Zircon mantle evolution

Figure 3 Mantle evolution defined by the initial snf of juvenile granites and their zircon separates. The snf compositions (closed symbols) have been recalculated using the most recently proposed Lu decay constant of Bizzarro et al. (2003). For comparison are shown the initial values (open symbols) calculated using the Blichert-Toft and Albarede (1997) decay constant. Note that the change of decay constant results in an increase in calculated initial SHf compositions of some Early Archean samples. The current database suggests rapid Lu/Hf fractionation in the early Earth and the possibility of episodic changes in mantle evolution similar to that seen in SNd evolution (sources Vervoort and Blichert-Toft, 1999 Amelin et al., 1999, 2000 ...

It has been recognized that the Lu-Hf isotopic system in zircon is a powerful tool for deciphering the evolution of the earth s crust and mantle. " Zircon normally contains 0.5-2 wt % Hf, which results in an extremely low Lu/Hf ratio (" Lu/" Hf < 0.002) and consequently a negligible radiogenic growth of Hf due to the decay of Lu. Therefore, the Hf/" Hf ratio of zircon can be regarded as the initial value at the time when it crystaUized. LA-ICP-MS with a multiple ion collector system has also been employed to study the hafnium isotopic composition of zircon and baddeleyite standards in U-Pb geochronology. °°... 

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