Determination of the equilibrium fO2 in bulk samples of H,L, and LL ordinary chondrites by solid‐state electrochemistry          下载免费PDF全文

Valentin O. Osadchii  Mark V. Fedkin  Evgeniy G. Osadchii 《Meteoritics & planetary science》2017,52(10):2275-2283

High‐temperature solid‐state electrochemistry techniques (EMF method) were used to measure the oxygen fugacity (fO₂) of the ordinary chondrites Ochansk (H4), Savtschenskoje (LL4), Elenovka (L5), Vengerovo (H5), and Kharkov (L6). The fO₂ results are presented in the form of the following equations: It was found that fO₂ regularly increases from H chondrites to LL chondrites. Measured fO₂ are ~1.5 higher than those previously calculated from mineral assemblages. Kharkov (L6) is a little more oxidized than Elenovka (L5) in agreement with the progressive oxidation model. At the same time, Ochansk (H4) is more oxidized than Vengerovo (H5) and exhibits a slightly different slope compared to other chondrites and at T > 1200 K, becomes more reduced than Kharkov (L6) or Elenovka (L5). Measured oxygen fugacity values of meteorites fall within (0.1–1.0)·log fO₂ of one another. The possible explanation of discrepancies between measured and calculated values is discussed.  相似文献   

Sacred ground; the Maipés necropolis of north‐west Gran Canaria     

Valentin R. Troll  Alejandro Rodriguez‐Gonzalez  Frances M. Deegan  Francisco Jos Perez‐Torrado  Juan Carlos Carracedo  Konstantinos Thomaidis  Harri Geiger  Fiona C. Meade 《Geology Today》2019,35(2):55-62

Gran Canaria, like most of the Canary Islands, shows evidence for young basaltic volcanism in the form of cinder cones and valley‐hugging lava flows. These landforms were of no particular use to the aboriginal population, nor to the subsequent Spanish settlers, and young lava flows and lava fields are still referred to as ‘malpaís’ (badlands) in the Canary Islands. In north‐west Gran Canaria, one such lava flow fills the bottom of a steep‐sided valley, which reaches the sea at the present day village of Agaete. The lava flow erupted c. 3030 ± 90 yr bp and displays a total length of ～ 11 km. At its distal end, just outside Agaete, it hosts one of Europe’s largest and most important pre‐historic burial sites constructed of volcanic rock: the Maipés necropolis. Over 700 pre‐historic tombs (or tumuli) constructed from the aa‐type clinker materials have been identified on top of the valley‐filling lava flow. The up to soccer‐ball sized vesicular clinker fragments are sufficiently low in density to provide abundant, workable basalt blocks for the construction of the tumuli, allowing the pre‐hispanic aboriginal population to create a large and magnificent ‘sacred ground’ in an otherwise barren landscape.  相似文献   

A new approach to precious metals recovery from brown coals: Correlation of recovery efficacy with the mechanism of metal-humic interactions     

Svetlana Yu. Bratskaya  Alexandra S. Volk  Alexander Yu. Ustinov  Valentin A. Avramenko 《Geochimica et cosmochimica acta》2009,73(11):3301-176

The presence of gold and platinum group elements (PGE) in low-rank brown coals around the world has promoted interest in the industrial exploitation of this alternative source of precious metals. However, due to low efficacy of the methods traditionally used for the processing of mineral ores, there exists a high demand for new strategies of precious metal recovery from refractory carbonaceous materials that could significantly increase the economic potential of gold- and PGE-bearing organic resources. Here we discuss the possibility of gold and PGE recovery from alkaline extracts of brown coals using the difference in colloidal stability of bulk organic matter and its fractions enriched with precious metals. This approach enables one to avoid complete oxidation or combustion of brown coals prior to gold recovery, to minimize organic content in gold concentrate, and to obtain a valuable by-product - humic extracts. Using gold-bearing brown coals from several deposits located in the South Far East of Russia, we show that up to 95% of gold can be transferred to alkaline extracts of humic acids (HA) and up to 85% of this gold can be recovered by centrifugation at pH 4.0-6.0, when only 5-15% of HA precipitated simultaneously. We have shown that the high efficacy of gold recovery can be attributed to the occurrence of fine-dispersed elemental gold particles stabilized by HA, which differ significantly in colloidal stability from the bulk organic matter and, thus, can be separated by centrifugation.  相似文献   

Influence of agricultural development and climate changes on the drainage valley density of the southern half of the Russian Plain   总被引：1，自引：1，他引：0  

Valentin Golosov  Nadezhda Ivanov  Saniya Kurbanova 《国际泥沙研究》2017,32(1)

The southern half of the Russian Plain is characterized by a relatively short history of intensively ploughed lands.The duration varies from approximately three centuries in the southern part of the forest zone to less than one century in some parts of the steppe zone.It was found that after cultivation,on more than 40％ of lands in river basins the drainage valley density (Ddv) decreased by 15-58％ in all landscape zones.In the first stage,the Ddv decrease was mostly associated with increasing surface runoff coefficient after cultivation of virgin lands with proportional decreases in groundwater runoff.In the second stage,usually after reaching areas of arable lands in river basins ＞ 60％,the volume of eroded sediments entering small fiver channels exceeded the transport capacities of the permanent water-courses.As a result,the river channels completely silted.In later stages,the sediment redistribution cascade within the small river basins of the Russian Plain stabilized because of the increasing proportion of sediment eroded from the basin areas and re-deposited before entering the river channels because of the increasing area of sediment sinks due to the increase in dry valley lengths and total areas.The morphological parameters of small valleys and groundwater discharges are the key parameters that affect the intensity of small river aggradation on the regional scale.  相似文献   

Volcanic and structural evolution of Pico do Fogo,Cape Verde          下载免费PDF全文

Juan‐Carlos Carracedo  Francisco J. Perez‐Torrado  Alejandro Rodriguez‐Gonzalez  Raphaël Paris  Valentin R. Troll  Abigail K. Barker 《Geology Today》2015,31(4):146-152

In recent months the media have drawn attention to the Cape Verde archipelago, with particular focus on the island of Fogo, the only island presently active and with an eruption that began on 23 November 2014, finally ceasing on 7 February 2015. The Monte Amarelo conical shield forms most of the 476 km² almost circular island of Fogo. After attaining a critical elevation of about 3500 m, the Monte Amarelo shield volcano was decapitated by a giant landslide that formed a caldera‐like depression (Cha das Caldeiras), which was subsequently partially filled by basaltic nested volcanism. This younger eruptive activity culminated in the construction of the 2829 m‐high Pico do Fogo stratocone, apparently entirely made of layers of basaltic lapilli. Continued growth of the Pico do Fogo summit eruptions was interrupted in 1750, most likely after the stratocone reached a critical height. Since then, at least eight eruptions have taken place inside the landslide depression at the periphery of the Pico do Fogo cone, including the 2014–2015 eruptive event. Strong geological similarities with the Canary Islands, 1400 km to the north, have been frequently noted, probably as a consequence of a common process of origin and evolution associated with a mantle hot‐spot. These similarities are particularly evident when comparing Fogo with the Teide Volcanic Complex on Tenerife, where a lateral collapse of the Las Cañadas stratovolcano also formed a large depression (the Caldera de Las Cañadas), now partially filled with the 3718 m‐high Teide stratocone. However, important geological differences also exist and probably relate to the contrasting evolutionary stages of both islands. The Las Cañadas volcano on Tenerife formed at a late post‐erosional stage, with predominantly evolved (trachyte and phonolite) magmas, while at Fogo basaltic volcanism is still dominant.  相似文献   

Isotopic fingerprints of Milankovitch cycles in Pennsylvanian carbonate platform‐top deposits: the Valdorria record,Northern Spain          下载免费PDF全文

Valentin Chesnel  Óscar Merino‐Tomé  Luis Pedro Fernández  Elisa Villa  Elias Samankassou 《地学学报》2016,28(5):364-373

Sedimentary cyclic sequences deposited during the Late Palaeozoic Ice Age are widespread. Glacio‐eustatic control of the cyclic patterns is commonly accepted, and the durations of the cyclothems generally match the short‐ and long‐eccentricity Milankovitch orbital parameters. Nevertheless, geochemical fingerprints of orbital parameters are poorly documented in deep‐time sedimentary records. Here, we report on well‐exposed Bashkirian cyclothems of c. 123 ka and c. 400 ka durations from the Valdorria platform. The shorter‐term cyclothems can be grouped into longer‐term composite sequences that are consistent with generally accepted durations of c. 125 ka and c. 400 ka for Milankovitch eccentricity cycles. The stratigraphic pattern is mirrored by the isotope geochemical signals, which show distinct recurring trends. These trends are confirmed by statistical tests. Whereas intrinsic factors and/or subaerial exposure related to sea‐level lowstands might have truncated cycle patterns in tectonically stable basins, rapid subsidence of the Valdorria platform's foreland basin appears to have contributed to a faithful recording of cyclothems of different orders. The patterns and biostratigraphic constraint revealed in this study demonstrate the power of orbital forcing in imprinting sedimentary and geochemical signals in the rock record.  相似文献   

Thermal tracer testing in a sedimentary aquifer: field experiment (Lauswiesen,Germany) and numerical simulation   总被引：1，自引：0，他引：1  

Valentin Wagner  Tao Li  Peter Bayer  Carsten Leven  Peter Dietrich  Philipp Blum 《Hydrogeology Journal》2014,22(1):175-187

An active and short-duration thermal tracer test (TTT) was conducted in a shallow sedimentary aquifer at the Lauswiesen test site, near Tübingen, Germany. By injecting 16  m³ of warm water at 22°C, a thermal anomaly was created, which propagated along the local groundwater flow direction. This was comprehensively monitored in five observation wells at a few meters distance. The purpose of this well-controlled experiment was to determine the practicability of such a TTT and its suitability to examine hydraulic characteristics of heterogeneous aquifers. The results showed that the thermal peak arrival times in the observation wells were consistent with previous observations from alternative field testing such as direct-push injection logging (DPIL). Combined analysis of depth-dependent temperatures and peak arrival times, and comparison with a numerical heat transport model, offers valuable insights into the natural flow field and spatial distribution of hydraulic conductivities. The study was able to identify vertical flow focusing and bypassing, which are attributed to preferential flow paths common in such sedimentary sand and gravel aquifers. These findings are fundamental for further development of experimental designs of active and short-duration TTTs and provide a basis for a more quantitative analysis of advective and conductive transport processes.  相似文献   

Case study: a 3D resistivity and induced polarization imaging from downstream a waste disposal site in Brazil   总被引：2，自引：2，他引：0  

Andréa Teixeira Ustra  Vagner Roberto Elis  Giulliana Mondelli  Lázaro Valentin Zuquette  Heraldo Luiz Giacheti 《Environmental Earth Sciences》2012,66(3):763-772

A contaminated site from a downstream municipal solid waste disposal site in Brazil was investigated by using a 3D resistivity and induced polarization (IP) imaging technique. This investigation purpose was to detect and delineate contamination plume produced by wastes. The area was selected based on previous geophysical investigations, and chemical analyses carried out in the site, indicating the presence of a contamination plume in the area. Resistivity model has successfully imaged waste presence (ρ < 20 Ωm), water table depth, and groundwater flow direction. A conductive anomaly (ρ < 20 Ωm) outside wastes placement was interpreted as a contamination plume. Chargeability model was also able to imaging waste presence (m > 31 mV/V), water table depth, and groundwater flow direction. A higher chargeability zone (m > 31 mV/V) outside wastes placement and following conductive anomaly was interpreted as a contamination plume. Normalized chargeability (MN = m/ρ) confirmed polarizable zone, which could be an effect of a salinity increase (contamination plume), and the clay presence in the environment.  相似文献   

Large-scale failures on domes and stratocones situated on caldera ring faults: sand-box modeling of natural examples from Kamchatka, Russia     

Alexander Belousov  Thomas R. Walter  Valentin R. Troll 《Bulletin of Volcanology》2005,67(5):457-468

Edifices of stratocones and domes are often situated eccentrically above shallow silicic magma reservoirs. Evacuation of such reservoirs forms collapse calderas commonly surrounded by remnants of one or several volcanic cones that appear variously affected and destabilized. We studied morphologies of six calderas in Kamchatka, Russia, with diameters of 4 to 12 km. Edifices affected by caldera subsidence have residual heights of 250–800 m, and typical amphitheater-like depressions opening toward the calderas. The amphitheaters closely resemble horseshoe-shaped craters formed by large-scale flank failures of volcanoes with development of debris avalanches. Where caldera boundaries intersect such cones, the caldera margins have notable outward embayments. We therefore hypothesize that in the process of caldera formation, these eccentrically situated edifices were partly displaced and destabilized, causing large-scale landslides. The landslide masses are then transformed into debris avalanches and emplaced inside the developing caldera basins. To test this hypothesis, we carried out sand-box analogue experiments, in which caldera formation (modeled by evacuation of a rubber balloon) was simulated. The deformation of volcanic cones was studied by placing sand-cones in the vicinity of the expected caldera rim. At the initial stage of the modeled subsidence, the propagating ring fault of the caldera bifurcates within the affected cone into two faults, the outermost of which is notably curved outward off the caldera center. The two faults dissect the cone into three parts: (1) a stable outer part, (2) a highly unstable and subsiding intracaldera part, and (3) a subsiding graben structure between parts (1) and (2). Further progression of the caldera subsidence is likely to cause failure of parts (2) and (3) with failed material sliding into the caldera basin and with formation of an amphitheater-like depression oriented toward the developing caldera. The mass of material which is liable to slide into the caldera basin, and the shape of the resulted amphitheater are a function of the relative position of the caldera ring fault and the base of the cone. A cone situated mostly outside the ring fault is affected to a minor degree by caldera subsidence and collapses with formation of a narrow amphitheater deeply incised into the cone, having a small opening angle. Accordingly, the caldera exhibits a prominent outward embayment. By contrast, collapse of a cone initially situated mostly inside the caldera results in a broad amphitheater with a large opening angle, i.e. the embayment of the caldera rim is negligible. The relationships between the relative position of an edifice above the caldera fault and the opening angle of the formed amphitheater are similar for the modeled and the natural cases of caldera/cone interactions. Thus, our experiments support the hypothesis that volcanic edifices affected by caldera subsidence can experience large-scale failures with formation of indicative amphitheaters oriented toward the caldera basins. More generally, the scalloped appearance of boundaries of calderas in contact with pre-caldera topographic highs can be explained by the gravitational influence of topography on the process of caldera formation.Editorial responsibility: J. Stix  相似文献   

Experiments on rift zone evolution in unstable volcanic edifices   总被引：1，自引：0，他引：1  

Thomas R. Walter  Valentin R. Troll   《Journal of Volcanology and Geothermal Research》2003,127(1-2):107-120

Large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses. Flank deformation is often caused by slip along a décollement within or underneath the volcanic edifice. We studied how such a stressed volcanic flank may bias the rift zone development. The influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence; here our analog experiments provide new insights. We injected colored water into gelatin cones and found systematic orientations of hydro-fractures (dikes) propagating through the cones. At the base of the cone, diverse friction conditions were simulated. By variation of the basal creep conditions we modeled radial dike swarms, collinear rift zones and three-armed rift systems. It is illustrated that a single outward-creeping flank is sufficient to modify the entire rift architecture of a volcano. The experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano’s architecture.  相似文献