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Lithium isotope evidence for magmatic assimilation of hydrothermally influenced crust beneath oceanic large igneous provinces

By
Takashi Sano
Takashi Sano
Department of Geology and Paleontology, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba 305-0005, Japan
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Yoshiro Nishio
Yoshiro Nishio
Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsushima 2-15, Yokosuka 237-0061, Japan
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Published:
May 01, 2015

Fresh basalts from the Ontong Java Plateau (OJP) and the Shatsky Rise show lithium enrichments comparable to those of mid-oceanic ridge basalts (MORBs) and ocean island basalts (OIBs), with Li contents being significantly higher at a given MgO content. The Li isotopic compositions of the Shatsky Rise basalts (δ7Li = +6‰ to +7‰) are at the higher end of the range exhibited by OIBs, whereas OJP basalts (δ7Li = +3‰ to +5‰) have Li isotopic compositions similar to MORBs. Among all the basalts from the two oceanic large igneous provinces (LIPs), one sample from the Shatsky Rise is isotopically enriched (e.g., low 143Nd/144Nd and 176Hf/177Hf) and has higher K/Ti and lower La/Nb than the other samples. Relationships between δ7Li and K/Ti, La/Nb, and Rb/Nb of this sample indicate that it may have been affected by mantle that was metasomatized by slab-derived fluids. Apart from this isotopically enriched sample, δ7Li values of basalts from the two oceanic LIPs are positively correlated with K/Ti and Rb/Nb. Obvious linear relationships exist between δ7Li and Yb/Li, Y/Li, and Dy/Li for samples from the Shatsky Rise. These geochemical relationships can be explained by magmatic assimilation of hydrothermally influenced crust. The high δ7Li values of the Shatsky Rise basalts imply that the degree of assimilation is high because shallow magma chambers allow greater assimilation of hydrothermally influenced crust. In contrast, the low δ7Li values of the OJP samples may indicate they have undergone little assimilation as compared with the Shatsky Rise basalts.

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GSA Special Papers

The Origin, Evolution, and Environmental Impact of Oceanic Large Igneous Provinces

Clive R. Neal
Clive R. Neal
Department of Civil & Environmental Engineering & Earth Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, Indiana 46556, USA
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William W. Sager
William W. Sager
Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5007, USA
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Takashi Sano
Takashi Sano
Department of Geology and Paleontology, National Museum of Nature and Science, Tsukuba 305-0005, Japan
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Elisabetta Erba
Elisabetta Erba
Department of Earth Sciences, Università degli Studi di Milano, 20133 Milan, Italy
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Geological Society of America
Volume
511
ISBN print:
9780813725116
Publication date:
May 01, 2015

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