关键词: 俯冲带, 平板俯冲, 俯冲角, 岩石圈板块西向漂移, 地幔东向流动

Abstract: At the convergent boundaries of plates, when one plate subducts into the another, the form of the subduction boundaries (trench, mountain belt) bears a close relation with the properties of the subducting and subducted plates. In this paper, we mainly use plate subduction model to calculate and simulate some major subduction boundaries all over the world, and discuss the problem of the dip angle. Here we consider the subducting plate as a plane plate and the subducted plate as a part of the spherical surface of the Earth. And we suppose that the dip angle calculated from the model is the initial dip angle of the plate. From the simulation we find that many large subducting plates can be approximately regarded as plane plates. Plate subdution model, however, is not fit for some reversed-arc subduction boundaries such as Izu trench, which is fit for spherical subduction model. From the simulation we get the positions of six large subduction boundaries, in good accordant with the positions of the present subduction boundaries. Besides, we calculate also the initial dip angle of the subducting plate. The recent studies show that the lithosphere exhibits universal westward drift. From our calculation, it is shown that in the east part of the Pacific the initial dip angle of the subducting plate is less than the recent dip angle of the Benioff zone, but it is not true for the west part of the Pacific where the initial dip angle is larger than the recent dip angle of the Benioff zone. This result directly tallies with the westward drift of the lithosphere, and with the eastward flow of the mantle relative to the lithosphere. Because the westward motion of the subducting plate in the Pacific is opposite to the eastward movement of the mantle, it will lead to an additive resistant force on the subducting plate, which makes the dip angle becomes larger and larger. In east pacific, however, the subduction direction of the subducting plate is the same as that of the flow of the mantle, so the current dip angle of the Benioff zone will be larger than the initial dip angle.

Key words: subduction zone, plate subduction, dip angle, westward drift of lithospere, eastward flow of mantle