Tectonic Deformation and Volatile Loss in the Formation of Noctis Labyrinthus, Mars.

Noctis Labyrinthus is a little‐studied and structurally complex area situated between the Tharsis Rise and Valles Marineris on Mars. Noctis Labyrinthus is dissected by normal faults that form horst and graben, pit craters situated inside the graben, and large troughs that cross‐cut both graben and pit craters. Mass wasting, periglacial, and some erosive fluvial features are observed at the bases of the troughs, suggesting that the troughs hosted liquid and perhaps even ice at some point in the past. We mapped and analyzed these structural and morphological features in Noctis Labyrinthus to establish the region's formational history. Fault throw profiles, combined with morphometric data from pit craters, were used to assess how the pit craters relate to the much larger troughs in the region and whether those troughs were formed by extensional tectonic deformation alone. This comparative analysis suggests that some pit craters grew deeper than the amount of throw accommodated by their bounding faults. We hypothesize that layers with subsurface volatiles (such as ground ice) were intersected and exposed by the larger Noctis Labyrinthus pit craters, enabling sublimation that further promoted mass wasting and the growth and coalescence of pits and graben into the large troughs. Under this scenario, subsurface volatiles played an important role in forming this structurally complex region, and may still be present there. Plain Language Summary: Noctis Labyrinthus (Lat., "Labyrinth of the Night") on Mars is a topographically complex region situated between Mars' largest volcanic province, Tharsis, and the vast canyon system, Valles Marineris. The Noctis Labyrinthus region has many fractures, pits, craters, and troughs, but how these features formed and interacted with one another is still not fully understood. We mapped the fractures, pits, craters, and troughs in this region to better understand the relative timing of the formation of Noctis Labyrinthus. We conclude that extension of the crust led to pit crater formation through the drainage of surface material into fractures. Further dissection of the landscape was enhanced by the exposure of ice in the subsurface during pit formation that was then melted or sublimated to create ever‐larger depressions. We estimated the depth of this subsurface ice from the distribution and sizes of craters with fluidized ejecta deposits. The bottoms and walls of the troughs show physical evidence for a long‐term role played by ice in the formation of this distinctive part of Mars. Key Points: Noctis Labyrinthus is host to more than 200 pit craters, over 100 deep troughs, and thousands of normal faultsEvidence of erosional processes is present in the form of mass wasting and periglacial landforms located in the deep troughsThe formation of Noctis Labyrinthus was enhanced through substantial volatile loss, as recorded by the periglacial features in the troughs [ABSTRACT FROM AUTHOR]