Fluid-rich subducting topography generates anomalous forearc porosity
Fluid-rich subducting topography generates anomalous forearc porosity
复制标题
DOI：
10.1038/s41586-021-03619-8
复制
发表时间：
2021-07-08
期刊：
影响因子：
64.8
通讯作者：
Bassett, Dan
中科院分区：
文献类型：
--
作者：
Chesley, Christine;Naif, Samer;Bassett, Dan
俯冲地形对断层滑动模式的作用，特别是它是阻碍还是促进大型逆冲断层地震，在俯冲动力学中仍然是一个有争议的话题（1-5）。模型已经说明了俯冲地形严重改变俯冲带结构、应力状态和力学的可能性（4-6）;然而，对所提出的复杂断裂网络以及俯冲地形和相关的上板块损伤带的水文的直接地球物理成像仍然是难以捉摸的。在这里，我们使用被动和受控源海底电磁数据收集在北方希库朗吉边缘，新西兰，以限制在一个地区的主动海山俯冲电阻率。我们表明，海山上的传入板包含一个薄的，低孔隙度的玄武岩帽，陷阱的导电矩阵porousvolcaniclastics和蚀变材料的电阻核心，这使得3.2至4.7倍的水俯冲，相比正常的，无故障的海洋岩石圈。在弧前，我们的形象，缺乏沉积物的板块界面以上的俯冲海山具有类似的电气结构传入的板块海山。俯冲海山内的一个尖锐的电阻峰值直接位于一个突出的上板导电异常之下。这种上板块异常与爆发型重复地震的位置和与最近的缓慢滑动事件相关的地震活动的重合直接将俯冲地形与前弧中富含流体的破坏区的形成联系起来，这些破坏区通过调节流体超压来改变板块界面处的有效正应力。除了严重改变上板块的结构和物理条件外，俯冲海山是一种未得到充分认识的机制，可将大量的水输送到弧前和更深的地幔。
The role of subducting topography on the mode of fault slip-particularly whether it hinders or facilitates large megathrust earthquakes-remains a controversial topic in subduction dynamics(1-5). Models have illustrated the potential for subducting topography to severely alterthe structure, stress state and mechanics of subduction zones(4-6); however, direct geophysical imaging of the complex fracture networks proposed and the hydrology of both the subducting topography and the associated upper plate damage zones remains elusive. Here we use passive and controlled-source seafloor electromagnetic data collected at the northern Hikurangi Margin, New Zealand, to constrain electrical resistivity in a region of active seamount subduction. We showthat a seamount on the incoming plate contains a thin, low-porosity basaltic cap that traps a conductive matrix of porousvolcaniclastics and altered material over a resistive core, which allows 3.2 to 4.7 times more water to subduct, compared with normal, unfaulted oceanic lithosphere. In the forearc, we image a sediment-starved plate interface above a subducting seamount with similar electrical structure to the incoming plate seamount. A sharp resistive peak within the subducting seamount lies directly beneath a prominent upper plate conductive anomaly. The coincidence of this upper plate anomaly with the location of burst-type repeating earthquakes and seismicity associated with a recent slow slip event' directly links subducting topography to the creation of fluid-rich damage zones in the forearc that alter the effective normal stress at the plate interface by modulating the fluid overpressure. In addition to severely modifying the structure and physical conditions ofthe upper plate, subducting seamounts represent an underappreciated mechanism for transporting a considerable flux of water to the forearc and deeper mantle.