Sensitivity analysis of rift induced delamination with application to Rwenzori Mountains
Sensitivity analysis of rift induced delamination with application to Rwenzori Mountains
复制标题
裂谷诱发分层的敏感性分析及其在鲁文佐里山脉的应用
DOI：
10.1111/j.1365-246x.2011.05237.x
复制
发表时间：
2011
影响因子：
2.8
通讯作者：
H. Schmeling
中科院分区：
文献类型：
--
作者：
H. Wallner;H. Schmeling
裂谷诱导脱层（RID）被认为是一种地球动力学过程，解释了位于大陆裂谷系鲁文佐里山脉的一个高度极高的古老地壳块体的特殊情况。RID的概念是一个上涌的软流圈包围着坚硬的岩石圈。如果最下面的下地壳的温度和应力依赖的粘度降低和强度失败，冷而致密的地幔岩石圈根的拆离被破坏。地表表现为围绕着一个隆起的密度较低的地壳块体的裂缝尖端的传播。本研究旨在检验RID假说的适用范围。数值模型的特征保持不变，而控制初始温度异常、流变学性质和背景地热的参数系统地变化。系统的答案是一个分叉，要么异常冷却或中央地幔岩石圈分离和下沉，或者，更确切地说，一个不成功的和成功的RID。规定的初始异常的过高温度是最敏感的，并且在从冷却到分层的过渡处作为临界温度。分层只在一定范围内起作用。异常全宽在20 ~ 50 km之间，对称异常的偏移距在64 ~ 180 km之间，顶部异常必须到达下地壳。Rwenzori区域的相应几何特征总是位于所发现的脱层制度的参数范围内，甚至接近最佳。有关流变学的定量参数是不确定的，但定性，符合现有的调查结果。因此，我们建立RID作为一个可能的机制大致符合当地的观测，如，一个老的地壳地垒内的一个年轻的裂谷系统，一个失踪的山根，高地震活动，低地震速度在下地壳，轻微的火山活动和极端的地形。如果RID对于Rwenzoris的非常特殊的情况是有效的，并且到目前为止是唯一的例子，那么应该推广它，并且所探索的参数制度可以用作搜索类似地质情况的模式。
SUMMARY Rift induced delamination (RID) was favoured as a geodynamic process explaining the special situation of an extremely elevated old crustal block located in a continental rift system, the Rwenzori Mountains. The concept of RID is an upwelling asthenosphere encircling stiff lithosphere. If temperature- and stress-dependent viscosity of the undermost lower crust is reduced and strength fails, the detachment of cold and dense mantle-lithosphere root is trigged. Surface expressions are propagating rift tips surrounding an uplifting less dense crustal block. This study was performed to test the scope of application of RID hypothesis. Characteristic features of the numerical models are kept constant, whereas parameters controlling the initial temperature anomaly, rheological properties and the background geotherm are varied systematically. The system answer is a bifurcation, either the anomaly cools down or the central mantle lithosphere detaches and sinks down, or, rather an unsuccessful and successful RID. The excess temperature of the prescribed initial anomaly is most sensitive and serves at the transition from cooling to delamination as a critical temperature. Delamination works only in certain ranges. The anomaly full width ranges between 20 and 50km, the offset of the symmetric anomalies lies between 64 and 180km and the top anomaly has to reach into the lower crust. The corresponding geometric characteristics of the Rwenzori region always lies inside the found parameter ranges for the delamination regime, even near the optimum. Quantitative parameters concerning rheology are uncertain but, qualitatively, conform to the available findings. Thus, we establish RID as a possible mechanism coinciding roughly with the local observations, such as, an old crustal horst inside a young rift system, a missing mountain root, the high seismicity, low seismic velocities in the lower crust, minor volcanism and extreme topography. If RID is valid for the very special situation of the Rwenzoris and by now the sole example, one ought to generalize it and the parameter regimes explored can be used as a pattern for searching similar geological situations.