Hypolimnetic density currents traced by sulphur hexafluoride (SF6)

The artificial tracer sulphur hexafluoride (SF₆) has been used to study the density-driven deep water exchange between two sill-separated basins of Lake Lucerne, Gersauersee and Urnersee. The sources of the density gradients between the two basins are (1) salinity differences between the major inlets due to the different geology of their drainage areas, and (2) temperature differences due to spatial variation of wind forcing. Wind speeds are generally larger in Urnersee, especially in spring during the so-called Föhn events, when winds blow from the south. In contrast, Gersauersee is protected form these winds. In spring 1989, a total of 630 g of SF₆ was released at 80 to 120 m depth in the small Treib Basin located between Urnersee and Gersauersee. During about 100 days the distribution of SF₆ in the lake was determined by gaschromatography. Two models are used to quantify the exchange flow, (1) a one-box mass balance model for SF₆ in the deep part of Treib Basin, and (2) a one-dimensional diffusion/advection model describing the temporal and vertical temperature variation in Urnersee. According to the first model, the flow into the deep hypolimnion of Urnersee, decreases from 21·10⁶ m³·d^?1 at the end of March to about 8·10⁶ m³·d^?1 in late April. The second model yields similar flow rates. The decrease of the flow rate during spring, confirmed by both approaches, is consistent (1) with the decreasing strength of the density gradient above the sill during spring and early summer, and (2) with hydrographic information collected in Lake Lucerne during other years.     

Tidal effects on temperature front in the Yellow Sea

Temperature front (TF) is one of the important features in the Yellow Sea, which forms in spring, thrives in summer, and fades in autumn as thermocline declines. TF intensity ⋎S _T ⋎ is defined to describe the distribution of TF. Based on the MASNUM wave-tide-circulation coupled model, temperature distribution in the Yellow Sea was simulated with and without tidal effects. Along 36°N, distribution of TF from the simulated results are compared with the observations, and a quantitative analysis is introduced to evaluate the tidal effects on the forming and maintaining processes of the TF. Tidal mixing and the circulation structure adapting to it are the main causes of the TF. Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No. 49736190).     

考虑边界反射作用河流污染混合区的简化算法

以排污口为坐标原点,通过数学推证了岸边排放时P(x,y)点与中心排放时Q(x/4,±y/2)点的污染物浓度对应相等.通过计算实验和曲线拟合,分别给出了中宽河流污染混合区最大长度、最大宽度和相应的纵坐标、面积等参数以及河流中心线和两岸线沿程浓度分布的实用化公式,给出了污染混合区的近似外边界曲线方程.对中宽河流污染混合区范围的计算和环境敏感点的浓度预测,具有重要实用价值,为工程技术人员提供了准确、简便、快捷的实用化方法.     

Geochemical modeling of magma mixing and magma reservoir volumes during early episodes of Kīlauea Volcano’s Pu‘u ‘Ō‘ō eruption

Geochemical modeling of magma mixing allows for evaluation of volumes of magma storage reservoirs and magma plumbing configurations. A new analytical expression is derived for a simple two-component box-mixing model describing the proportions of mixing components in erupted lavas as a function of time. Four versions of this model are applied to a mixing trend spanning episodes 3–31 of Kilauea Volcano’s Puu Oo eruption, each testing different constraints on magma reservoir input and output fluxes. Unknown parameters (e.g., magma reservoir influx rate, initial reservoir volume) are optimized for each model using a non-linear least squares technique to fit model trends to geochemical time-series data. The modeled mixing trend closely reproduces the observed compositional trend. The two models that match measured lava effusion rates have constant magma input and output fluxes and suggest a large pre-mixing magma reservoir (46±2 and 49±1 million m³), with little or no volume change over time. This volume is much larger than a previous estimate for the shallow, dike-shaped magma reservoir under the Puu Oo vent, which grew from ∼3 to ∼10–12 million m³. These volumetric differences are interpreted as indicating that mixing occurred first in a larger, deeper reservoir before the magma was injected into the overlying smaller reservoir. Electronic Supplementary Material Supplementary material is available at and is accessible for authorized users.     

浙江沐尘石英二长岩体的岩石地球化学特征及构造意义

出露于江山-绍兴断裂带西南段东南侧的沐尘岩体,以发育暗色包体和环斑长石为特征,具有显著的岩浆混合作用.寄主岩为二长岩-石英二长岩组合,包体岩石为二长闪长岩.二长岩组合.造岩矿物有钾长石、斜长石、石英、普通角闪石和黑云母.岩石富碱(Na2O K2O=6.58%～10.42%,平均8.41%)、高钾(K2O/Na2O=0.72～1.45,平均1.16)、贫钛(TiO2=0.37%～1.22%,平均0.76%)、富集大离子亲石元素和轻稀土元素,具有钾玄质系列的岩石地球化学特征.该岩体侵位于后碰撞弧构造环境,是早白垩世早期该区重要的构造.岩浆热事件的产物.     

砂井联合水泥土搅拌桩复合地基固结解析解

砂井联合水泥土桩复合地基是一种新型的复合地基加固技术,既可以加快软土地基固结时间,又可以增强软土地基的强度。针对该组合型复合地基的布桩特点,该类复合地基可以简化成以水泥土搅拌桩为中心的轴对称固结模型,并假定孔隙水沿径向渗流到砂井体内的流量等同于砂井体内排出的水量,考虑砂井的涂抹效应,推导出该类型下砂井联合水泥土搅拌桩复合地基固结方程。根据实际工程荷载多数单级施加和地基附加应力呈梯形分布的特点,得出了砂井联合水泥土桩复合地基固结解析解。通过对单级荷载情况下的复合地基固结解析解的退化,得出了瞬时施加荷载下的解析解。最后分别针对井径比、加荷历时、桩-土模量比、砂井渗透系数等影响因素,对复合地基固结性状进行了分析。该解答对提高此类复合地基的设计和计算水平有一定的理论指导意义。     

Organic carbon inputs,common ions and degassing: rethinking mixing dissolution in coastal eogenetic carbonate aquifers

Caves deliver freshwater from coastal carbonate landscapes to estuaries but how these caves form and grow remains poorly understood. Models suggest fresh and salt water mixing drives dissolution in eogenetic limestone, but have rarely been validated through sampling of mixing waters. Here we assess controls on carbonate mineral saturation states using new and legacy geochemical data that were collected in vertical profiles through three cenotes and one borehole in the Yucatan Peninsula. Results suggest saturation states are primarily controlled by carbon fluxes rather than mixing. Undersaturation predicted by mixing models that rely on idealized end members is diminished or eliminated when end members are collected from above and below actual mixing zones. Undersaturation due to mixing is limited by CO₂ degassing from fresh water in karst windows, which results in calcite supersaturation. With respect to saline groundwater, controls on capacity for mixing dissolution were more varied. Oxidation of organic carbon increased pCO₂ of saline groundwater in caves (pCO₂ = 10^–2.06 to 10^–0.96 atm) relative to matrix porosity (10^–2.39 atm) and local seawater (10^–3.12 atm). The impact of increased pCO₂ on saturation state, however, depended on the geochemical composition of the saline water and the magnitude of organic carbon oxidation. Carbonate undersaturation due to mixing was limited where gypsum dissolution (Cenote Angelita) or sulfate reduction (Cenote Calica) increased concentrations of common ions (Ca²⁺ or HCO₃^?, respectively). Maximum undersaturation was found to occur in mixtures including saline water that had ion concentrations and ratios similar to seawater, but with moderately elevated pCO₂ (Cenote Eden). Undersaturation, however, was dominated by the initial undersaturation of the saline end member, mixing was irrelevant. Our results add to a growing body of literature that suggests oxidation of organic carbon, and not mixing dissolution, is the dominant control on cave formation and enlargement in coastal eogenetic karst aquifers. Copyright © 2016 John Wiley & Sons, Ltd.     

Exploring nonlinear characteristics in seismogenic process

Power spectral characteristics of the seismic activities before and after the seven large earthquake — Haicheng, Tangshan, Lancang, Longling, Mabian, Puer and Songpan are studied by spectrum analysis method. The results show that they all have continuous power spectrum and aperiodic behaviour. When the time away from the large earthquake occurrence, the characteristics of the seismic activities are obviously accompanied by stochastic components. About one year before main shock, the moving orbits constructed by spectrum amplitudes showed the contracting tendency. And the properties during that time may display as flicker noise. One’s another time almost mixed whole phase space. But the essence of seismic activities after main shocks is a chaotic state accompanied with much noises. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 276–281, 1993. This subject is supported by the Chinese Joint Seismological Foundation.     

延边开山屯花岗闪长岩-石英闪长岩体年代学、地球化学特征及对古太平洋板块俯冲作用时限的制约

近年来古太平洋构造域的构造演化备受学者关注。本文报道的延边开山屯地区花岗闪长岩-石英闪长岩体LAICP-MS U-Pb年龄表明其形成时间为早侏罗世早期(198±1Ma),所采样品可根据Zr/Hf值分为高Zr/Hf值组花岗闪长岩和低Zr/Hf值组石英闪长岩。高Zr/Hf值组花岗闪长岩起源深度浅,富集Rb、Th、U、K等大离子亲石元素(LILEs),贫Nb、Ta、Ti等高场强元素(HFSEs),具壳源岩浆的特点。低Zr/Hf值组为壳源岩浆与来自深部的亏损地幔岩浆混合而成,岩石亏损Nb、Ta、Zr、Hf、Ti等高场强元素,具有典型的弧型岩浆地球化学特征。岩体中存在细粒闪长质包体,镜下可见针柱状磷灰石。开山屯岩体属钙碱性系列岩石,结合前人资料,认为其与该地区同时代火成岩组成北-东向分布的早侏罗世活动大陆边缘型火成岩带,而位于该带西侧的小兴安岭-张广才岭地区存在同时代弧后拉张带,两者构成典型的大陆弧与弧后拉张带模型,共同揭示了早侏罗世早期古太平洋板块对东北地区的俯冲作用。     

含矿流体混合反应与成矿作用的动力平衡模拟研究

本文在约定热液体系中成矿元素成矿速率(成矿过程中单位时间内单位体积所合成矿元素重量的变化)的基础上。借助于物质-热-化学-成矿四重全耦合的研究思路,构建了均匀热液体系、层状热液体系、岩浆侵入热液体系下成矿元素的迁移、富集、溶解与沉淀作用数值模型。模拟结果表明;(1)硫化物(H2S)和硫酸盐(SO42-)流体的混合反应是成矿热液体系中铅、锌、铁成矿元素成矿的重要控制因素;(2)均匀介质、岩浆侵入或地质构造的存在,对成矿元素在成矿流体运移的速度、流线、温度分布和成矿元素的溶解与沉淀分布都有着各自的特征．不同的成矿环境或成矿背景制约了成矿元素的迁移与富集以及矿体的产出定位。暗示成矿环境及成矿速率对热液体系中成矿元素的沉淀与溶解具重要作用;成矿流体的混合反应是成矿作用发生的重要机制之一。在成矿理论研究中必须充分考虑不同地质构造因素的约束。