Koptev Alexander, Gerya Taras, Calais Eric, Leroy Sylvie, Burov Evgueni
Sorbonne Université, CNRS, Institut des Sciences de la Terre de Paris (ISTeP), Paris, France.
Department of Geosciences, University of Tübingen, Tübingen, Germany.
Sci Rep. 2018 Oct 3;8(1):14742. doi: 10.1038/s41598-018-33117-3.
Divergent ridge-ridge-ridge (R-R-R) triple junctions are one of the most remarkable, yet largely enigmatic, features of plate tectonics. The juncture of the Arabian, Nubian, and Somalian plates is a type-example of the early development stage of a triple junction where three active rifts meet at a 'triple point' in Central Afar. This structure may result from the impingement of the Afar plume into a non-uniformly stressed continental lithosphere, but this process has never been reproduced by self-consistent plume-lithosphere interaction experiments. Here we use 3D thermo-mechanical numerical models to examine the initiation of plume-induced rift systems under variable far-field stress conditions. Whereas simple linear rift structures are preferred under uni-directional extension, we find that more complex patterns form in response to bi-directional extension, combining one or several R-R-R triple junctions. These triple junctions optimize the geometry of continental break-up by minimizing the amount of dissipative mechanical work required to accommodate multi-directional extension. Our models suggest that Afar-like triple junctions are an end-member mode of plume-induced bi-directional rifting that combines asymmetrical northward pull and symmetrical EW extension at similar rates.
离散型脊-脊-脊（R-R-R）三联点是板块构造中最显著但又大多神秘莫测的特征之一。阿拉伯板块、努比亚板块和索马里板块的交界处是三联点早期发育阶段的一个典型例子，在阿法尔中部的一个“三联点”处，三条活动裂谷交汇。这种结构可能是由于阿法尔地幔柱撞击应力分布不均一的大陆岩石圈所致，但这一过程从未在自洽的地幔柱-岩石圈相互作用实验中得到重现。在此，我们使用三维热-力学数值模型，研究在可变远场应力条件下由地幔柱诱发的裂谷系统的形成。虽然在单向伸展作用下，简单的线性裂谷结构更为常见，但我们发现，在双向伸展作用下会形成更复杂的模式，其中包含一个或多个R-R-R三联点。这些三联点通过将适应多向伸展所需的耗散机械功降至最低，优化了大陆裂解的几何形态。我们的模型表明，类似阿法尔地区的三联点是地幔柱诱发双向裂谷作用的一种端元模式，它以相似的速率结合了向北的不对称拉伸和东西向的对称伸展。
