Experimental Investigation of Oxidation of Pyroxene and Basalt: Implications for Spectroscopic Analyses of the Surface of Venus and the Ages of Lava Flows

Abstract

Alteration of basalt on the surface of Venus should be dominated by nanophase hematite and sulfate coatings, but the timescale of oxidation and how that affects spectroscopic measurements has not been extensively studied. The oxidation rate and the effect on reflectance spectroscopy are needed to constrain the age of lava flows with high emissivity that were previously measured by the European Space Agency's Venus Express Mission. Here we investigate the effects of oxidation on the mineralogy and visible to near-infrared (VNIR) spectroscopy of augite, diopside, pyroxenite, and an alkali basalt. The experimental and spectroscopic data are used to constrain the surface basaltic weathering rates for Venus. Further, we use the spectroscopic measurements to constrain how quickly igneous signatures would degrade during oxidation of the surface. Our results show that basalt and olivine oxidize within weeks to months on the surface of Venus and their VNIR results are dominated by hematite. Pyroxenes take longer to alter with minor hematite forming on the surface—largely in cracks. Instead, Fe3+ is predominantly forming in the crystal structure. Our work suggests that if basalt on the surface of Venus contains olivine and/or glass, the high emissivity lavas previously measured would be only a few years old. If, instead, those high emissivity lavas are fully crystalline and contain no olivine or glass (which is unlikely), they would still only be decades to hundreds of years old. Therefore, this is consistent with recent work suggesting that Venus is volcanically active today.

Venus, An Active Planet: Evidence for Recent Volcanic and Tectonic Activity

“…slowly. The spectral signal of oxidized basalt, glass, and olivine become dominated by hematite even before a full coating forms on the surface of the sample (Cutler et al 2020;Filiberto et al 2020). Applying these experimental results to Venus' lava flows suggests that any lava flow on the surface of Venus with an infrared signature of fresh lava may only be a few years old.…”

“…These coatings could, in theory, be used to date different lava flows, because the amount of alteration should correlate with the age of the rock exposed to the atmosphere. Recently, experimental laboratory studies investigated exactly this-how quickly alteration minerals would coat the surface of basaltic rocks and minerals in contact with a Venus-simulated atmosphere (Berger et al 2019;Cutler et al 2020;Filiberto et al 2020). In order to constrain the age of the freshest lava flows at Idunn Mons, Filiberto et al (2020) and Cutler et al (2020) investigated how the oxidation coatings would affect the spectral signals of the basalt.…”

“…Recently, experimental laboratory studies investigated exactly this-how quickly alteration minerals would coat the surface of basaltic rocks and minerals in contact with a Venus-simulated atmosphere (Berger et al 2019;Cutler et al 2020;Filiberto et al 2020). In order to constrain the age of the freshest lava flows at Idunn Mons, Filiberto et al (2020) and Cutler et al (2020) investigated how the oxidation coatings would affect the spectral signals of the basalt. The experimental results showed that alteration and oxidation minerals form on the rock and mineral surfaces on laboratory timescales-olivine, basaltic glass, and alkali-basalt alter on timescales of weeks to months (Fig.…”

Volcanically extruded phosphides as an abiotic source of Venusian phosphine

“…Rescaling the steady resurfacing model with a rate of 1 km 3 /y would lead to an age of 25,000 y, the more likely ages for those young flow features (52). Experiments measuring the weathering rate at Venus surface conditions (54)(55)(56) support even younger ages of the lava flows identified by Smrekar et al (52), possibly decades to hundreds of years. VIRTIS emissivity data also show evidence of recent volcanism at Quetzelpetlatl Corona, in which volcanism is on the scale of the Deccan Traps (51,53).…”

Laboratory Studies in Support of Venus Exploration: Surface and Near-Surface

“…Oxidation reactions of basalt and basaltic minerals with either a Venus-like atmosphere or a terrestrial atmosphere at Venus-temperatures produce iron-oxide coatings, as well as Fe 3+ in the mineral structure. Recent work has shown that the rates of oxidation reactions on Venus should be quick -only weeks to months to coat mineral and rock surfaces with a NIRopaque coating of iron oxides, particularly hematite but also possibly magnetite or maghemite (19)(20)(21). The speed of these oxidation reactions suggests that they could be quantified and extrapolated to Venus as measures of the ages of basalt lava flow.…”