湘东南南华系—寒武系砂岩地球化学特征及对华南新元古代—早古生代构造背景的制约  

Geochemistry of Nanhuan-Cambrian Sandstones in Southeastern Hunan, and Its Constraints on Neoproterozoic-Early Paleozoic Tectonic Setting of South China

作　　者：柏道远[1] 周亮[1] 王先辉[1] 张晓阳[1] 马铁球[1] 

机构地区：[1]湖南地质调查研究院,湖南湘潭411100

出　　处：《地质学报》2007年第6期755-771,共17页Acta Geologica Sinica

基　　金：中国地质调查局地质大调查项目(编号200213000035)资助成果

摘　　要：湘东南位于扬子板块与华夏地块的交接地带,南华纪—寒武纪期间形成了巨厚的复理石、类复理石连续沉积。其中的砂岩总体上以中等的SiO2含量、高的K2O/Na2O值和Al2O3/(Na2O+CaO)值、较高的(Fe2O3*+MgO)含量及低的CaO含量为特征。稀土元素球粒陨石标准化曲线与典型的后太古宙页岩和上陆壳相似,以轻稀土富集、重稀土平坦、铕负异常显著为特征。主量元素和微量元素特征显示出被动大陆边缘、活动大陆边缘和大陆岛弧等多种环境信息。从不同构造背景下的剥蚀原岩及风化条件和搬运沉积过程来看,大陆岛弧和活动大陆边缘形成的砂岩应具有显著区别于被动大陆边缘的地球化学特征,而被动大陆边缘形成的砂岩则可能包含较多的大陆岛弧和活动大陆边缘环境的地球化学信息。因此,湘东南南华系—寒武系砂岩应形成于被动大陆边缘环境。这一判断与古元古代—中元古代岛弧与活动大陆边缘形成岩石为重要原岩,以及沉积盆地因强烈陆内伸展断陷而具一定活动性等客观事实相吻合。华南板溪群与冷家溪群间至少存在40～60Ma的沉积缺失,江南造山带新元古代碰撞造山成因的岩浆活动,板块交接带南华纪—早古生代沉积物中岛弧火山物质的缺乏,以及湘(东)南中元古界(甚至更早)结晶基底横向上的连续性等,表明扬子板块与华夏地块之间新元古代—早古生代期间的沉积盆地不是洋盆,而是陆内裂谷盆地。上述基于湘东南砂岩地球化学研究,和根据区域资料分析所得出的关于扬子板块与华夏地块间新元古代—早古生代盆地构造性质的结论,彼此提供了良好的约束。Southeastern Hunan lies in the transition area of the Yangtze and Cathaysia block. Thick flysch formation formed during the Nanhuan--Cambrian in the area. The sandstones of the sediments on the whole are characterized by intermediate SiO2 contents, high K2O/Na2O and Al2O3/ （Na2Oq-CaO） ratios, clearly high Fe2O3 ＊ ＋MgO and CaO contents. The REE distribution patterns are uniform and similar to typical post-Archean shales and the upper continental crust, with LREE enrichment, falt HREE, and significant negative Eu-anomalies. Characteristics of major and trace elements show information of several different tectonic settings of passive continental margin, active continental margin and continental arc. According to the corroded protoliths, efflorescent conditions and carry-subside processes for sediment, the rocks formed in continental arc and active continental margin should possess geochemical characteristics different observably from those in passive continental margin, while the rocks formed in passive continental margin can embrace some geochemical information of continental arc and active continental margin. Therefore the Nanhuan--Cambrian sandstones from southeastern Hunan were formed in a tectonic setting of passive continental margin. The idea coincide with the objective fact that Paleo-Mesoproterozoic rocks formed in continental arc and active continental margin were major protoliths of the Nanhuan-- Cambrian sandstones, and that the violently down-faulted sedimentary basin took on some activity. Some evidences such as at least 40-60 Ma absence of sediment between the Banxi Group and Lengjiaxi Group, Neoproterozoic magmatism related with collisional orogeny in Jiangnan orogens, the absence of island-are volcanic material in the Nanhuan--Early Paleozoic sediments and the continuous Mesoproterozoic （even earlier） crystalline basement in southeastern Hunan indicate that the Neoproterozoic--Early Paleozoic sedimentary basin between the Yangtze and Cathaysia block was not an oceanic but intraconti

关 键 词：砂岩 地球化学 构造背景 新元古代-早古生代 湘东南 华南 

分 类 号：P588.212.3[天文地球—岩石学]