Development of Shalbatana Vallis (Mars) by dry volcanic processes

Shalbatana Vallis is a large Martian outflow system that extends into Chryse Planitia from areas of topographic disturbance located north of Ganges Chasma. Development of this system has previously been attributed to processes including: 1) the expulsion of groundwater generated by interactions between magmatic intrusions and ground ice; and 2) the northward conveyance of water along subsurface conduits connected to a deep lake impounded within Ganges Chasma. However, aqueous interpretations of Shalbatana Vallis suffer from weaknesses such as the implausible nature of hypothesized outburst processes, discrepancies between the magnitudes of subsidence that characterize parts of the system and realistic volumes of excess ice that might have once existed in the subsurface, and contradictions between the nature of hypothesized aqueous processes and the mineralogy of associated geological materials. The attributes of Shalbatana Vallis are instead consistent with dry development as a result of the rapid and voluminous effusion of low-viscosity lavas of mafic or ultramafic composition. Volcanic development of the main channel of Shalbatana Vallis is estimated to have required a minimum effusion of ∼360,000 ​km³ of lava, though a total of several times this volume is more likely to have been necessary since channel development cannot be assumed to have taken place with full efficiency. Involved lavas are hypothesized to have been fed by a deeply-rooted igneous plumbing system, and terrain collapse and disturbance located at the head of the system is expected to be partly related to the collapse of intrusions during the latter stages of igneous events. A volcanic origin for Shalbatana Vallis further highlights the critical role played by igneous processes in channel development on rocky bodies of the inner solar system.