在对安徽省北部宿州新元古代史家组砂岩地球化学特征分析的基础上,结合前人发表的淮南和凤阳新元古代刘老碑组页岩的地球化学数据,对它们的物源和构造背景进行了对比讨论.结果表明:刘老碑组页岩的地球化学特征表明其来自于中-酸性火成岩高程度的首次风化,而史家组砂岩则来自于经历了再循环的古老地壳物质较低程度的风化.刘老碑组页岩相对史家组砂岩具有高(MgO+Fe2O3)、TiO2含量和Al2O3/SiO2 比值的特征,结合La-Th-Sc和Th-Sc-Zr/10判别图解,表明二者可能沉积于不同的构造背景,其中前者属于大陆岛弧(也可能是弧后盆地),而后者则形成于相对稳定的被动大陆边缘或者板内.结合前人关于皖北新元古代研究的相关进展,证实了华北板块东南缘构造背景在新元古代时期经历了从活动向稳定的转变.%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.
展开▼
