5:00 PM - 5:15 PM
[J09-2-03] Flexural mechanics and curvature evolution of the bending-unbending transition zone of subducting oceanic lithosphere
○Ryohei Sasajima, Takeo Ito (Nagoya University, Nagoya, Japan)
1. Introduction
Oceanic lithosphere is bended just before subduction, and is un-bended sooner or later after it subducts from the trench. Many previous studies analyzed flexure of the oceanic lithosphere in outer rise from topography and gravity anomalies for estimating the strength and rheology of the oceanic lithosphere [e.g., Goetze and Evans, 1979; Hunter and Watts, 2016]. The targets of their studies were limited to offshore from the trench, and flexural mechanics of subducting part of the oceanic lithosphere is poorly understood. Thus, the purpose of this study is to clarify the flexural mechanics of the bending-unbending transition zone of subducting oceanic lithosphere.
2. Method
This study expanded the flexural analysis to subducting part (up to 50 km depth) and estimated curvature evolution of the oceanic lithosphere in the bending-unbending transition zone. The target is the Pacific plate subducting from the Japan Trench (120-130 Ma).
First, we estimated the bending moment evolution of the Pacific plate from topography and gravity anomalies. Next, we conducted a numerical model of bending-unbending of the oceanic lithosphere in order to investigate how the bending moment develops with curvature. Finally, we estimated the curvature evolution of the bending-unbending transition zone of the Pacific slab by fitting modeled bending moment with estimated it from topography and gravity anomalies.
3. Results
When unbending initiates after bending, residual bending stress is released elastically. Thus, only slight curvature changing causes rapid bending moment changing. However, spatial changing of the bending moment must be gradual to satisfy force equilibrium. Consequently, curvature changing in the bending-unbending transition zone must be much slow. This result will be useful to constrain maximum curvature of subducting oceanic lithosphere for estimating e.g., bending energy dissipation.
Oceanic lithosphere is bended just before subduction, and is un-bended sooner or later after it subducts from the trench. Many previous studies analyzed flexure of the oceanic lithosphere in outer rise from topography and gravity anomalies for estimating the strength and rheology of the oceanic lithosphere [e.g., Goetze and Evans, 1979; Hunter and Watts, 2016]. The targets of their studies were limited to offshore from the trench, and flexural mechanics of subducting part of the oceanic lithosphere is poorly understood. Thus, the purpose of this study is to clarify the flexural mechanics of the bending-unbending transition zone of subducting oceanic lithosphere.
2. Method
This study expanded the flexural analysis to subducting part (up to 50 km depth) and estimated curvature evolution of the oceanic lithosphere in the bending-unbending transition zone. The target is the Pacific plate subducting from the Japan Trench (120-130 Ma).
First, we estimated the bending moment evolution of the Pacific plate from topography and gravity anomalies. Next, we conducted a numerical model of bending-unbending of the oceanic lithosphere in order to investigate how the bending moment develops with curvature. Finally, we estimated the curvature evolution of the bending-unbending transition zone of the Pacific slab by fitting modeled bending moment with estimated it from topography and gravity anomalies.
3. Results
When unbending initiates after bending, residual bending stress is released elastically. Thus, only slight curvature changing causes rapid bending moment changing. However, spatial changing of the bending moment must be gradual to satisfy force equilibrium. Consequently, curvature changing in the bending-unbending transition zone must be much slow. This result will be useful to constrain maximum curvature of subducting oceanic lithosphere for estimating e.g., bending energy dissipation.