Lithosphere Effective Elastic Thickness and Its Tectonic Implications in Taiwan Strait and Its Adjacent Regions
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摘要: 台湾海峡及邻区地处欧亚板块与菲律宾海板块相互作用的构造前锋部位,经历了挤压、剪切和伸展交替或并重的构造作用,这种复杂应力环境下岩石圈的均衡调整对台湾地区的构造演化具有深远影响.通过采用均衡响应函数法计算穿越台湾海峡及邻区剖面岩石圈的有效弹性厚度,利用剥离法消除台湾海峡及东邻岛区较厚沉积层的影响,得到了穿越台湾海峡地区剖面岩石圈弹性厚度的变化.结合反演的莫霍面和居里面深度对剖面有效弹性厚度的构造意义进行了综合分析.结果表明:台湾海峡及邻区岩石圈有效弹性厚度变化范围为22~8 km,剖面有效弹性厚度整体上自西往东呈楔形递减趋势,反映中国东部大陆岩石圈往东伸展减薄;台湾岛附近有效弹性厚度出现局部向东倾斜增大的趋势,可能与东侧菲律宾海板块的仰冲挤压有关.有效弹性厚度与居里面具有较高相关性,反映了有效弹性厚度受岩石圈热结构的影响.Abstract: Taiwan Strait and its adjacent regions are located in the tectonic interaction front of Eurasia plate and Philippine Sea plate, they have alternately or jointly undergone extrusion, shearing and stretching tectonic processes. The isostatic adjustment has a profound effect on the tectonic evolution of Taiwan region under the complex stress environment. In this paper, we calculated the lithosphere effective elastic thickness (Te) of Taiwan Strait and its adjacent regions by isostatic response function method, and eliminated the sediment effect by stripping method, then we attained the effective thickness changes along the profile across Taiwan Strait. The effective thickness changes and its tectonic significance were analyzed, combining inversion results of Moho depth and Curie depth. The results show that the lithosphere effective elastic thickness of Taiwan Strait and its adjacent regions range from 22 to 8 km. The continental lithosphere in eastern China shows thinning trend eastward by decreasing effective elastic thickness from west to east. The effective elastic thickness increasing eastward under Taiwan Island is likely to be associated with obduction extrusion of Philippine plate. A high correlation between effective elastic thickness and Curie depth reflects Te is controlled by lithosphere temperature structure.
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表 1 模型计算中用到的参数
Table 1. Parameters used by the flexural model
参数 定义 值/单位 D 挠曲刚度 N·m Te 有效弹性厚度 km ρw 海水密度 1 030 kg/m3 ρs 沉积层密度 2 000 kg/m3 ρc 地壳密度 2 670 kg/m3 ρm 地幔密度 3 270 kg/m3 g 重力加速度 9.8 m/s2 E 杨氏模量 8.0×1010 Pa μ 泊松比 0.25 -
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