Abstract

Studies of Mariner 9 imagery have included the mapping and analysis of fractures from A frames spaced roughly 20° apart in a band parallel to the equator from 30°S to 30°N. Fracture rosettes were produced and plotted for each picture analyzed. Geometric analysis of these fracture patterns indicates the existence of a coherent global fracture system. This system Is especially pronounced within the cratered terrains of the southern hemisphere. These fractures form orthogonal sets with a concentration of azimuths trending NW-SE (the major set) and NE-SW (the minor set). This global orthogonal pattern is obscured (but still present) in the northern “smooth” terrains. This suggests that the global fractures may be older than the regional fractures of the Tharsis complex.

The uplift of the Tharsis region appears to have been a dominant factor in the creation of the more recent tectonic features in the western hemisphere. The basic regional pattern in this area is one of extension fractures roughly radial to the Tharsis volcanic complex apparently produced during doming of the region and associated lateral compression.