UCLA

Although Alba Patera is the largest volcano in aerial extent in the solar system (~6.8 km high and >1000 km in radius), the geologic processes responsible for shaping its exceedingly low-angle flanks remain poorly constrained. These flanks are covered in lava flows, valleys and both radial and annular grabens. Previous attempts, limited by the resolution of the satellite images, assume that the annular grabens formed during the terminal stage of volcanic development whereas surface water flow occurred in the early stage of volcanic construction. In this study, we analyze high-resolution CTX satellite images in conjunction with digital topographic data from MOLA. Our work reveals complex cross cutting relationships between faults, drainage network development and lava flows on the northwestern flank of Alba Patera. We observe a minimum of three generations of lava flows, three generations of drainage channels and three generations of faults. Mutual and successive cross-cutting relationships between drainage channels and faults indicate that the tectonic processes responsible for creating grabens on the volcano flank operated continuously and were coeval with drainage formation. The lava flows are observed to be the oldest geomorphic features and the third generation of faults as the youngest geomorphic features in our mapped region. Crater counting indicates that the surface within the mapped region is Amazonian in age. An analysis of the crater densities reveals a decline in crater densities from the south to the north section of the mapped region. This could be attributed to resurfacing in the north due to sediments deposited by northward flowing drainage channels. Crater counting age estimates for the south section yield a result of ~ 1.74 Ga, +/- 0.12 Ga and ~ 1.35 Ga, +/- 0.26 Ga for the north section. Hence, the younger age estimates of the northern surface could help further constrain the age of the drainage channels and faults on the northwest flank of Alba Patera.