板块俯冲起始与成熟阶段的差异变质响应

Different Metamorphic Records between Subduction Initiation and Mature Subduction

板块俯冲起始是俯冲带最不为人知的关键过程之一,对理解全球板块构造如何启动有重要意义。本文综合了最新的数值模拟、变质岩石学和年代学研究结果,探讨板块俯冲起始到成熟阶段的热结构和变质作用差异。从俯冲起始到成熟阶段,俯冲带热结构由"热"变"冷",初始俯冲更可能形成的是角闪岩或麻粒岩,形成于热俯冲环境,以逆时针p-t轨迹为主,通常伴随板块部分熔融过程;而成熟阶段形成的主要是低温蓝片岩和榴辉岩,形成于冷俯冲环境,具有典型的顺时针p-t轨迹,以板块变质脱水为主。对俯冲带高t/p变质岩(如变质底板)的进变质过程、时间以及构造背景等方面需进一步加强研究,以获取更详实的现代板块俯冲起始阶段的地质过程。

Subduction initiation is one of the most enigmatic and controversial domains in subduction zones. This key process through geological time plays an important role on the activation of Earth’s plate tectonics. This study aims to discuss the discrepancies of thermal structure and metamorphism between subduction initiation and mature subduction,on the basis of numerical,petrological and geochronological data. The thermal structure of subduction zones may become cold from initial to mature stages,with the increases of subducted dip angle and subduction rate. The hot subduction during subduction initiation would form amphibolite or granulite with counterclockwise p-t paths. Partial melting of subducted slab likely occur at this stage. In contrast,mature subduction at steady-state is mostly characterized by cold subduction and therefore forms low-temperature blueschist and eclogite. These rocks are expected to record clockwise p-t paths and metamorphic dehydration reactions. Although metamorphic petrological studies for subduction initiation has come a long way,recently,several key issues involving prograde metamorphism,precise age data and geological settings of high t/p rocks in subduction zones still need further works. Detailed geological processes during subduction initiation in modern subduction zones could be revealed by metamorphic soles through combined petrological,thermo-mechanical modeling and geochronological studies.