Seminar

In the solar system, Earth is a unique planet with continent crust, much of which formed during Archean (>2.5 million years), involving partial melting of mafic crust to form tonalite–trondhjemite–granodiorite (TTG) rock suites. Controversy has long surrounded the issue of whether the partial melting of mafic crust to form Archean TTG rocks occurred under plate tectonic settings (e.g. magmatic arc) or under some pre-plate tectonics (e.g., mantle plume, sagduction, etc).

The North China Craton (NCC) is one of the oldest continental blocks of the Earth (~3.8 Ga). The NCC is subdivided into the Eastern Block (EB) and the Western Block (WB) and the intervening Trans-North China Orogen (TNCO), while the EB and the TNCO exhibit different geological characters, correlated with horizontal and vertical tectonic setting respectively. Therefore, Neoarchean TTG rocks from the TNCO and the EB of the NCC are chosen to trace the origin of TTG in this study.

Based on the variations in water contents, oxygen isotopes, hafnium isotopes and trace element of zircons, associated with whole-rock major and trace elements, we propose that TTG (High δ¹⁸O, high H₂O) from the TNCO were generated in a magmatic arc tectonic setting correlated to oceanic crust subduction from 2.51 Ga to 1.86 Ga, while minor TTG (mantle-like δ¹⁸O) and voluminous TTG (High δ¹⁸O, low H₂O) from the EB were generated in the two-stage mantle plume and sagduction setting (~2.7Ga and ~2.5 Ga).

Additional information: Miss ZHAO Dingyi, zhaodingyi@hku.hk