A numerical simulation of mental evolution based on a two-dimentional mentle GCM

将早期岩浆-地幔耦合对流系统的数值模型扩展为包含了活动板块，并将扩展后的耦合系统（或地幔GCM）模型应用于地幔演化问题。数值模型表明，地幔的演化经历了两个阶段。在地幔被放射性元素强烈加热的早期阶段，下地幔足够热，经常引起地幔翻转和由此产生的羽流活动。羽流活动引起的岩浆活动使板块运动和脊状火山活动具有强烈的时间依赖性。然而，当放射性元素的内部加热变得弱于一个阈值（第二阶段）时，地幔翻转突然停止，地幔对流和脊状火山作用变得更加稳定。尽管俯冲板块深侵下地幔引起整体地幔对流，但由于地幔翻转引起的脊状火山作用和热点火山作用使地幔在整个地球历史上形成了岩浆产物占据下地幔深层、残余岩浆占据上地幔的化学分层。数值模拟的地幔的热化学状态很好地反映了地球化学和地震观测揭示的现今地幔的总体特征。从第一阶段到第二阶段的过渡可能对应于地球历史的太古宙-元古代边界。

The earlier numerical model of coupled magmatism-mantle convection system has been extended by including moving plates and the extended model of the coupled system (or mantle GCM) has been applied to the problem of mantle evolution. The numerical model suggests that the earth's mantle has evolved in two stages. On the earlier stage when the mantle is strongly heated by radioactive elements, the lower mantle are hot enough to frequently induce mantle overturn and the resulting plume activity. The magmatism induced by the plume activity makes plate motion and ridge volcanism strongly time-dependent. As the internal heating by radioactive elements becomes weaker than a threshold (the second stage), however, the mantle overturn suddenly stops and mantle convection and ridge volcanism becomes more steady. The ridge volcanism and hot spot volcanism induced by mantle overturn make the mantle chemically stratified with the deeper part of lower mantle occupied by magmatic products and the uppermost mantle occupied by residue of magma throughout the earth's history in spite of the whole mantle convection induced by subducting slabs that penetrate deep into the lower mantle. The thermal and chemical state of the numerically modeled mantle well captures the overall features of the present earth's mantle revealed by recent geochemical and seismological observation. The transition from the first to the second stage may corresponds to the Archean-Proterozoic boundary of the earth's history.