Kinetic Models for Healing of the Subduction Interface Based on Observations of Ancient Accretionary Complexes
Kinetic Models for Healing of the Subduction Interface Based on Observations of Ancient Accretionary Complexes
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DOI：
10.1029/2019gc008256
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发表时间：
2019-07-01
影响因子：
3.5
通讯作者：
Yamaguchi, A.
中科院分区：
文献类型：
--
作者：
Fisher, D. M.;Smye, A. J.;Yamaguchi, A.
来自日本Kodiak增生杂岩和Shimanto带的砂-页岩混杂岩记录了沿着古俯冲界面在150 - 350 ℃范围内的俯冲过程中的变形。我们使用这些混杂岩的观测结果来构建一个简单的动力学模型，该模型估计密封单个裂缝所需的最大时间，以衡量断裂带愈合的速率。裂缝封闭涉及硅从具有鳞片状组构的泥岩扩散再分布到砂岩块体中的欠饱和流体填充裂缝。考虑了驱动裂缝封闭的化学势梯度的两种驱动力：（1）流体压力P-f的瞬时下降，以及（2）泥岩中鳞片状滑动面与较强砂岩块体中裂缝之间的平均应力差。密封时间对平均应力比P-f更敏感，密封速度快四个数量级。密封持续时间取决于裂缝间距，二氧化硅扩散动力学，块和矩阵之间的强度对比的大小，其中每一个都是松散的约束条件有关的孕震区。我们将该模型应用于三个活跃的俯冲带，发现密封率是最快的沿着卡斯卡迪亚和几个数量级慢沿着尼加拉瓜和东北板顶地热给定的深度。该模型提供了（1）一个地球化学过程的框架，通过裂缝封闭和剪切组构的发展影响俯冲力学，（2）证明了在地震间隔期间动力学驱动的质量再分布是一种合理的机制，可以沿着光滑的沉积物为主的会聚边缘产生粗糙体。慢滑动事件，以及对于不同板块边界和沿沿着给定边界下倾而在空间和时间上变化的地震。从古俯冲板块边界暴露在陆地上的断层岩提供了沿着活动边界滑动过程中可能发生的变形过程的记录，因此我们回顾了这些古老岩石的特征，以深入了解俯冲带的滑动行为。我们发现，在这些情况下，板块边界变形发生在一个广泛的断层带内，通过过程，涉及二氧化硅从剪切泥岩开裂砂岩块重新分配。我们使用的地球化学模型来计算需要多长时间来密封裂缝的这个过程，并得出结论，裂缝密封的速度，可能会影响地震周期，与裂缝愈合的速度取决于温度结构和滑动发生的深度。我们的研究结果表明，下行沉积物中的摩擦破坏和地球化学愈合过程可能会影响沿着俯冲界面的滑动稳定性。
Sand-shale melanges from the Kodiak accretionary complex and Shimanto belt of Japan record deformation during underthrusting along a paleosubduction interface in the range 150 to 350 degrees C. We use observations from these melanges to construct a simple kinetic model that estimates the maximum time required to seal a single fracture as a measure of the rate of fault zone healing. Crack sealing involves diffusive redistribution of Si from mudstones with scaly fabric to undersaturated fluid-filled cracks in sandstone blocks. Two driving forces are considered for the chemical potential gradient that drives crack sealing: (1) a transient drop in fluid pressure P-f, and (2) a difference in mean stress between scaly slip surfaces in mudstones and cracks in stronger sandstone blocks. Sealing times are more sensitive to mean stress than P-f, with up to four orders of magnitude faster sealing. Sealing durations are dependent on crack spacing, silica diffusion kinetics, and magnitude of the strength contrast between block and matrix, each of which is loosely constrained for conditions relevant to the seismogenic zone. We apply the model to three active subduction zones and find that sealing rates are fastest along Cascadia and several orders of magnitude slower for a given depth along Nicaragua and Tohoku slab-top geotherms. The model provides (1) a framework for geochemical processes that influence subduction mechanics via crack sealing and shear fabric development and (2) demonstration that kinetically driven mass redistribution during the interseismic period is a plausible mechanism for creating asperities along smooth, sediment-dominated convergent margins.Plain Language Summary Geophysical monitoring of active subduction zones has revealed plate boundary slip behaviors such as creep, slow slip events, and earthquakes that vary spatially and temporally for different plate boundaries and downdip along a given boundary. Fault rocks exposed on land from paleosubduction plate boundaries provide a record of the deformation processes that likely occur during slip along active boundaries, so we review the characteristics of these ancient rocks to develop insight into slip behavior in subduction zones. We find that plate boundary deformation in these cases occurs within a wide fault zone through processes that involve redistribution of silica from shearing mudstones to cracking sandstone blocks. We use a geochemical model to calculate how long it would take to seal a crack by this process and conclude that cracks seal at rates that could influence the earthquake cycle, with rates of crack healing dependent on the temperature structure and the depth where slip occurs. Our results suggest that processes of frictional failure and geochemical healing in downgoing sediments may influence the slip stability along the subduction interface.