基于自然伽马测井的莺歌海盆地中央凹陷地层生热率及岩石圈热结构研究

Natural gamma-ray log-derived heat production rates of strata and lithospheric thermal structure in the central depression,Yinggehai Basin

【目的】岩石圈热结构对探索盆地热演化的动力学过程、地热资源评价和开发利用具有重要意义。由于莺歌海盆地生热率数据的匮乏,限制了岩石圈热结构的研究。【方法】利用莺歌海盆地23口钻井的自然伽马测井数据,通过GR(自然伽马值)-A(岩石放射性生热率)经验公式,计算莺歌海盆地中央凹陷的地层生热率;依托OBS地壳速度结构模型建立地层生热率参数柱,计算壳幔热流及其比值、莫霍面温度和热岩石圈厚度,获取岩石圈热结构。【结果和结论】结果表明:莺歌海盆地中央凹陷地壳热流为19.2~27.1 mW/m^(2),平均值为(23.5±2.8) mW/m^(2),地幔热流为49.2~57.2 mW/m^(2),平均值为(52.8±2.8) mW/m^(2);莫霍面温度为613~707℃,平均温度为(671±31)℃;热岩石圈厚度为61.23~64.89 km,平均厚度为(63.58±1.35) km;壳幔热流配比为0.45±0.08,岩石圈热结构表现出“冷壳热幔”的特征,反映出莺歌海盆地中央凹陷的热状态受深部热源的影响。研究成果不仅为该地区地热资源的进一步勘探和开发提供了科学依据,还为盆地的地球动力学研究提供重要参考。

[Objective]Understanding the lithospheric thermal structure is significant for exploring the dynamics of a basin's thermal evolution,as well as for the assessment,exploitation,and utilization of geothermal resources in a basin.However,the limited data on heat production in the Yinggehai Basin has constrained research into the lithospheric thermal structure of the basin.[Methods]Using natural gamma-ray(NGR)logs from 23 wells in the Yinggehai Basin,this study calculated the heat production rates of strata in the central depression using the fitted gamma-ray value(GR)-radiogenic heat production rate(A)empirical formula.Based on the ocean bottom seismometer(OBS)-derived crustal velocity structure model,this study established a parameter column of the heat production rates of strata.Accordingly,this study calculated the crustal and mantle heat flow,the crustal-mantle heat flow ratio,Moho temperature,and thermal lithospheric thickness,thereby determining the lithospheric thermal structure.[Results and Conclusions]The results indicate that the central depression of the Yinggehai Basin exhibits crustal heat flow ranging from 19.2 to 27.1 mW/m^(2),with an average of (23.5±2.8) mW/m^(2);mantle heat flow from 49.2 to 57.2 mW/m^(2), with an average of (52.8±2.8) mW/m^(2);Moho temperature from 613 to 707 ℃, with an average of (671±31) ℃, and thermal lithospheric thicknessfrom 61.23 to 64.89 km, with an average of (63.58±1.35) km. With a crust-mantle heat flow ratio of (0.45±0.08), thelithospheric thermal structure is characterized by cold crust and hot mantle, indicating the impacts of deep heat sourceson the thermal state of the central depression in the Yinggehai Basin. The results of this study not only provide a scientificbasis for further exploration and exploitation of geothermal resources in the central depression but also serve as a valuablereference for research on the geodynamics of the basin.