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Upper-mantle tomography and dynamics beneath the North China Craton

机译:华北克拉通下方的上地幔层析成像和动力学

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A high-resolution tomographic model of the upper mantle beneath the North China Craton (NCC) is determined using a large number of precisely hand-picked teleseismic P wave arrival times. The results are generally consistent with previous results but high-quality arrivals provide new insights into the dynamics beneath the NCC. Obviously north-south trending low-velocity (low-V) zones are revealed down to ~300-400 km depth under the Shanxi rift and Tanlu fault zone, while a north-south trending high-velocity (high-V) zone representing the remainder of detached lithosphere is visible down to ~200 km depth under the western portion of eastern NCC. High-V anomalies representing the detached lithosphere are detected at 200-400 km depth under central and eastern NCC. Under the Ordos block high-V anomalies are visible above ~400 km depth, indicating intact lithosphere. Broad high-V anomalies representing the stagnant Pacific slab are imaged with a low-V anomaly from Datong volcano to the edge of Bohai Sea in the mantle transition zone beneath eastern and central NCC, suggesting that the Pacific slab has subducted to central NCC but with a gap. A continuously Y-shaped low-V structure is clearly imaged under Datong volcano and Bohai Sea from the lower mantle through this gap in the mantle transition zone to the upper mantle, indicating the existence of a lower mantle plume. These results suggest that in addition to the subduction of the Pacific plate, the plume has also played an important role in lithospheric destruction by thermal erosion of the asthenosphere and detachment of the lithosphere beneath the NCC.
机译:华北克拉通(NCC)下上地幔的高分辨率层析成像模型是使用大量精确挑选的远震P波到达时间确定的。结果通常与以前的结果一致,但是高质量的到达可以为NCC下的动态提供新的见解。在山西裂谷和Tan鹿断裂带下,南北向低速(低V)带明显露出到〜300-400 km深度,而南北向低速(高V)带则代表了低速带。在NCC东部的西部,深至〜200 km的深度都可以看到其余的分离的岩石圈。在NCC的中部和东部,在200-400 km深度处检测到代表分离岩石圈的High-V异常。在〜400 km深度以上可见到高V异常,表明岩石圈完整。代表停滞的太平洋板块的宽高V异常影像是从大同火山到NCC东部和中部以下的地幔过渡带中的渤海边缘的低V异常影像,这表明太平洋板块俯冲到了NCC中央,但是一个沟。在大同火山和渤海之下,从下地幔穿过地幔过渡带到上地幔的缝隙,清晰地成像出连续的Y形低V结构,表明存在下地幔羽。这些结果表明,除了太平洋板块俯冲作用之外,羽流在软流圈的热侵蚀和NCC下方的岩石圈的脱离中也对岩石圈的破坏起了重要作用。

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