MULTIPLE MECHANISMS RESPONSIBLE FOR VARIABLE SURFACE MORPHOLOGIES OF FISSURES AT CERBERUS FOSSAE, MARS

The Cerberus Fossae, Mars, is a ~1200 km-long system of fissures that may be associated with a protracted history of volcanism, tectonism, and fluvial activity. The fissures are oriented approximately radial to Elysium Mons, and likely formed in response to underlying dike intrusions that emanated from the central volcano. The surface manifestation of the fossae has been variably hypothesized to be the result of subsidence-related depressions caused by magmatic melting of the cryosphere, collapse into evacuated magmatic fissures, or dike-induced faulting. While significant aspects of the volcanic and fluvial history have been well documented, the primary formation mechanisms of the fossae have not been satisfactorily explained. To constrain the primary formation mechanisms, we classify the topography and geomorphology of the fossae using altimetry data from the Mars Orbiter Laser Altimeter and CTX imagery. The most prominent fossae are up to 2 km wide, 1.2 km deep, 200 km long, and crosscut Elysium lavas, the heavily cratered Tatarus Montes region, and young Cerberus lavas. These fossae were the source of the Athabasca Valles megafloods and subsequent basalt lavas. In contrast, less pronounced fossae are up to 0.5 km wide, 0.1 km deep, 50 km long, and primarily crosscut the Cerberus lavas. These significantly smaller fossae are located in a region ~300 km ESE of the Athabasca Valles source, and exhibit subdued topography surrounding the fossae edges. This morphology is unique to the smaller fossae, and may represent near-surface magmatic dikes that melted the cryosphere and produced lahars, or erupted and deposited lava flows. The similar orientations and en echelon patterns along the entire 1200 km-long fissure system suggest an identical underlying process for fissure initiation, but with two or more disparate near-surface mechanisms responsible for differences in surface morphology. In one mechanism, applicable to the deeper fossae, dike-induced faulting predominates, producing fissures with throw profiles similar to terrestrial normal faults, and sharp fossae edges. In the second mechanism, dikes propagate all the way to the surface to produce linear volcanic vents, lahars, scalloped fossae margins, and skylights above underlying caves that may be related to evacuated dikes.