Response to the Early Neoarchean tectono-thermal events in the North China Craton: Evidence of ca. 2. 7Ga TTG gneisses from the Zuoquan metamorphic complex

Abstract

The Early Neoarchean was an important period of crust formation, and rocks at ca. 2. 7Ga are widespread in many cratons globally. The North China Craton (NCC) experienced its main period of crustal growth in the Late Neoarchean, whereas whole-rock Nd and Hf-in-zircon isotopic geochronology revealed that ca. 2.5Ga granitoids mainly formed through reworking of Late Mesoarchean to Early Neoarchean continental material. Thus, the spatial distribution of ca. 2. 7Ga rocks is of great scientific value for studying crustal growth and evolution of the NCC. It is identified to be well exposed in a few areas in the NCC, including eastern Shandong, western Shandong, Wuchuan, Zanhuang and Taihua. And it also locally occurres in the Hengshan, Fuping and Zhongtiao complexes in the Trans-North China Orogen (TNCO) . The Zuoquan metamorphic complex is to the southwest of the Zanhuang complex, located at the middle-southern segment of the TNCO. Geochemistry and geochronology revealed that ca. 2. 7Ga ages were recorded by types of rocks here, for example paragneiss, leucosome, magnetite-bearing amphibole gneiss, and TTG gneiss. TTG gneiss is tonalitic in composition, and contains zircons with metamorphic rims and magmatic cores. Two LA-ICP-MS laboratories gave upper concordia intercept ages of magmatic zircon cores with 2727 ± 14Ma and 2731 ± 12Ma, respectively. It was interpreted to be formation age of the tonalite. The Zuoquan rocks also recorded both metamorphic and magmatic ages of the Late Neoarchean, and the tectono-thermal event was probably related to the intrution and underplating of large amounts of mantle-derived magma occurred at ca. 2. 5Ga in the NCC.