俯冲带流体不混溶及其演化  

Fluid immiscibility and evolution in subduction zones

作　　者：刘颖员 张立飞[1] LIU Yingyuan;ZHANG Lifei(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing100871,China)

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《地质学报》2022年第12期4101-4130,共30页Acta Geologica Sinica

基　　金：国家重点研发项目(编号2019YFA0708501)资助的成果。

摘　　要：流体在俯冲加工厂中扮演着重要的角色。岩石学研究通常针对矿物中的“固定流体”,而对俯冲带内自由活动的流体,特别是自由流体不混溶分离演化过程及其影响的研究较为缺乏。流体的不混溶及其演化在自然界普遍存在,这一点在自然样品研究、高温压实验和流体状态方程理论计算的结果中得到验证。俯冲带中实际的流体体系是多元的、开放的和复杂的系统。随着流体的运移和演化过程,流体及流体-岩石体系将更加多样化。因此流体不混溶及其演化具有普遍性、复杂性和多样性的特点。地球物理的证据表明俯冲带内的流体集中在俯冲板片靠近海沟处、俯冲板片与上覆地幔楔界面附近和上覆地幔楔内部。这些单相或多相的流体可以通过多种路径、机制和传输方式进行运移。在大范围尺度上,流体可以沿着俯冲板片与上覆地幔楔之间的密封界面自下而上倾斜流动。在一些密封破裂的排泄口处(如岩体形变或断裂/断层处)流体向上流入地幔楔。不排除由岩石裹挟或在俯冲板片弯折处向下运移的流体。在局部尺度上,流体运移受到不同岩性以及具有各向异性渗透率的构造界面的控制。通过结合俯冲带中流体运移可能的路径、流体高温压范围的P-T-X相图和俯冲带热结构模型,我们构建并探讨了简单二元体系流体在俯冲带弧前运移过程中不混溶演化的理想理论模型。一方面,不同热结构俯冲带中的流体具有不同的循环和演化特征,冷俯冲带相比热俯冲带具有更深更广阔的流体不混溶空间。另一方面,在相同俯冲带中,不同体系流体具有不同的可以发生不混溶的空间范围(对于二元体系流体表现为H_(2)O-CO_(2)<H_(2)OCH_(4)<H_(2)O-N_(2)<H_(2)O-H_(2))。流体在俯冲带中不同的位置和不同运移路径也控制着流体的演化过程。此外,俯冲热结构随长期演化逐渐变冷,以及更长�Fluids play an important role in subduction factories.Petrological studies usually focus on“immobile fluid”in minerals,while research on free-flowing fluid in subduction zones,especially the process and effect of the immiscible fluid evolution and subsequent separation,is relatively lacking.Fluid immiscibility and evolution are common in nature,which has been verified by natural sample studies,high P-T experiments,and theoretical calculations of the equation of state for fluids.The actual fluid system in the subduction zone is a multivariate,open and complex system.As the fluid migrates and evolves,the fluid and fluid-rock system become more diverse.Therefore,fluid immiscibility and evolution have the characteristics of universality,complexity and diversity.Geophysical evidence indicates that fluids in the subduction zone are concentrated in the subducting slab near the trench,near the interface between the subducting slab and the overlying mantle wedge,and inside the overlying mantle wedge.These singlephase or multi-phase fluids can migrate through a variety of paths,mechanisms and transport modes.On a large scale,the fluids flow updip under a sealed plate interface between the subducting slab and the overlying mantle wedge.In some locations(such as deformations or fractures/faults),the seal breaks,and fluids escape upward through vents into the mantle wedge.Fluids entrapped by rocks or migrating downward at bends in the subducting slab are not excluded.Locally,fluid migration is governed by different lithologies and structural interfaces with anisotropic permeability.By combining the possible paths of fluid migration in the subduction zone,the fluid P-T-X phase diagram in the high P-T range,and the thermal structural model of the subduction zone,we built and discussed an ideal theoretical model for the immiscibility evolution of fluid in simple binary system during migration in the forearc of the subduction zone.On the one hand,the fluids in subduction zones with different thermal structures have different

关 键 词：俯冲带流体 不混溶 流体运移 P-T-X相图 俯冲带热结构 

分 类 号：P542[天文地球—构造地质学]