Is PREMA exclusively associated with LLSVPs?

Abstract

Studies of ocean island basalts (OIBs) have identified a “Prevalent Mantle” component (or PREMA) that appears to represent one of the fundamental constituents of Earth’s mantle. Recent documentation of this signature in deep-sourced kimberlitic magmatism has increasingly linked PREMA with thermochemical structures above the core mantle boundary (LLSVPs). Yet, kimberlites provide geographically limited sampling of Earth’s mantle, which makes it difficult to identify the spatial association between LLSVPs and the PREMA component sampled by these magmas. To further investigate the global distribution of the PREMA mantle component, we utilize a much more widespread class of mantle-derived magmatism – global Cenozoic alkali basalts, nephelinites and basanites (‘sodic basalts’ hereafter) – that are derived from both continental and oceanic settings. Statistical treatment of the available ~3500 geochemical and isotopic analyses of Cenozoic sodic basalts worldwide shows that at low degrees of melting these magmas exhibit similar Sr-Nd-Hf isotopic characteristics to PREMA. There is no apparent spatial relationship between the distribution of PREMA-like sodic basalts and LLSVPs, implying that the PREMA component is not exclusively associated with LLSVPs. The PREMA-like signature of low-degree sodic basalts occurs in both OIBs and continental magmas, negating an exclusive link to continental lithosphere. Geochemical modelling and mantle convection simulations indicate that PREMA could have been generated soon after Earth accretion, experiencing only minimal melting or enrichment, and then scattered throughout the mantle, including the upper mantle, rather than being the result of mixing between depleted and enriched mantle components. This work indicates that PREMA probably represent a widespread fusible component that can be mingled with other components at various scales to generate all types of mantle magmatism.