Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p42b..03g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P42B-03
Physics
[6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution, [8147] Tectonophysics / Planetary Interiors, [8160] Tectonophysics / Rheology: General
Scientific paper
Knowledge about the terrestrial core formation mechanism is still very limited. Several core formation modes have been proposed: The fracturing mode suggests that a central unmelted region is displaced by a degree one mode from the center of the accreting body and is fragmented due to the large stresses created by an overlying asymmetric iron layer (Stevenson, 1981). In contrast, core formation via iron diapirs (e.g. Ziethe and Spohn, 2007), which can be formed by giant impacts (e.g. Ricard et al, 2009), has been proposed. We investigate which core formation mode is active under certain conditions. Therefore we perform 2D simulations using the code I2ELVIS applying the newly developed “spherical-Cartesian” methodology (Gerya and Yuen, 2007). It combines finite differences on a fully staggered rectangular Eulerian grid and Lagrangian marker-in-cell technique for solving momentum, continuity and temperature equations as well as the Poisson equation for gravity potential in a self-gravitating planetary body. In the model, the planetary body is surrounded by a low viscosity massless fluid (“sticky air”) to simulate a free surface. We apply a temperature- and stress-dependent viscoplastic rheology inside Mars- to Earth-sized bodies and include heat release due to radioactive decay, shear and adiabatic heating. As initial condition we use stochastically distributed iron diapirs with random sizes in the range of 50 to 100 km radius inside the accreting planet, representing the iron delivered by pre-differentiated impactors. Additionally, we add a giant impactor core into several models. For simplicity, we neglect the heating of the planetary body by the impact itself. We assume the impactor core to be at rest at the beginning of the simulation. A systematic investigation of the influence of silicate rheology, temperature and diapir radii on different-sized protoplanets is being performed. We show that depending on the silicate rheology, which is strongly dependent on the water content of olivine (Katayama and Karato, 2008) and the initial temperature profile, plastic yielding and shear localization take place and different regimes of core formation appear: For weak planetary interiors iron diapirs sink in collective groups, similar to already published core formation models (e.g. Ziethe and Spohn, 2007). For highly viscous bodies an asymmetric iron layer forms, which surrounds the central part of the planet or a mixture of diapirism and fracturing mechanism develops. Results including large diapirs indicate that for Mars-sized and larger bodies a runaway differentiation process can be induced. We derive scaling laws, which predict the onset of plastic yielding and shear localization in the silicates and of the runaway differentiation process and the associated core formation modes. The final temperature profiles of the different core formation modes are discussed with regard to their influence on the onset of mantle convection. References: Gerya, T.V. & Yuen, D.A., PEPI, 163, 83-105, 2007. Katayama, I. & Karato, S.-i., PEPI, 168, 125-133, 2008. Ricard, Y., Šrámek, O. & Dubuffet, F., EPSL, 284, 144-150, 2009. Stevenson, D.J., Science, 214, 611-619, 1981. Ziethe, R. & Spohn, T., JGR, 112, B09403, 2007.
Gerya Taras
Golabek Gregor J.
Kaus B. J.
Moll G.
Tackley Paul J.
No associations
LandOfFree
Influence of rheology and giant impactors on the terrestrial core formation does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Influence of rheology and giant impactors on the terrestrial core formation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Influence of rheology and giant impactors on the terrestrial core formation will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1772128