Impact craters vs volcanic explosions on Mars
In addition to Gordons approach it might be possible to differentiate between impact and volcanic craters by comparing the characteristics of the ejecta [1]. The apparent thermal inertia (defined for example in [2]) seems to be higher around volcanic craters [3]. Unfortunately the linked papers about the method are conference abstracts about ongoing research and I did not find a paper where they try to apply the method to remote sensing data from mars.

[1] Peet, V. M., M. S. Ramsey, and D. A. Crown. "Comparison of Terrestrial Morphology, Ejecta, and Sediment Transport of Small Craters: Volcanic and Impact Analogs to Mars." 36th Annual Lunar and Planetary Science Conference. Vol. 36. 2005.

[2] Putzig, Nathaniel E., and Michael T. Mellon. "Apparent thermal inertia and the surface heterogeneity of Mars." Icarus 191.1 (2007): 68-94.

[3] Peet, V. M., M. S. Ramsey, and D. A. Crown. "Remote Sensing Analyses of Small Terrestrial Volcanic and Impact Craters: A Mars Analog for Formation, Morphology, and Erosional Processes." Lunar and Planetary Science Conference. Vol. 38. 2007.