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Cumulate Xenolith in Oahu, Hawaii: Implications for Deep Magma Chambers and Hawaiian Volcanism

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Science  07 Sep 1990:
Vol. 249, Issue 4973, pp. 1154-1157
DOI: 10.1126/science.249.4973.1154

Abstract

The maximum depth at which large (>1000 km3) terrestrial mafic magma chambers can form has generally been thought to be the Moho, which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins. However, the presence of layers of cumulus magnesium-rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from Oahu, Hawaii, suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers; Hawaiian shield-building magmas may pond and fractionate in such magma chambers before continuing their ascent. This depth is at or near the base of the 90-million-year-old lithosphere beneath Oahu; thus, rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere.

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