THE GEOLOGIC RECORD OF MEGA VOLATILE DISCHARGE AND EROSIONAL EVENTS ON MARS

The surface of Mars reveals a suite of features indicative of large-scale, catastrophic discharge and erosional events. Geologic activity, including heavy bombardment during the early part of the Noachian, and the availability of water and perhaps carbon dioxide may have resulted in a thick megaregolith of volatile-rich, loosely consolidated impact breccias and sedimentary and volcanic fines. Development of permafrost sealed in liquids. Intense seismicity and/or heating produced by magmatic, tectonic, and impact events acting on such deposits may explain deeply eroded terrains on Mars. Such events could lead to high pore fluid pressures in near-surface aquifers and fracturing through permafrost zones, resulting in catastrophic disruption and discharge of rock material and volatiles. Magma-volatile interactions may account for erosion of a kilometer or more of Hellas and Isidis basin rim material during the Late Noachian. Deeply eroded areas along the highland margins of the northern plains indicate origin by collapse and erosion that may represent a collection of rapidly formed structures involving the evacuation of volatile-rich material during the Late Noachian through much of the Hesperian. Release of volatiles from aquifers perhaps related to magmatic and tectonic activity led to formation of huge chaotic terrains and outflow channels in the region north and east of Valles Marineris. Further magma-volatile interactions along the margins of the Elysium rise fed outflow-channel systems during the Amazonian. Vent-like features and unusual sinuous ridges exemplified by Dorsa Argentea formed during the Hesperian in the south polar region may be due to discharges triggered by magmatic and/or impact activity. In each case, the erosional and discharge events apparently resulted in vast, thick deposits. The potential history of such events on Mars is only partly revealed due to subsequent resurfacing. No megaregolith is preserved on Earth, which may explain the general lack of similar, huge discharge and erosional terrains on this planet. However, methane hydrate rich seafloor sediments have led to mass flows, collapse structures, and mud volcanism, offering an analogy to catastrophic discharge features on Mars.