南海西南次海盆的地热流特征与分析

The characteristics and analysis of heat flow in the Southwest sub-basin of South China Sea

为系统地了解南海西南次海盆的地热流特征,本文通过对研究区及邻域地热流数据的补充采集、收集整理和统计分析,获得了87个有效的地热流数据、一批热导率和生热率的地热参数资料,地热流测点在空间上覆盖了整个区域.研究区的地热流数据分布结果表明,西南次海盆热流密度的平均值为98.1±14.8mW·m^(-2),洋陆过渡带为103.6±19.4mW·m^(-2),南沙岛礁区和西部陆缘分别为79.0±15.5mW·m^(-2)和78.3±15.6mW·m^(-2).研究区表层沉积物热导率的平均值0.86±0.06 W·mK^(-1),生热率的平均值1.11±0.17μW·m^(-3),海底温度的平均值为2.43±0.01℃.综合海底地形地貌、地质与地球物理资料,认为研究区的热流特征在空间上具有一定的分布规律,表现为:(1)洋盆区测点的热流密度平均值高于两侧陆缘;(2)东南缘洋陆过渡带上测点的地热流密度值高于邻近海盆和南沙岛礁区的测点,而西北缘这种特征不明显;(3)西北翼的热流密度值总体比东南翼高;(4)沿着古扩张中心方向,西南次海盆热流值具有自东北向西南端方向逐步增大的趋势,表明海盆区同时存在着洋中脊与大陆裂谷两种不同的热状态,西南段裂谷热流值比东北段洋中脊高.对西南次海盆沉积物的热导率和生热率值参数的测量及数据空间分析可见,这两种热参数的空间分布无明显规律性,可能与海盆形成之后复杂的沉积环境相关.根据热流-洋壳年龄之间的关系,在西南次海盆东北段26个测站数据中,发现靠近古扩张中心的数据与理论值呈负偏移,而远离古扩张中心的数据呈正偏移,此现象是海盆内地热流数据受不同类型的地下流体影响所致.

To have a better understanding of the heat flow characteristics in the Southwest subbasin of South China Sea（SWSB）,we have acquired and re-collected 87 sets of valid heat flow data and multiple kinds of geothermal parameters data,including thermal conductivity and heat generation rate.The heat flow sites could cover whole study area in space.The distribution of heat flow shows that the average values of heat flow in oceanic basin is 98.1±14.8 mW·m^-2.Besides,it is 103.6±19.4 mW·m^-2 in continent-ocean transition zone while 79.0±15.5 mW·m^-2 and 78.3±15.6 mW·m^-2 in Nansha and west margin of SWSB respectively.The average values of thermal conductivity and heat generation rate in surface sediment are 0.86±0.06 W·mK^-1 and 1.11±0.17μW·m^-3 respectively.The mean seafloor temperature is 2.43±0.01 ℃.Combined with the newest geomorphology of SWSB and its geological-geophysical data,it is learned that the distribution of heat flow is under certain regularity as follows.（1）The average value of heat flow in oceanic basin is higher than continental margins.（2）The heat flow in the continental-ocean transition zone of southeastern margin is higher than adjacent oceanic basin and Nansha area.Differing from the southeastern margin,this situation in northwestern margin is not obvious.（3）The heat flow in northwestern margin is generally higher than southwestern margin of SWSB.（4）Along the direction of ancient residual spreading ridge center,the heat flow have the tendency of increase from the northeastern toward southwestern side.It shows that there are two different thermal characteristics of mid-ocean ridge and rifted continent in SWSB.The heat flow of rifted continental in southwestern side is higher than mid-ocean ridge in northwestern side.By analyzing and studying the spatial distribution of measured sediment thermal conductivity and heat generation rate,it indicates that the distribution of these two kinds of thermal parameters has no obvious regularity.It may be associated with the complex depositional environment after basin formed.According to the relationship of heat flow and oceanic age,it is found that the heat flow in the southwestern oceanic basin is lower than theoretical value when the sites are close to the residual spreading ridge and higher than theoretical value when the sites are far from the residual spreading ridge.These results imply that the heat flow in oceanic basin is affected by different types of underground fluid.