Cretaceous volcanic-intrusive magmatism in western Guangdong and its geological significance

Systematic zircon LA-ICPMS U-Pb dating reveals that Cretaceous volcanic-intrusive activities developed in western Guangdong. Representative volcanic rocks, i.e. Maanshan and Zhougongding rhyodacites, have zircon U-Pb isotopic ages of 100±1 Ma, and the intrusive ones including the Deqing monzonitic granite body and the Xinghua granodiorite body in the Shidong complex, as well as the Tiaocun granodiorite body in the Guangping complex yield ages of 99±2 Ma, ca. 100 Ma, and 104±3 Ma respectively. The biotite-granites of the Shidong complex main body (461±35 Ma) and that of the Guangping complex (444±6 Ma) are Caledonian. In spite of the big time interval between Cretaceous volcanic-intrusive magmatisms and Caledonian intrusive ones, both of them are characterized by enrichment in Rb, Th, Ce, Zr, Hf, Sm, depletion in Ba, Nb, Ta, P, Ti, Eu, and weakly REE tetrad effect. Eu negative anomalies are: Cretaceous volcanic rocks (Eu/Eu*=0.74), Cretaceous intrusive rocks (Eu/ Eu*=0.35-0.58), Caledonian biotite granites (Eu/ Eu*=0.31-0.34). Studies of Sr-Nd isotope data show that all these igneous rocks have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7105-0.7518), and low ε_Nd(t) values (-7.23 - -11.39) with their Nd two-stage model ages ranging from 1.6-2.0 Ga, which suggest that they all derived from the Proterozoic crustal basement of southeast China. The occurrence of Cretaceous volcanic-intrusive magmatisms in western Guangdong is related with the important lithospheric extension event in southeast China (including Nanling region) at ca. 100 Ma. The "volcanic line" defined by the large scale Mesozoic intermediate-acidic volcanic magmatisms in southeast China may further extend to the southwest margin of Nanling region.