地幔底层及其在全球物质演化中的意义

在核幔界面之上的下地幔一侧,地震波速分布极不均匀,厚度在50~300 km范围内变化的一层物质称为地幔底层。地幔底层由具有高地震波速和高密度的D″区和超低速带(ULVZ)组成。地幔底层是地核热能向地幔传播的必经之路,也是地幔中温度和温度梯度最高的地区。地幔底层既是俯冲板块的最终归宿,又是热柱和超级热柱的源区。因此,地幔底层既是全地幔对流的起点,又是全地幔对流的终点。在地幔底层可能发生地幔物质(包括俯冲板块物质在内)的部分熔融作用,也可能存在外核液态铁与地幔硅酸盐的化学反应。所以地幔底层在全球物质演化中占有重要的地位。

Lowermost mantle layer and its significance in the Earth's material evolution

The lowermost mantle layer is above the core mantle boundary (CMB) and composed of D″ region and ultra-low velocity zone (ULVZ). The seismic velocities in the CMB are very heterogeneous and its thickness varies from 50 km to 300 km. The CMB is not only the medium transferring thermal energy from core to mantle, but also the region in which the temperature and temperature gradient is the highest in the whole mantle. The CMB is the impinged by subducted slAbs and is the source of mantle plumes and super plumes. Therefore, the CMB is the beginning and the end of whole mantle convection. Within this lowermost mantle layer, the partial melting of material of lower mantle and chemical reaction of core mantle material can occur.Therefore,the CMB is significant in the Earth's material evolution.