Characterization of the present-day lithospheric thermal structure and main controlling factors in Songliao Basin
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摘要: 【目的】松辽盆地的热结构分析多局限在南北分区的沉积层尺度,缺乏岩石圈尺度的全盆地热结构刻画,制约了以地球动力学为背景的成因分析。【方法】综合利用已发表的地表热流、地温梯度以及热物性参数,补充了姚家组、青山口组和泉头组的热物性测试分析,并增加了多个地温场数据,全面刻画了整个松辽盆地的地温场特征,剖析了现今岩石圈尺度的热结构特征。【结果】结果表明,松辽盆地地温梯度范围是21.10-63.45℃/km,平均值是41.41℃/km,高于全球平均的地温梯度值30℃/km;地表热流值的分布范围是30.38-106.58mW/m2,平均值是71.85mW/m2,也高于全球平均的地表热流值60mW/m2,是一个典型的“热”盆。受太平洋板块俯冲作用、拆沉作用和热侵蚀作用的影响,热岩石圈明显减薄至现今的58.59km。由减薄地壳中放射性元素生热产生的热流仅为16.40 mW/m2,占地表热流的22.83%;而受滞留板片脱水作用的影响,部分熔融的地幔热物质上涌,地幔热流贡献高达55.45 mW/m2,占地表热流的77.17%。【结论】因此,受控于岩石圈减薄作用和地幔上涌作用,松辽盆地具有“热”盆属性和“热幔冷壳”的岩石圈热结构特征。Abstract: [Objective] Thermal structure analyses in the Songliao Basin are mostly confined to the sedimentary scale in the north-south zoning, and the lack of basin-wide thermal structure portrayal at the lithospheric scale constrains the genesis analysis in a geodynamic background. [Methods]Based on the published parameters of surface heat flow, geothermal gradient and thermophysical properties, this paper supplements the thermophysical properties of Yaojia Formation, Qingshankou Formation and Quantou Formation, and adds several geothermal field data to comprehensively characterize the geothermal field of the whole Songliao Basin, and analyze the characteristics of the present-day lithospheric thermal structure. [Results]The results show that the geothermal gradient in Songliao Basin ranges from 21.10 to 63.45℃/km, with an average value of 41.41℃/km, which is higher than the global average value of 30℃/km; the distribution of surface heat flow values ranges from 30.38 to 106.58mW/m2, with an average value of 71.85mW/m2, which is higher than the global average value of 60mW/m2 and belongs to a typical "hot" basin. Under the influence of the Pacific plate subduction, the delamination and thermal erosion made the thinned thickness of the thermal lithosphere of 58.59 km. The heat flow contribution by radioactive elements in the thinned crust is only 16.40 mW/m2, accounting for 22.83% of the surface heat flow; and under the influence of the dehydration of the stagnant plate, part of the molten mantle heat material is upwelled, the mantle heat flow contributes as high as 55.45 mW/m2, accounting for 77.17% of the surface heat flow. [Conclusion] Therefore, controlled by lithospheric thinning and mantle upwelling, the Songliao Basin has "hot" basin properties and "hot mantle and cold crust" lithospheric thermal structure characteristics.
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