Article,
A komatiite analog to potential ultramafic materials on Io
Journal of Geophysical Research-Planets, 105 (E1): 1671--1684 (2000)
Abstract
Ultramafic volcanism is one model which fits currently available data
for some eruptions on Jupiter's moon, Io. Assuming that such activity
does occur, it is possible to apply komatiitic analogs and terrestrial
ultramafic flow models to Io, We have used such analogs and models
along with Galileo data to investigate the nature of ultramafic materials
that are assumed to occur at high-temperature hotspots on Io. The
unusual komatiites of the Commondale greenstone belt, South Africa,
are consistent with available Galileo data on the temperatures and
composition of potential Ionian ultramafic materials. These komatiites
had high SiO2 (similar to 50 wt %) and MgO (similar to 31 wt %) contents,
which are inferred to result in high liquidus temperatures (similar
to 1610 degrees C), low dynamic viscosities (similar to 0.2 Pa s),
and low densities (similar to 2680 kg/m(3)) and in the crystallization
of orthopyroxene phenocrysts (not found in other komatiites). We
used the Commondale composition and the model of Williams et al.
1998 to investigate potential ultramafic flow behavior on Io. Compared
to their terrestrial counterparts, Ionian ultramafic lava flows would
have less potential for turbulent flow, lower maximum emplacement
distances, and lower thermal erosion rates because of the lower Ionian
gravity and their more silicic composition. Shallow (<10 m deep)
thermal erosion channels are predicted to occur more proximally to
the lava source than on Earth. Deep (>10 m) thermal erosion channels
seem less likely on Io, unless (1) lavas are superheated, (2) lavas
are more ultramafic (>31% MgO), (3) eruption rates, eruption durations,
or flow volumes are high, or (4) substrates are unconsolidated, partly
consolidated, or volatile-rich and thus more erodable, If volatiles
are present in the lava as vesicles, then increasing lava vesicularity
results in decreasing maximum emplacement distances, decreasing thermal
erosion rates, and decreasing erosion channel depths: for given eruption
durations.
