地球深部水循环的动力学机制与相关问题研究进展

Dynamics Mechanism of Deep-Earth Water Cycling and Its Research Progress

地幔转换带是上下地幔的过渡区域,其内部发生的地质过程深刻影响着相关的地球动力学过程。俯冲带作为壳幔相互作用最强烈的地区之一,所产生的广泛分布在地表的大陆溢流玄武岩是研究壳幔循环动力学机制的重要对象之一。地幔转换带中含有相当数量的水,都赋存在名义上无水矿物之中,通过俯冲作用引发的残余板片脱水产生的流体交代大陆岩石圈,所产生的大陆玄武岩具有弧型特征的地球化学信息,使得在判别大陆玄武岩与岛弧玄武岩时容易误判。传统的玄武岩构造判别图在区分2类玄武岩(CFB、IAB)时判别精度不够高,可以通过敏感元素进一步划分,所以需谨慎地使用构造判别图。新提出的地幔转换带水过滤器模型将地球深部水流体循环、大规模陆内岩浆作用和超大陆拼合与裂解组成了一个体系。这个模型揭示了超大陆的聚合潜在地导致了含水大洋板片在地幔转换带内的积累,并且可能改变了地幔对流的模式。

Mantle transition zone（MTZ）is the transitional region between the upper and lower mantle,the geological processes occurred within its interior have a profound influence on the related geodynamic processes.The subduction zone is one of the strongest crust-mantle interaction regions,and the widespread continental flood basalt（CFB）on the Earth＇s surface is one of most important objects to study crust-mantle cyclic dynamics.Mantle transition zone has a large amount of water,which is stored within the nominal anhydrous minerals（NAMs）.The fluids were caused by the dehydration of residual slab in the subdution process,and these fluids replaced the continental lithosphere,producing the intra-continental basalts with arc-like signature and leading to the misidentification between continental basalt and island-arc basalt.The traditional discrimination diagrams of basalts are not validity distinguishing two types of basalts（CFB and IAB）,and it can be further divided by sensitive elements,thus the tectonic discrimination diagrams need to be used.Newly proposed water-filtering model of mantle transition zone links thedeep-Earth fluid cycling,large-scale intra-continental basaltic magmatism,and supercontinent cycles into a system.This model reveals that the assemblage of supercontinent could potentially lead to the accumulation of water-bearing oceanic plates in the mantle transition zone and may also change the mode of mantle convection.