The volcanic history of Mars: High-resolution crater-based studies of the calderas of 20 volcanoes

Determining absolute surface ages for bodies in the Solar System is, at present, only possible for Earth and Moon with radiometric dating for both bodies and biologic proxies such as fossils for Earth. Relative ages through cratering statistics are recognized as one of the most reliable proxies for relative ages, calibrated by lunar geologic mapping and Apollo program sample returns. In this work, we have utilized the Mars Reconnaissance Orbiter’s ConTeXt Camera’s images which provide the highest resolution wide-scale coverage of Mars to systematically crater-age-date the calderas of 20 of Mars’ largest volcanoes in order to constrain the length of time over which these volcanoes - and major volcanic activity on the planet, by extension - were active. This constitutes the largest uniform and comprehensive research on these features to date, eliminating unknown uncertainties by multiple researchers analyzing different volcanoes with varied data and methods. We confirm previous results that Mars has had active volcanism throughout most of its history although it varied spatially and temporally, with the latest large-scale caldera activity ending approximately 150 ma in the Tharsis region. We find a transition from explosive to effusive eruption style occurring in the Hesperian, at approximately 3.5 Ga ago, though different regions of the planet transitioned at different times. Since we were statistically complete in our crater counts to sizes as small as ∼60 m in most cases, we also used our results to study the importance of secondary cratering and its effects on crater size-frequency distributions within the small regions of volcanic calderas. We found that there is no “golden rule” for the diameters secondaries become important in crater counts of martian surfaces, with one volcano showing a classic field of secondaries ∼2 crater diameters from the center of its primary but not affecting the size-frequency distribution, and another clearly showing an influence but from no obvious primary.