Tectono‐Magmatic, Sedimentary, and Hydrothermal History of Arsinoes and Pyrrhae Chaos, Mars

Erica Luzzi,Cristian Carli,Angelo Pio Rossi,Francesca Altieri

doi:10.1029/2019je006341

Abstract

AbstractArsinoes and Pyrrhae Chaos are two adjacent chaotic terrains located east of Valles Marineris and west of Arabia Terra, on Mars. In this work, we produced a morpho‐stratigraphic map of the area, characterized by a volcanic bedrock disrupted into polygonal mesas and knobs (Chaotic Terrain Unit) and two nondisrupted units. The latter present a spectral variation, likely associated with hydrated minerals, and they are here interpreted as sedimentary units. The reconstructed geological history of the area starts with the emplacement of the basaltic bedrock, followed by the collapse that caused the formation of the chaotic terrains. Since evidences of volcano‐tectonic activity are widespread across the area (e.g., fissure vents/graben, radial and concentric systems of faults, y‐shaped conjunctions, lava flows, and pit chains), and an intricate system of lava conduits is hypothesized for the occurrence of such features, we propose the possibility that the whole collapse was caused primarily by volcano‐tectonic processes. In a late stage, after the end of the volcano‐tectonic activity, a lacustrine/evaporitic depositional environment could have set, with the deposition of the nondisrupted units. The hydrated minerals found in the periphery of the Chaos could be the result of hydrothermal alteration of the basaltic bedrock.

Highlights

Arsinoes and Pyrrhae Chaos are two adjacent chaotic terrains, respectively, centered at 7.8°S, 332°E and 10.3°S, 331.5°E (Figure 1), a few tens of kilometers south of Aureum Chaos and a few hundred kilometers SW of Aram Chaos, sharing with the latter many structural and depositional characteristics
The stratigraphic relationships indicate that the oldest unit observed in Arsinoes and Pyrrhae Chaos is the Chaotic Terrain Unit, composed of three subunits: Fractured Plains, the Knobby Terrain, and the High Thermal Inertia Chaotic Terrain
The information that we gathered on the precollapse stratigraphy is limited to a few observations: (i) the basaltic mesas of the Chaotic Terrain Unit present different layers, suggesting multiple volcanic resurfacing events before the collapse; (ii) the ancient impact craters occurring in NE Arsinoes Chaos and SE Pyrrhae Chaos predate the collapse since they are filled with materials affected by the collapse-related structures; (iii) it is still unclear if the three subunits of the Chaotic Terrain Unit represent just a different lateral erosional evolution of the same material or if the different erosional patterns are due to a lateral mineralogical variations as yet undetected

Summary

Introduction

Arsinoes and Pyrrhae Chaos are two adjacent chaotic terrains, respectively, centered at 7.8°S, 332°E and 10.3°S, 331.5°E (Figure 1), a few tens of kilometers south of Aureum Chaos and a few hundred kilometers SW of Aram Chaos, sharing with the latter many structural and depositional characteristics. Several mechanisms of formation were proposed in literature to explain the nature of the putative collapse responsible for the disruption of the bedrock into polygonal blocks that characterizes the chaotic terrains.

Results

Discussion

Conclusion