TY - JOUR
T1 - Petrology of the diamond-grade eclogite in the Kokchetav Massif, northern Kazakhstan
AU - Okamoto, K.
AU - Liou, J. G.
AU - Ogasawara, Yoshihide
PY - 2000
Y1 - 2000
N2 - The Kokchetav Massif of northern Kazakhstan is unique because of the abundant occurrence of microdiamond inclusions in garnet, zircon and clinopyroxene of metasediments. In order to determine precise pressure-temperature (P-T) conditions, we have systematically investigated mineral inclusions and the compositions of major silicates in Ti-clinohumite-garnet peridotite and diamond-grade eclogite from Kumdy-Kol. It was found that garnet peridotites from Kumdy-Kol contain assemblages of garnet, olivine, Ti-clinohumite and ilmenite. The garnet contains inclusions that are indicative of both ultrahigh pressure (UHP) and retrograde conditions. Inclusions of hydrous phases such as chlorite, amphibole and zoisite were formed at the post-UHP stage. The study also found that eclogite from Kumdy-Kol contains albite-augite symplectites after omphacitic pyroxene. The core of pyroxene (sodic augite) contains high K2O (up to 1wt%; average 0.24wt%). Phengite is included in the core. Applying the K2O-in-augite geobarometry, which is based on recent experiments, and the garnet-clinopyroxene (Grt-Cpx) geothermometer for peak metamorphism, the eclogites yield P-T estimates of >6 GPa and > 1000°C, and the diamond-grade eclogites yield lower temperature estimates at 900-1000°C and 5 GPa.
AB - The Kokchetav Massif of northern Kazakhstan is unique because of the abundant occurrence of microdiamond inclusions in garnet, zircon and clinopyroxene of metasediments. In order to determine precise pressure-temperature (P-T) conditions, we have systematically investigated mineral inclusions and the compositions of major silicates in Ti-clinohumite-garnet peridotite and diamond-grade eclogite from Kumdy-Kol. It was found that garnet peridotites from Kumdy-Kol contain assemblages of garnet, olivine, Ti-clinohumite and ilmenite. The garnet contains inclusions that are indicative of both ultrahigh pressure (UHP) and retrograde conditions. Inclusions of hydrous phases such as chlorite, amphibole and zoisite were formed at the post-UHP stage. The study also found that eclogite from Kumdy-Kol contains albite-augite symplectites after omphacitic pyroxene. The core of pyroxene (sodic augite) contains high K2O (up to 1wt%; average 0.24wt%). Phengite is included in the core. Applying the K2O-in-augite geobarometry, which is based on recent experiments, and the garnet-clinopyroxene (Grt-Cpx) geothermometer for peak metamorphism, the eclogites yield P-T estimates of >6 GPa and > 1000°C, and the diamond-grade eclogites yield lower temperature estimates at 900-1000°C and 5 GPa.
KW - Diamond-grade garnet, peridotite and eclogite
KW - Kokchetav ultrahigh-pressure rocks
KW - Pressure-temperature estimation
KW - Symplectitic clinopyroxene.
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U2 - 10.1046/j.1440-1738.2000.00284.x
DO - 10.1046/j.1440-1738.2000.00284.x
M3 - Article
AN - SCOPUS:0033753385
VL - 9
SP - 379
EP - 399
JO - Island Arc
JF - Island Arc
SN - 1038-4871
IS - 3
ER -