Metamorphic P-T-t paths retrieved from the amphibolites, Lushan terrane, Henan Province and reappraisal of the Paleoproterozoic tectonic evolution of the Trans-North China Orogen

Abstract

Garnetiferous amphibolites preserving prograde inclusion assemblages (M1) within garnet porphyroblasts, metamorphic peak assemblages (M2) and post-peak symplectitic assemblages (M3) have been found in the Lushan terrane, Henan Province, Taihua Metamorphic Complex, southernmost section of the NS-striking Palaeoproterozoic Trans-North China Orogen (TNCO). Geothermobarometric computation shows that the M1, M2 and M3 assemblages were formed under the P–T conditions of 650–730°C/4.9–8.1kbar, 740–810°C/9–10.8kbar and 750–760°C/5.0–7.7kbar, respectively, suggesting that these amphibolites record clockwise P–T paths including nearly isothermal decompression (ITD) segments similar to the west-Alpine type P–T paths, indicative of being resulted from an orogenic process. High resolution SIMS U–Pb dating of metamorphic zircons suggests that the metamorphism took place at ca. 1.95–1.75Ga. These data imply that the Palaeoproterozoic collision between the Eastern and Western Blocks of the North China Craton along the southernmost terminal of the TNCO not only started earlier, but also continued longer, than the middle and north sections of the TNCO.