Petrology of metamorphic rocks from the Atbashy complex, Southern Tien-Shan, Kyrgyzstan

摘要

The high- to ultrahigh-pressure metamorphic rocks of the Atbashy complex were petrologically investigated. The eclogites of the Choloktor Formation show a prograde evolution from epidote-blueschist facies ( P ?=?17–21?kbar and T ?=?450–515?°C) to peak eclogite-UHP conditions ( P ?=?26–29?kbar and T ?=?545–615?°C) with a subsequent epidote-amphibolite and greenschist facies overprint. The mica-schists of the Choloktor Formation also show a clockwise P-T path from blueschist/epidote-blueschist facies conditions through peak eclogite facies conditions ( P ?=?21–23?kbar and T ?=?530–580?°C) to retrograde epidote-amphibolite and greenschist facies stages. A comparison of the P-T paths in the eclogites and mica-schists of Choloktor Formation reveal that they may have shared their P-T history from peak to retrograde stages. The mica-schists of the Atbashy Formation record peak metamorphism of P ?=?10–12?kbar and T ?=?515–565?°C, which indicates that the highest grade of regional metamorphism in the Atbashy Ridge was epidote-amphibolite facies. The newly obtained P-T conditions for the mica-schists of Choloktor Formation indicate that sheets of sedimentary rocks were brought to great depths along the subduction zone and they metamorphosed under eclogite facies HP conditions. The eclogite blocks were amalgamated with mica-schists of Choloktor Formation in the eclogite facies HP conditions and together they experienced isothermal decompression to ～40?km. During this path, the eclogites and mica-schists of Choloktor Formation docked with mica-schists of Atbashy Formation at 10–12?kbar and 515–565?°C, and from this depth (～40?km) the whole sequence was exhumed together. These new results improve our understanding of high-pressure metamorphism in subduction-related accretionary prism zones and the exhumation processes of deeply-seated rocks in the Atbashy HP-UHP complex. Graphical abstract Display Omitted Highlights ? The Choloktor eclogites record peak UHP conditions (P?=?26–29?kb & T?=?545–615?°C). ? The host mica-schists of Choloktor Fm. experienced eclogite facies metamorphism. ? The mica-schists of Atbashy Fm. record peak conditions ( P ?=?10–12?kb & T ?=?515–565?°C). ? These rock units shared exhumation P-T path from ～40?km depth.