大陆俯冲化学地球动力学

详细介绍了本世纪６０年代以来高温高压条件下岩石弹性波速度测量的发展历史,重点介绍了高温高压条件下岩石弹性波速测量的基本原理和有代表性的三个研究小组（德国Ｃｈｒｉｓｔｉａｎ Ａｌｂｒｅｃｈｔｓ大学Ｋｅｒｎ领导的研究小组,美国威斯康星大学Ｃｈｒｉｓｔｅｎｓｅｎ领导的研究小组,中国科学院地球化学研究所谢鸿森领导的研究小组）采用的实验方法,举例说明了高温高压条件下岩石弹性波速测量在推测深部地质过程和构筑区域岩石圈结构及物质组成模型方面的应用。     

地球深部物质弹性的实验研究

“地球深部物质弹性的实验研究”是1989年国家自然科学基金资助项目(编号:48970206)。在实验室模拟地球内部的高温高压条件下,对矿物岩石进行就位弹性波速测量是开展本项目研究的主要方法。由于实验技术难度大,到目前为止已发表的较系统的高压波速测量的数据大多是在室温下获得的,压力范围多在1.0GPa以下。为了提高弹性波速测量的压力和温度范围,获得与地球内部物质更接近的弹性波速的实验数据。三年来该课题组全力以赴,首先对原有的YJ—3000吨压力机的静态超高压大腔体实验设备进行了技术改造。使其温度、压力控制系统实现了自动化,大大改善了升降压、升降温过程中高压腔体的压力温度品质。在此基础上,根据自己实验设备的特点,设计和安装了高温超高压超声脉冲法波速测量装置和样品组装方式。经过反复实验和改进,获得了高压同时加热条件下清晰的超声波图形。并将全波震相分析理论应用于图形的识     

地球深部物质科学——在静高压大腔体实验研究方面的某些进展

介绍近年来使用静态超高压大腔体实验技术 ,在模拟地球内部的高温高压条件下 ,对地球物质进行的若干物理和化学性质的实验研究。高压同时高温条件下多种岩石样品的弹性波速就位测量揭示出物质的声软化现象和振幅效应 ;高温高压下陨石和岩石的熔融结晶实验发现了陨石硅酸盐相的不混溶现象以及玄武岩熔体结构的变化 ,在玄武岩转变为榴辉岩的实验中观测到了刚玉相 ;在高温高压水的实验中 ,发现了冰 Ⅶ 的亚稳相和熔融前效应以及超临界水及其稀溶液的一些新性质。这些实验结果为探索地球深部物质的性质和状态以及迁移和演化提供了新的依据。     

地幔转换带条件下岩石矿物波速测量方法:超声波与多面砧技术的结合

地幔矿物的波速测量研究是认识地球深部物质组成和性质的重要方法.国际上在大压机中利用超声波技术对地幔矿物材料开展了广泛的波速测量研究,实验温压范围达到地幔转换带条件,而国内大压机超声波波速测量局限于6 GPa压力以内.在中国地质大学(武汉)地球深部研究实验室1 000 t Walker型多面砧大压机上,利用超声波技术,建立了一套高压波速测量系统,对地幔转换带矿物Mg₂SiO₄瓦兹利石多晶样品在18 GPa压力范围内的弹性波速进行了测量,测量结果与前人超声波波速测量结果相比总体吻合程度良好.利用多面砧大压机和超声波技术,在国内首次实现了地幔转换带高压条件下的波速测量,缩短了我国高压波速测量水平与国外先进水平的差距,同时可以为中国及周边地区地球物理观测资料的解析提供矿物物理方面的实验约束,为国内岩石矿物和固体材料的弹性研究提供实验技术支持.      

实验矿物物理的发展现状与趋势:1.相变和状态方程、电导率、热导率

实验矿物物理是高温高压实验地球科学的重要分支学科之一,它主要是通过高温高压实验模拟地球内部的物理化学环境,并原位测定地球深部物质（矿物、岩石和熔/流体等）的相变和状态方程、电导率、热导率等物理参数,探讨地球内部的圈层结构、物质组成、地球动力学过程等地球物理性质相关的一系列重要科学问题. 综述了实验矿物物理的发展历史、近二十年的研究现状与趋势,并展望了该学科未来发展的方向、关键科学问题与面临的主要挑战.      

超高温高压流变仪的研发及应用

随着我国能源勘探及地球深部探测等向深部发展,深井越来越多,地层温度、压力越来越高。保证高温高压状态下钻井液流变性能的稳定是深井安全钻进的必要前提,测定钻井液高温高压流变性是评价和优选钻井液体系最基础的工作。依托国家科技部重大仪器设备开发专项,通过对压力控制系统、温度控制系统、剪率控制系统、粘度检测系统等方面技术难题的攻关,研制成功了国内首台超高温高压流变仪。该仪器可在高温高压及低温高压条件下对钻井液、完井液、压裂液等样品的流变性进行高精度测量。     

高温高压微束衍射实验进展及其地学应用

同步辐射X射线微束衍射技术与静态高压装置(包括金刚石压砧设备和大腔体压力机设备)结合运用是研究高温高压下物质晶体结构、相变等的有效方法。金刚石压砧高温高压实验技术的发展体现在:在产生极端高温高压的同时,获得准确的实验温度压力值,采用充装气体传压介质等方法减小压力梯度,采用激光双面加温技术和改进激光光路以减小样品径向和轴向的温度梯度。大腔体压力机高温高压实验技术的发展主要表现在产生更高的实验压力,以及测试过程中使样品在一定幅度摆动以消除晶体生长和择优取向对衍射数据的影响。同步辐射X射线微束衍射技术的发展主要表现在更高亮度和更宽能量范围的同步辐射光源的使用、X射线聚焦技术的发展,以及角色散X射线衍射测试技术的进步。介绍了近年来高温高压微束衍射实验在地球科学领域所取得的一些最新进展,包括硅酸盐超钙钛矿的实验发现,铁的高温高压相变及熔融曲线、SiO2 超斯石英相变、橄榄石尖晶石相—超尖晶石相转变压力的精确测定等研究结果;认为硅酸盐超钙钛矿的进一步深入研究,水对地球深部矿物岩石力学性质及熔融行为的影响,高温高压下物质的化学反应性和地球深部元素的地球化学行为等,是今后高温高压实验研究的重要方向。     

角闪石高温高压实验研究进展及其地球物理意义

高温高压实验作为地球科学研究的重要方向之一,通过模拟地球深部的温度和压力条件,了解地球深部物质的物理化学性质、地球内部结构和动力学演化。角闪石属于双链硅酸盐矿物,为地幔岩石圈的重要组成,广泛分布在海洋地壳、俯冲板块、变质岩和火成岩中。作为俯冲带的重要含水矿物,角闪石的广泛分布和高温高压下的脱水对于理解俯冲带水含量以及水迁移具有重要作用,同时在俯冲带的地震活动、高电导率异常、地震波速异常和岩浆活动中扮演重要角色。在过去的近百年时间里,国内外学者对角闪石高温高压物理化学性质进行了大量的研究。角闪石具有非常复杂的元素组成和结构特征,由此也导致了不同角闪石物理化学性质存在显著不同,包括脱水与脱羟基反应中元素迁移的差异、角闪石形成与分解过程中碱性元素(K+Na)和H2O含量对热稳定的影响、不同空间群结构下的高压结构相变、原位条件下不同结晶方向的电导率异常、不同结晶学优选方位(CPO)下的波速异常等。已有的研究对于角闪石的物理化学性质以及其在俯冲带中发挥的作用有了比较清楚的认识,但仍然有许多问题需要进一步研究,如角闪石的高压脱水动力学、热物性和变形机制等。     

地球内部极端条件下流体和物质相互作用:透过金刚石窗口探测地球深部流体

报道关于地球内部极端条件下的流体实验研究的最新进展。使用金刚石压砧结合各种谱学方法及同步辐射光源技术,在高温超高压条件下原位直接测量物质的结构和性质,已经获得分子-原子尺度信息新的实验数据。本项工作使用金刚石压砧对高压(10GPa)和高温高压(800℃,3GPa)条件下的NaCl-H2O进行红外谱原位直测,研究了高压和高温高压下水分子结构,发现水分子的O—H振动特征峰频率随温度向高波数变化,而且,在临界态区域时水分子间的氢键网格被破坏。实验说明:地球内部流体性质由深到浅不断变化,如水的密度、介电常数等物理参数随温度压力而改变,在临界态出现突变。这些变化可以用高压高温的物质的各种谱学特征来表征。水的性质与它的分子结构、分子振动有关。在跨越临界区时水的性质异常涨落是由水分子结构异常变化、分子振动形式变化和氢键网格破坏所导致的。从分子尺度认识地球内部流体在极端条件下的性质和高压原位实验观测有助于我们进一步了解地球深部物质的性质及其相互作用,有助于认识深部过程。     

D-DIA装置与同步辐射源结合技术及其在矿物高温高压变形实验中的应用

高温高压变形实验是研究地球深部组成矿物流变学性质的重要技术手段之一.D-DIA(deformation-DIA)装置是最近10年来兴起的一种新的高温高压变形实验设备,通常可实现的最高压力为15 GPa和温度约为2 000 K;而同步辐射X射线衍射已经广泛地应用到物质结构科学的研究中,二者相结合,能够有效原位地研究材料物质在高温高压下的流变学性质.以美国布鲁克海文国家实验室配合有同步辐射源的D-DIA装置为例,介绍该装置的基本结构、工作原理及D-DIA装置与X射线结合技术如何实现矿物高温高压下变形过程的原位观测及相关定量力学数据的获取.这一技术突破了传统流变仪的压力局限,为在更高压力(P＞4 GPa)条件下研究地球深部组成物质的高温高压流变学性质提供了有效途径.      

Thermal expansion and crystal structure of FeSi between 4 and 1173 K determined by time-of-flight neutron powder diffraction

The thermal expansion and crystal structure of FeSi has been determined by neutron powder diffraction between 4 and 1173?K. No evidence was seen of any structural or magnetic transitions at low temperatures. The average volumetric thermal expansion coefficient above room temperature was found to be 4.85(5)?×?10^?5?K^?1. The cell volume was fitted over the complete temperature range using Grüneisen approximations to the zero pressure equation of state, with the internal energy calculated via a Debye model; a Grüneisen second-order approximation gave the following parameters: θ_D=445(11)?K, V ₀=89.596(8)?ų, K ₀′=4.4(4) and γ′=2.33(3), where θ_D is the Debye temperature, V ₀ is V at T=0?K, K ₀′ is the first derivative with respect to pressure of the incompressibility and γ′ is a Grüneisen parameter. The thermodynamic Grüneisen parameter, γ_th, has been calculated from experimental data in the range 4–400?K. The crystal structure was found to be almost invariant with temperature. The thermal vibrations of the Fe atoms are almost isotropic at all temperatures; those of the Si atoms become more anisotropic as the temperature increases.     

Raman spectra of bixbyite,Mn<Subscript>2</Subscript>O<Subscript>3</Subscript>, up to 40 GPa

The Raman spectra of bixbyite, Mn₂O₃, were measured up to 40 GPa at room temperature. Mn₂O₃ undergoes a phase transition from the C-type rare earth structure to the CaIrO₃-type (post-perovskite) structure at 16–25 GPa. The transition pressure measured in Raman spectroscopy is significantly lower than the pressure reported previously by an X-ray diffraction study. This could be due to the greater polarizability in the CaIrO₃-type structure, consistent with high-pressure observation on the CaIrO₃ type in MgGeO₃, although it is still possible that experimental differences may cause the discrepancy. Unlike the change at the perovskite to CaIrO₃-type transition, the spectroscopic Grüneisen parameter does not decrease at the C-type to CaIrO₃-type transition. The spectroscopic Grüneisen parameter of the low-pressure phase (C type) is significantly lower than thermodynamic Grüneisen parameter, suggesting significant magnetic contributions to the thermodynamic property of this material. Our Raman measurements on CaIrO₃-type Mn₂O₃ contribute to building systematic knowledge about this structure, which has emerged as one of the common structures found in geophysically important materials.     

An alternative use of Kieffer’s lattice dynamics model using vibrational density of states for constructing thermodynamic databases

We use Kieffer’s model to represent the vibrational density of states (VDoS) and thermodynamic properties of pure substances in pressure–temperature space. We show that this model can be simplified to a vibrational model in which the VDoS is represented by multiple Einstein frequencies without significant loss of accuracy in thermodynamic properties relative to experimental data. The resulting analytical expressions for thermodynamic properties, including the Gibbs energy, are mathematically simple and easily accommodated in existing computational software for making thermodynamic databases. We show for aluminium, platinum, orthoenstatite and forsterite that thermodynamic properties can be represented with comparable accuracy as with Kieffer’s model with the same number of fitting parameters as in the Mie–Grüneisen–Debye model. We demonstrate that the method enables to achieve thermodynamic properties with superior accuracy relative to the Mie–Grüneisen–Debye method. The method is versatile in the sense that it allows incorporating dispersion of Grüneisen parameters. It is possible to extend the formalism to include other physical effects, such as intrinsic anharmonicity in the same way as in vibrational models based on Kieffer’s formalism.     

Pressure dependence of the elastic constants of nonmetamict zircon

The single crystal elastic constants of nonmetamict zircons have been measured as a function of pressure to 12 kb at room temperature and also as a function of temperature between 25 and 300° C at atmospheric pressure. The pressure derivatives of the elastic constants are: C ₁₁=10.78, C ₃₃=5.88, C ₄₄=0.99, C ₆₆=?0.31, C ₁₂=3.24, C ₁₃=6.20. The anomalous negative behaviour of C ₆₆ versus pressure could be associated with a high pressure phase transition. The pressure and temperature derivatives of the isotropic elastic wave velocities and elastic moduli for nonmetamict zircon are calculated from the present single crystal data by the Voigt, Ruess, and Hill approximations and compared with the values of some other oxides and silicates. The pressure derivative of the isotropic adiabatic bulk modulus is relatively high (dK _S/dP=6.50), and the pressure derivative of the shear modulus is relatively low, (dG/dP=0.78), compared to the corresponding values for some other oxides and silicates. The Debye temperature, ?_D, and the high temperature limit of the Grüneisen parameter, γ_Ht, calculated from the elastic constants and their pressure derivatives, agrees well with the Debye temperature and the thermal Grüneisen parameter, γ_th, calculated from the thermal expansion, heat capacity, and compressibility data.     

The hildebrand equation of state for minerals relevant to geophysics

The Hildebrand thermal equation of state (EOS) is revived and applied to minerals appropriate to the earth's interior. The chief virtue of this EOS is that it escapes the necessity of evaluating a Grüneisen parameter at high compression and high temperature. The classical Grüneisen parameter is replaced by the product of two experimentally measured parameters: α, the coefficient of thermal expansivity, and K _T , the isothermal bulk modulus. In order for the Hildebrand EOS to be useful in geophysical conditions it is necessary to show that α K _T is, to a large extent, independent of volume. This can be done directly by experiment, following Yagi, or indirectly using thermodynamic formulae where other measurements are used in place of α K _T . Four such tests are proposed, two of them following tests proposed by Swenson. The result indicates that most, if not all, of the close-packed minerals relevant to geophysics follow the rule that the value of α K _T is to a satisfactory extent independent of compression.     

高温高压下叶蜡石脱水电导率实验

在压力为1.0～4.0 GPa、温度为873～1 223 K下采用Sarltron-1260阻抗/增益-相位阻抗谱分析仪测定了叶蜡石的电导率.实验结果表明,电导率与温度间的关系符合Arrenhius关系式;叶蜡石的脱水引起电导率的突然变化,使电导率急剧上升;脱水前,电导率随着压力增大而减小,其导电机制为电子导电;脱水后,电导率随着压力增大而增大,其导电机制为离子导电.     

P-V-T equation of state of magnesiowüstite (Mg0.6Fe0.4)O

The lattice parameter of magnesiowüstite (Mg_0.6Fe_0.4)O has been measured up to a pressure of 30 GPa and a temperature of 800 K, using an external heated diamond anvil cell and diffraction using X-rays from a synchrotron source. The experiments were conducted under quasi-hydrostatic condition, using neon as a pressure transmitting medium. The experimental P-V-T data were fitted to a thermal-pressure model with the isothermal bulk modulus at room temperature K _T0 = 157 GPa, (?K _TO /?P) _T =4, (?K _T /?T) _P =-2.7(3) × 10^-2 GPa/K, (?K _T /?T) _v =-0.2(2) × 10^-2 GPa/K and the Anderson-Grüneisen parameter δ _T =4.3(5) above the Debye temperature. The data were also fitted to the Mie-Grüneisen thermal equation of state. The least-squares fit yields the Debye temperature θ _DO = 500(20) K, the Grüneisen parameter γ ₀=1.50(5), and the volume dependence q=1.1(5). Both thermal-pressure models give consistent P-V-T relations for magnesiowüstite to 140 GPa and 4000 K. The P-V-T relations for magnesiowüstite were also calculate by using a modified high-temperature Birch-Murnaghan equation of state with a δ _t of 4.3. The results are consistent with those calculated by using the thermal-pressure model and the Mie-Grüneisen relation to 140 GPa and 3000 K.     

In situ impedance spectroscopy on pyrophyllite and CaCO<Subscript>3</Subscript> at high pressure and temperature: phase transformations and kinetics of atomistic transport

In situ impedance spectroscopy in laboratory experiments at high pressure and temperature can provide crucial quantitative information on properties of rock materials at depth as well as on physical and chemical processes occurring in the deep Earth. We developed an experimental setup for in situ electrical impedance measurements in a piston-cylinder apparatus and applied it to study the kinetics of charge carriers and phase transformations in pyrophyllite and CaCO₃ aggregates. From comparison with previous studies, we found that absolute values of electrical conductivity and pressure–temperature conditions for dehydration reactions in pyrophyllite and phase transformations in CaCO₃ can be accurately determined using our setup. Dehydration of pyrophyllite significantly enhances the transport kinetics and the effect is more pronounced under undrained conditions than under drained conditions. When dehydroxylation and decomposition temperatures for pyrophyllite under undrained and drained conditions are combined, they appear independent of pressure rather than increasing with pressure as previously suggested. Electrical conductivity of CaCO₃ varies with impurity content and grain size, and is most likely controlled by diffusion of oxygen along wet grain boundaries. When applied to the Earth, the results on pyrophyllite suggest that the increase in electrical conductivity in rocks that undergo dehydration should be taken into account in interpreting magnetotelluric surveys of regions with anomalously high conductivity found above subducting plates. The results on CaCO₃ indicate that grain boundary transport controls the electrical conductivity in fine-grained calcite rocks; hence calcite mylonites may be detected using magnetotelluric methods. Order–disorder transformations, such as occurring in calcite, possibly affect the physical properties of rocks (e.g., rheology) by changing the kinetics of atomistic transport processes.     

Geochemistry, mineralogy and genesis of pyrophyllite deposits in the Pötürge Region (Malatya, Eastern Turkey)

In the Pötürge (Malatya, Turkey) area pyrophyllite occurrences are common in the shear zones, mostly in the form of lenses along faults. Mineralogical investigations (XRD, FTIR and SEM) revealed that pyrophyllite, kaolinite (dickite) and quartz are present in the form of major phases and muscovite (sericite), kyanite, chlorite, and alunite are only present in the form of minor phases. This study revealed that the existence of the kyanite phase points out to high pressure and temperature conditions which the rocks were underwent. On the other hand, the minerals such as pyrophyllite, kaolinite, and alunite are products of a low degree metamorphism (retrograde). The mineral paragenesis in the pyrophyllite deposits suggests that the formation of minerals took place in two ways: (1) the transformation of kyanite into pyrophyllite and quartz through retrograde metamorphism by a high degree temperature, (2) then pyrophyllite and probably muscovite were transformed into kaolinite and alunite through reactions with relatively low temperature hydrothermal fluids. The geochemical data indicate that during the retrograde metamorphism the elements K, Rb, Sr, Ba, S, and Fe were mobile, the elements Si, Al, P moderately mobile to immobile and the HPS elements (Zr, Ti, and Nb) were immobile. It was shown that the formation of pyrophyllite, kaolinite and alunite was associated with depletion in alkalis, Mg, Fe and enrichment of elements including Sr, Ba, and S. Mineralogical and geochemical data suggest that parent rocks (pre-metamorphism) of the Pötürge pyrophyllite were probably kaolinite, Al-rich clays or bauxites.     

Thermal expansion of single-crystal forsterite to 1023 K by Fizeau interferometry

Using a Fizeau interferometry technique, we have measured the coefficients of linear thermal expansion of single-crystal forsterite (Mg₂SiO₄) along three axial directions to 1023 K during heating and cooling cycles. Overall, the present data are consistent in magnitude (within 1 to 2%) with those previously reported but have less scatter. We used the Grüneisen statistical mechanical approach in analzying the data. The least-squares method was applied to evaluate thermal parameters (?, Q ₀, k and a) in two cases. The expansion coefficients in wider temperature ranges were extrapolated by using the parameters of solution 2 (i.e., solution by fixing ? and k). In contrast to earlier findings, our results show that for forsterite the Grüneisen parameter decreases with temperature, implying that it does not behave too differently from fayalite (Fe₂SiO₄) and periclase (MgO).