北山地区各时代火山岩组合特征及分布

STRATIGRAPHIC SEQUENCE AND AGE OF THE BIKOU GROUP

摘要: 总结了北山地区各时代火山岩的岩石组合及分布特征。指出大部层位的火山岩属正常钾钠类型、钙碱性的、中—酸性为主的连续分异组合，钠质的、拉斑系列的基性和双峰式火山岩组合仅在元古界、中奥陶统、上志留统、下二叠统等层位发育，碱性系列较少，区内无碱性岩（σ＞９．０）。在部分地区如白产堂、公婆泉、狼娃山等可出现钾质类型的中酸性岩。火山岩特征反映了北山多次“开”和“合”的构造演化历史。

Abstract: The Bikou Group is a sequence of rift margin type deposits occurring between the platform and rift. Various types of rock show features of regular facies change. On the basis of rock types and rock associations, it may be divided into 7 lithostratigraphic units of formation rank. This group rests unconformably on the Silurian Maoxian Group or Shuijing Formation and is in turn covered by the Middle Devonian Carboniferous Lueyang Formation, and contains such fossils as Amphissites pulcher, Bairdia sp., Desquamatia sp. and Schizo phoria sp. So its age is determined to be Early Middle Devonian.