江南造山带雪峰隆起区元古宙浊积岩沉积构造背景的地球化学制约

Geochemical constraints on the tectonic setting of the Proterozoic turbidites in the Xuefeng Uplift region of the Jiangnan orogenic belt

江南造山带雪峰隆起区元古宙浊积岩的地球化学组成良好地反映了沉积盆地的板块构造性质,并为解释区域大地构造的性质和演化提供了有用的信息。中元古代冷家溪群和新元古代板溪群(包括下部马底驿组和上部五强溪组)地层在主元素成分上无明显区别,总体上以中等SiO2含量和K2O/Na2O比值以及较高的(Fe2O3+MgO)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(如PAAS或NASC)和上陆壳相似,以轻稀土富集、显著的铕负异常和重稀土平坦为特征。大离子亲石元素和铁镁族元素的含量中等。主元素和微量元素特征指示了研究区元古宙浊积岩很可能代表了一套活动大陆边缘弧后沉积盆地的产物。陆内裂谷盆地模式对于解释新元古代华南地区的构造性质和演化可能并不合适。华夏陆块与扬子陆块的拼接以及Rodinia超大陆的最终形成可能发生在约0.8Ga左右的晋宁(雪峰)造山运动期,而不是全球Grenville造山期末的四堡(东安)运动期。

The geochemical compositions of the Proterozoic turbidites in the Jiangnan orogenic belt well reflect plate tectonic setting of the sedimentary basin and provides some useful information for interpretation of the nature and evolutionary history of the regional tectonics of South China.In terms o f major element compositions,diffe rent Proterozoic groups and formations h ave no distinct differences and on th e whole are characterized by interme diate SiO 2 contents and K 2 O /Na 2 O ratios and relatively high Fe 2 O 3 +MgO contents.The REE distribution patterns are uniform and similar to typical post-Archean shales(e.g.,PAAS and NASC)and the upper continental crust,with LREE enrichment,flat HREE,and sign ificant negative Eu-anomalies.Abundances of ferromagnesian trace elements and large-ion lithophile(LIL)elements are moderate.Characteris tics of major and trace elements indi cate that the Proterozoic turbidites of t he study area most probably represen t the infill of an active continental back arc basin.An intracontinental rift mod el,as proposed by some workers,is in valid as interpreting the Neoproterozoic tectonic setting of South China.Sut uring between the Yangtze and Cathaysia blocks as well as the final assemb ly of the supercontinent Rodinia in South China occurred during the Jingning(Xuefeng)orogeny at around 0.8Ga,rather than the Sibao(Dongan)orogeny at the late stage of the global Grenville movement.