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Homogenization of magmas from the Ontong Java Plateau: Olivine-spinel compositional evidence

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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Published:
May 01, 2015

High-Mg Kroenke-type basalts containing 9–11 wt% MgO from the Ontong Java Plateau (OJP) include spinels. These spinels have nearly identical Cr/(Cr + Al) ratios (0.45–0.54), and are generally hosted by olivine phenocrysts with relatively primitive compositions, with Fo contents [100 × Mg/(Mg + Fe2+) in atomic ratios] as high as 88. This implies that the primary OJP magmas were in equilibrium with refractory peridotites (i.e., harzburgites) and were homogenized by large-scale melting and magmatic evolutionary processes. Oxygen geobarometry indicates that the OJP primary magmas record uniform oxygen fugacity (fO2) conditions and are slightly more oxidized (0.6 log units) than normal mid-ocean ridge basalts, but record less-oxidized fO2 conditions than ocean island basalts. These data are consistent with previous studies that suggest the OJP primary magmas were generated by large-scale and extensive melting of a mantle source region under relatively oxidized conditions.

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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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