Asthenospheric injection and back-arc opening: Isotopic evidence from northeast Japan

Nohda, Susumu; Tatsumi, Yoshiyuki; Otofuji, Yo–ichiro; Matsuda, T.; Ishizaka, Kyoichi

doi:10.1016/0009-2541(88)90029-0

Cited by 132 publications

(76 citation statements)

References 35 publications

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“…A possibility of the existence of a primitive mantle in the oceanic and continental regions, termed the DUPAL anomaly, has been shown in the Southern Hemisphere on the basis of Sr, Pb and Nd isotope data (Dupre and Allegre, 1983, Hart, 1984, Hawkesworth et al, 1986. For the Japan Arc, the possibility of a primitive or enriched mantle has been suggested only on the basis of Sr and Nd isotopic and/or major element compositions (Kagami et al, 1986, Nohda et al, 1988). …”

Section: Geochemiscal Constraints On Island Arc Tholeiite Magma Genesismentioning

confidence: 99%

Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of Northeast Japan.

et al. 1992

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Section: Geochemiscal Constraints On Island Arc Tholeiite Magma Genesismentioning

confidence: 99%

Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of Northeast Japan.

et al. 1992

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“…The process responsible for such a structural transition of source region is presumably related to injection of N-MORB source-like asthenosphere into pre-existing IA source material beneath BABs at initial stage, as propos ed by Nohda et al (1988) for the opening of the Sea of Japan BAB. This may have caused the rif ting of the Okinawa Trough and the resultant retreat of the Ryukyu IA towards the NW Pacific.…”

Section: Comparison With Mid-ocean Ridge and Other Back-arc Basin Basmentioning

confidence: 99%

Petrology and geochemistry of volcanic rocks dredged from the Okinawa Trough, an active back-arc basin.

1990

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Volcanic rocks dredged from the Okinawa Trough, an active back-arc basin behind the Ryukyu island arc (IA)-trench system associated with a subduction of the Philippine Sea plate, encompass a wide variety of petrology and geochemistry, ranging from basalts to rhyolites through andesites. The basalts, consisting of highly vesicular pillow lavas, are moderately porphyritic with phenocrysts of olivine, plagioclase and minor clinopyroxene. Their glass and bulk rock compositions , especially their large-ion lithophile element (LILE) abundances, are transitional between the Ryukyu IA basalts (LILE enriched) and normal-type mid-ocean ridge basalts (N-MORBs, LILE-depleted) . The rhyolites are moderately porphyritic, including phenocrysts of plagioclase and orthopyroxene with or without clinopyroxene and hornblende, and have the close geochemical affinity with the Ryukyu IA rhyolites . It follows that the rhyolites were derived from an IA-type source material similar to that for the Ryukyu IA volcanics, but the basalts were derived from a less LILE-enriched source material approaching that for N-MORBs. Available K-Ar ages indicate the rhyolitic volcanism prior to the basaltic one . It is, therefore, most likely that the magma source region beneath the Okinawa Trough has changed with time from an IA type to a N-MORB type during the back-arc rifting. On the other hand , the andesites are highly porphyritic with phenocrysts of plagioclase, orthopyroxene and clinopyroxene , and have the K Ar age similar to that of the basalts. Most importantly, the andesites exhibit many lines of textural and compositional evidence for mixing between basaltic melt, and rhyolitic partial melt of pre-existing IA lower crust that was presumably heated by the former melt. This again suggests the structural transition of the magma source region beneath the Okinawa Trough, which may be most characteristic of the in itial stage of back-arc basin volcanism in general.

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“…The 40 Ar dates of three dredged samples from the slope of the Japanese Islands in the basin yielded ages of 23-24 Ma and an age of 26 Ma for an andesite from the Yamato Bank (Kaneoka and Yuasa, 1988). Nohda and Wasserburg (1986) and Nohda et al (1988) reported Nd and Sr isotopic compositions for Tertiary volcanic rocks from the northeast Japan arc and documented secular variation in the isotopic composition of the enriched to depleted signature of the magma source region through time. This secular variation was considered in the framework of backarc opening in the Japan Sea and attributed to the growth of depleted asthenospheric materials into the preexisting enriched upper mantle.…”

Section: Introductionmentioning

confidence: 99%

Nd and Sr Isotopic Study of Leg 127 Basalts: Implications for the Evolution of the Japan Sea Backarc Basin

Nohda¹,

Tatsumi²,

Yamashita³

et al. 1992

Proceedings of the Ocean Drilling Program

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Sr and Nd isotopic compositions are reported for basaltic rocks collected during ODP Leg 127 from the Yamato Basin, a rifted backarc basin in the Japan Sea. The basalts are classified into two groups in terms of Nd isotopic composition: the upper sills at Site 797 are characterized by higher 143 Nd/ 144 Nd ratios (0.513083-0.513158, ε Nd = 8.68-10.14) and the basalts from Site 794 and the lower sills at Site 797 have lower 143 Nd/ 144 Nd ratios (0.512684-0.512862, ε Nd = 0.90-4.37). All of the basalts show higher Sr isotopic compositions than those of the mantle array, which is attributed to seawater alteration. The basalts with lower Nd isotopic values ranging in age from 20.6 to 17.3 Ma have tapped an enriched subcontinental upper mantle (SCUM) with the minor involvement of a depleted asthenospheric mantle (AM). Subsequent change in composition through the physical replacement of SCUM by AM yielded the basalts of the upper sills of higher Nd isotopic compositions. This event within the upper mantle was associated with the breakup of the overlying lithosphere during the rifting of the Japan Sea backarc basin.

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Asthenospheric injection and back-arc opening: Isotopic evidence from northeast Japan

Cited by 132 publications

References 35 publications

Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of Northeast Japan.

Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of Northeast Japan.

Petrology and geochemistry of volcanic rocks dredged from the Okinawa Trough, an active back-arc basin.

Nd and Sr Isotopic Study of Leg 127 Basalts: Implications for the Evolution of the Japan Sea Backarc Basin

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