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Impact of Early Plate Tectonics on Earth’s Dynamics

Analyzing the role of plate tectonics in Earth's evolution, Geoff Davies from Australian National University investigates convection with plates, tracers, and mantle composition. Examining crust thickness, tracer concentrations, and the effects of different crust types, the study questions the viability of early plate tectonics and explores bimodal thermal evolution scenarios. Results suggest an early mantle depletion, thin oceanic crust from a refractory upper mantle, and the influence of dense layers in the upper mantle on apparent ages and mantle overturn rates. This research sheds light on Earth's dynamic history.

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Impact of Early Plate Tectonics on Earth’s Dynamics

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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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