上地幔含水量对海底扩张过程中洋壳厚度的影响:数值模拟  

The Effect of Water Content in the Upper Mantle on the Oceanic Crustal Thickness during Seafloor Spreading: Numerical Modeling

作　　者：邵佳 许鹤华[1,2] 谌永强 施小斌 王晓芳[1,2] Shao Jia;Xu Hehua;Shen Yongqiang;Shi Xiaobin;Wang Xiaofang(Key Laboratory of Ocean and Marginal Sea Geology,South China Sea Institute of Oceanology,Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences,Guangzhou 511458,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院边缘海与大洋地质重点实验室,南海海洋研究所,南海生态环境工程创新研究院,广东广州511458 [2]南方海洋科学与工程广东省实验室(广州),广东广州511458 [3]中国科学院大学,北京100049

出　　处：《地球科学》2021年第3期826-839,共14页Earth Science

基　　金：NSFC-广东联合基金项目(No.U20A20100);国家自然科学基金项目(Nos.91428205,41376061);中国科学院战略性先导科技专项A类项目(No.XDA13010303);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(No.GML2019ZD0104)。

摘　　要：地幔中不同含量的水会对洋壳的生成产生重要影响,但目前不同含水量下的均匀和局部含水地幔会怎样影响洋壳厚度还不清楚.利用动力学数值模拟的方法,对上地幔均匀含水和局部含水两种情况下洋壳的生成过程展开研究.结果表明:当上地幔均匀含水时,含水量的增加在减小最大熔融分数的同时,会增大初始熔融深度和熔融面积,因而生成的洋壳厚度会增加.当上地幔局部含水时,局部含水地幔熔融后也会增大生成的洋壳厚度,但开始影响洋壳厚度的时间与其含水量有关.结合南海洋壳特征进一步分析认为:南海扩张期间其地幔源含水量具有非均质性.东部次海盆的洋壳比西南次海盆厚1 km,可能是因为前者地幔源含水量整体高于后者(本模型表明约高50×10^(-6)).南海玄武岩中碳酸盐化硅酸盐熔体的存在,可能是由局部高含水量地幔在深部熔融产生的熔体携带上来的.南海洋壳厚度在时间上没有大幅度变化,可能是因为局部高含水量地幔的体积相对较小或体积虽大但其含水量没有显著高于地幔背景含水量.Different contents of water in the mantle have significant effects on the formation of oceanic crust. However, how the homogeneous and local hydrous mantle with different water contents will affect the thickness of oceanic crust are also not clear.Thus we conduct numerical simulations to represent the process of formation. Results show that, in the homogeneous hydrous models, the higher the water content in the upper mantle is, the smaller the maximum melt fraction, the deeper the initiation melting and the bigger melting area will be, finally leading to larger melt volume and the thicker oceanic crust. And in the local hydrous models, the melt of local hydrous mantle can also increase the thickness of oceanic crust, however, the initial time of the effect will depend on its water content. Combining with the characteristics of oceanic crust of the South China Sea, we suggest that the water content in the mantle source during the opening of South China Sea is heterogeneous. The oceanic crustal thickness in eastern sub-basin is 1 km thicker than that of the southwestern sub-basin, possibly because the overall water content of the former is higher than the latter(about 50×10^(-6), according to our model). And carbonated silicate melts in the basalt of South China Sea may be carried out from deep by the melt which the local hydrous mantle produce in the deep.Moreover, the oceanic crustal thickness does not change greatly with time, which may be due to the volume of the local hydrous mantle is small or the volume is large but its water content is not significantly higher than that in the background.

关 键 词：上地幔含水量 洋壳厚度 海底扩张 南海 数值模拟 海洋地质 

分 类 号：P311.3[天文地球—固体地球物理学] P738.1[天文地球—地球物理学]