VOLCANOTECTONIC PROCESSES NEAR MARS’ DICHOTOMY BOUNDARY (Invited Presentation)

The formation of widespread late Hesperian chaotic terrain and extensional fractures to the east of Tharsis has frequently been attributed to the interaction between intrusive volcanism and a thickened post-Noachian cryosphere [e.g. 1, 2], suggesting that magmatism was intimately involved in both tectonics and fluid outflow during this period. However, evidence for associated surface volcanism is limited [3], casting doubt upon these connections.

We show widespread evidence for flat-topped deposits with steep, lobate margins intimately associated with Hesperian to Amazonian extensional fractures across the Margaritifer Terra region, particularly within the Ladon basin and floor-fractured impact craters. The morphology and inferred mineralogy of these deposits is most consistent with lava flow sourced from the fractures. A volcanic interpretation is supported by the discovery of several constructive edifices around the margin of the Ladon basin associated with diffuse-margined material with a similar spectral signature, which we interpret as pyroclastic. The lava deposits overlie Noachian sediments scoured by fluid outflow from the fractures and are themselves eroded by such fluids, indicating a complex history of fracture-sourced volcanic and aqueous activity. Thus, we show that volcanic activity at Mars’ dichotomy boundary was indeed closely associated with extensional tectonics and fluid outflow, supporting a genetic relationship between these three processes.

[1] Chapman, M. & Tanaka, K. (2002) Icarus, 155:2, 324-339. [2] Rodriguez, J.A.P. et al. (2005) Icarus, 175, 36-57. [3] Meresse, S. et al. (2008) Icarus, 194, 487-500.