Seismic Tomography of the Trans-North China Orogen and Its Dynamic Implications
Seismic Tomography of the Trans-North China Orogen and Its Dynamic Implications
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DOI：
10.3389/feart.2022.948040
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
Xiaoming Xu;Z. Ding;Huili Guo;Xinfu Li
中科院分区：
文献类型：
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作者：
Xiaoming Xu;Z. Ding;Huili Guo;Xinfu Li
利用中国密集阵列地震台网记录的地壳运动波形的S波走时残差，建立了华北造山带及其邻区的高分辨率S波速度模型。我们的模型揭示了研究区下方的S波速度异常，表明上地幔结构的强烈横向非均匀性。大同火山上地幔存在明显的低速异常。大同火山区除了地幔过渡带的低速带外，还有两个低速层，分别向西北方向延伸至河套地堑和向西南方向延伸至南天山，深度分别为100-300 km。根据这些低速异常，我们对大同火山的成因提供了新的认识，认为大同火山的成因可能与富水地幔过渡带的软流圈上涌和青藏高原东北向挤压驱动的水平地幔流有关。鄂尔多斯块体和TNCO下300 km深度以上的上地幔存在明显的速度对比，表明在TNCO岩石圈发生改造的同时，鄂尔多斯块体仍保存着较厚的地幔根。我们认为，软流层的上涌和青藏高原向东北方向的推挤作用是造成青藏高原及邻区岩石圈变形的主要原因。
We present a high-resolution S wave velocity model of the Trans-North China Orogen (TNCO) and its adjacent areas derived from S wave traveltime residuals of teleseismic waveforms recorded by the dense ChinArray seismic network. Our model reveals S wave velocity anomalies beneath the study area, suggesting the strong lateral heterogeneities of the upper mantle structures. The upper mantle of the Datong volcano is dominated by the significant low velocity anomalies. In addition to the low-velocity zone rooted in the mantle transition zone beneath the Datong volcano region, two low velocity layers extend northwestward to the Hetao graben and southwestward to the southern TNCO within depths of 100–300 km, respectively. Based on these low-velocity anomalies, we provide new insights into the origin of the Datong volcano, which may be related to the asthenospheric upwelling originated from the water-rich mantle transition zone and horizontal mantle flows driven by the extrusion northeastward of the Tibetan plateau. A clear velocity contrast in the upper mantle above 300 km depth beneath the Ordos block and the TNCO implies that the Ordos block still preserves thick cratonic root while the lithosphere of the TNCO is modified. We propose that the asthenospheric upwelling and northeastward push of the Tibetan plateau account for the lithospheric deformation of the TNCO and its adjacent areas.