安徽庐枞盆地南部花岗岩的成岩时代及其意义

庐枞中生代火山盆地位于长江中下游断陷带，地处扬子板块的北缘。庐枞盆地内火山岩和侵入岩分布广泛，包括龙门院、砖桥、双庙和浮山4组火山岩以及34个出露地表的侵入岩体。庐枞盆地内与成矿关系密切的侵入岩体的时空格架和岩浆演化等相关研究工作已经广泛开展，但对于盆地南部的花岗岩类侵入岩研究工作则相对薄弱，制约了对庐枞盆地岩浆作用及深部成矿预测的深入研究。本次工作在详细野外地质工作的基础上，系统对盆地南部的沙墩岩体、船艄石岩体、青山岩体、何家凹岩体、梅林岩体、古塘冲岩体和周家山岩体开展了岩石学、地球化学和年代学研究，确定其主要岩性为石英正长岩和钾长花岗岩，岩石全碱含量均较高，准铝质或过铝质，稀土含量中等，较强Eu亏损，呈略右倾的海鸥型稀土配分模式，成岩时代分别为：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和124.9±1.3 Ma，均形成于早白垩世。通过与庐枞盆地不同侵入岩的系统对比，提出这些岩体与庐枞盆地晚期侵入岩时代接近，岩石学特征类似，应为同一岩浆作用的产物，形成于区域岩石圈伸展的构造环境。

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.