Refertilized continental root controls the formation of the Mianning–Dechang carbonatite-associated rare-earth-element ore system

Rare earth element ore deposits associated with carbonatite derived from Earth’s mantle supply half of the world’s rare earth element. However, the formation of carbonatite and initial enrichment and transport of rare earth element in the mantle, is unclear. Here, we image the lithospheric architecture of a Cenozoic rare earth element ore belt in southwestern China by integrating seismic tomography with geochemical data. The subduction of the Indian continent caused vertical upwelling and lateral flow of the asthenosphere, which triggered the melting of the overlying subcontinental lithospheric mantle to generate carbonatites. Such a mantle source that previously metasomatized by fluids from recycled marine sediments is a precursor process critical for forming a giant rare earth element system. For the studied ore belt, three key factors are prerequisites to generating ore-forming carbonatites: thick lithosphere with a continental root; prior fertilization of the subcontinental lithospheric mantle; and trans-lithospheric weakness for magma ascent.

与源自地球地幔的碳酸岩（carbonatite）伴生的稀土元素（rare earth element）矿床，占据了全球稀土元素供应量的半壁江山。然而，碳酸岩的形成机制，以及地幔中稀土元素的初始富集与运移过程，目前仍未明晰。本研究通过整合地震层析成像（seismic tomography）与地球化学数据，对中国西南部一处新生代稀土元素矿带的岩石圈架构开展了成像解析。印度大陆的俯冲作用引发软流圈（asthenosphere）发生垂直上涌与侧向流动，进而触发上覆大陆下岩石圈地幔（subcontinental lithospheric mantle）熔融，形成碳酸岩。这类此前经再循环海洋沉积物衍生流体发生交代作用的地幔源区，是形成巨型稀土元素成矿系统的关键前置环节。针对本次研究的矿带，生成成矿碳酸岩需满足三项核心前提条件：一是发育含大陆根的厚层岩石圈；二是大陆下岩石圈地幔曾发生富集交代作用；三是存在可供岩浆上升的跨岩石圈薄弱带（trans-lithospheric weakness）。