Crystal-ring microstructures in Oceanographer Fracture Zone basalts     

David Walker  Stephen E. DeLong  Tsugio Shibata 《Contributions to Mineralogy and Petrology》1980,74(1):1-6

Pillow basalt fragments from the Oceanographer Fracture Zone contain spherical microstructures seen in section as rings of equant microphenocrysts of olivine±plagioclase±augite. They are uniformly 1 mm in diameter and have the same vitreous or crystalline material on the inside and outside. These structures occur in the same sections as vesicles and segregation vesicles and are clearly distinguishable from them.The occurrence of these structures in pillow basalt fragments suggests a mode of formation resulting from pillow basalt extrusion. Mechanical disruption of the partially solidified inner surface of the pillow skin produces a dispersion of cool globules in the pillow interior. Crystals adhere to these tacky globules during continued pillow extrusion in a manner analogous to the formation of armored mud balls.  相似文献   

Abyssal tholeiites from the Oceanographer Fracture Zone   总被引：17，自引：0，他引：17  

David Walker  Tsugio Shibata  Stephen E. DeLong 《Contributions to Mineralogy and Petrology》1979,70(2):111-125

Unusual effects have been discovered in the major element phase relations of basalts from the Oceanographer Fracture Zone (OFZ) which suggest that magma mixing of primitive basalt with the differentiation residue of a previous batch of primitive magma has occurred. These effects include a reversal in mineral crystallization sequence which cannot happen during normal differentiation processes or be explained by any plausible change in physical conditions. This unusual effect is encountered as a result of curvature in composition space of the liquid-line-of-descent equilibria involving olivine, plagioclase, and high-calcium clinopyroxene. Mixing of magmas at different stages of their evolution produces mixtures that do not lie on the curved liquid-line-of-descent. Observation of such anomalous compositions in the OFZ suite supplements accumulating petrographic and trace-element geochemistry evidence that magma mixing is an important petrogenetic process. Mixing of fractionated residual liquids can produce mixtures which are either superheated or supercooled depending on the sense of ‘thermal curvature’ of the liquid-line-of-descent. Both senses are encountered in the tholeiitic system, and this effect may exert a qualitative control on the crystallization texture of the mixture. A comparison of approximately 2,000 abyssal tholeiite compositions to the experimental liquid-line-of-descent reveals that erupted differentiates which would be expected from advanced fractionation are scarce. Just this sort of phenomenon (the ‘perched’ steady state) was proposed by O'Hara (1977) as an earmark of the operation of a continuously fractionating magma chamber into which fresh magma is periodically remixed.  相似文献   

Initial 87Sr/86Sr ratios of plutonic rocks from Japan     

Ken Shibata  Shunso Ishihara 《Contributions to Mineralogy and Petrology》1979,70(4):381-390

Initial ⁸⁷Sr/⁸⁶Sr rations were determined for more than 80 plutonic rocks in Japan. The ⁸⁷Sr/⁸⁶Sr ratios of gabbroic and granitic rocks show no significant difference in plutonic terranes where both rocks occur closely associated, implying a genetic relationship between them (e.g., Green Tuff belt) or reequilibration at deep level (e.g., Ryoke belt). Wherever granitic rocks occur independently from gabbroic rocks, the granites have higher ratios than the gabbros.Initial ⁸⁷Sr/⁸⁶Sr ratios of the granitic rocks are low (<0.706) in Northeast Japan but high (<0.706) in Southwest Japan, the boundary being the Tanakura Tectonic Line. Within Southwest Japan, the ratios are low along the Japan Sea side of the southernmost area. This regional variation is generally correlated with thickness of the continental crust as deduced from the Bouguer anomaly.Initial ⁸⁷Sr/⁸⁶Sr ratios of the granitic rocks vary from 0.7037 to 0.7124. The low group (<0.706) is considered to consist of essentially mantle-derived magmas contaminated by crustal material in lesser but varying degree, because of its geological setting and initial ⁸⁷Sr/⁸⁶Sr values. The high group may have been formed by contamination of a deep-seated magmas by crustal material or by generation of the main part of the magmas within the continental crust. The ratios of individual belts reflect their own history depending upon age and Rb/Sr ratio of the crustal material.Initial ⁸⁷Sr/⁸⁶Sr ratios of granitic rocks are generally low for the magnetite-series but high for the ilmenite-series. Thus, a negative correlation is observed between initial ratios and ³⁴S for most Cretaceous-Paleogene granites. However, Neogene ilmenite-series granites are low in both initial ⁸⁷Sr/⁸⁶Sr and ³⁴S indicating interaction of the granitic magma with young sedimentary rocks enriched in ³²S.  相似文献   

Peridotites from the Mid-Atlantic Ridge at 43° N and their petrogenetic relation to abyssal tholeiites     

Tsugio Shibata  Geoffrey Thompson 《Contributions to Mineralogy and Petrology》1986,93(2):144-159

Whole-rock, major and trace element analyses and microprobe mineral analyses were conducted on serpentinized peridotites recovered from the walls of a MAR (Mid-Atlantic Ridge) 43° N fracture zone. These peridotites are extensively serpentinized; serpentine usually makes up 30–100 vol. percent of the bulk rocks. The relict minerals observed consist mainly of olivine and orthopyroxene with subordinate amounts of clinopyroxene and brown spinel. The range in olivine composition is very limited (Fo_91–92). Orthopyroxene forms large, anhedral crystals with clinopyroxene exsolution lamellae and shows undulose extinction with bent cleavages and lamellae. Broad beam microprobe analyses indicate that the composition range of orthopyroxene is also limited (En_89.1–87.6Fs_8.2-8.0Wo_2.7–4.4; Al₂O₃=1.82–2.64 wt%; Cr₂O₃=0.63–0.88 wt%). Clinopyroxene tends to fringe large orthopyroxene crystals or fills the interstices between them. The Mg/Fe ratios of clinopyroxene are practically constant; however, the Ca/(Ca + Mg + Fe) ratios range from 0.48 to 0.45. The Cr/(Cr+Al) and Mg/(Mg+ Fe²⁺) ratios of brown spinel range from 0.57 to 0.36 and 0.69 to 0.56, respectively. The geothermometers utilizing coexisting spinel lherzolite mineral assemblages suggest that the MAR 43° N peridotites attained equilibrium at temperatures from 1100° to 1250° C.Peridotites recovered from the ocean floor are generally considered to have been subjected to partial melting processes and are regarded as residues left after primary magma was removed. Major element chemistry of the MAR 43° N peridotites are compared with those of the ocean-floor ultramafic tectonites reported previously and used together with those published data to demonstrate that the major element abundances of the oceanfloor peridotites define an average trend which is compatible with removal of primary magma from these peridotites at moderate pressures (10–15 kb). Then, the most primitive abyssal tholeiite glasses could be produced by ca. 10% olivine fractionation of such primary magma. Extensive fractionation of olivine and/or orthopyroxene from picritic liquids which are in equilibrium with the lherzolitic or harzburgitic mantle sources at higher pressures (>20 kb) could not yield the majority of the most primitive abyssal tholeiite glasses.  相似文献   

内蒙古苏尼特地下水氟污染形成机理研究   总被引：4，自引：1，他引：3  

李海霞  罗汉金  赤井纯治  金井章雄  寺崎紘一  横井英纪  吉村尚久 《水文地质工程地质》2008,35(6):107-111

为了研究内蒙古苏尼特地区地下水氟污染机理,本文运用水文地球化学分类方法,从水文地质、水化学特征两方面研究其地下水的水质特征、氟的起源、分布规律及污染形成机理。研究结果发现:高氟地下水的主要水质类型为HCO3—Na型,pH值在7.08～9.38之间,氟浓度与井深有关,即井越浅,氟浓度越高;地下水中氟浓度最高达14.78mg/L,5～9月地下水氟浓度相对增长率在7.8～23.1之间;F-浓度与Li+、Br-相关系数达0.89和0.82,受断层影响的深层地下水中F-浓度几乎与Li+、Br-没有相关关系,这暗示着氟来源于浅部,并受到强烈的蒸发作用影响而使水中的氟浓缩;地质调查发现该地区还有数个萤石矿存在,显微镜分析结果证实表层土壤中普遍存在CaF2,地下水中的氟来自CaF2。高氟地下水存在于潜水层,深部含水层的地下水可供开采。从断层带涌出的水对潜水层有稀释作用。  相似文献   

Particulate-associated potentially harmful elements in urban road dusts in Xi’an,China     

Yongming Han  Junji Cao  Eric S. Posmentier  Kochy Fung  Hui Tian  Zhisheng An 《Applied Geochemistry》2008

Sixty five urban road dust samples were collected from different land use areas of ∼240 km² in Xi’an, China. The concentrations of Ag, As, Cr, Cu, Hg, Pb, Sb and Zn were determined to investigate potentially harmful element (PHE) contamination, distribution and possible sources. In addition, the concentrations in different size fractions were measured to assess their potential impact on human health. The highest concentrations were found in the fraction with particle diameters between 80 μm and 101 μm, the finest particles (<63 μm) were not the most important carriers for Ag, As, Cd, Cr, Cu, Hg, Pb and Zn. The percentages of these elements in particles with diameters less than 63 μm (PM₆₃) and less than 101 μm (PM₁₀₁) were in the range of 7–15%, and 30–55%, respectively. Three main factors influencing element distributions have been identified: (a) industrial activities; (b) prior agricultural land use; and (c) other activities commonly found in urban areas, such as traffic, coal combustion, waste dumping, and building construction/renovation. The highest concentrations were found in industrial areas for As (20 mg kg⁻¹), Cr (853 mg kg⁻¹), Cu (1071 mg kg⁻¹), Pb (3060 mg kg⁻¹) and Zn (2112 mg kg⁻¹), and in previous agricultural areas for Ag and Hg, indicating significant contributions from industrial activities and prior agricultural activities.  相似文献   

Preface to the Special Issue on Carbon Neutrality: Important Roles of Renewable Energies,Carbon Sinks,NETs, and non-CO₂ GHGs     

Junji CAO  Ning ZENG  Yi LIU  Bengang LI  Pengfei HAN 《大气科学进展》2022,39(8):1207-1208

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A self-consistent model of the magnetosphere with centrifugal wind,II     

Shinpei Shibata 《Astrophysics and Space Science》1985,108(2):337-362

In order to construct an axisymmetric model of magnetospheres with centrifugal wind, especially of the type II magnetosphere in Paper I (Shibata and Kaburaki, 1984), we present a numerical iterative scheme, in which a tenuous plasma with conspicuous trans-field motion are treated self-consistently with the electromagnetic field. Since the characteristic equations of the flow are solved, we are free from numerical diffusion terms obscuring the cause of the trans-field motion. The obtained properties of type II magnetosphere are as follows. (1) Plasma particles in fact flow out across the closed magnetic field lines. (2) The centrifugal force is exerted powerfully on the positive particles to form a disk-like structure, and the strong electric force makes the negative particles drift to the disk. (3) There appears the electric field parallel to the magnetic field,E , which is shown to be necessary for the steady wind to exist. Within the range of the model-parameters selected in this study we find two reasons for the appearance ofE : (1) plasma density decreases owing to the centrifugal acceleration, and it becomes insufficient to shieldE ; (2) the plasma with large inertia moves so as to reduce the charge separation, which would be necessary to shieldE .The notation and definitions are the same as in Paper I.  相似文献   

A magnetodynamic mechanism for the heating of emerging magnetic flux tubes and loop flares     

Yutaka Uchida  Kazunari Shibata 《Solar physics》1988,116(2):291-307

A new magnetodynamic model for loop flares is proposed to explain the following observational facts obtained from space during the last solar activity maximum: (i) Blueshifted lines of Ca xix and Fe xxv appear in some cases a minute or so before the initiation of impulsive bursts and relax into the unshifted lines with large width by the time of the onset of impulsive bursts, (ii) the hot source is formed by that time at the top of a loop-like structure, and confined there for a considerable time, and (iii) -ray line enhancement occurs at about the same time as hard X-ray spikes.In our model, the supply of energy to the loop top comes from below the chromosphere immediately before the flare (30 s-1 min before the hard X-ray impulsive bursts) in the form of the relaxing fronts of magnetic twist of opposite sign. These packets are thought to be built up in the process of loop emergence, stored at the footpoints of the loop below the photosphere, and released when the part of the feet floats up further. These released packets of magnetic twist drive the mass in the high chromosphere and transition zone into helical flows with pinch heating, and when these collide at the top of the loop, a very hot region appears there with a violent unwinding of the twists, resulting in the rapid dynamical annihilation of the magnetic energy, . Electrons and ions, raised to medium energies in the pinch at the incidence of the packets to the loop, are accelerated further by the Fermi-I mechanism between the approaching fronts of magnetic twist, and when B is weakened by unwinding they are released towards the chromosphere, and cause simultaneous -ray and hard X-ray bursts.  相似文献   

A monitoring result of polychlorinated biphenyls (PCBs) in deep-sea organisms and sediments off Tohoku during 2012–2014: temporal variation and the relationship with the trophic position     

Naohiko Ohkouchi  H. Shibata  Y. Chikaraishi  H. Nomaki  N. O. Ogawa  T. Nagata  T. Goto  K. Fujikura  H. Kitazato 《Journal of Oceanography》2016,72(4):629-639

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