Multi-stage crust-mantle interaction in SE China: temporal, thermal and compositional constraints from the Mesozoic felsic volcanic rocks in eastern Guangdong-Fujian provinces

The Mesozoic geology of southeastern (SE) China was characterized by emplacement of voluminous felsic magmas. We present zircon U-Pb-Hf isotopic compositions and whole-rock major and trace elemental compositions of a series of felsic volcanic rocks from the eastern Guangdong and Fujian provinces. The volcanic rocks have been divided into three formations (the Douling, Nanyuan and Shimaoshan Fms.). Zircon U-Pb dating defines three eruption cycles: 168-145Ma for the Douling Fm., 143-130Ma for the Nanyuan Fm., and 104-95Ma for the Shimaoshan Fm. In situ Hf isotope analyses on dated zircon yield an ε_Hf(t) range of -13.8 to +6.9 and a T_DM(Hf) range from 1400 to 486 Ma with a peak at ca. 930 Ma. The majority of the Mesozoic felsic lavas have more radiogenic Hf than that of metamorphic basement rocks and related igneous rocks, requiring the involvement of a juvenile component in their origin. The Mesozoic felsic magmas are predominantly dacites and rhyolites - with only minor basalt and andesite - and show relatively homogeneous Hf isotopic compositions of zircon in single sample. Combined these data indicated that neither differentiation of a mantle-derived magma, nor mixing of magmas from different sources, was a dominant petrogenetic process. Both the ε_Hf(t) of zircon and the magma temperature increase from the Douling and Nanyuan Fms. to the Shimaoshan Fm. All these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle-derived magmas, as both a heat source inducing crustal melting and as a source of material (melt) that variably mixed with the local crustal melts. The felsic crustal melt component was generated at amphibolite-facies conditions with a residual assemblage of plagioclase +/-hornblende +/- garnet +/-zircon. Our results suggest a progressive role of crust-mantle interaction in generating the episodic felsic volcanic eruption during the Mesozoic.