An early high-pressure history preceeded pelitic ultrahigh-temperature granulite formation in the Tuguiwula area, Khondalite Belt, North China Craton

Following the first petrological studies on UHT metamorphic pelitic granulite of the Tuguiwula area, Jining complex, North China Craton, considerable work has been done in the past decades that revealed an anticlockwise P-T path, reaching a maximum pressure range at ca.10 kbar. In this study, we re-investigated pelitic granulite from this locality and determined four distinct metamorphic stages, P-max (M2), T-max (M3), cooling (M4), and decompression (M5), which document a clockwise P-T trajectory, providing evidence for an early high-pressure metamorphic scenario at pressures >11.8 kbar. The P-max (M2) conditions were calculated using garnet domains with highest X-Ca (grt) isopleths, which contain inclusions of kyanite. The entire mineral assemblage in equilibrium is Grt + Ky + Qz + Rt + Kfs + liq +/- Ilm, suggesting minimum pressures of 11.8 kbar. The T-max metamorphism (M3) is characterized by the assemblage Grt + Qz + Pl + Ilm + Kfs + Sil + liq. Geothermobarometrical studies which include two-feldspar geothermometry and Zr-in-rutile thermometry yields a P-T range of 990 degrees C-995 degrees C and 9-10 kbar, indicating an ultra-high temperature (UHT) metamorphic overprint. The subsequent retrograde metamorphic stages M4 and M5 are characterized by the formation of Bt + Sil + Qz + symplectites and cordierite replacing garnet rims, suggesting P-T conditions of 840 degrees C-960 degrees C/8.5-9.5 kbar and 800 degrees C-850 degrees C/5.5-6.8 kbar, respectively. SHRIMP U-Pb age dating provided a weighted mean Pb-207/Pb-206 age of 1911.6 +/- 4.5 Ma that represents the timing of the UHT metamorphic stage. The current study on pelitic granulite documents two novel results which have a significant impact on the geotectonic evolution: (1) a clockwise P-T path instead of an anticlockwise one was derived, and (2) P-T estimates are much higher than those reported from previous studies of both, pressure and temperature. The available P-T data of the pre-HP metamorphic stage together with the clockwise P-T trajectory, UHT-, cooling- and decompression-stages of the current study reflect a possible collision or subduction origin.