Multi-scale approach using remote sensing images to characterize the iron deposit N1 influence areas in Carajás Mineral Province (Brazilian Amazon)

Mining activities cause a wide range of changes to the environment, substantially affecting both the physical and biological environmental sectors. In the Carajás Mineral Province, located in the Amazon rainforest, environmental regulations tend to be more rigorous, due to the fragility of the environment in which large iron deposits are found. The characterization of the impact of mining on environment considers: the type and extent of the impact, the physical chemistry differences and similarities of the mineral deposits, the deposit size, the adopted mining process, and the environment (both natural and economic) in which the mining process was developed. Remote sensing technology is utilized in this study, in particular, the use of ortho-aerial photograph, and optical and radar images with distinct spatial resolution. These permit the elaboration in synoptic maps, multi-scale and dynamic, of the changes wrought upon the environment: deforestation, removal of vegetation cover, topographic surface and landscape alteration, and slope instabilities among others. In this aspect, determining the extent of influence of the mining activity is directly tied to the characterization of its impact on various natural systems at the observed scale, and not by simply defining a predetermined Euclidean distance. The results showed that remote sensing technology, optical and radar images, proved to be efficient in the study of environmental information and the areas of influence on the semi-regional and local scales in the Amazon forest.     

Methodology and applications for the benefit cost analysis of the seismic risk reduction in building portfolios at broadscale

This article presents a methodology for an estimate of the benefit cost ratio of the seismic risk reduction in buildings portfolio at broadscale, for a world region, allowing comparing the results obtained for the countries belonging to that region. This methodology encompasses (1) the generation of a set of random seismic events and the evaluation of the spectral accelerations at the buildings location; (2) the estimation of the buildings built area, the economic value, as well as the classification in structural typologies; (3) the development of vulnerability curves for each typology; (4) the estimation of the annual average loss of the buildings portfolio in the current conditions as well as in the case of a hypothetical structural intervention. The benefit cost ratio is estimated as the difference between the estimates of the present value of these two annual average losses, divided by the retrofitting costs. This methodology has been applied to the portfolio of public schools of 14 countries of Latin America and the Caribbean, for evaluating the feasibility of the seismic risk reduction at a national scale.     

Estimates of the transition zone temperature in a mechanically mixed upper mantle

Partial melting of mantle peridotite generates a physically and chemically layered oceanic lithosphere that is cycled back into the mantle in subduction zones. Stirring times of the mantle are too long to allow for complete re-homogenization of subducted basalt and harzburgite, given the low chemical diffusivity of the solid mantle. This suggests that the Earth's mantle is a mechanical mixture of basaltic and harzburgitic components. Using a recently developed thermodynamic formulism we determine the phase equilibria and the seismic properties of a mantle comprised of a mechanical mixture of basalt and harzburgite (MM) and a homogeneous mantle (EA) with identical pyrolitic bulk chemistry. We use the theoretical shear velocity profiles as a new thermometer of the mantle below the magma-genetic zone by modeling the difference ΔT_410-660 between traveltimes of shear wave reflections off the 410-km and 660-km with the potential temperature T_P. ΔT_410-660 are measured from waveform stacks. They indicate that, over 1000+ km wave lengths, the temperature varies by about 200 K. Lowest and highest temperatures are resolved for the western Pacific subduction zones and the central Pacific, respectively. This variation is similar for the EA and MM and is in excellent agreement with estimates of transition zone thickness and shear velocity variations. The median value of T_P for the EA is 1720 K. It is about 1625 K for the MM, a value that is in better agreement with the Normal-MORB values of 1610 ± 40 K inferred from olivine-liquid equilibria given that our sampling region encompasses the Western Pacific subduction zones and the oldest parts of the Pacific Plate. We argue therefore that a mechanical mixed mantle, with generally higher velocities and steeper velocities gradients, represents a better physical reference model than a model based on a fully equilibrated assemblage.     

Bedload hysteresis in a glacier‐fed mountain river

Sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before (counterclockwise hysteresis) or after (clockwise hysteresis) the peak of bedload. Hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability. Counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions, respectively. Hysteresis has been mainly explored for the case of suspended sediment transport, but it was rarely reported for bedload transport in mountain streams. This work focuses on the temporal variability of bedload transport in an alpine catchment (Saldur basin, 18.6 km², Italian Alps) where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0.5m‐long steel pipe. Runoff dynamics are dominated by snowmelt in late spring/early summer, mostly by glacier melt in late summer/early autumn, and by a combination of the snow and glacier melt in mid‐summer. The results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period, likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin. On the contrary, counterclockwise hysteresis tend to be more frequent during late glacier melting period, possibly due to the time lag needed for sediment provided by the glacial and peri‐glacial area to be transported to the monitoring section. However, intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis, thus indicating the activation of different sediment sources. These results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams. Copyright © 2014 John Wiley & Sons, Ltd.     

Stratigraphic expression of the lateral propagation and growth of isolated fault-related uplifts

The lateral propagation of faults and folds is known to be an important process during the development of mountain belts, but little is known about the manner in which along‐strike fault–fold growth is expressed in pre‐ and syntectonic (growth) strata. We use a coupled tectonic and stratigraphic model to investigate the along‐strike stratigraphic expression of fault‐related folds/uplifts that grow in both the transport and strike directions. We consider faults that propagate following a quadratic (nonself‐similar evolution) or linear (self‐similar evolution) scaling law, using different slip distributions per episode of fault propagation, under general background sedimentation. We find that the long‐strike geometry of pre‐ and syntectonic strata and the geometry of growth axial surfaces reflect the mode of fault propagation. The geometry of strata observed in the model is similar to that observed in natural contractional structures when: (1) the evolution of the fault is nonself‐similar, or (2) the fault grows as a result of thrust faulting events with similar displacements along strike that are terminated abruptly at the fault tips.     

Seasonal Variation in the Phytoplanktonic Community,Seston and Environmental Variables During a 2-Year Period and Oyster Growth at Two Mariculture Sites,Southern Chile

Phytoplankton and its relationships with physical and chemical variables were analysed over a 2-year period in Hueihue and Linao Bays (southern Chile). Samples were collected on a monthly basis from May 1991 to May 1993. The growth rate of a single stock of hatchery-produced oysters (Ostrea chilensis) distributed between these two bays was also monitored monthly. The growth rate of oysters maintained at Linao Bay (site associated with a fish farm) was significantly higher, at every depth, compared with the oysters maintained at Hueihue Bay. Temperature and salinity values and their annual fluctuations were similar at both locations, presenting higher variations at the surface (1 m) due to the influence of air temperature and local precipitation than at depth. However, significant differences in phytoplankton abundance and composition were found between the two locations. The phytoplankton community was characterized by high biomass values during spring and summer, the dominance of diatoms and an inverse relationship between temperature and species diversity. However, phytoplankton cell abundance, biovolume and chlorophyll a concentration were significantly higher at Linao at every depth sampled. Cell abundance ranged between 4.49 × 10⁴ and 7.45 × 10⁶ cells · l^?1 in Hueihue and between 6.48 × 10⁴ and 8.71 × 10⁶ cells ·1^?1 in Linao. The influence of temperature on chlorophyll a concentration was significant except at 8 m at both locations. The instantaneous oyster growth rate was found to be positively correlated with temperature, chlorophyll a concentration and particulate organic matter at both locations. A significant negative relationship between oyster growth and amount of particulate inorganic matter was found; this confirms the important role played by seston composition in oyster growth. The demonstration of variation in oyster growth rate associated with differences in food availability between the two locations provides insight into the ecological role played by fish farms in southern Chile. The results suggest a strong link between food availability and oyster growth.     

Reconciling strong slab pull and weak plate bending: The plate motion constraint on the strength of mantle slabs

Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude of this resistance is not known because of poor constraints on slab strength. However, because slab bending slows the relatively rapid motions of oceanic plates, observed plate motions constrain the importance of bending. We estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity. Predicting plate motions using a global mantle flow model, we constrain the viscosity of the bending slab to be at most ~ 300 times more viscous than the upper mantle; stronger slabs are intolerably slowed by the bending deformation. Weaker slabs, however, cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of ~ 10^− 15 s^− 1. The constrained bending viscosity (~ 2 × 10²³ Pa s) is larger than previous estimates that yielded similar or larger bending resistance (here ~ 25% of forces). This apparent discrepancy occurs because slabs bend more gently than previously thought, with an average radius of curvature of 390 km that permits subduction of strong slabs. This gentle bending may ultimately permit plate tectonics on Earth.     

Topotaxy

Summary It is proposed to clarify the nomenclature of oriented solid state reactions by distinguishing between terms which are (a) used todescribe observations of oriented growth of new phases: —SYNTAXY; and (b) used tointerpret these oriented reactions in terms of crystal structure: —TOPOTAXY. Polymorphic transformations may be designated assyntactic (ortopotactic) transformations ortransitions, distinguishing them fromsyntactic (ortopotactic) reactions. Someepitaxial reactions (where the substrate reacts) may besyntactic (ortopotactic), the criterion for topotaxy being three-dimensional orientational and structural resemblance between reagent and product crystals. Detailed study of the mechanism of reaction may confirm or deny the causal nature of the resemblance. Intermediate cases, difficult to classify, are pointed out.The influence of symmetry and morphology on topotaxy is discussed. Examples, some of them new, are given from the manganese, nickel and iron oxide/hydroxide systems.

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Zusammenfassung Es wird vorgeschlagen, die Nomenklatur von Reaktionen im festen Zustand dadurch klar zu machen, daß man zwischen Ausdrücken unterscheidet, welche benützt werden, a) um Beobachtungen über das orientierte Wachstum neuer Phasen zubeschreiben: SYNTAXIE, oder b) um diese orientierten Reaktionen in Begriffen der Kristallstruktur zuinterpretieren: TOPOTAXIE. Polymorphe Übergänge können alssyntaktische (odertopotaktische) Transformationen) oder Übergänge bezeichnet werden, zum Unterschied vonsyntaktischen (odertopotaktischen) Reaktionen. Mancheepitaxiale Reaktionen (bei denen das Substrat reagiert) könnensyntaktisch (odertopotaktisch) sein; das Kriterium für Topotaxie ist dreidimensionale Ähnlichkeit in Orientierung und Struktur zwischen reagierenden und End-Kristallen. Das detaillierte Studium des Reaktionsmechanismus kann die kausale Natur der Ähnlichkeit bestätigen oder verneinen. Übergangsfälle, die schwer zu klassifizieren sind, werden aufgezeigt.Der Einfluß von Symmetrie und Morphologie auf die Topotaxie wird besprochen. Einige Beispiele, von denen manche neu sind, werden aus den Systemen Mangan-, Nickel- und Eisenoxyd/Hydroxyd gebracht.

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Dedicated to Prof.F. Machatschki on the occasion of his 70th birthday.