MODIFICATION OF MINERAL INCLUSIONS IN GARNET UNDER HIGH-PRESSURE CONDITIONS: EXPERIMENTAL SIMULATION AND APPLICATION TO THE CARBONATE-SILICATE ROCKS OF THE KOKCHETAV MASSIF
A.L. Perchuka,b, V.V. Davydovac, M. Burchard d , W.V. Maresch e ,H.-P. Schertl e , V.O. Yapaskurt c , O.G. Safonov b
a Institute of Geology of Mineral Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, 35 Staromonetny per., Moscow, 119017, Russia
b Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Moscow Region, 142432, Russia
c Lomonosov Moscow State University, Department of Geology, Vorob'evy Gory, Moscow, 119899, Russia
d Institut fГјr Mineralogie, Ruprecht-Karls-Universitet, Heidelberg, Germany
e Institut fГјr Geologie, Mineralogie, und Geophysik, Ruhr-Universitet, Bochum, Germany
Keywords: Eclogite, melting, garnet, diamond, carbonate-silicate Rock, Kumdy-Kol
Pages: 1153-1168
Abstract
Samples of poikoblastic garnets from the Escambray (Cuba), Maksyutov (Russia), and Sambagawa (Japan) eclogite complexes were heated to 700-1100°C at 3 to 4 GPa (30-40 kbar). Epidote, amphibole, and chlorite inclusions in the garnets underwent dehydration melting over the entire experimental PT -range, which is typical of ultrahigh-pressure (UHP) metamorphic complexes. In the presence of aqueous fluids, carbonate minerals in the inclusions began to melt at 800°C and 3 GPa. Melting gave rise to new garnet, with the composition controlled by the chemistry of the primary inclusions and by PT run conditions. Garnet either grew directly from the melt or formed by replacement of host garnet walls leaving residual melt at the substitution front in the latter case. Partial melting of inclusions decreased the mechanical strength of the garnet host and led to local shearing. The experimental results were used to interpret observed features in two samples of a diamond-bearing and a diamond-free carbonate-silicate rocks from the Kumdy-Kol deposit in the Kokchetav Massif. Multiphase inclusions in both samples contain newly formed garnet with morphologies and compositions consistent with those produced experimentally under the given PT -conditions. Minerals in the inclusions are compositionally similar to those in matrix, thus suggesting that melting may have occurred on a large scale.
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