2024年5月3日出版的《自然—地球科学》杂志发表了中国地质大学(武汉)刘勇胜研究团队的最新成果，他们报道了软流圈中广泛存在的双层熔体结构。
结合Hf-Nd同位素测量，研究团队对华北玄武岩进行了主元素和微量元素的测量。此外，研究人员收集了来自不同海洋和大陆背景的玄武岩数据，并发现了玄武岩熔体提取深度与其平均Y/Yb比值之间的定量联系。研究表明，在海洋和大陆玄武岩中广泛存在双峰Y/Yb分布，这与软流圈中两个不同深度的熔体堆积相一致。
富硅玄武岩熔体积聚在80-110km深度，贫硅、富铁熔体积聚在140-165km的深度，在110-140km的深度有一个无熔体的缝隙。研究表明，双层熔体结构在软流圈中可能比之前认为的更为普遍，特别是在主动或被动地幔上流的地区。快速扩张的板块和裂陷的大陆边缘下存在两个熔体层，可能会减少对克拉通根部的基底阻力，并有助于克拉通和超大陆的分裂。
据研究人员介绍，地球对流地幔中的部分熔融影响其物理和化学状态，特别是软流圈的可塑性和板块构造动态。熔体成分随地幔熔融深度的变化而发生系统的变化，但目前缺乏定量的约束。
附：英文原文
Title: Widespread two-layered melt structure in the asthenosphere
Author: Zhang, Jun-Bo, Liu, Yong-Sheng, Foley, Stephen F., Moynier, Frdric, Zhao, Liang, Xu, Rong, Wang, Cheng-Yuan
Issue&Volume: 2024-05-03
Abstract: Partial melts in the Earth’s convecting mantle influence its physical and chemical state, particularly the plasticity of the asthenosphere and the dynamics of plate tectonics. Melt compositions change systematically with the depth of mantle melting, but there are currently few quantitative constraints. Here we measure major and trace elements, combined with Hf–Nd isotope measurements, for basalts from North China. In addition, we compile a dataset of basalts from various oceanic and continental settings and find a quantitative link between the depth of basaltic melt extraction and its mean Y/Yb ratio. We show that a bimodal Y/Yb distribution is widespread in oceanic and continental basalts, consistent with two distinct depths of melt accumulation in the asthenosphere. Silica-rich basaltic melt accumulates at depths of 80–110km and silica-poor, iron-rich melt at depths of 140–165km, with a melt-free gap at a depth of 110–140km. Our findings suggest that a two-layered melt structure may be more widespread in the asthenosphere than previously thought, particularly in areas of active or passive mantle upflow. The presence of two melt layers beneath fast-spreading plates and rifted continental margins may reduce the basal drag force on cratonic roots and aid with the breakup of cratons and supercontinents.
DOI: 10.1038/s41561-024-01433-1
Source: https://www.nature.com/articles/s41561-024-01433-1