中国科学技术大学黄金水团队报道了，基于三维数值模拟的地幔对流构造模式及其对地球构造演化的意义。相关论文于2024年10月28日发表于国际顶尖学术期刊《中国科学：地球科学》杂志上。

据介绍，研究团队利用球壳域三维数值模型，获得并分析了地幔对流的五种构造模式。五种构造对流模式分别为非板块活动盖、板块活动盖、幕式板块活动盖、幕式停滞盖和停滞盖对流模式。

研究人员提出并阐述了这五种构造模式的典型特征，以及基于板块性、活动性及其标准差为依据的数值分类标准。结果表明，岩石圈的屈服应力对构造对流模式有深远的影响。随着屈服应力的逐渐增大，地幔对流的构造模式通过上述五种模式依次发生变化。此外，随着Rayleigh数的增加，板块活动盖对流模式的屈服应力范围减小，不同构造模式之间的无量纲转换应力增大。

其中，非板块活动盖对流模式与板块活动盖对流模式之间的空间转换应力，随Rayleigh数的增加而增大，而其他构造模式之间的空间转换应力则减小。此外，研究人员发现不同构造模式间的转换应力与内加热速率成反比，随着内加热速率的增大，转换应力减小。

构造模式间转换应力的拟合分析表明，地球当前板块构造对应的岩石圈屈服应力为150-250MPa，与实验岩石学测定的蛇纹岩化地幔岩石强度一致。如果太古宙的地幔温度比现在高300°C，那么地球就处于一种间歇性的停滞盖对流模式。

地球表面的构造演化与岩石圈强度和热演化过程密切相关。如果岩石圈的强度只有150MPa，早期地幔快速冷却模型中的板块构造应该在3.Ga之前开始，晚期地幔快速冷却模式中的板块构造大约开始于1.5Ga。然而，在岩石圈强度为200MPa时，晚期地幔快速冷却模型中的板块构造开始于0.95Ga，早期地幔快速冷却模式中的板块构造应该在大约2Ga开始。

早期的地球处于间歇性的停滞盖对流模式，这意味着在那个时候可能还会发生俯冲。在地球后期历史中，幕式板块活动盖对流模式的存在表明，在板块构造过程中，也可能存在间歇性的地表停滞，这可能为地球上约1.0Ga的构造活动平静期提供了一种解释，表明地质时期的构造不活跃并不意味着板块构造没有开始。

附：英文原文

Title: Tectonic modes of mantle convection and their implications for Earth’s tectonic evolution based on three-dimensional numerical simulations

Author: Song XIANG, Jinshui HUANG, Bingcheng WU

Issue&Volume: 2024/10/28

Abstract: Five tectonic modes of mantle convection are obtained and analyzed with three-dimensional numerical models in a spherical shell domain. The five tectonic convective modes are non-plate mobile-lid, plate-like mobile-lid, episodic plate-like mobile-lid, episodic stagnant-lid, and stagnant-lid convective modes, respectively. The typical characteristics of these five tectonic modes and their numerical classification criteria based on plateness, mobility, and their standard deviations are presented and discussed. The results show that the yield stress of the lithosphere has profound effects on the tectonic convective modes. With the gradual increase of yield stress, the tectonic mode of mantle convection changes from one to another sequentially through the aforementioned five modes. Additionally, as the Rayleigh number increases, the range of yield stress for the plate-like mobile-lid convective mode decreases, and the dimensionless transition stress between different tectonic modes increases. Specifically, the dimensional transition stress between the non-plate mobile-lid convective mode and plate-like mobile-lid convective mode increases with the increase of Rayleigh number, but decreases between other tectonic modes. Furthermore, we find that the transition stress between different tectonic modes is inversely proportional to the internal heating rate, with the transition stress decreasing as the internal heating rate increases. The fitting analysis of the transition stress between tectonic modes shows that Earth’s current plate tectonics correspond to a lithospheric yield stress of 150–250MPa, which aligns with the strength of serpentinized mantle rock determined by experimental petrography. If the Archean mantle was 300°C warmer than it is today, then the Earth was in an episodic stagnant-lid convective mode. The tectonic evolution of the Earth’s surface is closely related to the lithospheric strength and the process of thermal evolution. If the lithospheric strength was only 150MPa, plate tectonics in the early mantle rapid cooling model would have begun before 3.8Ga, and plate tectonics in the late mantle rapid cooling model would have begun at approximately 1.5Ga. However, at a lithospheric strength of 200MPa, plate tectonics in the late mantle rapid cooling model would have begun later than 0.95Ga, and plate tectonics in the early mantle rapid cooling model would have begun at approximately 2Ga. The early Earth was in the episodic stagnant-lid convective mode, which means that subduction might still have occurred at that time. The presence of the episodic plate-like mobile-lid convective mode in Earth’s later history indicates that there might also have been intermittent surface stagnation during plate tectonics, which may provide an explanation for the quiet period of tectonic activity at approximately 1.0Ga on Earth. This indicates that tectonic inactivity during a geological period is not an indicator that plate tectonics did not begin.

DOI: 10.1007/s11430-024-1393-4

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-024-1393-4