大洋-大陆俯冲系统中上覆板块热状态对板片倾角的影响
The effects of the overriding plate thermal state on the slab dip in an ocean-continent subduction system
摘要：
为了评估大洋-大陆俯冲系统中覆盖板块的热状态变化对板块倾角的影响，建立了一个二维有限元热-力学模型。岩石圈基底位于1600 K等温线的深度。进行了数值模拟，同时考虑到四种不同的初始厚度的海洋岩石圈（60，80，95和110公里）和五个不同的厚度覆盖板块，比较大陆-大洋板块的厚度比（100，120，140，160和200%的海洋岩石圈厚度）。数值模拟的结果表明，大洋岩石圈厚度在60 ~ 80 km范围内，俯冲板块的几何形状变化较大，而大洋板块厚度越大（95 ~ 110 km），俯冲板块的几何形状变化越小。此外，板片倾角强烈地依赖于上覆板块的热状态，并且，特别地，板片倾角随着上覆板块厚度的增加而减小。模型预测还证实，板块倾角和大洋岩石圈年龄之间不存在直接相关性，至少对于薄于110公里的俯冲板块来说是这样。这些结论得到了模式结果与世界大洋-大陆俯冲带的自然数据之间良好一致性的支持。
英文摘要：
To evaluate the effects of variations in the thermal state of the overriding plate on the slab dip in an ocean-continent subduction system, a 2-D finite element thermo-mechanical model was implemented. The lithosphere base was located at the depth of the 1600 K isotherm. Numerical simulations were performed while taking into account four different initial thicknesses for the oceanic lithosphere (60, 80, 95 and 110 km) and five different thicknesses of the overriding plate, as compared in terms of the continental-oceanic plate thickness ratio (100, 120, 140, 160 and 200% of the oceanic lithosphere thickness). The results of numerical modeling indicate that a high variability of the subducting plate geometry occurs for an oceanic lithosphere thickness ranging from 60 to 80 km, while the variability decreases where the oceanic plates are thicker (95 and 110 km). Furthermore, the slab dip strongly depends on the thermal state of the overriding plate, and, in particular, the slab dip decreases with the increase in the upper plate thickness. The model predictions also confirm that a direct correlation between the slab dip and the age of the oceanic lithosphere does not exist, at least for subduction plates thinner that 110 km. These conclusions are supported by the good agreement between the model results and the natural data referring to worldwide ocean-continent subduction zones.
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