P-T conditions of earliest Late Cretaceous metamorphism in the Western Sonobari Complex,northwestern Mexico: tectonic implications

The Western Sonobari Complex in northwestern Mexico consists of metamorphosed rocks mostly derived from Palaeozoic (?) sedimentary and Mesozoic igneous protoliths. Rocks of this complex display amphibolite facies orogenic metamorphism, pervasive foliation, migmatization, and four folding phases. These features are ascribed to a contractional tectonic event with NNW–SSE shortening direction, which caused thrusting, thickening of the crust, and sinking of the lithological units. U–Pb geochronology of migmatitic leucosome bands indicates that peak metamorphic conditions were reached between ~93 and 89 Ma. Post-tectonic Late Cretaceous peraluminous aplite-pegmatite dikes transect the metamorphic foliation. Traditional thermobarometry in the metamorphic rocks yields average pressures and temperatures of 9.0–7.1 kbar and 745–663°C, typical of intermediate P/T Barrovian metamorphism. On the basis of its age and contractional character, the thickening event originating the metamorphism may be related to collision of the Alisitos island arc against crustal blocks of Mexico. Thermobarometric data of post-tectonic intrusives including Late Cretaceous granodiorite and Eocene gabbro indicate emplacement within an overthickened crust, while P-T conditions of post-tectonic dikes point towards an almost isothermal decompression path along the amphibolite facies field. Rock units of similar age and metamorphic character are discontinuously exposed from the Islas Marias offshore the Nayarit coast to the Peninsular Ranges batholith of Baja California, and even extend north into the Sierra Nevada batholith and the Sevier hinterland. This extensive belt of Barrovian metamorphic rocks thus provides a record of middle Cretaceous shortening and crustal thickening related to arc-continent collision followed by subduction resuming.     

Three-dimensional discrete element method for granular materials

This paper describes a three-dimensional discrete element method of analysis for granular materials. Individual particles are modelled as rigid, six-sided solids with six degrees of freedom. Various types of contacts are possible among the three-dimensional discrete elements. Models for these contact types are described. Computational aspects of the method, such as techniques for contact detection and data structure, are addressed. Selective results of three examples that demonstrate the application of the method to granular flow problems are presented and discussed.     

FedIDS: a federated cloud storage architecture and satellite image delivery service for building dependable geospatial platforms

Earth observation satellites produce large amounts of images/data that not only must be processed and preserved in reliable geospatial platforms but also efficiently disseminated among partners/researchers for creating derivative products through collaborative workflows. Organizations can face up this challenge in a cost-effective manner by using cloud services. However, outages and violations of integrity/confidentiality associated to this technology could arise. This article presents FedIDS, a suite of cloud-based components for building dependable geospatial platforms. The Fed component enables organizations to build shared geospatial data infrastructure through federation of independent cloud resources to withstand outages, whereas IDS avoids violations of integrity/confidentiality of images/data in sharing information and collaboration workflows. A FedIDS prototype, deployed in Spain and Mexico, was evaluated through a study case based on a satellite imagery captured by a Mexican antenna and another based on a satellite imagery of a European observation mission. The acquisition, storage and sharing of images among users of the federation, the exchange of images between Mexican and Spanish sites and outage scenarios were evaluated. The evaluation revealed the feasibility, reliability and efficiency of FedIDS, in comparison with available solutions, in terms of performance, storage consume and integrity/confidentiality when sharing images/data in collaborative scenarios.     

Shallow-level differentiation of phonolitic lavas from Sumaco Volcano,Ecuador

Sumaco Volcano is located in the rear-arc of Ecuador and produces phonolitic alkaline lavas hosting a unique assemblage of minerals including haüyne and titanaugite. The most mafic lavas are picrobasalts that contain titanaugite as the primary mineral phase; the most evolved tephri-phonolite lavas contain titanaugite?+?anorthoclase?+?haüyne. Titanaugite forms at middle to deep crustal pressures, whereas haüyne is only stable at shallow depths in highly oxidizing conditions. The Sumaco mineral assemblages and geochemistry indicate that fractionation of the titanaugite- and haüyne-bearing assemblage took place over a range of pressures from 5 to 25 kbar (14–75 km), with at least 50% of differentiation taking place at shallow crustal levels. Minerals record multiple cycles of recharge and mixing accompanied by an increase in fO₂ and sulfur concentration during differentiation. Mantle-like Sr and Nd isotope values (⁸⁷Sr/⁸⁶Sr = 0.70406–0.70423; ¹⁴³Nd/¹⁴⁴Nd = 0.512880–0.512913) indicate minimal crustal assimilation. Sumaco’s unique geochemical composition is not observed in the nearby volcanoes Antisana, Pan de Azucar or El Reventador suggesting that its unique magma source is confined to this volcano. The high temperature and sulfate-saturated conditions at shallow depths suggest that magma ascends rapidly to a shallow reservoir where the majority of crystallization and recharge takes place prior to eruption. An important conclusion of this research is that Sumaco does not represent typical rear-arc subduction processes, and caution should be used when using Sumaco as an end-member to evaluate across-arc processes in the Northern Volcanic Zone.     

Precipitation trends using in-situ and gridded datasets

Six in situ precipitation time series of varying time periods in the northwestern region and the Global Precipitation Climatology Centre (GPCC) v6 0.5° monthly dataset (1901–2010) were statistically examined for monotonic trends in Trinidad. The Pettit test was used to investigate the abrupt changes in the mean while the Mann–Kendall test was employed to assess the monotonic trends. It was found that three in situ stations and the six grids experienced abrupt changes in the rainfall patterns and that there was an apparent shift in the seasons. In addition, for five out of the six in situ stations no monotonic change was detected in the monthly, seasonal, and annual rainfall patterns. Gradual decreases were detected in the calculated weighted area average for five stations, the GPCCv6 dataset and St. Ann’s time series. The GPCCv6 data indicated that the dry season in the southern Trinidad is becoming drier. Results also suggested that the range between the greatest and lowest recorded rainfall values for some months have increased while others decreased. The gridded dataset appears to give a good representation of the dry season (January to May) rainfall compared with the wet season (June to December) and was found to be negatively biased for the north-western region but may not necessarily be so for the entire island. The results suggested that in the north-western region mirco-climates may exist. It is recommended that further investigations are needed using in situ data.     

Rockfall detachment susceptibility map in El Hierro Island, Canary Islands, Spain

A semi-quantitative heuristic methodology is developed to map a rockfall detachment susceptibility zonation of El Hierro Island (Canary Archipelago). The rationalized procedure, which we called non-weighted bounded indicators, is based on overlapping thematic maps of conditioning factors to mass movement, which are appropriately and individually rescaled and then composed by addition to obtain a susceptibility numerical index through a GIS. As the consistency of the geomorphological analysis depends on the expert subjective criteria and the appropriate interpretation of the landscape, the use of this methodology reduces subjectivity and quantifies the degree of susceptibility. The main factors affecting the mass movement phenomena (rockfalls events), also recognized in the field and, therefore, considered in the presented GIS arrangement, are slope, profile curvature, lithology, vegetation cover and dykes density. To calculate the slope threshold or minimum angle characteristic of rockfall source areas, mixed Gaussian slope frequency decomposition is used. The curvature index reveals stepwise areas. Qualitative geomechanical characteristics are linked to a quantitative index according to a volcanic lithological-complexes classification. Both destabilization (root-wedging) and stabilization effects are considered into the vegetation cover index. The dyke density index incorporates the bearing rock capacity decrease produced in the halo around a dyke network intrusion. Slope, curvature and vegetation indexes thresholds have been fitted following field observations. A rockfall detachment susceptibility map is obtained and classified based on the histogram maxima. The rockfall inventory, based on rockfall events reported within the island, was used for the model validation. A 12?% of the whole island shows medium to very high susceptibility.