Mantle xenoliths in a Mesoproterozoic lamprophyre dyke at Elliot Lake, Ontario, located on the east margin of the Midcontinent Rift (MCR), erupted at ~ 1.1 Ga. These xenoliths enable a study of critical metal enrichment in the sub-cratonic lithospheric mantle (SCLM). Whole-rock major and trace element data from a suite of peridotite xenoliths document a combination of melt depletion and cryptic metasomatic processes. Trace element whole-rock and mineral systematics show a specific endowment in Nb-U-REE (ca. 5–30 ppm mean value), linked to carbonated silicate metasomatism. Geochronological data from the lamprophyre host (Rb–Sr age of 1112.8 ± 4.95 Ma) and the mantle xenoliths (Re-Os) indicate that our samples document the state of the mantle during the earlier stages of magmatism of the MCR. Mineral thermobarometry reveals a hot geotherm reflecting the thinning of the Superior cratonic root to 110 km. Most of the Nb-U-REE deposits and anomalies associated with the MCR event are located around Lake Superior. Here we document for the first time north of Lake Huron, metasomatic processes in the lithosphere that may have created Nb-U-REE metal endowment. The mantle events documented here relate to other observations made in the Slave and North China craton and show how silico-carbonated mid-lithospheric metasomatism up-grades the cratonic lithospheric mantle into a fertile source. Comparison with other small degree melts such as kimberlites, and mantle metasomes related to the MARID suite, show that small degree melts are very efficient at transporting critical metals from the HFSE group plus U and Th, into Earth’s lithosphere.

位于中大陆裂谷 (MCR) 东缘的安大略省埃利奥特湖中元古代辉斑岩岩脉中的地幔捕虏体在约 1.1 Ga 时喷发。这些捕虏体使得研究克拉通下岩石圈地幔 (SCLM) 中的关键金属富集成为可能）。来自一组橄榄岩捕虏体的全岩主量元素和微量元素数据记录了熔体消耗和神秘交代过程的结合。微量元素全岩石和矿物系统学显示 Nb-U-REE（平均值约 5-30 ppm）具有特定的禀赋，与碳化硅酸盐交代作用有关。来自萤岩体宿主（Rb-Sr 年龄为 1112.8 ± 4.95 Ma）和地幔捕虏体 (Re-Os) 的年代学数据表明，我们的样本记录了 MCR 岩浆作用早期阶段地幔的状态。矿物温压测量揭示了炎热的地温，反映了上克拉通根部变薄至 110 公里。大多数与 MCR 事件相关的 Nb-U-REE 沉积物和异常现象都位于苏必利尔湖周围。在这里，我们首次记录了休伦湖以北的岩石圈交代过程，该过程可能创造了铌-铀-稀土金属禀赋。这里记录的地幔事件与在奴隶克拉通和华北克拉通进行的其他观测有关，并显示了硅碳酸盐岩中岩石圈交代作用如何将克拉通岩石圈地幔升级为肥沃的来源 岩石圈中的交代过程可能产生了 Nb-U-REE 金属禀赋。这里记录的地幔事件与在奴隶克拉通和华北克拉通进行的其他观测有关，并显示了硅碳酸盐岩中岩石圈交代作用如何将克拉通岩石圈地幔升级为肥沃的来源 岩石圈中的交代过程可能产生了 Nb-U-REE 金属禀赋。这里记录的地幔事件与在奴隶克拉通和华北克拉通进行的其他观测有关，并显示了硅碳酸盐岩中岩石圈交代作用如何将克拉通岩石圈地幔升级为肥沃的来源。与其他小程度熔体（例如金伯利岩）和与 MARID 套件相关的地幔变体的比较表明，小程度熔体在将 HFSE 族以及 U 和 Th 中的关键金属输送到地球岩石圈方面非常有效。