超慢速扩张洋中脊岩浆形成和迁移汇聚动力学研究

Geodynamic process of melt generation, migration and focusing at ultraslow mid-ocean ridges

超慢速扩张洋中脊具有不同于其他扩张速率洋中脊的特征,表现为剧烈变化的洋壳厚度和典型的非岩浆段。本文对前人研究的洋中脊岩浆形成关键因素和迁移聚集模式进行综合分析,结合实际地球物理和地球化学的观测数据,探讨了超慢速扩张洋中脊岩浆从地幔源区形成、迁移汇聚、形成洋壳的整个地质过程,进一步指出了影响洋壳结构的关键控制因素。研究结果表明,超慢速扩张洋中脊沿轴洋壳厚度的变化受岩浆补给量和迁移汇聚的共同制约。其中,岩浆补给量受控于洋中脊的地幔潜热、地幔成分和扩张速率的变化;岩浆迁移和汇聚过程则与超慢速扩张洋中脊密集的分段特征和阻渗层的空间结构密切相关。

Accretion of oceanic crust has experienced the mantle partial melting by decompression,melt extraction,migration and focusing into the oceanic crust,which emplaced in the oceanic crust forming of dike and erupted on the bottom of sea after fractional crystallization.The dramatic variation of crustal thickness along the ultraslow mid-ocean ridge and ammagmatic segmentation is concerned to be the typical characteristics to others.Based on previous studies of melt generation key factors and migration model of mid-ocean ridge basalt,this paper discussed the process of melt at ultraslow mid-ocean ridge and analyzed the key factors controlling the crustal thickness.Besides,this process and its result is constrained by geophysical and geochemical observation.The result shows that the crustal thickness along the ultraslow mid-ocean ridge is constrained by melt volume and lateral migration collectively.Among this process,mantle potential temperature,mantle compositions and spreading velocity controlled the melt volume.The segmentation of ultraslow mid-ocean ridge and the corresponding permeability barrier construct guide the migration and focusing of melt.