1.

論文

論文
Hirano, Akihiro ; Nakayama, Kenji ; Arai, Shoji
出版情報: Proceedings of the 2003 International Workshop on Acoustic Echo and Nose Control (IWAENC2003), Kyoto, Japan.  pp.143-146,  2003-09-01.  Institute of Electrical and Electronics Engineers (IEEE)
URL: http://hdl.handle.net/2297/11895
2.

論文

論文
Arai, Shoji
出版情報: Proceedings of the Japan Academy Series B: Physical and Biological Sciences.  81  pp.14-19,  2005-01-01.  日本学士院
URL: http://hdl.handle.net/2297/10556
概要: 金沢大学理工研究域自然システム学系<br />Dunite and related rocks from the Moho transition zone of the East Pacific Rise (EPR) and the Mid -Cayman Trough (MCT) are examined to know the spreading-rate dependence of their compositions. The rocks from both ridges are basically a reaction product between peridotite and primitive MORB. Despite the large difference of prevalent peridotite chemistry, depleted harzburgite for EPR and lherzolite for MCT, the dunite has less different compositional ranges. The Al2O3 content of spinel differs only by 5 wt%, which may be equivalent to the difference of about 1 wt% of Al2O3 in the melt. This is almost equal to the possible spreading-rate dependent compositional difference of observed Mg-rich MORB. The relatively unfractionated MORBs erupted are in equilibrium with the oceanic dunite of which composition is independent of or only slightly dependent on spreading rate. Dunite is calculated to be about half of the total oceanic mafic crust by weight. The dunite is concentrated as the Moho transition zone, and is sparsely distributed as small lenses within the uppermost mantle peridotite. 続きを見る
3.

論文

論文
Arai, Shoji ; Shimizu, Yohei ; Gervilla, Fernando
出版情報: Proceedings of the Japan Academy Series B: Physical and Biological Sciences.  79  pp.145-150,  2003-06-01.  日本学士院
URL: http://hdl.handle.net/2297/10555
概要: We found quartz diorite veins (up to 5 mm thick), composed mainly of plagioclase and quartz, in a plagioclase-bearing spinel lherzolite xenolith in alkali basalt from Tallante, Southern Spain. The quartz diorite veins are coarse-grained, the average grain size being 0.5 mm, and have thin orthopyroxenite rim along olivine wall. Thinner veins free of quartz and composed solely of plagioclase with orthopyroxene selvage are much more common in other xenoliths from Tallante. The involved melt was strongly reactive with olivine to form orthopyroxene, which can protect against further reaction. This suggests how the silica-oversaturated melts, after supplied from downgoing slabs, can move through peridotite and reach the shallow mantle with preserving the silica-oversaturated character. The armor of orthopyroxenite is of vital importance for the melt, to keep its silica-oversaturated character within peridotite. Precipitation of orthopyroxene combined with olivine consumption somewhat controls the general chemical trend of adakite. Orthopyroxenite vein network at the expense of olivine is expected to be common as fossil conduits within the mantle wedge. This kind of orthopyroxenite has contributed to Si-enrichment of the mantle wedge. 続きを見る
4.

論文

論文
Ali, Murad ; Arai, Shoji
出版情報: Journal of Mineralogical and Petrological Sciences.  102  pp.137-142,  2007-05-16.  日本鉱物学会
URL: http://hdl.handle.net/2297/7287
概要: 金沢大学大学院自然科学研究科自然計測<br />Ultramafic xenoliths in Pliocene-Quaternary basalts from Bir Ali, the Shabwa Governorate, southe rn Yemen, were studied to examine upper mantle processes related to continental rifting. They show a great variety of rock types: spinel lherzolites, harzburgites, dunites, clinopyroxene (= cpx)-rich lherzolites, wehrlites and pyroxenites. The cpx-rich lherzolites and wehrlites with high clinopyroxene/orthopyroxene ratios (> 1), which are characteristic of the Bir Ali xenolith suite, contain lower Fo contents of olivine than ordinary lherzolites at a given Cr# of spinel. Their clinopyroxenes are higher in TiO2 and REE contents than those in the ordinary therzolites, which are restite. These features strongly indicate metasomatic addition of clinopyroxene from alkali basalts at the expense of orthopyroxene to depleted peridotites for genesis of the cpx-rich lherzolites. The cpx-rich lherzolites are one of common constituents of lithospheric mantle at rifted continental margins. 続きを見る
5.

論文

論文
Python, Marie ; Ishida, Yoshito ; Ceuleneer, Georges ; Arai, Shoji
出版情報: Journal of Mineralogical and Petrological Sciences.  102  pp.143-149,  2007-05-16.  日本鉱物学会
URL: http://hdl.handle.net/2297/7288
概要: 金沢大学大学院自然科学研究科自然計測<br />We discovered a new kind of dyke in the mantle section of the Oman ophiolite composed mainly of diopside that we called diopsidite, although traces of forsterite, anorthite, titanite or andradite may be also observed. The texture and chemical composition, and the relationship between antigorite and diopside or rare forsterite, suggest that they formed by high-T metamorphism of serpentine (antigorite) and are the result of interaction between hydrothermal fluid and percolating magma in the shallow mantle. Chemical data, obtained by electron microprobe and in situ laser ablation coupled to ICP-MS, show large heterogeneities from one sample to another and between diopside crystals in each sample. The trace element patterns are characterised by strong positive anomalies in Sr and Eu and a negative anomaly in Ti. Small-scale heterogeneities reflect the disequilibrium conditions in the dyke formation and show that a relatively Ti-rich- and Al-Eu-Sr-LREE-poor phase may be included in the diopside. The exact nature of this phase is difficult to determine but the Eu negative anomaly, and the low Sr and LREE concentration suggest that it is probably some partially altered, relict protolith mineral. 続きを見る
6.

論文

論文
Gahlan, Hisham A. ; Arai, Shoji
出版情報: Journal of Mineralogical and Petrological Sciences.  102  pp.69-85,  2007-05-16.  日本鉱物学会
URL: http://hdl.handle.net/2297/7289
概要: 金沢大学大学院自然科学研究科自然計測<br />The peculiar Co, Zn and Mn-rich chromian spinels are hosted by magnetite veins, serpentinites an d chromitites of the mantle section of the Proterozoic Bou-Azzer ophiolite, Morocco. The spinel is complexly zoned either optically or chemically, and exhibits anomalously high MnO, ZnO and CoO contents (up to 22, 7.5 and 2 wt%, respectively). It has four distinct optical zones particularly in the magnetite veins and less typically in serpentinites. The highest level of these elements, probably divalent, is recorded within the ferritchromite zone and/or within the core zone if the ferritchromite zone is absent. These elements as well as Fe exhibit enrichment along grain boundaries and fractures of the altered spinels. Fe, Mn, Zn and Co were most probably supplied from olivine upon severe serpentinization during and after obduction of the ophiolite. The enrichment of the Bou-Azzer chromian spinel in Mn, Zn and Co was governed mainly by the fluid/mineral (spinel) ratio and partition coefficient between spinel and the relevant fluid among many factors. The Co-, Zn- and Mn-rich chromian spinels can be used as an exploration guide for Co-Ni-Zn-Cu sulfide mineralization associated with serpentinized peridotites. 続きを見る
7.

論文

論文
Arai, Shoji ; Okamura, Hidenobu ; Kadoshima, Kazuyuki ; Tanaka, Chima ; Suzuki, Kenji ; Ishimaru, Satoko
出版情報: Island Arc.  20  pp.125-137,  2011-03-01.  Blackwell Publishing Asia Pty Ltd.
URL: http://hdl.handle.net/2297/27101
概要: 金沢大学理工研究域自然システム学系<br />We summarize chemical characteristics of chromian spinels from ultramafic to mafic plutonic rocks (lherzolites, harzburgites, dunites, wehrlites, troctolites, olivine gabbros) with regard to three tectonic settings (mid-ocean ridge, arc, oceanic hotspot). The chemical range of spinels is distinguishable between the three settings in terms of Cr# (=Cr/(Cr+Al) atomic ratio) and Ti content. The relationships are almost parallel with those of chromian spinels in volcanic rocks, but the Ti content is slightly lower in plutonics than in volcanics at a given tectonic environment. The Cr# of spinels in plutonic rocks is highly diverse; its ranges overlap between the three settings, but extend to higher values (up to 0.8) in arc and oceanic hotspot environments. The Ti content of spinels in plutonics increases, for a given lithology, from the arc to oceanic hotspot settings by mid-ocean ridge on average. This chemical diversity is consistent with that of erupted magmas from the three settings. If we systematically know the chemistry of chromian spinels from a series of plutonic rocks, we can estimate their tectonic environments of formation. The spinel chemistry is especially useful in dunitic rocks, in which chromian spinel is the only discriminating mineral. Applying this, discordant dunites cutting mantle peridotites were possibly precipitated from arc-related magmas in the Oman ophiolite, and from an intraplate tholeiite in the Lizard ophiolite, Cornwall. © 2010 Blackwell Publishing Asia Pty Ltd. 続きを見る
8.

論文

論文
Arai, Shoji ; Tamura, Akihiro ; Ishimaru, Satoko ; Kadoshima, Kazuyuki ; Lee, Yong-Il ; Hisada, Ken-ichiro
出版情報: Island Arc.  17  pp.485-501,  2008-01-01.  Blackwell Publishing
URL: http://hdl.handle.net/2297/19548
概要: 金沢大学理工研究域自然システム学系<br />Peridotites exposed in the Yugu area in the Gyeonggi Massif, South Korea, near the boundary with the Okcheon Belt, exhibit mylonitic to strongly porphyroclastic textures, and are mostly spinel lherzolites. Subordinate dunites, harzburgites, and websterites are associated with the lherzolites. Amphiboles, often zoned from hornblende in the core to tremolite in the rim, are found only as neoblasts. Porphyroclasts have recorded equilibrium temperatures of about 1000°C, whereas neoblasts denote lower temperatures, about 800°C. Olivines are Fo 90-91 in lherzolites and Fo 91 in a dunite and a harzburgite. The Cr# (=Cr/(Cr + Al) atomic ratio) of spinels varies together with the Fo of olivines, being from 0.1 to 0.3 in lherzolites and around 0.5 in the dunite and harzburgite. The Na2O content of clinopyroxene porphyroclasts is relatively low, around 0.3 to 0.5 wt% in the most fertile lherzolite. The Yugu peridotites are similar in porphyroclast mineral chemistry not to continental spinel peridotites but to sub-arc or abyssal peridotites. Textural and mineralogical characteristics indicate the successive cooling with hydration from the upper mantle to crustal conditions for the Yugu peridotites. Almost all clinopyroxenes and amphiboles show the same U-shaped rare earth element (REE) patterns although the level is up to ten times higher for the latter. The hydration was associated with enrichment in light REE, resulting from either a slab-derived fluid or a fluid circulating in the crust. The mantle-wedge or abyssal peridotites were emplaced into the continental crust as the Yugu peridotite body during collision of continents to form a high-pressure metamorphic belt in the Gyeonggi Massif. The peridotites from the Gyeonggi Massif exhibit lower-pressure equilibration than peridotites, with or without garnets, from the Dabie-Sulu Collision Belt, China, which is possibly a westward extension of the Gyeonggi Massif. © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd. 続きを見る
9.

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論文
Kaneoka, Ichiro ; Takahashi, Natsuko ; Arai, Shoji
出版情報: Island Arc.  10  pp.22-32,  2001-01-01.  Blackwell Publishing
URL: http://hdl.handle.net/2297/19562
概要: 金沢大学理工研究域自然システム学系<br />40Ar-39Ar analysis of phlogopite separated from a plagioclase lherzolite of the Horoman Peridotit e Complex, Hokkaido, Japan, has yielded a plateau age of 20.6 ± 0.5 Ma in an environment where the metamorphic fluid was characterized by an almost atmospheric Ar isotopic ratio. The age spectrum is slightly saddle-shaped, implying some incorporation of excess 40Ar during the formation of the phlogopite at a depth. As the phlogopite has been inferred to have formed in veins and/or interstitials during exhumation of the peridotite body, metasomatic fluids, to which ground- and sea water might have contributed, were probably involved in the formation of phlogopite in the crustal environment. A total 40Ar-39Ar age of 129 Ma of a whole rock sample of the plagioclase lherzolite, from which the phlogopite was separated and is representative of the main lithology of the Horoman Peridotite Complex, indicates the occurrence of excess 40Ar. Hence, the age has no geological meaning. 続きを見る
10.

論文

論文
Zaki Khedr, Mohamed ; Arai, Shoji ; Python, Marie
出版情報: Journal of Mineralogical and Petrological Sciences.  108  pp.13-24,  2013-01-01.  日本鉱物科学会 JAMS
URL: http://hdl.handle.net/2297/36185
概要: We studied basal lherzolites that are exposed along the metamorphic sole at the base of the central Oman ophiolite (Wadi Sarami). We recognized two types of lherzolites (Types I and II) based on field occurrences, textures, and mineral compositions. Type I lherzolites are massive and transition into harzburgites, whereas Type II lherzolites are strongly foliated with mylonitic to porphyroclastic textures. Type II lherzolites only crop out within a direct contact with the amphibolitic sole to few meters above this sole and are overlain and/or surrounded by Type I. The clinopyroxenes [Mg# = Mg/(Mg + Fe) = 0.89-0.94] of Type II lherzolites show higher contents of Al2O3 (4.5-7.3 wt%), Na2O (0.5-1.2 wt%), Cr2O3 (0.6-1.4 wt%), and TiO2 (0.2-0.4 wt%) than those of Type I lherzolites. Positive correlations among the Al2O3, Na2O, and TiO2 contents of clinopyroxenes show a pronounced residual trend from Type I lherzolites to depleted harzburgite, giving rise to chemical heterogeneities at the base of the mantle section. Clinopyroxenes in lherzolites and harzburgites show compositional trends that are similar to those in abyssal peridotites from normal ridge segments. Olivines (Fo89.4-Fo91.5) show a residual character of the Sarami peridotites. Primary spinels show a wide range of Cr# [= Cr/(Cr + Al) from 0.04 to 0.53] and low YFe [Fe3+/(Cr + Al + Fe3+), <0.046], similar to spinels in abyssal peridotites. The wide range of spinel Cr# is a result of a wide range of partial-melting degrees, which are up to 10% for lherzolites and ~ 10-25% for harzburgites. The Type II lherzolites, which occur near the paleo-fracture zone located to the east of Wadi Sarami, represent a remnant of asthenospheric materials trapped at the base of oceanic lithosphere mantle (Type I) during detachment and obduction. The Type I lherzolites experienced high-degree partial melting, resulting in the formation of harzburgites at the refractory end. The modal and compositional variations of Sarami pyroxenes and spinels indicate intrinsic mantle heterogeneity of Oman ophiolite formed as residues at an oceanic spreading center. 続きを見る