Evolving mantle convection from bottom up to top down

The Earth's mantle is a dynamic layer where heat transfer occurs through convection. While convection is generally mass balanced, the balance of buoyancy forces is not necessarily fixed. Prior research has shown that convection can be driven by either positive or negative buoyancy forces, depending on the thermal conditions at the top and bottom boundaries of the mantle. The core-mantle boundary and the lithosphere-asthenosphere boundary are key regions influencing these forces. Bottom-up convection is associated with plume ascent, while top-down convection is linked to subduction processes. However, it remains unclear whether mantle convection is symmetric, dominantly top-down, dominantly bottom-up, or time-dependent. This uncertainty has motivated further investigation into the mechanisms and balance of mantle convection.

This study aims to clarify the nature of mantle convection by examining whether it is symmetric, dominantly top-down, dominantly bottom-up, or time-dependent. The specific problem addressed is the lack of consensus on the dominant mode of convection in Earth's mantle. The motivation stems from the need to better understand the forces driving mantle dynamics and their implications for surface processes like plate tectonics. The study seeks to determine whether convection is driven primarily by plume ascent, subduction, or a balance of both. By analyzing the balance of buoyancy forces, the research aims to shed light on the mechanisms governing mantle convection and how they evolve over time.

The study employs a theoretical framework to analyze the balance of buoyancy forces in mantle convection. It considers the thermal conditions at the core-mantle boundary and the lithosphere-asthenosphere boundary as key factors influencing convection. The approach involves comparing the forces driving plume ascent and plate subduction. The study does not rely on numerical simulations but instead uses conceptual and physical reasoning to evaluate the balance of forces. The analysis focuses on whether positive or negative buoyancy forces predominate in different scenarios. The study also examines the possibility of symmetric convection, where both forces are balanced. The approach is primarily deductive, based on known principles of convection and buoyancy.

The study suggests that mantle convection is not necessarily force balanced and can be driven by either positive or negative buoyancy forces. Bottom-up convection is driven by plume ascent, while top-down convection is driven by subduction. The balance of these forces depends on the thermal conditions at the top and bottom boundaries of the mantle. The study finds that convection can be symmetric when plume ascent and subduction are balanced. However, the study does not provide definitive evidence for whether convection is dominantly top-down, bottom-up, or time-dependent. The findings indicate that the dominant mode of convection may vary over time depending on boundary conditions. The study also highlights the importance of the core-mantle and lithosphere-asthenosphere boundaries in determining the direction of convection.

The study concludes that mantle convection is not necessarily force balanced and can be driven by either positive or negative buoyancy forces. The authors suggest that convection can be symmetric when plume ascent and subduction are balanced. However, the study does not provide definitive evidence for whether convection is dominantly top-down, bottom-up, or time-dependent. The findings indicate that the dominant mode of convection may vary over time depending on boundary conditions. The study emphasizes the importance of the core-mantle and lithosphere-asthenosphere boundaries in determining the direction of convection. The authors propose that further research is needed to clarify the mechanisms governing mantle convection and how they evolve over time. The study does not make claims about the necessity of any specific mechanism but highlights the variability of convection based on boundary conditions.