Fig. 6
From: Mantle-derived fluids in the Nankai Trough Kumano forearc basin
Mean Ra values from arc-related fluids worldwide versus age of the subducted sediment. Data from Hilton et al. 2002 (green circles), Moreira et al. 2003 (purple square) and Chavrit et al. 2016 (red diamonds). The trend to lower helium isotope ratios with increasing slab age is due to a combination of mantle helium lost and ingrowth of radiogenic helium. Own data (blue circles) show additional input of crustal helium from another source