The deep structure of continental detachment faults remains debated. Thermo-mechanical models generate detachments that either transect the lithosphere or become distributed shear zones in the mid-lower crust, depending on prescribed thermo-rheological conditions. However, these geometries and prescribed conditions remain little constrained by geology-based reconstructions. We present stepwise, balanced reconstructions of a 160 km-long cross-section through two detachment faults in the southwest USA. Reconstructions form the basis of iteratively improved 2D forward thermo-kinematic numerical simulations of detachment fault slip, footwall exhumation, heat advection, and footwall zircon (U-Th)/He cooling ages. Thermo-kinematic model solutions are calibrated iteratively against surface heat flow, pre- and post-extensional geotherms, inferred Moho temperatures, and thermochronometric data from one detachment footwall. Best-fit models predict the thermal and geometric evolution of the crust and detachments, respectively, during extension. The detachment initially rooted into a mid-crustal shear zone (~7.5–12 km depth) and was probably delocalized in the deep middle crust (>12–15 km). The maximum principal stress was likely non-vertical in the middle crust at detachment initiation, possibly due to mantle upwelling. Our reconstructions suggest that the upper crust and lower crust-mantle lithosphere were decoupled by a weak, mid-crustal layer during early detachment faulting. The weak layer was thinned, cooled, partially embrittled, and therefore strengthened by continued detachment slip. This increased lithospheric mechanical coupling and caused the locus of upper-crustal extension to shift. Thinning of a weak mid-crustal layer, as is thought to precede coupled hyperextension and mantle exhumation during rifting, was mostly complete in our study area by ~7–6 Ma.

大陆脱离断层的深层结构仍存在争议。根据规定的热流变条件，热力学模型会产生横穿岩石圈或成为中下地壳分布的剪切带的分离现象。但是，这些几何形状和规定的条件仍然很少受到基于地质的重建的约束。我们通过美国西南部的两个脱离断层，逐步，平衡地重建了一条160公里长的断面。重建构成了迭代改进的二维正向热运动数值模拟的基础，该二维模拟是分离断层滑动，下盘挖掘，热对流和下盘锆石（U-Th）/ He冷却年龄的模拟。热运动模型解决方案针对地表热流，延伸前和延伸后的地热进行了迭代校准，推算出莫霍面温度，并从一个拆卸下垫板测得的热力计时数据。最佳拟合模型分别预测延伸过程中地壳和分离的热演化和几何演化。分离最初扎根于中地壳剪切带（约7.5–12 km的深度），并且可能在深部中地壳（> 12–15 km）中散布了。在剥离开始时，中地壳的最大主应力可能是非垂直的，这可能是由于地幔上涌所致。我们的重建结果表明，在早期脱离断层期间，上地壳和下地壳-幔幔岩石圈被弱的中地壳层解耦。薄弱的层变薄，冷却，部分变脆，因此通过持续的剥离滑移而得到加强。这增加了岩石圈的机械耦合，并导致上地壳伸展的轨迹发生偏移。在我们的研究区域中，薄弱的中壳薄层的变薄（通常被认为是在裂谷过程中伴随着过度的扩张和地幔发掘而来）在我们的研究区域中大约在7-6 Ma时就完成了。