鄂尔多斯地区黄旗口组地球化学特征及其沉积环境与构造背景
Geochemical Characteristics, Sedimentary Environment and Tectonic Setting of Huangqikou Formation, Ordos Basin

鄂尔多斯盆地西南部及邻区沉积了一套以黄旗口组为代表的巨厚的中元古界碎屑岩系，该套地层具有重要的油气勘探潜力，但目前人们对该套地层的勘探认识尚不够深入，利用碎屑组分、主微量、稀土元素等地球化学手段，结合区域及深部背景特征，探讨了该套地层形成时期的沉积环境和构造背景.结果显示，黄旗口组整体形成于气候干燥的淡水氧化或富氧的过渡环境，沉积期古海水温度较高(平均为32℃)；黄旗口组碎屑组分及其主微量元素特征与东非裂谷区相似，加之其沉积于淡水环境，并具有自下段至上段石英砂岩含量逐渐增加的特征，表明研究区黄旗口组应处于陆内裂谷构造背景，自早至晚构造沉积环境日趋稳定，其中早期应为陆内裂谷环境，晚期可能变为坳陷环境，该构造背景的形成可能与华北克拉通逆时针旋转有关.
A set of ultra thick Middle Proterozoic clastic sedimentary rocks deposited in and around southwestern Ordos basin, with the Huangqikou Formation(HKF) as the most typical one, has great potential for oil and gas exploration. However, our understanding of HKF needs to be enhanced. Thus, by means of main trace, rare elements and detrital component method, we probed into the sedimentary environment and tectonic setting of the HKF. The sedimentary environment discrimination diagrams of both main and trace elements show that the HKF was deposited wholly under a dry environment with fresh water oxidized, or an oxygen enriched environment，with an average paleoseawater temperature of 32℃. The tectonic environment discrimination diagrams of clastic composition, and main and trace elements all show similarity to those of the East African rift basin, and gradual increasing of the quartz sandstone content from the lower to the upper parts, suggesting that HKF deposited under an intracontinental rift tectonic sedimentary setting, which may have been caused by the counterclockwise rotation of North China Craton. It is concluded that the HKF was deposited in an intracontinental rift basin in the fresh water, and the tectonic setting became more stable from early to late stage, which was intra continental rift in the early stage and postrift depression in the late one