Planetary Geology Lecture Outline - Venus
Major processes shaping surface:
Odd or significant facts about Venus:
Thoughts on use of terms crust, mantle, lithosphere: compositional vs. mechanical layers.
Nature of tectonic processes?
Right now there is a focus on models of vertical tectonics (hotspots) for Venus. This mirrors the earlier evolution of thought for the earth's tectonics. It is relatively easy to 'see' the vertical component of deformation. Horizontal motions were thought to be secondary, topography and gravity driven activity in response to primary vertical motions (e.g. the geosynclinal theory). On Venus the numerous and widespread volcanic features clearly indicate sites of upwelling. Associated radial and concentric fracture patterns are part of the upwelling picture. Vertical tectonics rule.
However, there are also pervasive regional fracture and rift patterns, other fracture arrays suggestive of lateral (strike-slip) motion, and areas of regionally strained features on Venus. These are good hints of significant horizontal motions. Sites of downwelling are usually depressions (e.g. trenches on earth) and thus would fill in and be buried, perhaps with flow material. Also, there is no reason why the crust of Venus should not be mechanically laminated in a manner similar to earth. This would also promote thin-skinned tectonism associated with crustal detachments. It is clear the earth-like plate tectonics does not exist, but a permobile regime of small, fast changing and rheid terranes might very well exist. Reading the literature I am struck by how far we have to go before we have a good understanding of the tectonics on Venus.
Topographic map of Venus
Discussion question for next time: What are the ways water played a role in Martian landscape development (I can think of at least three)?
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