Studies of electrical properties of rocks under high temperature and pressure

Studies of the rocks′ electrical properties under high temperature and pressure have found favors in the geophysicist′s eyes, because those studies are becoming to be the important methods to understand the earth′s interior materials, their migration and evolution. This article introduces the development and significant of those studies from the measurements, instruments and affections, etc.     

Impedance spectroscopy analysis on electrical properties of serpentine at high pressure and high temperature

The electrical conductivity of serpentine is measured and the microscopic conductance mechanisms are investigated with impedance spectroscopy at 2.5–4.0 GPa and 220–780°C. The results show that the electrical conductivity is strongly dependent on the frequencies used, and that only arc I, which reflects grain interior conductance, occurs and dominates the whole conductance processes over 12-10⁵Hz at high pressure before dehydration. The arc II, which indicates the grain boundary process, begins to occur at the initial stage of dehydration. After dehydration, due to the presence of highly conductive networks of free water, the electrical conductivity is not dependent on frequencies any longer and the total electrical conductivity is dominated by process of ionic conductance of free water in interconnected networks. Dehydration of serpentine enhances pronouncedly the total electrical conductivity, through which highly conductive layers (HCL) may be formed in the earth’s interior.     

Raman spectroscopy of nanocrystals in rock

Nanocrystals were detected and identified in rocks by the method of Raman spectroscopy. The experiments showed that the Raman scattering spectra of fine-lamellar arkosic sandstone exhibit bands corresponding to lattice vibrations of anatase, α-quartz, and plagioclase. In all spectra of the rock, the bands are displaced towards high frequencies as compared with their position in spectra of single crystals and widen on the same side. These results show that, in all of the studied places of the sample, the particles of anatase, quartz, and plagioclase have nanometer sizes, namely, of the order of 10 nm in anatase and quartz and about 20 nm in plagioclase. Moreover, in different places of the sample, not only the shape and position of the bands under study but also their intensity vary, the latter being directly proportional to the concentration of nanocrystals.     

高温高压下矿物岩石电导率的实验研究进展

高温高压下矿物、岩石电性性质的实验研究是了解地球内部物质成分、演化过程及进行地球物理探测资料解释的有力工具.本文主要介绍了高温高压下电导率实验在如何保持良好绝缘性能,如何消除或减小极化效应及如何减小外界电信号对测量信号的干扰等方面的技术、方法,阐述了温度、压力、氧逸度、水含量以及熔体等因素对矿物、岩石电导率的影响以及一些主要的研究结果和进展情况,讨论了电性研究的地球物理和地质意义,并指出了尚需研究的不足之处.     

大陆岩石圈流变研究进展与高温高压流变实验现状

大陆岩石圈类似于“三明治”的多层流变结构已经被广泛接受,并用于大陆动力学研究的各方面．然而近年来地震资料和高温高压流变实验结果表明,大陆岩石圈流变可能不是单一模式,流变结构具有多样性,而下地壳流变特性是其中最复杂的层次,这不仅受下地壳成分和结构本身的非均匀控制,而且与其含水程度相关．高温高压流变实验已经积累了大量的数据,但基性岩流变实验目前仍然处于数据积累阶段,缺乏系统性,特别是缺少含水基性岩的流变实验结果,因此,加强干的和含水的基性岩流变实验研究是深入认识下地壳岩石流变必不可少的手段和方法之一．     

Experimental studies on elastic and rheological properties of amphibolites at high pressure and high temperature

The experimental studies done at high temperature and high pressure find that increased temperature can lead to dramatic velocity and strength reductions of most of rocks at high confining pressure[1,2]. What causes this phenomenon? Is it due to dehydrati…     

Anisotropic thermal properties of talc under high temperature and pressure

The anisotropic thermal conductivity and diffusivity of talc were simultaneously measured up to 5.3 GPa and 900 K using the pulse transient method. Although significant anisotropy was observed in the thermal conductivity of talc, the average thermal conductivity is comparable to that of olivine and roughly three times greater than that of antigorite. From the ratio of the thermal conductivity to the thermal diffusivity, the heat capacity of talc was evaluated. The pressure derivative of heat capacity was found to be positive, which is related to the anomaly of thermal expansivity of talc above 50 °C at atmospheric pressure.     

高温高压下辉石弹性及相变研究进展

辉石(pyroxene)是地壳中重要的造岩矿物,同时也是上地幔中除橄榄石以外含量最多的矿物,对其弹性及相变的研究有助于更好的理解壳幔的物质组成、地震波速异常及动力学过程等.高温高压实验和理论模拟计算是目前探测地球深部物质物性的两种最有效的间接方法,因此本文在介绍了辉石矿物学特征的基础上,从实验和计算两个方面论述了近十几年来国内外学者对辉石的弹性及相变的研究进展,然后探讨了辉石相变与上地幔X不连续面的关系,最后指出了目前的研究存在的问题以及未来的研究展望.     

高温高压下地幔矿物岩石电导率影响因素研究进展

实验室高温高压条件下获得的地幔矿物岩石电导率值可以帮助获得地球内部物质组成、物质运动变化状态和解释地球物理探测资料.研究表明,电导率测量影响因素(外部因素和内部因素)控制不当将使得测量的电导率值产生较大差异.本文综述了近20年来这些影响因素对地幔矿物岩石电导率的影响程度及进展情况,电导率随着温度,铁含量和水含量的增加而增加;不含水条件下,电导率随着氧逸度和压力的增加分别增加和减小,含水条件下则恰恰相反;忽略颗粒边界的影响;测量频率和结晶方向对电导率的影响尚存在一定争议;进行电导率测量时有必要考虑系统平衡时间和样品中铁含量的流失.最后探讨了高温高压条件下电导率实验研究的不足和发展方向.     

Paleo-Moho depth determined from the pressure of CO2 fluid inclusions: Raman spectroscopic barometry of mantle- and crust-derived rocks

The density, and therefore the pressure, of CO₂ fluid inclusions in minerals can be estimated from the Fermi diad splitting of Raman spectra of CO₂. An accurate determination of the pressure of CO₂ fluid inclusions enables the estimation of the depth origin of rocks from the deep Earth. A micro-Raman densimeter was applied to ultramafic–mafic xenoliths sampled along the Ohku coast of Oki-Dogo Island in the Sea of Japan (East Sea). The density of CO₂ fluid inclusions in the mafic granulite was 1.02–1.05 g/cm³, while those of lherzolites were 0.98–1.02 g/cm³. In contrast, the density of CO₂ fluid inclusions measured in olivine gabbro, clinopyroxenite, and harzburgite were lower ranging from 0.86–to 0.99 g/cm³. Taking into account the temperature condition estimated using a pyroxene thermometer, the mafic granulite originated from a depth of 27–30 km and the lherzolites from 25–29 km. The overlapping depth of 27–29 km can be interpreted as the depth including the Moho discontinuity under Oki-Dogo Island 3.3 Ma. This estimation is consistent with geophysical observations.     

高温高压条件下纳米材料强度的测试和分析方法

基于高温高压同步辐射X射线衍射和飞行时间中子衍射实验,我们提出了一种通过衍射研究纳米材料本征力学性能的方法.实验通过高压压缩实验对纳米晶和微米晶Ni的变形行为进行了对比研究;二者在不同压力下的晶胞体积数据表明,纳米晶Ni具有明显的弹性软化现象,体弹模量比微米晶Ni减小约10%.研究结果表明,纳米晶Ni的整体抗压缩性减小是由于该材料纳米晶壳层呈现为张应力状态,具有较低的抗压缩性,这与分子动力学模拟结果一致.基于该方法,通过定量分析衍射峰的宽化和偏移,我们可以获得晶粒之间的高应力聚集区所产生的"微观/局部"屈服,以及整个样品在应力下所产生的"宏观/整体"屈服.我们的应变/应力图形分析方法还可以研究材料的屈服强度、高温高压条件下的晶粒破碎/长大、加工硬化/软化,以及多晶体中的固有残余/表面应变.本文提出的方法可以用于岩石矿物的高温高压流变强度的定量测定,为研究岩石圈以及地幔物质的蠕变对流提供了高科技的研究手段.     

高温高压下上地幔岩石电导率实验研究

为了建立具有普遍适用性的上地幔电性结构,本文利用Kawai-1000t压机和Solartron IS-1260阻抗/增益-相位分析仪,在4.0~14.0 GPa、873~1673 K的条件下,采用交流阻抗谱法（频率范围10^-1~10⁶Hz）测量了不含水的地幔岩电导率.实验结果显示,岩石的电导率随温度升高而大幅度的增大;在较大的温度范围内岩石的导电机制发生了变化,中低温时为小极化子导电,此时激活焓为0.94 eV （±0.13） eV,激活体积为0.11（±0.92） cm³·mol^-1,高温时为和镁空穴相关的离子导电,此时激活焓为1.6~3.17 eV,激活体积为6.75（±7.43） cm³·mol^-1;本次测量的电导率比低压下岩石的电导率要高,比矿物的电导率也要高.用本次的实验结果回归计算得到Fennoscandian地区的上地幔的一维电导率剖面,发现200 km以上本次实验计算的结果和大地电磁测深的电导率剖面吻合的比较好,在200 km以下本次实验得到的要比野外测量的电导率稍稍高一点,可能是因为实验过程中没有完全避免水的影响.本次的实验结果比用有效均匀介质方法计算得到的pyrolite矿物模型的电导率要高出两个数量级,这样的结果显示只用一种矿物的电导率或是几种矿物理论计算的结果有一定的不合理性.     

高温高压下上地幔岩石电导率实验研究

为了建立具有普遍适用性的上地幔电性结构,本文利用Kawai-1000t压机和Solartron IS-1260阻抗/增益-相位分析仪,在4.0~14.0 GPa、873~1673 K的条件下,采用交流阻抗谱法（频率范围10^-1~10⁶Hz）测量了不含水的地幔岩电导率.实验结果显示,岩石的电导率随温度升高而大幅度的增大;在较大的温度范围内岩石的导电机制发生了变化,中低温时为小极化子导电,此时激活焓为0.94 eV（±0.13）eV,激活体积为0.11（±0.92）cm³·mol^-1,高温时为和镁空穴相关的离子导电,此时激活焓为1.6~3.17 eV,激活体积为6.75（±7.43）cm³·mol^-1;本次测量的电导率比低压下岩石的电导率要高,比矿物的电导率也要高.用本次的实验结果回归计算得到Fennoscandian地区的上地幔的一维电导率剖面,发现200 km以上本次实验计算的结果和大地电磁测深的电导率剖面吻合的比较好,在200 km以下本次实验得到的要比野外测量的电导率稍稍高一点,可能是因为实验过程中没有完全避免水的影响.本次的实验结果比用有效均匀介质方法计算得到的pyrolite矿物模型的电导率要高出两个数量级,这样的结果显示只用一种矿物的电导率或是几种矿物理论计算的结果有一定的不合理性.

     

高温高压下麻粒岩电导率研究

麻粒岩是下地壳的重要组成物质,模拟其在下地壳温压条件下的电导率对于认识下地壳的电导率分布具有十分重要的意义.本文用交流法在1 GPa下,373~1002 K范围内研究了麻粒岩样品的复阻抗,并且对测量结果进行了阻抗谱分析.研究结果表明,复阻抗对频率具有依赖性,且随温度的升高,复阻抗的实部、虚部均变小.在实验给出的温度范围内,电导率结果符合Arrhenius关系式.当温度在373~663 K范围内时,实验所获得的激化焓为0.31 eV,表明样品的电导率由低能带杂质离子所控制;当温度在673~1002 K范围内时,激化焓为0.67 eV,此时可能为小极化子导电.将所得电导率结果与西南峨边—马边地区以及华北应县―商河地区的大地电磁结果进行了对比,发现在所模拟的下地壳温压范围内,实验室测得的电导率位于野外MT数据范围内.     

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1.0~4.0 GPa、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-4.73 cm3·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-0.11 cm3·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.     

The dependence of transport properties ofin situ rocks on pore fluid composition and temperature

Fluids saturating cracked rocks within the crust can vary widely in composition and physical properties, which depend greatly on pressure and temperature. External non-hydrostatic stress applied to a cracked medium may result in a significant change of crack volume (and hence, for the undrained regime, pore-fluid pressure) due to the processes of crack closure (opening), and thus lead to a drastic change of the overall physical parameters of a rock. The purpose of the study is to estimate theoretically, using the effective-medium theory, the macroscopic seismic and transport parameters (such as permeability) of cracked rocks (granites) saturated with hydrocarbon gases, oils, brines and water. Variations of crack geometry and fluid parameters in the closed system (at constant fluid mass) under uniaxial compression are considered as well. The results show that composition of a saturating fluid as well as fluid temperature greatly influence the effective permeability and shear velocities of a rock mass, while thermal conductivity is not so sensitive to variations of fluid parameters.     

高温高压下碳酸盐熔体对地幔岩电导率的影响

为了观测含碳酸盐地幔岩部分熔融过程中电导率的变化,厘清碳酸盐熔体在金伯利岩岩浆形成过程中所起的作用,并探讨Slave克拉通中部Lac de Gras地区约80~120 km深处的高导成因,我们利用DS 3600 t六面顶压机和Solartron 1260阻抗/增益-相位分析仪在1.0~3.0 GPa、673~1873 K温压条件下分别测量了含碳酸钠（Na₂CO₃）、碳酸钙（CaCO₃）和大洋中脊玄武岩（MORB）的地幔岩样品的电导率.实验结果表明,地幔岩样品的电导率主要受到温度和组分的影响,而压力对其影响较小.在温度低于1023 K时,含Na₂CO₃地幔岩样品的电导率明显高于含同比重CaCO₃和MORB的;温度达到1023 K时,含Na₂CO₃地幔岩样品开始熔融;但在之后的200 K温度区间内,该部分熔融样品的电导率随温度的增加几乎不发生变化.这一现象或许揭示：地幔深部的碳酸质岩浆在快速上升过程中会同化吸收岩石圈地幔中的斜方辉石（Opx）,进而形成金伯利岩岩浆,期间岩浆的电导率几乎不发生变化.含CaCO₃和MORB的地幔岩样品分别在1723 K和1423 K开始熔融,其部分熔融样品的电导率随温度的增加而快速增加.依据前人的研究结果和我们的实验结果,我们认为可以用含碳酸盐的部分熔融样品来解释Slave克拉通中部Lac de Gras地区约80~120 km深处的异常高导现象,并推测熔体中碳酸盐的熔体比例小于2 wt.%.

     

高温高压下角闪片麻岩的电导率研究

在1.0 GPa压力、343～962 K温度和0.1～106Hz频率的条件下,使用Solartron 1260阻抗-增益/相位分析仪对含角闪石的片麻岩从平行和垂直面理两个不同方向分别进行了电阻抗的测定,并且进一步分析了片麻岩的微观导电机制.高温高压实验结果表明:片麻岩的复阻抗对温度、频率表现出明显的依赖性.片麻岩的电导...     

Jadeitic rocks within high pressure metamorphic zone from northeastern Jiangxi Province and their forming and surviving conditions

There is a close relation in time, space and origin between the NEJXO, NEJXDFZ and HPMZ from NEJXP which are located in and constrained by both Yangtze Craton and Cathaysia. These HPMRs principally include (i) Jd-Q-Ab schist, (ii) Lw-Jd-Ab schist, (iii) Jd-Ab schist, and (iv) Gl-schist. The Jd is nearly pure (Jd91-98). Jd surrounded by Ab is separated from Q and survived due to the reaction between Jd and Q, while Lw encircled by Ab remains as a pseudomorph composed of CZo+An. The minerals associated with Jd are Lw, Gl, Ab, Q, CZo, An, Pa, II, Ru, Sp, Ap, and Zr. According to the textures, the mineral paragenesis is classified into four groups (i) PI-Am-Q, (ii) Jd-I,w-GI-Q, (iii) CZo-An-Ab-Q, (iv) Ab-Ana-Ser-Ur, corresponding to (i) 1.0–0.93 Ga, 250°C, 2–3 × 10⁸ Pa; (ii) 0.93–0.79 Ga, 300–350°C, 5–12 × 10⁸ Pa; (iii) 0.79–0.223 Ga, 350–400–120°C, 12–5–3 × 10⁸ Pa; and (iv) < 0. 223 Ga, < 120–50°C, < 3 × 10⁸ Pa, in time, temperature and pressure respectively. A clockwiseP-T-t path is isothermal increasing inP (up to 45 km)—isothermal decreasing inP (up to 5 km)— nearly isobar decreasing in T. Project supported by the National Natural Science Foundation of China.     

Influence of fluid composition on the elastic properties of sandstone and quartzite at high temperature and pressure in application to the problem of crustal waveguides

Recent geophysical studies have revealed zones with anomalously low seismic velocities and increased electric conductivity in the middle part of the Earth’s crust. It is suggested that these zones can probably be related with the variations in the porosity and permeability of the rocks and the presence of fluids, and that they can explain the existence of crustal waveguides. In order to verify this model, we carried out an experimental study. Among the studied metamorphic processes, the acid metasomatose most completely explains the silicification of rocks. The present work considers the physico-chemical causes of the redeposition of quartz from the solutions, the influence of the pH of the solutions on the mass transfer and deposition of quartz during silicification, and alteration of the physical properties of the rocks. Silicification leads to the increase in density, change in microtexture, and cementation of rocks. It also causes the change in seismic velocities in the Earth’s crust.