Strike slip motion and the triggering of subduction initiation
Strike slip motion and the triggering of subduction initiation
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DOI：
10.3389/feart.2023.1156034
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发表时间：
2023-04
期刊：
影响因子：
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通讯作者：
Yida Li;M. Gurnis
中科院分区：
文献类型：
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作者：
Yida Li;M. Gurnis
在西太平洋，对伊祖-波宁-马里亚纳、瓦努阿图和普塞格尔三个最明确的新生代俯冲起始（SI）事件进行了板块构造重建，显示了在俯冲起始之前和期间走滑运动的重要组成部分。通过计算模型，我们发现走滑运动对早期边缘的有效强度和俯冲起始的难易程度有很大的影响。研究了与粘弹塑性流变学、板块弱化、板块力和运动学相关的参数空间，结果表明，在更大的力、更快的弱化或更大的走滑运动下，俯冲更容易开始。通过解析解，我们证明走滑运动的影响可以用修正的弱化速率等效地表示。在逆压边缘，洋壳块体可以被困在一个新的逆冲断层和之前的走滑断层之间，这与Puysegur边缘的构造重建和重力模型一致。总之，模型和观测表明，当边缘逐渐减弱到阻力小于驱动力的程度，并且随着负浮力的积累，板内应力最终从挤压变为伸展时，就会触发俯冲的开始。用计算模型验证了启动时间t SI的解析公式，t SI标志着板内应力翻转标志的时刻。解析解表明，t SI以收敛速度为主，而板块年龄、走滑速度和减弱速率对俯冲起始时间尺度的影响较小，但仍很重要。
Plate tectonic reconstructions of three of the best-defined Cenozoic subduction initiation (SI) events in the western Pacific, Izu-Bonin-Mariana, Vanuatu, and Puysegur subduction zones, show substantial components of strike-slip motion before and during the subduction initiation. Using computational models, we show that strike-slip motion has a large influence on the effective strength of incipient margins and the ease of subduction initiation. The parameter space associated with visco-elasto-plastic rheologies, plate weakening, and plate forces and kinematics is explored and we show that subduction initiates more easily with a higher force, a faster weakening, or greater strike-slip motion. With the analytical solution, we demonstrate that the effect of strike-slip motion can be equivalently represented by a modified weakening rate. Along transpressive margins, we show that a block of oceanic crust can become trapped between a new thrust fault and the antecedent strike-slip fault and is consistent with structural reconstructions and gravity models of the Puysegur margin. Together, models and observations suggest that subduction initiation can be triggered when margins become progressively weakened to the point that the resisting forces become smaller than the driving forces, and as the negative buoyancy builds up, the intraplate stress eventually turns from compressional into extensional. The analytical formulation of the initiation time, t SI , marking the moment when intraplate stress flips sign, is validated with a computational models. The analytical solution shows that t SI is dominated by convergence velocity, while the plate age, strike-slip velocity, and weakening rate all have a smaller but still important effect on the time scale of subduction initiation.