North-northeastern Brazil Research Articles

Lu–Hf constraints on pre-, syn, and post-collision associations of the Gurupi Belt, Brazil: Insights on the Rhyacian crustal evolution

The Gurupi Belt (together with the São Luís cratonic fragment), in north-northeastern Brazil, has been described in previous studies that used extensive field geology, structural analysis, airborne geophysics, zircon U–Pb dating, and whole-rock Sm–Nd isotope and geochemical data as a polyphase orogenic belt, with the Rhyacian being the main period of crust formation. This was related to a 2240 Ma to 2140 Ma accretionary processes that produced juvenile crust, which has subsequently been reworked during a collisional event at 2100 ± 20 Ma, with little evidence of Archean crust. In this study, we use Lu–Hf isotopic data in zircon from granitoids (including gneiss) of variable magmatic series, and amphibolite to improve the knowledge of this scenario, and investigate additional evidence of recycling of Archean basement. Pre-collisional high Ba-Sr and ferroan granitoids and amphibolite formed in island arc (2180–2145 Ma), show only zircons with suprachondritic εHf values (ca. +1 to +8) indicating the large predominance of juvenile magmas. Only 10% of the data show slightly negative εHf values (0 to −4), which have been observed in granodiorite-gneiss formed in continental arc (2170–2140 Ma), and in strongly peraluminous collisional granites (2125–2070 Ma), indicating the rework of older Paleoproterozoic to Archean components (HfTDM = 2.11–3.69 Ga). A two-component mixing model using both Hf and published Nd isotope data are in line with this interpretation and indicate more than 90% of juvenile material, and less influence of Archean materials. Comparing with other Rhyacian terranes that are interpreted to have been close to Gurupi in a pre-Columbia configuration (ca. 2.0 Ga), our results differ from those of SE-Guiana Shield, which show strong influence of Archean protoliths, and are very similar to those of the central-eastern portion of the Baoulé-Mossi Domain of the West African Craton, which has also been formed largely by juvenile magmas in an accretionary-collisional orogen.

Rhyacian and Neoproterozoic magmatic associations of the Gurupi Belt, Brazil: Implications for the tectonic evolution, and regional correlations

The Gurupi Belt, in north-northeastern Brazil, is a mobile belt developed in the south-southwestern margin of the São Luís cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover. Field, petrographic, geochemical, geochronological, and Nd isotopic information (new and published) constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed. The Rhyacian was the main period of magmatic activity, which can be grouped into two main stages. (1) ~2185–2130 ​Ma: pre-collisional, juvenile, calc-alkaline magnesian and calcic ferroan granitoid suites, and minor calc-alkaline and tholeiitic mafic plutonism (now amphibolites), formed in intra-oceanic to transitional/continental arcs; and intra- or back-arc volcano-sedimentary basin. (2) ~2125–2070 ​Ma: syn- (two-mica granites) to late-collisional (potassic to shoshonitic granites and quartz-syenite) plutonic suites produced after crustal thickening and melting, with localized migmatization, that intruded during the compressive D1 deformational phase and concomitantly with greenschist to amphibolite metamorphism. There is a zonation of the Rhyacian episodes, with intra-oceanic stages occurring to the northeast, and the continental arc and collisional phases occurring to the southwest, indicating the presence of an active continental margin to the southwest, and subduction from NE to SW (present-day configuration). This magmatic framework is a continuation to the south of what is described for the São Luís cratonic fragment to the north, and the orogenic scenario is identical to what is observed for the same period in the West African Craton (Eburnean/Birrimian orogen), which additionally supports previous geological correlations. In the Neoproterozoic, a few magmatic occurrences are recognized. An extensional event allowed the intrusion of an anorogenic, nepheline syenite at ca. 730 Ma, which was followed by the intrusion of a crustal, calc-alkaline microtonalite, of uncertain tectonic setting, at 624 ​Ma. Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 ​Ma. This metamorphic event is probably related to crustal thickening, which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 ​Ma. The absence of oceanic and arc-related assemblages, along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic–Early Cambrian evolution of the Gurupi Belt, with rifting and posterior closure of the basin, without oceanization. Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly, respectively, but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events, but, instead, as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time.

Predictive Mapping of Prospectivity in the Gurupi Orogenic Gold Belt, North–Northeast Brazil: An Example of District-Scale Mineral System Approach to Exploration Targeting

The Gurupi Belt hosts a Paleoproterozoic gold province located in north–northeastern Brazil, at the borders of Para and Maranhao states. It is considered to be an extension of the prolific West African Craton’s Birimian gold province into South America. Additionally, the belt has been the object of recent mineral exploration programs with significant resource discoveries. This study presents the results of predictive mapping using up-to-date mineral system concepts and recently finished regional-scale geological mapping, stream sediment and airborne geophysical surveys conducted by the Geological Survey of Brazil. We relate gold mineralization to an initially enriched crust, metamorphism, deep fluid pathways, structurally controlled damage zones and hydrothermal alteration. Prospective targets were generated using only regional public datasets and knowledge-driven targeting technique. This work did not incorporate any known gold deposits, yet it predicted the largest known deposits and their satellite targets. Besides, high prospective targets mapped almost 40% of known primary gold occurrences within 7% of the project area. This work allowed considerable search area reduction and identification of new target areas, thus collaborating on reducing costs, time and risk of mineral exploration. Results indicate that we achieved an efficient understanding of the geological processes related to the Gurupi Belt mineral system.

The influence of extratropical Atlantic Ocean region on wet and dry years in North-Northeastern Brazil

The rainy season of north-Northeastern Brazil (NE), one of the tropical regions with the largest rainfall interannual variability, is associated with the Intertropical Convergence Zone (ITCZ) influence, which is located in the southermost position during this season (March-April-May). However, there is a large interannual variability in the ITCZ position, associated with atmospheric and oceanic anomalies, responsible for dry or wet years in the region. Besides the tropical Pacific Sea Surface Temperature (SST) anomalies and the Tropical Atlantic SST gradient influences on this variability, extratropical atmospheric influences are identified over the North and South Atlantic. Composites of cases with anomalous precipitation during the middle of the rainy season (April) indicate the El Nino-Southern Oscillation (ENSO) features and northern and southern Atlantic atmospheric anomalies in December-January-February (DJF). When El Nino and La Nina years are removed from the composites of dry and wet cases, respectively, the centers of action over the extratropical North Atlantic in DJF remain, and features of extratropical South Hemisphere become more evident. The tropical SST dipole is still present with inverted signs in each case, consistent with the NE precipitation anomalies. The main mode of variability in the Southern Hemisphere (South Annular Mode) and in the Northern Hemisphere (North Annular Mode) is present in DJF during the dry cases. These annular patterns occur in the composites of Northeast Brazil precipitation anomalies including or excluding ENSO years. Therefore, besides ENSO relations with SAM discussed in previous studies, another connection exists over the South Atlantic, linking anomalies between high and tropical latitudes. The precipitation anomalies over NE have contributions of the two extratropical Atlantic hemispheres regions. The atmospheric anomalies observed in the pre-rainy season can be a helpful tool in monitoring the North Northeastern B

Determination of CYP2D6 *3, *4, and *10 frequency in women with breast cancer in São Luís, Brazil, and its association with prognostic factors and disease-free survival

The CYP2D6 enzyme is crucial for the metabolism of tamoxifen. The CYP2D6 gene is highly polymorphic, and individuals can be extensive, intermediate, or poor tamoxifen metabolizers. The aim of this study was to determine the frequencies of the CYP2D6 *3, *4, and *10 alleles in women with breast cancer who were treated with tamoxifen and analyze the association of enzyme activity with prognostic factors and disease-free survival. We observed a high frequency of CYP2D6 *10, with an allelic frequency of 0.14 (14.4%). The *3 allele was not present in the studied population, and *4 had an allelic frequency of 0.13 (13.8%). We conclude that patients with reduced CYP2D6 activity did not present worse tumor characteristics or decreased disease-free survival than women with normal enzyme activity, as the difference was not statistically significant. We also observed a high frequency of CYP2D6 *10, which had not been previously described in this specific population. This study is the first in north-northeastern Brazil that aimed to contribute to the knowledge of the Brazilian regional profile for CYP2D6 polymorphisms and their phenotypes. These findings add to the knowledge of the distribution of different polymorphic CYP2D6 alleles and the potential role of CYP2D6 genotyping in clinical practice prior to choosing therapeutic protocols.

Metallogenesis of the Paleoproterozoic Piaba orogenic gold deposit, São Luís cratonic fragment, Brazil

Piaba is an orogenic gold deposit (~3.5Moz) of the São Luís cratonic fragment in north-northeastern Brazil. The deposit is epizonal–mesozonal and associated with the development of a subvertical strike–slip fault that cut across Rhyacian metavolcano-sedimentary rocks and granitoids. The metavolcano-sedimentary sequence comprises carbon-bearing schists, andesite/dacite, ultramafic rocks and felsic tuffs formed at 2240±5Ma to 2227±33Ma that were intruded at 2214±3Ma by fine-grained, subvolcanic granophyric granodiorite. Whole-rock geochemistry indicates that the hosting metavolcano-sedimentary sequence formed in a subduction-related (arc, back-arc?) setting, which has previously been interpreted as the early-arc stage of an accretionary orogen (2240–2214Ma) that was followed by voluminous subduction-related calc-alkaline arc magmatism (2168–2145Ma) and by a collisional phase (2100±15Ma) that produced several bodies of peraluminous granites. The hydrothermal alteration of the host rocks produced early, distal carbonization and hematitization and proximal, ore-related chlorite–sericite–carbonate–sulfide alteration. Two styles of mineralization, occurring in association, are present: (1) a network of thin quartz±sulfide veinlets and subordinate narrow breccia veins with refractory- to free-milling gold dissemination in hydrothermally-altered host rocks, and (2) subordinate low-sulfide Au-quartz veins with free-milling gold. Fluid inclusions and stable isotopes characterize the mineralizing solution as a relatively reduced (log fO2=−30 to −35), neutral to slightly alkaline (pH5 to 6.2), low-salinity (average 5% NaCl), aqueous-carbonic (XCO2=5 to 59mol%, XH2O=40 to 93mol%, XN2 and XCH4 <1mol%) metamorphic fluid (δ18OH2O=+5.5 to +8.9‰, δDH2O=−8 to −69‰), and suggest that gold mineralization occurred at 250° to 330°C and 1.25 to 2.8kbar in response to phase separation and fluid–rock interactions that produced sulfidation and minor carbonatization. Sulfur (δ34S=−2.7 to −3.8‰) is from an undetermined source, probably magmatic (oxidized) or sedimentary. Lead isotope compositions of gold, ore-related pyrite and K-feldspar from regional rocks suggest that collision-related granitoids of ca. 2100±15Ma are the most likely sources for Pb in the ore, although mantle and lower crustal sources are also observed. 40Ar/39Ar in hydrothermal sericite yielded a plateau age of 1980±13Ma, which is similar to the Pb–Pb model age of gold of 1959Ma. These are considered the minimum age for gold mineralization, whereas the maximum age of 2009±11Ma is given by a small gold-hosting intrusion in the same region.

Mafic dykes intrusive into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt (Parnaíba Province), north–northeastern Brazil: Geochemistry, Sr–Nd–Pb–O isotopes, 40Ar/39Ar geochronology, and relationships to CAMP magmatism

Dykes of diabase and microgabbro intruded into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt, which are tectonic and erosive windows of the Parnaíba Basin in north–northeastern Brazil. Ar–Ar ages were determined, and major, trace element, and Nd–Sr–Pb–O isotopic compositions of these dykes were measured to provide insights into their age, and into the nature of their mantle sources and petrogenetic processes. The data have also been used to compare the chemical and isotopic signatures of the dykes with those of the Central Atlantic Magmatic Province (CAMP). Four chemical groups of mafic dykes have been identified. These comprise two subtypes of high-Ti rocks (i) HTi-1 (TiO2<2.3wt.%; SiO2>47 wt.%), (ii) HTi-2 (TiO2>2.7wt.%; SiO2>47wt.%), in addition to (iii) evolved high-Ti (TiO2>4wt.%; SiO2 of ~46wt.%) and (iv) low-Si (TiO2>2.2wt.%; SiO2<45wt.%) rocks. 40Ar/39Ar geochronology of plagioclase returned ages of 201±4 Ma and 193±10 Ma for the HTi-2 subtype, and of 201±2 Ma and 207±9Ma for the evolved high-Ti group. The HTi-1 and low-Si groups presented highly disturbed age spectra, and did not allow the definition of their emplacement ages. The Argon data indicate an age >200Ma for the low-Si group and are dubious with respect to the age of theHTi-1 subtype, if coeval with (i.e., ~200Ma), or older than, the HTi-2 and evolved high-Ti types. All groups present δ18O values of pyroxene that are compatible with uncontaminated mantle-derived magmas. The HTi-1 subtype (average 143Nd/144Nd200=0.512644; 87Sr/86Sr200=0.7035; 206Pb/204Pb of 17.86) shows the less enriched and less fractionated (more primitive) trace element distribution of all groups. The HTi-2 subtype shows enriched trace element pattern and depleted Nd–Sr signature (143Nd/144Nd200=0.512610; 87Sr/86Sr200=0.7037) and average 206Pb/204Pb ratios of 17.23. The evolved high-Ti chemical group shows average ratios of 143Nd/144Nd200=0.512558, 87Sr/86Sr200=0.7035, and 206Pb/204Pb of 16.88, and the more enriched trace-elements signature among the four groups. The chemical and isotopic compositions and trends of the HTi-1/HTi-2/EHTi types are consistent with their derivation from an asthenosphere-derived parental magma further modified by differentiation and minimal crust contamination (higher in the HTi-2 and EHTi types), and by the derivation of one type from another via fractional crystallization. These high- and evolved high-TiO2 types show ages and some chemical and isotopic features that are consistent with those of the CAMP magmatism. Some differences found are ascribed to petrogenetic processes, such as magma differentiation. A combination of warming of the mantle and edge-driven convection beneath the Pangea supercontinent after the closure of the Neoproterozoic (Brasiliano/Pan-African) orogenies in the Ediacaran–Cambrian boundary might have triggered the magmatic event. The low-Si type shows paired Ta–Nb and Zr–Hf depletions, and depleted Sr–Nd (average 143Nd/144Nd200=0.512687; 87Sr/86Sr200=0.703) and enriched Pb (206Pb/204Pb of 18.66) isotopic compositions that may be interpreted to result either from interaction of a subcontinental lithospheric mantle with products of an earlier subduction or by contamination of the mantle-derived magma during ascent and emplacement in the continental crust. It is hypothesized that these dykes were emplaced in the Ediacaran–Cambrian boundary, after the Neoproterozoic orogeny that built up the Gurupi Belt and in the early extensional stages that preceded the formation of the Parnaíba Basin.

Record of Edessa scabriventris Stål (Hemiptera: Pentatomidae) associated to Eugenia uniflora (Brazilian-Cherry) and Psidium guajava (Guava) (Myrtaceae), in north-northeastern Brazil

This study reports for the first time Edessa scabriventris Stål on Eugenia uniflora (Brazilian-cherry) and on Psidium guajava (guava) (Myrtaceae), fruit trees with economic value. Its geographic distribution is extended with records for the states of Alagoas (Maceió Municipality 35°45'11.16''W; 9°40'18.52''S) and Pará (Belém Municipality 48°28'14.65''W; 1°26'14.83''S), north-northeastern Brazil.

O fenômeno da brisa e sua relação com a chuva sobre Fortaleza-CE

A análise da freqüência horária de chuva sobre a cidade de Fortaleza, situada na costa do Ceará e no norte do Nordeste do Brasil, reafirmou a já conhecida maior incidência de precipitação no período noturno do dia, principalmente durante a madrugada, até o início da manhã, ao longo do ano. Essa análise também mostrou uma redução das chuvas no local, no período vespertino do dia. A observação de imagens fornecidas por satélites meteorológicos, registros de chuva e campos de ventos a partir de modelos numéricos de tempo sugerem neste estudo, que a passagem da porção ocidental da frente de brisa terrestre (sistema freqüentemente formado entre o leste do Ceará e o norte do Rio Grande do Norte), pela área de Fortaleza (e vizinhanças) facilita, a partir da sua convergência com os ventos alísios de sudeste, a ocorrência de chuvas em geral rápidas e pouco intensas notadamente entre a madrugada e o início da manhã. Além disso, a convergência dessa brisa com sistemas meteorológicos de grande escala também deve contribuir para a freqüência elevada de precipitação no período mencionado. Neste caso, em geral as chuvas são mais intensas. Por outro lado, a brisa marítima coopera para a menor incidência de chuva em Fortaleza (sob área de supressão de cumulus), no período da tarde.

Impacto de alterações nas exportações de açúcar e álcool nas regiões Centro-Sul e Norte-Nordeste sobre a economia do Brasil

Este trabalho teve por objetivo estimar o impacto de um aumento nas exportações brasileiras de açúcar e de álcool sobre os níveis de produção e de emprego do país. Para tal, utilizou-se uma matriz de insumo-produto inter-regional da economia brasileira. Verificou-se, a princípio, que um choque de demanda, resultante de uma expansão das exportações de açúcar, apresenta um maior impacto sobre o produto e o emprego do país, comparado ao derivado de um incremento nas exportações de álcool. A análise regional mostrou ainda que o impacto de um choque de demanda - seja esse resultado de uma expansão de exportações de açúcar ou de álcool - sobre a produção e emprego na região Norte-Nordeste, é mais expressivo que na região Centro-Sul. Esses resultados são importantes para subsidiar a identificação de políticas e o estabelecimento de metas para incentivar um produto ou região, considerando-se a propagação dos benefícios econômicos.

Impacts of Changes in Regional Sugar and Ethanol Exports Upon Brazilian Overall Economy

This paper estimates the impact of an increase in Brazilian sugar and ethanol demand for exports upon the countries’ overall production and employment. The impacts were simulated considering each of the major cane producing areas of the country (Center-South and North-Northeast). An inter-regional input-output matrix for the Brazilian economy was used for that purpose. It was observed that a demand shock, resulting from an expansion of sugar exports presented an impact of greater magnitude upon the countries’ production and employment when compared to the impact from an increase in ethanol. In addition, the results indicated that when the impact is generated at the North-Northeastern Brazil, production and employment is more affected than when it begins at the Center-South region of the country. The result of how the economic benefits are disseminated in the economy is important to identify policies and establish targets for regional production.

The South Atlantic Convergence Zone: Intensity, Form, Persistence, and Relationships with Intraseasonal to Interannual Activity and Extreme Rainfall

The characteristics of intensity, geographical location, and persistence of the South Atlantic convergence zone (SACZ) during the austral summer are investigated. Intensity and spatial features of the SACZ are identified by performing a factor analysis of structural properties of outgoing longwave radiation (OLR) data. The first two leading factors explain 65% of the total variance of structural properties and characterize the SACZ according to intensity and location (oceanic versus continental). An index is constructed based on the magnitude of the factor scores to identify intense (weak) and oceanic (continental) SACZ. The intense SACZ category is associated with negative OLR anomalies over a large area of tropical South America, extending from the western Amazon to the Atlantic Ocean. The weak SACZ category is observed with positive OLR anomalies over tropical South America and negative OLR anomalies over southeastern South America. Oceanic and continental aspects of the SACZ are related to a midlatitude wave train pattern. The Madden–Julian oscillation (MJO) modulates intense SACZ events with persistence longer than 3 days. Interannual variability of persistent events indicates that the ratio of oceanic to continental SACZ as well as their frequency depends on the phase of El Niño–Southern Oscillation (ENSO). Occurrence of extreme rainfall in Brazil is discussed in the context of variations in the SACZ and MJO. Intense (weak) SACZ increases (decreases) the 95th daily rainfall percentile over central-eastern Brazil compared to the climatology. Oceanic (continental) SACZ increases (decreases) the 95th daily rainfall percentile over southeastern Brazil. The MJO phase characterized by suppression of convective activity over Indonesia and enhancement over the central Pacific increases the 95th daily rainfall percentile over north-northeastern Brazil, whereas opposite features are observed for the phase of the MJO characterized by the enhancement of convection over Indonesia and suppression over the central Pacific.