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Blueschist exposed in the northwestern Qiangtang terrane, northern Tibet, western China (～84°30′E, 34°24′N), provides new constraints on the tectonic evolution of Qiangtang as well as northern Tibet. The blueschist represented by lawsonite-and glaucophane-bearing assemblages equilibrated at 375-400 °C and ～11 kbar. 40Ar-39Ar analysis on mineral separate from one blueschist sample yielded a well-defined plateau age of ～242 Ma. Geochemical studies show the blueschist is metamorphosed within-plate basalts. The high pressure-low temperature blueschist indicates a Triassic event of lithosphere subduction, and clearly represents an extension of the central Qiangtang metamorphic belt, and defines an in situ suture between eastern and western Qiangtang.
Blueschist exposed in the northwestern Qiangtang terrane, northern Tibet, western China (~ 84 ° 30’E, 34 ° 24’N) provides new constraints on the tectonic evolution of Qiangtang as well as northern Tibet. The blueschist represented by lawsonite-and glaucophane-bearing assemblages equilibrated at 375-400 ° C and ~ 11 kbar. 40Ar-39Ar analysis on mineral separate from one blueschist sample yielded a well-defined plateau of ~ 242 Ma. Geochemical studies show the blueschist is metamorphosed within-plate basalts The high pressure-low temperature blueschist indicates a Triassic event of lithosphere subduction, and clearly represents an extension of the central Qiangtang metamorphic belt, and defines an in situ suture between eastern and western Qiangtang.