Xia Qun-Ke, Liu Jia, Kovács István, Hao Yan-Tao, Li Pei, Yang Xiao-Zhi, Chen Huan, Sheng Ying-Ming
School of Earth Sciences, Zhejiang University, Hangzhou 310027, China.
CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei 230026, China.
Natl Sci Rev. 2019 Jan;6(1):125-144. doi: 10.1093/nsr/nwx016. Epub 2017 Feb 24.
Understanding the concentration and distribution of water in the Earth's mantle plays a substantial role in studying its chemical, physical and dynamic processes. After a decade of research, a comprehensive dataset of water content in upper-mantle samples has been built for eastern China, which is now the only place with water-content data from such diverse types of natural samples, and provides an integrated picture of the water content and its distribution in the upper mantle at a continental scale. The main findings include the following: (i) the temporal heterogeneity of the water content in the lithospheric mantle from early Cretaceous (∼120 Ma) to Cenozoic (<40 Ma) was tightly connected with the stability of the North China Craton (from its destruction to its consolidation); (ii) the heterogeneous water content in the Cenozoic lithospheric mantle beneath different blocks of eastern China was not only inherited from tectonic settings from which they came, but was also affected later by geological processes they experienced; (iii) the distinct water content between the lowermost crust and lithospheric mantle of eastern China and its induced rheological contrast at the base of the crust indicate that the continental crust-mantle boundary could behave either in a coupled or decoupled manner beneath different areas and/or at different stages; (iv) the alkali basalts of eastern China demonstrate a heterogeneous distribution of water content in the mantle; local and regional comparisons of the water content between the lithospheric mantle and basalts' source indicate that the Cenozoic alkali basalts in eastern China were not sourced from the lithospheric mantle. Instead, the inferred high water contents in the mantle sources suggest that the Cenozoic eastern China basalts were likely sourced from the mantle transition zone (MTZ); and (v) both oceanic and continental crusts may carry a certain amount of water back into the deep mantle of eastern China by plate subduction. Such recycled crustal materials have not only created a local water-rich zone, but have also introduced crustal geochemical signatures into the mantle, both accounting for crustal geochemical imprints in the intra-plate magmatic rocks of eastern China.
了解水在地球地幔中的浓度和分布对于研究其化学、物理和动力学过程具有重要作用。经过十年研究，已建立了中国东部上地幔样本含水量的综合数据集，中国东部是目前唯一拥有如此多样类型天然样本含水量数据的地区，它提供了大陆尺度上地幔含水量及其分布的整体情况。主要发现如下：（i）从早白垩世（约120 Ma）到新生代（<40 Ma）岩石圈地幔中含水量的时间异质性与华北克拉通的稳定性（从其破坏到巩固）紧密相关；（ii）中国东部不同地块下新生代岩石圈地幔中含水量的不均一性不仅继承于它们所来自的构造环境，还受到它们后来经历的地质过程的影响；（iii）中国东部最下部地壳与岩石圈地幔之间明显的含水量差异及其在壳底引起的流变学对比表明，大陆壳幔边界在不同区域和/或不同阶段可能表现为耦合或解耦方式；（iv）中国东部碱性玄武岩显示出地幔中含水量的不均一分布；岩石圈地幔与玄武岩源区之间含水量的局部和区域比较表明，中国东部新生代碱性玄武岩并非源自岩石圈地幔。相反，地幔源区推断的高含水量表明，中国东部新生代玄武岩可能源自地幔过渡带（MTZ）；以及（v）海洋地壳和大陆地壳都可能通过板块俯冲将一定量的水带回中国东部的深部地幔。这种再循环的地壳物质不仅形成了局部富水区，还将地壳地球化学特征引入地幔，二者共同构成了中国东部板内岩浆岩中的地壳地球化学印记。
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