青藏高原冈底斯岩浆岩带西段新近纪达若-壮拉火山构造的地层序列及活动时序重塑OA北大核心CSTPCD

The volcanic strata,lithofacies(rocks),and structures of the Cenozoic volcanoes in the Xizang Plateau are important records to decipher the evolution process of the plateau.In order to reconstruct the Neogene volcanism process in the Daruo-Zhuangla volcano-tectonic depression,a"three-facies geological survey"was carried out for the volcanic rocks in the study area using 1∶50000 geological survey,1∶50000 remote sensing geological interpretation,1∶2000 lithostratigraphic section,zircon U-Pb isotope dating and other methods.It is found that the Neogene volcanic activities in the study area are characterized by early and late stages,in which the early volcanic activity is dominated by simple central-type eruption accompanied by small-scale eruption,forming a shield lava dome or lava platform,and the volcanic eruptions are trachyandesite,trachyandesitic ignimbrite,and trachyandesitic tufflava,etc;the late volcanic activity is dominated by small-scale eruption,invasion and intrusion,forming a volcanic cone composed of lava and volcanic cinder.The volcanic eruptions are trachyandesitic ignimbrite,trachyandesitic tufflava,trachyandesitic volcaniclastic and vitroporphyric rocks.On the whole,the Neogene volcanic eruption index in the study area is low.The eruption style belongs to the Stromboli type or Hawaiian type.The distribution scale is small,and the spatial and Early Paleogene volcanic edifice are cross-cutting and stacked,which reflects the local migration characteristics of the volcanic activity center.New zircon U-Pb dating ages of the two stages of volcanic products are 11 Ma and 10 Ma,respectively.The ages of the rocks overlap with the development time of the regional extensional structure,indicating that the Neogene volcanic activity was formed in the intracontinental extensional environment after the collision of the Xizang Plateau,and its formation and distribution are controlled by the nearly N-S graben generated by the Late Cenozoic detachment and extension of the Xizang Plateau.