Computer Science
Scientific paper
May 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988e%26psl..88..321h&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 88, no. 3-4, May 1988, p. 321-329.
Computer Science
14
Earth Mantle, Geochemistry, High Pressure, Magnesium Oxides, Minerals, Aluminum Compounds, Calcium Compounds, Melting
Scientific paper
Experimental melting relations to 20 GPa are used to show that the commonly accepted model of komatiite formation by noninvariant melting (olivine + liquid) is not exclusive. Komatiites could also have formed by pseudoinvariant melting (olivine + pyroxene + garnet + liquid; modified spinel + majorite + liquid) along the anhydrous solids at high pressures. The MgO content of komatiites may be used to determine the depth, but not the degree of partial melting. There would have been little change in MgO content at a high-pressure invariant point. It is estimated that early Archean komatiites, containing 20-28 percent MgO, formed at a depth of 130 to 260 km, with late Archean komatiites forming at depths corresponding to the present day transition zone, or at shallower levels from a primitive mantle source. Komatiites which originated by partial melting in a lower mantle formed by majorite fractionation should have geochemical characteristics that have not yet been reported. Either melting did not extend into the lower mantle or, if it did, the upper and lower mantles were isolated by a chemical and thermal boundary layer in Archean times.
Herzberg Claude T.
Ohtani Eiji
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