Crust generation history revealed by analysis of platinum-group alloys

(13 September 2007)

The timing and mode of extraction of the Earth’s continental crust from the mantle have remained important but controversial issues for the past 40 years. Radiometric ages for the formation of new continental crust cluster around key times, at 1.2 Gy, 1.9 Ga, 2.7 Ga and 3.3 Ga. This age clustering can be interpreted in numerous different ways, varying from preferential preservation to pulsed generation of crust through time. Research carried out at the Northern Centre for Isotopic and Elemental Tracing by Graham Pearson, Steve Parman and Geoff Nowell reveals the first record of major mantle melting events in the earth’s mantle that can be linked to the crustal age peaks. The mantle ages, derived by laser-ablation of platinum-group alloy grains for Os isotope compositions, cluster around the same ages as those of crust formation, but older ages become scarcer in the mantle because of the destructive effects of convection. The data provide robust evidence that the Earth’s crust evolved in pulses. The mantle melting events responsible for leaving these signatures must have been major and indicate that crust formation may be more intimately associated with the production of basic magmatism than previously thought. The reference is:- A link between large mantle melting events and continent growth seen in osmium isotopes, D.G. Pearson, S.W. Parman and G.M. Nowell (2007) Nature, Sept 13th.