|Title||Hadean silicate differentiation preserved by anomalous Nd-142/Nd-144 ratios in the Reunion hotspot source|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Peters B.J, Carlson R.W, Day JMD, Horan M.F|
|Type of Article||Article|
|Keywords||base; crust; deep-mantle; earths mantle; He-3/He-4; hf; high; Magma Ocean; nd; nd-142; ocean island basalts; Science & Technology - Other Topics|
Active volcanic hotspots can tap into domains in Earth's deep interior that were formed more than two billion years ago(1,2). High-precision data on variability in tungsten isotopes have shown that some of these domains resulted from differentiation events that occurred within the first fifty million years of Earth history(3,4). However, it has not proved easy to resolve analogous variability in neodymium isotope compositions that would track regions of Earth's interior whose composition was established by events occurring within roughly the first five hundred million years of Earth history(5,6). Here we report Nd-142/Nd-144 ratios for Reunion Island igneous rocks, some of which are resolvably either higher or lower than the ratios in modern upper-mantle domains. We also find that Reunion Nd-142/Nd-144 ratios correlate with helium-isotope ratios (He-3/He-4), suggesting parallel behaviour of these isotopic systems during very early silicate differentiation, perhaps as early as 4.39 billion years ago. The range of Nd-142/Nd-144 ratios in Reunion basalts is inconsistent with a single-stage differentiation process, and instead requires mixing of a conjugate melt and residue formed in at least one melting event during the Hadean eon, 4.56 billion to 4 billion years ago. Efficient post-Hadean mixing nearly erased the ancient, anomalous Nd-142/Nd-144 signatures, and produced the relatively homogeneous Nd-143/Nd-144 composition that is characteristic of Reunion basalts. Our results show that Reunion magmas tap into a particularly ancient, primitive source compared with other volcanic hotspots(7-10), offering insight into the formation and preservation of ancient heterogeneities in Earth's interior.