坡缕石晶体化学和成因研究现状与进展

综述了坡缕石(凹凸棒石)矿物晶体化学和成因研究的新进展和存在问题,最新研究表明:坡缕石是分布广泛很有成因意义的标型矿物。还着重介绍了我国坡缕石石棉和苏皖一带坡缕石晶体化学研究以及坡缕石成因研究的新成果和存在问题。     

成岩带、近变质带与一维纳米级层状硅酸盐

运用X射线衍射分析技术，计算了成岩带、近变质带粘土矿物C^*方向的粒度。根据阿尔卑斯造山带前陆碎屑岩粘土矿物粒度与伊利石结晶指数的关系，推导出了伊利石、绿泥石、蒙脱石、伊蒙混层、高岭石和叶蜡石的c^*方向粒度变化趋势曲线。结果表明，大多数产于成岩带和近变质带的粘矿物其c6*方向粒工为几至几十纳米。成岩带和近为质带是一维天然纳为级土帮物的产地。     

Multi-stage zeolite facies mineralization in the Hvalfjördur area,Iceland

The Hvalfjördur area, 30 km north of Iceland’s capital Reykjavik, belongs to the sequence of Late Tertiary to early Quaternary flood basalts with minor intercalations of hyaloclastites and rhyolites. The basalts are affected by progressive low-temperature metamorphism, caused by the burial of the lava succession and higher heat flow from nearby central volcanoes. Low-grade zeolite facies metamorphism of basaltic lavas in the Hvalfjördur area results in two distinct mineral parageneses that can be correlated to events in the burial and hydrothermal history of the lava pile. Stage Ia represents syn-eruptive near-surface alteration in which celadonite and silica were precipitated along primary pores. During regional burial metamorphism (stage Ib), hydrolysis of olivine and glass led to the formation of mixed-layer chlorite/smectite clays. The chlorite content of stage Ib phyllosilicate vesicle rims increases with increasing burial depth and temperature. Stage II occurred after the burial and is marked by zeolite mineralization caused by higher heat flow from the Laxárvogur and Hvalfjördur central volcanoes. Altogether 11 different zeolites were found in the Hvalfjördur area: analcime, chabazite, epistilbite, heulandite, laumontite, levyne, mesolite, stilbite, stellerite, thomsonite and yugawaralite. In total, three separate depth and temperature-controlled “zeolite zones” occur in the Hvalfjördur area.     

Scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite-grade phyllites, SE Vermont

Detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south‐eastern Vermont show that grain‐scale zoning is common, and sympathetic zoning in adjacent minerals is nearly universal. We interpret this to reflect a pressure‐solution mechanism for cleavage development, where precipitation from a very small fluid reservoir fractionated that fluid. Multiple analyses along single muscovite, biotite and chlorite grains (30–200 μm in length) show zoning patterns indicating Tschermakitic substitutions in muscovite and both Tschermakitic and di/trioctahedral substitutions in biotite and chlorite. Using cross‐cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite‐grade, chlorite‐grade overprinted by biotite‐grade and biotite‐grade. Zoning patterns are comparable in all three settings, requiring a similar cleavage‐forming mechanism independent of metamorphic grade. Moreover, the use of ⁴⁰Ar/³⁹Ar geochronology demonstrates this is true regardless of age. Furthermore, samples with chlorite‐grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of Al, Si, Mg and Fe ions are greater than the temperature of the biotite isograd (>～400 °C). Parallel and smoothly fanning tie lines produced by coexisting muscovite–chlorite, and muscovite–biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization. These results do not support theories suggesting cleavages form in fluid‐dominated systems. If crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir, then the compositions of individual grains defining these cleavages would be uniform. On the contrary, the fine‐scale chemical zoning observed probably reflects a grain‐scale process consistent with a pressure‐solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation. Thus the role of fluids was probably limited to one of catalysing pressure‐solution and fluids apparently did not drive cleavage development.     

右江中生代极低级变质带的变质变形过程

右江中生代三叠系槽盆相浊流沉积岩系遭受了区域强烈变形和极低级变质作用，伊利石结晶度指数为０．３３１°～０．２６５°△２θ，属于浅层或近变质带；在野外和光学显微镜观察基础上，运用Ｘ射线衍射、透射电镜及电子探针等现代测试技术，对绿泥石－白云母堆垛集合体、细粒基质层状硅酸盐矿物的化学成分及结构进行了详细研究，指出绿泥石－白云母堆垛的碎屑成因及母矿物的变质过程；强调右江中生代极低级变质带具有板内造山带的构造变形特征     

Apports des phyllosilicates dans la différenciation entre altération hypogène et altération supergène dans le basalte triasique du Moyen Atlas (Maroc)Contribution of phyllosilicates to distinguish between hypogene alteration and weathering in Triassic basalt from Middle Atlas (Morocco)

Triassic basalt of the Middle Atlas has been subject to metamorphic transformation then weathering. Occurrence in both metabasalt and saprolite of ubiquitous clay minerals, such as smectite and mixed layers chlorite–smectite, makes it difficult to distinguish between the two alteration facies and explains the interest of complementary sources of information. In the Bhallil weathering profile, petrographical and mineralogical analyses of primary igneous minerals and their alteration products coupled with Fe oxidation state determination in clay fractions allow to identify three alteration facies: (i) metamorphic basalt, where iron occurs mainly as the ferrous form; (ii) the lower part of saprolite, where iron is partially oxidized to its ferric form; (iii) the upper part of saprolite, where iron is completely oxidized. To cite this article: A. Dekayir et al., C. R. Geoscience 334 (2002) 877–884.     

双层地基中气体聚集与土体变形机制的试验研究

采用层状硅酸镁锂（magnesium lithium phyllosilicate,简称MLPS）透明土构建了上硬下软的双层地基模型,通过针孔注气来模拟沉积层中产生的气源,基于图像识别技术开展了地层气体聚集过程中气囊形态变化以及上层土体隆起变形的试验研究。结果表明：（1）气体在聚集过程中呈现出不同的气囊形态,上层土体的强度和高度决定了气囊突破的时间以及突破时的形态。（2）气囊形态、体积和压力的变化大致可分为两个阶段,第一阶段气囊体积、宽度基本呈线性增大,而气囊高度则由于底部收缩而逐渐减小,气压缓慢增大;第二阶段气囊宽度增加放慢,气囊体积膨胀速度加快,而气囊高度开始显著增加,气囊气压由最高点迅速降低。上层土体隆起的高度和宽度在第二阶段才开始明显增大。（3）气囊突破前的宽度、体积以及上层土体隆起宽度和高度与上层透明土的屈服强度、高度具有良好的拟合关系。（4）薄板理论可较合理地解释气体聚集引起的上层土体变形的机制,而中厚板理论则并不适用。     

五氯苯酚在矿物表面吸附——实验、表面反应模式及其环境意义

利用批量平衡技术研究了石英、高岭石、伊利石、蒙脱石和铁氧化物对五氯苯酚(PCP)吸附的pH关系等温线和浓度关系等温线,发现所有矿物的pH关系等温线都表现出典型的峰形曲线特征,峰位在pH=5～6之间,依矿物不同而不同。基于矿物表面羟基位化合态和PCP的化合态考虑,提出一种包含表面络合反应和表面静电吸附反应的模式,对pH关系等温线计算拟合发现有很好的相关性。模式计算还表明,石英和层状硅酸盐矿物对PCP吸附以表面络合反应为主,而氧化铁矿物则包含表面络合反应和表面静电吸附反应,但以后者占主导,其反应平衡常数比前者大1～3个数量级。高岭石和氧化铁矿物的浓度吸附等温线可用Langmuir方程很好拟合,最大吸附量的大小顺序是赤铁矿>纤铁矿>针铁矿>高岭石>石英>蒙脱石≈伊利石,并可以用矿物表面羟基位浓度和反应机制加以解释。PCP在矿物表面可观的吸附量说明矿物表面吸附对憎水性可离解有机化合物(HIOCs)在天然水相体系和沉积中的迁移转化过程起着相当重要的作用。     

Self-organized crystallization mechanism of non-equilibrium 2:1 type phyllosilicate systems

The crystallization mechanism of 2:1 type regular interstratified minerals is investigated in views of non-equilibrium thermodynamics. The structural chemistry of relative layers and their interstratified combinations is analyzed and six kinds of non-equilibrium chemical systems have been induced. The universal laws of chemical reactions which happened in the interface region of these non-equilibrium systems have been summarized. From these laws, two reaction systems crystallizing out Tosudite and Rectorite respectively have been recovered. The kinetic model of chemical reactions has been developed by means of the mass conservation law. The oscillatory solution showing regular interstratified features has also been obtained numerically. These results indicate that the difference in original chemical composition among systems can affect the chemical connotation of reactants, intermediate products and resultants, and the flow chart of chemical reaction, but cannot change their crystallization behavior of network-forming cations, bigger and smaller network-modifying cations during crystallization. Hence, their kinetic model reflecting the universal crystallization law of these cations is just the same. These systems will crystallize out regular interstratified minerals at suitable parameters, which always exist as domain with nanometer-sized in thickness and can be called the self-organized ordering structure.     

用红外吸收光谱确定层状硅酸盐中羟基键的方向

层状硅酸盐样品用于红外二色性研究,当射线的电场矢量与振动的偶极矩方向成一角度时,这吸收与角度成比例,当某振动的偶极矩与电场矢量平行时,产生最大吸收,而这两矢量彼此垂直时将不产生吸收。在云母和有关晶体中可看到,在二八面体组成中,在改变电场矢量时倾斜OH团的OH振动强度保持不变,而与在三八面体组成中垂直于解理面方向的八面体OH团相比,当层状定向颗粒方向改变时显示强度大大增加,由此能获得层状硅酸盐OH键的方向,在晶体结构分析中能提供有价值的信息。