T12 Ultrahigh-Pressure Metamorphism: Observations from Nano- through Outcrop- to Plate-Tectonic Scales I: In Honor of J.G. Liou, 2011 MSA Roebling Medalist

Sunday, 9 October 2011
8:00 AM - 12:00 PM
Room 102D-F

AEM CHARACTERIZATION OF METAMORPHIC MICRODIAMONDS FROM GARNET-CLINOPYROXENE ROCK (KUMDY KOL) AND GNEISS (BARCHI KOL), KOKCHETAV MASSIF

Paper number: T12-5
Program: Technical Sessions
Time: 9:05 AM – 9:20 AM

Authors

Abstract

Metamorphic microdiamonds within two Kumdy Kol garnet-clinopyroxene rock samples and two Barchi Kol gneissic samples from the Kokchetav ultrahigh-pressure (UHP) terrane were analyzed by analytical electron microscopy (AEM). Whereas syngenetic nano-meter sized facetted fluid inclusions are highly abundant in microdiamonds from garnet-clinopyroxene rock samples, with chemical characteristics of inclusions closely resembling those in microdiamonds from Kokchetav dolomite marbles (Hwang et al., 2005, 2006), microdiamonds in Barchi Kol gneissic samples surprisingly contain no inclusions whatsoever. These observations, in conjunction with the characteristic rugged, spheroids/cuboid morphology of microdiamond in Kumdy Kol garnet-clinopyroxene rock samples and the {111} facetted octahedral morphology of microdiamond from Barchi Kol gneissic samples, indicate that the diversified characteristics of the formation media of metamorphic microdiamond in UHP rocks due to host-rock buffering must have played a decisive role for the different morphologies and growth rates/mechanisms of metamorphic microdiamonds (Hwang et al., 2005, 2006). The formation media of metamorphic microdiamonds from the Barchi Kol and the Kumdy Kol areas might just represent two extremes of the whole compositional spectrum: one is a highly viscous silica-rich melt leading to slow growth and formation of inclusion-free octahedral microdiamonds, the other is a silica-poor, low viscous, ultrapotassic fluid causing fast growth, entrapment of fluid inclusions at the growth fronts, and formation of rugged spheroids/cuboid microdiamonds.

Hwang, S.L., P., Shen, H.T., Chu, T.F., Yui, J.G.., Liou, N.V., Sobolev, and V.S., Shatsky, 2005. Potassic COH fluid in metamorphic microdiamond. Earth and Planetary Science Letters, 231, 295-306.

Hwang, S.L., P., Shen, H.T., Chu, T.F., Yui, H.-P., Schertl, J.G.., Liou, N.V., Sobolev, 2006. Nanometer-size P/K-rich silica glass (former melt) inclusions in microdiamond from the gneisses of Kokchetav and Erzgebirge massifs: Diversified characteristics of the formation media of metamorphic microdiamond in UHP rocks due to host-rock buffering, Earth and Planetary Science Letters, 243, 94-106.