1. Vanished diamondiferous root beneath the Southern Superior Province Christine Miller Master’s Candidate, UBC Maya Kopylova Department of Earth and Ocean Sciences, UBC John Ryder Dianor Resources Inc.

2. Outline Study Area Samples/Methods Results: Carbon Isotopes Inclusion Chemistry Thermobarometry Origin of Diamonds Thermal Regime Destruction of the Diamondiferous Root

3. Study Area (Kopylova et al, 2011) (Kaminsky et al, 2002) (Heaman and Kjarsgaard, 2000)

4. Samples/Methods: Diamonds 65 diamonds of variable size, color, resorption and morphology Analysis: Carbon Isotopes

5. Results: Carbon Isotopes Mantle range Metaconglomerate Diamonds (N=14) Eclogitic Peridotitic

6. 1-21 inclusions in each diamond (avg. 5) Colors: purple, colorless, brown/ black <100-500  m in size Morphology dominantly diamond controlled Analysis: Polishing to expose inclusions Electron microprobe Samples/Methods: Inclusions

7. Results: Inclusion Chemistry Polished and exposed inclusions in 46 diamonds Microprobe analyses of 173 inclusions

8. Garnet (N=19) (Gurney and Zweistra 1995; Grutter et al. 2006) HarzburgiticLherzolitic

9. Chromite (N=94) (Gurney and Zweistra 1995; Sobolev et al 2004) Average FeO ~ 14 wt%

10. Olivine/Orthopyroxene Average Al 2 O 3 ~0.6 wt%OPX OLV

11. Mineral Equilibration Mg# orthopyroxene (94) > Mg# olivine (93) Low Al content in orthopyroxene (>1.5 wt%) = garnet peridotite High Fe in chromite = garnet peridotite Mineral phases are well equilibrated and suitable for thermobarometry Origin within garnet facies peridotite (i.e. spinel-garnet or garnet only) (Brey and Kohler 1990; Boyd et al. 1997)

12. Results: Thermobarometry Thermometers: O’Neill and Wood (1979): garnet- olivine/ 1055-1232°C @ 50 kbar Ryan et al. (1996): Zn-in-chromite/ 993-1558°C Barometers: Grutter et al. (2006): 35-49 kbar (41 mW/m 2 ) Girnis and Brey (1999): 55-58 kbar @ 1000-1100°C Sample Wsc13: garnet-olivine-orthopyroxene 9 PT pairings: 5 thermometers, 2 barometers (Gurney and Zweistra 1995; Grutter et al. 2006)

13. (Kennedy and Kennedy, 1976; O’Neill, 1981; Rudnick et al, 1998; Girnis and Brey, 1999) 39 41 Minimum Lithospheric Depth

14. Dominantly octahedral morphology/ peridotitic minerals Mineral chemistry combined with carbon isotopes = depleted Harzburgite host Cool thermal regime (39-41 mW/m 2 ) and deep LAB (~190 km) Tectonic Origin/ Thermal Regime Origin in Pre-2.7 Ga Cratonic Root (Stachel and Harris 2008)

15. Proterozoic Kimberlite Barren kimberlite ~50 km NE of metaconglomerate 1.1 Ga (Kaminsky et al., 2002)

16. Jurassic Kimberlite Max diamond grade ~0.02 ct/t (Brummer 1992, Vicker, unpublished data) ~156 Ma, (Heaman and Kjarsgaard 2000) Present Day T @ Moho

17. Archean: 39-41 mW/m 2 LAB ≥190 km Jurassic: 42-44 mW/m 2 LAB ~145 km Current: 41-42 mW/m 2 LAB <150 km Archean: 39-41 mW/m 2 LAB ≥190 km Proterozoic: 45-46 mW/m 2 LAB ~150 km Current: 41-42 mW/m 2 LAB <150 km Thermal Evolution/Lithosphere Thickness WawaOpatica Heating

18. (Faure et al. 2011) Destruction of the diamondiferous cratonic root WA OP

19. Dharwar Craton (Kumar et al. 2007) (Zhang et al. 2011) North China Craton

20. Conclusions: 1.Harzburgitic mantle host 2.Cool, deep Archean lithosphere in the diamond stability field prior to 2.7 Ga 3. Minor heating of the mantle lithosphere from the Archean to present day 4. Thinning of the Southern Superior lithospheric root removing it from the diamond stability field (Faure et al. 2011)

21. Current Thermal State Archean average (41 mW/m 2 ), Superior average (42 mW/m 2 ) Variable heat flow measurements within subprovinces Heat flow not affected by crustal thickness or age, only composition (Mareschal et al. 2000) Remove crustal component to get mantle heat flow 48 28 42 46

22. Dharwar Craton, India Past lithospheric root in the DSF Partial destruction/thinning Modern seismic studies reveal lithospheric thickness of ≤100 km or less (Kumar et al. 2007)

23. North China Craton Weakening of lithosphere through subduction-related hydration Lithospheric folding during Mesozoic causes dripping or delamination of weakened lithosphere (Zhang et al. 2011) (Kusky et al. 2007) Complete removal of lithospheric root beneath Eastern Block

24. (Kennedy and Kennedy, 1976; Rudnick et al, 1998; Girnis and Brey, 1999)