Metamorphic petrology of the Barchi-Kol metabasites, western Kokchetav ultrahigh-pressure-high-pressure massif, northern Kazakhstan

In the Barchi-Kol area, located at the westernmost part of the Kokchetav ul trahigh pressure (UHP) to high-pressure (HP) massif, northern Kazakhstan, m etabasites from the epidote amphibolite (EA) facies to the coesite eclogite (CEC) facies are exposed. Based on the equilibrium mineral assemblages, th e Barchi-Kol area is divided into four zones: A, B, C and D. Zone A is char acterized by the assemblage: epidote + hornblende + plagioclase + quartz, w ith minor garnet. Zone B is characterized by the assemblage: garnet + hornb lende + plagioclase + quartz + zoisite. Zone C is defined by the appearance of sodic-augite, with typical assemblage: garnet + sodic-augite + tscherma kite-pargasite + quartz +/- plagioclase +/- epidote/clinozoisite. Zone D is characterized by the typical eclogite assemblage: garnet + omphacite + qua rtz + rutile, with minor phengite and zoisite. Inclusions of quartz pseudom orph after coesite were identified in several samples of zone D. Chemical c ompositions of rock-forming minerals of each zone were analyzed and reactio ns between each zone were estimated. Metamorphic P-T conditions of each zon e were estimated using several geothermobarometers as 8.6 +/- 0.5 kbar, 500 +/- 30 degrees C for zone A; 11.7 +/- 0.5 kbar, 700 +/- 30 degrees C for z one B; 12-14 kbar, 700-815 degrees C for zone C; and 27-40 kbar, 700-825 de grees C for zone D.