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
Before the 1944 Tonankai earthquake along the Nankai Trough, seismic activity increased in the shallow depths, and then the activity gradually migrated downwards. When it reached its limit (a depth of approximatelty 70 km), the main shock occurred. Several deep earthquakes, including one ofM5.3, occurred several months prior to the Tonankai earthquake. A similar downward migration pattern also can be recognized regarding the 1952 Tokachi-oki earthquake. In this case the deepest earthquakes reached about 400 km. This may be one of the intermediate-term precursory phenomena of great thrusttype earthquakes in subduction zones. Recent observations in the Tokai district along the Suruga Trough, where a large earthquake is expected to occur in the future, suggest a similar downward migration pattern in the land area. 相似文献
1 IntroductionSalinization is one of the major problems in arid and semi-arid regions in relation to land use and in particular to agricultural production[1]. Excessive salinity leads to toxicity in crops and reduction of the availability of water to crops, by reducing the osmotic potential of the soil solution[2]. Movement of soil water induces solute transport, and solutes are transferred towards the ground surface by the upward soil-water movement caused by evaporation, resulting in an accu… 相似文献
The observed microfracturing before faulting in rocks provides a basis for a physical model for the internal friction and the cohesive stress of the Coulomb criterion. Based on recent experimental results in the literature, the applicability of the Coulomb criterion is reexamined. The pressure dependence of strength of brittle rocks can be predicted approximately by the Coulomb criterion using measured values of sliding friction, except for a low-pressure region for certain rocks and near the brittle-ductile transition pressure. Deviation at low pressure seems to be explained either by the effect of cracked state or by different fracture mechanisms at low confining pressures, and deviation near the transition pressure is attributed to the increase of local yielding or fracturing before faulting. 相似文献
Coupled 186Os/188Os and 187Os/188Os enrichments of plume-derived lavas have been suggested to reflect contributions of materials from the outer core (Brandon et al., 1998). This hypothesis is based on the assumption that the Earth’s liquid outer core has high Pt/Os and slightly high Re/Os ratios as a result of the crystallization of the solid inner core, and shows coupled enrichments in the 186Os/188Os and 187Os/188Os ratios, reflecting the decay of 190Pt and 187Re to 186Os and 187Os, respectively. Partitioning experiments of Pt-Re-Os between solid and liquid metal were performed at 5-20 GPa and 1250-1400 °C, to examine the effects of pressure in the Fe-Ni-S system. The ratios (DOs/DPt, DOs/DRe) of measured partition coefficients of Pt, Re and Os are almost constant with increasing pressure. DOs/DPt increases significantly, whereas DOs/DRe decreases, with increasing sulphur content in the liquid metal. On the basis of the present experimental results, it is unlikely that the required Pt-Re-Os fractionation is generated during inner core crystallization, assuming that the light element in the Earth’s core is sulphur. 相似文献
The origin of the Earth's ocean has been discussed on the basis of deuterium/hydrogen ratios (D/H) of several sources of water in the Solar System. The average D/H of carbonaceous chondrites (CC's) is known to be close to the current D/H of the Earth's ocean, while those of comets and the solar nebula are larger by about a factor of two and smaller by about a factor of seven, respectively, than that of the Earth's ocean. Thus, the main source of the Earth's ocean has been thought to be CC's or adequate mixing of comets and the solar nebula. However, those conclusions are correct only if D/H of water on the Earth has remained unchanged for the past 4.5 Gyr. In this paper, we investigate evolution of D/H in the ocean in the case that the early Earth had a hydrogen-rich atmosphere, the existence of which is predicted by recent theories of planet formation no matter whether the nebula remains or not. Then we show that D/H in the ocean increases by a factor of 2-9, which is caused by the mass fractionation during atmospheric hydrogen loss, followed by deuterium exchange between hydrogen gas and water vapor during ocean formation. This result suggests that the apparent similarity in D/H of water between CC's and the current Earth's ocean does not necessarily support the CC's origin of water and that the apparent discrepancy in D/H is not a good reason for excluding the nebular origin of water. 相似文献
A new experimental setup for simultaneous P-wave velocity (VP) and density (ρ) measurements for liquid alloys is developed using ultrasonic and X-ray absorption methods combined with X-ray tomography at high pressures and high temperatures. The new setup allows us to directly determine adiabatic bulk moduli (KS) and to discuss the correlation between the VP and ρ of the liquid sample. We measured VP and ρ of liquid Ni68S32 up to 5.6 GPa and 1045 K using this technique. The effect of pressure on the VP and ρ values of liquid Ni68S32 is similar to that of liquid Fe57S43. (Both compositions correspond to near-eutectic ones.) The obtained KS values are well fitted to the finite strain equation with a value (KS at ambient pressure) of 31.1 GPa and a dKS/dP value of 8.44. The measured VP was found to increase linearly with increasing ρ, as approximated by the relationship: VP [m/s] = 1.29 ρ [kg/m3] – 5726, suggesting that liquid Ni–S follows an empirical linear relationship, Birch's law. The dVP/dρ slope is similar between Ni68S32 and Fe57S43 liquids, while the VP–ρ plot of liquid Ni–S is markedly different from that of liquid Fe–S, which indicates that the effect of Ni on Birch's law is important for understanding the VP–ρ relation of planetary and Moon's molten cores. 相似文献
The temperature distribution at depth is a key variable when assessing the potential of a supercritical geothermal resource as well as a conventional geothermal resource. Data-driven estimation by a machine-learning approach is a promising way to estimate temperature distributions at depth in geothermal fields. In this study, we developed two methodologies—one based on Bayesian estimation and the other on neural networks—to estimate temperature distributions in geothermal fields. These methodologies can be used to supplement existing temperature logs, by estimating temperature distributions in unexplored regions of the subsurface, based on electrical resistivity data, observed geological/mineralogical boundaries, and microseismic observations. We evaluated the accuracy and characteristics of these methodologies using a numerical model of the Kakkonda geothermal field, Japan, where a temperature above 500 °C was observed below a depth of about 3.7 km. When using geological and geophysical knowledge as prior information for the machine learning methods, the results demonstrate that the approaches can provide subsurface temperature estimates that are consistent with the temperature distribution given by the numerical model. Using a numerical model as a benchmark helps to understand the characteristics of the machine learning approaches and may help to identify ways of improving these methods.
