Cratonic lamproites bear extreme Sr−Nd−Pb isotopic compositions widely known as enriched mantle I (EMI), yet the origin of the EMI reservoir remains controversial. Here, we explore this issue by examining Mg−Sr−Nd−Pb isotopic compositions of lamproites from Leucite Hills, Wyoming, USA. The δ²⁶Mg values vary from the range of the normal mantle to lower values (− 0.43 to − 0.18 ‰), correlating with indices of the degree of carbonate metasomatism, an observation that can be best explained through mantle metasomatism by subducted carbonate-bearing sediments. With increasing extent of carbonate metasomatism, these samples display less extreme EMI Sr−Nd−Pb isotopic signatures, arguing for at least two metasomatic events that occurred in their mantle sources. The early metasomatic event associated with subducted continent-derived siliciclastic sediments led to the formation of the EMI Sr−Nd−Pb isotopic signatures while the recent carbonate metasomatism produced the light Mg isotopic signature but diluted the EMI Sr−Nd−Pb isotopic signatures. Our study indicates that a combination of Mg and Sr−Nd−Pb isotopes could be an effective tool in deciphering multiple-stage metasomatic events in mantle sources and places new constraints on the generation of enriched mantle reservoirs.

克拉通火山岩具有极端的Sr-Nd-Pb同位素组成，被广泛称为富地幔I（EMI），但EMI储层的成因仍然存在争议。在这里，我们通过检查来自美国怀俄明州莱克特山的锰铁矿的Mg-Sr-Nd-Pb同位素组成来探索这个问题。该δ ²⁶Mg值从正常地幔的范围变化到较低的值（-0.43至-0.18‰），与碳酸盐交代度的指数相关，这一观察结果最好通过俯冲的含碳酸盐沉积物的地幔交代来解释。随着碳酸盐交代作用程度的增加，这些样品显示出较少的极端EMI Sr-Nd-Pb同位素特征，认为在其地幔源中至少发生了两次交代事件。与俯冲大陆衍生的硅质碎屑沉积物相关的早期交代事件导致EMI Sr-Nd-Pb同位素特征的形成，而最近的碳酸盐交代作用产生了轻的Mg同位素特征，但稀释了EMI Sr-Nd-Pb同位素特征。