南海东北部陆坡水合物钻探区海底表层热导率分布特征

依据获取的热导率测量数据和多波束数据所反映的海底地貌特征,分析了南海东北部陆坡天然气水合物钻探区表层沉积物矿物组成、粒级以及区域地貌特征对热导率分布的控制作用。研究结果表明,钻探区表层沉积物热导率平均值为(1.26±0.12) W/(m·k),相对于南海北部陆坡热导率背景偏高,沉积物组分中既含有陆源浊流沉积体中的高热导率矿物,也含有由甲烷等为主要气源的生物化学反应而形成的具有高热导率特性的碳酸盐。钻探区表层沉积物热导率区域细节分布具有非常明显的特征,2区和5区属于海台地貌,海底表层分布有大面积的碳酸盐结壳,由于底流的剥蚀作用导致沉积物粒级相对较粗,呈现高值热导率(1.32±0.06) W/(m·k)和(1.34±0.06) W/(m·k),并以此为中心向周缘逐级降低;位于海底海槽处的1区和8区则属于海槽地貌,海底表层易于接受来自海台的过滤沉积物,粒级相对较细但压实程度较低,呈现低值热导率,分别为(1.10±0.06) W/(m·k)和(1.01±0.06) W/(m·k)。钻探区表层沉积物热导率偏高主要受控于内生地质作用控制下高流体疏导所携带的化学组分,而热导率的非均匀分布则受控于外生地质作用诸如地貌地形变化导致的粒级分布状况。

DISTRIBUTION PATTERN OF SEAFLOOR THERMAL CONDUCTIVITIES AT THE DRILLING AREA FOR GAS HYDRATE ON THE NORTHEASTERN SLOPE OF SOUTH CHINA SEA

We investigated thermal conductivity, mineral composition, grain size and geomorphy of seafloor sediments and their variations in the drilling area on the northeastern slope of South China Sea using the thermal conductivities and multi-beam data as tools. Data reveals that the thermal conductivities of seafloor sediments are 1.26±0.12 W/(m·k) higher than the background values on average, possibly due to deposition of terrigenous turbidites and methane related high-thermal-conductivity carbonate deposits. The detailed distribution pattern of the thermal conductivities is interesting. The thermal conductivities as high as 1.32±0.06 W/(m·k) and 1.34±0.06 W/(m·k) are discovered in the areas of No. 2 and No. 5 respectively on the submarine platforms where large area is deposited by coarse grained carbonate due to bottom current denudation. Thermal conductivities as low as 1.10±0.06 W/(m·k) and 1.01±0.06 W/(m·k) are found in the typical submarine troughs of No. 1 and No. 8 areas respectively attributing to the compaction of fine grained deposits avalanched from the submarine plateaus. The seafloor sediments thermal conductivity at the drilling area decreases from the central plateaus to the peripheral troughs, probably owing to the chemical composition of highly migrating fluid under the control of endogenic process and the grain size decrease up to geomorphic changes under the control of the exogenic process.