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681.
Spatial averaging of hydraulic conductivity in three-dimensional heterogeneous porous media 总被引:4,自引:0,他引:4
A. J. Desbarats 《Mathematical Geology》1992,24(3):249-267
Numerical models of groundwater flow require the assignment of hydraulic conductivities to large grid blocks discretizing the flow domain; however, conductivity data is usually available only at the much smaller scale of core samples. This paper describes a geostatistical model for hydraulic conductivity at both the core or point scale and that of grid blocks. Conductivity at the block scale is obtained empirically as a spatial power-average of point scale values. Assuming a multivariate Gaussian model for point log-conductivity, expressions are derived for the ensemble mean and variance of block conductivity. The expression for the ensemble mean of block scale conductivity is found to be similar to an expression for the ensemble effective conductivity of an infinite field derived analytically by earlier authors. Here, block conductivities obtained by power averaging are compared with effective conductivities obtained from a numerical flow model and are found to be in excellent agreement for a suitably chosen averaging exponent. This agreement deteriorates gradually as the log variance of conductivity increases beyond 2. For arbitrary flow field geometry and anisotropic conductivity covariances, the averaging exponent can be calibrated by recourse to numerical flow experiments. For cubic fields and an isotropic spatial covariance, the averaging exponent is found to be 1/3. In this particular case, it was found that flow field discretization at the block scale through local averaging of point conductivities gave similar results to those obtained directly using a point scale discretization of the flow field. 相似文献
682.
本文对冀东迁安麻粒岩及有关岩石中的辉石进行了研究,结果表明:辉石的含铁度
明显受寄主岩石化学成分的制约,寄主岩石的/Mg0和=(Fe203 ×0.8999 + Fa0)
值愈高,辉石的含铁度也愈高;共存辉石对的Fe2+ 一Mg分配系数(KD劝不仅受结晶温压条件
控制,同时也受辉石其它成分的影响。但Ca-Mg-Fe 三角图解等资料研究表明:共存的二辉
石对是平衡结晶的产物,其KD平均值也符合张儒媛等(1)统计的变质辉石平均值为1.85的规
律。通过二辉石温度计计算和矿物共生组合等资料的分析,得出辉石形成的温度为869±60ºC.压力为5 ×108-9 ×108 Pa。本区与铁矿体成过渡关系的辉石岩全铁含量与工业铁矿大致相等,铁矿的成因与其有着非常密切的关系。 相似文献
683.
珲春矿产于吉林东部珲春河第四系冲积砂金矿中,矿物粒度十分细小,常与自然金或阿纽依矿(AuPb_2)呈文象交生。在光学显微镜下新鲜面为灰白色,金属光泽,氧化后颜色变暗。等轴晶系,Fd3m空间群,显微硬度128~149kg/mm~2。化学成分:Au 63.38%~66.26%,Pb 31.60%~24.64%,Ag 1.76%~2.96%。矿物化学式为Au_2Pb。 相似文献
684.
吉黑东部斑岩型-浅成热液型铜金矿床多重成矿模型 总被引:5,自引:0,他引:5
通过四个典型矿床(小西南岔、闹枝、五凤和刺猬沟)的对比,发现它们在形成时间-空间一成因上既相互联系,又相互区别。小西南岔和闹枝矿床存在三个成矿流体系统:加热天水系统(A)、排放流体系统(B)、蒸气缕(steam plume)反应系统(C);五凤和刺猬沟矿床只有一个成矿流体系统,即排放流体系统(B)。前者的成矿流体由浅成岩浆房的补给;后者的成矿流体主要为循环天水,浅成岩浆房的补给不明显。小西南岔金铜矿床产于中生代火山岩盆地边缘的隆起带,属于斑岩型矿床;闹枝金(铜)矿床产于中生代火山岩盆地内的断隆块,属于斑岩-浅成热液过渡型矿床;五凤和刺猬沟金(银)矿床产于中生代火山岩盆地内断裂带,属于浅成热液型矿床。在区域成矿上,由浅入深,浅成热液型斑岩-浅成热液过渡型和斑岩型构成多重成矿模型。 相似文献
685.
Suo Shutian 《中国地质大学学报(英文版)》1995,(1)
Crustal Texture and Rheological Evolution ofTongbai-Dabie Orogenic Belt,China¥SuoShutian(FacultyofEarthSciences,ChinaUniversi... 相似文献
686.
687.
滇黔桂三角区微细浸染型金矿床成矿热液一种可能的演化途径:年代学证据 总被引:24,自引:1,他引:24
本文主要根据年代学资料和金活化迁移的地球化学属性,探讨了滇黔桂三角区微细浸染型金矿床成矿热液的演化途径。多种定年方法揭示,该区金成矿初始流体(古流体)的年龄为260Ma左右;金成矿年龄约为140~75Ma。考虑到该区燕山晚期岩浆岩富含Cl,本文认为古流体(260~140Ma)向成矿流体(140~75Ma)的转化,可能主要是通过燕山晚期岩浆活动产生的富氯流体加入原已存在的贫氯古流体,从而使这种新的混合流体具有浸取金的能力来实现的。 相似文献
688.
689.
Deep crustal growth of quartz, kyanite and garnet into large-aperture, fluid-filled fractures, north-eastern Connecticut, USA 总被引:1,自引:1,他引:1
J. J. AGUE 《Journal of Metamorphic Geology》1995,13(2):299-314
Abstract A petrographic and petrological analysis of exceptionally well-preserved hydrothermal veins from the Merrimack synclinorium, north-eastern Connecticut, has been carried out in order to place new field-based constraints on fracture aperture dimensions and porosity in the lower continental crust. The veins preserve substantial open space today in outcrop, and contain mineral assemblages including subhedral to euhedral crystals of quartz, kyanite and almandine-rich garnet. Textural evidence indicates unequivocally that the vein minerals grew into macroscopic (mm- to cm-scale) open space between the vein walls. The veins are interpreted to have been large-aperture fractures along which significant advective fluid infiltration and chemical reaction occurred. The porosity of the rock mass due to open space between fracture walls today is c . 0.3%, but it could have been as large as several percent when the flow system was active. Quantitative thermobarometry results from vein mineral assemblages indicate that the fractures formed at pressures and corresponding crustal depths of c. 0.8 GPa and c. 30km, and temperatures of 550–600° C. The depth of fracture formation corresponds to published estimates of the maximum burial depth of the Merrimack synclinorium during the Acadian orogeny. The formation of large-aperture fractures could increase significantly the transient permeability of the deep crust, and therefore influence metamorphic heat and mass transfer. 相似文献
690.
Abstract Quartz-hosted, synthetic CO2 -H2 O fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory-simulated metamorphic re-equilibration at 650, 750 and 825°C and 1.5 kbar total pressure with fO2 defined by the C-CH4 buffer. Microthermometry and Raman spectroscopy show that the initial CO2 -H2 O inclusions become CO2 -CH4 -H2 -H2O
inclusions after diffusive influx of hydrogen from the reducing confining medium. Measurable changes are observed in inclusion compositions after only 15 days of re-equilibration, implying significant hydrogen mobility at still lower temperatures over geological time spans. Results of synthetic inclusion re-equilibrium experiments have profound implications for the interpretation of natural fluid-inclusion data; failure to account for potential hydrogen migration in inclusions from high-temperature geological environments may lead to erroneous estimates of P-T, and/or the compositions of metamorphic fluids. 相似文献
inclusions after diffusive influx of hydrogen from the reducing confining medium. Measurable changes are observed in inclusion compositions after only 15 days of re-equilibration, implying significant hydrogen mobility at still lower temperatures over geological time spans. Results of synthetic inclusion re-equilibrium experiments have profound implications for the interpretation of natural fluid-inclusion data; failure to account for potential hydrogen migration in inclusions from high-temperature geological environments may lead to erroneous estimates of P-T, and/or the compositions of metamorphic fluids. 相似文献