GROWTH, PRESERVATION AND RECYCLING RATE OF THE LITHOSPHERE SINCE THE ARCHEAN

A global 1 deg x 1 deg compilation of tectono-thermal ages of continental lithosphere combined with a global 1 deg x 1 deg model of lithospheric thermal thickness for the continents (Artemieva, 2006, Tectonophysics), is used to (a) to evaluate the volume of the preserved continental lithosphere of different ages and (b) to calculate lithospheric growth and recycling rates over the past 3.6 Ga. The age of the crust is assumed to be representative of the age of the underlying subcrustal lithosphere; submerged areas with continental crust are excluded from the analysis. The results show a general agreement between the growth rates of the continental lithosphere and juvenile crust. A pronounced peak in the rate of lithospheric growth (10-18 km3/year) at 2.1-1.7 Ga correlates with a peak in the growth of juvenile crust. However, growth models for the lithosphere do not reveal a peak in litho¬spheric volume at 2.6-2.7 Ga as expected from growth curves for juvenile crust. The absence of the peak can be attributed to a lithosphere recycling back into the mantle, since the curves for the “growth” rate of the continental lithosphere refer not to the volume of the juvenile lithosphere, but reflect the cumulative effect of lithospheric growth and preservation. Assuming that the ratio of juvenile crust to juvenile lithospheric mantle produced by mantle differentiation is constant throughout the geological evolution, recycling rates for lithospheric mantle since Archean until present are calculated for several models of crustal growth. The results suggest that, in the Archean, both the crust and the lithospheric mantle were recycled into the mantle at the same rate. Alternatively, they can be interpreted as indicating no recycling of the Archean lithospheric mantle older than 3.0 Ga and very limited recycling of the Archean lithosphere that is 3.0-2.0 Ga old, reflecting stabilization of cratonic lithosphere by the late Archean.