5:15 PM - 7:15 PM
[SCG54-P02] Numerical simulation on the effects of plumes and serpentinization on oceanic plate subduction
Keywords:Oceanic plate subduction initiation, Serpentinization, High-temperature thermal plume, Hydration-induced weakening
The Earth's surface is covered by seawater, forming a thermally cold boundary layer, namely a rigid rock. On a geological time scale, surface materials are transported into the Earth's interior as oceanic plates subduct through plate tectonics. However, the mechanism that triggers subduction initiation remains a subject of debate. In this study, we investigate the effects of peridotite serpentinization and deep mantle plumes on subduction initiation using a two-dimensional numerical simulation model, a topic that has gained attention in the past two decades.
Our study incorporates the current thermal structure of the Earth's mantle and the compositional structure from the surface to the deep interior, considering systematic physical properties. We focus on the weakening effects of ocean water infiltration into pre-existing transform faults and the deep crust. In the simulation model, we evaluate the factors that localize new subduction zones, focusing on the density contrast between the serpentinized fracture zone—formed due to extensive water infiltration—and the surrounding plates, as well as the horizontal and vertical forcing exerted by a mantle upwelling that is approximately 60 K hotter than the surrounding mantle.
The results reveal two critical characteristics that promote oceanic plate subduction. (1) In a model incorporating the weakening effects of fluid infiltration into pre-existing transform faults and the deep crust, when a relatively small density contrast (200 kg/m³) is applied to the fracture zone, rapid plate boundary extension occurs, followed by spontaneous subduction. (2) In a model where the plates on either side of the fracture zone have a significant age difference (70 million years), the mantle upwelling, after reaching the base of the plate, exerts large horizontal and vertical forces. However, it does not serve as the primary driver of subduction initiation. Instead, when the upwelling breaks into the plate boundary, it facilitates subduction.
The density contrast of 200 kg/m³ in the fracture zone corresponds to approximately 28.6% of the density difference between serpentine (2600 kg/m³) and peridotite (3300 kg/m³). If the degree of serpentinization correlates with density reduction, our results suggest that serpentinization in some fracture zones could act as a contributing factor to spontaneous subduction initiation. As phase transitions also occur in the mantle at depths of approximately 410–660 km, the exact behavior of mantle plumes from the deep mantle to the surface remains unclear. However, our model examines whether the forcing exerted by plumes promotes subduction initiation by assuming high-temperature spheres with diameters of 100, 200, and 300 km at a depth of 300 km.
Since the extent of serpentinization is strongly influenced by temperature and water supply conditions, and melting effects due to plume-induced forcing are also expected, future studies should further investigate their impact on subduction initiation.
Our study incorporates the current thermal structure of the Earth's mantle and the compositional structure from the surface to the deep interior, considering systematic physical properties. We focus on the weakening effects of ocean water infiltration into pre-existing transform faults and the deep crust. In the simulation model, we evaluate the factors that localize new subduction zones, focusing on the density contrast between the serpentinized fracture zone—formed due to extensive water infiltration—and the surrounding plates, as well as the horizontal and vertical forcing exerted by a mantle upwelling that is approximately 60 K hotter than the surrounding mantle.
The results reveal two critical characteristics that promote oceanic plate subduction. (1) In a model incorporating the weakening effects of fluid infiltration into pre-existing transform faults and the deep crust, when a relatively small density contrast (200 kg/m³) is applied to the fracture zone, rapid plate boundary extension occurs, followed by spontaneous subduction. (2) In a model where the plates on either side of the fracture zone have a significant age difference (70 million years), the mantle upwelling, after reaching the base of the plate, exerts large horizontal and vertical forces. However, it does not serve as the primary driver of subduction initiation. Instead, when the upwelling breaks into the plate boundary, it facilitates subduction.
The density contrast of 200 kg/m³ in the fracture zone corresponds to approximately 28.6% of the density difference between serpentine (2600 kg/m³) and peridotite (3300 kg/m³). If the degree of serpentinization correlates with density reduction, our results suggest that serpentinization in some fracture zones could act as a contributing factor to spontaneous subduction initiation. As phase transitions also occur in the mantle at depths of approximately 410–660 km, the exact behavior of mantle plumes from the deep mantle to the surface remains unclear. However, our model examines whether the forcing exerted by plumes promotes subduction initiation by assuming high-temperature spheres with diameters of 100, 200, and 300 km at a depth of 300 km.
Since the extent of serpentinization is strongly influenced by temperature and water supply conditions, and melting effects due to plume-induced forcing are also expected, future studies should further investigate their impact on subduction initiation.