Polyphase tectonics support accretion of the Venus highlands

Since the first radar images were acquired of Venus’ complex, radar-bright highlands, there have been questions as to how they formed. The highlands of Venus host multiple sets of crosscutting tectonic structures, appear embayed by plains lavas, and represent the locally stratigraphically oldest terrain. There is some evidence that at least one highland may contain high-silica (i.e., felsic) rock, sharing a fundamental similarity with Earth’s continents. Current hypotheses suggest that the highlands of Venus may be formed through upwelling, downwelling, or lateral movement of crustal blocks. Here, we present large-scale (<1:5,000,000) tectonic maps of two sites in the Aphrodite Terra highland and one site in the Tellus Regio highland. At each study site, our mapping indicates multiple distinct phases of tectonic deformation. Crustal blocks that exhibit different tectonic histories within these sites are demarcated by long (~150 km) thrust faults and narrow (10s of km-wide) belts of high shortening strain. These findings support previous work at various regional mapping scales that found evidence for crustal blocks having different deformational histories in close proximity to one another in Tellus and Ovda Regiones. If these spatial arrangements of contrasting tectonic deformational histories are the result of lateral motions of crustal blocks, the highlands of Venus record tectonic history from a time when Venus’ lithosphere was experiencing a version of mobile-lid tectonics, much like how plate tectonics has helped develop high-standing, tectonically diverse continents on Earth. Our detailed mapping and quantitative analysis of map linework support the hypothesis that Venus’ highlands were formed through polyphase, lateral collisions unlike that recorded anywhere else in the inner Solar System except for Earth’s continents.