Structure and dynamics of the Ecuador Fracture Zone, Panama Basin
Structure and dynamics of the Ecuador Fracture Zone, Panama Basin
复制标题
巴拿马盆地厄瓜多尔断裂带的结构和动力学
DOI：
10.1093/gji/ggad315
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发表时间：
2023
影响因子：
2.8
通讯作者：
Peirce C
中科院分区：
文献类型：
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作者：
Peirce C
在这项研究中，多种地球物理数据类型被用来调查厄瓜多尔断裂带的结构和动力学，一个复杂的多股走滑断层系统位于巴拿马盆地。重力模拟显示，在该系统下方有一个25-30公里宽、厚1.3公里的低密度地壳区域，在上地幔有一个非常低密度的区域。沿着沿着边缘，向厄瓜多尔和哥斯达黎加裂谷形成的“正常”结构和厚度洋壳的过渡是突然的。在厄瓜多尔断裂带本身，正断层界定了中央山脊。这些断层穿过整个沉积层厚度，使海床偏移，而沉积层的几何形状记录了相对隆起的多个阶段，最近的阶段仍在进行中。在6-7 Ma的哥斯达黎加裂谷地壳中也观察到了活动的伸展断层，其走向近似于伸展的脊状平行走向。厄瓜多尔断裂带东部边缘的中脊和横脊也具有对比鲜明的地壳密度结构。两个中脊的地壳密度低于中间山谷之间的地壳密度，而横脊地壳的厚度和密度结构与哥斯达黎加裂谷相当。活动的中央山谷基底切割正断层允许海水进入和地壳下盘的交替，也流到地幔深处，根据重力模型，地幔橄榄岩发生30- 50%的蛇纹石化。由此产生的蛇纹岩驱动的浮力作为观察到的中脊相对垂直构造作用的主要控制。相反，横向脊的相对隆起是由于厄瓜多尔和哥斯达黎加裂谷之间扩张方向的变化引起的岩石圈挠曲。与广泛接受的断裂带是构造不活跃系统的假设相反，厄瓜多尔断裂带提供了由于持续的热液循环和相对隆起而导致的延伸、蛇纹化的证据。
In this study, multiple geophysical data types are used to investigate the structure and dynamics of the Ecuador Fracture Zone—a complex multistranded strike-slip fault system located in the Panama Basin. Gravity modelling reveals a 25–30-km-wide region of ∼3-km-thick, low-density crust beneath this system and an anomalously low-density region in the uppermost mantle. Along both edges, the transition to the ‘normal’ structure and thickness oceanic crust formed at both the Ecuador and Costa Rica Rifts is abrupt. Within the Ecuador Fracture Zone itself, normal faults bound the median ridges. These faults traverse the entire thickness of accumulated sediment and offset the seabed, while sediment layer geometries document multiple phases of relative uplift, with the most recent phase still ongoing. Active extensional faulting, with an approximately spreading ridge-parallel strike, is also observed in 6–7 Ma Costa Rica Rift crust. The median ridges and the transverse ridge at the eastern edge of the Ecuador Fracture Zone also have contrasting crustal density structures. Both median ridges have a lower density crust than between the intervening valleys, while the transverse ridge crust has an equivalent thickness and density structure to that formed at the Costa Rica Rift. The active median valley basement-cutting normal faults allow seawater ingress and alternation of the crustal footwall, and also flow to mantle depth where, based on gravity modelling, 30–50 per cent serpentinization of mantle peridotite occurs. The resulting serpentinite-driven buoyancy acts as the primary control on the observed median ridge relative vertical tectonism. In contrast, the relative uplift of the transverse ridge results from lithospheric flexure in response to a change in spreading direction between the Ecuador and Costa Rica Rifts. Contrary to the widely accepted assumption that fracture zones are tectonically inactive systems, the Ecuador Fracture Zone provides evidence of extension, serpentinization due to ongoing hydrothermal circulation and relative uplift.