Metamorphic evolution and zircon ages of a Barrovian metamorphic series in central-western Inner Mongolia, China: Insights into the tectonic evolution of the Central Asian Orogenic Belt

The P-T path provides clues to the tectonic setting associated with Barrovian metamorphism. A typical Barrovian metamorphic series occurs in the metapelite suite of the Baoyintu Group in central-western Inner Mongolia in the eastern Central Asian Orogenic Belt. However, the tectonic significance of this series is unknown because the P-T path has yet to be established. In this study, systematic data on the metamorphic evolution of this series are presented for the mica schist samples in different zones. Phase modelling using THERMOCALC suggests peak metamorphic conditions of-7 kbar/570-575 degrees C in the garnet zone,-8 kbar/595 degrees C in the staurolite zone, 9-10 kbar/630-650 degrees C in the kyanite zone, and-12 kbar/710-720 degrees C in the sillimanite zone. The P-T path of the Barrovian metamorphic series records a crustal over-thickening event during the prograde metamorphic stage, followed by post-peak decompression and cooling stages. U-Pb dating of detrital zircon in the mica schist sample in the biotite zone by laser ablation-inductively coupled plasma-mass spectrometry yields ages of 3740-1726 Ma with major peaks at 2501 and 1821 Ma, suggesting the detrital zircons were sourced from the North China Craton. Moreover, the metamorphic age of 397 +/- 3 Ma of the mica schist sample in the sillimanite zone is consistent with the timing of the Devonian orogeny previously identified in central Inner Mongolia. We thus suggest that the Barrovian metamorphic series can be attributed to metamorphism associated with Devonian orogenic processes after the closure of the Paleo-Asian Ocean in the central Inner Mongolia domain.