New geologic mapping reveals that Artemis, a unique 2400-km-diameter feature on Venus, is much larger than previously recognized, including a wide outer trough (>5000 km diameter), a radial dike swarm (12,000 km diameter), and a concentric wrinkle ridge suite (13,000 km diameter). Artemis's evolution included formation of its interior and chasma, accompanied by lateral propagation of radial dikes. The escape of dike magma to the surface formed local cover deposits that buried parts of the remaining radial fracture suite. Cover deposits are cut, in turn, by wrinkle ridges that likely formed by coupling of convective mantle flow with the lithosphere. The outer trough formed late relative to radial fractures, cover deposits, and wrinkle ridges. We suggest that Artemis represents the magmatic signature of a deep mantle plume acting on relatively thin lithosphere. As such, it appears to represent the largest tectonomagmatic feature in the solar system. The newly recognized vast extent of Artemis holds implications for the formation of giant radial dike swarms, wrinkle ridge formation, terrestrial planet mantle-lithosphere coupling, and Venus's surface and geodynamic evolution.

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