High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece
High-angle, not low-angle, normal faults dominate early rift extension in the Corinth Rift, central Greece
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DOI：
10.1130/g39560.1
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发表时间：
2017-12
期刊：
影响因子：
5.8
通讯作者：
R. Bell;G. Duclaux;C. Nixon;R. Gawthorpe;L. McNeill
中科院分区：
文献类型：
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作者：
R. Bell;G. Duclaux;C. Nixon;R. Gawthorpe;L. McNeill
低角度正断层（LANF）在后期裂谷和解体过程中适应伸展，但更难以解释的是LANF在伸展程度较低的大陆裂谷中的存在。一个重要的例子是希腊中部<5 Ma的科林斯裂谷，那里的微震活动性、暴露断层面的几何形状和深地震成像断层被用来证明存在倾角<30°的正断层。然而，新的和重新解释的数据质疑LANF是否在控制观察到的裂谷几何形状方面具有影响力，其中包括（1）暴露的陡峭断层面，（2）南部裂谷边缘的显著隆起，（3）时间平均（数万至数十万年）的上升-沉降比横跨南部海岸断层为1：1-1：2，以及（4）北部边缘沉降。我们测试是否滑上一个成熟的LANF可以重现长期（数万年）的几何形状和形态的科林斯裂谷使用有限元方法，模拟隆起和沉降场与拟议的断层几何形状。涉及LANF在深度的模型产生非常小的同震隆起的南部边缘，和震后松弛的净沉降的结果。与此相反，模型涉及陡峭的平面断层脆-韧性转换产生位移场，涉及上升的南缘的升降比约为1：2-3，与地质观测兼容。因此，我们认为LANF不可能在数万年的时间尺度上控制科林斯裂谷的几何形状。我们认为，虽然LANF可能会成为重要的过渡到分手，在经历了温和的拉伸，没有显着的岩浆活动，并没有最佳取向的预先存在的低角度结构的地区，高角度断层将是主要的应变适应机制，在早期裂谷的上地壳。
Low-angle normal faults (LANFs) accommodate extension during late-stage rifting and breakup, but what is more difficult to explain is the existence of LANFs in less-stretched continental rifts. A critical example is the <5 Ma Corinth Rift, central Greece, where microseismicity, the geometry of exposed fault planes, and deep seismically imaged faults have been used to argue for the presence of <30°-dipping normal faults. However, new and reinterpreted data call into question whether LANFs have been influential in controlling the observed rift geometry, which involves (1) exposed steep fault planes, (2) significant uplift of the southern rift margin, (3) time-averaged (tens of thousands to hundreds of thousands of years) uplift-to-subsidence ratios across south coast faults of 1:1–1:2, and (4) north margin subsidence. We test whether slip on a mature LANF can reproduce the long-term (tens of thousands of years) geometry and morphology of the Corinth Rift using a finite-element method, to model the uplift and subsidence fields associated with proposed fault geometries. Models involving LANFs at depth produce very minor coseismic uplift of the south margin, and post-seismic relaxation results in net subsidence. In contrast, models involving steep planar faults to the brittle-ductile transition produce displacement fields involving an uplifted south margin with uplift-to-subsidence ratios of ~1:2–3, compatible with geological observations. We therefore propose that LANFs cannot have controlled the geometry of the Corinth Rift over time scales of tens of thousands of years. We suggest that although LANFs may become important in the transition to breakup, in areas that have undergone mild stretching, do not have significant magmatic activity, and do not have optimally oriented preexisting low-angle structures, high-angle faulting would be the dominant strain accommodation mechanism in the upper crust during early rifting.