1 / 24

Vanished diamondiferous root beneath the Southern Superior Province

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. Outline. Study Area Samples/Methods Results: Carbon Isotopes

connley-bogue
Download Presentation

Vanished diamondiferous root beneath the Southern Superior Province

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 (Kaminsky et al, 2002) (Heaman and Kjarsgaard, 2000) (Kopylova et al, 2011)

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

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

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

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

  10. Olivine/Orthopyroxene OPX Average Al2O3 ~0.6 wt% 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/m2) • 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. Minimum Lithospheric Depth 41 39 (Kennedy and Kennedy, 1976; O’Neill, 1981; Rudnick et al, 1998; Girnis and Brey, 1999)

  14. Tectonic Origin/ Thermal Regime • Dominantly octahedral morphology/ peridotitic minerals • Mineral chemistry combined with carbon isotopes = depleted Harzburgite host • Cool thermal regime (39-41 mW/m2) and deep LAB (~190 km) 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. Thermal Evolution/Lithosphere Thickness Wawa Opatica Archean: 39-41 mW/m2 LAB ≥190 km Proterozoic: 45-46 mW/m2 LAB ~150 km Current: 41-42 mW/m2 LAB <150 km Archean: 39-41 mW/m2 LAB ≥190 km Jurassic: 42-44 mW/m2 LAB ~145 km Current: 41-42 mW/m2 LAB <150 km Heating

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

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

  20. Conclusions: Harzburgitic mantle host 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 42 28 46 48 • Archean average (41 mW/m2), Superior average (42 mW/m2) • 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

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

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

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

More Related