- E_SIT20-P04 -
[S-IT20]
[SIT20-P04]
©Japan Geoscience Union 
Japan Geoscience Union Japan Geoscience Union Meeting 2018 
[EE] Evening  Poster | S (Solid Earth Sciences) | S-IT Science of the Earth's Interior & Tectonophysics
Structure and Dynamics of Earth and Planetary Mantles
convener:Takashi Yoshino(Institute for Planetary Materials, Okayama University), Dapeng Zhao(Department
of Geophysics, Tohoku University), Takashi Nakagawa(海洋研究開発機構数理科学・先端技術研究分野)Mon. May 21, 2018 5:15 PM - 6:30 PM  Poster Hall (International Exhibition Hall7, Makuhari Messe)
Interdisciplinary approach can lead to a better understanding of dynamics and evolution of the deep interiors
of the Earth and planets. We welcome any submissions of recent results in observational, theoretical and
experimental studies on seismology, geomagnetism, mineral physics, dynamics of deep interiors, and any
other relevant fields from researchers in many countries. Integration of such results is also welcome. In
particular, we encourage any contributions focusing on "plate and mantle dynamics in Earth and terrestrial
planets". 
A new approach to thermal-mechanical modeling of
subducting slab with real-time update of thermal boundary
condition in a framework of solid mechanics
*Jae-Yoon Keum1, Byung-Dal So1 (1.Kangwon National University)
Keywords:Thermal tongue structure, Temperature boundary condition, spontaneous subduction, solid
mechanics 
To simulate subduction dynamics numerically, there are two contrasting approaches depending on whether
the subducting slab is assumed as a viscous fluid (i.e., fluid mechanics) and viscoelastic solid (i.e., solid
mechanics). In the approach of solid mechanics, a viscous mantle resistance against subduction is
reproduced by viscous dashpot elements attached on surface of subducting oceanic plates. The dashpot
approximation for mantle was successful for modeling realistic features of subducting slabs, such as slab
advancing, retreating and stagnation on 660 km phase boundary, in frameworks of viscoelastic solid
mechanics. However, it is difficult to calculate a temperature change of subducting slab due to nonexistence
of hot mantle which provides thermal energy to the slab by conduction. Thermal structure of the subducting
plate is important in various geodynamical phenomena such as dehydration of hydrous minerals, metastable
olivine, and subduction initiation. In present study, we performed thermal-mechanical finite element
modelling for subducting slab sinking spontaneously into mantle by gravity, based on linear Maxwell
viscoelasticity. A wide range of temperature profiles of mantle is applied as depth-dependent temperature
boundary conditions of subducting slabs. In each time-step, temperature boundary condition of surface
enveloping the slab is evolved in real-time following the location of the surface. Our model displayed a clear
tongue thermal structure in which cold core and hot surface of subducting slab are formed. An extent of
metastable olivine is systematically correlated with slab dip, sinking velocity, and age of subducting plate. In
addition, we adopted temperature-dependent viscosity of dashpots to investigate the effect of basal viscosity
of oceanic plate before subduction initiation. When we defined local high temperature structure (e.g., plume)
around the dashpots, the lateral heterogeneity in viscosity along the basal boundary of oceanic plate
emerges. Above thermally weakened dashpot, the oceanic plate is bent downward and subsequently
collapsed to start subduction. We argue that our model with viscoelastic plate, dashpot approximation for
mantle, and real-time update of temperature boundary condition can successfully reproduce geodynamics of
subducting plates including the formation of metastable olivine and subduction initiation by plume
impingement. This means that our new method has a potential to simultaneously solve physics of elastic
short timescale (e.g., earthquakes and rupture dynamics) and viscous long timescale (e.g., slab deformation
and dehydration), which are both greatly affected by temperature.