Metal-residence sites in lavas and tuffs from Volcán Popocatépetl, Mexico: implications for metal mobility in the environment

 Volcan Popocatépetl is a Quaternary stratovolcano located 60 km southeast of Mexico City. The summit crater is the site of recent ash eruptions, excess degassing, and dacite dome growth. The modern cone comprises mainly pyroclastic flow deposits, airfall tephras, debris flows, and reworked deposits of andesitic composition; it is flanked by more mafic monogenetic vents. In least-degassed fallout tuffs and mafic scoria, transition metals are concentrated in phases formed before eruption, during eruption, and after eruption. Preeruptive minerals occur in both lavas and tephra, and include oxides and sulfides in glass and phenocrysts. The magmatic oxides consist of magnetite, ilmenite, and chromite; the sulfides consist of both (Fe,Ni)_1-xS (MSS) and Cu–Fe sulfide (ISS). Syn- and posteruptive phases occur in vesicles in both lavas and tephra, and on surfaces of ash and along fractures. The mineral assemblages in lavas include Cu–Fe sulfide and Fe–Ti oxide in vesicles, and Fe sulfide and Cu–Fe sulfide in segregation vesicles. Assemblages in vesicles in scoria include Fe–Ti oxide and rare Fe–Cu–Sn sulfide. Vesicle fillings of Fe–Ti oxide, Ni-rich chromite, Fe sulfide, Cu sulfide, and barite are common to two pumice samples. The most coarse-grained of the vesicle fillings are Cu–Fe sulfide and Cu sulfide, which are as large as 50 μ in diameter. The youngest Plinian pumice also contains Zn(Fe) sulfide, as well as rare Ag–Cu sulfide, Ag–Fe sulfide, Ag bromide, Ag chloride, and Au–Cu telluride. The assemblage is similar to those typically observed in high-sulfidation epithermal mineralization. The fine-grained nature and abundance of syn- and/or posteruptive phases in porous rocks makes metals susceptible to mobilization by percolating fluids. The abundance of metal compounds in vesicles indicates that volatile exsolution prior to and/or during eruption played an important role in releasing metals to the atmosphere. Received: March 1997 · Accepted: 27 May 1997     

A new approximation for pore pressure accumulation in marine sediment due to water waves

The residual mechanism of wave‐induced pore water pressure accumulation in marine sediments is re‐examined. An analytical approximation is derived using a linear relation for pore pressure generation in cyclic loading, and mistakes in previous solutions (Int. J. Numer. Anal. Methods Geomech. 2001; 25 :885–907; J. Offshore Mech. Arctic Eng. (ASME) 1989; 111 (1):1–11) are corrected. A numerical scheme is then employed to solve the case with a non‐linear relation for pore pressure generation. Both analytical and numerical solutions are verified with experimental data (Laboratory and field investigation of wave– sediment interaction. Joseph H. Defrees Hydraulics Laboratory, School of Civil and Environmental Engineering, Cornell University, Ithaca, NY, 1983), and provide a better prediction of pore pressure accumulation than the previous solution (J. Offshore Mech. Arctic Eng. (ASME) 1989; 111 (1):1–11). The parametric study concludes that the pore pressure accumulation and use of full non‐linear relation of pore pressure become more important under the following conditions: (1) large wave amplitude, (2) longer wave period, (3) shallow water, (4) shallow soil and (5) softer soils with a low consolidation coefficient. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of atmospheric pressure and temperature on entrapped gas content in peat

Entrapped biogenic gas in peat can greatly affect peatland biogeochemical and hydrological processes by altering volumetric water content, peat buoyancy, and ‘saturated’ hydraulic conductivity, and by generating over‐pressure zones. These over‐pressure zones further affect hydraulic gradients which influence water and nutrient flow direction and rate. The dynamics of entrapped gas are of global interest because the loss of this gas to the atmosphere via ebullition (bubbling) is likely the dominant transport mechanism of methane (CH₄) to the atmosphere from peatlands, which are the largest natural terrestrial source per annum of atmospheric CH₄. We investigated the relationship between atmospheric pressure and temperature on volumetric gas content (VGC) and CH₄ ebullition using a laboratory peat core incubation experiment. Peat cores were incubated at three temperatures (one core at 4 °C, three cores at 11 °C, and one core at 20 °C) in sealed PVC cylinders, instrumented to measure VGC, pore‐water CH₄ concentrations, and ebullition (volume and CH₄ concentrations). Ebullition events primarily occurred (71% of the time) during periods of falling atmospheric pressure. The duration of the drop in atmospheric pressure had a larger control on ebullition volume than the magnitude of the drop. VGC in the 20 °C core increased from the onset of the experiment and reached a fluctuating but time‐averaged constant level between experiment day 30 and 115. The change in VGC was low for the 11 °C cores for the initial period of the experiment but showed large increases when the growth chamber temperature increased to 20 °C due to a malfunction. The core maintained at 4 °C showed only a small increase in entrapped gas content throughout the experiment. The 20 °C core showed the largest increase in VGC. The increases in VGC occurred despite pore‐water concentrations of CH₄ being below the equilibrium solubility level. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical predictions of water–air wave slam using incompressible–compressible smoothed particle hydrodynamics

The high-speed impact between a body and water is an important practical problem, whether due to wave impact on a structural deck or wall, or due to a moving body such as a ship or aircraft hitting water. The very high pressures exerted are difficult to predict and the role of air may be significant. In this paper, numerical simulations are undertaken to investigate the impact of a rigid horizontal plate onto a wave crest and, in the limit, onto a flat water surface. A two-phase incompressible–compressible smoothed particle hydrodynamics (SPH) method for water and air, respectively, is applied where the water phase imposes kinematics on the air phase at the air–water interface and the air phase imposes pressures on the water at the interface. Results are compared with experimental measurements undertaken using a drop rig positioned over a wave flume so that a horizontal plate impacts the water surface in free flight. Numerical predictions of impact pressure are quite accurate; air is shown to have a significant cushioning effect for impact on to flat water and this reduces for waves as the ratio of wave height to wavelength increases.     

基于生态系统服务的海洋健康评估与调控:以莱州湾为例

近岸海域的生态系统管理,要求对海洋健康进行综合的评估以及对人工调控进行科学的指导,进而促进可持续发展。本文构建了定量化方法,用于评估当前的和近期的基于生态系统服务的海洋健康。以莱州湾为例的研究结果表明,当前的海洋健康指数分值为0.7856(总分为1.0);通过对负面压力进行不同强度的人工调控,得到近期海洋健康预计的变化范围为0.5551到0.8041。具体地说,本文评估得到当前的海洋健康主要表现为文化服务和供给服务基本优秀,而支持服务和调节服务不够良好。若不对持续增长的压力采取有效的调控措施,该近岸海域生态系统会在近期丧失部分支持服务和调节服务;若负面压力被完全控制,该近岸海域生态系统服务的分类等级会得到小幅提升。另外,应进一步加强对生态系统服务尤其是文化服务和调节服务的宣传教育。本文的分析过程和量化结果,为进一步指导人工调控提供了灵活的工具,有助于海岸带区域的生态系统管理。     

A laboratory study on capillary sealing efficiency of Iranian shale and anhydrite caprocks

Caprock has the most important role in the long term safety of formation gas storage. The caprocks trap fluid accumulated beneath, contribute to lateral migration of this fluid and impede its upward migration. The rapid upward passage of invasive plumes due to buoyancy pressure is prevented by capillary pressure within these seal rocks. In the present study, two main seal rocks, from the Zagros basin in the southwest of Iran, a shale core sample of Asmari formation and an anhydrite core sample of Gachsaran formation, were provided. Absolute permeabilities of shale and anhydrite cores, considering the Klinkenberg effect, were measured as 6.09 × 10⁻¹⁸ and 0.89 × 10⁻¹⁸ m², respectively. Capillary sealing efficiency of the cores was investigated using gas breakthrough experiments. To do so, two distinct techniques including step by step and residual capillary pressure approaches were performed, using carbon dioxide, nitrogen and methane gases at temperatures of 70 and 90 °C, under confining pressures in the range 24.13–37.92 MPa. In the first technique, it was found that capillary breakthrough pressure of the cores varies in the range from 2.76 to 34.34 MPa. Moreover, the measurements indicated that after capillary breakthrough, gas effective permeabilities lie in range 1.85 × 10⁻²¹ – 1.66 × 10⁻¹⁹ m². In the second technique, the minimum capillary displacement pressure of shale varied from 0.66 to 1.45 MPa with the maximum effective permeability around 7.76 × 10⁻²¹ – 6.69 × 10⁻²⁰ m². The results indicate that anhydrite caprock of the Gachsaran formation provides proper capillary sealing efficacy, suitable for long term storage of the injected CO₂ plumes, due to its higher capillary breakthrough pressure and lower gas effective permeability.     

新太阳光压模型在GNSS定轨中的应用

太阳光压摄动是影响卫星定轨中重要的误差源,在GNSS导航卫星精密定轨过程中使用最为广泛的光压模型为ECOM模型。为了探究几种ECOM模型及其适用性,该文以超快速星历为起算轨道,分析对比经典ECOM-1模型与最新13参数ECOMC模型对GPS/BDS卫星轨道的影响。结果显示:相较于ECOM-1模型,ECOMC模型在GPS定轨中精度有所提升,特别体现在径向精度提升,单天与三天弧段在径向的解算精度分别提升了12.73%和24.74%;在BDS定轨中,采用ECOMC模型,部分GEO卫星在径向方向单天精度有12.38%的提升,而对于IGSO与MEO卫星二者精度差异不大;分析可得,由于星体结构不对称引起卫星在沿太阳-卫星方向作用的偶数阶短周期谐波扰动,引入卫星-太阳方向偶数阶项的参数估计可提升卫星径向精度。     

An experimental study of effect of pre‐existing fabric on deformation of foliated mylonite at high temperature and pressure

We performed deformation experiments on a foliated mylonite under high temperature and pressure conditions in this study. To investigate the effect of pre‐existing fabric on the rheology of rocks, our samples were drilled from natural mylonite with the cylinder axis parallel to the foliation (PAR) and perpendicular to the foliation (PER). We performed 25 tests on seven PAR samples and 21 tests on seven PER samples at temperatures ranging from 600 to 890 °C, confining pressures ranging from 800 to 1400 MPa, and steady‐state strain rates of 1 × 10⁻⁴, 1 × 10⁻⁵ and 2.5 × 10⁻⁶ s⁻¹. In the temperatures of 600–700 °C, the deformation is accommodated by semi‐brittle flow, with the average stress exponent being 6–7 assuming power law flow; in the temperature range of 800–890 °C, deformation is mainly by plastic flow, with an average stress exponent of n = 3 and activation energies of Q = 354 ± 52 kJ/mol (PER and PAR samples). The experimental results show that the strengths of PER samples are higher than those of PAR samples. Deformation microstructures have been studied by optical and electron microscopy. The original foliation of PER samples is destroyed by deformation and replaced by a new foliation, but the deformation of PAR samples followed the original foliation. Electron backscatter diffraction (EBSD) measurements show a strong lattice preferred orientation (LPO) of the quartz c axis fabrics of the starting samples and deformed PER and PAR samples. However, the c axis fabric of quartz in experimentally deformed PER and PAR samples varied with temperature and strain rate is different from that seen in the starting mylonite sample. The initial quartz c axis fabric of the starting mylonite sample has been transformed into a new fabric during experimental deformation. Dehydration melting of biotite and hornblende occurred in both PER and PAR samples at temperatures of 800–890 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

谈滑坡勘察中的几个地下水压力问题

鉴于目前在滑坡勘察中对地下水压力问题尚有一些不够明确和难以确定之处,本文首先讨论地下水压力的分类及其概念,并简要叙述地下水压力的时、空变化和影响因素;然后结合实例分析不同条件下地下水压力在滑坡形成中的实际效用,并就地下水压力的确定问题发表了看法。