H. Masago, Metamorphic petrology of the Barchi-Kol metabasites, western Kokchetav ultrahigh-pressure-high-pressure massif, northern Kazakhstan, ISL ARC, 9(3), 2000, pp. 358-378
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.