美国亚利桑那大学Liang, Weigang和Evans, Alexander J.团队的一项最新研究提出，重力数据揭示地幔翻转后月球上钛铁矿层的遗迹。该研究成果于2024年4月8日发表于国际一流学术期刊《自然—地球科学》杂志上。

研究人员将重力反演与地球动力学模型结合起来，以揭示月球演化的这一关键阶段。研究发现，围绕近侧海区观测到的的线性重力异常的多边形模式，与全球地幔翻转后残留在过去片状下降流位置的含钛铁矿堆积的特征一致。这一解释得到了观测到的重力异常的模式、幅度和尺寸与含钛铁矿堆积残余物的地球动力学模型所预测的相似性的支持。这些特征为全球地幔翻转的性质提供了物理证据，将翻转限制在Serenitatis和Humorum盆地形成冲击之前发生，并支持了高钛玄武岩的深部富钛地幔的存在。

据研究人员介绍，月球地壳和地幔是通过岩浆海洋的结晶形成的，最终形成了一个固体堆积地幔，其上有一层富含不相容元素的致密钛铁矿堆积。这种重力不稳定的构造可能导致全球地幔的翻转，含钛铁矿的堆积物沉入内部。然而，尽管有丰富的地球化学证据，但缺乏关于翻转性质的物理证据。

附：英文原文

Title: Vestiges of a lunar ilmenite layer following mantle overturn revealed by gravity data

Author: Liang, Weigang, Broquet, Adrien, Andrews-Hanna, Jeffrey C., Zhang, Nan, Ding, Min, Evans, Alexander J.

Issue&Volume: 2024-04-08

Abstract: The lunar crust and mantle formed through the crystallization of a magma ocean, culminating in a solid cumulate mantle with a layer of dense ilmenite-bearing cumulates rich in incompatible elements forming above less dense cumulates. This gravitationally unstable configuration probably resulted in a global mantle overturn, with ilmenite-bearing cumulates sinking into the interior. However, despite abundant geochemical evidence, there has been a lack of physical evidence on the nature of the overturn. Here we combine gravity inversions together with geodynamic models to shed light on this critical stage of lunar evolution. We show that the observed polygonal pattern of linear gravity anomalies that surround the nearside mare region is consistent with the signature of the ilmenite-bearing cumulates that remained after the global mantle overturn at the locations of past sheet-like downwellings. This interpretation is supported by the compelling similarity between the observed pattern, magnitude and dimensions of the gravity anomalies and those predicted by geodynamic models of the ilmenite-bearing cumulate remnants. These features provide physical evidence for the nature of the global mantle overturn, constrain the overturn to have occurred before the Serenitatis and Humorum basin-forming impacts and support a deep Ti-rich mantle source for the high-Ti basalts.

DOI: 10.1038/s41561-024-01408-2

Source: https://www.nature.com/articles/s41561-024-01408-2