Heat fluxes at the Earth's surface and core–mantle boundary since Pangea formation and their implications for the geomagnetic superchrons
2011
Zhang, Nan | Zhong, Shijie
The Earth's surface and core–mantle boundary (CMB) heat fluxes are controlled by mantle convection and have important influences on Earth's thermal evolution and geodynamo processes in the core. However, the long-term variations of the surface and CMB heat fluxes remain poorly understood, particularly in response to the supercontinent Pangea — likely the most significant global tectonic event in the last 500Ma. In this study, we reconstruct temporal evolution of the surface and CMB heat fluxes since the Paleozoic by formulating three-dimensional spherical models of mantle convection with plate motion history for the last 450Ma that includes the assembly and break-up of supercontinent Pangea. Our models reproduce well present-day observations of the surface heat flux and seafloor age distribution. Our models show that the present-day CMB heat flux is low below the central Pacific and Africa but high elsewhere due to subducted slabs, particularly when chemically dense piles are present above the CMB. We show that while the surface heat flux may not change significantly in response to Pangea assembly, it increases by ~16% from 200 to 120Ma ago as a result of Pangea breakup and then decreases for the last 120Ma to approximately the pre-200Ma value. As consequences of the assembly and breakup of Pangea, equatorial CMB heat flux reaches minimum at ~270Ma and again at ~100Ma ago, while global CMB heat flux is a maximum at ~100Ma ago. These extrema in CMB heat fluxes coincide with the Kiaman (316–262Ma) and Cretaceous (118–83Ma) Superchrons, respectively, and may be responsible for the Superchrons.
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