TY - JOUR

T1 - Dynamical influences of depth-dependent properties on mantle upwellings and temporal variations of the moment of inertia

AU - Moser, Jiří

AU - Yuen, David A.

AU - Larsen, Tine B.

AU - Matyska, Ctirad

N1 - Funding Information:
We thankP .J. Tackley,S . Zhanga ndZ . Martinec for valuabled iscussionasn dc ommentWs. e thankA . Lenardicf or his providingu s with a photograpohf the Venus 'yelda'a nd discussionso f its role in homoclinico rbitsa ndR . Moserov~L,. M. Weyera nd T. Bui for technicahl elp. This researchh as been supportedb y the GermanB MFT foundationt,h e DanishR esearchA cademyN, ASA grant( LAGEOS-II), theC zechG rantA gencyu ndert heg rantn umbers 205/96/02122, 05/97/1015a nd by the US-CzechoslovaJko int Fund in cooperationw ith the MSMT (~R,U SGS andN SF underp roject9 3002.

PY - 1997/7

Y1 - 1997/7

N2 - The influences of the depth-dependent thermal expansivity and viscosity on mantle flows have been investigated with an axisymmetric spherical-shell model and a comparison has been made with Cartesian box results. This comparison between the Cartesian and spherical-shell geometries shows that there are present in both configurations large thermal plumes, while the downwellings are stronger in the Cartesian geometry. Spherical models with a small core, as perhaps in the case of Mars, produce huge megaplumes with large heads, which can extend several tens of degrees on the planetary surface. We have also investigated the influence of the Rayleigh number, internal heating and depth-dependent properties on the time-dependent phase-space trajectories of the dynamically induced moments of inertia and the surface Nusselt number. Large, homoclinic-like, excursions in the phase-space trajectories can occur occasionally in the depth-dependent models and are due to the time-dependent nature of the plume dynamics. The time-scales associated with changes of the surface Nusselt number are faster than those associated with variations in the moment of inertia for earth-like Raleigh numbers. There are substantial temporal variations in the moment of inertia due to the plume-plume collisional dynamics. In the case of Earth, the magnitudes of perturbed moment of inertia may reach as large as 10-5 of the principal moments of inertia. Such a possibility points to a fundamentally important role played by the lower mantle dynamics in polar wander over geological time scales.

AB - The influences of the depth-dependent thermal expansivity and viscosity on mantle flows have been investigated with an axisymmetric spherical-shell model and a comparison has been made with Cartesian box results. This comparison between the Cartesian and spherical-shell geometries shows that there are present in both configurations large thermal plumes, while the downwellings are stronger in the Cartesian geometry. Spherical models with a small core, as perhaps in the case of Mars, produce huge megaplumes with large heads, which can extend several tens of degrees on the planetary surface. We have also investigated the influence of the Rayleigh number, internal heating and depth-dependent properties on the time-dependent phase-space trajectories of the dynamically induced moments of inertia and the surface Nusselt number. Large, homoclinic-like, excursions in the phase-space trajectories can occur occasionally in the depth-dependent models and are due to the time-dependent nature of the plume dynamics. The time-scales associated with changes of the surface Nusselt number are faster than those associated with variations in the moment of inertia for earth-like Raleigh numbers. There are substantial temporal variations in the moment of inertia due to the plume-plume collisional dynamics. In the case of Earth, the magnitudes of perturbed moment of inertia may reach as large as 10-5 of the principal moments of inertia. Such a possibility points to a fundamentally important role played by the lower mantle dynamics in polar wander over geological time scales.

UR - http://www.scopus.com/inward/record.url?scp=0031423390&partnerID=8YFLogxK

U2 - 10.1016/S0031-9201(97)00012-5

DO - 10.1016/S0031-9201(97)00012-5

M3 - Article

AN - SCOPUS:0031423390

SN - 0031-9201

VL - 102

SP - 153

EP - 170

JO - Physics of the Earth and Planetary Interiors

JF - Physics of the Earth and Planetary Interiors

IS - 3-4

ER -