Geochemistry and geochronology of pre-Brasiliano rocks from the Transversal Zone, Borborema Province, Northeast Brazil

Proterozoic metamorphosed sequences are identified in the Transversal Zone (TZ) domain of the Borborema geological province, Northeast Brazil. This TZ domain is located between the well-known E–W Patos and Pernambuco continental shear zones. In its eastern part, in the Taquaritinga region, a large mass of augen gneisses with a conspicuous horizontal to subhorizontal tectonic foliation forms one of the most important rock types in the region that displays U–Pb zircon ages ca. 1.52 Ga. Paleoproterozoic orthogneisses dated by U–Pb on zircon at ca. 1.97 Ga and older paragneisses and banded gneisses represent basement rocks, which were cross-cut by these Mesoproterozoic augen gneisses, and have been in turn intruded by plutonic rocks in upper Neoproterozoic (U–Pb and Rb–Sr, ca. 0.6 Ga) times.Chemical analyses of major, minor, and trace elements (including REE) for the basement orthogneisses indicate calcalkaline affinities and a signature very similar to volcanic arc granites, representing crustal accretion during the Paleoproterozoic Transamazonian/Eburnean orogenesis in the region. In turn, the chemical data for augen gneisses indicate that they are relatively homogeneous and evolved metaluminous metaplutonic rocks with characteristics very similar to A-type granites generated and emplaced in an extensional anorogenic setting. Relatively high ⁸⁷Sr/⁸⁶Sr initial ratio and negative _Nd(t) are signatures of crustal components in these rocks.Based on geochemical, geochronological, and structural data, the Taquaritinga region is composed of Paleoproterozoic (>1.97 Ga) rocks intruded by Mesoproterozoic (ca. 1.5 Ga) anorogenic granites and Neoproterozoic granites (ca. 0.6 Ga). These data also suggest that the tectonometamorphic structures displayed by Meso and Neoproterozoic suites were developed by the Brasiliano/Pan-African orogeny and that the record of Transamazonian/Eburnean orogeny is restricted to basement rocks. This means that there is no evidence for a compressional event in Mesoproterozoic times (Cariris Velhos=Grenville) as suggested for the central and western part of the TZ. It is important to remark that the Taquaritinga augen gneisses are, up to now, the only unit that represents magmatic pulses associated with extensional episodes with this age (ca. 1.5 Ga) in the TZ and in the whole Borborema Province.

Resumen

A zona Transversal da Província Borborema está geologicamente situada entre os lineamentos Pernambuco e Patos. Na sua parte oriental, na região de Taquaritinga (PE), dominam augen gnaisses com uma penetrativa e proeminente foliação tectônica subhorizontal, com idade de cristalização de 1.52 Ga obtida em zircão. Estas rochas são intrusivas em ortognaisses e paragnaisses do embasamento com idade mínima em torno de 1.97 Ga, e são intrudidas por rochas plutônicas associadas ao Ciclo Brasiliano (ca. 0.6 Ga).Análises de elementos maiores, menores e traços (incluindo terras raras) nos augen gnaisses mostram caráter metaluminoso para esta suíte ígnea e fortes semelhanças com os granitos tipo-A gerados em ambiente anorogênico. Razões iniciais ⁸⁷Sr/⁸⁶Sr relativamente altas e _Nd(t) negativos são assinaturas indicadoras de forte contribuição crustal nestes augen gnaisses.A conjunção dos dados geoquímicos, geocronológicos e de campo indicam que na região de Taquaritinga onde são identificadas rochas de idades paleo (>1.95 Ga), meso (ca. 1.5 Ga) e neoproterozóicas (ca. 0.6 Ga), o ciclo orogênico Transamazônico é restrito às rochas do embasamento, e que todas as estruturas dúcteis identificadas nas rochas meso e neoproterozóicas foram desenvolvidas durante o Ciclo orogênico Brasiliano. Não foram encontradas evidências que atestem a existência do Ciclo Cariris Velhos nesta parte da Província Borborema. Contudo, está bem marcado que nesta Zona Transversal e na Província Borborema, os augen gnaisses de Taquaritinga são, até o momento, os únicos marcadores de pulsos magmáticos associados com eventos extensionais crustais datados do Mesoproterozóico inferior.     

Paleomagnetism,magnetic fabric,and <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of Pliocene and Quaternary ignimbrites in the Arequipa area,southern Peru

⁴⁰Ar/³⁹Ar ages and paleomagnetic correlations using characteristic remanent magnetizations (ChRM) show that two main ignimbrite sheets were deposited at 4.86 ± 0.07 Ma (La Joya Ignimbrite: LJI) and at 1.63 ± 0.07 Ma (Arequipa Airport Ignimbrite: AAI) in the Arequipa area, southern Peru. The AAI is a 20–100 m-thick ignimbrite that fills in the Arequipa depression to the west of the city of Arequipa. The AAI is made up of two cooling units: an underlying white unit and an overlying weakly consolidated pink unit. Radiometric data provide the same age for the two units. As both units record exactly the same well-defined paleomagnetic direction (16 sites in the white unit of AAI: Dec = 173.7; Inc = 31.2; α95 = 0.7; k = 2749; and 10 sites in the pink unit of AAI; Dec = 173.6; Inc = 30.3; α95 = 1.2; k = 1634), showing no evidence of secular variation, the time gap between emplacement of the two units is unlikely to exceed a few years. The >50 m thick well-consolidated white underlying unit of the Arequipa airport ignimbrite provides a very specific magnetic zonation with low magnetic susceptibilities, high coercivities and unblocking temperatures of NRM above 580°C indicating a Ti-poor titanohematite signature. The Anisotropy of Magnetic Susceptibility (AMS) is strongly enhanced in this layer with anisotropy values up to 1.25. The fabric delineated by AMS was not recognized neither in the field nor in thin sections, because most of the AAI consists in a massive and isotrope deposit with no visible textural fabric. Pumices deformation due to welding is only observed at the base of the thickest sections. AMS within the AAI ignimbrite show a very well defined pattern of apparent imbrications correlated to the paleotopography, with planes of foliation and lineation dipping often at more than 20° toward the expected vent, buried beneath the Nevado Chachani volcanic complex. In contrast with the relatively small extent of the thick AAI, the La Joya ignimbrite covers large areas from the Altipano down the Piedmont. Ti-poor titanomagnetites are the dominant magnetic carriers and AMS values are generally lower than 1.05. Magnetic foliations are sub horizontal and lineations directions are scattered in the LJI. The AMS fabrics are probably controlled by post-depositional compaction and welding of the deposit rather than transport dynamics. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Physical modelling of cracked/fractured media using downscaled laboratory experiments has been used with great success as a useful alternative for understanding the effect of anisotropy in the hydrocarbon reservoir characterization and in the crustal and mantle seismology. The main goal of this work was to experimentally verify the predictions of effective elastic parameters in anisotropic cracked media by Hudson and Eshelby–Cheng's effective medium models. For this purpose, we carried out ultrasonic measurements on synthetic anisotropic samples with low crack densities and different aspect ratios. Twelve samples were prepared with two different crack densities, 5% and 8%. Three samples for each crack density presented cracks with only one crack aspect ratio, whereas other three samples for each crack density presented cracks with three different aspect ratios in their composition. It results in samples with aspect ratio values varying from 0.13 to 0.26. All the cracked samples were simulated by penny‐shaped rubber inclusions in a homogeneous isotropic matrix made with epoxy resin. Moreover, an isotropic sample for reference was constructed with epoxy resin only. Regarding velocity predictions performed by the theoretical models, Eshelby–Cheng shows a better fit when compared with the experimental results for samples with single and mix crack aspect ratio (for both crack densities). From velocity values, our comparisons were also performed in terms of the ε, γ, and δ parameters (Thomsen parameters). The results show that Eshelby–Cheng effective medium model fits better with the measurements of ε and γ parameters for crack samples with only one type of crack aspect ratio.     

Observing the critical zone on a critical budget: The Peri Lake experimental catchment

The Peri Lake Experimental Catchment, in Southern Brazil, is a small coastal lake (5 km², 7 m depth) with a total catchment area of 20 km². The catchment is mainly covered by subtropical Atlantic Forest. Peri Lake is a recreational destination, an important ecosystem for biodiversity preservation, and a major water supply source. Even though there is a clear social and economic relevance, the information on this ecosystem is scarce, especially regarding the dynamics of water balance and water quality. We built this observatory using a low-cost, low-technology monitoring system to estimate the major components of the water budget on what we called a critical budget. We monitor meteorology, rainfall interception in two plots, overland flow and groundwater connectivity in a representative hillslope; and streamflow and velocity are measured in several small headwater rivers mostly starting during 2015. Geographic information on topography, land cover, geology, soil characteristics and the location of all the equipment installed in the field are also provided. The data set can be used to understand rainfall interception in Atlantic forests, catchment connectivity and streamflow permanence in coastal areas, spatial patterns of baseflow, and the modelling of complex processes in the critical zone involving the interaction between surface and groundwater, that are important in coastal lake ecosystems. Besides being used for research and education, we hope this observatory built on a shoestring budget will encourage fieldwork particularly in underrepresented and underfunded regions of the world.     

Precise topography- and aperture-dependent motion compensation for airborne SAR

Efficient synthetic aperture radar (SAR) processing algorithms are unable to exactly implement the aperture- and topography-dependent motion compensation due to the superposition of the synthetic apertures of several targets having different motion errors and potentially different topographic heights. Thus, during motion compensation, a reference level is assumed, resulting in residual phase errors that impact the focusing, geometric fidelity, and phase accuracy of the processed SAR images. This letter proposes a new short fast Fourier transform-based postprocessing methodology capable of efficient and precise compensation of these topography- and aperture-dependent residual phase errors. In addition to wide beamwidth (very high resolution) SAR systems, airborne repeat-pass interferometry especially benefits from this approach, as motion compensation can be significantly improved, especially in areas with high topographic changes. Repeat-pass interferometric data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach.     

Caractérisation des ignimbrites néogènes du bassin d'Arequipa,Pérou

Four ignimbritic units have filled the Arequipa Basin and outcrop around the Chachani Volcano. (1) The oldest Río Chili ignimbrite is 13.33 Ma old; (2) the most widespread La Joya ignimbrite is 4.9 Ma old; (3) the Arequipa Airport ignimbrite (1.65 Ma) flowed from an area buried beneath Chachani; (4) the Yura Tuffs, 1.02 Ma old, are restricted to the west of Chachani. All are calc-alkaline rhyolites with plagioclase, biotite, quartz, sanidine, and opaques, but the Río Chili and La Joya ignimbrites also contain amphibole. Trace elements of the older ignimbrites reflect stronger crustal influence. To cite this article: P. Paquereau et al., C. R. Geoscience 337 (2005).     

Hercynite–quartz-bearing granulites from Brejões Dome area, Jequié Block, Bahia, Brazil: Influence of charnockite intrusion on granulite facies metamorphism

In the present study, we describe and discuss the geology of aluminous–magnesian granulites and associated garnet-bearing charnockitic granulite from the Brejões Dome area, located in the Jequié Block, part of the São Francisco Craton in Bahia, Brazil. Investigation of metamorphic mineral assemblages allows the evaluation of P–T conditions for the formation of these rocks, and therefore to obtain constraints for the better understanding of the geological evolution of the area. We conclude that the rocks from the Brejões Dome area were formed under granulite facies conditions of low to intermediate pressure (5–8 kbar). Temperatures determined in samples of aluminous–magnesian granulites collected away from the dome are in the order of 850 °C, similar to those determined elsewhere in the southern part of the Itabuna–Salvador–Curaçá Orogen. However, samples of the same rock type collected close to the Brejões Dome are hercynite + quartz-bearing and record higher temperatures of about 900–1000 °C. It is suggested that the intrusion of the Brejões charnockite diapir was responsible for a local increase in temperature above the peak temperature of regional granulite metamorphism.     

Estimation of the seismic wavelet through homomorphic deconvolution and well log data: application on well-to-seismic tie procedure

Wavelet estimation and well-tie procedures are important tasks in seismic processing and interpretation. Deconvolutional statistical methods to estimate the proper wavelet, in general, are based on the assumptions of the classical convolutional model, which implies a random process reflectivity and a minimum-phase wavelet. The homomorphic deconvolution, however, does not take these premises into account. In this work, we propose an approach to estimate the seismic wavelet using the advantages of the homomorphic deconvolution and the deterministic estimation of the wavelet, which uses both seismic and well log data. The feasibility of this approach is verified on well-to-seismic tie from a real data set from Viking Graben Field, North Sea, Norway. The results show that the wavelet estimated through this methodology produced a higher quality well tie when compared to methods of estimation of the wavelet that consider the classical assumptions of the convolutional model.     

Inter-annual changes in fish communities of a tropical bay in southeastern Brazil: What can be inferred from anthropogenic activities?

We assessed inter-annual changes in fish assemblages of a tropical bay which experienced a heavily industrialized process in the last decades. A highly significant difference in community structure among the bay zones, and a decrease in fish richness and abundance over time were found. Changes in fish richness and abundance between the two first (1987–1988 and 1993–1995) and the two latter time periods (1998–2001 and 2012–2013) were sharpest in the inner bay zone, the most impacted bay area, and in the middle zone, whereas the outer zone remained comparatively stable over time. These changes coincided with increased metal pollution (mainly, Zn and Cd) in the bay and with the enlargement of the Sepetiba Port. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable acting as a buffer stabilizing temporal community changes.     

A two-dimensional probabilistic acute human-health risk assessment of insecticide exposure after adult mosquito management

Ultra-low-volume (ULV) aerosol applications of insecticides are used to manage high densities of adult mosquitoes. We used two-dimensional probabilistic risk assessment methodologies to evaluate three pyrethroid insecticides (phenothrin, resmethrin, and permethrin), pyrethrins, and two organophosphate insecticides (malathion and naled), applied by truck-mounted ULV sprayer. Piperonyl butoxide, a synergist commonly used in pyrethroid and pyrethrins formulations, was also assessed. The objective of our study was to evaluate probabilistically if a deterministic human-health risk assessment of mosquito insecticides was sufficiently conservative to protect human-health. Toddlers and infants were the highest risk groups while adult males were the lowest risk group assessed in this study. Total acute exposure ranged from 0.00003 to 0.0003 mg/kg day⁻¹ for the chemicals and subgroups assessed examining inhalation, dermal, oral, and hand-to-mouth exposure. We used the risk quotient (RQ) method for our risk assessment, which is calculated by dividing the total potential exposure for each subgroup and chemical by its ingestion toxic endpoint value (RfD). Mean RQs ranged from 0.000004 to 0.034 for all subgroups and chemicals, with none exceeding the RQ level of concern. Naled had the highest RQs of any chemical assessed while PBO had the lowest. Sensitivity analysis demonstrated that the exposure from inhalation and deposition contributed the largest variance to the model output. Results support the findings of previous studies that the risks from adult mosquito management are most likely negligible, and that the human-health deterministic risk assessment is most likely sufficiently conservative.