The age of the kyanite-sillimanite metamorphism of the Southern Chuya Complex, Gornyi Altai: U-Pb isotopic dating of zircon

The example of the Southern Chuya metamorphic complex was utilized to obtain the first (for the Altai) U-Pb isotopic zircon dating of metamorphic rocks of the kyanite-sillimanite type. Metamorphism of this type in the Southern Chuya Complex was determined to occur early in the Early Cambrian (T = 555 +/- 6 Ma). These data are at variance with the viewpoint that the Southern Chuya metamorphic complex was a fragment of the Early Precambrian Altai-Mongolia microcontinent (terrane). The example of the Southern Chuya Complex was used to demonstrate that the U-Pb zircon dating of kyanite-bearing metamorphic rocks should be based on the sampling of the highest temperature gneisses (starting from the transition zone between the epidote-amphibolite to amphibolite facies). It can be expected that concordant age values can be obtained for the smallest size fractions of zircon, which could most probably crystallize during the metamorphic process.