Structural Control of Fluvial Network Morphology on Titan

Titan fluvial networks have been classed based on identification of network pattern morphology. Drainage network patterns have specific geologic implications, as the pattern is affected by regional slope, structures, and bedrock resistance. Qualitative identification of network patterns has resulted in a lack of consistent classifications for networks. In this work, a global map of fluvial features on Titan is presented with features delineated based on their appearance in Cassini Titan Radar Mapper synthetic aperture radar (SAR) data. The networks imaged by the Huygens Descent Imager/Spectral Radiometer (DISR) are also included in this work. Networks were classified using a quantitative terrestrial drainage pattern classification algorithm modified for use for Titan. This drainage pattern analysis, performed on the 48 networks of 10 or more links imaged in SAR data, results in 56% rectangular networks, 25% dendritic networks, 8% parallel networks, and 10% unclassified networks. All of the 5 networks imaged in DISR are classified as rectangular. This result is inconsistent with the results of previous network pattern identifications that indicated that the majority of networks have a dendritic pattern. Because rectangular networks imply control by joints or faults that intersect at near right angles, the predominance and distribution of rectangular networks suggests that Titan’s crust is widely fractured or faulted. A review of terrestrial river networks also classified as rectangular by the same algorithm indicates that tensional stress formed the joints and/or faults controlling the rivers. Based on the similar response of rock and ice to stress, it is inferred that the joints and/or faults controlling rectangular networks on Titan also formed in a tensional tectonic regime. Most of the Titan rectangular networks occur at the north and south poles, indicating that these areas have undergone regional extension. Rectangular networks are also located in Xanadu, but because of the unique geologic history of this region, those networks are not considered in comparison with the published results of global stress mechanisms. This comparison suggests that regional extension in these locations is not consistent with the stress regimes expected from non-synchronous rotation and polar wander and is more consistent with stress regimes expected from despinning or orbital recession.