新疆北部富蕴县沙尔布拉克玻安岩的地球化学特征及构造意义

详细的地球化学研究表明，新疆北部富蕴县沙尔布拉克中泥盆统北塔山组的辉石安山岩具有中等的SiO2含量（52.13%-60.45%)；高MgO(3.91%-9.31%)和相容元素（包括Ni、Cr、Co等）含量，以及高Mg^#和Al2O3／TiO2比值；低TiO2含量（0.21%-0.35%)；同时具有U型稀土元素分布模式；并强烈亏损高场强元素。这些特征均与玻安岩的地球化学特征一致，应属于玻安岩，形成于前弧环境。沙尔布拉克玻安岩的存在表明，古亚洲洋在早－中泥盆世向南发生了洋壳俯冲作用。     

On Two-Dimensional Modeling Of Magnetotelluric Field Data

In this paper, some recent topics on the modeling of magnetotelluric data are introduced. The focus is on the handling of real field data for two-dimensional resistivity modeling. First, the removal of the effects of near surface heterogeneity is reviewed. It covers telluric distortions (phase mixing and static shift) and magnetic distortions using conventional Groom-Bailey type 3D/2D model (three-dimensional local anomaly underlain by regional two-dimensional structure). The extension of a 3D/2D distortion model for multi-site, multi-frequency is a new development. Magnetic distortion seems to be less significant for land observations, but significant for sea floor data, where the regional magnetic field is weak due to seawater. In special cases involving for example, distortion due to topography and bathymetry, explicit removal is possible. There are some schemes proposed for a 3D/3D model (three-dimensional local anomaly underlain by regional three-dimensional structure). Along with the removal of the distortion, it is important to recognize the dimensionality of the dataset prior to modeling. A property using strike estimates for each site is an indicator for dimensionality which is unaffected by local distortion. Mapping the local strike or a rose diagram is an effective visualization of the dimensionality.Two-dimensional inversion is becoming routine. For the fast calculation of derivatives, approximate calculation, reciprocity or conjugate gradient methods are used. In order to incorporate a priori information and to overcome the intrinsic ill-posed nature of the inversion problem, imposing constraints on the model structure is important. A proper tradeoff between the data fit and constraints should be optimized to obtain minimum structures that are required by the field data. However, the choice of constraints is rather subjective and depends on the geological situations. For field data, two-dimensional inversion has limits on modes, area, and period range. Special care must be taken for the structure outside the profile. Two-dimensional inversion incorporating anisotropy is interesting and becoming popular, but the structure may not be unique. Future development in three-dimensional inversion for real datasets should take the above points into consideration.     

Induction of female‐to‐male sex change in a large protogynous fish,Choerodon schoenleinii

Most behavioral studies on hermaphroditic fishes have focused on small‐sized species, which are tractable for research. Although many species of large hermaphroditic fishes are important fishery resources, their proximate mechanisms (visual, chemical and/or behavioral cues) in the social regulation of sex change have not been determined. Determination of these would inform resource management and aquaculture. In order to get closer to understanding the proximate mechanisms underlying the social regulation of female‐to‐male sex change in large hermaphroditic fishes, this study reports situations that induced female‐to‐male sex change in black‐spot tuskfish, Choerodon schoenleinii, a species of large protogynous fish, in massive laboratory tanks. The situations differed in the possibility of male‐to‐female tactile contact and in the group sex ratio, enabling us to infer plausible proximate mechanisms underlying sex change induction. Tactile contact between individuals is suspected to be closely related to the incidence of female‐to‐male sex change in C. schoenleinii. Visual and chemical cues alone may be insufficient to inhibit such sex changes. Male‐to‐female tactile contact may have an important influence on female‐to‐male sex change, i.e., inhibition of this sex change, in this species. The effect of sex ratio of a social group on the incidence of sex change may be due to the relative frequency and intensity of male tactile contact with each female, which may vary with the number of females. In the absence of a dominant male, tactile contact among females may affect the incidence of sex change, as well as determine which individuals change sex.     

Groundmass pargasite in the 1991–1995 dacite of Unzen volcano: phase stability experiments and volcanological implications

Pargasite commonly occurs in the dacitic groundmass of the 1991–1995 eruption products of Unzen volcano. We described the occurrence and chemical compositions of amphibole in the dacite, and also carried out melting experiments to determine the low-pressure stability limit of amphibole in the dacite. The 1991–1995 ejecta of the Unzen volcano show petrographic evidence of magma mixing, such as reverse compositional zoning of plagioclase and amphibole phenocrysts, and we used a groundmass separate as a starting material for the experiments. Reversed experiments show that the maximum temperature for the crystallization of amphibole is 930°C at 196 MPa, 900°C at 98 MPa, and 820°C at 49 MPa. Compared with the experimental results on the Mount St. Helens dacite, present experiments on the Unzen dacitic groundmass show that amphibole is stable to pressures ca. 50 MPa lower at 850°C. Available Fe–Ti oxide thermometry indicates the crystallization temperature of the groundmass of the Unzen dacite to be 880±30°C, suggesting that the groundmass pargasite crystallized at >70 MPa, corresponding to a depth of more than 3 km in the conduit. The chlorine content of the groundmass pargasite is much lower than that of phenocrystic magnesiohornblende in the 1991–1995 dacite of Unzen volcano, indicating that vesiculation/degassing of magma took place before the crystallization of the groundmass pargasite. The present study shows that the magma was water oversaturated and that the degassing of magma along with magma mixing caused crystallization of the groundmass amphibole at depths of more than 3 km in the conduit.     

Audio frequency magneto-telluric survey of Norikura Volcano in central Japan

Norikura Volcano has not been active during the last 10,000 years in spite of the activity of the surrounding volcanic mountains. To study past volcanic activities, geological studies were carried out extensively. However, quite a few geophysical investigations were conducted to contribute to volcanology. Our objective is to detect the present subsurface structure of Norikura Volcano and to define volcanic stratifications. In the vicinity of Norikura Volcano, geothermal fields are still active. Subsurface volcanic rocks in this area have been exposed to geothermal activity and altered. To comprehend volcanic stratifications of Norikura and geothermal activity, we conducted audio frequency magneto-telluric (AMT) surveys around Norikura Volcano. AMT survey is useful in clearly defining the resistivity structure related to volcanic regions. The AMT data were acquired over a frequency range 10 Hz–10 kHz. Decomposition analysis was applied to the tensor impedance data. Subsequently, apparent resistivity and phase data were inverted using a two-dimensional magneto-telluric (MT) inversion and a model of Norikura was derived. The final model manifests that the surface resistors are in agreement with andesite lava or dacite lava. As for the deeper structure, a horizontal conductor is situated above resistive basements. The alteration of the conductor was weak, while basement rocks were strongly altered and/or heated through the thermal activity. The existence of these layers seems to indicate the degree of thermal activity of Norikura Volcano.     

Distribution of ductile deformation around the Main Central Thrust zone at the frontal part of nappe in southeastern Nepal Himalaya

A geological survey and morphological analysis of quartz grains were performed to investigate the distribution of ductile deformation caused by the Himalayan Main Central Thrust (MCT) around Dhankuta, southeastern Nepal. The MCT was mapped as the lithological boundary between the gneiss of the Higher Himalayan Crystalline (HHC) as the hanging wall and the inverted metamorphic sequence of the Lesser Himalayan Sediments (LHS) as the footwall. The MCT was found to truncate various stratigraphic levels of LHS and cuts a map‐scale gentle fold developed in the LHS. Ductile deformation was quantified by fractal dimension between size and perimeter of dynamically recrystallized quartz grains in bedded metaquartzite intercalated in both HHC and LHS. Serrate and polygonal shapes of quartz indicate large and small strain rates, respectively, when the temperature during ductile deformation was assumed to be uniform. A peak of strain rate was found at the lithological boundary with the peak width of ca. 500 m. Such a thin shear zone is favorable for producing frictional heat to promote the inverted metamorphism in LHS.     

Local deformation‐based design of minimal‐disturbance arm damper for retrofitting steel moment‐resisting frames

This paper presents a design approach for seismic rehabilitation of frames having a beam‐collapse mechanism using a technique termed minimal‐disturbance seismic rehabilitation. This technique pursues enhancing the seismic performance of buildings with the intention of improving the continuity of business. It minimizes obstruction of the visual and physical space of building users and the use of heavy construction equipment and work requiring fire permit (welding/cutting). The developed design approach is simple to use. Yet it leads to designs that limit the beams' plastic rotations to allowable values, while minimizing the number of locations where devices are installed and the devise dimensions. Furthermore, the effectiveness of the design approach and the rehabilitation technique is numerically studied through retrofitting a four‐story steel moment‐resisting frame. Copyright © 2017 John Wiley & Sons, Ltd.     

Analytical and centrifuge studies of pile groups in liquefiable soil before and after site remediation

The objectives of this paper are to show practically: (1) the validation of a proposed three-dimensional effective stress analysis for the pile foundations, and (2) the effectiveness of remedial deposits on pile stresses under liquefaction by making comparisons between the results of centrifuge tests and those of the proposed analysis. Two foundation models supported by end-bending piles were studied with improved and unimproved deposits. There exists a good consistency between the numerical and experimental results for excess pore water-pressure ratios ranging from 0 to about 0·9. From the numerical results, the bending moment at the pile top with the improved deposit is about 50 per cent lower than that with the unimproved deposit. However, it was found that the smaller the bending moment develops in the pile with the improved deposit, the larger the compressive and/or tensional axial stresses in the pile. This is due to the predominant excitation of rocking vibration of the foundation. From the analytical and experimental results, it has been found that the remedial method can be a variable means to protect piles from soil liquefaction hazards. However, both axial stress and bending moment produced in piles should be considered in assessing the liquefied seismic capacity of group pile-foundation–structural systems with improved soil deposits. © 1998 John Wiley & Sons, Ltd.     

Public acceptance of the oceanic carbon sequestration

CO₂ ocean sequestration may be an effective option for mitigating global warming. There are risks associated with this process, particularly the local impact on deep-sea environments. Public acceptance is required for the implementation of this technology, even though the impacts have been proven to be trivial. In this study, a questionnaire survey was conducted to find the correlation between public acceptance of CO₂ sequestration and influential factors by covariance structure analysis. In addition, risk communication via the Internet was carried out. These analyses revealed that careful investigation of the target oceanic site and field experiments are important in gaining public acceptance of CO₂ sequestration.     

Height variability from the MIROC – IPCC model for the 20th century compared to that of the TOPEX/POSEIDON altimeter

Planetary waves are key to large-scale dynamical adjustment in the global ocean as they transfer energy from the east to the west side of oceanic basins; they connect the forcing in the ocean interior with the variability at its boundaries; and they change the local heat content, thus coupling oceanic, atmospheric, and biological processes. Planetary waves, mostly of the first baroclinic mode, are observed as distinctive patterns in global time series of sea surface height anomaly (SSHA) and heat storage. The goal of this study is to compare and validate large-scale SSHA signals from coupled ocean-atmosphere general circulation Model for Interdisciplinary Research on Climate (MIROC) with TOPEX/POSEIDON satellite altimeter observations. The last decade of the models’ time series is selected for comparison with the altimeter data. The wave patterns are separated from the meso- and large-scale SSHA signals by digital filters calibrated to select the same spectral bands in both model and altimeter data. The band-wise comparison allows for an assessment of the model skill to simulate the dynamical components of the observed wave field. Comparisons regarding both the seasonal cycle and the Rossby wave field differ significantly among basins. When carried within the same basin, differences can occur between equal latitudes in opposite hemispheres. Furthermore, at some latitudes the MIROC reproduces biannual, annual and semiannual planetary waves with phase speeds and average amplitudes similar to those observed by the altimeter, but with significant differences in phase.