Dynamic topography and vertical motion of the U.S. Rocky Mountain region prior to and during the Laramide orogeny
Dynamic topography and vertical motion of the U.S. Rocky Mountain region prior to and during the Laramide orogeny
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DOI：
10.1130/b31431.1
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发表时间：
2016-05
影响因子：
4.9
通讯作者：
P. Heller;Lijun Liu
中科院分区：
文献类型：
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作者：
P. Heller;Lijun Liu
地球表面的动力学地形是对柔性岩石圈下地幔流动引起的流体动力学应力的响应。在这里，我们比较预测的动态地形从逆对流模型，包括平板俯冲与已知的地质历史的美国西部从晚白垩世到古新世的时间来评估模型结果的有效性。在晚三叠世开始后，在不断发展的科迪勒拉火山弧后面发生了向下弯曲，最终在晚白垩世形成了西部内陆航道。弧后沉降是大多数动力地形模型的一致预测。一个更详细的对流模型在这里进行评估，将其与落基山脉中部地区100至50 Ma的地质历史进行比较。在拉腊米造山运动引起的局部变形开始之前，预测的构造沉降和观测到的构造沉降的匹配度良好。这很可能是由于造山运动的局部挠曲效应压倒了区域动力效应。连续时间间隔的地图显示，该模型通过时间和空间匹配的地质历史相当不错，特别是，俯冲以前假设的海洋高原共轭沙茨基上升，有一个显着的影响地表运动。(1)从95至88马，最显着的区域不整合面的位置相匹配的高地形带向东迁移。(2)从90至85 Ma，最大沉降带与共轭沙茨基隆起前缘的运动相吻合。(3)78 ~ 60 Ma，Laramide变形的起始位置与共轭沙茨基隆起的中心位置一致。(4)70 ~ 60 Ma，研究区南部的薄河流砾岩单元的时间-海侵沉积与共轭沙茨基隆起的尾部所引起的地表隆升基本一致。这些结果表明，逆模型近似的垂直运动历史相当不错。同步性的中心的位置通过共轭沙茨基隆起，向陆地的限制，不断发展的科迪勒拉火山弧，并启动Laramide变形表明，法拉隆板块成为耦合与上覆的北美板块俯冲的海洋高原通过下面。接骨板之间逐渐增强的机械耦合可能是Laramide缩短的动力。这种模型结果与地表地质历史的比较提供了一种手段来验证，但不是验证，动态地幔流模型的预测。
Dynamic topography of Earth’s surface occurs in response to hydrodynamic stresses due to mantle flow beneath a flexible lithosphere. Here, we compare the predicted dynamic topography from an inverse-convection model that includes flat slab subduction with the known geologic history of the western United States from Late Cretaceous through Paleocene time to evaluate the validity of the model results. Downwarping behind the evolving Cordilleran volcanic arc took place after its inception in Late Triassic time, culminating in the formation of the Western Interior Seaway in Late Cretaceous time. Subsidence behind arcs is a consistent prediction of most models of dynamic topography. A more-detailed convection model is evaluated here by comparing it to the geologic history of the central Rocky Mountain region from 100 to 50 Ma. The match of predicted and observed tectonic subsidence is good up until the time that local deformation by the Laramide orogeny begins. This is most likely due to local flexural effects of mountain building overwhelming regional dynamic effects. Maps for successive time intervals show that the model matches the geologic history quite well through time and space; in particular, the subduction of the previously postulated oceanic plateau—the conjugate Shatsky Rise—has a significant impact on surface movements. (1) From 95 to 88 Ma, the locations of most significant regional unconformities match the eastward migration of a zone of high topography. (2) From 90 to 85 Ma, the zone of maximum subsidence coincides with the motion of the leading edge of the conjugate Shatsky Rise. (3) From 78 to 60 Ma, the site of initiation of Laramide deformation migrates coincidently with the position of the center of the conjugate Shatsky Rise. (4) From 70 to 60 Ma, the time-transgressive deposition of thin fluvial conglomerate units in the southern part of the study area is generally coincident with surface uplift caused by the trailing part of the conjugate Shatsky Rise. These results suggest that the inverse model approximates the vertical motion history quite well. Synchroneity of the position of the center of the passing conjugate Shatsky Rise, the landward limit of the evolving Cordilleran volcanic arc, and the initiation of Laramide deformation suggests that the Farallon plate became coupled with the overlying North American plate as the subducted oceanic plateau passed beneath. Progressively enhanced mechanical coupling between the plates was likely the impetus for Laramide shortening. This comparison of model results with surface geologic history provides a means to validate, but not verify, predictions of dynamic mantle-flow models.