Thermo-kinematic modeling of detachment-dominated extension, northeastern Death Valley area, USA: Implications for mid-crustal thermal-rheological evolution
Thermo-kinematic modeling of detachment-dominated extension, northeastern Death Valley area, USA: Implications for mid-crustal thermal-rheological evolution
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DOI：
10.1016/j.tecto.2021.228755
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发表时间：
2021-02
期刊：
影响因子：
2.9
通讯作者：
B. Lutz;R. Ketcham;G. Axen;M. Beyene;M. Wells;J. Wijk;D. Stockli;J. Ross
中科院分区：
文献类型：
--
作者：
B. Lutz;R. Ketcham;G. Axen;M. Beyene;M. Wells;J. Wijk;D. Stockli;J. Ross
大陆拆离断层的深部结构仍有争议。热-力学模型产生的断层要么横切岩石圈，要么成为分布在中下地壳的剪切带，这取决于规定的热流变条件。然而，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。我们提出了一个160公里长的横截面通过两个拆离断层在美国西南部的逐步，平衡重建。重建形成的基础上，迭代改进的二维正向热运动学数值模拟的剥离断层滑动，下盘折返，热平流，下盘锆石（U-Th）/He冷却年龄。热运动学模型的解决方案进行了反复校准，对表面热流，前和后的伸展地热，推断莫霍面温度，和热年代学数据从一个拆离下盘。最佳拟合模型分别预测了地壳和大陆架在伸展过程中的热演化和几何演化。拆离作用最初植根于中地壳剪切带（~7.5-12 km深），可能离域于中地壳深部（>12-15 km）。拆离初始阶段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。我们的重建表明，上地壳和下地壳-地幔岩石圈解耦的一个弱，中地壳层早期拆离断层。薄弱层变薄，冷却，部分脆化，并因此加强了持续的剥离滑动。这增加了岩石圈的力学耦合，并导致上地壳伸展的轨迹转移。在我们的研究区，一个薄弱的中地壳层的减薄，被认为是在裂谷过程中耦合的超伸展和地幔折返之前，大约在7-6 Ma完成。
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.