Geologic mapping of Inari: A large Venusian corona dominated by subsurface processes

Abstract

Venus and Earth are planets similar in size, mass, and presumed internal heat budget, and thus one might expect similar processes of heat transfer recorded at the surface. However, Venus lacks plate tectonics and therefore its heat transfer mechanisms are unknown. Due to the planets’ similarities, understanding heat transfer processes on Venus can give insight into Earth’s processes and those of other planets. NASA’s Magellan mission employed synthetic aperture radar (SAR) to penetrate Venus’ dense atmosphere to view and image 98% of the surface. Linear mesolands form broad zones, characterized by fracture zone terrain, that connect contemporary volcanic rises. Inari Corona is a unique tectonomagmatic structure within the fracture zone. Unlike many fracture zone coronae, Inari Corona sits relatively isolated and it lacks obvious evidence of volcanic activity at the surface; both of these characteristics contribute to preservation of its rich geologic history. I constructed broad and detailed geologic maps of Inari Corona in order to understand its geologic history and thus gain insight into geologic processes of heat transfer through the lithosphere at this location. Geologic mapping of structural elements revealed three key points: 1) Inari Corona is much larger than previously proposed (>1,000 km vs 300 km diameter); 2) Inari Corona is dominated by subsurface processes, as opposed to extensive surface flows; and 3) Inari Corona evolved dynamically through time and space. In addition, Inari Corona preserves two types of features/deposits that play a critical role in Inari evolution: 1) the extensive development of pit chains, and 2) possible extensive pyroclastic flow deposits. Radial and concentric pit chains, evidence of subsurface processes, dominate Inari Corona’s center. Pit chains occur on numerous planetary surfaces including Earth, Moon, and Mars; however, the pit chains on Venus differ from those on other bodies based on width, length, spacing, and penetrative development across extensive regions (up to 100,000 km2). Surface deposits that cover preexisting features are mainly focused on Inari Corona’s outermost flanks; however, patches of surface cover (veneer) appear randomly across Inari, only partially obscuring features. Patches of veneer may result from selective deposition and erosion from pyroclastic flow deposits. Veneer patches are huge (potentially covering 150,000 km2) compared to relatively minor deposits recently reported (covering up to 40,000 km2).