论文部分内容阅读
陕南汉中碑坝地区是扬子克拉通少数可能存在太古宙结晶基底的地区之一。本文系统地研究了元素和同位素地球化学表明，后河“群”主要岩石类型之一的ＴＴＧ片麻岩形成时代约为２４００Ｍａ，其ＲＥＥ和岩石化学特征与新太古代ＴＴＧ片麻岩类似；混合岩类Ｓｍ－Ｎｄ同位素模式年龄表明其原岩或源岩的形成时代约为２７００Ｍａ的新太古代，在岩石化学成分上与钾质花岗岩或闪长质岩石相当，与太古宙高级区新太古代典型钾质花岗岩相近似；区内斜长角闪岩形成于２２００Ｍａ，与区内混合岩化作用发生的时代稍早或基本一致；局部存在的变流纹岩与火地垭群铁船山组双峰火山岩属同一岩浆作用过程在区内不同区段的体现；后河“群”各类基底岩石有基本同一的Ｒｂ－Ｓｒ等时线年龄（１２０１Ｍａ±２４０Ｍａ），反映了元古宙中晚期构造热事件对早期各类岩石Ｒｂ－Ｓｒ同位素体系有深刻影响。
The Hanzhongbei dam area in southern Shaanxi is one of the few areas where the Yangtze Craton may have an Archean crystalline basement. This paper systematically studied the elemental and isotopic geochemistry. It shows that the TTG gneiss, one of the main rock types of the Houhe “group”, was formed with an age of about 2400 Ma and its REE and petrochemical characteristics are similar to that of the Neo-Archean TTG gneiss. The Sm-Nd isotopic ages of the rocks show that the Neo-Archean age of the protolith or source rocks with a age of about 2700 Ma is similar to that of potassic granodiorites or dioritic rocks in chemical composition, Typical potash granites are similar; the regional amphibolite is formed at 2200Ma, which is earlier or almost consistent with the occurrence of mixed lithification in the area; the locally existing rhyolite and The volcanic rocks belong to the same magmatism in different sections of the area. The Rb-Sr isochron age (1201Ma ± 240Ma) of all kinds of basement rocks in the Houhe “group” reflects the middle and late Proterozoic tectonics The thermal events have a profound impact on the early Rb-Sr isotope system of various rocks.