Geochemical features and seismic imaging of the tectonic zone between the Tibetan Plateau and Ordos Block, central northern China
Geochemical features and seismic imaging of the tectonic zone between the Tibetan Plateau and Ordos Block, central northern China
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DOI：
10.1016/j.chemgeo.2023.121386
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发表时间：
2023-02
期刊：
影响因子：
3.9
通讯作者：
Ying Li;Zhi Chen;Anhui Sun;Zhaofei Liu;A. Caracausi;G. Martinelli;Chang Lu
中科院分区：
文献类型：
--
作者：
Ying Li;Zhi Chen;Anhui Sun;Zhaofei Liu;A. Caracausi;G. Martinelli;Chang Lu
青藏高原在垂直隆升和水平拉张的双重作用下不断生长。青藏高原与其周边板块和块体的相互作用一直是一个争论不休的问题。青藏高原东北缘与稳定的鄂尔多斯地块之间的构造带，由于强烈的构造活动而产生了灾难性的地震，引起了人们的极大兴趣。本研究调查了天然气地球化学异常的空间分布（例如，高通量CO2），并结合该构造带对应的地震层析成像，确定鄂尔多斯块体与青藏高原的汇聚边界域，追踪两个主要地质单元之间的地壳层间流体输送构造间断。青藏高原东北缘与鄂尔多斯地块构造带地球化学、地球物理特征的空间分布自西北向东南有明显差异。东北区（A区）以逆冲走滑断裂为主，其下有明显的速度边界，中下地壳低的裂隙密度（ε）、饱和度（ε）和泊松比（σ）与低的热流值和CO2排放值相吻合，构造挤压和区域性断层闭锁可能是诱因。东南区（C区）以伸展构造为主，P波方位各向异性的快速度方向（FVD）大致为E-W向，高渗透率和高孔隙度可从地壳高ε、ε和相对高的σ异常推断，导致地表热流、CO2浓度和通量高，主要为壳源气。中间区（B带）也是以逆冲和走滑断层为主的异常带，强烈的闭锁断层清晰地显露出来，而中地壳的优势各向异性FVD变化明显，浅层气组分的贡献更大，上地壳的CO2通量、热流和区域ε、ε、σ比A带高。表明B区下方存在区域性破碎破碎。多学科综合研究表明，B带是青藏高原与鄂尔多斯地块的汇聚边界。
The Tibetan Plateau is growing by both vertical uplift and horizontal extension. It is a continuing debate how the Tibetan Plateau interacts with its surrounding plates and blocks. Due to intense tectonic activity, which produced catastrophic earthquakes, the tectonic zone between the northeast margin of the horizontal extending Tibetan Plateau and the stable Ordos Block has garnered considerable interest. This study investigated the spatial distribution of gas geochemical anomalies (e.g., high flux of CO2in correspondence of the main faults) at regional scale together with the seismic tomography in correspondence of this tectonic zone with the aim to figure out the domain of convergent boundary between the Ordos block and Tibetan plateau, and trace the tectonic discontinuities which are able to transfer fluids through the crustal layers between the two main geological units. From northwest to southeast, obvious difference of spatial distributions of geochemical and geophysical features in the tectonic zone between the northeast margin of the Tibetan Plateau and the Ordos Block is inferred. The northeast area (Zone A) is dominated by thrust and strike-slip faults with clear velocity boundary underneath, where low crack density (ε), saturation rate (ξ) and Poisson’ ratio (σ) in the middle-lower crust coincided with the low values of heat flow and CO2emissions, tectonic compression and regional locked-fault can be inducements. The southeast area (Zone C) is dominated by extensional tectonics with roughlyE-W fast-velocity direction (FVD) of P-wave azimuthal anisotropy, where high permeability and porosity can be deduced from crustal highε,ξand relatively highσanomalies, resulting in high heat flow, CO2concentrations and fluxes at the surface, and predominantly crustal-derived gases. The intermediate area (Zone B) also dominated by thrust and strike-slip faults is an extraordinary zone, where intensely locked-fault were clearly revealed, while the predominant anisotropic FVDs in the middle crust changed obviously, more contribution of shallow gas component was detected, and CO2flux, heat flow, and regional ε, ξ, and σ in the upper crust were higher, compared with those in Zone A, which indicated the regional crushing fragmentation underneath Zone B. The adopted multidisciplinary approach demonstrated that Zone B is the convergent boundary between the Tibetan Plateau and the Ordos Block.