structural framework of these units. To reach this objective, and besides field work and interpretation of traditional aerial photographs, other tools were employed like of remote sensing products (Landsat 7 ETM+, aeroradiometrics, aeromagnetics and topographical images), lithogeochemical (whole rock) analyses and geochronological dating (U-Pb in zircon), besides integration with literature data. In the area, several precambrian geological units outcrop, represented in the TAP by the paleoproterozoic Serra Talhada and Afogados da Ingazeira complexes, Riacho Gravatá Complex (metavolcano-sedimentary sequence of Stenian-Tonian age) and Cariris Velhos orthogneisses (of Tonian age). The TPAB comprises the Santana do Garrote (lower unit) and Serra do Olho d'Água (upper unit) formations of the Cachoeirinha Group (Neoproterozoic III), besides the Piancó orthogneisses and Bom Jesus paragneisses; the latter correspond to an older (basement ?) block and a possible high grade equivalent of the Cachoeirinha Group (or Seridó Group ?), respectively. Several Brasiliano-age plutons occur in both terranes.The aeromagnetic data show the continuity, at depth, of the main shear zones mapped in the region. The Patos, Pernambuco, Boqueirão dos Cochos, Serra do Caboclo, Afogados da Ingazeira/Jabitacá and Congo-Cruzeiro do Nordeste shear zones reach depths greater than to 6-16 km. The aeromagnetic signature of other shear zones, like the Juru one, suggests that these structures correspond to shallower crustal features. The satellite images (Landsat 7 ETM+) and aerogamaspectrometric images discriminate different geological units, contributing to the mapping of the structural framework of the region. The Serra do Caboclo Shear Zone was characterized as the boundary/suture between the TPAB and TAP. This structure is an outstanding, pervasive feature that separates contrasting geological units, such as the Neoproterozoic III Cachoeirinha Group in the TPAB and the Riacho Gravatá Complex and the Cariris Velhos metaplutonics, of Stenian-Tonian age, in the TAP. Occupying different blocks, these units are not found in authoctonous relations, like unconformities and intrusive contacts. Concerning the Cariris Velhos (ca. 1,0 Ga old) event is recorded by radiometric ages of the Riacho Gravatá Complex metavolcanics and intrusive augen and orthogneisses, all of them displaying geochemical affinities of arc or collisional settings. A structural signature of this event was not recorded in the region, possibly due to its low grade/low strain style, obliterated by the overprinting of younger, higher grade/high strain Brasiliano-age fabrics.The first tectonic event (D1) observed in the Cariris Velhos lithotypes presents contractional kinematics with transport to the NW. Neoproterozoic III geochronologic dates, obtained in late-D1 granitoids, imply a Brasiliano age (ca. 610-600 Ma) for this deformation event. The second tectonic event (D2) characterized in the region corresponds to the Brasiliano transcurrent kinematics of the outstanding shear zones and associated granitoid plutons. The geochronological (U-Pb in zircon) data obtained during this thesis also confirms the occurrence of the Cariris Velhos magmatic suite in the TAP, as well as the Neoproterozoic III age to the Cachoeirinha Group in the TPAB. The TAP (Riacho Gravatá Complex, augen and orthogneisses) is interpreted as a continental arc possibly accreted to a microcontinent during the Cariris Velhos (Stenian-Tonian) event. Later on, this terrane collided with the TPAB at the beginning of the Brasiliano orogeny (D1 contractional deformation), and both domins were reworked by the transcurrent shear deformation of the D2 event

Sismicidade e correlação com feições geológicas: o caso do lineamento Pernambuco e seu entorno

This thesis presents and discusses the results of the various seismic areas in the State of Pernambuco, with the aim of having a vision of regional seismicity and its causes. To the papers published in journals were added two new original works submitted to international journals, dealing with seismic areas located in the counties of São Caetano, Cupira, and Agrestina. All seismic areas mentioned in this thesis are located on the Pernambuco Lineament and its surroundings (both in branches or single faults within 40 km of it). The Pernambuco Lineament is a Neoproterozoic shear zone of continental-scale that deformed the Borborema Province, and presents as branches, shear zones with NE-SW direction. The new submitted papers are from the analysis of data collected by three local networks of stations that operated in the following areas: network SO07 (seismicity in the district of Santa Luzia - São Caetano, 2007), network BM10 (data from seismic areas of Serra Verde ( Cupira) and Barra do Chata (Agrestina), in 2010), network SO10 (seismicity near the urban center of São Caetano in 2010). These data were used for determining the hypocenters and focal mechanisms in order to discuss the relationship between the seismicity and geological features of the area. The new mechanisms obtained, as well as the previously published allowed the determination of the direction of the average stress in the region. The direction of stress in the region involving the various seismic areas, now or previously studied, is quite stable and approximate EW direction (SHmax). The correlation between seismicity and geological features is observed on the lineament and north of it. In the south (Cupira and Agrestina), in seismic areas nearby shear zones NE-SW, there is no correlation and seismogenic EW normal faults are active and its motion is compatible with regional stresses. It is probable that these active faults are more recent than the Neoproterozoic, probably of the Cretaceous period, when the last great movement of the Pernambuco Lineament occurred

Evolução termocronológica do sistema de falhas Senador Pompeu-CE

The region of the Senador Pompeu Shear Zone (SPSZ), in the North Tectonic Domain of the Borborema Province (BP), has its recent history associated with to South Atlantic Ocean formation event at the Jurassic. A lot of geologics models have discussed about crustal axis elevation in local scale and large scale (Borborema Province), relative to importants regionals tectonics directions of it. The identification and the relationship among this surfaces, stepped in many topographyc levels by tectonics mecanisms, is dificult because of the erosion process on it. Over there, sedimentary deposits is complex and it has not biostratigraphyc record in continental deposits. The analysis metodology on apatita fission-track, in the region of the SPSZ, purpose the more knowledge about morphotectonics mecanisms of the area and the impruvement of its morphotectonics models. For this, it was moleled the age and thermal history of the 11 apatites samples collected on both sides of this shear zone, taking relationships among other results of the thermochronology studies in the BP. Based on the thermal studies in this search, the region of the BP developed on two distint cooling events, separated for one period of relative stabilited. The first episode occur between 130 and 90 M.y., has been began when the samples cross the 120°C isoterm for last time and fineshed at 70°C. The second moment of the cooling process was began about 30 M.y., when the temperature was 90°C, from this to the equlibrium with present surface temperature at 30°C. Some evidences indicated a relacionship between thermal episodes and uplift events of the regional relief. The fundaments of the interpretation was based mainly on comparatives studies among results of the thermochronology analysis and geologics studies about BP. Nóbrega et al.(2005), e.g., on studies about the Portalegre Shear Zone, got similar results on SPSZ, with some details relative to local tectonic activity. Morais Neto et al. (2000) interpreted two importants cooling events in the BP based on their regional studies, that can be associated to regional uplift events. When Assine (1992) studied the stratigraphyc sequences of the Araripe Basin, in the south of Ceará state, conclude that the abrupt return to continentals condictions from the last sedimentar sequency (albiano-cenomaniane) indicate a regional uplift of the NE region of the Brazil at the 100 M.y., in the Albiano Intermediate/Superior. This ages are compatible to termal model of the SPSZ. This two periods of the thermal history of the BP are completely registered in the apatites samples just one age groups of the fission-track, that it is the most ancient age groups. This one suggest it has happened in response to heating before 75 M.y and it has erased the last report of the first moment relief evolution of the BP. The NNE-SSW and E-W structure reativation can have created ideal condictions for heating and local elevations of the geothermal gradients. The equilibrium between the apatites temperatures of this groups and the regionais temperatures took place about 50 M.y., when the samples of the two ages groups had a simillar evolution to present surfaces temperatures

Aspectos morfo-tectônicos nos platôs de Portalegre, Martins e Santana/RN

A morpho-structural analysis was performed in the uplifted siliciclastic deposits of the Serra do Martins Formation along the Portalegre, Martins and Santana plateaux, in the southeastern and central regions of Rio Grande do Norte State. Due to the lack of biostratigraphic records, this formation has a disputable age.The adopted approach was based on the analysis of the drainage patterns and in the recognition of topographic surfaces and regional structures, subjected to neotectonic deformation and rejuvenation the present stress field. These events are recorded in the lineament arrays and as anomalous features of the landscape, such as the uplifted plateaux.The morpho-sculptural evolution of the studied blocks is expressed as erosive and accumulative processes. The former ones include erosional scarpments, cuestas and amphitheaters as the most characteristic features, while debris slopes represent acumulative examples. Such elements attest to the recent disequilibrium of the plateaux, and the absence of well developed alluvium terraces suggest an accelerated uplift process. The directions of the linear features observed in remote sensing products evidence the control of the basement structural trends, inherited from the pre-Cenozoic evolution. The NNE-SSW direction controls the main erosional features of the plateaux, while the N-S direction is a major drainage control, being also recognized in the Potiguar Basin. An E-W trend occurs as a less developed direction, reflecting either a system of mesozoic basic dykes or precambrian brittle structures. As regards to the drainage arrays, an arborescent, varying to a roughly N-S rectangular pattern, was identified in the Portalegre-Martins block. The Santana plateau displays rectilinear (northern border) and dendritic arborescent (southern border) patterns. In the sedimentary cover, the drainage pattern varies from rectangular to angular, reflecting inheritance from the crystaline basement. The most significative directions, N, NE and NW, mark the erosional fronts of the plateaux. Drainage anomalies, characterized by elbows or paralell confluencies, reinforce the arguments mentioned above. The data sets evidence the relationships between endogenous (lithology, structures) and exogenous features as the main controls of terrain dissecation, associated to vertical (epirogenesis) movements and horizontal tectonics. A final discussion addresses the relationships of the Serra do Martins Formation with the sedimentary record of Potiguar Basin, trying to establish chronostratigraphic links with the main evolutionary steps of this part of the Borborema Province, and possible mechanisms involved in the uplift of the plateaux and other stratigraphic units in the region

Estudo da atividade sísmica em São Caetano-PE em 2007

In this dissertation we studied the seismic activity in the São Caetano county, Pernambuco State, Northeastern Brazil, located near the Pernambuco Lineament. The Pernambuco Lineament is a one of Neoproterozoic continental-scale shear zones that deforms the Borborema province. The seismicity estudied occurred in a NE trending branch of Pernambuco Lineament. The seismic activity in São Caetano started in 2006 and in May 20th, 2006 a 4,0 mb earthquake hit there. This was the largest earthquake ever reported in Pernambuco State. This dissertation is the result of a campaign done in the period from Februay 1th 2007 to July 31 th 2007. In this campaign up to nine three-component digital seismographic stations were deployed and the collected data was used to determine hypocenters and focal mechanism. A total of 214 earthquakes, recorded at least by three stations, were analyzed. To determine hypocenters and time origin the HYPO71 program was used assuming a half-space model with parameters : VP (P-wave velocity) equal to 5.90 km/s and the ratio VP/VS 1.70, where VS is the S-wave velocity. The earthquakes hypocentral distribution was approximately 4 km long and agrees with the NE-SW direction of the Pernambuco Lineamento branch. Hypocentres depth range from 2 to 8 km. The composed focal mechanism was made from a group of 14 selected earthquakes. We try firstly to find the fault plane solution matching the polarity distribution at stations, using the FPFIT program. The result was 43 deg ± 15 deg for strike, 59 deg ± 9 deg for dip and -142 deg ± 15 deg for rake. We also fitted a plane using the hypocentral distribution to obtain the dip and azimuth of the hypocentral distribution. The results obtained by this fit were 58 deg for the azimuth, 55 deg for the dip and -155 deg for rake. This result shows a mechanism of a strike-slip dextral fault with a normal component. This dissertation shows, once more, that there is a good correlation between the seismic activity and geological features in the region near the Pernambuco Lineament and its NE branches

Estruturação do grupo Serra Grande região de Santana do Acaraú- CE e a reativação do lineamento Sobral Pedro II, integração com dados geofísicos

The study area is located in the NW portion of the Ceará state nearby the city of Santana do Acaraú. Geologically it lies along the Sobral-Pedro II lineament which limits the domains of Ceará Central and Noroeste do Ceará, both belonging to the Borborema Province.The object of study was a NE trending 30km long siliciclastic body (sandstone and conglomerate) bounded by transcurrent dextral faults. The sediments are correlated to the Ipú Formation (Serra Grande Group) from the Parnaiba basin, which age is thought to be Siluro-Devonian. Existing structural data shown that bedding has higher but variable dips (70-45) near the borders faults and much lower to subhorizontal inward the body. The brittle deformation was related to a reactivation, in lower crustal level, of the Sobral-Pedro II lineament (Destro (1987, 1999; Galvão, 2002).The study presented here was focused in applying geophysicals methods (gravimetry and seismic) to determine the geometry of the sandstone/conglomeratic body and together with the structural data, to propose a model to explain its deformation. The residual anomalies maps indicate the presence of two main graben-like structures. The sedimentary pile width was estimated from 2D gravimetric models to be about 500-600 meters. The 3D gravimetric model stressed the two maximum width regions where a good correlation is observed between the isopach geometry and the centripetal strike/dip pattern displayed by the sediments bedding. Two main directions (N-S and E-W) of block moving are interpreted from the distribution pattern of the maximum width regions of the sedimentary rock

O graben de Palestina: contribuição à estratigrafia e estrutura do estágio rifte na bacia do Araripe, nordeste do Brasil

The Palestina Graben is one of the NE-trending asymmetric grabens of the Araripe Basin. This basin rests on the precambrian terrains of the Transversal Zone, Borborema Province, immediately to the south of the Patos Lineament. It is part of the Interior Basins province of Northeastern Brazil, being related to the fragmentation of the Gondwana supercontinent and the opening of the South Atlantic ocean. The Palestina Graben trends NE-SW and presents an asymmetric geometry, controled by the NW extensional eocretaceous strain. The graben borders display distinct geometries. The SE border is a flexural margin, characterized by the non conformity of the eopaleozoic Mauriti Formation (the oldest unit of the basin) overlying the crystalline basement, but also affected by normal faults with small displacements. On the opposite, the NW border is continuous and rectilinear, being marked by normal faults with major displacements, that control the general tilting of the layers to the NW. In this sense, the Mauriti Formation is overlain by the Brejo Santo, Missão Velha (which also occurs in the Brejo Santo-Mauriti horst, to the NW of the fault border) and Abaiara formations, the latter restricted to the graben. The interpretation of available gravity data and a seismic line indicates that the main fault has a variable dip slip component, defining two deeper portions within the graben, in which the sedimentary column can reach thicknesses of up to 2 km. Regarding to the stratigraphy of Araripe Basin in the study area, the sedimentary package includes three distinct tectonosequences. The Paleozoic Syneclisis Tectonosequence is composed by the Mauriti Formation, deposited by a braided fluvial system. The Jurassic Tectonosequence, whose tectonic setting is still debatable (initial stage of the Neocomian rift, or a pre-rift syneclisis ?), is represented by the Brejo Santo Formation, originated in a distal floodplain related to ephemeral drainages. The Rift Tectonosequence, of neocomian age, includes the Missão Velha Formation, whose lower section is related to a braided to meandering fluvial system, outlining the Rift Initiation Tectonic Systems Tract. The upper section of the Missão Velha Formation is separated from the latter by a major unconformity. This interval was originated by a braided fluvial system, overlain by the Abaiara Formation, a deltaic system fed by a meandering fluvial system. Both sections correspond to the Rift Climax Tectonic Systems Tract. In the area, NE-trending normal to oblique faults are associated with NW transfer faults, while ENE to E-W faults display dominant strike slip kinematics. Both NE and E-W fault sets exhibit clear heritage from the basement structures (in particular, shear zones), which must have been reactivated during the eocretaceous rifting. Faults with EW trends display a dominant sinistral shear sense, commonly found along reactivated segments of the Patos Lineament and satellyte structures. Usually subordinate, dextral directional movements, occur in faults striking NNW to NE. Within this framework bearing to the Palestina Graben, classical models with orthogonal extension or pull-apart style deserve some caution in their application. The Palestina Graben is not limited, in its extremeties, by E-W transcurrent zones (as it should be in the case of the pull-apart geometry), suggesting a model close to the classic style of orthogonal opening. At the same time, others, adjacent depocenters (like the Abaiara-Jenipapeiro semi-graben) display a transtensional style. The control by the basement structures explains such differences

Análise da deformação pós-Rifte na Bacia do Araripe, Nordeste do Brasil

The Araripe Basin is located over Precambrian terrains of the Borborema Province, being part of Northeast Brazil inner basins. Its origin is related to the fragmentation of the Gondwana supercontinent and consequently opening of South Atlantic during early Cretaceous. The basin has a sedimentary infill encompassing four distinct evolution stages, comprising Paleozoic syneclisis, pre-rift, rift and post-rift. The target of this study comprises the post-rift section of the basin focusing deformational styles which affect evaporates from Ipubi Member of the Santana Formation, which is composed by gypsum and anidrite layers interbedded with shales. These units occur widespread across the basin. In the central part of the basin, near Nova Olinda-Santana do Cariri, evaporites are affected by an essentialy brittle deformation tipified by fibrous gypsum filled fractures, cutting massive layers of gypsum and anidrite. Veins with variable orientations and dips are observed in the region distributed over three main populations: i) a dominant NWSE with shallow to moderate NE dipping population, consisting of gypsum filled veins in which fibers are normal to vein walls; i) NE-SW veins with moderate SE dips containing subhorizontal growth fibers; and iii) N-S veins with shallow E-W dips with fibers oblique to vein walls. In the west portion of the basin, near Trindade-Ipubi-Araripina towns, evaporate layers are dominantly constituted by gypsum/anidrite finely stratified, showing a minor density of veins. These layers are affected by a unique style of deformation, more ductile, typified by gentle to open horizontal normal folding with several tens of meters length and with double plunging NW-SE or NE-SW hinges, configuring domic features. In detail, gypsum/anidrite laminae are affected by metre to decimeter scale close to tight folding, usually kinked, with broken hinges, locally turning into box folds. Veins show NE-SW main directions with shallow NE dips, growth fibers are parallel to vein walls, constituting slickenfibers. This region is marked by faults that affect Araripina Formation with NW-SE, NE-SW and E-W directions. The main structural styles and general orientations of structures which affected the post-rift section of Araripe Basin yielded important kinematic information analysis which led us to infer a E-W to NE-SW extension direction to the northeastern part of the Basin, whereas in the southeastern part, extension occurred in N-S direction. Thus, it was possible to determine a regional kinematic setting, through this analysis, characterizing a NE-SW to ENE-WSW system for the post-rift section, which is compatible with the tension settings for the Sout American Plate since Albian. Local variations at the fluid pressure linked (or not) to sedimentary overload variation define local tension settings. This way, at the northeastern portion of the basin, the post-rift deformation was governed by a setting which σ 1 is sub-horizontal trending NE-SW and, σ 3 is sub-vertical, emphasizing a reverse fault situation. At the southwestern portion however there was characterized a strike slip fault setting, featuring σ 1 trending ENEWSW and σ3 trending NNW-SSE

Caracterização geológica, geoquímica e geocronológica da suíte plutônica enoproterozóica da região de Serrinha, porção centro-leste do maciço São José de Campestre, sudeste do RN

The of Serrinha plutonic suite, northeastern portion of the Borborema Province (NE Brazil), is characterized by a voluminous and diversified magmatism of Neoproterozoic age, intrusive in the Archean to Paleoproterozoic gneissic-migmatitic basement of the São José de Campestre massif. Field relations and petrographic and geochemical data allowed us to individualize different lithologic types among this plutonic suite, which is represented by intermediate to mafic enclaves, porphyritic diorites, porphyritic granitoids, porphyritic granodiorites, microporphyritic granites and dykes/sheets of microgranite. The intermediate-to-mafic enclaves occur associated with porphyritic granitoids, showing mixture textures. The porphyrytic diorites occur as isolated bodies, generally associated with intermediate-to-mafic enclaves and locally as enclaves within porphyritic granites. The granodiorites represent mixing between an intermediate to mafic magma with an acidic one. The micropophyritic granites occur as isolated small bodies, generally deformed, while the microgranite dykes/sheets crosscut all the previous granitoids. A U-Pb zircon age of 576 + 3 Ma was obtained for the Serrinha granite. This age is interpreted as age of the peak of the regional ductile deformational event (D3) and of the associated the E-W Rio Jacu shear zone, which control the emplacement of the Neoproterozoic syntectonic plutons. The porphyrytic granitoids show monzogranitic composition, transitional between peraluminous and metaluminous types, typically of the high potassium subalkaline-calc-alkaline series. The intermediate-to-mafic enclaves present vary from quartz diorite to tonalite/granodiorite, with metaluminous, shoshonitic affinity. The diorites are generally quartz-monzodiorite in composition, with metaluminous, subalkaline affinity. They display coarse-grained, inequigranular, porphyrytic texture, with predominance of plagioclase phenocrystals immersed in a matrix composed of biotite and pyroxenes. The microporphyrytic granites are essentially monzogranites of fine- to medium-grained texture, whereas microgranite dikes/sheets varying from monzogranites to syenogranites, with fine to media texture, equigranular. The diversified magmatism occurring at a relatively small surface associated with shear zones, suggests lithospheric dimensions for such structures, with magma extractions from different depths within the lower crust and upper mantle. The geological, geochemical and geochronological characteristics of the Serrinha plutonic suite suggest a pos-collisional geodynamic context for the Neoproterozoic magmatism. Thermobarometric data show emplacement conditions in the range 5-6 kbar (AlTamphibole) and 730-740°C (plagioclase-amphibole) for the porphyrytic granitoids (Serrinha body) and the intermediate-to-mafic enclaves

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceara (NE Brazil): geodynamic implications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The 3.4-3.5 Ga Sao Jose do Campestre massif, NE Brazil: remnants of the oldest crust in South America

The oldest fragment of continental crust recognized in South America occurs as an isolated Archean enclave in northeastem Brazil's Borborema Province, ca. 600 Ma Brasiliano-Pan African orogenic belt. This Archean fragment, the Sao Jose do Campestre massif, is surrounded by large tracts of 2.2-2.0 Ga Paleoproterozoic gneisses and is located more than 600-1500 km from the much larger assemblages of Archean rocks found in the Sao Fransciso and Amazonian cratons, located to the south and west, respectively. Geochronological studies of the Sao Jose do Campestre massif show that its oldest rocks contain zircons with U-Pb ages up to 3.5 Ga and Sm-Nd T-DM model ages of more than 3.7 Ga, indicating that they represent reworked crust. This older nucleus is flanked by both reworked and juvenile 3.25 and 3.18 Ga rocks which arc intruded by both 3.00 and 2.69 Ga plutonic bodies. The protracted evolution the Sao Jose do Campestre massif is consistent with that of a larger continental mass as opposed to a small crustal fragment that grew in isolation. As such, the Sao Jose do Campestre massif is interpreted as representing a detached piece of an evolved craton that became entrained with younger rocks during a subsequent Paleoproterozoic accretionary-orogenic event. This hypothesis is bolstered by the presence of Paleoproterozoic gneisses that envelop the Sao Jose do Campestre massif, as well as the existence of ca. 2.0 Ga metamorphic zircon and monazite within its rocks. The occurrence of several different Archean cratonic basement inliers within the greater Paleoproterozoic crustal framework of the Borborema Province suggests that cratonic slices spalled off one or more larger Archean masses prior to the ca. 2.2-2.0 Ga Paleoproterozoic orogenic collage. A important challenge is to link these older fragments to their parent cratons. Although results are not unique, the pattern of ages and isotopic signatures observed in the Sao Jose do Campestre massif is similar to that seen in parts of the Sao Francisco Craton, and it is possible that the Sao Jose do Campestre massif is a fragment of an Archean continental fragment formed during an episode of continental breakup prior to 2200 Ma. (C) 2003 Elsevier B.V. All rights reserved.