Layered Features Hint at the Origin of Tesserae on Venus

Alpha Regio on Venus, seen here in a three-dimensional rendering, is some of the oldest terrain on Venus. Credit: NASA JPL.

The tesserae of Venus are some of its oldest and most tectonically deformed regions. Standing at high elevations compared to the volcanic plains that dominate the planet, their morphology, gravity signature, and possible low-iron mineral composition have led to theories that they may be remnants of Venus’s continental crust, left exposed after the rest of the planet was resurfaced by volcanism. A new study led by Paul Byrne of North Carolina State University advances a different hypothesis that the tesserae are composed of folded layers of rock, possibly like flood basalts or sedimentary rocks on Earth.

The authors analyzed radar mosaics of the tesserae returned by the Magellan spacecraft, focusing on ridges and troughs that displayed a terrace-like pattern along their flanks. Mapping these features, they found that the radar-bright (smooth), curvilinear lines that formed the terraces followed local topography in a way similar to exposed sedimentary layering on Earth. The bottom of these troughs was characterized by radar-dark (rough) patches that could be piles of eroded material. The authors also investigated the patterns caused by folding of these putative layers and found that they were similar to the complex structures formed by intersecting fold belts on Earth.

The authors note that these observations run counter to the theory that the tesserae are continental crust, as intrusive igneous rocks like granite do not form layers. Instead, tesserae may have formed from a succession of lava flows or might even be the remnants of ancient layered sedimentary rocks that formed when water flowed on the surface of Venus. While data for determining the compositions of these rocks, and therefore constrain their origin, is not currently available, a future mission to Venus that explores the tesserae could help determine whether these enigmatic features are, in fact, evidence of a very different geologic period in Venus’s history. READ MORE