Filiberto, Justin

The recently selected missions to Venus have opened a new era for the exploration of this planet. These missions will provide information about the chemistry of the atmosphere, the geomorphology, local-to-regional surface composition, and the rheology of the interior. One key scientific question to be addressed by these future missions is whether Venus remains volcanically active, and if so, how its volcanism is currently evolving. Hence, it is fundamental to analyze appropriate terrestrial analog sites for the study of possibly active volcanism on Venus. To this regard, we propose Mount Etna - one of the most active and monitored volcanoes on Earth - as a suitable terrestrial laboratory for remote and in-situ investigations to be performed by future missions to Venus. Being characterized by both effusive and explosive volcanic products, Mount Etna offers the opportunity to analyze multiple eruptive styles, both monitoring active volcanism and identifying the possible occurrence of pyroclastic activity on Venus. We directly compare Mount Etna with Idunn Mons, one of the most promising potentially active volcanoes of Venus. Despite the two structures show a different topography, they also show some interesting points of comparison, and in particular: a) comparable morpho-structural setting, since both volcanoes interact with a rift zone, and b) morphologically similar volcanic fields around both Mount Etna and Idunn Mons. Given its ease of access, we also propose Mount Etna as an analog site for laboratory spectroscopic studies to identify the signatures of unaltered volcanic deposits on Venus.

Ultramafic pseudotachylytes have been regarded as earthquake fossils formed at mantle depths (i.e., >30 km). Here we show that pseudotachylytes hosted by ultramafic rocks from three localities have distinct magnetic properties. Fresh host peridotites contain only small amounts of coarse-grained magnetite. In contrast, the ultramafic pseudotachylytes contain variable amounts of significantly finer magnetite that formed coseismically through melting. Among each locality, magnetite abundance in the pseudotachylytes ranges over several orders of magnitude (4–2,000 ppm), and magnetic grain size varies considerably (from single domain to multidomain). Because the host peridotites are compositionally similar, the pseudotachylyte magnetic properties are interpreted to primarily reflect the physical and cooling conditions prevailing during seismic slip. Further, the examination of laboratory-produced ultramafic pseudotachylytes shows that quenching does not produce superfine magnetite. We hypothesize that the magnetic properties of ultramafic pseudotachylytes are controlled by fO2 and in consequence vary systematically with depth of formation. Therefore, these properties can be used to assess if the ruptures producing the earthquakes that these pseudotachylytes represent nucleated at actual mantle depths or at shallow depths during exhumation of mantle rocks. ©2017. American Geophysical Union. All Rights Reserved.