Diagenetic age of the intrusions in southern part of the Lu-Zong Basin and its significance

LA-ICP MS zircon U-Pb dating for the hidden intrusions; such as Shadun intrusion, Chuanshaoshi intrusion, Qingshan intrusion, Hejiaao intrusion, Meilin intrusion, Gutangchong intrusion, Zhoujiashan intrusion in the south of the Lu-Zong Basin was carried out in this paper. These intrusions consist of alkali-feldspar granite and quartz syenite which contain a lot of K-feldspar. LA-ICP MS zircon U-Pb dating yields the ages of 126.5±1.1 Ma, 126.2±1.2 Ma, 126.7±1.3 Ma, 126.9±1.4 Ma, 125.9±1.3 Ma, 126.7±1.4 Ma, 124.9±1.3 Ma for five intrusions, respectively. The results indicate that all the hidden intrusions in the south of Lu-Zong Basin formed in the Early Cretaceous. These intrusions are characterized by relative high silica and alkalis, ascribed to metaluminous or peraluminous, moderate REE and strong Eu depletion with a slightly right-inclined sea-gull REE patterns. These data, together with other accuracy dating data of volcanic rocks and intermediate-acid high-K calc-alkalic plutons in the middle and lower reaches of the Yangtze River area, support the intrusions formed in a within-plate tensional tectonic environment. The results of the study are important for discussing the geodynamic settings of these intrusions in the middle and lower reaches of the Yangtze River area.