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

作　　者：S. Y. O’Reilly 

机构地区：[1]GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia

出　　处：《Science China Earth Sciences》2006年第7期696-713,共18页中国科学（地球科学英文版）

基　　金：This work was supported by the National Natural Science Foundation of China (Grant Nos. 40221301,40125007 and 40132010).

摘　　要：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 in-cluding the Deqing monzonitic granite body and the Xinghua granodiorite body in the Shidong com-plex, 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 εNd(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.Systematic zircon LA-ICPMS U-Pb dating reveals that Cretaceousvolcanic-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 theintrusive ones including the Deqing monzonitic granite body and the Xinghua granodiorite body in theShidong complex, as well as the Tiaocun granodiorite body in the Guangping complex yield ages of99±2 Ma, ca. 100 Ma, and 104±3 Ma respectively. The biotite-granites of the Shidong complex mainbody (461 ±35 Ma) and that of the Guangping complex (444±6 Ma) are Caledonian. In spite of the bigtime interval between Cretaceous volcanic-intrusive magmatisms and Caledonian intrusive ones, bothof 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 highinitial ^(87)Sr/^(86)Sr ratios (0.7105— 0.7518), and low ε_(Nd)(t) values (-7.23--11.39) withtheir Nd two-stage model ages ranging from 1.6— 2.0 Ga, which suggest that they all derived fromthe Proterozoic crustal basement of southeast China. The occurrence of Cretaceous volcanic-intrusivemagmatisms in western Guangdong is related with the important lithospheric extension event insoutheast China (including Nanling region) at ca. 100 Ma. The ''volcanic line'' defined by the largescale Mesozoic intermediate-acidic volcanic magmatisms in southeast China may further extend to thesouthwest margin of Nanling region.

关 键 词：Cretaceous  volcanic-intrusive rocks  zircon U-PB dating  SR-ND isotope  WESTERN Guangdong. 

分 类 号：P534.53[天文地球—古生物学与地层学]