Earth Science Department, Rice University, Houston, Texas 77005-1892, USA.
Nature. 2011 Apr 28;472(7344):461-5. doi: 10.1038/nature10001.
The Colorado plateau is a large, tectonically intact, physiographic province in the southwestern North American Cordillera that stands at ∼1,800-2,000 m elevation and has long been thought to be in isostatic equilibrium. The origin of these high elevations is unclear because unlike the surrounding provinces, which have undergone significant Cretaceous-Palaeogene compressional deformation followed by Neogene extensional deformation, the Colorado plateau is largely internally undeformed. Here we combine new seismic tomography and receiver function images to resolve a vertical high-seismic-velocity anomaly beneath the west-central plateau that extends more than 200 km in depth. The upper surface of this anomaly is seismically defined by a dipping interface extending from the lower crust to depths of 70-90 km. The base of the continental crust above the anomaly has a similar shape, with an elevated Moho. We interpret these seismic structures as a continuing regional, delamination-style foundering of lower crust and continental lithosphere. This implies that Pliocene (2.6-5.3 Myr ago) uplift of the plateau and the magmatism on its margins are intimately tied to continuing deep lithospheric processes. Petrologic and geochemical observations indicate that late Cretaceous-Palaeogene (∼90-40 Myr ago) low-angle subduction hydrated and probably weakened much of the Proterozoic tectospheric mantle beneath the Colorado plateau. We suggest that mid-Cenozoic (∼35-25 Myr ago) to Recent magmatic infiltration subsequently imparted negative compositional buoyancy to the base and sides of the Colorado plateau upper mantle, triggering downwelling. The patterns of magmatic activity suggest that previous such events have progressively removed the Colorado plateau lithosphere inward from its margins, and have driven uplift. Using Grand Canyon incision rates and Pliocene basaltic volcanism patterns, we suggest that this particular event has been active over the past ∼6 Myr.
科罗拉多高原是美国西南部科迪勒拉山系中一个大型的、构造完整的、地形学上的省份，海拔约为 1800-2000 米，长期以来一直被认为处于均衡状态。这些高海拔的起源尚不清楚，因为与周围经历了大规模白垩纪-古近纪挤压变形和新近纪伸展变形的省份不同，科罗拉多高原基本上没有内部变形。在这里，我们结合新的地震层析成像和接收函数图像，解决了高原中西部一个延伸超过 200 公里的深垂直高地震速度异常问题。该异常的上表面由一个从下地壳延伸到 70-90 公里深处的倾斜界面在地震上定义。异常上方的大陆地壳底部也有类似的形状，莫霍面升高。我们将这些地震结构解释为下地壳和大陆岩石圈持续的区域性拆沉式沉降。这意味着上新世（260-530 万年前）高原的抬升和边缘的岩浆作用与持续的深部岩石圈过程密切相关。岩石学和地球化学观测表明，晚白垩纪-古近纪（约 90-40 百万年前）的低角度俯冲使科罗拉多高原下的大部分元古代构造地幔水合，并可能使其弱化。我们认为，中生代中期（约 35-25 百万年前）到现代的岩浆渗透随后赋予了科罗拉多高原上地幔底部和侧部负的成分浮力，引发了下地壳的下降。岩浆活动的模式表明，以前的类似事件已经从其边缘向内逐渐移除了科罗拉多高原的岩石圈，并导致了抬升。根据大峡谷的侵蚀速率和上新世玄武岩火山活动模式，我们认为这一特定事件在过去的 600 万年里一直很活跃。
