Tourmaline breakdown in a pelitic system: implications for boron cycling through subduction zones

Pressure–temperature conditions of tourmaline breakdown in a metapelite were determined by high-pressure experiments at 700–900°C and 4–6 GPa. These experiments produced an eclogite–facies assemblage of garnet, clinopyroxene, phengite, coesite, kyanite and rare rutile. The modal proportions of tourmaline clearly decreased between 4.5 and 5 GPa at 700°C, between 4 and 4.5 GPa at 800°C, and between 800 and 850°C at 4 GPa, with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable. Decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite, and increasing that of clinopyroxene, garnet and kyanite; the boron content of phengite increases significantly. These changes suggest that, with increasing pressure and temperature, tourmaline reacts with coesite to produce clinopyroxene, garnet, kyanite, and boron-bearing phengite and fluid. Our results suggest that: (1) tourmaline breakdown occurs at lower pressures and temperatures in SiO₂-saturated systems than in SiO₂-undersaturated systems. (2) In even cold subduction zones, subducting sediments should release boron-rich fluids by tourmaline breakdown before reaching depths of 150 km, and (3) even after tourmaline breakdown, a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments.     

Helium isotopes in the Izu Peninsula,Japan: Relation of magma and crustal activity

The relation of magma and crustal activity has been studied from spatial distribution of ³He/⁴He ratios of gas and/or water samples over the Izu Peninsula, where significant crustal deformation associated with seismic swarm activities has been observed since 1970s. The air-corrected values of ³He/⁴He ratios ranged from 3.5 to 8.2 R_A, where R_A is the atmospheric ³He/⁴He ratio = 1.4 × 10^? 6, indicating that helium is mostly of magmatic origin. Among the three pressure sources proposed to explain the crustal deformation, two inflation sources beneath the inland of northeast and the mid east coast of the Izu Peninsula locate in the broad distribution of high ³He/⁴He ratios, which supports relation of magma to the crustal uplift. In contrast, the distribution of ³He/⁴He ratios around the tensile fault assumed in the area of seismic swarms appears not to indicate existence of significant amount of magma below the tensile fault. Alternatively, the results suggest magma below a point several kilometers south of the tensile fault. The seismic swarms are explained either by fluid pressurization of thermal water heated by this magma or by intrusion of magma to the tensile fault moved obliquely from the deep magma reservoir.     

A preliminary analysis of the formation of travertine and travertine cones in the Jifei hot spring,Yunnan, China

The Jifei hot spring emerges in the form of a spring group in the Tibet–Yunnan geothermal zone, southwest of Yunnan Province, China. The temperatures of spring waters range from 35 to 81°C and are mainly of HCO₃–Na·Ca type. The total discharge of the hot spring is about 10 L/s. The spring is characterized by its huge travertine terrace with an area of about 4,000 m² and as many as 18 travertine cones of different sizes. The tallest travertine cone is as high as 7.1 m. The travertine formation and evolution can be divided into three periods: travertine terrace deposition period, travertine cone formation period and death period. The hydrochemical characteristics of the Jifei hot spring was analyzed and compared with a local non-travertine hot spring and six other famous travertine springs. The results indicate that the necessary hydrochemical conditions of travertine and travertine cones deposition in the Jifei area are (1) high concentration of HCO₃ ⁻ and CO₂; (2) about 52.9% deep source CO₂ with significantly high value; (3) very high milliequivalent percentage of HCO₃ ⁻ (97.4%) with not very high milliequivalent percentage of Ca²⁺ (24.4%); and (4) a large saturation index of calcite and aragonite of the hot water.     

Movement of radiocaesium fallout released by the 2011 Fukushima nuclear accident

The moment magnitude (M _w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of ¹³⁴Cs and ¹³⁷Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of ¹³⁴Cs and ¹³⁷Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs.     

Study of simultaneous presence of DD and PP electric fields during the geomagnetic storm of November 7–8, 2004 and resultant TEC variation over the Indian Region

During very intense geomagnetic storm of November 7–8, 2004 simultaneous presence of storm time disturbance dynamo and eastward and westward directed prompt penetration electric fields inferred from the ground based magnetometer data in the 75^° E sector is presented. Magnetometer observations show that, on the whole, average ΔH variation on 8 November remains below the night time level compared to its quiet day variation. A number of upward and downward excursions have been observed between 0130 UT and 0800 UT in the ΔH variation on 8 November. These excursions in ΔH have been attributed to the episodes of eastward and westward prompt penetrating electric fields. Ionospheric response in the equatorial ionization anomaly region along 75^° E has also been studied using the total electron content data recorded at five GPS stations, namely Udaipur, Bengaluru (IISC), Hyderabad (HYDE), Maldives (MALD) and Diego Garcia (DGAR). Observation of markedly suppressed EIA, in conjunction with ΔH variation which was m negative during the daytime on 8 November, indicates the presence of an external field of opposite polarity (the disturbance dynamo electric field) that either undermined, or overshadowed the daytime ambient (eastward) electric field to the extent that the equatorial plasma fountain could not become effective.     

Metabolic activity of pelagic copepods from 5,000 to 7,000 m depth of the western subarctic Pacific,as inferred from electron transfer system (ETS) activity

This study demonstrates reduced electron transfer system (ETS) activity of mixed copepods collected from 5,000 to 7,000 m depths [3.21 ± 1.25 μl O₂ (mg protein)⁻¹ h⁻¹ at 10°C] as compared with mixed copepods from 0 to 200 m depths [5.93 ± 1.66 μl O₂ (mg protein)⁻¹ h⁻¹ at 10°C] of the western subarctic Pacific. At the in situ temperature of 1.5°C, the 5,000–7,000 m ETS data, in terms of wet mass (WM)-specific respiration rates (R), is equivalent to [0.052 ± 0.021 μl O₂ (mg WM)⁻¹ h⁻¹] which is similar to or greater than those reported for selected copepods or mixed mesozooplankton from <5,000 m depth by previous workers.     

Extinction curves expected in young galaxies

We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). We adopt Nozawa et al. (2003) for compositions and size distribution of grains formed in SNe II and PISNe. We find that the extinction curve is quite sensitive to internal metal mixing in supernovae (SNe). The extinction curves predicted from the mixed SNe are dominated by SiO₂ and are characterized by a steep rise from infrared to ultraviolet (UV). The dust from unmixed SNe shows a shallower extinction curve, because of the contribution from large-sized (∼0.1 μm) Si grains. However, the progenitor mass is important in unmixed SNe II: if the progenitor mass is smaller than  ∼20 M_⊙  , the extinction curve is flat in UV; otherwise, the extinction curve rises towards the short wavelength. The extinction curve observed in a high-redshift quasar  ( z = 6.2)  favours the dust production by unmixed SNe II. We also provide some useful observational quantities, so that our model might be compared with future high- z extinction curves.     

A new method for simulation of atmospheric effect on the emergent radiation over non-uniform terrain

For a precise atmospheric correction over the non-uniform terrain in satellite imageries, a numerical method for evaluating the upwelling radiation at the top of the atmosphere bounded by the non-uniform surface is developed as an extended doubling-adding method. The present method enable us to treat quantitatively the case of hazy atmosphere and (or) large albedo of the surface.     

Validation of the Deep Velocity Structure of the Tokachi Basin Based on 3-D Simulation of Long-Period Ground Motions

The construction of 3-D basin velocity structures is ongoing in many regions of Japan. The structure models are constructed mainly for the prediction of long-period ground motions from future large earthquakes. In this paper, we validate the 3-D velocity structure model of the Tokachi basin, a deep sedimentary basin located in eastern Hokkaido, Japan, based on 3-D simulation of long-period (2–20 s) ground motions from three nearby intermediate-depth earthquakes; this model was constructed by the National Research Institute for Earth Science and Disaster Prevention (NIED). We make comparisons between the observed and synthetic long-period ground motions for the basin-induced surface waves as well as the direct S-wave. We also try to revise the 3-D velocity structure in the western part of the Tokachi basin based on 1-D velocity structures estimated using long-period S-wave modeling and the microtremor survey method. We then perform the 3-D simulation again to validate the revised model. Based on quantitative comparisons of the long-period ground motions from these simulations with those observed, we conclude that the NIED and revised velocity structure models are generally good at the central basin sites, but that both models require modification at the basin edges to explain the details of the observed basin-induced surface waves.