Long‐Lived and Continual Volcanic Eruptions, Tectonic Activity, Pit Chains Formation, and Boulder Avalanches in Northern Tharsis Region: Implications for Late Amazonian Geodynamics and Seismo‐Tectonic Processes on Mars

Abstract

AbstractTharsis is the largest volcanic province on Mars. It consists of a few large shield volcanoes, one of which is Alba Mons (AM), located in northern Tharsis, with the Ceraunius Fossae (CF) graben system to the south of it. Previous workers argued in favor of episodic building of Tharsis volcanoes. In contrast, we show that volcanism in the AM and CF regions occurred continually, at least in the last few hundred million years, based on ages of >1,000 stratigraphically young lava flows. Central volcanism in AM terminated around 200 Ma, while subsequent young volcanism, fed by both small shields and fissures, migrated to the south in CF. Several generations of grabens hosting thousands of simple to complex pit chains were formed by magmatic intrusion through feeder dikes, and these activities also migrated to the south during the Late Amazonian epoch. Thousands of boulder avalanches mark the slopes of grabens, pit chains, and impact craters, with ages ranging from a few tens to thousands of years. The local geological settings of the boulder falls suggest that both tectonic and volcanic marsquakes triggered the boulder avalanches. The broad zone of boulder falls in northern Tharsis defines the potential epicentral zone of (MW 4.1) 18 September 2021 marsquake. We infer that long‐lived and active magma chambers and subcrustal magma underplating driven by a mantle plume are present beneath the AM volcano and that these probably migrated south toward CF in the Late Amazonian epoch.