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Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins

机译：顺序断层解释了共轭边距的不对称性和扩展差异

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摘要

During early extension, cold continental lithosphere thins and subsides, creating rift basins. If extension continues to final break-up, the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins. Although basins and margins are ubiquitous structures, the deformation processes leading from moderately -extended basins to highly stretched margins are unclear, as studies consistently report that crustal thinning is greater than extension caused by brittle faulting. This extension discrepancy might arise from differential stretching of brittle and ductile crustal layers, but that does not readily explain the typical asymmetric structure of conjugate margins-in cross-section, one margin displays gradual thinning accompanied by large faults, and the conjugate margin displays abrupt thinning but smaller-scale faulting. Whole-crust detachments, active from early in the rifting, could in theory create both thinning and asymmetry, but are mechanically problematical. Furthermore, the extension discrepancy occurs at both conjugate margins, leading to the apparent contradiction that both seem to be upper plates to a detachment fault. Alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic-resolution faulting, invisible deformation along top-basement 100-km-scale detachments or the structural complexity of cross-cutting arrays of faults. Here we use depth-migrated seismic images to accurately measure fault extension and compare it with crustal thinning. The observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault-controlled crustal thinning which progresses from a rift basin to the asymmetric structure, and extreme thinning of conjugate rifted margins. Contrary to current wisdom, the observations support the idea that thinning is to a first degree explained by simple Andersonian faulting that is unambiguously visible in seismic data.
机译：在早期伸展期间，寒冷的大陆岩石圈变薄并消沉，形成了裂谷盆地。如果延伸继续至最终破裂，则分裂且大大变薄的板块会在海平面以下沉陷，形成共轭的裂谷边缘。尽管盆地和边缘都是无处不在的结构，但从中等程度扩展的盆地到高度伸展的边缘的变形过程尚不清楚，因为研究一致报告说，地壳变薄大于脆性断层引起的扩张。这种延伸差异可能是由于脆性和延性地壳层的差异性拉伸引起的，但这不能轻易解释共轭边缘的典型不对称结构（在横截面中），一个边缘显示出逐渐变薄并伴有大断层，而共轭边缘显示出突变。细化但规模较小的断层。从裂谷早期开始活跃的全壳剥离理论上可能会同时变薄和不对称，但在机械上存在问题。此外，延伸差异出现在两个共轭边缘，导致明显的矛盾，即两者似乎都是脱离断层的上盘。备选模型提出，由于地震成像的局限性，或者是由次地震分辨率断层，沿顶部基底100 km尺度的分离所产生的不可见形变，或者是由断层横切阵列的结构复杂性引起的，因此没有发现很大的脆性扩展。在这里，我们使用深度偏移的地震图像来精确测量断层延伸并将其与地壳变薄进行比较。这些观测结果被用来创建一个平衡的裂谷运动学模型，该模型通过产生由裂谷盆地向非对称构造发展的断层控制地壳变薄和共轭裂谷边缘的极薄化来解决延伸差异。与当前的观点相反，这些观察结果支持稀疏化在第一程度上是由简单的安德森式断层解释的，这种断层在地震数据中是清晰可见的。

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  • 来源
    《Nature》 |2010年第7321期|p.294-299|共6页
  • 作者

    Cesar R. Ranero; Marta Perez-Gussinye;

  • 作者单位

    ICREA at CSIC, Barcelona Center for Subsurface Imaging, Instituto de Ciencias del Mar, CSIC, Passeig Maritim de la Barcelona 37-49,08003, Barcelona, Spain;

    rnDepartment of Earth Sciences, Royal Holloway, University of London, Egham TW20 OBD, UK;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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