The Origin of Tharsis

Abstract

The gravity potential field ofMars is characterized by a long-wavelength feature located at the Tharsis region. In addition, this region houses large volcanoes that have been active until geologically recently (200 to 100 Ma ago). Research has not succeeded in pinpointing the cause of this long-wavelength areoid high, while some researchers claim it is due to a mantle plume, others suggest that it is caused by volcanic construction and the associated flexure in the lithosphere. This work aims to contribute to resolving this question with the development of a new mantle convection model for Mars. It is renewing in four aspects; (1) A Mars model is developed in SFEC (Tosi, 2007), which has been primarily used for Earth studies, (2) mantle anomalies are analysed in order to determinewhether they could be involved in the creation of the Tharsis volcanoes, (3) the solutions challenge the current views upon the (pre-dominantly isostatic) support of Tharsis and (4) a new method is developed to assess the similarity of models and observations for low degree spherical harmonics (n Ç 5) fields. The research contributes to a better understanding of the Martian interior and the volcanic activity in the Tharsis region. Seismic studies of the Earth’s interior have correlated large provinces on the core-mantle-boundary with plume generation and hotspots that arise on Earth’s surface. This research investigates whether similar structures in the Martian mantle could be connected to, or even be the cause of, the volcanism in the Tharsis region. Firstly, a crustal reduction is performed to obtain the gravitational field of the mantle and core. An Airy model is used for this as research found this to be the dominant form of compensation for long-wavelength features on Mars (Mussini, 2020). Subsequently, density anomalies are positioned in the mantle and their gravity potential is computed and compared with the observations.