1. F ORMATION OF E ARTH ’ S CRUST Continental and oceanic crust Melissa Maisonneuve Oct 2011

2. M AJOR E LEMENTS & M INERALOGY Oceanic (MORB) Continental SiO 2 45.2 49.4 60.3 TiO 2 0.7 1.4 1.0 Al 2 O 3 3.5 15.4 15.6 MgO 37.5 7.6 3.9 FeO 8.5 10.1 7.2 CaO 3.1 12.5 5.8 Na 2 O 0.6 2.6 3.2 K 2 O 0.1 0.3 2.5 Total 99.2 99.3 99.5 Mantle *in weight percent Mineralogy (oxygen units, XFe 3+ = 0.10) Quartz 0.0 0.0 13.0 Feldspar 13.2 57.3 64.3 C-pyroxene 6.7 25.7 5.9 O-pyroxene 18.3 4.1 14.7 Olivine 59.9 9.9 0.0 Oxides 1.8 3.0 2.0

3. M AJOR E LEMENTS & M INERALOGY Oceanic (MORB) Continental SiO 2 45.2 49.4 60.3 TiO 2 0.7 1.4 1.0 Al 2 O 3 3.5 15.4 15.6 MgO 37.5 7.6 3.9 FeO 8.5 10.1 7.2 CaO 3.1 12.5 5.8 Na 2 O 0.6 2.6 3.2 K 2 O 0.1 0.3 2.5 Total 99.2 99.3 99.5 Mantle *in weight percent Mineralogy (oxygen units, XFe 3+ = 0.10) Quartz 0.0 0.0 13.0 Feldspar 13.2 57.3 64.3 C-pyroxene 6.7 25.7 5.9 O-pyroxene 18.3 4.1 14.7 Olivine 59.9 9.9 0.0 Oxides 1.8 3.0 2.0

4. T RACE ELEMENTS Concentration/Primitive mantle

5. C RUSTAL FORMATION WITH TIME Early crust  hot mantle melting (komatiites, TTGs) Increased stability of cratons over time allowing build- up of crust Taylor & McLennan 1995

6. P UNCTUATED CRUSTAL PRODUCTION ? McCulloch & Bennett (1994) Sm-Nd model crustal ages from Aus, N.Am, Scan. cratons (ziron & whole rock)

7. T RACE ELEMENTS

8. T WO - STAGE M ODEL (H OFMANN 1988) Primitive mantle Continental crust 1) extraction of continental crust (1.5% melting*) 2) formation of oceanic crust (8-10% melting*) Oceanic crust (MORB) *batch or partial melting- either are presented by the author

9. T HERMAL PULSE MODEL (D AVIES 1995) Thermal pulses Mantle overturn events

10. T HERMAL PULSE MODEL (D AVIES 1995) Thermal pulses Mantle overturn events Increased production @ ridges (thicker oceanic crust) Crustal thickening (stabilize of cratons?) Wait…. no subduction?! HOTTER NOT SO HOT Flood basaltsSpreading centre

11. L OW - ANGLE SUBDUCTION (F LAT - SUBDUCTION ) Smithies et al (2003) Many Archean low-Mg TTGs Dearth of calc-alkaline-type rocks in Archean Continental crust: p. melting right off the oceanic slab (without wedge) Eclogite residue from TTG formation delaminates back to mantle

12. B ACK TO … NOW

13. “G OD D IAGRAM ”  D ON F RANCIS

16. R EFERENCES Davies, G.F. (1995) Punctuated tectonic evolution of the earth. Earth & Planetary Science Letters, 136 : 363-379. Francis, D. Course notes from EPSC 423 Igneous Petrology, McGill University (2009) Hawkesworth, C.J. & Kemp, I.S. (2006) Evolution of the continental crust. Nature, 443 : 811-817 Hofmann, A.W. (1988) Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust. Earth & Planetary Science Letters, 90 : 297-314. McCulloch, M.T. & Bennett, V.C. (1994) Progressive growth of the Earth’s continental crust and depleted mantle: Geochemical constraints. Geochimica et Cosmochimica Acta, 58 (21): 4717-4738. Smithies, R.H., Champion, D.C. & Cassidy, K.F. (2003) Formation of Earth’s early Archaean continental crust. Precambrian Research, 127 : 89-101 Taylor, S.R. & McLennan, S.M. (1995) The geochemical evolution of the continental crust. Reviews of Geophysics, 33 : 241-265.

17. M IDTERM QUESTION Why is it difficult to model crustal production in the Archaen (e.g. any time before the Phanerozoic)? Tectonics, geochemistry…