Lithospheric Structure and Patera Formation on Io: Implications for Future Observations

Details Lithospheric Structure and Patera Formation on Io: Implications for Future Observations Lithospheric Structure and Patera Formation on Io: Implications for Future Observations

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43a1390j&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P43A-1390

Physics

5400 Planetary Sciences: Solid Surface Planets, 5480 Volcanism (6063, 8148, 8450), 8038 Regional Crustal Structure, 8178 Tectonics And Magmatism, 8434 Magma Migration And Fragmentation

Scientific paper

On Jupiter's moon Io, the interaction between volcanism and tectonism is strongly modulated by the structure of the lithosphere. Previous work has shown that Io's prodigious volcanism leads to the rapid burial of its surface and, consequently, the global subsidence of the materials that compose its lithosphere. This, in turn, generates large horizontal compressive stresses, which drive the thick-skinned thrust faulting that uplifts Io's mountains. Because horizontal compression is an ongoing process that proceeds ever more rapidly with increasing depth, we assume in our model that the lithosphere is pervasively fractured and its stress state is governed by frictional sliding. The result is that pore space within the crust disappears rapidly with depth, and SO2 (which is the dominant volatile species and which melts at a relatively low pressure) is confined to the near-surface region. Thus, Io's lithosphere is compositionally stratified, with a low-density SO2-dominated layer up to a few kilometers thick overlying a denser mafic or ultramafic silicate layer a few tens of kilometers thick. Rising magma should achieve neutral buoyancy near the interface between these two layers, and if that interface is abrupt, the magma may spread laterally there for purely mechanical reasons as well. The heat from these shallow sill-like intrusions is expected to mobilize the overlying volatiles, eventually unroofing the sill or lava lake. The overburden can be removed both by the melting and lateral flow of the volatiles and by their sublimation. (SO2 atop warm silicate lavas is predicted to sublimate at a rate of ~100 m/yr.) Hence, ionian paterae may be more analogous to the depressions formed in ice during terrestrial subglacial eruptions than to true volcanic calderas. These models for Io's lithospheric structure and its patera formation should be tested by future spacecraft missions. Three observations that would be particularly useful are (a) height and slope measurements of patera walls, which will provide a lower limit on the strength of the near-surface materials, (b) repeat stereo imaging of active paterae for ~1 year with a vertical precision of at least 100 m/pixel, and (c) high-resolution imaging of steep (i.e., exposed rock) scarps on mountain flanks, which will provide direct cross-sectional views of deeper parts of the lithosphere.

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