Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater,Brazil          下载免费PDF全文

Dailto Silva  Cristiano Lana  Carlos Roberto de Souza Filho 《Meteoritics & planetary science》2016,51(3):443-467

Petrographic and geochemical data obtained on the Araguainha impact crater (Goiás/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact‐induced congruent melting of an alkali‐granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium‐rich granite, similar to postcollisional, A‐type granites, also found in terrains outside the Araguainha crater, in the Brasília orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact‐induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact.  相似文献   

Threshold of motion of bivalve and gastropod shells under oscillatory flow in flume experiments     

Cristiano Fick  Eduardo Puhl  Elírio Ernestino Toldo Jr 《Sedimentology》2020,67(1):627-648

The threshold of motion of non-fragmented mollusc shells was studied for the first time under oscillatory flow. In this regard, flume experiments were used to investigate the threshold of motion of three bivalve and three gastropod species, two typical mollusc classes of coastal coquina deposits. The sieve diameters ranged from 2·0 to 15·9 mm. These experiments were performed on a flat-bottom setup under regular non-breaking waves (swell) produced by a flap-type wave generator. The critical Shields values for each species of mollusc were plotted against the sieve and nominal diameter. Moreover, the dimensionless Corey shape factor of the shells was evaluated in order to investigate the effect of mollusc shell shapes on the threshold of motion. According to their critical Shields parameter, the mollusc threshold data under oscillatory flow present smaller values than the siliciclastic sediments when considering their sieve diameter. In addition, the mollusc datasets are below the empirical curves built from siliciclastic grain data under current and waves. When considering the nominal diameter, the critical Shields parameter increases and the mollusc data are closer to siliciclastic sediments. Bivalves, which have a flat-concave shape (form factor: 0·27 to 0·37), have a higher critical Shields parameter for smaller particles and more uniform datasets than the gastropod scattered data, which have a rounded shape (form factor: 0·58 to 0·62) and have varied morphologies (ellipsoidal, conical and cubic). The comparison between previous current-driven threshold data of bioclastic sediment motion and the data of mollusc whole shells under oscillatory flow shows a fair correlation on the Shields diagram, in which all datasets are below the mean empirical curves for siliciclastic sediments. These findings indicate that the shape effect on the transport initiation is predominant for smaller shells. The use of the nominal diameter is satisfactory to improve the bioclastic and siliciclastic data correlation.  相似文献   

Morphosedimentary analysis of the Limoeiro Stream (center-northern Minas Gerais State,Brazil): clues to the eastward tilting of southern Espinhaco range sites     

Claudio E. Lana  Paulo de Tarso A. Castro 《Environmental Earth Sciences》2012,65(3):639-647

The morphosedimentary evolution of a sector of the southern Espinhaco range (northern Minas Gerais State, Brazil) and its regional neotectonic setting are presented herein. The studied site is a stream at base level flowing along the western border of the range. Its identification was accomplished by using remote sensing techniques including the analysis of 3D slope models generated with shuttle radar topography mission images. The main geomorphological features of the identified site were surveyed in a 1:500 scale. In addition, seven stratigraphic logs are described. A regional geologic compilation and facies diagrams were used as a basis for the integration of the geomorphological and stratigraphic data, which produced some conclusions about the recent tectonic reactivations at the eastern border of Sao Francisco Craton. The results point to a local eastward tilting of the Espinhaco range. This fact is in accordance with previous findings in neighboring areas and results in the asymmetric evolution of the fluvial valley, as well as the regional relief.  相似文献   

Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil   总被引：1，自引：0，他引：1  

Maikon Di Domenico  Paulo da Cunha Lana  & André R. S. Garraffoni 《Marine Ecology》2009,30(1):47-62

This study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Paraná (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and summer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sediment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO₃, chlorophyll a , omega indexes, temperature and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon's diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that polychaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P < 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal variability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes.  相似文献   

Land use dynamics in Brazilian La Plata Basin and anthropogenic climate change     

Ana Carolina F. de Vasconcelos  Sandro L. Schlindwein  Marcos A. Lana  Alfredo C. Fantini  Michelle Bonatti  Luiz R. D’Agostini  Sergio R. Martins 《Climatic change》2014,127(1):73-81

The La Plata Basin (LPB) is one of the most important regions for agriculture and livestock production in South America, playing a central role in the world food production and food security. Within its borders is also located the whole Brazilian Pantanal region. Identifying the most important land use sectors in LPB as well as the changes observed in the past years is fundamental to recognize which areas of the basin might be more vulnerable to climate change in order to design adaptation strategies. A general characterization of land use and livestock production of Brazilian LPB was done by using the System of Automatic Retrieving (SIDRA) of Brazilian Institute of Geography and Statistics (IBGE) platform as the major source of data. It was observed expressive increases in land areas used for temporary crops, such as soybean, sugarcane, and maize, as well as increases in poultry and swine production. These important changes in agricultural land use and livestock production are currently associated to non-climatic drivers, but this dynamic might be strongly affected by the consequences of climate change and variability, with negative socio-economic impacts for the whole region.  相似文献   

Coda-Q Distribution In the Iberian Peninsula     

L. G. Pujades  J. A. Canas  J. J. Egozcue  M. A. Puigví  J. Gallart  X. Lana  J. Pous  A. Casas 《Geophysical Journal International》1990,100(2):285-301

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Galaxy clustering and dark energy     

Dipak Munshi  Cristiano Porciani  Yun Wang 《Monthly notices of the Royal Astronomical Society》2004,349(1):281-290

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Testing tidal-torque theory – I. Spin amplitude and direction     

Cristiano Porciani  Avishai Dekel  Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2002,332(2):325-338

We evaluate the success of linear tidal-torque theory (TTT) in predicting galactic-halo spin using a cosmological N -body simulation with thousands of well-resolved haloes. The protohaloes are identified by tracing today's haloes back to the initial conditions. The TTT predictions for the protohaloes match, on average, the spin amplitudes of the virialized haloes of today, if linear growth is assumed until ∼ t ₀/3, or  55–70  per cent of the halo effective turn-around time. This makes it a useful qualitative tool for understanding certain average properties of galaxies, such as total spin and angular momentum distribution within haloes, but with a random scatter of the order of the signal itself. Non-linear changes in spin direction cause a mean error of ∼50° in the TTT prediction at t ₀, such that the linear spatial correlations of spins on scales ≥1  h ⁻¹ Mpc are significantly weakened by non-linear effects. This questions the usefulness of TTT for predicting intrinsic alignments in the context of gravitational lensing. We find that the standard approximations made in TTT, including a second-order expansion of the Zel'dovich potential and a smoothing of the tidal field, provide close-to-optimal results.  相似文献   

Partial duration series distributions of the European dry spell lengths for the second half of the twentieth century     

C. Serra  Xavier Lana  A. Burgueño  M. D. Martínez 《Theoretical and Applied Climatology》2016,123(1-2):63-81

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Cosmic evolution of quasar clustering: implications for the host haloes   总被引：1，自引：0，他引：1  

Cristiano Porciani  Manuela Magliocchetti  Peder Norberg 《Monthly notices of the Royal Astronomical Society》2004,355(3):1010-1030

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