Dong Junjie, Fischer Rebecca A, Stixrude Lars P, Brennan Matthew C, Daviau Kierstin, Suer Terry-Ann, Turner Katlyn M, Meng Yue, Prakapenka Vitali B
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA.
Department of the History of Science, Harvard University, Cambridge, Massachusetts, USA.
Nat Commun. 2025 Jan 26;16(1):1039. doi: 10.1038/s41467-025-56231-z.
Phase transitions in the mantle control its internal dynamics and structure. The post-spinel transition marks the upper-lower mantle boundary, where ringwoodite dissociates into bridgmanite plus ferropericlase, and its Clapeyron slope regulates mantle flow across it. This interaction has previously been assumed to have no lateral spatial variations, based on the assumption of a linear post-spinel boundary in pressure and temperature. Here we present laser-heated diamond anvil cell experiments with synchrotron X-ray diffraction to better constrain this boundary, especially at higher temperatures. Combining our data with results from the literature, and using a global analysis based on machine learning, we find a pronounced nonlinearity in the post-spinel boundary, with its slope ranging from -4 MPa/K at 2100 K, to -2 MPa/K at 1950 K, and to 0 MPa/K at 1600 K. Changes in temperature over time and space can therefore cause the post-spinel transition to have variable effects on mantle convection and the movement of subducting slabs and upwelling plumes.
地幔中的相变控制着其内部动力学和结构。尖晶石后相变标志着上地幔与下地幔的边界，在该边界处，林伍德石分解为布里奇曼石和铁方镁石，其克拉珀龙斜率调节着穿过该边界的地幔流动。基于压力和温度下线性尖晶石后边界的假设，此前人们认为这种相互作用不存在横向空间变化。在此，我们利用同步加速器X射线衍射进行激光加热金刚石压腔实验，以更好地约束这一边界，尤其是在更高温度下。将我们的数据与文献结果相结合，并使用基于机器学习的全局分析，我们发现尖晶石后边界存在明显的非线性，其斜率在2100K时为-4MPa/K，在1950K时为-2MPa/K，在1600K时为0MPa/K。因此，温度随时间和空间的变化会导致尖晶石后相变对地幔对流以及俯冲板块和上升地幔柱的运动产生不同的影响。
