Tracking Hadean processes in modern basalts with 142-Neodymium

The short-lived Sm-146 -> Nd-141 isotope system (t(1/2) = 103 Ma) provides constraints on the timing and processes of terrestrial silicate fractionation during the early Hadean. Although some Archean terranes preserve variability in Nd-142/Nd-144, no anomalies have been resolved previously in young rocks. This study provides high precision Nd-142/Nd-144 data on a suite of ocean island basalts from Samoa and Hawaii previously shown to have variable depletions in W-182/W-184 that are inversely correlated with He-3/He-4 ratios. Improved analytical techniques and multiple replicate analyses of Nd show a variation in mu Nd-142 values between -1.3 and +2.7 in the suite, relative to the JNdi standard. Given the reproducibility of the standard (+/- 2.9 ppm, 2 SD), two Samoan samples exhibit resolved variability in their Nd-142/Nd-144 ratios outside of their 95% confidence intervals, suggesting minor variability in the Samoan hotspot. One sample from Samoa has a higher mu Nd-142 of +2.7, outside the 95% confidence interval (+/- 1.0 ppm) of the average of the JNdi standard. Limited, but resolved, variation in Nd-142/Nd-144 within the suite suggests the preservation of early Hadean silicate differentiation in the sources of at least some basalts from Samoa. Larger variations of W-182/W-184 and He-3/He-4 ratios in the same samples suggest that metal-silicate separation and mantle outgassing left a more persistent imprint on the accessible mantle compared to Nd-142/Nd-144 ratios which are impacted by early silicate differentiation. (C) 2017 Elsevier B.V. All rights reserved.