Load-induced subsidence of the Ancestral Rocky Mountains recorded by preservation of Permian landscapes
Load-induced subsidence of the Ancestral Rocky Mountains recorded by preservation of Permian landscapes
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通过保存二叠纪景观记录了祖先落基山脉的荷载引起的沉降
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发表时间：
2012
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影响因子：
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通讯作者：
D. Sweet
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作者：
G. Soreghan;G. R. Keller;M. C. Gilbert;C. G. Chase;D. Sweet
古老的落基山脉（ARM）形成了一个系统的高地和邻近的盆地，在宾夕法尼亚-最早的二叠纪变形的北美西部内陆发展。这种克拉通内变形的原因仍然存在争议，尽管许多人将其与北美南部的石炭纪-二叠纪沃希塔-马拉松造山带相关的远场压缩联系起来。ARM隆起的最终消失长期以来一直被归因于侵蚀斜面，据推测，这种侵蚀斜面一直存在于三叠纪-侏罗纪。然而，新的观测结果表明，最大的ARM隆起突然而不寻常地终止了。来自俄克拉荷马州和科罗拉多中部ARM的古高地的现场证据表明，早二叠世地层上覆宾夕法尼亚时代的断层，并在古高地顶部掩埋了多达1000米的地形。在俄克拉荷马州和科罗拉多的部分地区，新生代晚期对这些古高地的部分剥露揭示了二叠纪时期的景观。这些关系表明，停止隆起，然后由一个广泛的区域，包括盆地和隆起的地壳块体，并开始在早二叠世的时间，直接以下的宾夕法尼亚构造远地点的ARM。独立于这些地质观测，地球物理数据揭示了区域规模的基性岩负载支撑这些古高地，在寒武纪裂谷与南俄克拉荷马州裂陷槽侵位。地球物理模型的影响，这样的负载在存在的水平应力场，如ARM造山作用所暗示的，表明弯曲支持功能的振幅调制非线性。这导致了在施加足够的压应力时形成屈曲和逆冲断层，以及在高压应力松弛时由屈曲形成的地形下沉。因此，我们推断，核心ARM高地下沉，由于存在高密度的上地壳根，这种沉降开始于早二叠世，由于松弛的平面内的压缩应力，伴随着最后阶段的瓦希塔马拉松orthopathy的南部和西南劳伦。我们的研究结果突出了构造继承在板内造山和造陆作用中的重要性，包括其在加速区域海拔降低和最终保护古地貌方面的潜在作用。
The Ancestral Rocky Mountains (ARM) formed a system of highlands and adjacent basins that developed during Pennsylvanian–earliest Permian deformation of interior western North America. The cause of this intracratonic deformation remains debated, although many have linked it to far-field compression associated with the Carboniferous–Permian Ouachita-Marathon orogeny of southern North America. The ultimate disappearance of the ARM uplifts has long been attributed to erosional beveling presumed to have prevailed into the Triassic–Jurassic. New observations, however, indicate an abrupt and unusual termination for the largest of the ARM uplifts. Field evidence from paleohighlands in the central ARM of Oklahoma and Colorado indicates that Lower Permian strata onlap Pennsylvanian-aged faults and bury as much as 1000 m of relief atop the paleohighlands. In parts of Oklahoma and Colorado, late Cenozoic partial exhumation of these paleohighlands has revealed landscapes dating from Permian time. These relationships suggest cessation of uplift followed by active subsidence of a broad region that encompassed both basins and uplifted crustal blocks and that commenced in Early Permian time, directly following the Pennsylvanian tectonic apogee of the ARM. Independent from these geological observations, geophysical data reveal a regional-scale mafic load underpinning these paleohighlands, emplaced during Cambrian rifting associated with the southern Oklahoma aulacogen. Geophysical modeling of the effects of such a load in the presence of a horizontal stress field, such as that implied by ARM orogenesis, indicates that the amplitude of flexurally supported features is modulated nonlinearly. This leads to buckling and thrust formation with the application of sufficient compressive stress, and subsidence of topography formed by buckling upon relaxation of the high compressional stresses. We therefore infer that the core ARM highlands subsided owing to the presence of a high-density upper crustal root, and that this subsidence began in the Early Permian owing to relaxation of the in-plane compressional stresses that had accompanied the last phase of the Ouachita-Marathon orogeny of southern and southwestern Laurentia. Our results highlight the importance of tectonic inheritance in intraplate orogenesis and epeirogenesis, including its potential role in hastening the reduction of regional elevation, and enabling the ultimate preservation of paleolandscapes.