Abstract
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS,
VOL. 12,
Q10016,
23 PP., 2011
doi:10.1029/2011GC003663
Continents, supercontinents, mantle thermal mixing, and mantle thermal isolation: Theory, numerical simulations, and laboratory experiments
- Supercontinents can cause a global transition in the thermal state of the mantle
- Supercontinent breakup has global effects from the core to climate
- Previous convection models that disagreed were mapping different regimes
Department of Earth Science, Rice University, MS 126, PO Box 1892, Houston, Texas 77251-1892, USA
School of Mathematical Sciences, Monash University, Clayton, Building 28, Victoria 3800, Australia
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia M5S 1A7, Canada
Department of Earth and Planetary Science, Macquarie University, Sydney, New South Wales 2109, Australia
School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA
Department of Earth Science, Rice University, MS 126, PO Box 1892, Houston, Texas 77251-1892, USA
Super-continental insulation refers to an increase in mantle temperature below a supercontinent due to the heat transfer inefficiency of thick, stagnant continental lithosphere relative to thinner, subducting oceanic lithosphere. We use thermal network theory, numerical simulations, and laboratory experiments to provide tighter physical insight into this process. We isolate two end-member dynamic regimes. In the thermally well mixed regime the insulating effect of continental lithosphere can not cause a localized increase in mantle temperature due to the efficiency of lateral mixing in the mantle. In this regime the potential temperature of the entire mantle is higher than it would be without continents, the magnitude depending on the relative thickness of continental and oceanic lithosphere (i.e., the insulating effects of continental lithosphere are communicated to the entire mantle). Thermal mixing can be short circuited if subduction zones surround a supercontinent or if the convective flow pattern of the mantle becomes spatially fixed relative to a stationary supercontinent. This causes a transition to the thermal isolation regime: The potential temperature increases below a supercontinent whereas the potential temperature below oceanic domains drops such that the average temperature of the whole mantle remains constant. Transition into this regime would thus involve an increase in the suboceanic viscosity, due to local cooling, and consequently a decrease in the rate of oceanic lithosphere overturn. Transition out of this regime can involve the unleashing of flow driven by a large lateral temperature gradient, which will enhance global convective motions. Our analysis highlights that transitions between the two states, in either direction, will effect not only the mantle below a supercontinent but also the mantle below oceanic regions. This provides a larger set of predictions that can be compared to the geologic record to help determine if a hypothesized super-continental thermal effect did or did not occur on our planet.
Received 15 April 2011; accepted 30 August 2011; published 22 October 2011.
Citation: (2011), Continents, supercontinents, mantle thermal mixing, and mantle thermal isolation: Theory, numerical simulations, and laboratory experiments, Geochem. Geophys. Geosyst., 12, Q10016, doi:10.1029/2011GC003663.
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