壳幔过渡层及其大陆动力学意义

On the Crust-Mantle Transition Layer and Its Implications in Continental Geodynamics

根据地震测量结果,造山带常见一个P波传播速度介于典型地壳和典型地幔之间的圈层,称为壳幔过渡层。这个圈层在地球物质科学领域常常被解释为壳幔混合层,形成机制不十分明确。提供了另一种选择,认为壳幔过渡层实际上可能是幔源岩浆底侵作用和地壳分异作用的产物,其密度随压力的逐渐变化是其波速特征的主要原因,是区域岩石圈重力不稳定的标志;也可能是软流圈物质岩石圈化的结果,是区域岩石圈逐渐冷却的象征。这个模型可以更好地解释造山带岩石圈拆沉作用、壳幔物质交换和岩浆活动,因而壳幔过渡层的查明具有重要的大陆动力学意义。

According to the seismological observations, there is usually a layer called as a transition layer which generally has an intermediate speed between P-wave speeds in typical crust and mantle rocks. This layer is often called as the crust mantle mixing layer in the Earth material science fields. This is not a term with a definite mechanism. In this paper, an other alternative choice is provided. In fact, the geophysical transition layer may be a product of mantle-derived magma underplating and crustal differentiation. The transitional P-wave velocity in this layer is caused by gradual variation of its density with pressure. Therefore, the P-wave transition layer is the mark of lithosphere instability. The layer may also be a product of asthenosphere transformation to lithosphere. In this case, the existence of the layer implies regional lithosphere cooling. Our model could better explain lithosphere delamination, crust-mantle material exchange and magmatism in orogens, and hence suggests important implications for the continental geodynamics.