Discovery of a flank caldera and very young glacial activity at Hecates Tholus, Mars

Abstract

The majority of volcanic products on Mars are thought to be mafic and effusive. Explosive eruptions of basic to ultrabasic chemistry are expected to be common, but evidence for them is rare and mostly confined to very old surface features. Here we present new image and topographic data from the High Resolution Stereo Camera that reveal previously unknown traces of an explosive eruption at 30 degrees N and 149 degrees E on the northwestern flank of the shield volcano Hecates Tholus. The eruption created a large, 10-km-diameter caldera approximately 350 million years ago. We interpret these observations to mean that large-scale explosive volcanism on Mars was not confined to the planet's early evolution. We also show that glacial deposits partly fill the caldera and an adjacent depression. Their age, derived from crater counts, is about 5 to 24 million years. Climate models predict that near-surface ice is not stable at mid-latitudes today, assuming a thermo-dynamic steady state. Therefore, the discovery of very young glacial features at Hecates Tholus suggests recent climate changes. We show that the absolute ages of these very recent glacial deposits correspond very well to a period of increased obliquity of the planet's rotational axis.

An extended period of episodic northern mid-latitude glaciation on Mars during the Middle to Late Amazonian: Implications for long-term obliquity history

“…This evidence for a long-lived era of recurring ice ages in broad areas of the northern mid-latitudes of Mars is consistent with earlier measurements in specific locales (e.g., Head et al, 2005Head et al, , 2006aHead et al, , 2006bHauber et al, 2005Hauber et al, , 2008Levy et al, 2007Levy et al, , 2010. This work, however, represents the first integrated calculation of the period of time when deposition of ice and glaciation across the northern mid-latitudes occurred.…”

“…Even outside the defined buffer, in the whole of the 25°-80°E, 30°-50°N region, we noted only 2 craters larger than 2.5 km that are candidates to postdate the last episode of glaciation. This low density of craters gives limited statistics for estimating an absolute age, but is consistent with ice accumulation in this region as recently as 20-50 Ma, an age in accord with suggestions based on the density of small superposed craters on the youngest glaciated surface (e.g., Hauber et al, 2005;Baker et al, 2010). Glaciation appears to have occurred less recently in regions such as Acidalia Planitia, Tempe Terra, and Utopia Planitia, where a greater concentration of postglacial craters is observed.…”

Recognizing life in the Solar System: guidance from meteoritic organic matter

“…On Mars, NASA's Mars Exploration Rovers (Squyres et al 2004) and ESA's Mars Express orbiter (e.g. Hauber et al 2005;Murray et al 2005) are currently setting the stage for future, more sophisticated vehicles that will carry instruments to search for molecular evidence of past life. In addition, NASA's Galileo space probe has revealed features on the icy surface of Jupiter's moon, Europa, that intimate the possibility of subsurface volcanic activity and the presence of liquid water below the ice crust (Carr et al 1998).…”

Arecibo radar imagery of Mars: The major volcanic provinces

“…Nearly the entire western half of the shield is radar-dark, except for a bit of brightness on the SSW edge near the shield base. Based on low crater counts and subdued features, Mouginis-Mark et al (1982b, 1984 proposed the existence of air-fall ash deposits on the western side of the shield, with the deposits just west of the caldera having an estimated thickness of 100 m. Hauber et al (2005) also proposed pyroclastic mantling of the northwest flank from explosive eruptions at a separate caldera at the northwest base of the Hecates shield. All of this west-side mantling would explain the low THEMIS nighttime temperatures and radar-darkness of this side of the volcano.…”