Sr-Nd-Pb isotopic compositions of ocean island basalts from the Crozet and Juan Fernandez archipelagoes

The geochemical signatures of nearly all Earth’s volcanic hotspots converge on a common isotopic composition, which is often termed the ‘focal zone’ (FOZO) and has been associated with a shared deep mantle source. Yet, unlike other characteristic geochemical components of hotspots, the origin and nature of FOZO remains unclear. Geochemical evidence has been invoked to support both an ancient and a relatively young age for FOZO, and long-lived radiogenic isotopic data support many potential geochemical relationships between geographically disparate hotspots. We examine this issue using the short-lived 146Sm-142Nd isotopic system, which can identify diverse geochemical origins originating in the Hadean Eon, more than four billion years ago. Two hotspots with strong geochemical affinity to FOZO, the Crozet and Juan Fernandez hotspots, have statistically distinct 142Nd compositions, meaning that despite the similarity in their long-lived radiogenic isotopic compositions, they must reflect different Hadean-aged geological heritages. Detailed analysis of the isotopic compositions of global hotspots using machine learning further reveals that FOZO is most likely not singular and but rather represents a spectrum of discrete domains that each have histories dating back to the first 10% of Earth’s history.