Evolution of Plume Volcanism at Atla Regio, Venus

Abstract

Atla Regio is a large topographic rise, at the equator of Venus, considered to sit above a young mantle upwelling. Hosting several giant shield volcanoes, including Maat Mons, it is a strong candidate for recent eruptive activity. Through detailed analysis of material units and structures at Ozza, Maat and Sapas Mons, northern Dali Chasma and the surrounding plains, we have unraveled the tectono-magmatic evolution at Atla Regio. Lithostratigraphic analysis, of the volcanic styles, lava flow relationships, rift–associated shield clusters, graben-fissure systems and pit cratering, in relation to the regional plains and other older features, has enabled the establishment of a model of the evolution of volcanism. Structural analysis reveals that graben-fissure systems at Ozza Mons transition outward into three major rifts, and two new, unnamed volcanoes are identified. Our model is evidenced by analysis of lava flow stratigraphy and cross-cutting relationships with respect to the stratigraphic marker provided by the ejecta halo of the Uvaysi impact, and using sound stratigraphic principles. A relative chronostratigraphic framework for the area around Ozza and Maat Mons has thus been constructed, and our findings are in agreement with prior research. A new regional history is proposed here, where volcanism was initially concentrated along Dali Chasma, before plume volcanism took over at Ozza Mons and finally, Maat Mons became the most recent locus of volcanism. We propose that the pattern of large shield volcanoes with displaced centers here is indicative of minor crustal adjustments above a relatively long-lived mantle plume.