贵州锦屏地区新元古代下江群地球化学特征及构造环境研究

对贵州锦屏新元古代下江群地层剖面常量元素及稀土元素系统分析结果表明，该区下江群地层常量元素具有中等 SiO2含量，介于57.54%～88.91%之间，平均68.32%，较低的CaO含量(一般<1%)，较高的K2O/Na2O，Al2O3/TiO2比值及较低 的TFe2O3+MgO含量。稀土总量ΣREE介于46.5×10-6～306.3×10-6之间，平均值为152.5×10-6，ΣLREE/ΣHREE为8.73～21.6， 平均12.96，表明轻稀土相对富集，重稀土相对亏损；下江群各组段δEu在0.7～0.8之间，为弱负异常。稀土配分模式总体 为右倾，而轻稀土分馏中等，重稀土分馏较低，表现在稀土配分曲线为轻稀土斜率较大，重稀土趋于平坦。通过各组段地 球化学特征参数与参数投点可得：番召组与清水江组、平略组与隆里组具有相似地球化学特征，表明其构造环境相似且呈 过渡变化，初步认为番召组与清水江组形成于活动大陆边缘的弧后盆地沉积，而平略组与隆里组为大陆边缘的边缘海沉积。
Based on the systematic sampling from the Neoproterozoic Xiajiang Group in the research area and the data analysis of major elements and rare earth elements, this study shows that rocks had moderate quantities in SiO2, which its value ranged from 57.54× 10-2 to 88.91×10-2 with an average of 68.32×10-2, low content of CaO (generally smaller than 1%), and high concentration in K2O/Na2O and Al2O3/TiO2 and low amount of TFe2O3+MgO. The ΣREE of total rare earth element is between 46.51×10-6 and 306.29×10-6 and its average value was 152.46×10-6. ΣLREE/ΣHREE changed in 8.73~21.6, average value was 12.96, which indicated that it was rich in LREE, loss in HREE. The δEu in each member of Xiajiang group ranged from 0.7 to 0.8, which was Weak negative anomaly. The REE patterns were slightly to right. LREE had medium fractionation and HREE was low, which demonstated that the REE patterns was high gradient in LREE and flat in HREE. Through the geochemistry parameter in each formation, it illustrated that it had similar geochemistry features between Fanzhao and Qingshui formation, also Pinglue and Longli formation. It further illustrated that similar or transitional structure background. It drew elementary conclusion that it was back-arc basin of active continental margin in Fanzhao and Qingping stages, and edge marine sedimentary environment of continental margin in Pinglue and Longli stages.