New major element analyses of proximal tephras from the Azores and suggested correlations with cryptotephras in North-West Europe

The Azores Archipelago is one of the most active volcanic areas in the North Atlantic region. Approximately 30 eruptions have been reported over the last 600 years with some major VEI 5 (Volcanic Explosivity Index) eruptions further back in time. The geochemical composition of associated tephra-derived glass, however, is not well characterized. An Azorean origin of cryptotephras found in distal areas such as North Africa, the British Isles and Greenland has been suggested, but proximal data from the Azores are scarce and the correlations have only been tentative. These tephras have a traychtic composition, which excludes an Icelandic origin. In a previous study, we presented major element analyses of proximal tephra-derived glass from five Holocene eruptions on the Azores Islands. There is a striking geochemical similarity between tephras from volcanoes on São Miguel and Irish cryptotephras, and especially with eruptives from the Furnas volcano. Here we present new analyses of proximal tephras that confirm and strengthen a link between Furnas and cryptotephras found in south-west Ireland. We also suggest a correlation between a previously unsourced tephra found in a Swedish bog with an eruption of the Sete Cidades volcano c. 3880 a cal BP.     

Prediction of ground displacements and velocities from groundwater level changes at the Vallcebre landslide (Eastern Pyrenees, Spain)

In active landslides, the prediction of acceleration of movement is a crucial issue for the design and performance of warning systems. The landslide of Vallcebre in the Eastern Pyreenes, Spain, has been monitored since 1996 and data on rainfall, groundwater levels and ground displacements are measured on a regular basis. Displacements observed in borehole wire extensometers have shown an immediate response of the landslide to rainfall episodes. This rapid response is likely due to the presence of preferential drainage ways. The occurrence of nearly constant rates of displacement in coincidence with steady groundwater levels suggests the presence of viscous forces developed during the movement. An attempt to predict both landslide displacements and velocities was performed at Vallcebre by solving the momentum equation in which a viscous term (Bingham and power law) was added. Results show that, using similar rheological parameters for the entire landslide, computed displacements reproduce quite accurately the displacements observed at three selected wire extensometers. These results indicate that prediction of displacements from groundwater level changes is feasible.     

Linear system techniques applied to the Fuenmayor Karst Spring, Huesca (Spain)

Black box identification techniques are very useful tools to study the relationship between rainfall and the discharge of karst aquifers. Autocorrelation, cross-correlation, cross-spectral, impulse response identification (Wiener–Hopf and error minimization methods) and parametric identification of transfer functions techniques have been used by different authors. A review of these techniques has been realized to assess the possibilities and limitations. The reviewed techniques are applied to a time rainfall–discharge series of Fuenmayor karst spring, (southern central Pyrenees, Spain) to establish the relative quality of the obtained models. The quality is evaluated with the Nash–Sutcliffe model efficiency coefficient. In addition, effective rainfall has been used to improve the performance of every model. The whitening technique has been used in the cross-correlation technique with good results. The studied spring shows a Fontestorbes type behavior. The linearity of the system has been analyzed by the coherence function. Fuenmayor has an acceptable linear response, except for high frequency events. The parametric identification provides the best efficiency value E = 0.8164 and provides a proper transfer function, with five parameters (one zero, two poles, the gain and the delay). The prediction power of this transfer function is validated with another time series, with an efficiency value of E = 0.7904.     

FTIR spectroscopy of Ti-chondrodite,Ti-clinohumite,and olivine in deeply subducted serpentinites and implications for the deep water cycle

Separated olivine grains from a deeply subducted serpentinized wehrlite (Changawuzi in the western Tianshan ultrahigh-pressure belt, China) were analysed with unpolarized transmission FTIR and the Ti contents were determined using LA-ICP-MS. The major bands in the olivine spectra display striking similarities to Ti-clinohumite and are interpreted as OH in lamellae. The quantification of the water content in lamellae requires calibration of the IR-absorption for such bands. We have obtained a new absorption coefficient for Ti-clinohumite of 0.125+/?0.017 ppm cm² based on polarized FTIR measurements on three orthogonal sections through a large single crystal of Ti-clinohumite from Val Malenco, which has a known water content of 1.53 wt%. The resulting water content in olivine using this calibration factor ranges from 440 to 2,600 ppm and correlates positively with the Ti content that ranges from 130 to 1,400 ppm. For the quantification of the water content in Ti-chondrodite and Ti-clinohumite that are associated with olivine, we developed a new method using attenuated total reflectance FTIR spectroscopy. Ti-chondrodite and Ti-clinohumite display similar IR bands at ~3,562, 3,525 and ~3,583–3,586 cm^?1. As in olivine, the water content and Ti content correlate in both Ti-clinohumite and Ti-chondrodite, indicating an intergrowth of these minerals, which has been confirmed by TEM analyses. Our results confirm previous suggestions that there is a strong correlation between the Ti content of ultramafic rocks and their capacity to transport water to the deeper mantle in subduction zones beyond conditions where hydrous phases are stable.     

Hydrogeological characterization of Gold Valley: an investigation of precipitation recharge in an intermountain basin in the Death Valley region, California, USA

Gold Valley is typical of intermountain basins in Death Valley National Park (DVNP), California (USA). Using water-balance calculations, a GIS-based analytical model has been developed to estimate precipitational infiltration rates from catchment-scale topographic data (elevation and slope). The calculations indicate that groundwater recharge mainly takes place at high elevations (>1,100?m) during winter (average 1.78?mm/yr). A resistivity survey suggests that groundwater accumulates in upstream compartmentalized reservoirs and that the groundwater flows through basin fill and fractured bedrock. This explains the relationship between the upstream precipitational infiltration in Gold Valley and the downstream spring flow in Willow Creek. To verify the ability of local recharge to support high-flux springs in DVNP, a GIS-based model was also applied to the Furnace Creek catchment. The results produced insufficient total volume of precipitational infiltration to support flow from the main high-flux springs in DVNP under current climatic conditions. This study introduces a GIS-based infiltration model that can be integrated into the Death Valley regional groundwater flow model to estimate precipitational infiltration recharge. In addition, the GIS-based model can efficiently estimate local precipitational infiltration in similar intermountain basins in arid regions provided that the validity of the model is verified.     

Palaeokarst and rauhwacke development,mountain uplift and subaerial sliding of tectonic sheets (northern Sierra de los Filabres,Betic Cordilleras,Spain)

The rauhwackes near Serón in the northern Sierra de los Filabres (S Spain), previously considered as true tectonic breccias, are reinterpreted on the basis of sedimentological, geomorphological and geometrical evidence as subaerial or nearly subaerial sedimentary deposits. Channel fills, parallel lamination, cross-lamination, graded bedding, sedimentary clastic dykes and other sedimentary structures and features occur in the rauhwacke body. These sedimentary rocks correspond to continental deposits of alluvial and karstic origin deposited over a karstified erosional surface of Nevado–Filabride marbles. Although no fossils have been found in the rauhwackes, a Tortonian age for these rocks is suggested on the basis of structural arguments and lithostratigraphic data from the nearby Almanzora basin. The rauhwackes were buried by slabs of Alpujarride rocks that gravitationally slid over them during the uplifting of the Sierra de los Filabres.     

Geological characteristics of 2011 Japan tsunami sediments deposited along the coast of southwestern Mexico

The tsunami of 11th March 2011 was originated at the east coast of Japan and deposited ca.1 cm thick sediment layer along the coast of southwestern Mexico up to a maximum distance of 320 m from the beach. The sedimentological, mineralogical and geochemical characteristics of the sediments deposited during the tsunami (JT) are compared with the pre-tsunami sediments (PRT). JT sediments consist of dominant coarser fractions (>54% of medium to coarse sand), whereas PRT deposits comprise abundant finer fractions (>58% of fine sand). Assemblage of mafic and heavy minerals suggests similar provenance for both. The higher abundance and variation of heavy minerals along with higher concentrations of bromine (Br) and sodium (Na) in the JT deposits reveal the influence of high energy sea waves in transportation of heavy mineral rich coarse sediments onto the coastal lowlands.     

Sedimentological and provenance response to Cambrian closure of the Clymene ocean: The upper Alto Paraguai Group,Paraguay belt,Brazil

Final Gondwana amalgamation was marked by the closure of the Neoproterozoic Clymene ocean between the Amazonia craton and central Gondwana. The events which occurred in the last stage of this closure were recorded in the upper Alto Paraguai Group in the foreland of the Paraguay orogen. Outcrop-based facies analysis of the siliciclastic rocks of upper Alto Paraguai Group, composed of the Sepotuba and Diamantino Formations, was carried out in the Diamantino region, within the eastern part of the Barra dos Bugres basin, Mato Grosso state, central-western Brazil. The Sepotuba Formation is composed of sandy shales with planar to wave lamination interbedded with fine-grained sandstone with climbing ripple cross-lamination, planar lamination, swaley cross-stratification and tangential to sigmoidal cross-bedding with mud drapes, related to marine offshore deposits. The lower Diamantino Formation is composed of a monotonous, laterally continuous for hundreds of metres, interbedded siltstone and fine-grained sandstone succession with regular parallel lamination, climbing ripple cross-lamination and ripple-bedding interpreted as distal turbidites. The upper part of this formation consists of fine to medium-grained sandstones with sigmoidal cross-bedding, planar lamination, climbing ripple cross-lamination, symmetrical to asymmetrical and linguoid ripple marks arranged in lobate sand bodies. These facies are interbedded with thick siltstone in coarsening upward large-scale cycles related to a delta system. The Sepotuba Formation characterises the last transgressive deposits of the Paraguay basin representing the final stage of a marine incursion of the Clymene ocean. The progression of orogenesis in the hinterland resulted in the confinement of the Sepotuba sea as a foredeep sub-basin against the edge of the Amazon craton. Turbidites were generated during the deepening of the basin. The successive filling of the basin was associated with progradation of deltaic lobes from the southeast, in a wide lake or a restricted sea that formed after 541 ± 7 Ma. Southeastern to east dominant Neoproterozoic source regions were confirmed by zircon grains that yielded ages around 600 to 540 Ma, that are interpreted to be from granites in the Paraguay orogen. This overall regressive succession recorded in the Alto Paraguai Group represents the filling up of a foredeep basin after the final amalgamation of western Gondwana in the earliest Phanerozoic.     

Significance of ancient sulfide PGE and Re–Os signatures in the mantle beneath Calatrava,Central Spain

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and CO₂ by silicic-carbonate-rich metasomatic melts/fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and ¹⁸⁷Os/¹⁸⁸Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and ¹⁸⁷Os/¹⁸⁸Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle.     

Effects of grain morphology on critical state: a computational analysis

We introduce a new DEM scheme (LS-DEM) that takes advantage of level sets to enable the inclusion of real grain shapes into a classical discrete element method. Then, LS-DEM is validated and calibrated with respect to real experimental results. Finally, we exploit part of LS-DEM potentiality by using it to study the dependency of critical state (CS) parameters such as critical state line (CSL) slope \(\lambda \), CSL intercept \(\varGamma \), and CS friction angle \(\varPhi _{\mathrm{CS}}\) on the grain’s morphology, i.e., sphericity, roundness, and regularity. This study is carried out in three steps. First, LS-DEM is used to capture and simulate the shape of five different two-dimensional cross sections of real grains, which have been previously classified according to the aforementioned morphological features. Second, the same LS-DEM simulations are carried out for idealized/simplified grains, which are morphologically equivalent to their real counterparts. Third, the results of real and idealized grains are compared, so the effect of “imperfections” on real particles is isolated. Finally, trends for the CS parameters (CSP) dependency on sphericity, roundness, and regularity are obtained as well as analyzed. The main observations and remarks connecting particle’s morphology, particle’s idealization, and CSP are summarized in a table that is attempted to help in keeping a general picture of the analysis, results, and corresponding implications.