Geochemical evidence for Archean plate tectonics in the 2. 7 to 3 Geochemical evidence for Archean plate tectonics in the 2.7 to 3.0 Ga Uchi Subprovince, northern Ontario Pete Hollings Lakehead University

The Uchi subprovince Multiple assemblages ranging in age from 2.7 to 3.0 Ga Younger assemblages formed on the margins of the ~3 Ga protocontinental North Caribou Terrane Modified after Stott & Corfu (1991)

2.9 to 3.0 Ga assemblages Komatiites Tholeiites From Hollings et al. (1999). Lithos, 46, 137-161

2.9 to 3.0 Ga assemblages Felsics From Hollings et al. (1999). Lithos, 46, 137-161 J ef fer son Lak e Bar Gar go yle 3 km N

~2.7 Ga assemblages From Hollings & Kerrich (2000). Contributions to Mineralogy and Petrology, 139, 208-226

Mantle Nb/Y vs Zr/Y arrays Phanerozoic arcs plot along the MORB array Archean Wawa basalts require a different source P = slope of the Iceland plume M = modern MORB array Arc data from Gamble et al. (1994), Pearce et al. (1995), Elliot et al. (1997), Wyman (2003) From Wyman & Hollings (2006)

Mantle Nb/Y vs Zr/Y arrays From Wyman & Hollings (2006)

Mantle Nb/Y vs Zr/Y arrays From Wyman & Hollings (2006)

Conclusions Greater role for plumes from 2.9 to 3.0 Ga but still evidence of arc magmatism Increasing evidence for Phanerozoic processes from 2.8 to 2.9 Ga By 2.7 Ga plate tectonic processes similar to those of the Phanerozoic generate comparable suites of rocks