This timing correlates well with the crystallization ages (~165-170 million years) determined for the youngest basaltic Martian meteorites.
Reference: The volcanoes on Mars, though inactive, stand as proof of past volcanic activity whose timing, duration, and cessation are hot topics in planetary science.
In fact, the planet's geologic history owes much of its action to volcanism (as well as tectonics, wind, water, and impact cratering).
We'll get back to impact cratering, but for now the map, below, shows the locations of 24 major volcanoes on Mars.
Ar Analyses of Historic Lava Flows.” Nevertheless, this is no way changes the argument in question. In order to establish this dating method in this application an attempt has been made to trace the sources of the anomalies.To illustrate these efforts, dating results from a rhyodacite of Mauna Kuwale, Oahu, Hawaii, are reported.We have found that gas released from such inclusions by crushing contains radiogenic argon, and that the constituent minerals give very old potassium-argon ages (circa 800 million years).Similar gaseous inclusions have been noted in a variety of other lava phenocrysts, and their presence in a dated sample may produce an anomalous old age.Determinations on several minerals and the whole rock of this ridge give a concordant age of 2.3 ± 0.3 million years, excluding some few results on minerals which show old age anomalies.