Geochemical Constraints on the Origin of the Ni–Cu Sulfide Ores in the Tejadillas Prospect (Cortegana Igneous Complex,SW Spain)

After the discovery of the Aguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic‐ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt % Ni and 0.08 wt % Cu with peaks of 1.2 wt % Ni and 0.2 wt % Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic‐ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole‐rock geochemical data between Aguablanca and Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle‐normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE‐depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R‐factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S‐rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high‐tenor Ni–Cu–PGE ore deposits in mafic‐ultramafic intrusions of the region.     

Focal depths and mechanisms of Tohoku-Oki aftershocks from teleseismic P wave modeling

Aftershocks of the 2011 Tohoku-Oki great earthquake have a wide range of focal depths and fault plane mechanisms. We constrain the focal depths and focal mechanisms of 69 aftershocks with M _w > 5.4 by modeling the waveforms of teleseismic P and its trailing near-surface reflections pP and sP. We find that the “thrust events” are within 10 km from the plate interface. The dip angles of these thrust events increase with depth from ~5° to ~25°. The “non-thrust events” vary from 60 km above to 40 km below the plate interface. Normal and strike-slip events within the overriding plate point to redistribution of stress following the primary great earthquake; however, due to the spatially variable stress change in the Tohoku-Oki earthquake, an understanding of how the mainshock affected the stresses that led to the aftershocks requires accurate knowledge of the aftershock location.     

Productivity cycles in the coastal upwelling area off Concepción: The importance of diatoms and bacterioplankton in the organic carbon flux

Recurrent coastal upwelling is recognized as one of the main factors promoting the exceptionally high productivity of the Humboldt Current System. Herein, we study time series data of gross primary production (2003-2006) and its fluctuation in relation to seasonal changes in the light and nutrient field of the Concepción upwelling ecosystem. Concurrent measurements of gross primary production, community respiration, bacterial secondary production, and sedimentation rates allowed a characterization of the main carbon fluxes and pathways in the study area. The integrated values of gross primary production were higher during the upwelling period (>1 g C m⁻² d⁻¹; October-April; that is, early spring to early austral fall). Seasonal changes in the system were also reflected in community respiration, organic matter sedimentation, and bacterial production rates, which varied along with the gross primary production. The significant correlation between gross primary production and community respiration (Spearman, r = 0.7; p < 0.05; n = 18) reflected an important degree of coupling between organic matter formation and its usage by the microplanktonic community during periods when gross primary production/community respiration were highly similar. Higher gross primary production values (>6 g C m⁻² d⁻¹) were consistently associated with maximum biomass levels of Skeletonema costatum and Thalassiosira subtilis. We observed a positive correlation between gross primary production and the sedimentation of intact diatom cells (Spearman, r = 0.5, p < 0.05, n = 17). Our data suggest that, in the Concepción upwelling ecosystem, bacteria utilize an important fraction of the gross primary production. If our interpretations are correct, they leave unanswered the question of how the system supports the extremely high fish biomass levels, therein pointing out the system’s limited capacity to buffer the evasion of CO₂ following upwelling.     

An application of the synthetic emitter-array method to improve GPR signals

Methods that employ arrays of emitters are potentially useful in improving weak or ambiguous signals in ground penetrating radar (GPR) prospecting. As in the seismic case, the electromagnetic responses from the subsurface can be obtained by employing true composite sources or synthesized from single emitter responses that are acquired with variable offset, both possibilities leading to similar results. In this article, the synthetic emitter-array method is examined as a way of improving GPR signals. Modeling of transmitted wave-fronts is carried out to analyze how the targets can be illuminated so that the reflected signals are effectively reinforced. The method is applied to different targets. A methodology that simultaneously increases the signal to noise ratio and the lateral coherence of the events is examined in order to facilitate the interpretation of the GPR data. Finally, the synthetic emitter-array method is successfully applied in a case study to determine the width and depth of mud walls at the Palo Blanco archaeological site in Argentina.     

Modern Vegetation and Pollen Relationships in Four Southwestern Atlantic Coastal Lagoons

Pollen studies and their relationship with modern vegetation facilitate paleoecological reconstructions while changes in pollen abundance are indicators of environmental fluctuations. We analyzed the relationships between recent pollen deposits in the sediments of four Uruguayan coastal lagoons and catchment vegetation and analyzed the temporal dynamics of submerged aquatic vegetation (SAV). We mapped terrestrial vegetation, sampled SAV biomass, and analyzed the pollen record in each lagoon. The sediment samples represented the last 49–76 years of deposition, and most vegetation types were well represented in the pollen records. Pollen of Chenopodiaceae, proposed as indicators of saltmarshes, decreased in the surface samples of all lagoons, possibly due to the salinity reduction promoted by precipitation changes in the region. Pollen of SAV was found in all lagoons but with gaps in the record, and a submerged vegetated phase was recorded. Simultaneous botanical and pollen analyses better captured the large fluctuations of SAV in coastal lagoons.     

The Deposition and Chronology of Cenote T’isil: A Multiproxy Study of Human/Environment Interaction in the Northern Maya Lowlands of Southeast Mexico

Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatán Peninsula, México. Detailed study of dated soil‐sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices.     

Improving seismotectonics and seismic hazard assessment along the San Ramón Fault at the eastern border of Santiago city,Chile

The San Ramón Fault is an active west-vergent thrust fault system located along the eastern border of the city of Santiago, at the foot of the main Andes Cordillera. This is a kilometric crustal-scale structure recently recognized that represents a potential source for geological hazards. In this work, we provide new seismological evidences and strong ground-motion modeling from hypothetic kinematic rupture scenarios, to improve seismic hazard assessment in the Metropolitan area of Central Chile. Firstly, we focused on the study of crustal seismicity that we relate to brittle deformation associated with different seismogenic fringes in the main Andes in front of Santiago. We used a classical hypocentral location technique with an improved 1D crustal velocity model, to relocate crustal seismicity recorded between 2000 and 2011 by the National Seismological Service, University of Chile. This analysis includes waveform modeling of seismic events from local broadband stations deployed in the main Andean range, such as San José de Maipo, El Yeso, Las Melosas and Farellones. We selected events located near the stations, whose hypocenters were localized under the recording sites, with angles of incidence at the receiver <5° and S–P travel times <2 s. Our results evidence that seismic activity clustered around 10 km depth under San José de Maipo and Farellones stations. Because of their identical waveforms, such events are interpreted like repeating earthquakes or multiplets and therefore providing first evidence for seismic tectonic activity consistent with the crustal-scale structural model proposed for the San Ramón Fault system in the area (Armijo et al. in Tectonics 29(2):TC2007, 2010). We also analyzed the ground-motion variability generated by an M _w 6.9 earthquake rupture scenario by using a kinematic fractal k ^?2 composite source model. The main goal was to model broadband strong ground motion in the near-fault region and to analyze the variability of ground-motion parameters computed at various receivers. Several kinematic rupture scenarios were computed by changing physical source parameters. The study focused on statistical analysis of horizontal peak ground acceleration (PGAH) and ground velocity (PGVH). We compared the numerically predicted ground-motion parameters with empirical ground-motion predictive relationships from Kanno et al. (Bull Seismol Soc Am 96:879–897, 2006). In general, the synthetic PGAH and PGVH are in good agreement with the ones empirically predicted at various source distances. However, the mean PGAH at intermediate and large distances attenuates faster than the empirical mean curve. The largest mean values for both, PGAH and PGVH, were observed near the SW corner within the area of the fault plane projected to the surface, which coincides rather well with published hanging-wall effects suggesting that ground motions are amplified there.     

Local economic development: Theory, evidence, and implications for policy in Brazil

Local economic development policies have surged in Brazil over the past decade—a major shift in this regionally diverse country of 27 states, over 5000 municipalities, and the largest economy in Latin America. We review the stylized facts, expected patterns and policy recommendations from the foundational studies in regional and urban economics. We then provide a summary of a more recent stream of scholarship focused on local economic development (LED) studies in developed and developing countries that have surged in the last 20 years. Based on this review, we then systemize the findings emerging from studies focused on analyzing local economic development policies in Brazil recognizing the distinctive contributions emerging from both the empirical and the case studies literatures. We identify key lessons for (and from) the Brazilian experience and conclude that Brazil and Latin American countries need a new generation of studies that undertake more rigorous evaluations of these policy experiments. Finally, we recommend steps to advance such research.     

GPR prospecting in a prehispanic village,NW Argentina

Palo Blanco is an approximately 1600 year old archaeological site located in Fiambalá Valley, in the Andean region of Argentina. Pioneer archaeological studies published in the 70s reported the existence of five residential units in this site. Also a small cemetery which included three circular tombs was discovered near to these buildings. Since that time, a profuse sedimentation covered the zone, so nowadays there are no evidences of most of these buildings on surface. Because of an imprecise location of the structures, most of the buildings became in fact missed. Then, in this work we aimed to re-localize two of the missed buildings, a residential unit and a tomb, by applying ground penetrating radar (GPR) methodology. We used fast fixed offset GPR configurations to investigate two areas in which these buildings could be expected. We used experimental and synthetic patterns to aid the identification of the characteristic signals due to the archaeological targets. We applied migration to the data to better define and resolve unclear anomalous signals. The employed methodology revealed the location of both buildings. Also a number of new non-reported structures were predicted and confirmed.     

An information system for monitoring the Chilean salmon industry sustainability

Today and years to come, one of the most challenging problems of the global economy is to keep maintaining and developing the correct balance of the environment from which resources are extracted. For this, we believe that Information Systems and formal methodologies for sustainability measures definition are related to decision making and management control. In this work, a methodology as a means to determining and implementing reliable, understandable, relevant and accessible sustainability indicators for the interaction between the environment, the economy and the society will be examined. Sustainability measures were implemented in a Decision Support System using a multidimensional modeling based architecture. The proposed methodology for indicators definition and the Information System were successfully applied to the Chilean salmon industry. The usage of the indicators and the stakeholders’ opinions over the resulting Information System, proved that the proposed Decision Support System is of great importance to the sustainable development of the Chilean salmon industry.