Lu–Hf and Sm–Nd isotopic systematics in chondrites and their constraints on the Lu–Hf properties of the Earth P.J. Patchett a, * , J.D. Vervoort a,1 , U. So ¨derlund a , V.J.M. Salters b a Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA b National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, Tallahassee, FL 32306, USA Received 15 August 2003; received in revised form 6 February 2004; accepted 19 February 2004 Abstract Sm – Nd and Lu – Hf isotopic data are presented for 19 chondritic meteorites: six carbonaceous chondrites, five L-chondrites, seven H-chondrites, and a single enstatite chondrite. The primary goal of the study is to better define the Bulk Silicate Earth (BSE) reference values for Hf isotopes. Except for one sample with lower Sm/Nd, the Sm – Nd data define a cluster around the accepted reference values for chondrites and terrestrial planets, giving a mean 147 Sm/ 144 Nd of 0.1960 F 0.0005, and a mean 143 Nd/ 144 Nd of 0.512631 F 0.000010 (uncertainties are two standard errors). It seems appropriate to retain the presently accepted Sm – Nd reference parameters, 147 Sm/ 144 Nd = 0.1966 and 143 Nd/ 144 Nd = 0.512638 (when fractionation-corrected to 146 Nd/ 144 Nd = 0.7219). Lu – Hf isotopic data are not clustered, but spread along an approximate 4.5-Ga isochron trend, with a range of 176 Lu/ 177 Hf from 0.0301 to 0.0354. The data are similar to many of the samples of chondrites presented by Bizzarro et al. [Nature 421 (2003) 931], but lack the range to lower Lu/Hf shown by those authors. Our chondrite data define a regression line of 4.44 F 0.34 Ga when 1.867 Â 10 À 11 year À 1 is used for the decay constant of 176 Lu [Science 293 (2001) 683; Earth Planet. Sci. Lett. 219 (2004) 311 – 324]. Combining our data with the main population of analyses from Bizzarro et al. [Nature 421 (2003) 931] yields 4.51 F 0.24 Ga. Unless samples of eucrite meteorites and deviating replicates of chondrites with 176 Lu/ 177 Hf less than 0.030 are employed, no combination of the main population of chondrite Lu – Hf data yields a regression with sufficiently low error to constrain the decay constant of 176 Lu. Sample heterogeneity seems to hinder the acquisition of reproducible Lu – Hf analyses from small, manually ground pieces of chondrites, and we suggest that analysis of powders prepared from large volumes of meteorite will be needed to adequately characterize the Lu – Hf isotope systematics of chondritic reservoirs and of BSE. Our results for carbonaceous chondrites show higher average 176 Lu/ 177 Hf and 176 Hf/ 177 Hf than ordinary chondrites, and the mean of carbonaceous chondrites also coincides with replicate analyses of a powder representing a large volume of meteorite, the Allende powder from the Smithsonian Institution. Use of the carbonaceous chondrite mean for BSE Lu – Hf characteristics results in a BSE Hf – Nd point that lies well within the array of terrestrial compositions, and leads to plausible initial e Hf values for Precambrian rocks. An improved objective resolution of meteorite data and of meteoritic models for the Earth needs to occur before BSE can be established for Lu – Hf. D 2004 Elsevier B.V. All rights reserved. Keywords: chondrites; Lu-Hf and Sm-Nd isotopic systematics; bulk silicate earth 0012-821X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2004.02.030 * Corresponding author. Tel.: +1-520-621-2070; fax: +1-520-621-2672. E-mail address: patchett@geo.arizona.edu (P.J. Patchett). 1 Present address: Department of Geology, Washington State University, Pullman, WA 99164, USA. www.elsevier.com/locate/epsl Earth and Planetary Science Letters 222 (2004) 29 – 41