5:15 PM - 7:15 PM
[BCG06-P01] Effects of plate flattening on the sea-level change and surface heat flow predicted from a theoretical model of the supercontinental cycle
Keywords:supercontinent cycle, continental drift, sea-level change, surface heat flux, plate flattening, theoretical model
The longest-term (first-order) sea-level change is considered to be within ~200–300 million years (Myr), which is roughly half or less of the period of the supercontinent cycle of ~500–700 Myr. It is recognized that the assembly of supercontinents involves either the closure of the ''interior ocean'' that resulted from the breakup of the supercontinent or the closure of the ''exterior ocean'' that surrounded the supercontinent. The former process is termed ''extroversion,'' while the latter is termed ''introversion,'' that is an end-member scenario of the supercontinent cycle. A ''combination'' process is also proposed to explain the complex behavior of continental drift on the actual Earth. Meanwhile, despite recent advances in numerical simulation studies of 3-D spherical mantle convection, some difficulties still remain in realizing plate tectonics and continental drift. In this study, a theoretical model of mantle convection with various supercontinent cycle processes was constructed, and the effects of the supercontinent cycle on the longest-term sea-level change and surface heat flux were addressed. The sea-level change is estimated from bathymetry over the oceanic plates under different free parameters that control the fluctuation of the sea-level change.
The present analytical results suggest that the asymptotic bathymetry due to the plate flattening effect of oceanic plates in the exterior and interior oceans is important to recover the realistic magnitude of sea-level fluctuations that is comparable to the sea-level curve of the past Earth. In addition, the volume change in the seawater due to its recycling into the mantle may be important to fit the observed sea-level curve from stratigraphic studies since 200 million years ago.
The heat released from the Earth's interior to the surface has a significant impact on the future of plate tectonics of the Earth. Owing to the secular cooling of Earth, surface heat flux has gradually decreased throughout Earth's history. The average surface heat flux would be subject to fluctuations in accordance with the supercontinent cycle on the order of 100 million years because the average age of the oceanic plate changes with time. Based on the half-space cooling model, a decrease in average plate age was associated with a decrease in bathymetry and an increase in average surface heat flux. Thus, in the present study, temporal changes in long-term surface heat flux during the supercontinental cycle were investigated using the present theoretical model. The results demonstrate that surface heat flux fluctuated between −10% and +25% during the supercontinent cycle, compared to surface heat flux at the time of supercontinental formation. In contrast, the parameterized convection theory for Earth's thermal budget suggests that the rate of secular cooling due to decay of radioactive elements was reduced by approximately 15% over the same period. These results imply that the effect of the supercontinental cycle on surface heat flux is comparable to or larger than secular cooling of the Earth.
The present analytical results suggest that the asymptotic bathymetry due to the plate flattening effect of oceanic plates in the exterior and interior oceans is important to recover the realistic magnitude of sea-level fluctuations that is comparable to the sea-level curve of the past Earth. In addition, the volume change in the seawater due to its recycling into the mantle may be important to fit the observed sea-level curve from stratigraphic studies since 200 million years ago.
The heat released from the Earth's interior to the surface has a significant impact on the future of plate tectonics of the Earth. Owing to the secular cooling of Earth, surface heat flux has gradually decreased throughout Earth's history. The average surface heat flux would be subject to fluctuations in accordance with the supercontinent cycle on the order of 100 million years because the average age of the oceanic plate changes with time. Based on the half-space cooling model, a decrease in average plate age was associated with a decrease in bathymetry and an increase in average surface heat flux. Thus, in the present study, temporal changes in long-term surface heat flux during the supercontinental cycle were investigated using the present theoretical model. The results demonstrate that surface heat flux fluctuated between −10% and +25% during the supercontinent cycle, compared to surface heat flux at the time of supercontinental formation. In contrast, the parameterized convection theory for Earth's thermal budget suggests that the rate of secular cooling due to decay of radioactive elements was reduced by approximately 15% over the same period. These results imply that the effect of the supercontinental cycle on surface heat flux is comparable to or larger than secular cooling of the Earth.