Petrology and metamorphic P–T path of high-pressure mafic granulites from the Jiaobei massif in the Jiao-Liao-Ji Belt, North China Craton

High-pressure mafic granulites from the Jiaobei massif in the southern segment of the Jiao-Liao-Ji Belt (JLJB) situating in the Eastern Block of the North China Craton (NCC) were examined based on an integrated study of petrology, mineral chemistry and pseudosection modeling. Microstructural relationships of the high-pressure mafic granulites indicate four metamorphic stages, including the pre-peak (M1) stage indicated by garnet core + inclusion-phase minerals of hornblende + clinopyroxene + plagioclase + quartz ± epidote ± rutile, the peak (M2) stage featured by garnet mantle/rim + matrix-phase minerals of clinopyroxene + plagioclase + quartz ± rutile, the post-peak (M3) stage characterized by the clinopyroxene + plagioclase + orthopyroxene symplectite, and the retrograde (M4) stage represented by the hornblende + plagioclase symplectite and symplectic clinopyroxene + ilmenite + quartz. By applying the THERMOCALC (Version 3.33) technique in the NCFMASHTO system, the P–T conditions are estimated at 9.4–9.8 kbar and 690–702 °C for the pre-peak (M1) stage, 13.1–15.1 kbar and 780–890 °C for the peak (M2) stage, 7.8–8.4 kbar and 820–880 °C for the post-peak (M3) stage and the 6.4–7.2 kbar and 690–760 °C for the retrograde (M4) stage. These mineral assemblages and their P–T conditions define a clockwise P–T path for the high-pressure mafic granulites in the Jiaobei massif, suggesting that the rocks underwent near-isothermal decompression and subsequent cooling after the peak metamorphism, which implies that the southern segment of the JLJB must have experienced subduction-/collision-related tectonic processes at ca. 1.93–1.90 Ga. Therefore, the Jiao-Liao-Ji Belt may represent another Paleoproterozoic collisional belt along which the Longgang and Langrim Blocks amalgamated to form the Eastern Block of the North China Craton.