Thermal evolution of two textural types of mafic granulites in the North China craton: evidence for both mantle plume and collisional tectonics

Mafic granulites from the North China craton can be divided into two textur al types, referred to as A- and B-types. A-type mafic granulites display ga rnet + quartz symplectic coronas, and outcrop in the eastern and western zo nes of the craton, whereas B-type mafic granulites exhibit orthopyroxene plagioclase + clinopyroxene symplectites or coronas, and are mainly exposed in the central zone of the craton. Most A-type mafic granulites preserve t he prograde (M-1), peak (M-2) and post-peak near-isobaric cooling (M-3) ass emblages, which are represented respectively by inclusions of hornblende plagioclase + quartz, a peak mineralogy of orthopyroxene + clinopyroxene plagioclase + quartz + garnet, and overprinted by garnet + quartz symplecti c coronas. These mineral assemblages and their P-T (pressure-temperature) e stimates define anticlockwise P-T evolutionary paths. The B-type mafic gran ulites preserve the peak (M-1), post-peak near-isothermal decompression (M- 2) and cooling (M-3) assemblages, which are represented by the peak assembl age of orthopyroxene + clinopyroxene + plagioclase + quartz + garnet +/- ho rnblende, post-peak orthopyroxene + plagioclase + clinopyroxene symplectite s or coronas, and later hornblende + plagioclase + magnetite symplectites, respectively. These mineral assemblages and their P-T estimates define cloc kwise P-T paths. The anticlockwise P-T paths of the A-type mafic granulites in the eastern a nd western zones of the North China craton are consistent with a model of u nderplating and intrusion of mantle-derived magmas. In combination with lit hological, structural and geochronological data, the eastern and western zo nes of the North China craton are considered to represent two continental b locks that developed through the interaction of mantle plumes with the lith osphere from the Palaeoarchaean to the Neoarchaean era. The B-type mafic gr anulites and associated rocks in the central zone represent a magmatic are that was metamorphosed and deformed during amalgamation of the eastern and western continental blocks in the late Palaeoproterozoic era. The mineral r eaction relations and clockwise P-T paths of the B-type mafic granulites fr om the central zone record the tectonothermal history of the collision that resulted in the final assembly of the North China craton at c. 1800 Ma.