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Dynamically viable early plate tectonics?

Dynamically viable early plate tectonics?. Geoff Davies Research School of Earth Sciences, Australian National University. Convection with plates and tracers (present mantle). Tracers:. Trace basaltic component of mantle composition

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Dynamically viable early plate tectonics?

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  1. Dynamically viable early plate tectonics? • Geoff Davies • Research School of Earth Sciences, Australian National University

  2. Convection with plates and tracers (present mantle)

  3. Tracers: • Trace basaltic component of mantle composition • Upper melting zone: - defined by melting depth - move tracers into “crust” • Store times of “sampling”

  4. Crust thickness and tracer concentration profile

  5. Tracer settling vs Temp

  6. Thickness of oceanic crust

  7. Presentcool mantleEarly hot mantle? ?

  8. Effect of buoyant oceanic crust

  9. Standard thermal evolution

  10. Effect of thick oceanic crust:

  11. Effect of buoyant crust(reduced by 1.8)

  12. Conclusions • Strong early depletion of the upper mantle • Thin oceanic crust from hot, refractory upper mantle • Viable plate tectonics? • Bimodal thermal evolution?

  13. Spacer

  14. Thinning crust at high T:

  15. Reduced effect of crust(like eclogite effect)

  16. To explain: apparent ages ~1.8Ga (Pb-Pb), MORB-OIB differences

  17. Results with heavy tracers: mean ages > 2 Ga dense layer at bottom gradient through upper mantle

  18. Run at present mantle temperature:same number of overturns

  19. Hot early mantle,1550°C

  20. Hot mantle,1550°C

  21. Thickness of oceanic crust

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