High‐resolution body wave tomography models of the upper mantle beneath eastern China and the adjacent areas
High‐resolution body wave tomography models of the upper mantle beneath eastern China and the adjacent areas
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DOI：
10.1029/2012gc004119
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发表时间：
2012-06
期刊：
影响因子：
3.7
通讯作者：
Liang Zhao-;R. Allen;T. Zheng;R. Zhu
中科院分区：
文献类型：
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作者：
Liang Zhao-;R. Allen;T. Zheng;R. Zhu
我们提出了新的三维层析成像模型的VP，VS和VP/VS比异常下EC和邻近地区的上地幔。这些数据的收集和解释的目的是澄清地球动力学过程，导致整个中国东部（EC）在中生代至新生代的时间在空间上可变的事件历史。断层图像是通过反演中国国家地震台网升级后的1300个台站和9个临时台阵记录的体波走时构建的。不同深度的分辨率测试和特征速度异常验证了层析成像图像捕捉到了700 km深度的上地幔速度非均匀性。VP、VS和VP/VS比值异常的显著特征可以清楚地识别。这些措施包括强烈的多尺度的异质性占据下EC和异常的空间尺度差异下发现的EC北方和南部地区的上地幔。这些特征表明，在EC的地球动力学演化的空间变异程度。我们提出了两种机制来解释这些模式。首先，俯冲板块的西部前缘可能在进一步向东撞击到EC的地区产生了更大的水平挤压应力。这些地区将经历更强的对流和上地幔应力状态的改变，从而在华南地块（SCB）下方相对于华北地块（NCC）东部产生显著的热异常。第二，不同的热状态和粘度的东部NCC和华夏地块（CaB）导致不同的响应区域变形。NCC东部的太古代腹地特别具有较冷的热状态和较高的粘度，因此由于剪切局部化的影响，仅表现出小尺度的非均质性。新元古代CaB具有相对温暖的热状态，粘度较低，因此变形更连续。
We present new 3‐D tomographic models of VP, VS and VP/VSratio anomalies in the upper mantle beneath EC and adjacent areas. This data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout Eastern China (EC) during Mesozoic to Cenozoic time. The tomographic images were constructed by inverting body wave travel‐times recorded at ∼1300 stations within the upgraded China National Seismic Network, and 9 temporary arrays. Resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km. The salient features of VP, VS and VP/VSratio anomalies can be clearly identified. These include strong multiscale heterogeneities occupying the upper mantle beneath EC and differences in the spatial scale of anomalies found beneath northern and southern areas of EC. These features demonstrate a degree of spatial variability in the geodynamic evolution of EC. We propose two mechanisms to explain these patterns. First, the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into EC. These areas would experience stronger convection and an altered stress regime in the upper mantle, creating significant thermal anomalies beneath the South China Block (SCB) relative to the eastern North China Craton (NCC). Second, differing thermal states and viscosities for the eastern NCC and the Cathaysia Block (CaB) resulted in differing responses to regional deformation. The Archean hinterland of the eastern NCC specifically has a colder thermal state and higher viscosity, and therefore exhibits only small‐scale heterogeneities due to the effect of shear localization. The Neoproterozoic CaB has a relatively warm thermal state with lower viscosity, and thus deformed more continuously.