Nd and Sr isotopic constraints on the origin of igneous rocks resulting from the opening of the Japan Sea, southwestern Japan |
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| Authors: | Y. Terakado T. Fujitani R. J. Walker |
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| Affiliation: | (1) Division of Earth and Environmental Sciences, Faculty of Human Development, Kobe University, Tsurukabuto 3–11, Kobe 657, Japan, JP;(2) Faculty of Liberal Arts, Marine Technical College, Nishikura-cyo, Ashiya 659, Japan, JP;(3) Department of Geology, University of Maryland, College Park, MD 20742, USA, US |
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| Abstract: | Strontium and Nd isotopic compositions and trace element abundances were determined for Cretaceous to late Cenozoic igneous rocks from the Japan Sea side of Southwest Japan in order to investigate the effect of the opening of the Japan Sea on igneous activity. The 87Sr/86Sr ratios for both high and low silica rocks decrease with decreasing age since the middle Miocene, when the opening occurred. Similarly, 143Nd/144Nd values for these rocks increase with decreasing age, and are negatively correlated with 87Sr/86Sr ratios. A two-component mixing process can best account for these isotopic and chemical characteristics. One end-member is likely the subcontinental lithospheric mantle (SCLM) and its derivative mafic to intermediate materials which had ɛNd values of around +3. The other endmember consists of mafic to intermediate rocks with low ɛNd values (e.g., −8), probably located in the lower crust. The mantle upwelling associated with the opening of the Japan Sea did not supply typical MORB or MORB-source materials to the crust, but did provide the heat that caused the melting of lithospheric mantle and lower crust. Received: 29 August 1996 / Accepted: 6 May 1997 |
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