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Trends of Sr and Nd isotopes through time near the Japan Sea in northeastern Japan

Nohda, S. and Wasserburg, G. J. (1986) Trends of Sr and Nd isotopes through time near the Japan Sea in northeastern Japan. Earth and Planetary Science Letters, 78 (2-3). pp. 157-167. ISSN 0012-821X. doi:10.1016/0012-821X(86)90057-9.

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Nd and Sr isotopic analyses were made on selected volcanic rocks of known stratigraphic age from a limited area in the “Green Tuff” region, northeastern Japan, and in adjacent areas. Two ultramafic inclusions from Ichinomegata were also analyzed. The volcanic rocks range in age from 27 to 6 Ma, and vary in ε_(Nd) from −0.9 to 5.7 and in ε_(Sr) from 14.1 to −16.3. The isotopic data plot generally along the region of the “mantle array”. When plotted against time, the isotopic ratios are found to be a regular function of geologic age. The results indicate that: (1) the volcanic rocks in the area are part of a “related” sequence or evolutionary pattern over a time period of 27 Ma; (2) the “evolutionary” pattern goes from an initially enriched source to that of a very depleted source. The shift in isotopic composition appears to reflect the ongoing lining of magma conduits or the decreasing extraction of lower crustal contributions with increasing infiltration of oceanic magma types in an environment where the crust is thinning. Based on the geotectonic development of this area due to the back-arc spreading of the Japan Sea, we identify two different stages: the pre-opening stage (> 15 Ma) and the post-opening stage (< 15 Ma). The volcanic rocks of the pre-opening stage are characterized by an enriched isotopic signature, and those of the post-opening era by a depleted signature. The host rocks of the Kuroko ore deposit lie within this evolutionary trend and contain a substantial amount of continentally derived materials processed through an oceanic environment. In general, we infer that the degree of continental crust involvement is high during the pre-opening stages of a back-arc basin when it is associated with a rifted continental mass.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1986 Elsevier Science. Received January 2, 1986; revised version received March 5, 1986. We are deeply indebted to Dr. Y. Otofuji and T. Matsuda for their cooperation throughout the field work and discussions. Dr. H.H. Ngo generously gave suggestions to S.N. throughout the analytical work at the Lunatic Asylum. Discussion with Prof. S. Banno, Dr. K. Ishizaka, Y. Tatsumi and H.W. Menard improved the manuscript. We thank Prof. K. Aoki who generously supplied samples of the ultramafic inclusions of Ichinomegata. S.N. was financially supported by a Kyoshin scholarship and the Kyoto Sangyo University. This report was improved by two supportive but anonymous reviewers. This work was supported by NSF grant EAR-8312882 in a laboratory operated under NASA grant NAG 9-43.
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Kyoshin scholarshipUNSPECIFIED
Kyoto Sangyo UniversityUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences4092
Lunatic Asylum Lab475
Issue or Number:2-3
Record Number:CaltechAUTHORS:20131023-105701825
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Official Citation:S. Nohda, G.J. Wasserburg, Trends of Sr and Nd isotopes through time near the Japan Sea in northeastern Japan, Earth and Planetary Science Letters, Volume 78, Issues 2–3, June 1986, Pages 157-167, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42024
Deposited By: Ruth Sustaita
Deposited On:23 Oct 2013 18:14
Last Modified:10 Nov 2021 04:37

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