Numerical modeling of thermal structure, circulation of H2O, and magmatism–metamorphism in subduction zones: Implications for evolution of arcs
Numerical modeling of thermal structure, circulation of H2O, and magmatism–metamorphism in subduction zones: Implications for evolution of arcs
复制标题
DOI：
10.1016/j.gr.2006.04.010
复制
发表时间：
2007
影响因子：
6.1
通讯作者：
H. Iwamori;C. Richardson;S. Maruyama
中科院分区：
文献类型：
--
作者：
H. Iwamori;C. Richardson;S. Maruyama
通过对俯冲带热结构、固体对流、富H_2O流体生成和输运的数值模拟，综合反映了俯冲带的热平衡、H_2O岩浆-变质作用的循环、弧的生长和大陆边缘等过程。一个大规模的对流模型与稳定俯冲的冷老板（1.3亿年）预测快速（约100万年）冷却俯冲带，导致岩浆活动的停止。该模型还预测，弧和大陆边缘下的地幔温度受俯冲板片有效温度的影响很大，即，俯冲板块的年龄如果一个年轻的热板块的俯冲，包括脊俯冲，发生在每60至120百万年，如东亚所建议的，弧下的平均温度增加了约300 °C，这可能解释了东亚长期持续的岩浆活动。伴随着年轻板片和洋脊的俯冲，热结构和H2O循环发生了很大的变化，导致从（1）正常弧岩浆活动，（2）弧前地幔熔融，到（3）板片熔融，产生大量（100 km ~ 3）花岗岩熔体，与高P/T和低P/T型变质作用有关。（3）的最后阶段可形成一个花岗岩基带和一对变质带。数值模拟和观测结果的综合表明，年轻板片和洋脊的幕式俯冲作用可以解释岩基大量花岗质岩浆产生的热源，岩基和区域变质带的同步形成，以及成对变质作用的P-T条件。即使是高P/T变质作用，也需要在弧前区有一个升高的地热结构，与洋脊俯冲有关。虽然目前对岩基和区域变质带的侵位以及俯冲带的物质平衡没有很好的约束，但与洋脊俯冲有关的幕式事件被认为是岛弧和大陆边缘净增长以及俯冲带长期热平衡所必需的。
Numerical models on thermal structure, convective flow of solid, generation and transportation of H2O-rich fluid in subduction zones are consolidated to have a comprehensive view of the subduction zone processes: heat balance, circulation of H2O magmatism–metamorphism, growth of arcs and continental margins. A large scale convection model with steady subduction of a cold old slab (130 Myr old) predicts rapid (∼100 Myr) cooling of subduction zones, resulting in cessation of magmatism. The model also predicts that the mantle temperature beneath arcs and continental margins is greatly affected by the effective temperature of the subducting slab, i.e., the age of the subducting slab. If subduction of a young hot slab, including ridge subduction, occurs every 60 to 120 Myr as is suggested for eastern Asia, the average temperature beneath arcs is increased by about 300 °C, which may explain the long-lasting magmatism in eastern Asia. Associated with subduction of young slabs and ridges, thermal structure and circulation of H2O are greatly modified to cause a transition from (1) normal arc magmatism, (2) forearc mantle melting, to (3) slab melting to produce a significant amount (100 km3) of granitic melts, associated with both high-P/T and low-P/T type metamorphism. The last stage of (3) can result in formation of a granitic batholith belt and a paired metamorphic belts. Synthesis of the numerical models and observations suggest that episodic subduction of young slabs and ridges can explain heat source for generating a large amount of granitic magmas of batholiths, synchronous formation of batholith and regional metamorphic belts, and P–T conditions of the paired metamorphism. Even the high-P/T metamorphism requires an elevated geothermal structure in the forearc region, associated with ridge subduction. Although the emplacement of the batholiths and the regional metamorphic belts, and the mass balance in subduction zones are not well constrained at present, the episodic event associated with ridge subduction is thought to be essential for net growth of arcs and continental margins, as well as for the long-term heat balance in subduction zones.