Geochemical evidence for Archean plate tectonics in the 2.7 to 3.0 Ga Uchi

Subprovince, northern Ontario

Pete HollingsLakehead 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

From Hollings et al. (1999). Lithos, 46, 137-161

Komatiites

Tholeiites

2.9 to 3.0 Ga assemblages

From Hollings et al.

(1999). Lithos, 46, 137-

161

Jefferson Lake

Bar Lake

Gargoyle Lake

3 km

N

Felsics

~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

From Wyman & Hollings (2006)

• 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)

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