Fig. 4: Relationship between external 3He, 4He and 40Ar excesses within the groundwater samples that have a mantle contribution.
From: Passive degassing of lithospheric volatiles recorded in shallow young groundwater
3He/4Heext vs 4He/40Ar*ext from the mantle-influenced samples (n = 13) is used to model the expected mixing between mantle and crustal endmembers (grey line). The black square represents the most likely mantle composition (SCLM) based on a 4He/40Ar* within the mantle range (2 ± 1 (ref. 8)). Tick marks represent a 75%, 50% and 25% mantle contribution. The crustal 4He/40Ar* is probably highly fractionated, but changing this value only has minimal effect on the mantle endmember composition. Symbol colours represent the 40Ar* concentration within the samples and external values ± 1σ uncertainties are shown. The four dominantly crustal samples high the highest 4He/40Ar*ext and lowest 3He/4Heext.
