Petrology and P-T path of the Fuping mafic granulites: implications for tectonic evolution of the central zone of the North China craton

The Fuping Complex and the adjoining Wutai and Hengshan Complexes are locat ed in the central zone of the North China craton. The dominant rock types i n the Fuping Complex are high-grade tonalitic-trondhjemitic-granodioritic ( TTG) gneisses, with minor amounts of mafic granulites, syntectonic granitic rocks and supracrustal rocks. The petrological evidence from the mafic gra nulites indicates three stages of metamorphic evolution. The M-1 stage is r epresented by garnet porphyroblasts and matrix plagioclase, quartz, orthopy roxene, clinopyroxene and hornblende. Orthopyroxene+plagioclase symplectite s and clinopyroxene+plagioclase +/- orthopyroxene coronas formed in respons e to decompression during M-2 following the peak metamorphism at M-1. Hornb lende+plagioclase symplectites formed as a result of further isobaric cooli ng and retrograde metamorphism during M-3. The P-T estimates using TWQ ther mobarometry are: 900-950 degrees C and 8.0-8.5 kbar for the peak assemblage (M-1), based on the core compositions of garnet, matrix pyroxene and plagi oclase; 700-800 degrees C and 6.0-7.0 kbar for the pyroxene+plagioclase sym plectites or coronas (M-2); and 550-650 degrees C and 5.3-6.3 kbar for the hornblende+plagioclase symplectites (M-3), based on garnet rim and correspo nding symplectic mineral compositions. These P-T estimates define a clockwi se P-T path involving near-isothermal decompression for the Fuping Complex, similar to the P-T path estimated for the metapelitic gneisses. The inferr ed P-T path suggests that the Fuping Complex underwent initial crustal thic kening, subsequent exhumation, and finally cooling and retrogression. This tectonothermal path is similar to P-T paths inferred for the Wutai and Heng shan Complexes and other tectonic units in the central zone of the North Ch ina craton, but different from anti-clockwise P-T paths estimated for the b asement rocks in the eastern and western zones of the craton. Based on lith ological, structural, metamorphic and geochronological data, the eastern an d western zones of the craton are considered to represent two different Arc hean to Paleoproterozoic continental blocks that amalgamated along the cent ral zone at the end of Paleoproterozoic. The P-T paths of the Fuping Comple x and other tectonic units in the central zone record the collision between the eastern and western zones that led to the final assembly of the North China craton at c. 1800 Ma.