Mantle Convection Study with Lherzolite Material Modeling

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Introduction

A mantle convection has been one of the hardest and most controversial parts of geology. In 1980, Dziewonski and Anderson performed an important study using a seismological method to explore the inner earth[1]. This PREM (Preliminary Reference Earth Model) study showed that the mantle is made of a solid material that has viscosity. Moreover, sophisticated GPS technology that allows observation of the
Temperature plot of 2D mantle convection simulaiton with BIISV model[2]
oceanic floor demonstrated that the earth’s plates are moving with a velocity of approximately 10 cm/yr. Therefore, many geophysicists studied and model the mantle’s convection mechanisms. However, mantle convection still remains a largely unsolved problem.

In modeling the mantle rock material, the geophysics community mainly uses the power-law creep method. Although this power-law creep gives approximate solutions, this method does not exactly capture various rock’s material behavior. Alternatively, the engineering society has developed a material modeling technique to satisfy the needs of industry. Integrated Computational Material Engineering (ICME) has been developed as one of the effective material modeling methods. In many modeling studies of several materials including steels, the Internal State Variable (ISV) method through ICME has shown good accuracy. A recent study was performed by Sherburn et al[3] showing that the Bammann Internal State Variable model captures the rock’s material behavior much more effectively than the power-law model. In this context, mantle rock material modeling with ICME method is expected to produce a more accurate plate tectonic model.

Peridotite is a dominant rock of the upper mantle. Geologists consider the peridotite group to make up 90% of the upper mantle. Since it is very difficult to observe the real mantle’s composition with the naked eye, nobody can be sure what composition comprises the mantle. However, several indirect methods such as laboratory experiments for magma imply that the mantle is usually composed of ultramafic minerals like olivine and pyroxene. Peridotite is divided to subgroups lherzolite, harzbergite, olivine websterite, wehrlite, and dunite) according to the particular mineral composition ratio. Lherzolite is a major subgroup among these groups. Lherzolite is a coarse grained rock that includes mainly 40 ~ 90 % olivine ((Mg, Fe)2SiO4) and pyroxene (XY(Si,Al)2O6 where X and Y can be metallic ions) minerals. Therefore, modeling lherzolite is very critical to investigating the patterns of mantle convection.

References

  1. Dziewonski, A. M., Anderson, D. L., “Preliminary reference Earth model”, Physics of the Earth and Planetary Interiors, Vol. 25 (1981), pp. 297-356.
  2. Sherburn, J. A., Horstemeyer, M. F., Bammann, D. J., Baumgardner, J. R., “Two-dimensional mantle convection simulations using an internal state variable model: the role of a history dependent rheology on mantle convection”, Geophys. J. Int., Vol. 186 (2011), pp. 945-962.
  3. Sherburn, J. A., Horstemeyer, M. F., Bammann, D. J., Baumgardner, J. R., “Application of the Bamman inelasticity internal state variable consititutive model to geological materials”, Geophys. J. Int., Vol. 184 (2011), pp. 1023-1036.
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