Abstract: In order to figure out the Mesozoic tectonic evolution of the northeastern Guangxi, this paper presented detailed petrological, chronological and geochemical data on the Guposhan composite rock mass and its dioritic enclaves. The chronological results show that the formation age of the dioritic enclaves is 142±1 Ma, for the first time to identify Early Cretaceous dioritic enclaves in this area. Elemental geochemical analysis results show that the contents of SiO₂, MgO and Fe₂O₃^T of the dioritic enclaves are 55.66%-56.72%, 2.26%-2.30% and 10.43%-10.77%, respectively; the contents of SiO₂, MgO and Fe₂O₃^T of the host granite sample are 68.33%-68.67%, 0.60%-0.64% and 3.73%-3.89%, respectively. The granites are characterized by high 10000*Ga/Al ratios and Zr+Nb+Ce+Y contents, similar with those of A-type granite. Both the host rock and the dioritic enclave are enriched in large ion lithophile elements and high field strength elements. The above data indicate that the dioritic enclaves are produced by magmatic mixing, and their formation is related to extension and thinning of the lithosphere in the Late Mesozoic. Together with regional geological data, it is suggested that the Mesozoic extension of the lithosphere in South China was episodic, which led to the development of multi-stage magmatism in South China.

Key words: dark enclave, Guposhan, granite, zircon U-Pb age, lithospheric extension and thinning