Abstract
The Makbal Formation of the Northern Kyrgyz Tien-Shan consists mainly of phengite-quartz schists (meta-quartzite), garnet-chloritoid-talc schists and marbles, all of which contain lenses of amphibolites and eclogites. The garnet-chloritoid-talc schists from the Makbal complex underwent UHP metamorphism. The mineral assemblage of the UHP stage is garnet + chloritoid + talc + phengite + rutile + coesite ± glaucophane ± florencite ± monazite ± apatite.
Electron microprobe analyses of monazites from the garnet-chloritoid-talc schists provide two similar CHIME ages. Monazites occurring in the matrix of the schists yield an age of 481 ± 26 Ma, and monazite inclusions in porphyroblastic garnets yield an age of 480 ± 56 Ma. These two ages are essentially the same within error, and suggest the peak UHP metamorphism in the Makbal area of the Northern Kyrgyz Tien-Shan occurred at ∼ 480 Ma.
