re: is Io an analogue for Mars
Idle thinking but could such volcanic plumes have occurred on Mars eg during eruptions leading to the Tharsis bulge. Could the material that formed what is the Meridiani sediments been been down thru such a process? Sulfurous snow is such a beautiful concept for laying down a reactive sediment that with deep burial and subsequent heating under goes a myriad of diagenetic changes. Being shot high into the atmosphere on Mars would also allow the photolytic oxidation latter required to get jarosite.