Where on Earth is the enriched Hadean reservoir? R. Andreasen a, ⁎ , M. Sharma a , K.V. Subbarao b , S.G. Viladkar c,1 a Radiogenic Isotope Geochemistry Laboratory, Department of Earth Sciences, Dartmouth College, 6105 Sherman Fairchild Hall, Hanover NH 03755, USA b Center for Earth & Space Sciences, University of Hyderabad, Hyderabad 500 046, India c Department of Geology, St. Xavier's College, 5, Mahapalika Marg, Mumbai 400 001, India Received 4 May 2007; received in revised form 3 October 2007; accepted 4 October 2007 Edited by: R.W. Carlson Available online 13 October 2007 Abstract We report the results of an exhaustive search conducted to find 142 Nd anomalies in the rocks associated with the Deccan and Iceland plumes. High-precision Nd isotopic measurements for the samples were inter-leaved with that for laboratory standards; the latter demonstrating an external reproducibility of 6 ppm (2σ). No measurable 142 Nd anomalies were found in Deccan picrites and basalts despite earlier indications to the contrary. Primitive Icelandic ankaramites and basalts with primordial He and Ne isotopic signatures, and ultrabasic Deccan rocks (carbonatite/nephelinite) also do not show any anomalies. It is likely that deep mantle plume-derived lavas do not carry the negative 142 Nd anomalies that are expected for an enriched Hadean reservoir with subchondritic Sm/Nd. It is evident from meteorite data that an enriched Hadean reservoir has to exist, unless the Bulk Earth accreted with a Sm/Nd ratio that was at least 3.5% higher than the chondrite average. The enriched Hadean reservoir may be (i) subducted protocrust in the D″ layer, in which case negative 142 Nd anomalies and primordial noble gases would be associated with each other, (ii) the first cumulates of a magma ocean in the lower mantle, in which case negative 142 Nd and primordial noble gases may be decoupled, or (iii) the core, in which case searches for negative 142 Nd anomalies in mantle derived rocks are futile. Experiments at core-forming temperatures, pressures, composition, and oxidation states are needed to constrain possible REE partitioning into the core. © 2007 Elsevier B.V. All rights reserved. Keywords: 142 Nd; mantle plume; early enriched reservoir; Magma Ocean; Deccan traps; Iceland 1. Introduction The segregation of Earth into distinct geochemical reservoirs shortly after its accretion is well established from temporal constraints on core (b 30 Ma) (Yin et al., 2002; Kleine et al., 2002) and atmosphere (b 50 Ma) (Allegre et al., 1987; Ozima and Podosek, 1999) formation. The time and magnitude of differentiation of the silicate mantle is less constrained. Enriched oxy- gen and hafnium isotope signatures, and Ti-thermometry in Hadean zircons have been interpreted as evidence of the presence of oceans, continental crust, and the operation of plate tectonics at 4.3–4.5 Ga (Wilde et al., 2001; Mojzsis et al., 2001; Harrison et al., 2005; Watson and Harrison, 2005). These interpretations, however, Available online at www.sciencedirect.com Earth and Planetary Science Letters 266 (2008) 14 – 28 www.elsevier.com/locate/epsl ⁎ Corresponding author. Present address: Department of Earth Science and Engineering, South Kensington Campus, Imperial College London, SW7 2AZ, United Kingdom. Tel.: +44 20 7594 6474; fax: +44 20 7594 7444. E-mail address: r.andreasen@imperial.ac.uk (R. Andreasen). 1 Present address: Carbonatite Research Centre Amba Dongar, Kadipani, 391175 Gujarat, India. 0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2007.10.009