Fig. 7: Comparison of Ne, He and Nd isotopes in kimberlites.
From: Primordial neon and the deep mantle origin of kimberlites
Olivine 21Ne/22NeS versus (a) 4He/3He; and (b) bulk-rock Nd isotopes in the samples from this study and Sumino et al. 22 (S + 2006). Each symbol represents analyses of the same sample, with smaller symbols indicating 20Ne counts <1 × 10−11. 21Ne/22NeS is the extrapolation of 21Ne/22Ne to 20Ne/22Ne = 12.5. Panel a shows mixing trajectories between a plume component from the lower mantle (either ‘source’, ‘melt’ or a ‘fluid’ exsolved therefrom) with the isotopic composition of the Baffin picrites (‘plume’6,16); or an upper mantle component with the isotopic composition of MORBs (‘DMM’1); and subducted oceanic crust (‘subducted crust’ mixed in the source), metasomatised sub-continental lithospheric wall rocks (‘SCLM’ assimilated during ascent) and continental crust contaminant (‘crust’ contributing to the exsolved fluid). The % values next to the mixing curves indicate the amount of crustal or lithospheric mantle component added. Details of the endmember compositions employed for mixing are in ‘Methods’. Note that while mixing models involving SCLM wall rocks intersect the compositions of olivine in kimberlites, these models require unrealistically large contributions (generally >70%) from the lithospheric mantle. The high 21Ne/22NeS calculated for Karowe and Letseng (Lesotho-Monastery) are probably unrealistic (see ‘Methods’).
