Characteristics of the difference and change in the comprehensive physical properties of rocks

Introduction The medium of the earth is made up of gas, liquid, and solid. The solid is the main material to form the structure of the earth, so it is very significant to study the solid matter of the earth. Rock, as a solid medium of the earth is a common object studied by geophysicists. The measurement of the comprehensive physical properties of rocks (ZHAO, et al, 1996; GUO, et al, 1989) considered that the minimal cell of rock is the atoms of chemical element, and all sorts of the rock …     

Laboratory electrical conductivity measurements on mantle relevant minerals

The influence of environmental conditions and the thermodynamic parameters which may determine the bulk electrical conductivity of, for instance, basaltic rocks are briefly discussed. At present it is not known to what extent these numerous variables determine the electrical conductivity of rocks quantitatively, since all too many laboratory measurements did not account for the required number of variables to define the system. Thus it is difficult to decide whether or not laboratory measurements on rocks have duplicated their in-situ electrical conductivity.One approach is to calculate the bulk conductivity of rocks from conductivities of constituent minerals, since it is much easier to define the thermodynamic equilibrium conditions for a single phase system. Therefore, laboratory data of the electrical conductivity of minerals, i.e. olivines and pyroxenes, are discussed to some extent particularly in the context of point-defect concentrations as a function of pO₂ and the chemical activitiesa of the binary components of the minerals.The evaluation of a quantitative relationship requires a careful sample characterization. To find a basis for a reasonable interpretation of in-situ resistivity data, the test samples should be selected in regard to those conditions which are believed to exist in the appropriate layer of the earth.     

Modelling the relationship between magnetic fabric and strain in polymineralic rocks

We present a model that is applicable to the relatively frequent case of rocks in which the magnetic fabric is dominated by uniaxial paramagnetic minerals, and in which the deformation (pure shear) corresponds to the March-Fernandez model. Borradaile et al.'s procedure for the isolation of the magnetic fabric of monocrystals of anisotropic components allows us to obtain the magnetic properties equivalent to those of all the component minerals if they should be artificially aligned. In the case of real component minerals with similar shape parameters, χ (dependent on dimension ratio), these properties will correspond to those of a theoretical equivalent mineral. Therefore, finite strain and orientation tensors may be determined from magnetic fabric measurements of such polymineralic rocks.     

岩石综合物性差异与变化的特征

从岩石物性与化学元素原子结构的关系出发，从密度、弹性、电性和放射性等诸方面，论述了岩石综合物性差异与变化的特征；并结合实例，得出岩石综合物性参数发生变化反映了组成岩石的原子、分子、矿物和结构发生了变化，且各参数之间具有某种相关性的结果．      

Electrical properties and geochemistry of carbonate rocks from the Qasr El‐Sagha Formation,El‐Faiyum,Egypt

Understanding petrographical, geochemical and electrical properties of rocks is essential for investigating minerals. This paper presents a study of the petrographical, geochemical and A.C. electrical properties of carbonate rock samples. The samples collected show six lithostratigraphic rock units. Electrical properties were measured using a non‐polarizing electrode at room temperature (～20°C) and a relative atmospheric humidity of ～50% by weight in the frequency range from 42 Hz to 5 MHz. The difference in electrical properties between the samples was attributed to the change in composition and texture between the samples. Electrical properties generally change with many factors (grain size, chemical composition, grain shape and facies). The dielectric constant decreases with frequency and increases with conductor composition. The conductivity increases with the increase of conductor paths between electrodes. Many parameters can contribute to the same result of the electrical properties. The main objective of the present study is to shed more light on the relation between the texture and geochemical composition of measured samples (carbonates that contain clays and quartz grains) through electrical laboratory measurements (conductivity and dielectric constant as a function of frequency).     

Changes of electrical conductivity in the vicinity of the curie temperature of basaltic rocks — theoretical model

Summary Samples of basalts, haematites and magnetites display either temporary or permanent (magnetite) weakening of the increase of the electrical conductivity with increasing temperature in the vicinity of their Curie temperature. Using the second quantization, this paper explains the observed pattern of the electrical conductivity adequately for magnetite and approximately for the other rocks by means of a quantum theory model of ferromagnetic minerals. This theory describes only the electron component of the electrical conductivity, which is responsible for the Curie temperature effect.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

Geoelectrical Classification of Gypsum Rocks

Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations, laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field examples. A geoelectrical classification of gypsum rocks defining three types of gypsum rocks has been elaborated: (a) Pure Gypsum Rocks (>75% of gypsum content), (b) Transitional Gypsum Rocks (75–55%), and (c) Lutites and Gypsum-rich Lutites (<55%). From the economic point of view, the Pure Gypsum Rocks, displaying a resistivity value of >800 ohm.m, can be exploited as industrial rocks. The methodology used could be applied in other geoelectrical rock studies, given that this relationship between the resistive particles embedded within a conductive matrix depends on the connectivity of the matrix particles.     

Joint elastic‐electrical effective medium models of reservoir sandstones

Improvements in the joint inversion of seismic and marine controlled source electromagnetic data sets will require better constrained models of the joint elastic‐electrical properties of reservoir rocks. Various effective medium models were compared to a novel laboratory data set of elastic velocity and electrical resistivity (obtained on 67 reservoir sandstone samples saturated with 35 g/l brine at a differential pressure of 8 MPa) with mixed results. Hence, we developed a new three‐phase effective medium model for sandstones with pore‐filling clay minerals based on the combined self‐consistent approximation and differential effective medium model. We found that using a critical porosity of 0.5 and an aspect ratio of 1 for all three components, the proposed model gave accurate model predictions of the observed magnitudes of P‐wave velocity and electrical resistivity and of the divergent trends of clean and clay‐rich sandstones at higher porosities. Using only a few well‐constrained input parameters, the new model offers a practical way to predict in situ porosity and clay content in brine saturated sandstones from co‐located P‐wave velocity and electrical resistivity data sets.     

Fractional-order derivative and time-dependent viscoelastic behaviour of rocks and minerals

A general constitutive equation for viscoelastic behaviour of rocks and minerals with fractional-order derivative is investigated. This constitutive law is derived based on differential geometry and thermodynamics of rheology, and the fractional order of derivative represents the degree of time delay. Analyzing some laboratory experimental data of high temperature deformation of rocks and minerals such as halite, marble and orthopyroxene, we propose how to determine the orders of fractional derivative for viscoelastic behaviours of rocks and minerals. The order is related to the exponents for the temporal scaling in the relaxation modulus and the stress power-law of strain rate, i.e., the non-Newtonian flow law, and considered as an indicator representing the macroscopic behaviour and microscopic dynamics of rocks.     

磁性矿物的磁学鉴别方法回顾

磁性矿物的组成和颗粒粒径的分布决定了岩石或沉积物的基本磁学性质及其所携带的天然剩磁在地质时期内的稳定性.由于自然界中磁性矿物的复杂性和多样性，如何有效的确定磁性矿物的成分和粒径分布一直是岩石磁学的基础和难点.本文对确定磁性矿物成分和粒径分布的常见方法进行了较为详细的总结和分析，并对常见磁性矿物在高温和低温下的磁学性质进行了详细的论述.最后对如何应用综合方法判定样品中的磁性矿物种类以及粒度分布进行了探讨.     

Petrochemistry of Kamen volcano: A comparison with neighboring volcanoes of the Klyuchevskoy group

The data on geology, petrography, mineralogy and petrochemistry for Kamen volcano in the Central Kamchatka Depression are presented. A study of the volcano??s rocks and comparison with rocks of neighboring active volcanoes of the Klyuchevskoy group allow the establishment of some relationships. The rocks and minerals of Kamen and Ploskie Sopky volcanoes show systematic differences in the chemistry of rocks and minerals such that they obviously could not be formed from the same primary melts. The rocks of dykes and Kamen stratovolcano on one hand and the rocks of the Klyuchevskoy Volcano on the other hand form differently directed trends on petrochemical diagrams and differ in their compositions of rock-forming minerals, such they also could not originate from the same primary melts. The lavas of the monogenetic cones of Kamen volcano and moderately magnesian basalts of Klyuchevskoy volcano are derivates of the same melts, i.e., the cones situated on the slopes of Kamen are cones of Klyuchevskoy. The rocks of Kamen and Bezymianny stratovolcanoes form a single narrow trend in all petrochemical diagrams in which the lavas of Bezymianny volcano show a silica-rich part, thus indicating a genetic relationship between these two volcanoes.     

Laboratory Electrical Conductivity Measurement of Mantle Minerals

Electrical conductivity structures of the Earth’s mantle estimated from the magnetotelluric and geomagnetic deep sounding methods generally show increase of conductivity from 10⁻⁴–10⁻² to 10⁰ S/m with increasing depth to the top of the lower mantle. Although conductivity does not vary significantly in the lower mantle, the possible existence of a highly conductive layer has been proposed at the base of the lower mantle from geophysical modeling. The electrical properties of mantle rocks are controlled by thermodynamic parameters such as pressure, temperature and chemistry of the main constituent minerals. Laboratory electrical conductivity measurements of mantle minerals have been conducted under high pressure and high temperature conditions using solid medium high-pressure apparatus. To distinguish several charge transport mechanisms in mantle minerals, it is necessary to measure the electrical conductivity in a wider temperature range. Although the correspondence of data has not been yet established between each laboratory, an outline tendency of electrical conductivity of the mantle minerals is almost the same. Most of mineral phases forming the Earth’s mantle exhibit semiconductive behavior. Dominant conduction mechanism is small polaron conduction (electron hole hopping between ferrous and ferric iron), if these minerals contain iron. The phase transition olivine to high-pressure phases enhances the conductivity due to structural changes. As a result, electrical conductivity increases in order of olivine, wadsleyite and ringwoodite along the adiabat geotherm. The phase transition to post-spinel at the 660 km discontinuity further can enhance the conductivity. In the lower mantle, the conductivity once might decrease in the middle of the lower mantle due to the iron spin transition and then abruptly increase at the condition of the D″ layer. The impurities in the mantle minerals strongly control the formation, number and mobility of charge carriers. Hydrogen in nominally anhydrous minerals such as olivine and high-pressure polymorphs can enhance the conductivity by the proton conduction. However, proton conduction has lower activation enthalpy compared with small polaron conduction, a contribution of proton conduction becomes smaller at high temperatures, corresponding to the mantle condition. Rather high iron content in mantle minerals largely enhances the conductivity of the mantle. This review focuses on a compilation of fairly new advances in experimental laboratory work together with their explanation.     

The Carboniferous of the Moscow syneclise: Paleomagnetic data

New data for the Early and Late Carboniferous sections of the Russian platform (Moscow syneclise and Donbass) are presented. Magneto-mineralogical studies are carried out to identify the magnetic minerals—carriers of natural remanent magnetization. Extensive Late Paleozoic remagnetization of Carboniferous rocks is revealed. The obtained paleomagnetic data allowed us to determine the average paleomagnetic poles for the Gzhelian, Serpukhovian, and Visean stages of Carboniferous deposits of the Moscow syneclise.     

EXPLORATION OF BURUNDI NICKELIFEROUS LATERITES BY ELECTRICAL METHODS*

The laterites in Burundi, which are formed by weathering of ultrabasic rocks, show a complete profile with the following horizons: canga, the ferruginous crust capping, ferralite, consisting essentially of iron hydroxides, and saprolite, which contains a large quantity of hydrosilicate minerals. Nickel bearing minerals occur in the saprolite and the lower portion of ferralite. Resistivity well-logging and resistivity sounding indicated that the electrical properties of rocks depend upon their composition: Canga and ferralite showed high resistivities of 6,500 Ωm and 800 Ωm, respectively. The resistivity of saprolite was found to be much lower, between 10 Ωm and 20 Ωm. The laterite is underlain by resistive peridotite. The chargeability of saprolite was found to be lower than that of the upper horizons and the bedrock. Electrolytic conductivity of laterite, which depends on the geometry of the deposit, was found to be low, because the laterite contains moisture and ground water, which are highly resistive. The relatively high conductivity of saprolite is caused by nickeliferous hydrosilicates, which exhibit the electrical properties of clay minerals, with an apparent maximum conductivity of 0.25 S/m. The conductivity of saprolite corresponds to a concentration between 30% and 50% of conductive silicate minerals distributed in the pore space of deposit. A nickel enrichment of up to 6% was estimated from the resistivity of the saprolite. Prospecting for laterites by electrical sounding showed that the development of laterite horizons in a nickel deposit correlates with the surface morphology of weathered ultrabasic massif. Thus the method can be used in preliminary exploration of such deposits.     

Study of changes in the rock formation medium of the Karadzha section (Azerbaijan) from the results of petromagnetic investigations

The petromagnetic characteristics of marine and subaqueous deposits on the upper marine terrace of the Karadzha section (Azerbaijan) are investigated. These deposits correspond to the great Khvalynsk transgression of the Paleocaspian. Thirteen meters of the section encompassing an age interval of ～45–20 ka are sampled continuously. Regular along-section changes are revealed, and their relation to environmental changes is established. Magnetite, maghemite, and hematite that were formed in the process of alteration of the maternal rocks in the Paleocaspian wash-down basin are the main ore minerals of the studied rocks. The ratios of these minerals in the deposits depend on the degree of alteration of the maternal rocks. Both the total amount of ore mineral (K and SIRM parameters) and the rigidity parameter B _cr regularly increase in the basal part of the section and in the sediments reflecting finer variations in the basin level. An increased magnetic rigidity and the sensitivity of petromagnetic parameters to weak variations in the sea level are characteristic features of sediments in this part of the Paleocaspian compared with normal marine sediments.     

高温高压下地幔岩和苦橄质榴辉岩的电导率实验

为了探讨地幔岩模型和苦橄质榴辉岩模型在上地幔存在的合理性,建立上地幔的电性结构,本文利用YJ-3000t紧装式六面顶压机和Solartron IS-1260阻抗/增益-相位分析仪,在1.0~4.0GPa、700~1150℃的条件下,采用交流阻抗谱法(频率范围10-1~106 Hz)分别测量了地幔岩和苦橄质榴辉岩的电导率.实验结果表明:随着温度的升高,地幔岩和苦橄质榴辉岩的电导率大幅增加;随着压力的增大,地幔岩的电导率略有增加,活化体积ΔV为-4.73cm3·mol-1,而苦橄质榴辉岩的电导率几乎没有变化,活化体积ΔV为-0.11cm3·mol-1;在电性方面,用苦橄质榴辉岩来表示深部的物质较为合理,地幔岩解释浅部可能更恰当,但浅部物质的分布不均匀,电导率随深度的变化主要受控于温度的影响,其次才是成分.     

Anisotropy of magnetic remanence: A brief review of mineralogical sources,physical origins,and geological applications,and comparison with susceptibility anisotropy

The magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low-field magnetic susceptibility (AMS). However, alternative methods based on remanent magnetization (measured in the absence of a magnetic field) rather than induced magnetization (measured in the applied field) have distinct advantages for certain geological applications. This is particularly true for; (1) adjunct studies in paleomagnetism, in order to assess the fidelity with which a natural remanence records the paleofield orientation; (2) studies of weakly magnetic or weakly deformed rocks, for which susceptibility anisotropy is very difficult to measure precisely; and (3) quantitative applications such as strain estimation. The fundamental differences between susceptibility and remanence (and their respective anisotropies) are due to several factors: (1) susceptibility arises from all of the minerals present in a sample, whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals; (2) ferromagnetic minerals are generally more anisotropic than para- and diamagnetic minerals; (3) for ferromagnetic minerals, remanence is inevitably more anisotropic than susceptibility; and (4) a number of common minerals, including single-domain magnetites, possess an inverse anisotropy of susceptibility, i.e., they tend to have minimum susceptibility parallel to the long axis of an individual particle; remanence is immune to this phenomenon. As a consequence of all these factors, remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample.Contribution number 9102 of the Institute for Rock Magnetism, University of Minnesota.     

基于QAPM矿物模型遗传算法评价火成岩储层

在松辽盆地深层发现了含气火成岩储层。由于火成岩矿物组成复杂和含量的变化,使得选择用于测井评价的解释参数很困难。基于IUGS提出的QAPF分类方案,本文提出了采用遗传算法,利用测井数据确定火成岩矿物含量的方法。根据QAPF分类方案,将火成岩中的矿物分为五类:Q-石英;A-碱性长石;P-斜长石和方柱石;F-副长石(研究区未出现);M-铁镁矿物。本文提出用包括孔隙度在内的QAPM模型对储层进行分析。建立密度、视中子孔隙度、声波时差、自然伽玛和体积光电吸收截面指数的测井响应方程,各矿物参数从斯伦贝谢的矿物参数手册中得到。用遗传算法计算骨架中四种矿物的体积,根据四种矿物的体积含量,依据QAPF分类对火成岩命名。基于解释参数计算的孔隙度可与岩心分析的孔隙度相比,本文给出的火成岩命名与岩心化学分析的命名相一致。     

Redistribution of REEs during metamorphism and its indicative significance for fluid processes

Detailed REE geochemical studies of the Xingzi Group metasedimentary rocks at Lushan and rock-forming minerals such as garnet have been conducted and the results show that the REEs are partly present in the rock-forming minerals and are dominantly contained in the lattice of accessory minerals. In the process of metamorphism the REEs reached partition equilibrium between garnet porphyroblast and rock and the partitioning of REEs between garnet and host rock is obviously controlled by the chemical composition of the system. The REE compositions of metamorphic veins and their minerals display remarked lanthanide tetrad effects and the element pairs Zr-Hf, U-Th and Y-Ho have also experienced remarkable fractionation with respect to the metamorphic rocks and they can be used as discriminating indicators for the occurrence of fluid processes in the process of metamorphism of the Xingzi Group.     

Alkali-rich intrusive rocks in the Qinghai-Xizang Plateau and its vicinities as exemplified by Kuganzi and Taihe plutons

The alkali-rich intrusive rocks in the Qinghai-Xizang Plateau can be divided into two series in terms of dark-colored rock-forming minerals, petrochemical composition and trace elements: ∣) sodic alkaline series rocks consisting of alkaline rocks and alkali granite which contain dark-colored minerals, such as aegirine augite, aegirine and riebeckite, and being petrochemically enriched in alkali and sodium but low in Ca, Sr and Ba; ║) potassic alkaline series rocks consisting of alkaline rocks and alkali granite which contain non-alkaline dark-colored minerals (diopside, edenite), and being petrochemically enriched in alkali, K and Ca with high abundances of Sr and Ba.