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Project Progress

We have begun a project to look at the evidence that the Earth’s water was partially brought in by cometary sources. The current inference that Earth’s oceans consist of some fraction comet water is based on the comparison of the D/H values in Earth’s ocean, which is much higher than solar nebula values, with cometary D/H which is about twice as high. We are seeking sources of primordial water on Earth as a preliminary step for a more comprehensive analysis of the origin of Earth’s water. A sampling campaign for the D/H Project was carried out in Iceland during the period of 5-27 June by Karen Meech and Thor Thordarson. The principal objectives of the campaign were to locate and collect primitive basalt samples from Holocene (<10 Ka old) volcanic formations that (1) contain abundance (>10 modal%) of mantle derived olivine and plagioclase phenocrysts containing melt inclusions trapped in the crystals during their growth in the source region and (2) exhibit geographic distribution representing the mantle plume as well as the mid ocean ridge derived magmatism in Iceland.

These objectives were largely achieved as we obtained samples of picrites and olivine tholeiites from the Western and Northern Volcanic Zones, which include a strong component of ridge magmatism, as well as samples of picrites and plagioclase-olivine phyric basalts from the young (<3 Ma) Eastern Volcanic Zone. This zone extends to the southwest from the presumed center of the Iceland mantle plume and is strongly influenced by the plume magmatism. Unfortunately, the area of the central highlands that is situated above the presumed plume center could not be sampled during this trip because of unusually extensive snow cover. This area will become accessible in late summer and at the end of August 2006 Thordarson will collect a site of samples from relevant localities. The samples will be processed and prepared for thin sectioning in early fall 2006. Two aliquots will be made of each sample: (a) one that will be used to measure the major, trace and volatile element compositions of melt inclusions and their host crystal phases using the Cameca electron microprobe at the University of Edinburgh and (b) another for D/H measurements using the new ion probe at the University of Hawaii, Manoa.

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