Quartz pseudomorph after coesite in garnet from a garnet-chloritoid-talc schist, northern Tien-Shan, Kirghiz SSR.

Abstract

Quartz pseudomorphs after coesite were discovered in garnet from a pelitic garnet-chloritoid-talc schist. The pseudomorphs accompany radial cracks developed from them. A metamorphic condition of low temperature (<600°C) and very high pressure (>2.4 GPa) is estimated from the mineral assemblage and mineral compositions.Sedimentary rocks were brought to the depth of about 80 km or more by subduction of oceanic lithosphere or by collision of two continents.

CHIME monazite ages of garnet-chloritoid-talc schists in the Makbal Complex, Northern Kyrgyz Tien-Shan: First report of the age of the UHP metamorphism

“…This is the first report of the age of the UHP metamorphism in the Makbal area, northern Kyrgyz Tien -Shan. The result allows resolution of the P -T -t path of the UHP metamorphic rocks, and provides an important constraint for the Caledonian tectonic development of the Ural -Mongolian folded belt (Tagiri and Bakirov, 1990).…”

“…Layers of the garnet -chloritoid -talc schists are intercalated within the meta -quartzites, and both are folded together. Eclogite blocks occur as lenses within the meta -quartzites and garnet -chloritoid -talc schists (Tagiri and Bakirov, 1990). The garnetchloritoid -talc schists in the Makbal Formation contain coesite and quartz pseudomorphs after coesite as inclusions in garnet porphyroblasts, suggesting a UHP metamorphism (Tagiri and Bakirov, 1990;Ishida et al, 2004).…”

“…Eclogite blocks occur as lenses within the meta -quartzites and garnet -chloritoid -talc schists (Tagiri and Bakirov, 1990). The garnetchloritoid -talc schists in the Makbal Formation contain coesite and quartz pseudomorphs after coesite as inclusions in garnet porphyroblasts, suggesting a UHP metamorphism (Tagiri and Bakirov, 1990;Ishida et al, 2004). High -celadonite content phengites (Si = 7.4 for O = 22) have also been described from the garnet -chloritoid -talc schists (Puelles and Takasu, 1996).…”

“…1). The Makbal Formation consists of meta -quartzites (phengite -quartz schists), garnet -chloritoid -talc schists and marbles, along with blocks of amphibolites and eclogites of various sizes (Tagiri and Bakirov, 1990). Layers of the garnet -chloritoid -talc schists are intercalated within the meta -quartzites, and both are folded together.…”

Newly described eclogites from the Neldy Formation, Makbal district, Northern Tien-Shan, Kyrgyzstan

“…The metamorphic sequence of the Akdzhon Group in the Northern Tien -Shan is divided into two contrasting metamorphic formations, the structurally lower Makbal Formation and the upper Neldy Formation (Tagiri and Bakirov, 1990;Fig. 1).…”