ICREA at CSIC, Barcelona Center for Subsurface Imaging, Instituto de Ciencias del Mar, CSIC, Passeig Marítim de la Barcelona 37-49, 08003, Barcelona, Spain.
Nature. 2010 Nov 11;468(7321):294-9. doi: 10.1038/nature09520. Epub 2010 Nov 3.
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.
在早期伸展阶段，寒冷的大陆岩石圈变薄并沉降，形成裂谷盆地。如果伸展继续到最终的分裂，分裂和大大变薄的板块会沉降到深海之下，形成一对共轭的裂谷边缘。尽管盆地和边缘是普遍存在的构造，但从中等伸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裂引起的伸展。这种伸展差异可能源于脆性和韧性地壳层的差异伸展，但这并不能轻易解释共轭边缘的典型不对称结构-在横截面上，一个边缘显示逐渐变薄伴随着大断层，而共轭边缘则显示突然变薄但较小规模的断层。从裂谷早期开始活跃的全地壳滑脱，可以从理论上产生变薄和不对称性，但在力学上存在问题。此外，伸展差异发生在两个共轭边缘，导致一个明显的矛盾，即两者似乎都是滑脱断层的上盘。替代模型提出，由于地震成像的限制，包括亚地震分辨率断层、沿顶部基底 100 公里尺度滑脱的不可见变形或断层交叉阵列的结构复杂性，大量脆性伸展可能未被检测到。在这里，我们使用深度偏移地震图像准确测量断层的伸展，并将其与地壳变薄进行比较。这些观测结果用于创建一个裂谷的平衡运动学模型，通过产生受断层控制的地壳变薄，该模型从裂谷盆地进展到不对称结构，以及共轭裂谷边缘的极端变薄，从而解决了伸展差异问题。与当前的观点相反，这些观测结果支持这样一种观点，即变薄首先可以通过简单的安德森断层来解释，而这种断层在地震数据中是明确可见的。
