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Morishita, Tomoaki ; Arai, Shoji ; Tamura, Akihiro ; Ishida, Yoshito
概要:
金沢大学フロンティアサイエンス機構<br />A peculiar amphibolite rich in deep vivid green-colored amphibole porphyroblast was found as a bo
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ulder in the Chiroro River of Hidaka Town, Hokkaido, Japan. The amphibolite mainly consists of deep vivid green-colored amphibole (porphyroblast), colorless amphibole (matrix) and plagioclase with a small amount of chlorite, epidote and chromian spinel. Deep vivid green-colored amphibole porphyroblast is more than 20 modal % in the rock. Chromian spinel rarely occurs as inclusions in deep vivid green-colored amphibole porphyroblast. The Cr2O3 content of the deep vivid green-colored domain is usually ∼1 wt% (up to 2.5 wt% nearby chromian spinel) whereas that of colorless amphibole in the matrix is low, < 0.1 wt%. Deep vivid green-colored amphibole porphyroblast is heterogeneous in chemical compositions within each grain and is divided into three domains as follows: (1) high-Cr2O3 (∼1 wt%, up to 2.5 wt%) and Al2O3 (> 10 wt%) green-colored domain, (2) relatively high-Cr2O3 (∼1 wt%) and low- Al2O3 (< 10 w%) green-colored domain and (3) low-Cr2O3 (< 0.1 wt%) and Al2O3 (< 10 wt%) colorless domain. Chondrite-normalized rare earth element (REE) patterns of both deep vivid green-colored amphibole porphyroblast and colorless amphibole in the matrix are characterized by low light REE with positive Eu anomaly. The Cr#[= Cr/(Cr + Al) atomic ratio] and TiO2 content of chromian spinel in the amphibolite are similar to those in a serpentinite complex of the Kamuikotan Zone. The amphibolite was formed by either amphibolitization of a rock containing chromian spinel derived from the surrounding serpentinite complex or extensively metasomatized serpentinite due to interaction with surrounding metamorphic rocks.
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| 2.
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Morishita, Tomoaki ; Andal, Eric S. ; Arai, Shoji ; Ishida, Yoshito
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金沢大学理工研究域自然システム学系<br />The Isabela ophiolite, the Philippines, is characterized by a lherzolite-dominant mantle section,
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which was probably formed beneath a slow-spreading mid-ocean ridge. Several podiform chromitites occur in the mantle section and grade into harzburgite to lherzolite. The chromitites show massive, nodular, layered and disseminated textures. Clinopyroxene (±orthopyroxene/amphibole) inclusions within chromian spinel (chromite hereafter) are commonly found in the massive-type chromitites. Large chromitites are found in relatively depleted harzburgite hosts having high-Cr# (Cr/(Cr + Al) atomic ratio = ∼0.5) chromite. Light rare earth element (LREE) contents of clinopyroxenes in harzburgites near the chromitites are higher than those in lherzolite with low-Cr# chromite, whereas heavy REE (HREE) contents of clinopyroxenes are lower in harzburgite than in lherzolite. The harzburgite near the chromitites is not a residual peridotite after simple melt extraction from lherzolite but is formed by open-system melting (partial melting associated with influx of primitive basaltic melt of deeper origin). Clinopyroxene inclusions within chromite in chromitites exhibit convex-shaped REE patterns with low HREE and high LREE (+Sr) abundances compared to the host peridotites. The chromitites were formed from a hybridized melt enriched with Cr, Si and incompatible elements (Na, LREE, Sr and H2O). The melt was produced by mixing of secondary melts after melt-rock interaction and the primitive basaltic melts in large melt conduits, probably coupled with a zone-refining effect. The Cr# of chromites in the chromitites ranges from 0.65 to 0.75 and is similar to those of arc-related magmas. The upper mantle section of the Isabela ophiolite was initially formed beneath a slow-spreading mid-ocean ridge, later introduced by arc-related magmatisms in response to a switch in tectonic setting during its obduction at a convergent margin. © 2006 The Authors; Journal compilation © 2006 Blackwell Publishing Asia Pty Ltd.
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| 3.
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Morishita, Tomoaki ; Arai, Shoji ; Ishida, Yoshito
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金沢大学理工研究域自然システム学系<br />Trace-element compositions of jadeite (±omphacite) in jadeitites from the Itoigawa-Ohmi district
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of Japan, analyzed by a laser-ablation inductively coupled plasma mass spectrometry technique showed chemical zoning within individual grains and variations within each sample and between different samples. Primitive mantle-normalized patterns of jadeite in the samples generally showed high large-ion lithophile element contents, high light rare earth element/heavy rare earth element ratios and positive anomalies of high field strength elements. The studied jadeitites have no signatures of the protolith texture or mineralogy. Shapes and distributions of minerals coupled with chemical zoning within grains suggest that the jadeitites were formed by direct precipitation of minerals from aqueous fluids or complete metasomatic modification of the precursor rocks by fluids. In either case, the geochemical characteristics of jadeite are highly affected by fluids enriched in both large-ion lithophile elements and high field strength elements. The specific fluids responsible for the formation of jadeitites are related to serpentinization by slab-derived fluids in subduction zones. This process is followed by dissolving high field strength elements in the subducting crust as the fluids continue to circulate into the subducting crusts and serpentinized peridotites. The fluids have variations in chemical compositions corresponding to various degrees of water-rock interactions. © 2007 The Authors; Journal compilation © 2007 Blackwell Publishing Asia Pty Ltd.
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Morishita, Tomoaki ; Takazawa, Eiichi ; Arai, Shoji ; Obata, Masaaki ; Kodera, Tadahiro ; Gervilla, Fernando
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金沢大学理工研究域自然システム学系
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Ishida, Yoshito ; Morishita, Tomoaki ; Arai, Shoji ; Shirasaka, Miki
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Department of Earth Sciences, Faculty of Science, Kanazawa University:Graduate School of Natural Science and Technology,
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Kanazawa University<br />In-situ trace-element analyses on minerals are especially useful for characterization of geological materials. We explored optimistic conditions of a inductively coupled plasma mass spectroscopy with laser-ablation sample introduction method (LA-ICP-MS) for in-situ quantitative trace-element analysis of geological materials on thin section. The sampling with an excimer laser with energy density of 8 J/cm^2 is appropriate for in-situ analysis of minerals on thin section based on ablation hole morphology. The rate of material removal is estimated from deep holes on a glass after 500 shots with energy on sample surface of 8 J/cm^2 to be approximately 0.2ƒﾊm/pulse. 150-200 shots might be available for a sample prepared as normal thin section (30ƒﾊm in thickness). All data were obtained by ablating in He gas prior to combination with the dominant Ar carrier flow because ablation in He minimized post-ablation surface condensation, resulting in high sensitivity. We examined the relationship between the size of laser-ablation hole and sensitivity of analysis in conducting in-situ simultaneous quantitative LA-ICP-MS analysis of 37 elements including rare earth elements (REEs). The diameter of laser beam can be as small as 30ƒﾊm to obtain sufficiently good dataset for trace-element concentrations of minerals from thin section.
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Shirasaka, Miki ; Arai, Shoji ; Ishimaru, Satoko ; Ishida, Yoshito ; Shimizu, Yohei ; Morishita, Tomoaki
概要:
Department of Earth Sciences, Faculty of Science, Kanazawa University<br />The solution introduction ICP-MS technique for trace element analysis of rock samples was constructed at Kanazawa University. Trace element concentrations of
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geological standards (JB-2, JP-1, JA-1, and JGB-2) and Avacha peridotite xenoliths, Russia, which are strongly depleted in major elements and the hardest matter for analysis, were determined by the ICP-MS equipment. The values of concentration of middle to heavy masses (Rb-U) in geological standards coincide with those reported by other studies with ICP-MS techniques. The reproducibility is within 5% of differences of values of Rb to Hf in JB-2 in response to the changes in dates, dilutions and calibration methods. In the case of peridotites (low trace elements concentrations in the order of ppb to sub-ppb), relative standard deviations and relative differences among the runs under the various conditions are larger than in basalt with trace element concentrations in the order of ppm. Especially, large relative standard deviations (>10s%) for alkaline elements (Li, Rb, Cs), HFSE (Zr, Nb, Ta), Pb and Bi are shown in the refractory Avacha peridotite xenoliths with trace element concentrations in the order of sub-ppb. The solution introduction ICP-MS technique is a powerful tool for a precise insight into trace element characteristics of rocks of wide chemical compositions.
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Morishita, Tomoaki ; Arai, Shoji
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Morishita, Tomoaki ; Arai, Shoji
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Morishita, Tomoaki ; Arai, Shoji ; Ishida, Yoshito
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金沢大学大学院自然科学研究科<br />Promoting Environmental Pesearch in Pan-Japan Sea Area : Young Researchers' Network, Schedule: March
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8-10,2006,Kanazawa Excel Hotel Tokyu, Japan, Organized by: Kanazawa University 21st-Century COE Program, Environmental Monitoring and Prediction of Long- & Short- Term Dynamics of Pan-Japan Sea Area ; IICRC(Ishikawa International Cooperation Research Centre), Sponsors : Japan Sea Research ; UNU-IAS(United Nations University Institute of Advanced Studies)+Ishikawa Prefecture Government ; City of Kanazawa
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| 10.
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Shimizu, Yohei ; Arai, Shoji ; Morishita, Tomoaki ; Ishida, Yoshito
概要:
金沢大学大学院自然科学研究科<br />Promoting Environmental Pesearch in Pan-Japan Sea Area : Young Researchers' Network, Schedule: March
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8-10,2006,Kanazawa Excel Hotel Tokyu, Japan, Organized by: Kanazawa University 21st-Century COE Program, Environmental Monitoring and Prediction of Long- & Short- Term Dynamics of Pan-Japan Sea Area ; IICRC(Ishikawa International Cooperation Research Centre), Sponsors : Japan Sea Research ; UNU-IAS(United Nations University Institute of Advanced Studies)+Ishikawa Prefecture Government ; City of Kanazawa
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