EVIDENCE FOR THE COLLAPSE AND PARTIAL BURIAL OF A SMALL CRUSTAL PLATEAU IN THE PASOM-MANA TESSERA REGION, VENUS

The Pasom-Mana Tessera region on Venus (centered on 30S, 37E) consists of a topographically high ring approximately 1000 km across rising 1-3 km above both a low center and the surrounding plains. The oldest units in the area are ribbon tessera that have been flooded and embayed by a succession of younger lava flows and cut by younger structures. The topographic ring consists of a continuous arc of ribbon tessera in the west, south, and southeast, patches of ribbon tessera in the northwest, and kipukas of tessera in the northeast. Structures suggest very shallowly-buried tessera beneath much of the central area. Orientation and age relationships of structures in the tessera are consistent with those that might be expected in a small crustal plateau that has collapsed and been flooded by younger lavas.

Evidence for progressive collapse and burial of the area is suggested by synthetic stereo data for the region. Differential vertical motion between the tessera ring and areas both inside and outside the ring is indicated by warping of grabens, warping of flows against the sides of the ring, and warping of flows over the ring. Evidence for differential vertical motion can be documented throughout the post-tessera history of the region to the very latest stages of flooding by young lava flows. Differential vertical motion is most logically explained by subsidence of the central portion of the area and surrounding plains relative to the tessera ring.

Modelling by Nunes and Phillips (2002) suggests that an uncompensated crustal plateau on Venus will collapse and develop a low center, high rims, and a low “moat” around the rims. The Pasom-Mana Tessera region exhibits precisely the kind of structures and history that would be consistent with collapse and partial burial of a small uncompensated crustal plateau.