南黄海盆地地层生热率及岩石圈热结构

Radiogenic Heat Production of Formation and Thermal Structure of Lithosphere in the South Yellow Sea Basin

岩石圈热结构的研究不仅可以了解岩石圈深部动力学演化机制,也是含油气区油气资源评价的重要组成部分.由于南黄海盆地生热率数据的匮乏,阻碍了岩石圈热结构的研究进展.本文通过GR(伽马值)-A(岩石生热率)的经验关系,计算了南黄海盆地沉积地层的生热率;在大地热流、地层生热率、南北向贯穿盆地的二维多道地震剖面及OBS2013地壳速度结构剖面的约束下,建立了南黄海盆地地壳生热模型,计算了盆地的岩石圈热结构.岩石圈热结构计算结果表明:(1)南黄海盆地北部坳陷、中部隆起及南部坳陷3个次级单元的平均莫霍面温度依次为602.2±15.25℃、592.7±2.56℃、650.6±20.24℃;(2)平均热岩石圈厚度依次为99.7±2.20 km、101.7±0.51 km、88.2±2.49 km;(3)壳幔热流比分别为0.76±0.02、0.88±0.01、0.71±0.15,具有“冷壳热幔”的特征.研究结果表明,南黄海盆地现今具有与全球新生代拉张构造区相似的较高热流,处于构造活动区向构造稳定区转换的过渡阶段.此外,现今南黄海盆地3个次级单元展现的不同岩石圈热结构特征,可能与印支期至早燕山期扬子块体与华北块体的俯冲碰撞,在苏鲁造山带南侧(现今北部坳陷的位置)形成类前陆盆地的构造背景有关.

The study of lithosphere thermal structure state can not only understand the deep dynamic evolution mechanism of the lithosphere,but also be an important part of the evaluation of oil and gas resources in oil-bearing areas.The lack of heat generation rate data in the South Yellow Sea basin gets in the way of the research progress of lithospheric thermal structure.In this paper,the heat generation rate of sedimentary strata in the South Yellow Sea basin is calculated by the empirical relationship of GR(gamma value)-A(rock heat generation rate).Under the constraints of the terrestrial heat flow,the formation heat generation rate,the twodimensional multi-channel seismic profile that passes through the basin in the south-north direction and the crust velocity structure profile OBS2013,the crust heat generation model of the South Yellow Sea basin was established,and the lithospheric thermal structure of the basin was calculated.The calculated results of lithospheric thermal structure show that:(1)the Moho average temperature of the three sub-units of the north depression,the central uplift and the south depression of the South Yellow Sea basin are 602.2±15.25℃,592.7±2.56℃and 650.6±20.24℃,respectively;(2)The average thermal lithosphere thickness is 99.7±2.20 km,101.7±0.51 km,88.2±2.49 km;(3)The crust-mantle heat flux ratios are 0.76±0.02,0.88±0.01,and 0.71±0.15,respectively,with the characteristics of“cold crust and hot mantle”.The results of this paper reveal that the South Yellow Sea basin not only has a high heat flow background,but also is in the transition stage from tectonic active area to tectonic stable area.In addition,the different lithospheric thermal structure characteristics of the three sub-units in the present South Yellow Sea basin may be related to the tectonic setting of the para-foreland basin formed on the south side of the Sulu orogenic belt(present northern depression)by the subduction collision of the Yangtze block and the North China block in the Late Triassic.