共查询到19条相似文献，搜索用时 180 毫秒
1.
橄榄石和辉石以及它们的高压相是地幔转换带主要矿物,系统研究橄榄石和辉石在转换带底部温度和压力条件下相变的差异是认识660km地震不连续面位置和形态的关键．本文使用多面砧压机开展了橄榄石和顽火辉石在压力为21．3～24．4GPa,温度为1600℃的相变实验研究．地幔转换带底部,橄榄石和顽火辉石相变主要的差异在于钙钛矿出现的压力不同．在橄榄石体系中,后尖晶石相分解发生在23．8GPa,与660km不连续面具有很好的对应关系;而在顽火辉石体系中,钙钛矿出现的压力小于23GPa．研究结果表明,橄榄石后尖晶石相变与辉石中钙钛矿的出现之间有约0．5—1GPa压力差．因此,在受大洋俯冲带影响地区（例如中国东部）,辉石体系中发生的秋本石（钛铁矿）．钙钛矿的相变能够合理解释660km地震不连续面向上的起伏或分裂． 相似文献
2.
3.
本文研究了橄榄石原位相变实验中加载、加热路径上的相变及其对确定相变动力学参数的影响.利用文献［1］所给出的退火后先加温后加压,且相对低温条件下实验结果确定出的Ni2SiO4橄榄石相变动力学参数,计算了加载、加热路径上所发生的相变对确定成核率、长大率及相变体积分数的影响.结果表明,退火后先加压后加温,且相对高温条件下的实验数据受到加热路径上成核的影响.根据这样的实验数据得到的成核率会明显高于实际温压条件下的成核率.尤其是当多数实验都是高温实验时,根据这些成核率数据所确定的成核率参数会严重偏离其真值,从而严重影响对俯冲带颗粒粒度及俯冲带流变结构的计算.尽管目前有很多关于Mg2SiO4橄榄石长大率的实验数据,也有通过对挤碰物理图像的分析对(Mg0.89Fe0.11)2SiO4橄榄石成核率的估算,但只有文献［2］通过退火后先加压后加温的原位实验得到了Mg2SiO4橄榄石的相变成核率,且属于高温实验.根据本文的研究结果,我们认为亟需补充退火后先加温后加压或相对低温的实验数据以得到正确的地幔橄榄石成核率参数. 相似文献
4.
0.4～5.0GPa和室温～500℃下NaCl溶液的电导率 总被引：2，自引：0，他引：2
NaCl-H_2O体系是地质上最基本的二元系.对高压(>0.5 GPa)下NaCl溶液电导率测量很少.测量了0.4～5.0 GPa和室温～500℃时 0.01 mol/L NaCl溶液的电导率.结果表明,在 0.4 GPa下,0.01 mol/L NaCl溶液的电导率为 Quist和Marshall(1968)的结果吻合的较好.NaCl溶液的电导率随温度升高而增大,当压力≤1.5 GPa时,随压力升高变化很小.当压力在 1.5 GPa以上时,NaCl溶液的电导率随压力升高迅速增大.高压下电导率随压力的迅速增大可能在许多地质过程(如热液条件下的矿床形成)以及其他领域上都具有重要意义. 相似文献
5.
岩石相变关系对限定地球内部物质成分和动力学关系有着重要意义.利用光探针在14~39 GPa压力区间对热压烧结的辉长岩样品进行了冲击波加载实验.从16 GPa开始,D-u线斜率发生明显变化,说明样品内发生了相变.利用原始的Hugoniot曲线结合地震波状态方程（Seismic Equation of State）得到了Birch-Murnaghan型的等熵压缩线和相变能.结合前人的实验结果,得到了辉长岩的Grü neisen参数γ0,约为2.3.计算得到相变后的矿物集合体在零压下的密度为3.41 g·cm-3.根据以上参数分析得出,在此压力段辉长岩相变主要由长石的分解反应和石英的高压相变控制. 相似文献
6.
7.
在压力4.0到17.5GPa、温度1200℃到1400℃范围,研究了模拟地幔岩成分中的辉石-石榴子石相转变。相转变大多出现在14～16GPa压力范围,单相铝亏损的石榴子石(镁铁榴石)在16GPa压力以上变得稳定。根据本实验和其他最近实验资料计算了地幔岩的矿物组合、密度、地震波速随深度的变化。所得到的密度和地震波速度剖面在550Km深度范围和根据地震观测所建立的模型相吻合。如果证实在550km到650km之间存在有一高密度、高速度梯度带确定,则可能表明镁铁榴石有新的相转变和或存在某种程度的化学不均匀性。 相似文献
8.
本文利用林伍德石、钙钛矿两种矿物在不同差应力下随温度变化的蠕变曲线,通过约束温度条件和板块俯冲引起的弹性应变率,得到了俯冲带670 km深度可能的应力范围. 结果显示,在俯冲带670 km深度基于林伍德石蠕变得到应力大小可能超过100 MPa,而相变为钙钛矿后仅为0.1~10 MPa. 通过分析认为钙钛矿的Si扩散引起的快速应变率使得670 km更深深度的俯冲带无法支持较大的应力,可能是下地幔地震终止的原因,而不需要考虑亚稳态相变导致反裂隙断层的消失或林伍德石分解后超塑性等影响. 相似文献
9.
10.
2.0 GPa块状斜长角闪岩部分熔融--时间和温度的影响 总被引：1，自引：0，他引：1
利用多顶砧压机, 以青藏高原北喜马拉雅构造带的天然斜长角闪岩为样品, 在2.0 GPa, 800～1000℃条件下进行了两个系列的块状样品脱水部分熔融实验: (1) 保持压力p = 2.0 GPa, 加热时间t = 12 h不变, 改变温度(800℃～1000℃)的实验; (2) 保持压力p = 2.0 GPa, 温度T = 850℃不变, 改变加热时间(12～200 h)的实验. 结果表明, 2.0 GPa, 加热12 h的条件下, 随温度升高, 斜长角闪岩中依次生成了石榴石、熔体和单斜辉石, 熔体的成分呈英云闪长质-花岗闪长质-英云闪长质的演化趋势. 2.0 GPa, 850℃条件下, 随加热时间增加, 斜长角闪岩中依次生成了石榴石、熔体和单斜辉石, 熔体的成分由英云闪长质向花岗闪长质演化.当块状岩石样品中熔体体积百分比的含量达到5%时, 熔体已经相互连通.温度大于850℃的条件下生成的熔体其粘度在104 Pas量级, 已经满足了在地质时间尺度上熔体分凝形成岩浆的粘度要求. 因此, 可以认为在增厚地壳的下部, 斜长角闪岩的脱水部分熔融可以形成英云闪长质-花岗质岩浆. 相似文献
11.
High-pressure polymorphs of olivine and enstatite are major constituent minerals in the mantle transition zone(MTZ).The phase transformations of olivine and enstatite at pressure and temperature conditions corresponding to the lower part of the MTZ are import for understanding the nature of the 660 km seismic discontinuity.In this study,we determine phase transformations of olivine(MgSi2O4) and enstatite(MgSiO3) systematiclly at pressures between 21.3 and 24.4 GPa and at a constant temperature of 1600℃.The most profound discrepancy between olivine and enstatite phase transformation is the occurency of perovskite.In the olivine system,the post-spinel transformation occures at 23.8 GPa,corresponding to a depth of 660 km.In contrast,perovskite appears at 23 GPa(640 km) in the enstatite system.The ~1 GPa gap could explain the uplifting and/or splitting of the 660 km seismic discountinuity under eastern China. 相似文献
12.
Experiments on MgSiO3 enstatite were conducted in the pressure range from 13 to 18 GPa under hydrous conditions in order to clarify the effect of water on the melting phase relations of enstatite at pressures corresponding to the Earth’s mantle transition zone. In some previous experiments [Geol. Soc. Am. Bull. 79 (1968) 1685; Phys. Earth Planet. Inter. 85 (1994) 237], incongruent melting behavior to form Mg2SiO4 forsterite and SiO2 enriched liquid up to 5 GPa was observed, and congruent melting behavior at pressures up to 12 GPa was observed. Under hydrous conditions, we found that the melting reaction changes from congruent to incongruent at around 13.5 GPa. Liquid formed above 13.5 GPa is enriched in MgO component relative to MgSiO3 because it coexists with stishovite (SiO2). Moreover, the solidus temperature decreases drastically at around 13.5 GPa, in unison with the change in the melting reaction. The solidus temperature is about 1400 °C at 13 GPa, but approximately 900 °C at 15 GPa. Our results show that the liquidus phase changes from clinoenstatite to stishovite with increasing pressure and water content above 13.5 GPa. MgSiO3 enstatite is one of the major constituent minerals in the Earth’s mantle, and it is expected that MgO-enriched liquid will be generated in the transition zone if water is present. 相似文献
13.
Tetsuya Komabayashi Soichi Omori Shigenori Maruyama 《Physics of the Earth and Planetary Interiors》2005,153(4):191-209
Fluid-undersaturated experiments were conducted to determine the phase relations in the simplified peridotite system MgO-SiO2-H2O (MSH) at 11.0-14.5 GPa and 800-1400 °C. Stability relations of dense hydrous magnesium silicates (DHMSs) under fluid-undersaturated conditions were experimentally examined. From the fluid-absent experimental results, we retrieved thermodynamic data for clinohumite, phase A, phase E, and hydrous wadsleyite, consistent with the published data set for dry mantle minerals. With this new data set, we have calculated phase equilibria in the MSH system including dehydration reactions. The dehydration reactions calculated with lower water activities of 0.68-0.60 match the fluid-present experiments of this study above 11.0 GPa and 1000 °C, indicating that considerable amounts of silicate component were dissolved into the fluid phase. The calculated phase equilibria illustrate the stability of the post-antigorite phase A-bearing assemblages. In the cold subducting slab peridotite, phase A + enstatite assemblage survives into the transition zone, whereas phase A + forsterite + enstatite assemblage forms hydrous wadsleyite at a much shallower depth of about 360-km. The slab is subducted with no dehydration reactions occurring when entering the transition zone. The phase equilibria also show the high temperature stability of phase E. Phase E is stable up to 1200 °C at 13.5 GPa, a plausible condition in the mantle of relatively low temperature, i.e., beneath subduction zones. Phase E is a possible water reservoir in the mantle as well as wadsleyite and ringwoodite. 相似文献
14.
YingXing Guo DuoJun Wang YaoLin Shi YongSheng Zhou YongSheng Dong Cai Li 《中国科学:地球科学(英文版)》2014,57(9):2071-2078
The electrical conductivity of Tibetan eclogite was investigated at pressures of 1.5–3.5 GPa and temperatures of 500–803 K using impedance spectroscopy within a frequency range of 10-1–106 Hz. The electrical conductivity of eclogite increases with increasing temperature(which can be approximated by the Arrhenius equation), and is weakly affected by pressure. At each tested pressure, the electrical conductivity is weakly temperature dependent below ~650 K and more strongly temperature dependent above ~650 K. The calculated activation energies and volumes are 44±1 kJ/mol and-0.6±0.1 cm3/mol for low temperatures and 97±3 kJ/mol and-1.2±0.2 cm3/mol for high temperatures, respectively. When applied to the depth range of 45–100 km in Tibet, the laboratory data give conductivities on the order of 10-1.5–10-4.5 S/m, within the range of geophysical conductivity profiles. 相似文献
15.
Tadao Nishiyama Hibiki Eguchi Dai Shiosaki Akira Yoshiasa Nobutatsu Mochizuki Yasushi Mori Kazumasa Sugiyama Hiroshi Arima Kunio Yubuta 《Island Arc》2021,30(1):e12382
Spinifex-like textured metaperidotites from the Higo Metamorphic Rocks (HMR), west-central Kyushu, Japan, may be formed by high-pressure dehydration of antigorite, and may indicate deep subduction of serpentinite reaching a pressure–temperature condition of 1.6 GPa and 740–750 °C. Three rock types have been identified based on mineral assemblage and rock texture: Type I (L) consisting of medium-grained (1–5 cm long) olivine + enstatite + chromite ±tremolite with secondary talc and anthophyllite that occurs in low-grade metamorphic rocks of the biotite zone, Type I (H) of coarse-grained (up to 10 cm long) olivine + enstatite (with clinoenstatite lamella) + chromite ±tremolite with secondary talc that occurs in high-grade metamorphic rocks of the garnet-cordierite zone, and Type II composed of Al-spinel + chlorite + olivine + apatite + ilmenite with minor sodic gedrite in the garnet-cordierite zone together with Type I (H). Olivines in all rock types are mostly serpentinized during exhumation. The chromite-olivine thermometer gives 560–690 °C for Type I (L) rocks, and the spinel-olivine thermometer gives 610–740 °C for Type II rocks. The peak metamorphic pressure will be higher than 1.6 GPa based on the location of the experimentally determined invariant point (P = 1.6 GPa and T = 670 °C) of antigorite + forsterite + enstatite + talc + H2O. This estimate is consistent with the occurrence of chlorite in Type II rocks, which is stable up to 890 °C at 2.0 GPa. The spinifex-like textured metaperidotites occur as small bodies in the low P/T type gneisses, implying tectonic juxtaposition of them probably during exhumation of the HMR. Recent findings of medium pressure (0.9–1.2 GPa) granulites and gneisses from the HMR may indicate that the HMR has a deep root into the wedge mantle from which the spinifex-like textured metaperidotites have derived. 相似文献
16.
Yousheng Xu Hongsen Xie Jie Guo Haifei Zheng Yueming Zhang Maoshuang Song 《中国科学D辑(英文版)》1997,40(4):398-402
NaCI-H2O is the most fundamental ternary system in geology. Until now, the measurements of electrical conductivity of NaCl solutions
are still little at high pressures (> O.5 GPa) We measured the conductivity of 0.01 m NaCl solution at 0.4–5.0 GPa and 25-500°C.
The results are consistent with that of Quist and Marshall (1968) at 0.4 GPa. The conductivity of NaCl solution increases
with increasing temperature. The results also show that the conductivity of NaCl solution changes little with increasing pressure
below 1.5 GPa and changes rapidly with increasing pressure above 1.5 GPa. The rapid increase of the conductivity of NaCl solution
may play an important role in many geological processes (such as the genesis of ore deposits under hydrothermal condition)
and other fields.
Project supported by the National Natural Science Foundation of China. 相似文献
17.
The melting curve of forsterite has been studied by static experiment up to a pressure of 15 GPa. Forsterite melts congruently at least up to 12.7 GPa. The congruent melting temperature is expressed by the Kraut-Kennedy equation in the following form: Tm(K)=2163 (1+3.0(V0 ? V)/V0), where the volume change with pressure was calculated by the Birch-Managhan equation of state with the isothermal bulk modulus K0 = 125.4 GPa and its pressure derivative K′ = 5.33. The triple point of forsterite-β-Mg2SiO4-liquid will be located at about 2600°C and 20 GPa, assuming that congruent melting persists up to the limit of the stability field of forsterite. The extrapolation of the previous melting data on enstatite and periclase indicates that the eutectic composition of the forsterite-enstatite system should shift toward the forsterite component with increasing pressure, and there is a possibility of incongruent melting of forsterite into periclase and liquid at higher pressure, although no evidence on incongruent melting has been obtained in the present experiment. 相似文献
18.
Christian Liebske Bettina Schmickler Hidenori Terasaki Brent T. Poe Akio Suzuki Ken-ichi Funakoshi Ryota Ando David C. Rubie 《Earth and Planetary Science Letters》2005,240(3-4):589-604
The viscosity of synthetic peridotite liquid has been investigated at high pressures using in-situ falling sphere viscometry by combining a multi-anvil technique with synchrotron radiation. We used a newly designed capsule containing a small recessed reservoir outside of the hot spot of the heater, in which a viscosity marker sphere is embedded in a forsterite + enstatite mixture having a higher solidus temperature than the peridotite. This experimental setup prevents spheres from falling before a stable temperature above the liquidus is established and thus avoids difficulties in evaluating viscosities from velocities of spheres falling through a partially molten sample.
Experiments have been performed between 2.8 and 13 GPa at temperatures ranging from 2043 to 2523 K. Measured viscosities range from 0.019 (± 0.004) to 0.13 (± 0.02) Pa s. At constant temperature, viscosity increases with increasing pressure up to 8.5 GPa but then decreases between 8.5 and 13 GPa. The change in the pressure dependence of viscosity is likely associated with structural changes of the liquid that occur upon compression. By combining our results with recently published 0.1 MPa peridotite liquid viscosities [D.B. Dingwell, C. Courtial, D. Giordano, A. Nichols, Viscosity of peridotite liquid, Earth Planet. Sci. Lett. 226 (2004) 127–138.], the experimental data can be described by a non-Arrhenian, empirical Vogel-Fulcher-Tamman equation, which has been modified by adding a term to account for the observed pressure dependence of viscosity. This equation reproduces measured viscosities to within 0.08 log10-units on average. We use this model to calculate viscosities of a peridotitic magma ocean along a liquid adiabat to a depth of 400 km and discuss possible effects on viscosity at greater pressures and temperatures than experimentally investigated. 相似文献
19.
R.L. Stocker 《Physics of the Earth and Planetary Interiors》1978,17(3):p34-p40
Oxygen partial pressure influences the electrical conductivity of enstatite because it affects the point-defect concentrations in enstatite. The behavior of the defect concentrations with PO2 are obtained for open and partially closed conditions. On the basis of the defect variations, models for the effect of oxygen pressure on the conductivity can be constructed. The first-order models, which assume one defect type transporting all the charge, predict log(PO2) vs. log(conductivity) slopes that are not in agreement with slopes derived from measurements on natural single crystals of enstatite. The disagreement could result from: (1) more defect species being present than the assumed charge-neutrality condition gives, or (2) the charge is transported by two or more defect types. The data suggesting the latter is the cause of the disagreement, and hence the experimentally derived activation energies must be treated carefully. 相似文献