甘肃景泰崔家墩下奥陶统阴沟组砂岩化学组分特征及物源区构造背景判别

甘肃景泰一带早奥陶世沉积了以浊流砂岩夹板岩为主的阴沟组。崔家墩剖面阴沟组较为发育，总体分为两个岩性段，但东西向逆冲断层造成地层垂向不连续。北段（下段）为粉-细砂岩、板岩夹硅质岩；南段（上段）为岩屑含量较多的岩屑砂岩夹板岩，硅质岩少或无。对阴沟组砂岩进行主化学组分特征分析，其特征指标：Fe₂O*3+MgO值为503%～17.63%，Al₂O₃/SiO₂值为0.12%～0.28%，K₂O/Na₂O值为0.25%～1.26%及 Al₂O₃/（CaO+Na₂O）值为1.01%～3.53%。利用砂岩的化学组分特征结合岩相学分析，可以判断物源区特征及大地构造背景。研究表明:该套浊积砂岩下部物源主要来自北部的阿拉善地块及该地块上的古老造山带，为被动大陆边缘背景；上部碎屑主要来自南侧岛弧中基性火山岩，为活动大陆边缘初始弧后盆地构造背景。

Chemical component characteristics of sandstone and recognition to provenance tectonic setting of the Yingou Formation of Lower Ordovician at Cuijiadun section, Jingtai County of Gansu Province

The Yingou Formation was dominated by turbidity sandstones intercalated with slates and it was deposited in Jingtai County of Gansu Province and its neighboring areas during the Early Ordovician. At Cuijiadun section it is not continuous vertically because of the east west thrusts. It can be divided into two lithologic members. The north member(lower member) is composed of siltstones, fine grained sandstones, and slates intercalated with siliceous rocks. The south member(upper member) is characterized by lithic sandstones with little or no siliceous rocks. The major chemical component analyses on the selected sandstones of the Yingou Formation show that Fe₂O*3+MgO has values of 5.03%～17.63%, Al₂O₃/SiO₂ values of 0.12%～0.28%, K₂O/Na₂Ovalues of 0.25%～1.26% and Al₂O₃/（CaO+Na₂O）values of 1.01%～3.53%. The characteristics of the major chemical components, combined with lithofacies analyses, are used to discriminate the features of the provenance and its tectonic setting. The results indicate that the lower part of the turbidites is mainly derived from the Alashan Block and its overlying orogenic belt in the north. The deposition take place in a passive continental margin setting, in contrast, the debris in the upper part mainly comes from the neuter basic volcanic rocks in the southern arc which belongs to an initial back arc basin environment.