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皖南地区前寒武纪地层广泛出露,包括上溪群和溪口群,其中上溪群羊栈岭组中段岩性以泥岩、粉砂岩和细砂岩等细碎屑岩为主,并含有多套砾岩层。通过对绩溪县杨溪镇和东至县葛公镇剖面羊栈岭组中段细碎屑岩的地球化学分析,发现羊栈岭组中段样品具有相对较高的Al_2O_3/TiO_2比值(21.57)、较高的LREE/HREE比值(6.98)和明显的负Eu异常(0.71),在TiO_2和Al_2O_3二元图解、Zr和TiO_2二元图解及La/Th-Hf二元图解中,大多数样品落入长英质物源区中。表明它们的物源以长英质岩石为主。此外,反映源区风化程度的参数CIA、CIW和PIA值均较低,平均值分别为71.6、75.4和71.2,分别低于PAAS的76.4、82.7和79.0,表明源区的风化程度较低。将样品的地球化学特征和皖南新元古代岩体和火山岩进行比较,发现它们具有亲缘性,结合其它岩石学和地层学证据认为这些岩体和火山岩为沉积物提供了重要的物源。在主量元素判别图中,样品主要落入活动大陆边缘区并受大陆岛弧的影响,在微量元素构造背景判别图中,样品均落入大陆岛弧区。此外,样品的各种REE元素特征值属于大陆岛弧来源的沉积物的范围,同时又与活动大陆边缘沉积物相近,指示羊栈岭组中段可能代表了一套活动大陆边缘的弧后盆地沉积。而羊栈岭组中段作为一次完整的海侵—海退序列中的一部分可以代表整个上溪群形成的构造背景。
The Precambrian strata in southern Anhui are widely exposed, including Shangxi Group and Xikou Group. The middle lithology of Qiaoling Formation in Shangxi Group is dominated by fine clastic rocks such as mudstone, siltstone and fine sandstone and contains more Conglomerate layer. Through the geochemical analysis of fine clastic rocks in the middle part of the Yangjialing Formation in Yangxi Town, Jixi County and Gegong Town, Dongzhi County, it was found that the middle part of the Yangtiaoling Formation had a relatively high Al_2O_3 / TiO_2 ratio (21.57) High LREE / HREE ratios (6.98) and significant negative Eu anomalies (0.71), most of the samples falling into the long British quality source area. Show that their provenance is mainly quartzite. In addition, the values of CIA, CIW and PIA, which reflect the degree of weathering in the source area, were lower with average values of 71.6, 75.4 and 71.2, respectively, which were lower than those of PAAS (76.4, 82.7 and 79.0, respectively), indicating low degree of weathering in the source area. Comparing the geochemical characteristics of the samples with the Neoproterozoic volcanic rocks in southern Anhui Province, they are found to have relatives. Combined with other petrology and stratigraphy evidence, these rock masses and volcanic rocks provide an important source of sediment. In the main element discriminant map, the samples mainly fall into the active continental margin and are affected by the continental island arc. In the discriminant map of the trace element structure, the samples all fall into the continental island arc region. In addition, the REE elemental eigenvalues of the samples belong to the range of continental arc-derived sediments and are similar to the active continental margin sediments, indicating that the middle part of the Yang-Qiaoling Formation may represent a set of back-arc basin sediments with active continental margins . The middle part of the Yang-Qiaoling Formation, as a complete part of the transgression-regression series, can represent the tectonic setting of the whole Shangxi Group.