Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity
Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity
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DOI：
10.3389/feart.2021.665185
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发表时间：
2021-02
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影响因子：
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通讯作者：
Melissa O. Anderson;Chantal Norris-Julseth;K. Rubin;K. Haase;M. Hannington;A. Baxter;M. Stewart
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文献类型：
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作者：
Melissa O. Anderson;Chantal Norris-Julseth;K. Rubin;K. Haase;M. Hannington;A. Baxter;M. Stewart
从俯冲到沿海沟水平终端的变换运动的转变与俯冲板片的撕裂和上覆板块中的走滑构造有关。一个突出的例子是汤加北部俯冲带，其中东北劳弧后盆地的丰富走滑断层活动与沿北部板块边界的转换运动和不对称板块回滚有关。在这里，我们解决一个基本问题：这种俯冲变换运动如何影响弧后区域的构造和岩浆演化？为了回答这个问题，我们通过分析地貌构造（远程预测地质测绘）和从船基多波束测深和质心矩张量数据解释的断层运动学，对该地区的地质和地球动力学进行了首次全面研究。我们的研究结果强调了NE Lau盆地的两个显着特征：1）与典型的以山脊为中心的弧后火山活动相比，出现了广泛分布的离轴火山活动；2）断层运动以浅地壳走滑断层（而不是正常断层）为主，从转换边界延伸超过~120公里。这些走滑断层的方向与左旋大剪切带中早期形成的正断层的重新活动一致。值得注意的是，确定了两组不同的 Riedel 巨型剪切力，表明最近靠近弧的弧后区域的部分应力场发生了逆时针旋转。重要的是，本研究中确定的 Riedel 结构直接控制着复杂火山成分区的发展，其特点是方向可变的扩张中心、离轴火山脊、广泛的熔岩流和点源弧后火山。这项研究增加了我们对现代弧后系统的地质和结构演化的理解，包括俯冲变换运动与海底火山活动的位置和类型之间的关联。
The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two notable features of the NE Lau Basin: 1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and 2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ∼120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, the Riedel structures identified in this study directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism.