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Published March 1977 | public
Book Section - Chapter

Slowly cooled microgabbros 15065 and 15555


Experimental equilibration of 15555 and 15065 in high-purity iron capsules in a closed system causes little change in the sample's bulk composition. Comparison of mineral zoning trends with the experimental sequence suggests that the early crystallizing phases in the rock maintained surface equilibrium with the liquid. Olivine and pyroxene chemistry indicates that 15555 cooled slightly more rapidly than 15065 which cooled at ~0.2-0.3°C/day. Even though the cooling rates are slow, significant amounts of accumulated olivine or pyroxene are not found in these rocks-they represent liquid compositions. These liquids appear to have been fractionated during ascent through the crust (15065) or to have been derived from an olivine-pyroxene source (15555) of Fe/Fe+ Mg ~ 0.73 at a depth between 150-200 km.

Additional Information

© 1977 Pergamon Press. This work was supported by NASA grant NGL-22-007-247 and the Committee on Experimental Geology and Geophysics of Harvard University. We appreciate review comments by J. S. Huebner, L.A. Taylor, and R. J. Williams.

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