Hf isotopic compositions of the Napier Complex, Antarctica

Moreover, the results demonstrate that even the silicic rocks in the Napier Complex are not likely to have formed from remobilized older crustal materials, but were instead juvenile products of mantle melting. Measurement of Lu-Hf isotopic compositions for garnet, opx, sapphirine, osmulite, rutile and whole rock samples from several localities in the Napier Complex have yielded isochrons with ages between 2459 - 23 Ma and 2173 - 37 Ma with rather uniform initial ratios between 0.280876 and 0.280884.

Although the calculated errors are larger than those often obtained from zircon U-Pb dating, it should be noted that they are only slightly large than one percent. Attempts are being made to add data points to the isochrones with the anticipation that this will reduce the errors further. Besides producing isochrons, one major contribution of this work has been demonstration of what happens to the Lu-Hf system at the mineral and whole-rock scale during ultra high temperature (UHT) metamorphism.

The main rock-forming minerals record an initial Hf ratio acquired during metamorphism while zircons ?see through? this event and record the initial ratio of the rocks acquired at the time of crystallization.