Shared metamorphic histories of various Palaeoproterozoic granulites from Datong-Huai'an area, North China Craton (NCC): constraints from zircon U-Pb ages and petrology

摘要

Different tectonic interpretations have been proposed for the various spatially associated Palaeoproterozoic granulite-facies lithologies (metasedimentary rocks, metabasites, and felsic granulites) from north-central part of the North China Craton, which hinges primarily on controversies about metamorphic histories of these granulites, especially on the timing of peak metamorphism. Published data exhibit two controversial peak metamorphic ages of 1950-1900 Ma and 1850-1800 Ma. We report here LA-ICPMS U-Pb zircon ages of seven representative granulite-facies samples of different lithologies to constrain the timing of metamorphism, and then discuss their geological significance. Most zircon grains from these rocks display weak core-and-rim structures and yield two comparable group metamorphic ages of 1970-1900 Ma and 1880-1790 Ma, although their formation ages vary from Neoarchaean to Palaeoproterozoic. The older population metamorphic ages are interpreted to approximate timing of high-pressure granulite-facies metamorphism, and the younger population ages as the approximate timing of intermediate- to low-pressure granulite-facies metamorphism. Combined with recent petrological studies, we propose these granulites have shared metamorphic histories at least since similar to 1970-1900 Ma, and they are probably formed in one single metamorphic cycle in response to crustal-scale subduction-collision-exhumation processes involved in Palaeoproterozoic mobile belt.