The bearing of phase equilibria in simple and complex systems on the origin and evolution of some well-documented garnet-websterites |
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| Authors: | Claude T Herzberg |
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| Institution: | (1) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, 02138 Cambridge, MA, USA |
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| Abstract: | The temperatures and pressures of subsolidus equilibration of garnet-websterites (garnet+clinopyroxene+orthopyroxene) can be determined to within 3 kilobars from alumina solubility properties of clinopyroxene (Herzberg, 1978) and orthopyroxene (Wood, 1974, 1975). These calculations require knowledge of the oxidation state of iron and the effect of alumina on the mutual solubility of the two pyroxenes. The conditions of total dissolution of exsolved garnet and orthopyroxene required to yield single-phase subcalcic clinopyroxenites from Salt Lake Crater and the French Pyrenees have been determined. Many of these clinopyroxenites were transported 20 to 60 km up the mantle column before exsolution was terminated. Such transport was probably accomplished by convective upwelling of hot mantle peridotite and its contained anatectic products, rather than by precipitation from ascending magmas. |
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