Formation and evolution of volcanic edifices on the Dione Regio rise, Venus

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Abstract
Mapping of Dione Regio, Venus, a regional highland 1200 by 2700 km in size with mean elevation of 6052 km located in the southern hemisphere to the NW of Lavinia Planitia, reveals a region characterized by early tectonically dominated structure and later widespread volcanism and centralized edifice construction. Small patches of complexly deformed terrain (tessera) and larger regions of plains characterized by a single direction of deformation (tectonized plains), preserved as inliers, are embayed by more recent widespread volcanic plains. Smaller‐scale plains resurfacing superposed these plains following a pervasive compressional event that lead to distributed wrinkle ridge formation. Four major volcanoes dominate the topographically irregular highland, each with similar early‐stage radar‐dark lava flow deposits but significantly different late‐stage eruptions. These late‐stage differences are manifested as dark, diffuse deposits (possibly pyroclastic in origin) and construction of a single steep‐sided dome at Ushas Mons, a small shield‐volcano field at Nepthys Mons, and bright diffuse deposits (possible pyroclastic deposits) with summit dome and pit formation at Innini and Hathor Montes. The presence at all of these volcanoes of radial lineaments and graben, interpreted to be related to near‐surface lateral dyke emplacement, and late‐stage summit constructional features indicate that shallow magma chambers occur at each edifice. Variations in the evolutionary history of and eruptions from these chambers may explain the differences observed in the deposits at these major edifices. It is also possible, however, that fundamental differences in the magma source region was a major factor in determining the appearance of the deposits. Of the several models considered for the formation of the region, secondary upwellings from a single large mantle plume or the near‐contemporaneous upwelling of multiple smaller plumes best explain the observed characteristics at the rise. A comparison to other volcanic highlands suggests that there are at least two classes of volcanic rises on Venus, an areally and topographically large type with significant volcanism and rift zone formation (like Beta Regio) and a smaller‐scale type with extensive volcanism but moderate rifting (like Western Eistla Regio). These two classes reflect a spectrum in size and vigor of mantle upwellings. The Dione rise is most like Western Eistla Regio in terms of areal extent, topographic elevation, and geologic complexity.