In situ strength measurements on natural upper-mantle minerals

Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700°C, we examined rheological properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential stress of 4–6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600°C. Neither orthopyroxene nor spinel shows complete stress relaxation, but both retain some stress even at 700°C. The strength of the minerals decreases in the order of chromian-spinel ≈ orthopyroxene > olivine for these conditions. This order of strength is consistent with the residual pressure of fluid inclusions in mantle xenoliths.     

Evapotranspiration from citrus trees growing in sandy soilunder drip irrigation with saline water

An experiment on evapotranspiration from citrus trees under irrigation with saline waterwas carried out for 4 months. Two lysimeters planted with a citrus tree in the green house wereused. One lysimeter was irrigated with saline water (NaCl and CaCl2 of 2000 mg/L equivalence,EC = 3.8 dS/m, SAR = 5.9) and the other was irrigated with freshwater using drip irrigation. Theapplied irrigation water was 1.2 times that of the evapotranspiration on the previous day.Evapotranspiration was calculated as the change in lysimeter weight recorded every 30 minutes.The lysimeters were filled with soil with 95.8% sand. The results of the experiment were as follows.(i) The evapotranspiration from citrus tree was reduced after irrigation with saline water. Theevapotranspiration returns to normal after leaching. However it takes months to exhaust the saltfrom the tree. ( ii ) To estimate the impact of irrigation with saline water on the evapotranspirationfrom citrus trees, the reduction coefficient due to salt stress (Ks) was used in this experiment.Evapotranspiration under irrigation with saline water (ETs) can be calculated from evapotranspira-tion under irrigation with freshwater (ET) by the equation ETs = Ks× ET. Ks can be expressed as afunction of ECsw. (iii) The critical soil-water electrical conductivity (ECsw) is 9.5 dS/m, beyondwhich adverse effects on evapotranspiration begin to appear. If ECsw can be controlled at below9.5 dS/m, saline water can be safely used for irrigation.     

Interpretation of charging on fracture or frictional slip surface of rocks

Fracturing and frictional sliding of quartz and granite under dry condition generates fractoluminescence, charged particle emission and electromagnetic radiation. Various kinds of experiments indicate that surface charge density on fracture or frictional slip surface of quartz and granite is 10⁻⁴ to 10⁻² C/m² which is larger than bound charges induced by the disappearance of piezoelectricity due to the release of stress. Hole and electron trapping centers, which is found in semiconductor devices with the Si–SiO₂ system, are causes of surface charging on fracture or frictional slip surface of quartz crystal. The quantity of the surface charge is enough to cause corona discharge that can generate earthquake lights. The mechanism considering the hole and electron trapping centers has a probability to explain why non-piezoelectric minerals or rocks generate electromagnetic phenomena. It can be one of origins of seismo-electromagnetic phenomena (SEP).     

Temperature and pH Dependence of Some Metals Leaching from Fly Ash of Municipal Solid Waste

Abstract. Municipal solid waste combustion leads to concentration of various metals in the solid residue (fly ash) remaining after combustion. These metals pose serious environmental hazard and require proper handling and monitoring in order to control their harmful effects. Leachability of some metals from fly ash was examined in fly ash and Milli-Q water mixture (liquid-to-solid ratio, 100) under various temperature and pH conditions in the laboratory. The leaching experiments conducted for 24 hours showed that pH was generally more important than temperature in controlling the amount of metals leached out of the fly ash. However, at a given pH, rise in temperature led to different degree of (usually one to two fold) enhanced or reduced leaching of metals. Owing to amphoteric nature of oxides of Al, Cr, Pb and Zn, these metals often yielded typical pattern of increase and decrease in their concentrations with change in pH. The extent of leaching of Cr and Pb in our experiments suggests that decrease of pH to acidic range in the case of Pb and to neutral to acidic range for Cr over a long period of storage of fly ash at solid waste dumping site may facilitate leaching of these metals from fly ash, leading to contamination of groundwater to the level that exceeds beyond the level permitted by the environmental laws.     

Authigenic rhodochrosite from a gas hydrate-bearing structure in Lake Baikal

International Journal of Earth Sciences - Early diagenetic carbonates are rare in Lake Baikal. Siderite (Fe carbonate) concretions in the sediments were discovered only recently. Here, we discuss...     

Reactions to define the biotite isograd in the Ryoke metamorphic belt,Kii Peninsula,Japan

Two types of biotite isograd are defined in the low-grade metamorphism of the Wazuka area, a Ryoke metamorphic terrain in the Kii Peninsula, Japan. The first, BI₁, is defined by the reaction of chlorite+K-feldspar= biotite+muscovite+quartz+H₂O that took place in psammitic rocks, and the second, BI₂, by the continuous reaction between muscovite, chlorite, biotite and quartz in pelitic rocks. The Fe/Mg ratios of the host rocks do not significantly affect the reactions. From the paragenesis of pelitic and psammitic metamorphic rocks, the following mineral zones were established for this low-pressure regional metamorphic terrain: chlorite, transitional, chlorite-biotite, biotite, and sillimanite. The celadonite content of muscovite solid solution in pelitic rocks decreases systematically with the grade of metamorphism from 38% in the chlorite zone to 11% in the biotite zone. Low pressure does not prohibit muscovite from showing the progressive change of composition, if only rocks with appropriate paragenesis are chosen. A qualitative phase diagram of the AKF system relevant to biotite formation suggests that the higher the pressure of metamorphism, the higher the celadonite content of muscovite at BI₁, which is confirmed by comparing the muscovites from the Barrovian and Ryoke metamorphism.     

Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels

A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi-orbit phases are used as a data set and are inverted by using 3-D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area.