摘要
庐枞盆地科学钻LZSD-01是"深部探测与实验研究"专项在庐枞盆地施工的中国大陆科学钻预导孔,该钻孔终孔深度3008.29m,成功揭露了庐枞盆地的深部地质结构。本次工作对科学钻深部的隐伏正长-二长岩开展了系统的年代学、岩石学及地球化学研究。结果表明,钱铺隐伏正长-二长岩锆石U-Pb年龄分别为132.6±1.2 Ma、133.28±0.4 Ma,属于盆地砖桥火山旋回末期岩浆侵入活动的产物。岩浆岩具有硅近饱和、高铝、高碱富钾、低钛,富集Rb、K、Pb等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素的特征,指示隐伏岩体为橄榄玄粗质岩石。结合Sr-Nd同位素特征,推测岩浆源区可能为EMI型富集地幔,元素的演化趋势显示斜长石、辉石、钛铁矿为主的矿物分离结晶作用可能是岩浆演化的主要机制。岩浆形成于板内伸展拉张的构造背景之下。
Scientific Drilling No.1 in the Lujiang-Zongyang basin is the pilot hole of Chinese Continental Scientific Drilling.The drilling with an end depth of 3008.29msuccessfully reveals the internal geological structure of the Luzhong basin.This study carried out a systematic study of geochronology,petrology and geochemistry on the concealed intrusions in LZSD-01.LA-ICPMS zircon U-Pb dating yields the ages of 132.6±1.2 Ma and 133.28±0.4 Ma respectively for concealed syenite and monzonite,suggesting that they were the product of magmatic intrusion at the end of Zhuanqiao volcanic cyclic in this basin.Magmatic rocks are characterized by nearly saturated SiO_2,high contents of Al_2O_3 and K_2O,and low TiO_2.The concealed intrusions of LZSD-01also have relatively high LILEs such as Rb,K,Pb,but depleted HSFEs such as Nb,Ta and Ti,indicating that the intrusion should be shoshonitic rock.The Sr-Nd isotopic composition suggests that the primary magma of the concealed intrusions in the Qianpu area may derive from enriched mantel type-I.Elemental evolution trend shows that fractional crystallization of major minerals such as plagioclase,pyroxene and ilmenite may be the leading mechanism and concealed intrusions likely formed in the tectonic setting of intraplate extension.