Tectono‐Magmatic, Sedimentary, and Hydrothermal History of Arsinoes and Pyrrhae Chaos, Mars. Issue 12 (23rd December 2020)

• Record Type: Journal Article
• Authors: Luzzi, Erica; Rossi, Angelo Pio; Carli, Cristian; Altieri, Francesca
• Is Part Of: Journal of geophysical research. Volume 125:Issue 12(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-23
• Subjects: chaotic terrains -- hydrothermal system -- mapping -- Mars -- spectral analyses; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2019JE006341
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Arsinoes 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. Plain Language Summary: Chaotic terrains are peculiar features on Mars. They consist of broad regions characterized by a variable surface disruption pattern of large polygonal blocks. Formation scenarios in the literature have always included a collapse, possibly caused by a range of processes, all including water or hydrated compounds (magma‐ice interactions, melting of buried ice, groundwater pressure, etc.). In this work, we propose volcano‐tectonic processes as mechanism of formation for closed chaotic terrains. Additionally, our mineralogical analyses suggest that during a late stage of the volcanic activity, a hydrothermal system could have set. In such scenario, hot water would have risen from the subsurface through fractures created by the volcanic activity, evolving from eruptive to hydrothermal. However, water would not have been directly involved in the initial collapse that formed the chaos. Key Points: We produced a morpho‐stratigraphic map of Arsinoes and Pyrrhae Chaos, including the volcanic grabens occurring throughout the study area Spectral analyses of the light‐toned deposits provide clues for sedimentary and hydrothermal minerals; spectral analyses of the bedrock are indicative of basaltic compositions The observed volcano‐tectonic surface features and the lack of evidences of any fluvial activity suggest that magmatic processes might be primarily responsible for the collapse of the chaotic terrain