Magmatic unmixing in spinel from late Precambrian concentrically-zoned mafic–ultramafic intrusions, Eastern Desert, Egypt     

Ahmed Hassan Ahmed  Hassan Mohamed Helmy  Shoji Arai  Masako Yoshikawa 《Lithos》2008,104(1-4):85-98

Spinel is widespread in the ultramafic core rocks of zoned late Precambrian mafic–ultramafic complexes from the Eastern Desert of Egypt. These complexes; Gabbro Akarem, Genina Gharbia and Abu Hamamid are Precambrian analogues of Alaskan-type complexes, they are not metamorphosed although weakly altered. Each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin. Silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma. Relatively high Cr₂O₃ contents are recorded in pyroxenes (up to 1.1 wt.%) and amphiboles (up to 1.4 wt.%) from the three plutons. The chrome spinel crystallized at different stages of melt evolution; as early cumulus inclusions in olivine, inclusions in pyroxenes and amphiboles and late-magmatic intercumulus phase. The intercumulus chrome spinel is homogenous with narrow-range of chemical composition, mainly Fe³⁺-rich spinel. Spinel inclusions in clinopyroxene and amphibole reveal a wide range of Al (27–44 wt.% Al₂O₃) and Mg (6–13 wt.% MgO) contents and are commonly zoned. The different chemistries of those spinels reflect various stages of melt evolution and re-equilibration with the host minerals. The early cumulus chrome spinel reveals a complex unmixing structures and compositions. Three types of unmixed spinels are recognized; crystallographically oriented, irregular and complete separation. Unmixing products are Al-rich (Type I) and Fe³⁺-rich (Type II) spinels with an extensive solid solution between the two end members. The compositions of the unmixed spinels define a miscibility gap with respect to Cr–Al–Fe³⁺, extending from the Fe³⁺–Al join towards the Cr corner. Spinel unmixing occurs in response to cooling and the increase in oxidation state. The chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products. Causes of spinel unmixing during late-magmatic stage are analogous to those in metamorphosed complexes. The chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations. Spinels from oxidized magmas are likely to re-equilibrate during cooling and are not good tools for genetic considerations.  相似文献   

Compositional variations in spinel-hosted pargasite inclusions in the olivine-rich rock from the oceanic crust–mantle boundary zone     

Akihiro Tamura  Tomoaki Morishita  Satoko Ishimaru  Kaori Hara  Alessio Sanfilippo  Shoji Arai 《Contributions to Mineralogy and Petrology》2016,171(5):39

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Peridotite xenoliths from the Shiribeshi Seamount,Japan Sea: insights into mantle processes in a back-arc basin     

Yuji Ichiyama  Tomoaki Morishita  Akihiro Tamura  Shoji Arai 《Contributions to Mineralogy and Petrology》2016,171(10):86

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Influence of non-thermal plasma after-treatment technology on diesel engine particulate matter composition and NOx concentration     

M. Babaie  T. Kishi  M. Arai  Y. Zama  T. Furuhata  Z. Ristovski  H. Rahimzadeh  R. J. Brown 《International Journal of Environmental Science and Technology》2016,13(1):221-230

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Habitat use by the European eel Anguilla anguilla in Irish waters   总被引：2，自引：0，他引：2  

T. Arai  A. Kotake  T.K. McCarthy 《Estuarine, Coastal and Shelf Science》2006,67(4):569-578

The apparent use of marine and freshwater habitats by European eel Anguilla anguilla was examined by analyzing the strontium (Sr) and calcium (Ca) concentrations in otoliths of the eels collected from Irish coastal and fresh waters. The age and growth of eels were also examined using their otolith annuli. The sizes and ages of the female eels were greater than those of the males. The somatic growth rates ranged from 15 to 62 mm/year, which is typical for Ireland and other European countries. Analyses of Sr:Ca ratios along a life history transect in each otolith showed peaks (maximum more than 25 × 10⁻³) between the core and elver mark corresponding to the period of their leptocephalus and early glass eel stages in the ocean. Outside the elver mark, the Sr:Ca ratios indicated that eels had remained in different habitats that included freshwater (average Sr:Ca ratios, 0.98–1.78 × 10⁻³) and areas with relatively high salinities (average Sr:Ca ratios, 6.73–8.89 × 10⁻³). Some individuals showed clear evidence of shifts from sea to fresh waters. These findings suggest that Irish eels have the same behavioral plasticity regarding whether or not to enter freshwater or remain in marine environments as has been recently documented in this species and several other temperate anguillid species. However, patterns of habitat use in Irish waters were somewhat different than those previously reported for other habitats.  相似文献   

Comparison of organotin accumulation in the masu salmon Oncorhynchus masou accompanying migratory histories     

Madoka Ohji  Takaomi Arai  Nobuyuki Miyazaki 《Estuarine, Coastal and Shelf Science》2007,72(4):721-731

In order to examine the accumulation pattern of organotin compounds (OTs) accompanying the migration pattern in diadromous fish, tributyltin (TBT) and triphenyltin (TPT) compounds and their derivatives were determined in the liver, muscle, gill, and ovary tissues of both sea-run and freshwater-resident masu salmon, which are of the same species, Oncorhynchus masou. Their migratory histories were estimated using strontium (Sr) and calcium (Ca) analysis in the otolith. A significant difference in the mean Sr:Ca ratio from the core to the edge of the otolith was found between sea-run and freshwater-resident masu salmon. The TBT concentration in the liver was significantly higher than that in the other tissues in both sea-run and freshwater-resident fishes. In sea-run masu salmon, the TBT concentrations in all tissues except for the ovary were significantly higher than in those of freshwater-resident individuals. In the sea-run type, the percentage of TBT was higher than that of the freshwater-resident type. The TPT concentration in the liver of the sea-run type was also significantly higher than that in the other tissues, while that in the gill of the freshwater-resident type was significantly higher than that in the other tissues except for the ovary. The TPT concentrations found in the liver and muscle of the sea-run type were significantly higher than those in the freshwater-resident type, whereas the values of the gill in the sea-run type were significantly lower than those in the freshwater-resident fish examined. The percentage of TPT in the sea-run type was higher than that of the freshwater-resident type. These results suggest that the sea-run O. masou has a higher ecological risk of TBT and TPT exposure than the freshwater-residents during their life history.  相似文献   

Buoyancy-driven perturbations in a rapidly rotating,electrically conducting fluid: part II – dynamo action     

Arnaud Chulliat  Hisayoshi Shimizu  David E. Loper 《地球物理与天体物理流体动力学》2013,107(6):471-487

The helicity, electromotive force and α-effect produced in a homogeneous, rapidly rotating, electrically conducting fluid by an isolated source of buoyancy at small Elsasser number are calculated, visualized and analyzed. Due to physical symmetries of the system, the integrals of helicity and electromotive force over all space are zero. However, each has a significant non-zero value when integrated over the cross section of the Taylor column. The local α-effect is found to be significantly anisotropic; it is strongest when the applied magnetic field is toroidal and the resulting EMF is parallel to the applied field.  相似文献   

Podiform chromitite in the arc mantle: chromitite xenoliths from the Takashima alkali basalt,Southwest Japan arc   总被引：3，自引：0，他引：3  

S. Arai  N. Abe 《Mineralium Deposita》1994,29(5):434-438

Chromitite xenoliths from the Takashima alkali basalt in the Southwest Japan arc are classified into two types: Type 1 chromitite in thin layers in dunite or wehrlite xenoliths; and Type 2 chromitite in discrete xenoliths which has an orbicular texture, previously documented only from podiform chromitites in ophiolites. Type 1 may be equivalent to layered chromitites in ophiolitic cumulates and Type 2 to podiform chromitites in the transition zone of ophiolites. This example of podiform chromitite from the Southwest Japan arc suggest that these podiform chromitites may exist in the upper mantle beneath an arc, where their formation is favored.  相似文献   

Extensive ash falls in and around the sea of Japan from large late quaternary eruptions   总被引：4，自引：0，他引：4  

Hiroshi Machida  Fusao Arai   《Journal of Volcanology and Geothermal Research》1983,18(1-4)

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Chromian spinel lamellae in olivine from the Iwanai-dake peridotite mass,Hokkaido, Japan     

Shoji Arai 《Earth and Planetary Science Letters》1978,39(2):267-273

Lamellar inclusions of chromian spinel (Cr/Cr + Al> 0.7), clinopyroxene and chromian spinel-clinopyroxene symplectite occur in olivines from alpine-type peridotites which have equilibrated at relatively low temperature (<700°C). They occur most commonly in dunite with very magnesian olivine (Fo₉₃ to Fo₉₅) and discrete grains of Cr-rich spinel. Olivine which initially equilibrated with magnesian and Cr-rich liquid had contained small amounts of calcium and trivalent chromium in the octahedral site, and lamellar chromian spinel and diopsidic clinopyroxene exsolved during the annealing process. The ordinary depletion of chromium or absence of chromian spinel lamellae in olivines in igneous rocks may be partly due to the effective exclusion of chromium from olivine upon cooling.  相似文献