New view of the stratigraphic division and age of the Gaiyang Group in northwestern Fujian—A case study of the Gaiyang area, Mingxi

Abstract: Located in the Nanping-Ninghua tectono-magmatic belt, the Gaiyang Group is composed of a low-grade metavolcanic series, which is divided into the Louqian Formation, Sanxizhai Formation and Longtou Formation by Huang Quan-zhen et al., and its age is assigned to the late Sinian. Through 1:50 000 detailed regional geological survey and reconstruction of the old volcanic structure, the Gaiyang Group is considered to be the product of volcanic activity in the same structural setting according to the stratigraphic sequence, rock association and volcanism. From the early stage to late stage, the rocks make up a complete volcanic-sedimentary cycle from strong to weak eruption. So the authors suggest that the Gaiyang Group may be divided into the Louqian Formation and Longtou Formation, and according to new isotopic data, the ages of the Louqian Formation and Longtou Formation should be assigned to the Nanhua period and Sinian period respectively.