南黄海中部隆起一个新的大地热流值:CSDP-2井热流测量结果

A new heat flow of the central uplift,the South Yellow Sea:from measurement of CSDP-2 borehole

大地热流值,是岩石圈、地壳和盆地等各种尺度的构造演化和地球动力学研究的重要参数.南黄海是东亚大陆边缘的重要组成部分,但与东海陆架、冲绳海槽、渤海湾盆地等的大地热流研究相比,其研究程度较低,只有10个大地热流测点且大部分位于南部坳陷,不能很好地表征南黄海的大地热流特征.系统和准确的地温和热导率测量,是获得可靠大地热流值的基础.南黄海中部隆起之上的大陆架科学钻探CSDP-2井,全取心钻进2843.18 m,2016年先后5次系统测温,给了我们一个绝佳的系统研究其大地热流的机会.对井中295块沉积物或沉积岩进行了热导率测量,并进行了温度压力等校正.根据热导率的垂向分布特征将全井分为6个井段,地温梯度分别为31.86、24.38、23.54、18.09、18.21和20.18℃·km^(-1),平均23.46℃·km^(-1),热导率则分别为1.776、2.765、3.182、3.623、4.184和2.825 W·(m·K)^(-1),大地热流分别为56.5、67.4、74.9、65.5、76.2和57.0 mW·m^(-2).全井平均大地热流为68.9 mW·m^(-2),考虑地层裂缝孔隙影响后,大地热流校正为66.7 mW·m^(-2).这个大地热流值,比北部坳陷稍高而比南部坳陷稍低,是中晚侏罗纪前陆挤压和新生代伸展等构造热演化的大致反映.南黄海热流在东亚大陆边缘处于偏低的水平,反映了南黄海在东亚陆缘相对偏冷的地质背景.

Heat flow is essential for tectonic and dynamical research of lithosphere,crust and basin.Hundreds of heat flow data have been obtained in the East China Sea shelf basin,the Okinawa Trough and the Bohai Bay basin,East Asia Continental Margin(EACM).Whereas,as an important part of EACM,only 10 heat flow values are reported in the South Yellow Sea(SYS),and even most of them are located in the southern depression.It is difficult to represent the heat flow characteristics in SYS.To obtain reliable heat flow value,it is necessary to measure geotemperature and thermal conductivity systematically and accurately.Continental Shelf Drilling Program CSDP-2 borehole in the central uplift of SYS,with a total coring drilling of 2843.18 m and five successive temperature measurements in 2016,provides an excellent opportunity to perform the research.The thermal conductivity of 295 sediments or sedimentary rocks in the borehole was measured with temperature and pressure corrected as well.According to the vertical distribution of thermal conductivity,the whole borehole is divided into 6 sections.The geothermal gradients are 31.86,24.38,23.54,18.09,18.21 and 20.18℃·km^(-1)respectively,with an average of 23.46℃·km^(-1).The thermal conductivity is 1.776,2.765,3.182,3.623,4.184 and 2.825 W·(m·K)^(-1)respectively.The heat flow is 56.5,67.4,74.9,65.5,76.2 and 57.0 mW·m^(-2)respectively with average value of 68.9 mW·m^(-2),which is corrected to 66.7 mW·m^(-2)considering the structural fractures.This heat flow value is slightly higher than that of the northern depression and lower than that of the southern depression,which is the general reflection of the tectonic thermal evolution,due to foreland compression in middle-late Jurassic and extension in Cenozoic.In EASM,the heat flow value of SYS is low,which reveals its relatively cold geological background.