Recently, Associate Researcher Liu Liang from the team led by Academician Xu Yigang of the Chinese Academy of Sciences, together with collaborators, adopted a research approach based on the deep Earth's physical state to establish a forward dynamic model. They constrained the current distribution of temperature in the upper mantle and used it to systematically and quantitatively simulate the impact of uneven temperature distribution in the upper mantle on the dynamic evolution of the Northern Hemisphere. They revealed the essence of the "black hole" phenomenon in the Northern Hemisphere, namely, the mantle convection driven by temperature differences attracts surrounding plates to converge towards it, significantly enhancing the mutual compression between plates. These findings were published in the journal "Geology".
Research on plate reconstructions suggests that since the Jurassic period, the Northern Hemisphere has gradually formed a long-term plate convergence center, with the eastern part of the Eurasian continent as its representative. This is manifested by the convergence of blocks such as Siberia, Mongolia, India, Arabia, and the (ancient) Tethys and (ancient) Pacific plates towards this region. Additionally, during this phase, the (re)initiation of one-way subduction processes mostly originated towards the eastern part of the Eurasian continent. From a qualitative perspective, it seems that a "black hole"-like structure has long been located beneath the eastern part of the Eurasian continent, attracting surrounding plates underneath itself, intensifying the squeezing between plates. However, existing models struggle to explain the fundamental reasons why plate squeezing has intensified and become the focal point of intracontinental tectonic-magmatic migration activities in the Northern Hemisphere for at least 200 million years.
This study suggests that mantle convection induced by the uneven temperature distribution in the upper mantle can drive the occurrence of representative plate convergence events in the Northern Hemisphere since the Jurassic period. According to statistical analysis of simulation results, within ~19 million years after the end of the original subduction process: one-way subduction towards the colder mantle end occurs in 88% of the test models; in about 43% of the models, lighter plates can subduct beneath heavier plates above the colder mantle end. In contrast, in models with uniformly hot mantle conditions, the timing for subduction restarts extends to ten times longer, and lighter plates never subduct beneath heavier plates.
This work explains why most of the newly initiated one-way subduction processes since the Jurassic period originate towards the eastern part of the Eurasian continent. Numerical simulation results also indicate that under different initial conditions in convergence zones, large-scale flat subduction, subduction of young marginal seas, and the stagnation of subducted slabs within the mantle transition zone, among other representative phenomena in the Northern Hemisphere, can spontaneously occur in the models. Furthermore, the numerical models in this study accurately reproduce the average convergence rate during the initiation of subduction in the Western Pacific Cenozoic, largely supporting the reliability of the model results in addressing large-scale plate convergence issues in both time and space.
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