2009 Annual Science Report
University of Hawaii, Manoa Reporting | JUL 2008 – AUG 2009
D/H Measurements in Samples From Mantle Hotspots
The origin of Earth’s water is an open question. We are trying to constrain the origin of Earth’s water by measuring the D/H ratios of glass inclusions inside olivine grains from lavas erupted at the Hawaiian and Icelandic hot spots. The hope is that these glass inclusions retain hydrogen from the deep mantle of the Earth, hydrogen that may preserve the original hydrogen isotopic composition of the Earth.
We have carried out the first round of D/H measurements on a suite of sample from the Hawaiian deep drill core. The selected samples are pillow lavas erupted at sufficient depth beneath the ocean surface that the hydrogen was retained in the lavas. The samples show significant secondary alteration that affects many of the olivine crystals. But some crystals remain pristine, and inclusions within these olivines appear to be unaltered. About 70% of these inclusions partially crystallized during initial cooling to form feathery pyroxene crystals. About 30%, typically the smaller ones, quenched as glasses. We measured a suite of melt inclusions from three different samples, including both partially crystallized and glassy inclusions. The precision of the measurements wasn’t as high as we had hoped, but we believe we can improve on the measurement precision in the next round of measurements. Based on the first round of measurements, we are working to find some better samples from within the Hawaii deep drill core that contain unaltered, pristine glass inclusions. A new round of measurements will take place in late fall or early winter.