Volcanic activity stages and distribution during the Permian in the Shunbei area, Tarim Basin

The Shunbei area, located in the Shuntuoguole Low Uplift in the central Tarim Basin, is covered by superimposed basalt and dacite, where volcanic activity stages in the Permian and areal distribution are more difficult to identify compared with those in the Tahe and Tazhong areas. Through core observations and sampling of Permian volcanic rocks from 27 wells in the Shunbei area, we carried out thin section identifications and geochemical element analyses. Five basic rock types were observed, including basalts, andesites, dacites, tuffs and volcanic breccias. In addition, the volcanic activity was subdivided into 5 eruption cycles (or periods) based on the lithology, the petrophysical log characteristics and the seismic characteristics of the Permian section. The first stage was an eruption of intermediate-acid pyroclastic rocks, with the eruption center located in the Shunbei 3D block. The second stage was an eruption of basic volcanic rocks, which was mainly controlled by paleotopo-graphy. The third and fourth stages featured cone-shaped and shield-shaped intermediate-acid volcanic lava, with stable volcanic sediments between the two stages. The fifth stage was an eruption of basic volcanic lava, which mainly distributed in the east of the study area.