Late neoarchean to paleoproterozoic tectonic evolution of the North China Craton : evidence from the Jianping complex in the eastern block

Abstract

As one of the oldest cratons on the Earth, the North China Craton (NCC) bears significant value in comprehending the Precambrian crustal evolution, geothermal changes, and tectonic regime. The NCC was subdivided into the Eastern Block, the Western Block and the Paleoproterozoic Trans-North China Orogen (TNCO). The Jianping Complex, located at the boundary between the Eastern Block and the TNCO, is a favorable site for investigating the Neoarchean to the Paleoproterozoic tectonic evolution of the NCC. The basement rocks of the Jianping Complex consist primarily of Neoarchean granitoids and supracrustal sequences. Based on a systematic study involving whole-rock chemical analyses, zircon U-Pb dating and zircon Hf data, the diverse Neoarchean granitoids were classified into TTGs, sanukitoids (diorites) and potassic granites. Their petrogenesis was linked with partial melting of juvenile crust, melting of the metasomatized mantle during crustal-mantle interaction, and melting of crustal lithology such as tonalite due to crustal reworking, respectively. Regarding the late Neoarchean to early Paleoproterozoic metamorphism of the Jianping Complex, felsic and intermediate granulites with ‘red eye socket’ texture were identified. Combining the petrographic observations and the modelling results, anticlockwise P-T paths were obtained with peak stage metamorphic P-T conditions constrained as 940–1000 ◦C/8.0–8.5 kbar. Integrating the above two studies and other lithological and structural evidence, it is inferred that underplating of plume-derived magma plays an important role in the ~2.5 Ga magmatic and metamorphic events, and the Jianping Complex as well as other complexes in the Eastern Block were governed by vertical tectonism in the late Neoarchean. Furthermore, Paleoproterozoic high-pressure mafic granulites with ‘white eye socket’ texture were identified with metamorphic age of ~1.85–1.82 Ga. Clockwise P-T paths involving near isothermal decompression (ITD) process or decompression with thermal relaxation were recovered with peak metamorphic P-T condition of 13.0–13.5 kbar/850–900 ◦C, which were comparable to the high-pressure granulites from the TNCO. Based on the metamorphic features and zircon U-Pb ages, it is interpreted that these high-pressure granulites resulted from the collision of the Eastern and Western Blocks along the TNCO at ~1.85 Ga.