Transition of Neoproterozoic Tectonic Background in Northern Anhui Province: Evidence from Geochemistry of Clastic Rocks
皖北地区新元古代构造背景的转换: 来自碎屑岩地球化学的证据

Based on a geochemical analysis of sandstones of Neoproterozoic Shijia Formation in Suzhou of northern Anhui Province, in combination with previously published geochemical data of shales of Neoproterozoic Liulaobei Formation, the authors made a comparatively study of the provenance and tectonic setting of these two suites of clastic rocks. The results indicate that the shales of Liulaobei Formation might have originated from the first cycle of intermediate-felsic volcanic rocks with intense weathering, whereas sandstones of Shijia Formation were probably generated by low-intense weathering of the recycled old crust material. The shales of Liulaobei Formation are characterized by high (MgO+Fe2O3) and TiO2 content and Al2O3/SiO2 ratios relative to the sandstones of Shijia Formation. These data, together with La-Th-Sc and Th-Sc-Zr/10 discrimination diagrams, imply that they were deposited in different settings, i.e., the former was deposited in a continental island arc (probably back-arc basin), whereas the latter was in a passive continental margin or intra-plate environment. In combination with previous studies of the Neoproterozoic evolution in northern Anhui Province, these results demonstrate that the tectonic background of the southeast margin of North China Craton underwent transition from active to passive during Neoproterozoic.