Supplement A Analytical Techniques 1. Electron Microprobe Analyser (EMPA) – external standard reproducibility The San Carlos (NMNH 111312-44) supplied by the Smithsonian acted as internal and external standard. To ensure stability, it was analysed as an external standard regularly throughout each of five analysis sessions between real unknowns. The mean and repeatability or relative standard deviation (RSD) is based on the total analysis performed over these sessions and is presented in S1. The accuracy is based on the values presented in Batanova et al. (2015). The oxides marked by a star have fewer analysis included for evaluation of instrumental effects due to a software glitch. S1. San Carlos olivine (NMNH-111312-44) Oxid e Mean n RSD% Accuracy % SiO 2 41 48 0.46 99 TiO 2 0.010 48 4.9 244 Al 2 O 3 0.037 46 2.6 112 FeO 9.8 48 0.25 103 MnO 0.14 48 0.81 101 MgO 49 48 0.50 99 CaO 0.093 48 1.0 100 Na 2 O 0.009 48 8.7 101 P 2 O 5 * 0.005 41 20 107 1
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Supplement A
Analytical Techniques
1. Electron Microprobe Analyser (EMPA) – external standard reproducibility
The San Carlos (NMNH 111312-44) supplied by the Smithsonian acted as internal and
external standard. To ensure stability, it was analysed as an external standard regularly
throughout each of five analysis sessions between real unknowns. The mean and
repeatability or relative standard deviation (RSD) is based on the total analysis performed
over these sessions and is presented in S1. The accuracy is based on the values presented in
Batanova et al. (2015). The oxides marked by a star have fewer analysis included for
evaluation of instrumental effects due to a software glitch.
Table S 5 End-member melt compositions used in the forward modelling for olivine compositions from a
pyroxenitic and peridotitic-derived source. The peridotitic composition is based on run 30.14 from Walter
(1998) and Ni content calculated by Sobolev et al. (2007) while the pyroxenitic melt composition is from
Sobolev et al. (2007).
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Evaluation of secondary effects on the 3He/4He isotopic composition in olivine
We tested for possible helium isotope modifications via secondary (crustal) processes in the suite of
samples used for this study to ensure that the variations observed are source controlled rather than
secondary. Melts which have experienced degassing and subsequent loss of helium, become more
susceptible to contamination from radiogenic 4He, either via crustal contamination or radiogenic in-
growth. Addition of atmospheric-derived helium, which would decrease the 3He/4He, to melts which
have undergone significant degree of degassing is also possible (e.g., Harðardóttir et al., 2018). We
tested for possible modifications following magmatic evolution by plotting the 3He/4He isotopic
composition of the olivines used in this study (from Harðardóttir et al., 2018) with the respective Fo
content, analysed in this study for the same sample set (Figure 1S). Importantly, lack of any
correlation confirms, that any variation recorded in 3He/4He is unlikely to be affected by secondary
magmatic processes such as fractional crystallisation, here represented by a lowering in Fo content.
Figure S 1 A plot of 3He/4He and their respective Fo content. A lack of correlation confirms that measured 3He/4He in the olivine used in this study are unaffected by magmatic processes and rather represent primary mantle-derived variations.
We further evaluated possible effects of degassing on the 3He/4He for the specific olivine samples
used in this study by making a graph similar to Harðardottir et al., (2018) which uses helium
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concentrations versus 3He/4He in Figure S2. Again, we observe no correlations between measured
3He/4He and He conc. confirming that degassing, which would lower the He concentration, does not
affect the He isotope systematics of the olivine targeted in this study, which is in line with the
observations by Harðardóttir et al., (2018) for Icelandic olivine.
Figure S 2 A plot of helium concentrations versus 3He/4He with data compiled by Harðardottir et al. (2018). A lack of correlation suggests, that degassing plays no role in controlling the helium isotopes measured in the sample suite used in this study.
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References
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