2. Mineralogy – Petrology – Geochemistry - SWISS GEOSCIENCE ...

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Symposium 1: Structural Geology, Tectonics and Geodynamics
1.A.1
Evidence of transition tectonic regime as seen at Hi’iaka and Zal regions on Io.
Leone Giovanni 1 , Gerya Taras 1 , Tackley Paul, J. 1 , & Moore William, B. 2
1 Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, CH-8092 Zürich (giovanni.leone@erdw.ethz.ch)
2 Department of Atmospheric and Planetary Sciences, Hampton University, 21 Tyler Street, VA 23668 Hampton
Io is the most volcanically active body of our Solar System, it’s average global thermal output of 2.4 W/m 2 is higher than
that of the Earth. It has been suggested that its mantle may be vigorously convecting (Tackley et al., 2001), but no signs
of plate tectonics have been seen so far on its surface. In some cases, mountains appear to be cut and laterally displaced
along a transform fault that seems to be a rifting margin (Figure 1 taken from Bunte et al., 2008) and occur as isolated
massifs also characterized by lineaments typical of tectonic activity (Figure 2a). A similar morphological pattern that occurs
in parts of the Earth oceanic crust (Figure 2b-c), although the timescale and the process differ according to the different
tectonic regimes and resurfacing rates.
Figure 1. “Galileo SSI mosaic obtained during orbit I27 flyby in
February 2000 from image I27ZALTRM01. Resolution is 335 m/
pixel. North is up. Illumination is from the left.” (from Bunte et
al., 2008). Zal mountains along with associated Zal Patera are
displaced along a transform fault from which lava flows erupted
on the surface.
Swiss Geoscience Meeting 2011
Figure 2. Comparison of Io surface structures (a) with numerical
models of magma-assisted spreading under terrestrial conditions
(b-c). (a) Galileo image PIA02540 showing Hi’iaka Mons
along with the associated Hi’iaka Patera (the darker semi-circular
feature in the middle of the image). (b) topographic pattern
for oceanic spreading associated with shallow elongated magma
chambers (Gerya, submitted). (c) topography rise associated
with an emplacement of large dike-like intrusion into the crust
(Gerya and Burg, 2007)
O’Neill et al. (2007) identified conditions in which mantle convection may lead (or not) to lithospheric failure and include
Io (as well as Venus and Europa) in a transition regime between stagnant and active (mobile) lid, being the latter on Earth
regarded as the unique case seen in the Solar System.
However, although failure of the lithosphere does occur (Figs. 1 and 2a), we think that a good coupling between the mantle
and the asthenosphere is not achieved on Io due to the low viscosity of the partially-molten asthenosphere and thus the
induced lithospheric stresses would be too small to form the observed mountains, which may instead be caused by ‘heat
pipe’ resurfacing being more rapid in some areas (above regions with high tidal dissipation) than others, causing lateral
differences in lithosphere-crust thickness and, hence, in stress. We plan to perform new simulations including the effect
of volatiles on partial melting, heat-pipe resurfacing, mantle-asthenosphere coupling, and laterally variable lithosphereasthenosphere
thicknesses, in order to understand lithospheric stresses and hence the formation of mountains, which
should allow us to better match the new models to the available spacecraft and groundbased data.
Platform Geosciences, Swiss Academy of Science, SCNAT