start-ver=1.4 cd-journal=joma no-vol=52 cd-vols= no-issue= article-no= start-page=51 end-page=70 dt-received= dt-revised= dt-accepted= dt-pub-year=1982 dt-pub=19820325 dt-online= en-article= kn-article= en-subject= kn-subject= en-title=Isotopic Analysis of Rb and Sr Using a Full Automatic Thermal Ionization Mass Spectrometer kn-title=MAT260によるSr同位体比測定及びRb･Sr定量分析 en-subtitle= kn-subtitle= en-abstract= kn-abstract=Analytical method for strontium isotope ratios and rubidium and strontium concentrations has been established using a full automatic thermal ionization mass spectrometer. The machine is a modified model "MAT 260" of Varian MAT LTD. Each of simultaneously loaded thirteen samples is successively analysed full automatically following to a specific controling program which has been selected as being most suitable for each sample. However, the most characteristic feature of this machine compared to other types is computer controled peak jumping and peak centering before measurment of the signal of each peak. By this the accuracy of isotopic measurement has been surprisingly improved. Analytical procedures are described in detail which include decomposition of samples, separation of Rb and Sr, loading samples on filament and mass spectrometry. Accuracy and reproducibility of isotope analyses are excellent : 43 separate analyses of standard sample NBS 987 over one year gave a mean (87)Sr/(86)Sr ratio of 0.710238 (normalized to the (88)Sr/(86)Sr ratio of 8.375209) with a value of　20δ of 0.000008. The ratio obtained is slightly　higher than the value of 0.71014 given by NBS,　but it is almost identical to the mean of recently　reported twenty analyses. Our determinations for Rb and Sr concentrations of standard samples are as follows : JG-1, Rb 184.4 ppm, Sr 185.5 ppm; JB-l, Rb 41.5Ppm, Sr 448.4 ppm , each of which is near the mean of reported values for corresponding element of the sample (ANDO et al., 1974). Concentrations of Rb and Sr in pure water and regents used in chemical treatement of samples were also measured; a possible error due to the contamination is negligible for most geochemical samples. en-copyright= kn-copyright= en-aut-name=KagamiHiroo en-aut-sei=Kagami en-aut-mei=Hiroo kn-aut-name=加々美寛雄 kn-aut-sei=加々美 kn-aut-mei=寛雄 aut-affil-num=1 ORCID= en-aut-name=OkanoOsamu en-aut-sei=Okano en-aut-mei=Osamu kn-aut-name=岡野修 kn-aut-sei=岡野 kn-aut-mei=修 aut-affil-num=2 ORCID= en-aut-name=SudoHiroshi en-aut-sei=Sudo en-aut-mei=Hiroshi kn-aut-name=須藤宏 kn-aut-sei=須藤 kn-aut-mei=宏 aut-affil-num=3 ORCID= en-aut-name=HonmaHiroji en-aut-sei=Honma en-aut-mei=Hiroji kn-aut-name=本間弘次 kn-aut-sei=本間 kn-aut-mei=弘次 aut-affil-num=4 ORCID= affil-num=1 en-affil= kn-affil=温泉地質学部門 affil-num=2 en-affil= kn-affil=温泉地質学部門 affil-num=3 en-affil= kn-affil=温泉地質学部門 affil-num=4 en-affil= kn-affil=温泉地質学部門 END start-ver=1.4 cd-journal=joma no-vol=16 cd-vols= no-issue=1 article-no= start-page=9 end-page=28 dt-received= dt-revised= dt-accepted= dt-pub-year=2009 dt-pub=20091225 dt-online= en-article= kn-article= en-subject= kn-subject= en-title=ガーナ，アシャンティ火山帯南部に分布する古原生代変火山岩類のSr-Nd 同位体組成 kn-title=Sr?Nd isotopic compositions of Paleoproterozoic metavolcanic rocks from the southern Ashanti volcanic belt, Ghana en-subtitle= kn-subtitle= en-abstract= kn-abstract=Neodymium (Nd) and strontium (Sr) isotopic data are presented for Paleoproterozoic metavolcanic rocks in the southern part of the Ashanti volcanic belt of Ghana. The metavolcanic rocks are predominantly basalts/basaltic andesites and andesites with minor dacites. Two types of basalts/basaltic andesites (B/A), Type I and Type II, have been identified. The Type I B/A are stratigraphically overlain by the Type II B/A, followed by the andesites and the dacites. The analyzed volcanic rocks commonly have low initial (87)Sr/(86)Sr ratios consistent with previous studies on Paleoproterozoic rocks from the West African craton. The LREE-depleted, tholeiitic Type I B/A exhibit back-arc basin geochemical signatures and show high positive epsilon Nd (i.e., ε(Nd) (2.1 Ga) = +3.89 to +7.21), which suggest a long term depleted source and also indicate that they were produced in an entirely oceanic environment devoid of influence of continental crust. The isotope signatures are thus consistent with the previously published trace element data of the Type I basalts/basaltic andesites in suggesting that their parent magma was generated from a depleted mantle. The Type I B/A have Nd model ages (T(DM2)) of 1.83?2.09 Ga similar to their formation ages, suggesting that they were juvenile at their time of formation. The andesites and the Type II B/A andesites show LREE-enriched patterns and exhibit characteristics of subduction zone-related magmas, and show initial ε(Nd) (2.1Ga) values of ?1.15 to + 1.35 and Nd model ages (T(DM2)) of 2.32?2.58 Ga. The LREE-enriched dacitic porphyry also exhibits characteristics of subduction zone-related magmas, and have initial ε(Nd) (2.1Ga) value of ?2.24 and Nd model ages (T(DM2)) of 2.64 Ga. The Nd isotopic data confirms the juvenile character of the Birimian crust, but also suggests some contributions of a pre-Birimian crustal material (or Archean?) in the genesis of some of the metavolcanic rocks. Our isotopic result is consistent with the island arc complex model which views Paleoproteozoic terranes of West Africa in the context of subduction?accretion processes. en-copyright= kn-copyright= en-aut-name=DampareSamuel en-aut-sei=Dampare en-aut-mei=Samuel kn-aut-name=ダムパリサムエル kn-aut-sei=ダムパリ kn-aut-mei=サムエル aut-affil-num=1 ORCID= en-aut-name=ShibataTsugio en-aut-sei=Shibata en-aut-mei=Tsugio kn-aut-name=柴田次夫 kn-aut-sei=柴田 kn-aut-mei=次夫 aut-affil-num=2 ORCID= en-aut-name=AsieduDaniel en-aut-sei=Asiedu en-aut-mei=Daniel kn-aut-name=アシードダニエル kn-aut-sei=アシード kn-aut-mei=ダニエル aut-affil-num=3 ORCID= en-aut-name=OkanoOsamu en-aut-sei=Okano en-aut-mei=Osamu kn-aut-name=岡野修 kn-aut-sei=岡野 kn-aut-mei=修 aut-affil-num=4 ORCID= en-aut-name=ManuJohnson en-aut-sei=Manu en-aut-mei=Johnson kn-aut-name=マーヌジョンソン kn-aut-sei=マーヌ kn-aut-mei=ジョンソン aut-affil-num=5 ORCID= en-aut-name=SakyiPatrick en-aut-sei=Sakyi en-aut-mei=Patrick kn-aut-name=サチパトリック kn-aut-sei=サチ kn-aut-mei=パトリック aut-affil-num=6 ORCID= affil-num=1 en-affil= kn-affil=岡山大学 affil-num=2 en-affil= kn-affil=岡山大学 affil-num=3 en-affil= kn-affil=Department of Earth Science, University of Ghana affil-num=4 en-affil= kn-affil=岡山大学 affil-num=5 en-affil= kn-affil=Department of Earth Science, University of Ghana affil-num=6 en-affil= kn-affil=Department of Earth Science, University of Ghana en-keyword=Sr?Nd isotopes kn-keyword=Sr?Nd isotopes en-keyword=petrogenesis kn-keyword=petrogenesis en-keyword=tectonic setting kn-keyword=tectonic setting en-keyword=Birimian metavolcanics kn-keyword=Birimian metavolcanics en-keyword=Ashanti volcanic belt kn-keyword=Ashanti volcanic belt END start-ver=1.4 cd-journal=joma no-vol=1 cd-vols= no-issue=1 article-no= start-page=27 end-page=36 dt-received= dt-revised= dt-accepted= dt-pub-year=1994 dt-pub=19940920 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Determination of Rb-Sr age for separated chondrules from the Allegan chondrite en-subtitle= kn-subtitle= en-abstract= kn-abstract=Rb-Sr isotopic study as well as petrologic investigations have been done on sixteen individul chondrule samples separated from the Allegan (H5) chondrite. The Rb-Sr chondrule isochron does not define a very precise age (4.42±0.17 Ga) and 87Sr/86Sr initial ratio (0.6997±0.0014) due to the very small variation in Rb/Sr ratio for the chondrules, whereas the model ages give a much more speciffic value (4.42±0.02 Ga). These ages may probably be indicative of the time of primary process (es) (e.g. chondrule formation) rather than secondary (metamorphic reheating) or tertiary (shock heating) processes in and/or on the H-chodrite parent body (or bodies). Chemical compositions of oliveines (Fa=17.5mol%, mean deviation (MD)=1.3%) and orthopyoxenes (Fs=15.4mol%, MD=3.2%) are moderately homogenized among the chondrules, while certains chemically uneguilibrated features are also distinctly preserved in this chondrite. Homogeneity of the mineral compositions, therefore, could not have been caused by thermal metamorphism but were probably inherited from processes prior to aggregation of the components. The overall implications of the chondrule isochron and model ages in relation to the petrological features and in comparison with Rb-Sr data of other chondrites of different chemical groups and petrologic types are discussed. en-copyright= kn-copyright= en-aut-name=OkanoOsamu en-aut-sei=Okano en-aut-mei=Osamu kn-aut-name=岡野修 kn-aut-sei=岡野 kn-aut-mei=修 aut-affil-num=1 ORCID= en-aut-name=NishiyaNanayo en-aut-sei=Nishiya en-aut-mei=Nanayo kn-aut-name=西谷七代 kn-aut-sei=西谷 kn-aut-mei=七代 aut-affil-num=2 ORCID= en-aut-name=KagamiHiroo en-aut-sei=Kagami en-aut-mei=Hiroo kn-aut-name=加々美寛雄 kn-aut-sei=加々美 kn-aut-mei=寛雄 aut-affil-num=3 ORCID= affil-num=1 en-affil= kn-affil=The Graduate School of Natural Science and Technology, Okayama University affil-num=2 en-affil= kn-affil=Department of Earth Sciences, Okayama University affil-num=3 en-affil= kn-affil=Institute for study of Earth's Interior, Okayama University en-keyword=chondrule kn-keyword=chondrule en-keyword=age kn-keyword=age en-keyword=Rb-Sr isochron kn-keyword=Rb-Sr isochron en-keyword=Allegan kn-keyword=Allegan en-keyword=H- chondrite kn-keyword=H- chondrite en-keyword=meteorite kn-keyword=meteorite en-keyword=metamorphism kn-keyword=metamorphism en-keyword=olivine kn-keyword=olivine en-keyword=pyroxene kn-keyword=pyroxene END start-ver=1.4 cd-journal=joma no-vol=2 cd-vols= no-issue=1 article-no= start-page=91 end-page=102 dt-received= dt-revised= dt-accepted= dt-pub-year=1995 dt-pub=19950920 dt-online= en-article= kn-article= en-subject= kn-subject= en-title=Rb-Sr age of K-rich LL-chondrite Yamato-74442 kn-title=Yamato-74442 LLコンドライトにおけるアルカリ分別年代 en-subtitle= kn-subtitle= en-abstract= kn-abstract=Yamato-74442, a brecciated LL-group chondrite, consists of fragments with igeous texture, chondrules, mineral fragments, and host. The fragments involve K-rich fragments as well as normal ones. Typically, both fragments consist mainly of euhedral porphyritic olivines and a few orthopyroxenes in a glassy grundmass. EPMA analyses for these fragments indicate that olivines and orthoptroxenes have a range of Fe/(Fe+Mg) ratio of 27.19〜31.33 and 20.10〜26.91 mol%, respectively. There is no significant difference in these rations between K-rich (Na2O/K2O<1) and normal framents. The K2O contents of groundmass for K-rich fragments range from 0.51 to 4.89 wt% and that of the normal fragments is 0.38〜090 wt%. K2O contents of groundmass vary from fragment to fragment but are rather homegeneous in a single fragment. Rb-Sr isotopic determination on eighteen K-rich fragments (1.5 to 9.5mg in weight) gave an internal isochron age of 4.514±0.022 (2σ) Ga (λ87Rb=1.42×10-11y-1) and initial 87Sr/86Sr ratio of 0.7016±0.0024. This age is somewhat old compared with a whole rock isochron age of LL chondrites (4.493±0.18 Ga; Minster and Allegre, 1981). From a comoarison of the present result with others so far reported, it is inferred that the alkali differentiation as observed in Yamato-74442 probably occurred prior to or during a process of accumulation from LL chondrite parent material in the early solar nebula.　 en-copyright= kn-copyright= en-aut-name=NishiyaNanayo en-aut-sei=Nishiya en-aut-mei=Nanayo kn-aut-name=西谷七代 kn-aut-sei=西谷 kn-aut-mei=七代 aut-affil-num=1 ORCID= en-aut-name=OkanoOsamu en-aut-sei=Okano en-aut-mei=Osamu kn-aut-name=岡野修 kn-aut-sei=岡野 kn-aut-mei=修 aut-affil-num=2 ORCID= en-aut-name=KagamiHiroo en-aut-sei=Kagami en-aut-mei=Hiroo kn-aut-name=加々美寛雄 kn-aut-sei=加々美 kn-aut-mei=寛雄 aut-affil-num=3 ORCID= en-aut-name=NakamuraNoboru en-aut-sei=Nakamura en-aut-mei=Noboru kn-aut-name=中村昇 kn-aut-sei=中村 kn-aut-mei=昇 aut-affil-num=4 ORCID= affil-num=1 en-affil= kn-affil=岡山大学理学部地球科学科 affil-num=2 en-affil= kn-affil=岡山大学自然科学研究科 affil-num=3 en-affil= kn-affil=岡山大学地球内部研究センター affil-num=4 en-affil= kn-affil=神戸大学理学部地球科学科 en-keyword=LL-chondrite kn-keyword=LL-chondrite en-keyword=Rb-Sr age kn-keyword=Rb-Sr age en-keyword=Sr isotope kn-keyword=Sr isotope en-keyword=K-rich fragment kn-keyword=K-rich fragment END start-ver=1.4 cd-journal=joma no-vol=6 cd-vols= no-issue=1 article-no= start-page=29 end-page=38 dt-received= dt-revised= dt-accepted= dt-pub-year=1999 dt-pub=19990920 dt-online= en-article= kn-article= en-subject= kn-subject= en-title=Chemical and Rb-Sr isotopic features of the shock-melted chondrite Yamato-793533 kn-title=衝突溶融隕石Y-793533コンドライトの化学組成とRb-Sr系 en-subtitle= kn-subtitle= en-abstract= kn-abstract=The Sr isotopic compositions and Rb and Sr abundances, as well as major element abundances in olivine, pyroxenes and glass, were determined for a chip and 21 fractions separated from a shock-melted chondrite Yamato-793533, a dark-colored, porous stone with glassy texture. Two lithologies were recognized for the 1.5g specimen studied (Yamato-793533, 67) ; L (Main portion) and L to LL (Dark portion) chondritic in terms of chemical compositions of olivine and pyroxenes. The chemical compositions of glass are relatively homogeneous (SiO2=67-77%) compared to those of other ordinary chondrites, suggesting a moderate cooling rate after shock-melting. The data points for fractions do not foem any isochron in a 87Rb/86Sr vs. 87Sr/86Sr diagram. However, it is noted that six out of nine points for the dark portion plot around a 1.2 Ga line, while most of points for the main portion plot around a 4.55 Ga chondrite isochron. The observed difference could be responsible for difference in melting degrees between the two portions. Similar Rb-Sr features have been found among shock-melted Yamato-79 LL-chondrites which are considered to be paired stones experienced the same shock-melting event at 1.2 Ga. Consequently, the Rb-Sr systematics as well as petrologic features strongly suggest that Yamato-793533 is a member of a series of the shock-melted Yamato-79 LL-chondrites. en-copyright= kn-copyright= en-aut-name=OkanoOsamu en-aut-sei=Okano en-aut-mei=Osamu kn-aut-name=岡野修 kn-aut-sei=岡野 kn-aut-mei=修 aut-affil-num=1 ORCID= en-aut-name=KatayamaHiroko en-aut-sei=Katayama en-aut-mei=Hiroko kn-aut-name=片山博子 kn-aut-sei=片山 kn-aut-mei=博子 aut-affil-num=2 ORCID= en-aut-name=NakamuraNoboru en-aut-sei=Nakamura en-aut-mei=Noboru kn-aut-name=中村昇 kn-aut-sei=中村 kn-aut-mei=昇 aut-affil-num=3 ORCID= affil-num=1 en-affil= kn-affil=岡山大学大学院自然科学研究科 affil-num=2 en-affil= kn-affil=岡山大学理学部地球科学科 affil-num=3 en-affil= kn-affil=神戸大学理学部地球惑星科学科 en-keyword=LL-chondrite kn-keyword=LL-chondrite en-keyword=Shock-melting kn-keyword=Shock-melting en-keyword=Sr isotope kn-keyword=Sr isotope END