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

Abstract

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.

Global tectonic evolution of Venus, from exogenic to endogenic over time, and implications for early Earth processes

“…outcrops define coherent patterns, indicating shallow subsurface continuity of tesserae and providing evidence of cross-cutting relations between different tessera suites (figure 4a,b) [13]. In NAMA, the delicate NE-and NW-trending lineament suites generally parallel adjacent tesserae fabric trends, consistent with tesserae reactivation, and the coherence of lowland tesserae patterns and lineament suites indicates a lack of plate tectonic processes, which would have destroyed regional continuity [3].…”

“…The related global stratigraphy hypothesis calls for catastrophic emplacement of 1-3 km thick 'wrinkle ridge plains' across approximately 80% of the surface [39][40][41][42]. However, a growing number of studies are inconsistent with the notion of catastrophic resurfacing and global stratigraphy [3,10,11,13,[43][44][45][46][47][48][49][50][51].…”

“…The Artemis superstructure, best viewed on a globe to alleviate distortion caused by map projection (figure 8a), post-dated tesserae formation and affected a thicker global lithosphere [3,14]. The superstructure includes the 12 000 km-diameter suite of Artemis Chasma-radial fractures and the 13 000 km-diameter suite of Artemis Chasma-concentric wrinkle ridges (figures 1-3 surface; however, a super plume this large would also have had a global effect on mantle dynamics.…”

“…In this contribution I provide a broad global overview that illustrates a rich Venus geologic history in both time and space. The recorded tectonic history is explored through structural relations documented in the Niobe-Aphrodite map area (NAMA), comprising over 25% of the Venus surface [3]. NAMA preserves at least three different tectonic domains that represent fundamental changes in tectonic regimes through time.…”

“…Mercator projection of Niobe-Aphrodite map area (NAMA) structural elements[3]. Structures and other prominent features are grouped in the key by the era in which they formed.…”