Petrogenesis and tectonic implications of Late Mesozoic granites in the NE Yangtze block, China: further insights from the Jiuhuashan-Qingyang complex

The Jiuhuashan-Qingyang complex is one of the Mesozoic granite complexes in the NE Yangzte Block, China. New petrographical and petrochemical data show that the complex comprises a dominant granodiorite-monzogranite, the Qingyang body, which was intruded by the Jiuhuashan granite body. The two are characterized by distinct mineral components and trace element patterns. Compared to the Qingyang granodiorite and monzogranite, the Jiuhuashan granite is enriched in Rb, Th, U, Nb, Ta, Hf, Yb and Lu, and depleted in Ba, Sr, Nd, Sm, Eu, Gd and Ti, which are ascribable to the separation of plagioclase and biotite, and crystallization of thorite and fergusonite during the magmatism. New LA-ICPMS zircon U-Pb dating suggests that the crystallization age of the Qingyang body is 139-133 Ma, and the Jiuhuashan granite followed at 127 Ma. Moreover, the new zircon U-Pb dates reveal that Archaean materials were involved in the formation of these magmas, and that a sodium-rich metasomatic event occurred at about 100 Ma. The CHIME monazite and zircon ages studied for the Jiuhuashan body agree well with the LA-ICPMS zircon ages. Integrating this information with previous studies for granites in the NE Yangtze Block and in the coastal area of SE China, we believe that all of these Late Mesozoic granites were produced under the tectonic regime of palaeo-Pacific plate subduction towards the SE China continent in a NW direction, but the granites in the NE Yangtze Block are basically derived by crustal melting with limited mixing of juvenile material during the magma generation.