REACTION TEXTURES IN CLINOZOISITE GNEISSES
A.V. Korsakov, K. Theunissen*, O.A. Kozmenko, and Yu.I. Ovchinnikov
Institute of Mineralogy and Petrography, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Department of Geology and Mineralogy, Royal Museum for Central Africa, B-3080, Tervuren, Belgium
Keywords: Clinozoisite gneiss, melting, reaction textures, Kokchetav, Kazakhstan
Pages: 497-510
Subsection: GEOCHRONOLOGY, GEOCHEMISTRY, PETROLOGY, AND MINERALOGY
Abstract
In the ultrahigh-pressure metamorphic (UHPM) Kokchetav massif (northern Kazakhstan), diamond-bearing clinozoisite gneisses of the western Barchi-Kol' area display three particular types of reaction textures involving melts: (1) kyanite + silicate-carbonaceous melt = clinozoisite-quartz symplectite + CO2; (2) rutile + silicate-carbonaceous melt = titanite + CO2; (3) silicate-carbonaceous melt = calcite + quartz + graphite. Recent experimental work provided constraining evidence on melt-carbonate interaction under UHP conditions and produced a clinozoisite-bearing rock at the interface between metacarbonates and metapelites. These results corroborate well our petrographic observations, illustrating silicate-carbonaceous melt formation under UHPM conditions. Since the amount of partial melts in pelitic material increases when carbonate is available, the carbonate-rich western part of the Kokchetav massif has endured a more extensive weakening. The melting under UHPM conditions induced rheological weakening and thus influenced the exhumation evolution of the UHPM Kokchetav massif.
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