The distribution of angular unconformity and included angle between strata above and below the unconformity in the Triassic and Cretaceous in the Xuefeng Mountain intracontinental tectonic system are studied.Based on that

we identify the range of deformation during the Early(T

1

) and Middle Triassic(T

2

) and the boundary line between high-angle and low-angle unconformities.It is indicated that the deformation intensity in the study area decreases from east to west during T

1

-T

2

.Since the Late Triassic

tectonic movements have been featured by east-to-west diachronous and progressive deformation

which helps to define the boundary lines among each period of deformation.Propagation rates of diachronous deformation in each period are calculated.From these propagation rates

it is concluded that the direct causes for the westward progressive deformation during the Yanshanian period are the thinning of lithosphere and the upsurging of asthenosphere in the cathaysia and other plates

while the indirect cause is the subduction of the Paleo-Pacific Plate beneath the Eurasia Plate.Moreover

the decollement surfaces also play an important role in tectonic propagation during the Yanshanian period.