Plate tectonics on a hotter Earth: the role of rheology Jeroen van Hunen ETH Zurich, Switzerland [email protected] in collaboration with: Arie van den Berg (Utrecht Univ) thanks to: Herman van Roermund (Utrecht Univ) Taras Gerya (ETH Zurich). Conclusions. In a hotter Earth:
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(van Thienen et al., 2004)
More melting at MOR implies thicker basalt & harzburgite layers
more compositional buoyancy
less gravitational instability
(slab pull? subduction? plate tectonics?)
DTpot = 0 K 100 K 200 K 300 K
For low DTpot subduction looks like today’s
For higher Tpot more frequent slab breakoff occurs,
… or subduction stops completely.
Higher yield stress 1 GPa: faster subduction in hotter Earth, because slab break-off occurs less frequent
Fault friction of 5 MPa (at 5 cm/yr subduction velocity): stabilizing effect
Slow eclogitization may keep plate too buoyant for efficient subduction in a 200-300 K hotter Earth
Crustal material experiences very high pressure/metamorphism, and
subsequently somehow makes it to the surface again.
More crustal decoupling, stronger wedge: crustal delamination + more frequent breakoff stop subduction process
Strong harzburgitic depleted mantle: thermal weakening still more important
Bulk density for a 100-km thick lithosphere with different
crustal thicknesses and compositions (from Cloos, 1993)
(Zegers & van Keken, 2001)
Flake tectonics (Hoffman & Ranalli, 1988)
Today, continental lithosphere
shows ‘sandwich’ rheology. In past
maybe all plates showed that, with
less plate and more ductile material
in between. The two layers might
have started convecting separately.
(Kohlstedt et al., 1995)
Continental overflow as Archean
Violent overturns in the mantle could have
produced Archean mantle lithosphere
(McCulloch and Bennett, 1994)
Remaining ~40 mW/m2 from cooling the Earth?
Or qs was 2 – 4 times higher than today (very efficient tectonics!), or Earth
heating up instead of cooling down.
Model setup (3)
surface heat flow from
Simple convection with T-dependent
viscosity gives ‘thermal catastrophe’.
(Calvert et al., 1995)
(Maruyama & Liou, 1998)