Cooling and exhumation of the Jiao-Liao-Ji Belt: Evidence from multi-isotopic systems in-situ geochronology

The investigation of subduction-collision-exhumation processes in Paleoproterozoic orogenic belts is crucial to better understand the tectonothermal history of early plate tectonics. High-pressure mafic granulites in the northern part of the Jiao-Liao-Ji Belt, North China Craton, contain several varieties of datable minerals with different closure temperatures of U-Pb and Lu-Hf isotopic systems, providing an opportunity to explore the cooling and exhumation history of a Paleoproterozoic orogenic belt. The recorded ages of metamorphic zircon, garnet, titanite, and apatite are 1884 Ma, 1881 Ma, 1868 Ma, and 1801 Ma, respectively. Combined with isotopic closure temperatures, the final collision in the northern part of the JLJB is speculated to occur around 1880 Ma. The rocks then experienced relatively fast cooling (8.69-5.81 degrees C/Myr) from 1880 to 1860 Ma, followed by slower cooling (4.01-3.15 degrees C/Myr) till 1800 Ma. This two-stage exhumation is consistent with that observed in the southern part of the JLJB, although the initial exhumation is noticeably slower in the northern region. Compared to the cooling rates of modern orogenic belts, the lower cooling rates of Paleoproterozoic orogenic belts may imply a higher mantle temperature and a tectonic style significantly different from modern plate tectonics.