Discovery of the oldest (ca. 2.87 Ga) granitic gneisses in the Qinling-Dabie Orogenic Belt: Direct evidence of Mesoarchean crust

1.Objectives Precambrian microcontinents(terranes)or continental fragments are generally essential components in the evolution and architecture of Phanerozoic orogenic belts.Formation of the Qinling-Dabie Orogenic Belt,a typical Paleozoic to Triassic collisional zone between the South China Block(including the Yangtze Block and the Cathaysia Block)and the North China Block(inset map in Fig.1a),is characterized by the occurrence of several Precambrian complexes or microcontinents.These complexes or microcontinents are dominated by Neoproterozoic rocks and thought to be of Yangtze affinity,but a scarcity of the older rock record has hampered further understanding of the earlier crustal evolution and origin of the Precambrian microcontinents.