Seminar

TTG is one of the archetypical lithologies of Archaean cratons, the origin of which is still hotly debated. According to its petrological characters, there are mainly two tectonic scenarios for TTGs’ origin: horizontal tectonic model (subduction) and vertical tectonic model (mantle plume or sugduction). My study area is in the North China Craton (NCC), which is one of the oldest cratons of the Earth. The NCC could be subdivided into the Eastern Blocks (EB) and Western Blocks, which amalgamated along the Trans-North China Orogen (TNCO) at ~1.85 Ga. It has been recognized that TTGs from TNCO and EB formed in horizontal and vertical tectonic models respectively. Therefore, there should be some difference between TTGs from these two areas. Through my work already done, it could be inferred that in TNCO, partial melting of subducted oceanic crust slab yields the magmas of TTGs, which subsequently interact with mantle wedge materials during ascent. TTGs from TNCO should be generated in an intra-oceanic subduction tectonic regime. By comparing Neoarchean TTG gneisses from TNCO and the EB, my study is to conclude the different characters of Neoarchean TTGs from two different tectonic settings. Furthermore, I could apply the results on TTGs from other areas to determine the related tectonic mechanism as an aspect of evidence. Besides, to determine the tectonic model of TTGs in the EB, whether it is sugduction-related or mantle-plume-related, is also one of the objectives. This study could also help to understand the tectonic regime of the Early Earth in the NCC.