Beta Regio, Venus: Evidence for uplift, rifting, and volcanism due to a mantle plume

Geophysical data have led to the interpretation that Beta Regio, a 2000×25000 km wide topographic rise with associated rifting and volcanism, formed due to the rise of a hot mantle diapir interpreted to be caused by a mantle plume. We have tested this hypothesis through detailed geologic mapping of the V-17 quadrangle, which includes a significant part of the Beta Regio rise, and reconnaissance mapping of the remaining parts of this region. Our analysis documents signatures of an early stage of uplift in the formation of the Agrona Linea fracture belts before the emplacement of regional plains and their deformation by wrinkle ridging. We see evidence that the Theia rift-associated volcanism occurred during the first part of post-regional-plains time and cannot exclude that it continued into later time. We also see evidence that Devana Chasma rifting was active during the first and the second parts of post-regional-plains time. These data are consistent with uplift, rifting and volcanism associated with a mantle diapir. Geophysical modeling shows that diapiric upwelling may continue at the present time. Together these data suggest that the duration of mantle diapir activity was as long as several hundred million years. The regional plains north of Beta rise and the area east and west of it were little affected by the Beta-forming plume, but the broader area (at least 4000 km across), whose center-northern part includes Beta Regio, could have experienced earlier uplift as morphologically recorded in formation of tessera transitional terrain.