Thermochemistry of monazite-(La) and dissakisite-(La): implications for monazite and allanite stability in metapelites   总被引：2，自引：2，他引：0  

E. Janots  F. Brunet  B. Goffé  C. Poinssot  M. Burchard  L. Cemič 《Contributions to Mineralogy and Petrology》2007,154(1):1-14

Thermochemical properties have been either measured or estimated for synthetic monazite, LaPO₄, and dissakisite, CaLaMgAl₂(SiO₄)₃OH, the Mg-equivalent of allanite. A dissakisite formation enthalpy of ?6,976.5 ± 10.0 kJ mol^?1 was derived from high-temperature drop-solution measurements in lead borate at 975 K. A third-law entropy value of 104.9 ± 1.6 J mol^?1 K^?1 was retrieved from low-temperature heat capacity (C _p) measured on synthetic LaPO₄ with an adiabatic calorimeter in the 30–300 K range. The C _p values of lanthanum phases were measured in the 143–723 K range by differential scanning calorimetry. In this study, La(OH)₃ appeared as suitable for drop solution in lead borate and represents an attractive alternative to La₂O₃. Pseudo-sections were calculated with the THERIAK-DOMINO software using the thermochemical data retrieved here for a simplified metapelitic composition (La = ∑REE + Y) and considering monazite and Fe-free epidotes along the dissakisite-clinozoïsite join, as the only REE-bearing minerals. Calculation shows a stability window for dissakisite-clinozoïsite epidotes (T between 250 and 550°C and P between 1 and 16 kbar), included in a wide monazite field. The P–T extension of this stability window depends on the bulk-rock Ca-content. Assuming that synthetic LaPO₄ and dissakisite-(La) are good analogues of natural monazite and allanite, these results are consistent with the REE-mineralogy sequence observed in metapelites, where (1) monazite is found to be stable below 250°C, (2) around 250–450°C, depending on the pressure, allanite forms at the expense of monazite and (3) towards amphibolite conditions, monazite reappears at the expense of allanite.  相似文献   

Seismic properties of the upper crust in the central Friuli area (northeastern Italy) based on petrophysical data     

M. Faccenda  G. Bressan  L. Burlini   《Tectonophysics》2007,445(3-4):210-226

The compressional and shear wave velocities have been measured at room temperature and pressure up to 450 MPa on 5 sedimentary rock samples, representative of the most common lithologies of the upper crust in the central Friuli area (northeastern Italy). At 400 MPa confining pressure the Triassic dolomitic rock shows the highest velocities (Vp  7 km/s, Vs  3.6 km/s), the Jurassic and Triassic limestones samples intermediate velocities (Vp  6.3 /s, Vs  3.5 km/s) and the Cenozoic and Paleozoic sandstones the lowest velocities (Vp  6.15 km/s, Vs  3.35 km/s). The Paleozoic sandstone sample is characterized by the strongest anisotropy (10%) and significant birefringence (0.2 km/s) is found only on the Cenozoic sandstone sample. We elaborated the synthetic profiles of seismic velocities, density, elastic parameters and reflection coefficient, related to 4 one-dimensional geological models extended up to 22 km depth. The synthetic profiles evidence high rheological contrasts between Triassic dolomitic rocks and the soft sandstones and the Jurassic limestones. The Vp profiles obtained from laboratory measurements match very well the in-situ Vp profile measured by sonic log for the limestones and dolomitic rocks, supporting our one-dimensional modelling of the calcareous-carbonatic stratigraphic series. The Vp and Vs values of the synthetic profiles are compared with the corresponding ones obtained from the 3-D tomographic inversion of local earthquakes. The laboratory Vp are generally higher than the tomographic ones with major discrepancies for the dolomitic lithology. The comparison with the depth location of seismicity reveals that the seismic energy is mainly released in correspondence of high-contrast rheological boundaries.  相似文献   

Fabric symmetry of low anisotropic rocks inferred from ultrasonic sounding: Implications for the geomechanical models     

Richard P&#x;ikryl  Tom&#x; Lokají ek  Zdenk Pros  Karel Klíma 《Tectonophysics》2007,431(1-4):83

The geomechanical models were established based on the absence or presence of certain rock fabric elements — texture (crystallographic preferred orientation), microstructure (shape preferred orientation) and microcracks (flat voids). The proposed models include both (i) the ideal material showing random texture and structure but no microcracks, i.e. the material which is hardly to be found in nature, and (ii) the materials possessing various combinations of fabric elements that show different spatial arrangements. The mutual relationship between those parameters and seismic and geomechanical properties are discussed.Selected models were experimentally verified during laboratory experiments. These consist of measurement of P-wave velocities in 132 independent directions under several confining pressures in the range 0.1–400 MPa. From measured data 3D P-wave patterns can be constructed and the influence of microcracks and of texture and structure on the rock seismic anisotropy can be determined. The seismic anisotropy established at different levels of confining pressure can be used for the interpretation of rock fabric symmetry of rocks showing low anisotropy in macroscale and for the selection of directions in which the geomechanical test can be performed. The measured P-wave velocities were then mathematically processed by using a fitting function which reflects contribution of P-wave velocity in the mineral skeleton of an ideal sample without microcracks extrapolated to the atmospheric pressure level from high confining pressure interval (ca. 200–400 MPa) (v₀), linear compressibility of the samples (k_v), and confining pressure during which most of the cracks are closed (P₀). These parameters improve the understanding of the response of various rock fabric elements on increasing confinement and corresponding changes in elasticity.The observed seismic and geomechanical anisotropies reflect intensity of the fabric of rock-forming minerals and microcracks. The magnitude of seismic anisotropy measured at atmospheric pressure corresponds to the anisotropy of static elastic modulus and is governed by the spatial arrangement of microcracks. The magnitude of strength anisotropy (uniaxial compressive strength) correlates more likely to the seismic anisotropy determined at high confining pressure and is connected to the preferred orientations (either CPO or SPO or both) of rock-forming minerals.  相似文献   

大型高尾矿坝灾变机制与防控方法     

杨春和  张超  李全明  于玉贞  马昌坤  段志杰 《岩土力学》2021,(1):1-17

大型高尾矿库隐患治理是"十三五"期间遏制重特大事故的重要任务和重点工程之一。高应力下尾矿材料的细观结构和宏观力学特性演化、大型尾矿坝沉积规律及复杂条件下高尾矿坝的劣化理论是其中的关键问题。为揭示尾矿细观结构特性,对尾矿材料进行了光学显微镜观察、电镜扫描和CT扫描处理,建立了尾矿材料的三维重构模型;为揭示高压下尾矿材料的力学特性,对尾矿进行了高应力三轴试验、高应力渗透固结联合试验,研究了高应力下尾矿材料的强度、渗透和固结特性;为揭示尾矿的沉积特性,进行了尾矿材料的大型模型试验,得到了矿浆流动、淤积形态、尾矿料物理力学性质的空间分布以及夹层结构在空间内的分布规律;为揭示高尾矿坝的失稳机制,通过理论分析与数值模拟,对高压下尾矿的强度准则进行了讨论,高尾矿坝的稳定性分析建议使用强度折减法;为揭示尾矿的排渗设施淤堵机制与服役性能,进行了尾矿-土工布渗透试验以及微观观测,发现细粒尾矿更容易产生物理淤堵,且化学淤堵程度与溶液中离子的种类和浓度有关;为了推进尾矿坝风险管控技术,搭建了尾矿库重大风险评估监测系统平台,以便实现尾矿库基础数据的提取、实时风险预警等智能化功能。通过以上坝体劣化理论研究、溃坝灾害评估与预警,提升了我国大型高尾矿库筑坝与灾害防控水平。  相似文献   

桂北牛塘界加里东期钨矿床年代学、成矿流体性质及其演化     

豆浩然  张文兰  王汝成  陈文迪 《地质学报》2018,92(11):2269-2300

牛塘界钨矿床是桂北地区苗儿山—越城岭岩体南部的一个大型钨矿床,与矿化密切相关的花岗岩为已绿泥石化的中细粒白云母花岗岩。对花岗岩进行了岩石地球化学研究,认为该岩体为高分异、高演化铝过饱和富钨花岗岩;对岩体中锆石进行了U- Pb定年分析,获得成岩年龄为410±4.9Ma;对与白钨矿共生的磷灰石进行了原位U- Pb定年,测得成矿年龄为418±37Ma,两组年龄数据表明,牛塘界钨矿床的成矿花岗岩及成矿作用都属加里东期。 本文还对牛塘界钨矿床的矿石进行了系统的研究,首先,根据蚀变类型划分出三种不同类型的矿石：矽卡岩化矿石、绿泥石化矿石及石英脉(块)型矿石;其次,根据三种矿石的特征划分出三个不同的成矿阶段,即三种矿石的形成与不同的成矿阶段相对应：矽卡岩化阶段、石英-硫化物阶段及晚期硅化-碳酸盐化阶段;第三,对各成矿阶段形成的白钨矿进行了原位微量元素分析,根据白钨矿中Mo含量的变化及白钨矿REE配分曲线中Eu的异常,阐释了成矿环境氧逸度的变化;根据白钨矿中微量元素Na和Nb含量的变化,结合白钨矿REE配分曲线特征,揭示了REE置换进入白钨矿的机理及成矿流体性质的演化趋势;第四,根据白钨矿氧同位素的分析结果,得出成矿流体为岩浆水混入部分经地层循环的大气水;第五,对成矿母岩中成矿元素W的分析结果表明,牛塘界钨矿成矿物质来源于成矿母岩。因此牛塘界钨矿床其成矿物质来源于矿区内高度分异演化的花岗岩,属加里东期晚期的产物。  相似文献   

青藏高原中东部三种草地类型土壤理化特征及金属元素在有机畜牧生产中的作用     

未亚西  杨永胜  贺慧丹  祝景彬  李红琴  李英年 《冰川冻土》2018,40(6):1265-1274

为明确高寒草地土壤理化特征及金属元素在有机畜牧生产中的作用,选取青藏高原中东部高山嵩草草甸、草甸化草原、温性草原三种草地类型为研究对象,分析土壤理化性质和重金属元素,并探讨其影响作用。结果表明：三种草地类型群落盖度由大到小依次是高山嵩草草甸（91%） > 草甸化草原（85%） > 温性草原（75%）,草甸化草原的物种数最多达25种,分别是高山嵩草草甸和温性草原的1.47倍和1.92倍。温性草原0~10 cm土层容重分别是高山嵩草草甸和草甸化草原的1.89倍和1.40倍,10~20 cm土层容重分别是高山嵩草草甸和草甸化草原的1.42倍和1.29倍。高山嵩草草甸土壤有机质、全氮含量最高,有机质含量分别是草甸化草原、温性草原的1.20倍和2.65倍,全氮含量分别是草甸化草原、温性草原的1.18倍和2.47倍。温性草原土壤pH值最高达8.46,分别是草甸化草原和高山嵩草草甸的1.04倍和1.10倍。总体来看,重金属元素含量在高山嵩草草甸最高,温性草原最低,草甸化草原居中。三种草地类型土壤7种重金属元素含量都在一级以内,其生态危害指数未出现强污染状况,适合构建示范区发展有机畜牧业。  相似文献   

高温高压下黄铁矿热力学性质的第一性原理研究   总被引：1，自引：0，他引：1  

刘善琪  李永兵  石耀霖 《岩石学报》2018,34(6):1813-1818

黄铁矿是自然界中分布最为广泛的硫化物矿物,同时也是重要的造矿矿物,在金属矿床、沉积岩、变质岩、花岗岩、基性-超基性岩浆岩、以及地幔岩中都有大量出现。因此,研究黄铁矿在不同温度压力下的热力学性质可以为深入探讨与黄铁矿有关的成岩、成矿、成藏问题提供有用的矿物学依据。本文利用基于密度泛函微扰理论的第一性原理方法,采用准谐近似计算了黄铁矿在高温高压下的热力学性质。我们计算的黄铁矿的晶格常数、零压下的体积模量及其对压力的导数与前人的实验及理论计算结果吻合得很好,零压下等压热容和熵随温度的变化与实验结果有很好的一致性。尤其是,本文计算了直至2500K、100GPa的高温高压下黄铁矿的等温体积模量、热膨胀系数、热容和熵等热力学性质。这为在有硫参与的情况下,人们开展下地壳-岩石圈地幔深度的地球动力学模拟和建立地球物理模型提供了有用的信息。  相似文献   

羌塘盆地岩石物理力学特性分析及其孔壁稳定技术          下载免费PDF全文

吴纪修  尚玉虎  李鑫淼  薛倩冰 《探矿工程》2018,45(3):9-13

羌塘盆地是青藏高原年平均地温最低、冻土层相对较厚的地区,所处的水文地质及工程地质环境极其复杂。由于勘探程度低,深孔钻探的实钻资料较少,缺乏对该区深部岩层的岩石物理力学特性研究。因此,结合地球物理测井技术、取心和实验测试结果对QK-7孔钻遇地层岩石物理力学参数进行分析,并对冻土带异常孔隙水压力极复杂地层孔壁稳定泥浆工艺技术进行总结和探索,以期为羌塘盆地油气资源战略开发深孔钻探的顺利实施提供基础理论支持。  相似文献   

Basic properties of saline soil in Da'an, western Jilin, China     

Xin Zhou  Qing Wang  XueFei Zhang  TianWen Yu  XuDong Zhang 《寒旱区科学》2015,7(5):568-572

This paper studied the basic properties of saline soil at different depths of a sampling site in Da'an, China, through field reconnaissance and laboratory analysis. A series of experiments which comprised the analyses of grain size distribution, mineral composition, soil physical properties, soluble salt concent, pH, organic content and cation exchange capacity were conducted. Through these experiments, the distribution rule of each property and their causes are discussed. These results could provide a fundamental base for the study of moisture migration.  相似文献   

Chondrule size and related physical properties: A compilation and evaluation of current data across all meteorite groups     

《Chemie der Erde / Geochemistry》2015,75(4):419-443

The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and “cratered” chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.  相似文献