K–Ar and Ar/Ar ages of dikes emplaced in the onshore basement of the Santos Basin, Resende area, SE Brazil: implications for the south Atlantic opening and Tertiary reactivation

New K–Ar and ⁴⁰Ar/³⁹Ar data of tholeiitic and alkaline dike swarms from the onshore basement of the Santos Basin (SE Brazil) reveal Mesozoic and Tertiary magmatic pulses. The tholeiitic rocks (basalt, dolerite, and microgabbro) display high TiO₂ contents (average 3.65 wt%) and comprise two magmatic groups. The NW-oriented samples of Group A have (La/Yb)_N ratios between 15 and 32.3 and range in age from 192.9±2.2 to 160.9±1.9 Ma. The NNW-NNE Group B samples, with (La/Yb)_N ratios between 7 and 16, range from 148.3±3 to 133.9±0.5 Ma. The alkaline rocks (syenite, trachyte, phonolite, alkaline basalts, and lamprophyre) display intermediate–K contents and comprise dikes, plugs, and stocks. Ages of approximately 82 Ma were obtained for the lamprophyre dikes, 70 Ma for the syenite plutons, and 64–59 Ma for felsic dikes. Because Jurassic–Early Cretaceous basic dikes have not been reported in SE Brazil, we might speculate that, during the emplacement of Group A dikes, extensional stresses were active in the region before the opening of the south Atlantic Ocean and coeval with the Karoo magmatism described in South Africa. Group B dikes yield ages compatible with those obtained for Serra Geral and Ponta Grossa magmatism in the Paraná Basin and are directly related to the breakup of western Gondwana. Alkaline magmatism is associated with several tectonic episodes that postdate the opening of the Atlantic Ocean and related to the upwelling of the Trindade plume and the generation of Tertiary basins southeast of Brazil. In the studied region, alkaline magmatism can be subdivided in two episodes: the first one represented by lamprophyre dykes of approximately 82 Ma and the second comprised of felsic alkaline stocks of approximately 70 Ma and associated dikes ranging from 64 to 59 Ma.

Resumo

Novos dados K–Ar e ⁴⁰Ar/³⁹Ar de enxames de diques toleíticos e alcalinos localizados no embasamento onshore da Bacia de Santos (SE Brasil) apontam para diferentes pulsos magmáticos ocorridos entre o Jurássico e o Terciário. Os diques de rochas toleíticas (basalto, diabásio e microgabro), são mais velhos, exibem altos teores de TiO₂ (3,65% peso na média) e podem ser subdivididos em dois grupos magmáticos. O Grupo A aflora a norte da Bacia de Resende, compreende diques orientados na direção NW, com razões (La/Yb)_N entre 15 e 32,3, e idades entre 192.9±2.2 e 160.9±1.9 Ma. O Grupo B aflora a sul e a leste da Bacia de Resende, engloba diques orientados na direção NNW e NNE, com razões (La/Yb)_N entre 7 e 16, e idades obtidas entre 148.3±3 e 133.9±0.5 Ma. As rochas alcalinas (sienito, traquito, fonolito, basalto alcalino e lamprófiro) possuem teores médios de K, e afloram como diques, plugs e stocks.. As idades obtidas são de ca. 82 Ma para os diques lamprofíricos, de ca. 70 Ma para os plugs sieníticos, e entre 64 e 59 Ma para os diques félsicos. Como estas idades Jurássicas para diques toleíticos ainda não foram descritas para a região sudeste do Brasil, pode-se especular que durante o emplacement dos diques do GrupoA o cenário tectônico indicaria esforços extensionais anteriores à abertura do Oceano atlântico Sul, e contemporânea ao derrame basáltico do Karoo na África do Sul. Já os diques do Grupo B são contemporâneos ao magmatismo Serra Geral e ao enxame de diques de Ponta Grossa, e portanto este episódio está diretamente relacionado à separação entre o Brasil e África no Cretáceo. O magmatismo alcalino está associado a diversos episódios tectônicos que sucedem à abertura do Oceano Atlântico Sul e que resultaram no desenvolvimento das Bacias terciárias do sudeste brasileiro. Está provavelmente relacionado à chegada da Pluma de Trindade e as idades obtidas para a região em estudo indicam que o magmatismo lamprofírico é mais antigo (ca. 82 Ma), seguido pelos plútons sieníticos (ca. 70 Ma) e diques associados (64 a 59 Ma.)     

Radio-continuum study of the Nearby sculptor group galaxies. Part 1: NGC 300 at λ=20 cm

A series of new radio-continuum (λ=20 cm) mosaic images focused on the NGC?300 galactic system were produced using archived observational data from the VLA and/or ATCA. These new images are both very sensitive (rms?=60 μJy) and feature high angular resolution (<10?″). The most prominent new feature is the galaxy’s extended radio-continuum emission, which does not match its optical appearance. Using these newly created images a number of previously unidentified discrete sources have been discovered. Furthermore, we demonstrate that a joint deconvolution approach to imaging this complete data-set is inferior when compared to an immerge approach.     

Coastal habitat degradation and green sea turtle diets in Southeastern Brazil

To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear.     

Petrogenetic links between lepidolite-subtype aplite-pegmatite,aplite veins and associated granites at Segura (central Portugal)

In the Segura area, Variscan S-type granites, aplite veins and lepidolite-subtype granitic aplite-pegmatite veins intruded the Cambrian schist-metagraywacke complex. The granites are syn D3. Aplite veins also intruded the granites. Two-mica granite and muscovite granite have similar ages of 311.0 ± 0.5 Ma and 312.9 ± 2.0 Ma but are not genetically related, as indicated by their geochemical characteristics and (⁸⁷Sr/⁸⁶Sr)₃₁₁ values. They correspond to distinct pulses of magma derived by partial melting of heterogeneous metapelitic rocks. Major and trace elements suggest fractionation trends for: (a) muscovite granite and aplite veins; (b) two-mica granite and lepidolite-subtype aplite-pegmatite veins, but with a gap in most of these trends. Least square analysis for major elements, and modeling of trace elements, indicate that the aplite veins were derived from the muscovite granite magma by fractional crystallization of quartz, plagioclase, K-feldspar and ilmenite. This is supported by the similar (⁸⁷Sr/⁸⁶Sr)₃₁₁ and δ¹⁸O values and the behavior of P₂O₅ in K-feldspar and albite. The decrease in (⁸⁷Sr/⁸⁶Sr)₃₁₁ and strong increase (1.6‰) in δ¹⁸O from two-mica granite to lepidolite-subtype aplite-pegmatite veins, and the behaviors of Ca, Mn and F of hydroxylapatite indicate that these veins are not related to the two-mica granite.     

Radio planetary nebulae in the Magellanic Clouds

We report the extragalactic radio-continuum detection of 15 planetary nebulae (PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact Array+Parkes mosaic surveys. These detections were supplemented by new and high-resolution radio, optical and infrared observations which helped to resolve the true nature of the objects. Four of the PNe are located in the Small Magellanic Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on Galactic PNe the expected radio flux densities at the distance of the LMC/SMC are up to ∼2.5 and ∼2.0 mJy at 1.4 GHz, respectively. We find that one of our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several times higher than expected. We suggest that the most luminous radio PN in the SMC (N S68) may represent the upper limit to radio-peak luminosity because it is approximately three times more luminous than NGC 7027, the most luminous known Galactic PN. We note that the optical diameters of these 15 Magellanic Clouds (MCs) PNe vary from very small (∼0.08 pc or 0.32 arcsec; SMP L47) to very large (∼1 pc or 4 arcsec; SMP L83). Their flux densities peak at different frequencies, suggesting that they may be in different stages of evolution. We briefly discuss mechanisms that may explain their unusually high radio-continuum flux densities. We argue that these detections may help solve the 'missing mass problem' in PNe whose central stars were originally  1–8 M_⊙  . We explore the possible link between ionized haloes ejected by the central stars in their late evolution and extended radio emission. Because of their higher than expected flux densities, we tentatively call this PNe (sub)sample –'Super PNe'.     

Direct Sequential Co-simulation with Joint Probability Distributions

The practice of stochastic simulation for different environmental and earth sciences applications creates new theoretical problems that motivate the improvement of existing algorithms. In this context, we present the implementation of a new version of the direct sequential co-simulation (Co-DSS) algorithm. This new approach, titled Co-DSS with joint probability distributions, intends to solve the problem of mismatch between co-simulation results and experimental data, i.e. when the final biplot of simulated values does not respect the experimental relation known for the original data values. This situation occurs mostly in the beginning of the simulation process. To solve this issue, the new co-simulation algorithm, applied to a pair of covariates Z ₁(x) and Z ₂(x), proposes to resample Z ₂(x) from the joint distribution F(z ₁,z ₂) or, more precisely, from the conditional distribution of Z ₂(x ₀), at a location x ₀, given the previously simulated value z₁^(l)(x₀)z_{1}^{(l)}(x_{0}) (F(Z₂|Z₁=z₁^(l)(x₀)F(Z_{2}|Z_{1}=z_{1}^{(l)}(x_{0}) ). The work developed demonstrates that Co-DSS with joint probability distributions reproduces the experimental bivariate cdf and, consequently, the conditional distributions, even when the correlation coefficient between the covariates is low.     

准噶尔盆地复杂地区地层压力预测方法研究及应用

准噶尔盆地地层压力分布复杂,长期以来由于地层压力预测不准,在钻井过程中常出现井壁失稳、卡钻、井壁坍塌、钻井液漏失等工程事故,严重影响了钻井速度.为减少工程复杂问题,准确预测地层压力至关重要.为此,在准噶尔盆地开展了断层相关褶皱理论解释复杂构造、利用地质构造建模指导速度建模,求出每层的层速度和真倾角,再用Terzaghi 理论计算地层孔隙压力,计算结果证实地层压力预测精度显著提高.     

厦门东海域鱼类食物网研究

本文分析了厦门东海域58种鱼类的营养关系.根据对它们的食性分析,并依其食料生物的生态类群,将厦门东海域的鱼类食性类型分为:浮游生物食性、底栖生物食性、游泳动物食性、浮游生物和底栖生物、底栖生物和游泳动物食性等5种.该海域鱼类的营养级可分为4级:杂食性鱼类、低级肉食性鱼类、中级肉食性鱼类和高级肉食性鱼类,其中低级肉食性鱼类占优势,为63.79%.本文还分析了厦门东海域鱼类的食物网及其能量流动途径,并提出合理利用和保护厦门东海域鱼类资源的建议.     

Crystal Structure and Chemical Composition of Ludwigite from Vranovac Ore Deposit (Boranja Mountain,Serbia)

The crystal structure of ludwigite from Vranovac ore deposit (Boranja Mt., Serbia) was refined using the X-ray powder diffraction (XRPD) Rietveld method in the space group Pbam to a final RB=7.45% and RF=5.26%. It has the unit cell dimensions of: a=9.2515(2) ?; b=12.3109(2) ?; c=3.03712(7) ?; and V=345.91(1) ?3. The calculated distances and angles are mostly in good agreement with the Mg2+-Fe2+ substitutions across the M(1) and M(3) sites, as well as with the Fe3+-Al3+ replacement in the M(4) site. However, the mean observed M(2)-O distance is considerably shorter than prescribed, due to a slight increase of the Fe3+ content in the M(2) site. Such replacement was compensated by slight increase of the Fe2+ content in the M(4) site, resulting in the (Mg1.48Fe2+0.46Fe3+0.05Mn0.02)2.01(Fe3+0.94Fe2+0.04Al0.02)1.00B1.00O5 composition. The formation temperature was estimated to be about 500–600°C. The influences of the various chemical compositions to the crystallographic parameters, M-O distances, M(3) and M(4) sites shift, distortion parameters and estimated valences, were also studied and compared with other reference samples.     

Radio-continuum study of the nearby Sculptor group Galaxies. Part 2: NGC 55 at λ=20, 13, 6 and 3 cm

A series of new radio-continuum (λ=20, 13, 6 and 3 cm) mosaic images focused on the NGC 55 galactic system were produced using archived observational data from the Australia Telescope Compact Array. These new images are both very sensitive (down to rms=33 μJy) and feature high angular resolution (down to <4″). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as H?ii regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large H?ii regions is consistent with the estimated low star formation rate of the galaxy at 0.06 M _⊙?year^?1. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between α=?0.2 and ?0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.