Synchronous Transformations of Mineral and Organic Constituents of Sedimentary Rocks in Geological Structure with an Initial Extension and Subsequent Compression Tectonic Regime

Sedimentary rocks of the section in the Red River fold zone of northern Viet Nam are considered. It is shown that secondary mineral parageneses formed in two stages. The first stage (35–17 Ma ago) corresponded to the period of structure extension and sediment subsidence to a depth of about 6 km. This period and subsequent 10 Ma were marked by the formation of a usual dia- and catagenetic zoning of metasedimentary rocks. The second stage (5–7 Ma ago) corresponded to processes of compression that were responsible for the deformation of rocks into gentle folds and 1.5 to 2.2 times contraction of the section thickness in different places. The sequential–mineralogical zoning was disturbed at this stage. Smectites and mixed-layer minerals were replaced by chlorites and hydromicas. Organic material also responded to compression simultaneously with inorganic components. The bituminous component was released from humic matter and rocks became enriched in hydrocarbons.     

Construction and analysis of higher order finite difference schemes for the 1D wave equation

In this article, we propose to: 1. Establish most of the properties conjectured in [2] about the higher order finite difference approximation of the 1D Laplace operator. 2. Generalize to any order the fourth-order accurate scheme in space and time of Shubin and Bell [20] and Cohen [6]. For this new family of 2m–2m schemes, we establish, via elementary mathematics, various stability and dispersion results that are helpful to compare these schemes to the 2–2m schemes of Anné et al. [2]. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessment with satellite data of the urban heat island effects in Asian mega cities

This study focuses on using remote sensing for comparative assessment of surface urban heat island (UHI) in 18 mega cities in both temperate and tropical climate regions. Least-clouded day- and night-scenes of TERRA/MODIS acquired between 2001 and 2003 were selected to generate land-surface temperature (LST) maps. Spatial patterns of UHIs for each city were examined over its diurnal cycle and seasonal variations. A Gaussian approximation was applied in order to quantify spatial extents and magnitude of individual UHIs for inter-city comparison. To reveal relationship of UHIs with surface properties, UHI patterns were analyzed in association with urban vegetation covers and surface energy fluxes derived from high-resolution Landsat ETM+ data. This study provides a generalized picture on the UHI phenomena in the Asian region and the findings can be used to guide further study integrating satellite high-resolution thermal data with land-surface modeling and meso-scale climatic modeling in order to understand impacts of urbanization on local climate in Asia.     

P–T–t paths and post-metamorphic exhumation of the Day Nui Con Voi shear zone in Vietnam

The Day Nui Con Voi belt in Vietnam is the southeasternmost part of the Red River shear zone in Asia. It is a narrow high-grade metamorphic core complex consisting of garnet–sillimanite–biotite gneisses, mylonite bands, amphibolite layers and migmatites. Geothermobarometric study of the complex revealed that the peak metamorphism took place under amphibolite-facies conditions of 690₋₆₀⁺³⁰°C and 0.65±0.15 GPa and the subsequent mylonitization occurred under greenschist-facies conditions of 480°C and under 0.3 GPa. Fifteen synkinematic hornblende and biotite separates from gneisses, amphibolites and mylonites were dated with the K/Ar method. Hornblende separates from the Day Nui Con Voi give K–Ar ages of 26.4–28.5 Ma, and the biotite separates do give 24.5–24.7 Ma. Combination of thermobarometric and geochronological data yields the cooling history of 500°C at 28 Ma and 300°C at 24 Ma with a cooling rate of 70–110°C Ma⁻¹, and 23 km post-metamorphic exhumation of the core complex. The first 16 km exhumation from the peak of metamorphism (at probably 31 Ma) to 28 Ma was triggered by the left-lateral strike-slip displacement of the Red River shear zone.     

Copper speciation survey from UK marinas, harbours and estuaries

The use of copper in antifouling paints has increased in the UK in the last 20 years as TBT and several other organic biocides have been phased out. To assess the probable impact of copper on estuarine systems a survey was undertaken to measure the different fractions of copper present in the water column at current usage. The different fractions measured were; labile copper, (LCu) considered as both the free copper ions and inorganically bound copper, the total dissolved copper (TDCu) present, and the difference between them taken as the organically bound likely non-toxic copper fraction. The survey considered sites with different levels of boat use, namely marinas, harbours and estuaries, differing physical parameters of suspended and dissolved organic matter, different seasons of the year and different depths in the water column all of which control speciation behaviour. Suspended particulate matter (SPM) values were measured at all sites and increased from West to East coast locations (5.7-34.4 mg/l). Dissolved organic matter (DOM) values ranged from 0.58 to 2.2mg/l C. The total dissolved copper concentrations ranged from 0.30 to 6.68 microg/l, with labile fraction ranging from 0.02 to 2.69 microg/l, and most labile copper concentrations below 1 microg/l. None of the yearly mean copper measurements exceeded the 76/464/EEC EQS of 5 microg/l. Of the 306 measurements, only one dissolved copper value in one season was above 5 microg/l. This ratio of labile to total copper was between 10 and 30%. The results from this survey suggest that if toxicity of copper is due to the labile fraction then using the total dissolved copper concentrations as an indicator of impact overestimate the risk by a factor of four times.     

Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam

Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using Mössbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO₄ from the sediment were investigated in leaching experiments with HCl and 10 mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2 months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers.     

Geochemistry and petrogenesis of Permian ultramafic-mafic complexes of the Jinping–Song Da rift (southeastern Asia)

The Jinping–Song Da rift structure in the Emeishan Large Igneous Province is composed of Permian high- and low-Ti volcanic and volcanoplutonic ultramafic-mafic associations of different compositions and genesis. High-Ti picrites, picrobasalts, basalts, and dolerites are enriched in LREE and depleted in HREE and show low Al₂O₃/TiO₂ ratios (~4), commensurate ε_Nd(T) values (+0.5 to +1.1), and low (Th/Nb)_PM ratios similar to those of OIB-enriched mantle source. The established geochemical characteristics evidence that the parental melts of these rocks were generated from garnet lherzolite at the depths of garnet stability (~200 to 400 km). Later, high-Mg low-Ti volcanics (komatiites, komatiitic basalts, and basalts) and associating small peridotite-gabbro massifs and komatiite-basalt dikes were produced as a result of ~20% partial melting of depleted water-poor (≤0.03 wt.% H₂O) peridotite substratum from the hottest upper part of mantle plume at relatively shallow depths (100–120 km). The LREE-depleted komatiites and komatiitic basalts are characterized by low (Ce/Yb)_CH values, ¹⁸⁷Re/¹⁸⁸Os = 0.05–1.2, ⁸⁷Sr/⁸⁶Sr = 0.704–0.706, positive ε_Nd(T) values (+3 to +8), γ_Os = –0.5 to +0.9, and strong negative anomalies of Ba, K, and Sr on the spidergrams. The scarcer LREE-enriched komatiites, komatiitic basalts, and basalts vary greatly in chemical composition and values of ε_Nd(t) (+6.4 to –10.2), ⁸⁷Sr/⁸⁶Sr (0.706–0.712), and γ_Os (+14.8 to +56), which is due to the different degrees of crustal contamination of parental magmas. The Rb-Sr isotopic age of basaltic komatiite is 257 ± 24 Ma. The Re-Os age determined by analysis of 12 komatiite samples is 270 ± 21 Ma. These data agree with the age of flood basalts of the Emeishan Large Igneous Province. The komatiite-basalt complex of the Song Da rift is still the only Phanerozoic PGE-Cu-Ni-complex of this composition. The geochemistry of accompanying Cu-Ni-PGE-ores confirms their relationship with komatiite-basaltic magmatism.     

Timing of Holocene sand accumulation along the coast of central and SE Vietnam

In Vietnam, the coastal sand barriers and dunes located in front of the steep slopes of the high rising Truong Son Mountains are sensitive to climate and environment change and give evidence for Holocene sea-level rise. The outer barrier sands were deposited shortly before or contemporaneous with the local sea-level high stand along the Van Phong Bay postdating the last glacial maximum (LGM). Optically stimulated luminescence (OSL) dating yielded deposition ages ranging from 8.3 ± 0.6 to 6.2 ± 0.3 ka for the stratigraphically oldest exposed barrier sands. Further periods of sand accumulation took place between 2.7 and 2.5 ka and between 0.7 and 0.5 ka. The youngest period of sand mobilisation was dated to 0.2 ± 0.01 ka and is most likely related to reworked sand from mining activities. At the Suoi Tien section in southern central Vietnam, the deposition of the inner barrier sands very likely correlate with an earlier sea-level high stand prior to the last glaciation. OSL age estimates range from 276 ± 17 to 139 ± 15 ka. OSL dating significantly improves our knowledge about the sedimentary dynamics along the coast of Vietnam during the Holocene.     

A roadmap for a dedicated Earth Science Grid platform

Due to its intensive data processing and highly distributed organization, the multidisciplinary Earth Science applications community is uniquely positioned for the uptake and exploitation of Grid technologies. Currently Enabling Grids for E-sciencE, and other large Grid infrastructures are already deployed and capable of operational services. So far however, the adoption and exploitation of Grid technology throughout the Earth Science community has been slower than expected. The Dissemination and Exploitation of GRids in Earth sciencE project, proposed by the European Commission to assist and accelerate this process in a number of different ways, had between its main goals the creation of a roadmap towards Earth Science Grid platform. This paper presents the resulting roadmap.     

Characterization of deep saline aquifers in the Bécancour area,St. Lawrence Lowlands,Québec,Canada: implications for CO2 geological storage

The present paper provides a case study of the assessment of the potential for CO₂ storage in the deep saline aquifers of the Bécancour region in southern Québec. This assessment was based on a hydrogeological and petrophysical characterization using existing and newly acquired core and well log data from hydrocarbon exploration wells. Analyses of data obtained from different sources provide a good understanding of the reservoir hydrogeology and petrophysics. Profiles of formation pressure, temperature, density, viscosity, porosity, permeability, and net pay were established for Lower Paleozoic sedimentary aquifers. Lateral hydraulic continuity is dominant at the regional scale, whereas vertical discontinuities are apparent for most physical and chemical properties. The Covey Hill sandstone appears as the most suitable saline aquifer for CO₂ injection/storage. This unit is found at a depth of more than 1 km and has the following properties: fluid pressures exceed 14 MPa, temperature is above 35 °C, salinity is about 108,500 mg/l, matrix permeability is in the order of 3 × 10^?16 m² (0.3 mDarcy) with expected higher values of formation-scale permeability due to the presence of natural fractures, mean porosity is 6 %, net pay reaches 282 m, available pore volume per surface area is 17 m³/m², rock compressibility is 2 × 10^?9 Pa^?1 and capillary displacement pressure of brine by CO₂ is about 0.4 MPa. While the containment for CO₂ storage in the Bécancour saline aquifers can be ensured by appropriate reservoir characteristics, the injectivity of CO₂ and the storage capacity could be limiting factors due to the overall low permeability of aquifers. This characterization offers a solid basis for the subsequent development of a numerical hydrogeological model, which will be used for CO₂ injection capacity estimation, CO₂ injection scenarios and risk assessment.