INTRODUCTION

The geologic map shows lava flows and fan-shaped deposits on Pavonis Mons, the central of three large shield volcanoes (Arsia, Pavonis, and Ascraeus Montes) that form the Tharsis Montes volcanic chain. The volcanoes lie along the crest of a regional northeast-trending rise that extends more than 3,000 km across the western equatorial region of Mars (fig. 1). The volcanic history of Pavonis Mons is similar to that of other volcanoes in the western equatorial region of Mars (Scott and others, 1981a–c; Scott and Tanaka, 1981, 1986; Zimbelman and Edgett, 1992). Previous geologic mapping of this region (Scott and others, 1981a–c; Scott and Tanaka, 1981, 1986) shows six major lava flows that were extruded from the Tharsis volcanoes during the Early Hesperian to Late Amazonian Epochs; four of these lava flow members are present in the map area. On the northwest flank of Pavonis Mons, broad, lobate, fan-shaped deposits form a surficial cover similar to other fan-shaped deposits on the northwest flanks of Arsia, Ascraeus, and (to a lesser degree) Olympus Montes. Similar to those of Arsia Mons, the fan-shaped deposits of Pavonis Mons consist of several facies whose origins are attributed to glaciation, mass wasting, and pyroclastic volcanism origins. The present map was compiled originally using four Viking 1:500,000-scale photomosaic bases (fig. 1). Then, to show more clearly the regional relations, the maps were reduced to 1:1,000,000 scale and combined on one map sheet. Image quality is generally poor throughout the map area, especially on the west flank of Pavonis Mons, even though most images have a resolution of about 75 m per pixel.

The purpose of the large-scale (1:500,000) mapping was to study the morphology and stratigraphy of the fan-shaped materials on Pavonis Mons for comparison with those on Arsia Mons (Scott and Zimbelman, 1995) and to determine whether they have similar origins and ages. The geologic units were mapped, dated, and interpreted more accurately using the larger scale than was possible on smaller scale 1:2,000,000 (Scott and others, 1981a–c; Scott and Tanaka, 1981) and 1:15,000,000 (Scott and Tanaka, 1986) maps. Map units generally correspond to those on the geologic map of the western equatorial region of Mars (Scott and Tanaka, 1986) and to units on the map of Arsia Mons (Scott and Zimbelman, 1995).