关键词: 大邑断裂, 构造变形样式, 活动时代, 隐伏断层

Abstract: Primary evidence of the latest tectonic deformation style and the activity age of the Dayi Fault in the Sichuan Basin are obtained by field geological mapping,and surveying with the help of 3D scanner and total station.In the region of Wenshangou-Longfengchang,northeast of Dayi county on the northwestern wall of the fault,the time of Cretaceous and Neogene strata's gentle folding was measured to be between late Neogene and early Pleistocene.And obviously its forming time is later than the Longmen Shan Fault which controls the northwest boundary of Sichuan Basin's Mesozoic strata and shows a thrust-nappe structure.With the help of oil prospecting data,fault plane inclines to northwest,dip angle changes from 10°～20° in the deep to 70° at near-surface,and depth of the upper faulted point is about 200～300m.Geological and geomorphologic evidence shows that Holocene is its latest active time.The latest tectonic deformation on the Dayi Fault is represented by Holocene fold.Topographically,the deformation appears as continuous piedmont hillocks with traceable length of 2.5km,distributed en echelon in the piedmont of the Longmen Mountains and with the plane shape of single hillock being ellipse.Accordingly the Dayi Fault is inferred as a Holocene active blind fault on the basis of hillocks' section shape.

Key words: Dayi Fault, tectonic deformation style, activity age, buried fault