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我们根据岩石层的热状态来定义现代裂谷和古裂谷,现代裂谷是断裂后的岩石层尚未达到热平衡状态,而古裂谷是断裂后的岩石层已处于热稳定状态。将现代裂谷与古裂谷的物理特征进行对比,结果表明,它们的地貌、构造和岩浆特征方面虽有很多相同之处,但在地球物理特征方面却有一些明显的差异。在由现代裂谷转变为古裂谷时采用一个简单的岩石层热释放模型,我们可以看到,现代裂谷与古裂谷之间在岩石层的上地幔地震波速度和密度、表面热流、热结构与居里点深度、以及大地电磁性质方面的差异可以用宕石层冷却来解释。而单用冷却不能解释与断裂有关以及紧接断裂之后的复杂沉陷过程,也不能解释古裂谷内为什麽出现一些高速的壳层,以及地壳有时为什麽会加厚。假如考虑到岩石层的抗弯强度和与断裂有关的地壳的岩浆加厚,这些现象就可以得到解释。我们认为,许多现代裂谷下面的“上地幔异常”可能与断裂地壳岩浆加厚过程有关。
We define the modern rift and the ancient rift according to the thermal state of the rock layer. The modern rift is that the fractured rock layer has not reached the thermal equilibrium yet, and the ancient rift is that the fractured rock layer is in a state of thermal stability. Comparing the physical features of the modern rift with that of the ancient rift, the results show that although there are many similarities in their topography, tectonics and magma characteristics, there are some obvious differences in geophysical characteristics. Using a simple lithospheric heat release model from a modern rift to an ancient rift, we can see that the upper mantle seismic velocity and density, surface heat flux, and heat in the lithosphere between modern and ancient rifts The difference in structure and Curie point depth, and in the earth’s electromagnetic properties, can be explained by the stratospheric cooling. Single-use cooling, however, fails to account for the complex subsidence associated with faults and immediately following the fault, nor does it explain why some high-velocity shells appear in the Paleo-rift and why the crust sometimes thickens. These phenomena can be explained by considering the flexural strength of the lithosphere and the thickening of the magma in the crust associated with the fault. We believe that the “upper mantle anomalies” beneath many modern rifts may be related to the magmatic thickening of the faulted crust.