The Serra da Graciosa A-type Granites and Syenites, southern Brazil. Part 3: Magmatic evolution and post-magmatic breakdown of amphiboles of the alkaline association

Amphiboles are the main mafic minerals in most metaluminous to peralkaline alkali-feldspar granites and syenites, and they usually preserve an important record of the compositional evolution of the melts from which they crystallize. In the alkaline association of the Serra da Graciosa A-type Granites and Syenites (southern Brazil), amphibole compositions span a large range, including calcic, sodic–calcic, and sodic amphiboles. Calcic amphiboles are typically observed in the metaluminous rocks, while sodic amphiboles are characteristic of the more strongly peralkaline rocks; sodic–calcic amphiboles are found in intermediate varieties. Compositional variations record the differentiation trends within two petrographic series of the alkaline association. The overall evolution of amphibole compositions is similar in both: they reveal a progressive increase in Na and Fe³⁺ with differentiation (increase in alkalinity of the magmas), a characteristic shared by undersaturated peralkaline (or agpaitic) differentiation trends. In detail, however, the evolutions of the amphibole compositions in the two series are distinct. In Alkaline series 1, the cores of the crystals form a continuum from calcic to sodic compositions, with the exception of a small compositional gap within the sodic–calcic amphiboles. The rims, however, show compositions that diverge from this main trend; this divergence results from increasing amounts of the oxy-amphibole component, and reflects more oxidizing conditions at the final stages of magmatic crystallization. In Alkaline series 2, these oxidation trends are much more subtle and a reverse trend is observed in the sodic amphiboles. Sodic–calcic amphiboles are in several cases replaced by intergrowths of post-magmatic sodic amphibole and Al-poor (“tetrasilicic”) biotite.     

A proposal for an approach to mapping susceptibility to landslides using natural language processing and machine learning

Landslides - Compiling an inventory is a fundamental step for carrying out assessments of landslide hazards. However, data in sufficient quantity and quality are not always available. Thus, this...     

Magnetite scavenging and the buoyancy of bubbles in magmas. Part 1: Discovery of a pre-eruptive bubble in Bishop rhyolite

Little is known about the presence, distribution and size of bubbles in rhyolitic magmas prior to eruption. Using X-ray tomography to study pumice from early-erupted Bishop rhyolite, we discovered a large vesicle with abundant magnetite crystals attached to its walls. Attachment of magnetite crystals to bubble walls under pre-eruptive conditions can explain the cluster of magnetite crystals as a result of bubbles rising and collecting magnetite crystals. Alternatively, bubbles may have nucleated on magnetite crystals and then coalesced to form one large bubble with multiple magnetite crystals attached to it. We argue that the clusters of magnetite crystals could not have formed during or after eruptive decompression, and conclude that this vesicle corresponds to a bubble present prior to eruptive decompression. The inferred presence of pre-eruptive bubbles in the Bishop magma confirms the interpretation that the magma was volatile-saturated prior to eruption. The pre-eruptive size of this bubble is estimated based on three independent approaches: (1) the current size of the vesicle, (2) the total cross-sectional area of the magnetite crystals, and (3) the bubble size required for the aggregate to be neutrally buoyant. These approaches suggest a pre-eruptive bubble 300–850 μm in diameter, with a preferred value of 600–750 μm. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Drainage reorganization and Laramide tectonics in north-central New Mexico and downstream effects in the Gulf of Mexico

The El Rito and Galisteo depocenters in north-central New Mexico archive tectonically-driven Paleogene drainage reorganization, the effects of which influenced sedimentation along the northwestern margin of the Gulf of Mexico. Although separated by ~100 km and lacking depositional chronology for the El Rito Formation, the two aforementioned New Mexican depocenters are commonly considered remnants of a single basin with coeval deposition and shared accommodation mechanism. Detrital zircon U-Pb maximum depositional ages indicate that the El Rito and Galisteo formations are not coeval. Moreover, stratigraphic thickness trends and mapping relationships indicate different accommodation mechanisms for the Galisteo and El Rito depocenters; tectonically-induced subsidence versus infilling of incised topography, respectively. The regional unconformity that bounds the base of both the El Rito and Galisteo formations is a correlative surface induced by local tectonic activity and associated drainage reorganization in the early Eocene, and was diachronously buried by northward onlap of fluvial sediments. Detrital zircon distributions in both depocenters indicate increased recycling of Mesozoic strata above the unconformity, but diverge upsection as topographic prominence of local basement-involved uplifts waned. Sediment capture in these depocenters is coeval with deposition in other externally-drained Laramide basins. Further, it corresponds to a period of low Laramide province-derived sediment input and replacement by Appalachian-sourced sediment along the northwestern margin of the Gulf of Mexico during a basin-wide transgression. This illustrates the potential effect that pockets of sediment storage within the catchment of a transcontinental drainage system can have over the sedimentary record in the receiving marine basin.     

Cloning a new cytochrome P450 isoform (CYP356A1) from oyster Crassostrea gigas

We have cloned the full-length cDNA of the first member of a new cytochrome P450 (CYP) family from the Pacific oyster Crassostrea gigas. This new CYP gene was obtained based on an initial 331bp fragment previously identified among the list of the differentially expressed genes in oysters exposed to untreated domestic sewage. The full-length CYP has an open reading frame of 1500bp and based on its deduced amino acid sequence was classified as a member of a new subfamily, CYP356A1. A phylogenetic analysis showed that CYP356A1 is closely related to members of the CYP17 and CYP1 subfamilies. Semi-quantitative RT-PCR was performed to analyze the CYP356A1 expression in different tissues of the oyster (digestive gland, gill, mantle and adductor muscle). Results showed slightly higher CYP356A1 expression in digestive gland and mantle, than the other tissues, indicating a possible role of the CYP356A1 in xenobiotic biotransformation and/or steroid metabolism.     

Differential gene expression in oyster exposed to sewage

In order to investigate the influence of domestic sewage on the gene expression of Pacific oysters Crassostrea gigas, suppression subtractive hybridization (SSH) method was employed. Oysters were sampled at a farming area and, after 10 days of acclimation in the laboratory, were exposed to untreated domestic sewage diluted 33% for 48 h. Gills of male oysters were excised for total RNA extraction. mRNA was purified and the differential gene expression was analyzed by SSH. We obtained 61 cDNA sequences but only 15 were identified, which includes fatty acid binding protein, multidrug resistance protein, omega glutathione S-transferase, cytochrome P450 isoform CYP356A1, among others. The identified genes are associated with different metabolic functions like biotransformation, membrane transport, aerobic metabolism and translational machinery, evidencing the potential toxic effects elicited by these effluents.     

Season‐based rainfall–runoff modelling using the probability‐distributed model (PDM) for large basins in southeastern Brazil

Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km²; water supply) and Emborcação (29,076 km²), Três Marias (51,576 km²), Furnas (52,197 km²), and Mascarenhas (71,649 km²; hydropower) for hydrological modelling. It made the first attempt at configuring a season‐based probability‐distributed model (PDM‐CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra‐annual and interannual variability of the upstream inflows during 1985–2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash–Sutcliffe efficiency and logarithmic Nash–Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984–2001, 0.87 and 0.88 for the validation period 2001–2010, and 0.93 and 0.90 for the validation period 2010–2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season‐based PDM‐CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM‐CEMADEN is a simple, efficient, and easy‐to‐use model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large‐sized upstream basins.     

Cascade multitemporal classification based on fuzzy Markov chains

This paper proposes a new fuzzy cascade multitemporal classification method based on Fuzzy Markov Chains. This method differs from prior fuzzy multitemporal approaches proposed thus far, as the method does not require the knowledge of the true class at an earlier date; instead it uses the attributes of the image object being classified at the earlier date. This method combines the fuzzy, non-temporal, classification of a geographical region at two points in time to provide a single unified result. A transformation law based on class transition possibilities projects the earlier classification onto the later date before combining both results. Performance analysis was conducted upon a sequence of three LANDSAT images from the central region of Brazil using a Genetic Algorithm to estimate transition possibilities. The analysis showed that the increase in performance is highly dependent on whether or not a significant correlation exists between the temporal data sets, as well as on the accuracy of the monotemporal classifier at the earlier date. While the monotemporal approach used in the experiments attained an average class accuracy of approximately 55%, the multitemporal scheme achieved between 65% and 95%. Similar results in terms of overall accuracy were also observed. Furthermore, compared to two alternative cascade multitemporal classification approaches, the proposed method consistently showed better results.