Baroclinic nonlinear exchanges of energy and potential enstrophy in the quasi-geostrophic two-layer model

Abstract

Merilees and Warn's (1975) nonlinear interaction analysis of two-dimensional nondivergent flow is extended to examine the quasi-geostrophic two-layer model. Two sets of triads exist in this model (Salmon, 1978). The purely barotropic triads are the same as the triads examined by Merilees and Warn. Baroclinic-barotropic triads are found to exchange more energy or potential enstrophy with smaller or larger scales depending on the scale of motion as compared with the internal Rossby deformation radius and the relative wavenumber position of baroclinic and barotropic components.     

Fluid generation, vein formation and the degree of fluid–rock interaction during decompression of high-pressure terranes: the Schistes Lustrés, Alpine Corsica, France

Centimetre‐ to decimetre‐wide quartz+calcite veins in schistes lustrés from Alpine Corsica were formed during exhumation at 30–40 Ma following blueschist facies metamorphism. The δ¹⁸O and δ¹³C values of the veins overlap those of the host schistes lustrés, and the δ¹⁸O values of the veins are much higher than those of other rocks on Corsica. These data suggest that the vein‐forming fluids were derived from the schistes lustrés. Fluids were probably generated by reactions that broke down carpholite, lawsonite, chlorite and white mica at 300–350 °C during decompression between c. 1400 and 800 MPa. However, the δ¹⁸O values of the veins are locally several per mil higher than expected given those of their host rocks. The magnitude of oxygen isotope disequilibrium between the veins and the host rock is inversely proportional to the δ¹⁸O value of the host rock. Additionally, calcite in some schists is in isotopic equilibrium with calcite in adjacent veins, but not with the silicate fraction of the schists. Locally, the schists are calcite bearing only within 1–20 cm of the veins. The vein‐forming fluids may have been preferentially derived from calcite‐bearing, high‐δ¹⁸O rocks that are common within the schistes lustrés and that locally contain abundant (>15%) veins. If the fluids were unable to completely isotopically equilibrate with the rocks, due to relatively rapid flow at moderate temperatures or being confined to fractures, they could form veins with higher δ¹⁸O values than those of the surrounding rocks. Alteration of the host rocks was probably inhibited by isolation of the fluid in ‘quartz‐armoured’ veins. Overall, the veins represent a metre‐ to hectometre‐scale fluid‐flow system confined to within the schistes lustrés unit, with little input from external sources. This fluid‐flow system is one of several that operated in the western Alps during exhumation following high‐pressure metamorphism.     

Self‐similar solution of a plane‐strain fracture driven by a power‐law fluid

This paper analyses the problem of a hydraulically driven fracture, propagating in an impermeable, linear elastic medium. The fracture is driven by injection of an incompressible, viscous fluid with power‐law rheology and behaviour index n?0. The opening of the fracture and the internal fluid pressure are related through the elastic singular integral equation, and the flow of fluid inside the crack is modelled using the lubrication theory. Under the additional assumptions of negligible toughness and no lag between the fluid front and the crack tip, the problem is reduced to self‐similar form. A solution that describes the crack length evolution, the fracture opening, the net fluid pressure and the fluid flow rate inside the crack is presented. This self‐similar solution is obtained by expanding the fracture opening in a series of Gegenbauer polynomials, with the series coefficients calculated using a numerical minimization procedure. The influence of the fluid index n in the crack propagation is also analysed. Copyright © 2002 John Wiley & Sons, Ltd.     

Geochronology, Geochemistry, Fluid Inclusion and C, O Isotope Compositions of Calcite Veins in the Paleogene of the Jiangling Basin, South China: Implications for Fluid Evolution and Brine Potash Mineralization

Deep-seated potassium-rich brines were identified in the Jiangling Basin, South China. Although magmatic-hydrothermal sources have been proposed, the relationship between brine-type potash mineralization and volcanism remains unclear. In this study, U-Pb geochronology, geochemistry, fluid inclusion and C-O isotopic compositions of hydrothermal vein minerals in the Jiangling Basin are examined. Laser ablation U-Pb dating of calcite veins indicates that the ages are slightly younger than the formation age of the Balingshan basalt. Fluid inclusions in hydrothermal minerals show medium–low homogenization temperatures (160–220°C) and low salinities (0.14 to 4.9 wt% NaCl eqv.) and densities (0.882–0.944 g/cm3). The liquid compositions of fluid inclusions in calcite veins from sedimentary strata have higher contents of potassium, compared with those from basalt. The coupled negative δ13CPDB (?10.3‰ to ?8.0‰) and positive δ18OSMOW (17.4‰ to 20.7‰) values imply that calcite precipitation resulted from CO2 degassing of the basaltic magmatic fluids, as indicated by the gas composition of these inclusions in hydrothermal minerals. Rare earth element patterns indicate that water-rock interaction between hydrothermal fluids and sedimentary wall rocks contributed to the calcite precipitation in sedimentary strata. It is proposed that high-temperature water-rock interaction between magmatic fluids and sedimentary strata resulted in the potassium enrichment in fluids, interpreted as one of the sources of potassium-rich brines in the Jiangling Basin.     

3D Modeling and Determination of Factors Responsible for Zinc-Lead Mineralization in the Mehdiabad Deposit, Central Iran, based on Statistical Analysis of Geochemical Data

Although the Mehdiabad zinc-lead deposit is one of the most well-known deposits in the central Iran structural zone, the genesis of the deposit remains controversial. The host rock of the ore is a dolomitic limestone of the Lower Cretaceous Taft Formation. In the two main orebodies of the deposit, which includes the Black Hill and East Ridge ore zones, the oxide and sulfide ores are observed at the surface and at depth, respectively. The elements Zn, Fe, Mn and Mg are more abundant in the East Ridge ore zone (in both sulfide and oxide ores), with Ba, Pb, Ag and Cu being more abundant in the Black Hill oxide ore. Based on the distribution of elements and their correlation with each other in these ore zones, the elements are divided into three general groups, that of terrigenous elements, chemically-deposited elements and ore-forming (hydrothermally deposited) elements, a division that is supported by the results of factor analyses. The spatial distribution of elements is jointly affected by contact with host rocks, the boundary of oxide-sulfide ores and fault zones. The main factors governing the distribution of elements are the mechanical transfer of detrital sediments, chemical sedimentation, transfer by hydrothermal fluids, oxidation and surface dissolution, all of which affected the spatial distribution of elements. The ore-forming elements are mostly affected by hydrothermal fluids and oxidation. This study not only provides additional information about the genesis of the Mehdiabad deposit, but also could assist in the exploitation of ore and further exploration purposes. The results of this study can aid in the exploration and exploitation of the Mehdiabad deposit and similar deposits in the region.     

川滇黔二叠系铅锌成矿物质来源：C-H-O-S-Pb同位素制约——以云南太平子铅锌矿为例

【研究目的】川滇黔地区铅锌矿成因具有多样性,特别是与峨眉山玄武岩的关系存在较大的争议,本文从前人关注较少的二叠系碳酸盐岩中的铅锌矿入手,研究成矿物质来源。【研究方法】以云南寻甸县太平子铅锌矿为研究对象,运用S、Pb、C、H、O同位素实验数据及流体包裹体测温等方法,对成矿物质来源及成矿流体特征进行探讨。【研究结果】矿石铅同位素组成比较均一,分布集中,²⁰⁶Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb、²⁰⁸Pb/²⁰⁴Pb的变化范围分别为18.543～18.584、15.646～15.694、38.799～38.958,属于正常普通铅,具壳源特征,主要来源于基底岩石,水岩反应可能使赋矿围岩贡献少量的成矿物质。矿石硫化物δ³⁴S变化范围为-13.6‰～-7.3‰,方铅矿的δ³⁴S高于闪锌矿,硫同位素分馏并未达到平衡,生物成因硫酸盐还原作用（BSR）是还原硫的主要来源。热液方解石δ¹³C_V-PDB范围为3.8‰～4.7‰,δ¹⁸O_V-SMOW范围为12.0‰～16.7‰,相较于滇东北其他重要的铅锌矿床,具有明显的低δD、高δ¹⁸O_fluid特点,成矿流体中的水主要来源于岩浆水和有机水的混合,具有中—高温、低盐度特征。【结论】太平子铅锌矿在成矿物质、流体、成矿温度等均与区域上其他典型铅锌矿有较明显差别,具有典型的岩浆-热液成因特点。     

耐230 ℃高温海水钻井液室内实验研究

为了解决深海油气井工程和大洋科学钻探深部高温井段钻井液流变稳定性和护壁性能等变差问题,以复合粘土为造浆材料,通过优选抗温抗盐降滤失剂、防塌剂和高温稳定剂等关键处理剂及钻井液配方优化研究,研发了一套耐230 ℃高温海水钻井液配方。采用高温高压流变仪、六速旋转粘度计和高温高压滤失仪等仪器,开展耐230 ℃高温海水钻井液的综合性能评价,如热稳定性、高温流变性等。实验结果显示,密度1.5 g/cm³的钻井液在230 ℃老化16 h前后,表观粘度变化率为2.5%,高温高压滤失量为23 mL。研究结果表明,该海水钻井液抗温可达230 ℃,具有良好的抗高温稳定性、高温流变性能以及较低的高温高压滤失量,可满足深海高温硬岩钻探要求。     

Rodingites from the Veria-Naousa ophiolite (Greece): Mineralogical evolution,metasomatism and petrogenetic processes

In the Veria-Naousa ophiolitic complex (north Greece), rodingite appears mainly in the form of cross cutting dykes within serpentinised peridotites. It is distinguished into three types, based upon the provenance of its protoliths, textural characteristics, mineralogical assemblages and geochemical affinities. Type I rodigites were derived from boninitic diabasic protoliths and their mineralogical assemblage include garnet + clinopyroxene + chlorite. Type II rodingites were formed at the expense of gabbroic precursors, comprising clinopyroxene + garnet + vesuvianite ± quartz, whereas Type III rodingites replaced diabasic tholeiitic protoliths comprising of garnets + vesuvianite + clinopyroxene + chlorite. Rodingitisation resulted in desilification, decrease of alkalies, Al, Fe, Mg and increase in Ca contents. In Type I rodingites the MREE (middle rare earth elements) and HREE (heavy rare earth elements) were slightly reduced. Type II rodingites experienced LREE (light rare earth elements) depletions, whereas MREE and HREE remained fairly stable. Restricted mobility of REE in Type III rodingites is assigned to shallow-level rodingitisation under decreasing pH.Rodingitisation occured in two distinct stages at fore-arc settings. The first stage occured under mildly oxidising conditions and enhanced CO₂/H₂O ratios. This stage affected the protoliths of all rodingite types. The second rodingitisation stage occured under more oxidising conditions and lower CO₂/H₂O ratios, which corresponds to the exhumation stage of the serpentinite-rodingite formations. Types II and III rodingites were subjected to further rodingitisation under the increasing influence of slab-derived hydrous phases at shallower depths, leading to the formation of late-stage andradite and vesuvianite. All stages of rodingitisation are estimated to have occurred under relatively moderate temperatures and pressure (~300 to 450 °C; ~2–6 kbar respectively).     

俯冲带硫的地球化学行为及硫循环SCIEI北大核心CSCD

俯冲带是全球最大的物质循环系统,控制着硫(S)在地球内部圈层及表层的循环,影响着大气圈、水圈、生物圈、岩石圈的稳定性以及地球的宜居性。厘清S在俯冲带中的地球化学行为和循环特征对理解地球各储库的氧化还原状态、岩浆作用与演化、成矿物质聚集、以及地球大气成分等具有重要意义。本文首先总结了进入俯冲带之前的大洋岩石圈的S结构模型,对S在大洋板片中的分布状态和地球化学特征进行了系统归纳。随后,系统阐述了俯冲带高压-超高压变质岩记录的板片变质及脱水过程中硫的地球化学行为。岩石学研究表明俯冲板片中的S多以硫化物相存在,硫酸盐矿物在弧前深度就已被释放或分解。相较于熔体,俯冲带流体中S的溶解度更高,是运移硫的更有效方式。DEW模型计算结果显示,流体中S含量总体较低,但在俯冲板片~90km处其含量有一个峰值(浓度0.5%~1.0%)。岩相学证据、地球化学测试结果、磷灰石S近边吸收结构(S-XANES)特征以及模拟结果都显示俯冲深部流体中S多以HS^(-)及H_(2)S形式存在,不含大量的SO_(4)^(2-)及硫酸盐;中f_(S_(2))流体有利于S迁移出俯冲板片,从而促进俯冲带大规模S循环,而高f_(S_(2))流体在流-岩交换过程沿流体通道发生S的锁固作用而不利于俯冲带S循环。质量平衡计算显示全球俯冲带S输入通量为4.65×10^(13)g/yr,弧下深度板片S输出通量为2.91×10^(12)g/yr,板片-岛弧S循环效率仅6.3%。俯冲板片在弧下深度可能存在一个短暂高效的S释放窗口,释放流体的δ^(34)S值为-2.1±3.0‰。基于高压-超高压变质岩中硫化物的研究,初步厘清了俯冲板片中S的地球化学行为,首次从板片角度全面、定量地限定了俯冲带的脱硫通量、效率、种型和同位素特征,提出俯冲带循环的S不是岛弧岩浆的氧化剂,与岛弧环境的正δ^(34)S值也无直接因果联系,对解析俯冲带S循环和理解地球长期的S循环具有重要意义。最后,本文还展望了俯冲带S循环的未来发展方向,应在俯冲带流体氧化还原性质(硫酸盐的命运)、俯冲沉积物对S循环的制约、俯冲带环境下多硫同位素的分馏效应、S循环与其它挥发分(如C等)循环之间的耦合关系、地球历史上深部S循环等方向做出探索,更深入地理解俯冲带及全球S循环过程。     

新城金矿稳定同位素地球化学特征及成矿物质的来源

新城金矿是胶东金矿集区招远—莱州成矿带的一个"焦家式"蚀变型金矿床。本文主要通过C、H、O、S、Pb同位素研究,对新城金矿成矿流体、物质来源和成矿作用进行探讨和研究。新城金矿矿石中δD值范围为-116‰~-91‰,δ18O水值范围为3.8‰~7.2‰,表明成矿流体早期来源于岩浆水,成矿晚期混入大气降水。矿石硫化物、郭家岭花岗闪长岩、玲珑花岗岩和胶东群δ34S平均值分为7.9‰、6.5‰、8.5‰和6.2‰,认为矿石硫具有对矿区地层及岩浆岩硫的继承性。硫化物矿石206Pb/204Pb=17.115~17.414,207Pb/204Pb=15.460~15.577,208Pb/204Pb=37.912~38.196,显示铅具有壳幔混合来源的特征。碳、氢、氧、硫、铅同位素反映新城金矿成矿物质和流体主要来源于深部岩浆。