Abstract
Earth’s surface and mantle sulphur reservoirs are connected via subduction, crustal recycling and volcanism. Although oceanic hotspot lavas currently provide the best constraints on the deep sulphur cycle, their restricted age range (<200 Ma) means they cannot reveal temporal variations in crustal recycling over Earth history. Sulphur-rich alkaline magmas offer the solution because they are associated with recycled sources (i.e. metasomatized lithospheric mantle and plumes) and, crucially, are found throughout the geological record. Here, we present a detailed study of sulphur isotope fractionation in a Mesoproterozoic alkaline province in Greenland and demonstrate that an enriched subduction-influenced source (δ34S of +1 to +5‰) can be reconstructed. A global δ34S compilation reveals secular variation in alkaline magma sources which support changes in the composition of the lithospheric mantle and/or Ga timescales for deep crustal recycling. Thus, alkaline magmas represent a powerful yet underutilized repository for interrogating crustal recycling through geological time.
Highlights
Earth’s surface and mantle sulphur reservoirs are connected via subduction, crustal recycling and volcanism
A key observation is that several OIBs2,3 show mass independent S isotope fractionation, a feature characteristic of Archaean age sedimentary rocks[4], which is usually expressed as Δ33S
A key issue is that the oceanic record only extends to ~200 Ma; ocean island basalts (OIBs) cannot reveal temporal variations in crustal recycling over Earth history
Summary
Gardar alkaline province (this study) Continental alkaline complexes Oceanic hotspot with alkaline volcanism
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