Primitive mantle neodymium isotopes

Mantle evolution curves for neodymium isotopic compositions in the Earth prior to 2.7 Ga are much less well defined than for younger time periods. Many studies have elected simply to extrapolate a linear evolution from 2.7 Ga to the composition of the primitive mantle (snu = 0) at 4.56 Ga (e.g., Goldstein et al., 1984). In contrast, other studies have attempted a more precise definition of the neodymium mantle evolution curve for the Archean based on observed compositions (e.g., Bennett et al., 1993 Bowring and Housh, 1995 Vervoort and Blichert-Toft, 1999). The justification of these efforts is that Archean mantle chemistry, particularly for the long-lived isotopic systems, provides a window into the first 700 Myr of Earth s history, prior to establishment... 

TrCHUR model ages The CHUR model assumes that the Earth s primitive mantle had the same isotopic composition as the average chondritic meteorite at the formation of the Earth, which in this case is taken to be 4.6 Ga. For neodymium isotopes CHUR is synonymous with the composition of the bulk Earth. A model age calculated reladve to therefore is the time in the past at which the... 

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