Metamorphic P-T-t path of Triassic eclogite from the Rongcheng region, eastern China: implications for the tectonic evolution of Sulu orogenic belt

Interpretation and inversion of P-T (Pressure-Temperature) paths of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks are critical to understanding the subduction and exhumation histories of an orogen. The Sulu orogen constitutes the eastern part of the Dabie-Sulu orogen, in which, HP metamorphic rocks are relatively poorly as studied compared to the well-documented UHP metamorphic rocks. This study presents the P-T paths of HP eclogites constructed by petrography, mineral chemistry, and pseudosection modelling by using the GeoPS software within the MnNCFMASKHTO (Mn-CaO-FeO-MgO-Al2O3-SiO2-K2O-H2O-TiO2-O-2) system. Sample 19LR70-1 mainly consists of omphacite, garnet, quartz, minor rutile, ilmenite, and amphibole. Sample 19LR71-1 is mainly composed of omphacite, garnet, kyanite, and accessory minerals of rutile and amphibole. These two eclogite samples recorded clockwise P-T paths with peak P-T conditions of P >= 21.3 kbar, T >= 755 degrees C and P >= 23.0 kbar, T >= 871 degrees C, respectively. Well-correlated U-Pb ages and trace element data show that the protoliths of eclogites were 655-699 Ma and 676-754 Ma, the metamorphic ages were 212-232 Ma, and the time of partial melting were 221-225 Ma. Combined with regional geological data, we conjectured that before 240 Ma, the South China plate was subducted to the North China craton; subsequently, at 240-220 Ma, HP eclogite facies metamorphism occurred at a depth of 60-70 km. This was followed by the exhumation of these HP metamorphic rocks, coupled with concurrent partial melting, around 220-200 Ma. [Graphical abstract]

Automated summary

The interpretation and inversion of P-T paths of high-pressure and ultrahigh-pressure metamorphic rocks in the Sulu orogen provide insights into the subduction and exhumation histories of the region. This study presents the P-T paths of HP eclogites using petrography, mineral chemistry, and pseudosection modelling. The results show clockwise P-T paths with peak conditions of P >= 21.3 kbar, T >= 755 degrees C and P >= 23.0 kbar, T >= 871 degrees C. Combined with geological data, the findings suggest subduction of the South China plate to the North China craton before 240 Ma, followed by HP eclogite metamorphism and subsequent exhumation with partial melting around 220-200 Ma.