Origin of K-cymrite and kokchetavite in the polyphase mineral inclusions from Kokchetav UHP calc-silicate rocks: evidence from confocal Raman imaging

Abstract

Confocal Raman Imaging revealed the coexistence of kokchetavite and K-cymrite (KAlSi 3 O 8 ·H 2 O) in association with muscovite/phengite, lollingite, calcite and α-cristobalite in polyphase mineral inclusions in clinopyroxene of calc-silicate ultrahigh-pressure metamorphic (UHPM) rocks from the Kokchetav Complex (northern Kazakhstan). Experiments have shown that K-cymrite is stable under high pressure conditions; however, this phase never had been reported from UHPM rocks before. The mode of occurrence of K-cymrite and kokchetavite in these rocks is strong evidence for kokchetavite formation through the dehydration of K-cymrite. The presence of fluid inclusions and K-cymrite in the polyphase mineral inclusions testify for water-saturated conditions in the rock-forming environment near peak metamorphic conditions.