| Co-Investigator(Kenkyū-buntansha) |
SHUTO Kenji Niigata Univ.Faculty of Science., Professor., 理学部, 教授 (50143748)
AKASAKA Masahide Interdisciplinaly Fac.Sci.& Eng., Professor., 総合理工学部, 教授 (20202509)
SAWADA Yoshihiro Interdisciplinaly Fac.Sci.& Eng., Professor., 総合理工学部, 教授 (80196328)
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| Research Abstract |
During the first and second years of this project, we established extraction method of Rb, Sr, Sm and Nd from powdered rock and mineral samples, and measuring methods of Sr and Nd isotope ratios using a thermal ionization mass spectrometer (MAT262), which has recently been installed in the Department of Geology. The mass spectrometer gave high precision Sr and Nd isotope data for international and domestic standard samples. These data have been summarized in three papers and have reported in the Memoirs of the Faculty of Science, Shimane University.
Using the mass spectrometer, we measured Sr and Nd isotope ratios of Cretaceous basic and intermediate intrusive and volcanic rocks in southwest Japan, and examined petrogenetic relationship betweeen these basic to intermediate rocks and voluminous Cretaceous felsic volcanic and intrusive rocks, which are widely distributed in southwest Japan. The basic to intermediate rocks show regional variations in initial Sr and Nd isotope ratios. The basic to intermediate rocks from the Sanyo Belt have high initial Sr and low initial Nd isotope ratios, whereas those from the San'in Belt have low low initial Sr and high Nd isotope ratios. This regional variations in Sr and Nd isotope ratios are comparable with that of the felsic igneous rocks in this district. These data indicate that magma sources of both basic to intermediate rocks and felsic rocks (mostly granitoid rocks), probably uppermost mantle and lower crust, were geochemically more enriched beneath the Sanyo Belt, compared with the sources beneath the San'in Belt.
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