A systematic 2-D investigation into the mantle wedge's transient flow regime and thermal structure: Complexities arising from a hydrated rheology and thermal buoyancy
A systematic 2-D investigation into the mantle wedge's transient flow regime and thermal structure: Complexities arising from a hydrated rheology and thermal buoyancy
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对地幔楔瞬态流态和热结构的系统二维研究：水合流变学和热浮力引起的复杂性
DOI：
10.1002/2013gc005022
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Le Voci G
中科院分区：
文献类型：
--
作者：
Le Voci G
俯冲带的弧火山活动可能受到地幔楔的流动状态和热结构的调节，因此，大量研究试图量化对地幔楔条件的主要控制。在本文中，我们在这些先前研究的基础上，通过系统的二维数值研究来研究水合流变学和热浮力如何影响楔形物的流动状态和相关的热结构。我们量化了一系列可能的作用：(i) 水含量 (0–5000 H/106Si)； (ii) 俯冲速度（2-10 厘米/年）； (iii) 上板块年龄（50-120 Myr），发现由瑞利-泰勒不稳定性或从上覆岩石圈底部滴落引起的小规模对流（SSC）是一种典型现象。 SSC 的形态随粘度和俯冲参数而变化，当俯冲速度和楔形粘度较低时，滴水现象最为突出。我们的结果证实，高俯冲速度和楔形粘度促进了主要的角流状态，以及弧区域下方强烈的上板块侵蚀。相比之下，我们发现SSC对弧后上板的侵蚀很大程度上是由楔形粘度控制的，发生在：（i）粘度为 < 5·1018Pa·s； (ii) 可用于失稳的上板长度超过了不稳定性的特征波长。因此，如果楔形流变学的含水弱化从沟槽延伸至少 100-150 公里，我们的二维模型预测不稳定的流态，导致 50-100 K 的温度波动，这足以影响含水矿物的熔化和稳定性。
Arc volcanism at subduction zones is likely regulated by the mantle wedge's flow regime and thermal structure and, hence, numerous studies have attempted to quantify the principal controls on mantle wedge conditions. In this paper, we build on these previous studies by undertaking a systematic 2‐D numerical investigation into how a hydrated rheology and thermal buoyancy influence the wedge's flow regime and associated thermal structure. We quantify the role of a range of plausible: (i) water contents (0–5000 H/106Si); (ii) subduction velocities (2–10 cm/yr); and (iii) upper‐plate ages (50–120 Myr), finding that small‐scale convection (SSC), resulting from Rayleigh‐Taylor instabilities, or drips, off the base of the overriding lithosphere, is a typical occurrence. The morphology of SSC varies with viscosity and subduction parameters, with drips at their most prominent when subduction velocities and wedge viscosities are low. Our results confirm that high subduction velocities and wedge viscosities promote a dominantly corner‐flow regime, and strong upper‐plate erosion below the arc region. By contrast, we find that back‐arc upper‐plate erosion by SSC is largely controlled by wedge viscosity, occurring when: (i) viscosities are < 5·1018Pa s; and (ii) the length of the upper plate, available for destabilization, exceeds the characteristic wavelength of instabilities. Thus, if hydrous weakening of wedge rheology extends at least 100–150 km from the trench, our 2‐D models predict an unstable flow regime, resulting in temperature fluctuations of 50–100 K, which are sufficient to influence melting and the stability of hydrous minerals.