Global Trends of Axial Relief and Faulting at Plate Spreading Centers Imply Discrete Magmatic Events
Global Trends of Axial Relief and Faulting at Plate Spreading Centers Imply Discrete Magmatic Events
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DOI：
10.1029/2020jb019465
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发表时间：
2020-08-01
影响因子：
3.9
通讯作者：
Buck, W. Roger
中科院分区：
文献类型：
--
作者：
Liu, Zhonglan;Buck, W. Roger
在扩展中心观测到的跨轴地形起伏和断层样式的变化一直难以解释。轴向高点见于快速扩散的中心，而山谷见于缓慢扩散的中心。断层偏移范围从快速扩张的山脊的几十米到一些缓慢扩张的山脊的几十公里。与轴向起伏拟合的模型不能产生观测到的断层形态，而与断层形态拟合的模型不能产生观测到的轴向起伏变化。最近的一项力学分析（Liu & Buck, 2018）表明，包括许多离散的堤坝事件的影响，可以导致轴向起伏随地壳厚度的逐渐变化。为了将这个力学模型与观测结果直接比较，我们需要将它与一个二维热模型结合起来。这使我们能够一致地估计轴向岩石圈厚度作为扩展速率和地壳厚度的函数。对于较薄的轴向岩石圈，该模型预测在轴向岩石圈下存在一个由低密度物质支撑的轴向高地。当岩石圈轴向厚度在地壳厚度的1 / 2到3 / 4之间时，轴向深度随着岩浆供给的增加而减小。对于较厚的轴向岩石圈，轴向山谷起伏受轴向脆性岩石圈厚度和近轴岩石圈几何形状的控制。我们将模型预测与数据进行了比较，这些数据是通过对测量了地震地壳厚度的所有扩展中心的轴向起伏和断层模式进行汇编观察得来的。在轴向岩石圈中岩脉宽度接近一米的模型参数与数据很好地拟合。
Observed variations in across-axis topographic relief and faulting style at spreading centers have been challenging to explain. Axial highs are seen at fast-spreading centers, while valleys occur for slow-spreading centers. Fault offsets range from tens of meters at fast-spreading ridges to tens of kilometers at some slow-spreading ridges. Models that fit the axial relief fail to produce observed fault patterns, while models that fit the fault patterns fail to produce observed variations in axial relief. A recent mechanical analysis (Liu & Buck, 2018, ) suggests that including the effect of many discrete diking events can result in a gradual change in axial relief with crustal thicknesses. To compare this mechanical model directly with observations requires us to couple it with a two-dimensional thermal model. This allows us to estimate the axial lithospheric thickness consistently as a function of the spreading rate and crustal thickness. For thinner axial lithosphere the model predicts an axial high with relief supported by low-density material beneath the axial lithosphere. For axial lithospheric thickness between approximately one half and approximately three fourths of the crustal thickness, the axial depth decreases with magma supply increase. For thicker axial lithosphere the axial valley relief is controlled by axial brittle lithospheric thickness and near-axis lithospheric geometry. We compared model predictions to data by compiling observations on axial relief and faulting mode for all spreading centers where seismic crustal thickness has been measured. Good fit to the data is obtained for model parameters giving dike widths in the axial lithosphere close to a meter.