Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p72b0504k&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P72B-0504
Physics
5418 Heat Flow, 5475 Tectonics (8149), 5480 Volcanism (8450), 6218 Jovian Satellites
Scientific paper
Io advects most of its tidal heat through its lithosphere (crust) by volcanism. In previous work (McKinnon et al., Geology 29, 103-106, 2001), it was shown that thermal stresses arising from a cessation of volcanism in a crust of fixed but plausible depth (25 km) exceed Byerlee`s rule in compression in ~0.5 Myr. Here we extend this model to variable rates of volcanism, and to different assumptions regarding the asthenospheric heat budget when the eruption rate changes. Considering the 25-km example, if the eruption (and hence subsidence) rate does not affect the asthenosphere (due to large heat capacity), then crustal thickness does not change. In this case reductions in the eruption rate by <50% do not lead to compressive stresses sufficient to cause brittle failure. If, however, the eruption rate is locally coupled to the asthenospheric heat budget, then reductions in the former imply crustal thinning. In this case, and starting with only elastic loading (overburden) as the initial stress state, thermal stresses reach failure in well under 0.5 Myr for complete volcanic shut down, and several km closer to the surface due to melting at the base of the crust. As the thermal wave propagates upward and the crust continues to thin, the entire crust is eventually thrown into compression. Significantly, with crustal thinning, smaller reductions in eruption rate generate thermal stresses that reach the failure limit than without; e.g., a decrease by 50% in the eruption rate can produce failure between depths of 15-20 km in 1-2 Myr. Volcanism, of course, can also increase as well as decrease, and if so the crust may thicken by freezing at its base. Deep but thick zones of tensile stress due to cooling can be created. These stresses easily exceed Byerlee`s rule in extension, even for an increase in eruption rate of only 25%, and on very short time scales due to preexisting overburden stresses. Such broad deep contractions could force the original (now upper) crust into compression. Thermal stresses are remarkably versatile! More generally, the initial stress state on Io includes stresses due to the steady state temperature profile and the remote subsidence stress; the latter ranges from overwhelmingly compressive to being an important contributor to compression, and may even be tensile regionally.
Kirchoff Michelle R.
McKinnon William B.
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