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Noble gas evidence for the presence of recycled material in magma sources of the Shatsky Rise

By
Takeshi Hanyu
Takeshi Hanyu
Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan
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Kenji Shimizu
Kenji Shimizu
Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan
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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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Published:
May 01, 2015

The Shatsky Rise is an oceanic plateau consisting of three main massifs that were constructed in the Pacific Ocean by intense volcanism during the Late Jurassic to Early Cretaceous. In order to explore the sources of this oceanic plateau, we present noble gas compositions from fresh quenched glasses cored by ocean drilling at Integrated Ocean Drilling Program Site U1347 on the Tamu Massif and Site U1350 on the Ori Massif. The studied glasses are normal-type basalts, the most abundant of four types of basalts defined by trace element compositions. Possible disturbances of noble gas compositions by posteruption radiogenic ingrowth in aged glasses are assessed by extraction of gases from glass vesicles by stepwise crushing. The 3He/4He ratios in glasses from Site U1347 are lower than atmospheric 3He/4He, presumably owing to magma degassing coupled with radiogenic ingrowth of 4He. In contrast, glasses from Site U1350 exhibit a limited range of 3He/4He (5.5–5.9 Ra). Uniform 3He/4He cannot be achieved if gases in glass vesicles have been affected by secondary contamination or posteruption radiogenic ingrowth. Therefore, the uniform 3He/4He in the normal-type basalts from Site U1350 is ascribed to their source characteristics. Relatively low 3He/4He among oceanic basalts suggests the involvement of recycled slab material in the source of the normal-type basalts. However, the depleted radiogenic isotope signatures are inconsistent with recycled slab being a distinct melting component. Instead, we propose that the normal-type basalts of the Shatsky Rise were sourced from a domain where subducted fertile material is dispersed in the mantle.

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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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