Slab Temperature Evolution Over the Lifetime of a Subduction Zone
Slab Temperature Evolution Over the Lifetime of a Subduction Zone
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DOI：
10.1029/2020gc009476
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发表时间：
2021-06-01
影响因子：
3.5
通讯作者：
Condit, C. B.
中科院分区：
文献类型：
--
作者：
Holt, A. F.;Condit, C. B.
俯冲板块的热演化控制着一系列的俯冲过程，但我们缺乏对俯冲带一生中热结构如何发展的强有力的理解。我们使用动态一致的时间演化模型研究了板坯热结构的时间相关性。沿板块莫霍面和板块顶部的压力-温度(P-T)条件在俯冲的不同阶段表现出很大的变异性：启动、自由下沉和成熟俯冲。这种可变性响应于依赖时间的俯冲特性(例如，快收敛与慢收敛)和从先前阶段继承的热结构(例如，由于上板老化)而发生。在给定的深度，板坯在启动过程中迅速冷却，之后发生较慢的冷却。在莫霍面的情况下，额外的冷却发生在自由下沉阶段。我们探讨了随时间变化的热结构对岩石折返和板片脱水的影响。模拟的板岩顶部P-T路径跨越了与出土岩石相关的P-T空间的大部分，这表明记录的变异性的一个重要组成部分可能具有动态起源。结合我们的P-T剖面和大洋岩石圈的热力学模型，我们发现，在早期阶段，板块莫霍面上的超镁铁质岩石脱水提供了弧下深度的大量含水流体。在随后的阶段，这些岩石将流体带入更深的地幔，沿着板块顶部的镁铁质地壳在弧下深度释放水。我们的结论是，不断变化的俯冲条件和非稳态的热结构，对恒定俯冲参数的运动学驱动模型的实用性提出了挑战，特别是在研究地质过去的热结构方面。
The thermal evolution of subducting slabs controls a range of subduction processes, yet we lack a robust understanding of how thermal structure develops over a subduction zone's lifetime. We investigate the time-dependence of slab thermal structure using dynamically consistent, time evolving models. Pressure-temperature (P-T) conditions along the slab Moho and slab top exhibit substantial variability throughout the various phases of subduction: initiation, free sinking, and mature subduction. This variability occurs in response to time-dependent subduction properties (e.g., fast vs. slow convergence) and thermal structure inherited from previous phases (e.g., due to upper plate aging). At a given depth, the slab cools rapidly during initiation, after which slower cooling occurs. In the case of the Moho, additional cooling occurs during the free sinking phase. We explore the implications of time-dependent thermal structure on exhumed rocks and slab dehydration. Modeled slab top P-T paths span much of the P-T space associated with exhumed rocks, suggesting a significant component of recorded variability may have dynamic origins. Coupling our P-T profiles with thermodynamic models of oceanic lithosphere, we show that dehydrating ultramafic rocks at the slab Moho provide the bulk of hydrous fluid at subarc depths during the earliest phases. Over subsequent phases, these rocks carry fluids into the deeper mantle, and it is mafic crust along the slab top that releases water at subarc depths. We conclude that varying subduction conditions, and non-steady-state thermal structure, challenge the utility of kinematically driven models with constant subduction parameters, particularly for investigating thermal structure in the geological past.