Detachment faulting related to oceanic core complexes (OCCs) has been suggested to be a manifestation of slow seafloor spreading. Although numerical models suggest OCCs form under low magma supply, the specific interaction between magmatism and tectonic faulting remains elusive. This paper examines seismic observations detailing the spatiotemporal interactions between magmatism, high-angle faulting, and detachment faulting at a slow-spreading mid-ocean ridge in the West Philippine Basin. We identified a magma-rich spreading phase, indicated by a magmatic top basement and oceanic crust with shallow-penetrating high-angle normal faults. An axial valley reveals an along-strike transition from magmatically-dominated to highly tectonized oceanic crust over a distance of 70 km. Two older OCCs with concave-down fault geometries and a younger OCC with steep-dipping faulting suggest sequential detachments with the same polarity. Our findings suggest: (1) slow seafloor spreading alternates between high-angle faulting with a relatively high magma supply and detachment faulting with a limited magma supply; (2) sequential development of younger detachments in the footwall of its predecessor leads to an asymmetric split in the newly accreted crust; and (3) the life cycle of OCC ends with high-angle faults that overprint the detachment and act as magma pathways, sealing the OCC. Our study captures the dynamic interaction between high-angle and detachment faults and their concurrent and subsequent relationship to magmatic systems. This reveals that strain distribution along strike is critical to OCC formation, thus enriching our understanding beyond conventional considerations such as spreading rates and melt budgets at mid-ocean ridges.

中文翻译：

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揭示海底缓慢扩张过程中岩浆与变形之间的联系


与大洋核心复合体（OCC）相关的拆离断层被认为是海底缓慢扩张的表现。尽管数值模型表明 OCC 是在低岩浆供应下形成的，但岩浆作用和构造断层之间的具体相互作用仍然难以捉摸。本文研究了地震观测，详细介绍了西菲律宾盆地缓慢扩张的洋中脊的岩浆作用、高角度断层和滑脱断层之间的时空相互作用。我们确定了一个富含岩浆的扩张阶段，由岩浆顶部基底和具有浅穿透性高角度正断层的洋壳表明。一个轴谷揭示了从岩浆主导的到高度构造洋壳的沿走向过渡，距离超过 70 公里。两个具有下凹断层几何形状的较老的 OCC 和一个具有陡倾断层的较年轻的 OCC 表明具有相同极性的连续分离。我们的研究结果表明：（1）缓慢的海底扩张在岩浆供应相对较高的高角度断层和岩浆供应有限的拆离断层之间交替； (2) 在其前身的下盘中，较年轻的滑脱层相继发育，导致新增生地壳的不对称分裂； (3) OCC 的生命周期以高角度断层结束，这些断层覆盖了分离层并充当岩浆通道，封闭了 OCC。我们的研究捕捉了高角度断层和滑脱断层之间的动态相互作用以及它们与岩浆系统同时发生和随后发生的关系。这表明沿走向的应变分布对于 OCC 的形成至关重要，从而丰富了我们对大洋中脊的扩散率和融化预算等传统考虑因素的理解。