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Early Plate Tectonics and Dynamically Viable Crustal Evolution

This research investigates the possibility of dynamically viable plate tectonics in the early Earth, focusing on the convection with plates and tracers in the mantle. It explores the effects of buoyant oceanic crust, crust thickness, and tracer settling on the thermal evolution and composition of the Earth's crust.

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Early Plate Tectonics and Dynamically Viable Crustal Evolution

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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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