吉林大学Shiwen Li和Yabin Li等人及其团队报道了通过电导率数据成像的北美西部地幔过渡带下的水运输系统。相关论文于2023年3月17日发表在《地质学》杂志上。

研究人员建立了北美地幔过渡带(MTZ)和下地幔最高处之下的电导率模型，证实了暖板的输水能力。在美国西部地下发现了一个高导电性异常。该异常的下地幔部分被解释为再水合超石英的含水区域，而异常的北美地幔过渡带部分则被认为是超石英释放的水(0.8 wt%)的存在。研究人员推测，温暖的板块，如法拉龙板块，可以导致大量致密水化镁硅酸盐的分解，主要向上地幔释放水。这些水在渗过板块时，使超石英再水化，使板块能够继续将水输送到下地幔中。所发现的高电导率异常，以及之前在上地幔中所发现的地幔电性特征，证明了跨北美地幔过渡带水传输系统的存在，该系统与法拉龙板块的热俯冲有关。

据了解，俯冲板携带的含水相的稳定场调节水在俯冲路径上的运移。这些水在地幔中不同深度的最终垂直分布是由板块的热状态决定的。温暖板块被认为主要在上地幔失水。然而，由于地球物理观测的缺乏，温暖板块能否将水带入下地幔(LM)是不确定的。

附：英文原文

Title: A water transport system across the mantle transition zone beneath western North America as imaged by electrical conductivity data

Author: Shiwen Li, Yabin Li, Junhao Guo, Zikun Zhou, Aihua Weng

Issue&Volume: 2023-03-17

Abstract: The stability field of hydrous phases carried by subducting slabs regulates water transport along the subduction pathway. The ultimate vertical distribution of this water at different depths in Earth’s mantle is governed by the thermal state of the slab. A warm slab is considered to lose water mainly in the upper mantle. However, whether a warm slab can carry water into the lower mantle (LM) is uncertain because of the scarcity of geophysical observations. We report an electrical conductivity model of the mantle transition zone (MTZ) and uppermost LM beneath North America to confirm the water-transporting ability of a warm slab. A high-conductivity anomaly was identified beneath the western United States. The LM portion of this anomaly is interpreted as a hydrous region containing rehydrated stishovite, whereas the lower MTZ portion of the anomaly is ascribed to the presence of water (~0.8 wt%) released by the hydrous stishovite. We speculate that warm slabs, such as the Farallon slab, can cause the breakdown of large amounts of dense hydrous magnesium silicates, releasing water mainly into the upper mantle. This water rehydrates stishovite when percolating through the slab, enabling the slab to continue to transport water into the LM. The identified high-conductivity anomaly, together with previously recognized electrical features in the upper mantle, demonstrates the existence of a trans-MTZ water transport system associated with the warm subduction of the Farallon slab.

DOI: 10.1130/G51005.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G51005.1/621092/A-water-transport-system-across-the-mantle