右江盆地中三叠统浊积岩系的物源和沉积构造背景分析

右江沉积盆地在大地构造位置上被称为右江印支褶皱带。浊积岩碎屑组分特征、重矿物组分特征和古流向等特征显示赋矿的中三叠统浊积岩系的主要物源区为盆地周围的“越北古陆”、“江南古陆”和东边地区包括钦防海西褶皱带在内的“云开古陆”。浊积岩的稀土元素特征、微量元素特征和常量元素特征一致显示其沉积构造背景介于大陆岛弧和活动大陆边缘之间的过渡构造环境。

PROVENANCE AND TECTONIC SETTINGS OF THE MIDDLE TRIASSIC TURBIDITES IN YOUJIANG BASIN

Geotectonically, the Youjiang sedimentary basin was referred as Youjiang Indosinian folded belt. The characteristics of turbidite clastics and heavy mineral compositions and palaeocurrent direction show that the Middle Triassic turbidites accumulated in the basin are derived from surrounding ancient lands including Yuebei, Jiangnan, and Yunkai. The REE characteristics of turbidites are similar to those of active continental margin and continental island arc. The overall shape of the average REE pattern is also similar to those of active continental margin and continental island arc. In the La Th Sc plot, samples are projected in the field for continental island arc, near the side of the field for active continental margin. The scope variations of major element contents and chemical parameters are relatively wide. The Fe2O3*+MgO content varies between 2.51-7.06 percent, average 4.46 percent. The TiO2 content varies between 0.34-0.64 percent, average 0.51 percent. Those characteristics are similar to that of active continental margin (Fe2O3*+MgO average 4.63 percent and TiO2 average 0.46 percent). In the K2O/Na2O-SiO2 plot, most of sam ples are projected in an active continental margin. In a word, all the characteristics of REE and trace elements and major elements of the turbidites show that tectonic setting of the sedimentary basin is between an active continental margin and a continental island arc.