Chuan Huang1, Zheng-Xiang Li1, Nan Zhang2
1Earth Dynamics Research Group, ARC Centre of Excellence for Core to Crust Fluid Systems and The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, Perth, Western Australia, Australia, 2Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing, China
We developed a series of new dynamic models aiming to more realistic model the full supercontinent cycle, testing parameters critical for introversion vs. extroversion assembly, and mantle response to the alternative supercontinent evolution paths. The numeric simulations allow for self-generated subduction and supercontinent break-up during the supercontinent cycle. Subduction within the oceanic realm is implemented by considering plastic yielding in the oceanic lithosphere, through which rapid viscous weakening occurs when convection stress is larger than the yield strength. For subduction along continental margins, weak zones are introduced in oceans near the continental edge when the age of oceanic lithosphere is greater than a certain value (e.g., 180 Ma). Under such a model setup, our models are able to naturally generate Earth-like ocean-ocean and ocean-continent subductions.
By simulating the mantle evolution from the breakup of a supercontinent to the formation of the next one, we found that heat distribution (monitored by mantle temperature) between the mantle domains under either the supercontinent or the surrounding superocean, divided by the subduction girdle, provides an important control on how the next supercontinent forms. During the breakup stage, the average mantle temperature beneath the supercontinent (here denoted by Tc) is higher than that under the superocean (To) partially due to thermal isolation by the supercontinent. After the breakup, Tc decreases with the vanish of the thermal isolation effect, but To maintains at a similar level. It causes To shifts to a value slightly larger than Tc in the time soon after the breakup. Despite the limited higher energy level in the superocean-side, subduction/girdle retreat maintains the continuous drift of continents. After that, dispersing continents will reach their maximum distance from each other. The relative value of Tc and To after the time that greatest distance is reached determines whether the next supercontinent assembles through introversion or extroversion. Generally, models with a dense chemical layer above the core-mantle boundary tend to have introversion cycle, due to the much higher heat level (~50 K) in the superocean-side reserved by its larger chemical layer volume than the continent side. Two LLSVPs formed in our models during the full cycle locating in the ocean and continent sides, respectively. However, migrations up to several thousand kilometers for the two structures can be also observed.
Chuan Huang is a research fellow at Curtin University. He is working on geodynamic modelings and is currently focusing on the coupled continent-mantle process during a supercontinent cycle.