Abstract. Transform margins represent ~30 % of the non-convergent margins worldwide. Their formation and evolution have long been addressed through kinematic models that do not account for the mechanical behaviour of the lithosphere. In this study, we use high resolution 3D numerical thermo-mechanical modelling to simulate and investigate the evolution of the intra-continental strain localization under oblique extension. The obliquity is set through velocity boundary conditions that range from 15° (high obliquity) to 75° (low obliquity) every 15° for strong and weak lower continental crust rheologies. Numerical models show that the formation of localized strike-slip shear zones leading to transform continental margins always follows a thinning phase during which the lithosphere is thermally and mechanically weakened. For low (75°) to intermediate (45°) obliquity cases, the strike-slip faults are not parallel to the extension direction but form an angle of 20° to 40° with the plates' motion while for higher obliquities (30° to 15°) the strike-slip faults develop parallel to the extension direction. Numerical models also show that during the thinning of the lithosphere, the stress and strain re-orient while boundary conditions are kept constant. This evolution, due to the weakening of the lithosphere, leads to a strain localization process in three major phases: (1) strain initiates in a rigid plate where structures are sub-perpendicular to the extension direction; (2) distributed deformation with local stress field variations and formation of transtensional and strike-slip structures; (3) formation of highly localized plates boundaries stopping the intra-continental deformation. Our results call for a thorough re-evaluation of the kinematic approach to studying transform margins.

中文翻译：

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超越运动学：3D热力学建模揭示了变换余量的动态

摘要。转换利润率占全球非会聚利润率的30％。长期以来，通过运动学模型已经解决了它们的形成和演化问题，而运动学模型并未考虑岩石圈的力学行为。在这项研究中，我们使用高分辨率的3D数值热机械模型来模拟和研究斜向延伸下大陆内应变局部化的演化。倾角通过速度边界条件设定，速度边界条件范围从15°（高倾角）到75°（低倾角），每15°分别对应于强和弱的下部大陆壳流变。数值模型表明，导致过渡大陆边缘的局部走滑剪切带的形成总是遵循变薄阶段，在此阶段岩石圈被热力和机械力削弱了。对于低（75°）到中间（45°）的倾斜情况，走滑断层不平行于延伸方向，而是与板块的运动形成20°至40°的角度，而对于较高的倾斜度（30°至15°），走滑断层平行于延伸方向发展。数值模型还表明，在岩石圈变薄的过程中，应力和应变重新定向，而边界条件保持恒定。由于岩石圈的减弱，这种演化导致了三个主要阶段的应变局部化过程：（1）应变在结构垂直于延伸方向的刚性板中产生；（2）具有局部应力场变化的分布变形，以及张拉和走滑结构的形成；（3）高度局部化的板块边界的形成阻止了大陆内部的变形。我们的结果要求对运动学方法的彻底重新评估，以研究变换余量。