Surface deformation in eastern Aphrodite Terra and Atla Regio, Venus

This study focuses on the structure and origin of eastern Aphrodite Terra and of the Ganis Chasma trench system and the associated volcanic constructs of Sapas, Ozza and Maat Montes in Atla Regio. Detailed morphological and stratigraphic analyses, combined with the available topography and gravity data, are used to distinguish between primary and secondary structures and thus to reconstruct the sequence of events that led to the present landforms. The earliest phase of the structural history of the study area is recorded by islands of ridge and groove terrain which testify to a period of compression, extension and crustal thickening/uplift. The next phase saw a period of both extensive and localised flood volcanism and continuing tectonic activity. There followed a period of major upper and lower mantle upwelling which produced the dominant landforms and much of the present morphology. The most recent activity is the volcanism at Maat Mons on the Atla Regio rise. The results favour the role of deep mantle plumes in the formation of the Ganis Chasma system and the three volcanic constructs, a mechanism previously proposed for other parts of Venus primarily by analogy with gross terrestrial morphology. The results also suggest that eastern Aphrodite Terra was a product of a number of diapirs originating in the mantle. Regions immediately to the north and south of eastern Aphrodite Terra, identified and named in this study as undulating terrain, are also likely to be the early result of diapiric action. The surface expression of diapirs in eastern Aphrodite Terra favours a relatively thin lithosphere, whereas the plume activity proposed for Atla Regio points to a comparatively thick lithosphere. Diapiric and plume activity is directly associated with crustal rifling both within the study area and elsewhere on Venus