GLOBAL 1°X1° THERMAL MODEL FOR THE CONTINENTAL LITHOSPHERE: IMPLICATIONS FOR LITHOSPHERE GROWTH SINCE ARCHEAN
Statistical analysis of continental geotherms reveals that thick (>250 km) lithosphere is restricted solely to young Archean terranes (2.6-3.0 Ga), while in old Archean cratons (3.0-3.6 Ga) lithospheric roots do not extend deeper than 200-220 km. It is proposed that the former were formed by tectonic stacking and underplating during paleocollision of continental nuclei. It is likely that such exceptionally thick lithospheric roots have a limited lateral extent and are restricted to paleoterrane boundaries. This conclusion is supported by an analysis of the present-day lithospheric volume for terranes of different ages, which does not reveal a peak in lithospheric volume at 2.6-2.7 Ga as expected from growth curves for juvenile crust. The absence of the peak can be attributed to lithosphere recycling back into the mantle; recycling rates for lithospheric mantle are presented for different geological ages since Archean until present.