This image (FDS 126), acquired during the spacecraft's first encounter with Mercury, includes part of the floor of the Caloris basin showing the ridges and fractures. Notice that the length and the width if the fractures increase toward the center of the basin (lower right to upper left) and that the fractures transect the ridges at various angles. The two irregular depressions at the right edge of the image near the center are rimless and apparently collapse structures rather than impact craters.
The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.