Gravity Profile Across the Wind River Mountains, Wyoming

A gravity profile was constructed across the central Wind River Mountains from data obtained by field measurements tied to unpublished oil company surveys. The total Bouguer anomaly relief is about 100 mgal from the Green River Basin to the crest of the range. Analysis of the profile confirms that the southwest flank of the mountains is underlain by a major low-angle thrust fault. However, an interpretation based on a relatively high basin-mountain density contrast of about 0.3 g per cm³ suggests that the thrust wedge of Precambrian rocks has an average thickness of 10,000 feet, thinner than previously mapped by reflection seismic data, and that subthrust sedimentary rocks may extend farther beneath the mountain flank, perhaps as much as 65,000 feet. An alternate interpretation based on a lower density contrast of about 0.2 g per cm³ also confirms a flank thrust in closer agreement with seismic data but results in an ''excess" anomaly of about 35 mgal over the range. This excess must be attributed to a more dense mass within or beneath the mountains for which no geologic evidence exists.