Mapping of Geologic Structures in the Niobe-Aphrodite Map Area of Venus: Unraveling the History of Tectonic Regime Change

Recent construction of 1:10 M IMaps of Niobe Planitia and Aphrodite Terra paints a rich picture of Venus evolution. Using the Niobe-Aphrodite map area (>25% of Venus) as an example, we illustrate the methodology and importance of detailed structural mapping at large regional scales in order to identify tectonic domains that lead to the discovery of global-scale geodynamic evolution and operative processes. We highlight differences between lithodemic and lithostratigraphic units in geologic mapping. We step through a series of structural element maps that reveal the character of at least three different tectonic domains and evolving tectonic regimes that reflect changing geodynamic processes, here divided into three eras. The ancient era encompasses formation of tessera terrain and represents a time of unique global and environmental conditions marked by globally thin lithosphere. The second era resulted in formation of the Artemis superstructure. The ~13,000-km-diameter footprint of the Artemis superstructure is huge but not global, although associated mantle flow patterns could have had a global reach. As formation of the Artemis superstructure waned, tectonic activity became more focused leading to formation of the fracture zone complex. This complex extends beyond the map area connecting with Atla, Beta, and Themis regiones and associated fracture zones, marking the youngest era. Structural mapping of the Niobe-Aphrodite map area indicates that Venus exhibits a complex, multistage history like other terrestrial planets, which probably extends to several billion years. Given that Venus never developed plate tectonics, Venus' preserved surface record is likely significantly richer than that of Earth.