【摘要】 华南奥陶—志留纪之交的五峰组—龙马溪组及华北新元古界下马岭组发现的钾质斑脱岩,都产自类似的黑色硅质-碳质页岩/板岩岩系。这两套黑色岩系与上、下地层的接触关系、岩性组成以及垂向序列所揭示的地质过程,具有良好的可对比性,都符合Ettensohn总结的黑色页岩与板块构造运动之间的成因关系模式。岩石元素地球化学研究表明,这两组不同时代的钾质斑脱岩具有相似的源岩岩浆背景,为中酸性的粗安岩-英安岩-流纹岩系列,源于同碰撞岛弧(synCOL-VA)背景的火山喷发活动,与板块边缘的俯冲碰撞密切相关。由于华南五峰组—龙马溪组内斑脱岩及黑色页岩沉积的形成与此间华夏地块与扬子地块的汇聚相关,华北下马岭组的黑色岩系与钾质斑脱岩的形成可能也和华北地块与相邻地块的碰撞相关。推测后者很可能为Rodinia超大陆或Pangea850Ma汇聚时的沉积-地层学响应。更多还原

【Abstract】 Recently, numerous K-bentonite beds have been recognized in the Wufeng-Longmaxi formations(Late Ordovician-Early Silurian) of South China and in the Xiamaling formation (~Tonian, Early Neoproterozoic) of North China. Both K-bentonite sequences occur in the same kind of black shale or slate successions and show similar facies changes in ascending order. This is in good agreement with Ettensohn’s lithospheric-flexure models of supracrustal loading, caused by the plate-margin subduction and collision. Geochemical analyses show that the parent magmas of the two K-bentonite sequences from widely separated geological eras, originated in similar syn-collision and volcanic arc tectonic settings, which produced mainly an intermediate-to-felsic series of trachyandesitic, rhyodacitic/dacitic, and rhyolitic magmas. This type of volcanism is associated with the collision and subduction of paleo-continental blocks/arcs. The large ash-falls of the peri-Iapetus Orogeny support the tectonic settings of this volcanism. Compared with the K-bentonites and the black-shale successions of the Wufeng and Longmaxi formations of South China, which are related to the accretion of the Cathaysia Block to the Yangtze Block during the Ordovician-Silurian transition, the Neoproterozoic K-bentonites and dark shale/slate deposition of the Xiamaling formation in North China probably reflect similar plate-tectonic movements. The Neoproterozoic succession of K-bentonites and black shales suggests that a similar accretionary process was active around the North China Block at this time. Consequently, with reference to the previously reported dating of this formation at about 1 000-850 Ma, it is likely that the K-bentonites and the dark shales/slates of the Neoproterozoic Xiamaling formation were probably volcanic and depositional responses that reflect accretion related to the North China Block during the assembly of the supercontinent, Rodinia or Pangea 850 Ma.更多还原