Under conditions of presseure that is similar to the depth at which crustal low velocity layer of the Qinghai Xizang plateau exists(20～30km),When heated to 900℃,plagio amphibolite shows plastic deformation and enters steady creep strain states in the light of high temperature and high pressure experiment results. Due to the plastic deformation,weakening and strength decline of rocks,and participation of water released from rocks,this zone becomes a weak interlayer in the crust.
