Structure and kinematics of a complex impact crater, Upheaval Dome, southeast Utah

Two vastly different phenomena, impact and salt diapirism, have been proposed for the origin of Upheaval Dome, southeast Utah. Detailed geologic mapping, seismic refraction data, and the presence of shock metamorphosed rocks indicate that the dome originated by collapse of a transient cavity formed by impact. Evidence is: (1) the occurrence of a lag deposit of rare impactites, (2) fan-tailed fracture surfaces (shatter surfaces) and rare shatter cones are present near the center of the structure, (3) the top of the underlying salt horizon is at least 500 m below the surface at the center of the dome and there are no exposures of salt or associated rocks of the Paradox Formation in the dome to support the possibility that a salt diapir has ascended through it, (4) sedimentary strata in the center of the structure are pervasively imbricated by top-toward-the-center thrust faulting and are complexly folded as well, (5) top-toward-the-center normal faults are found at the perimeter of the structure, and 6) clastic dikes are widespread.

We show that the dome formed mainly by centerward motion of rock units along listric faults. Outcrop-scale folding and upturning of beds, especially common in the center, are largely a consequence of this motion. We have also detected some centerward motion of fault-bounded wedges resulting from displacements on subhorizontal faults that conjoin and die out within horizontal bedding near the perimeter of the structure. The observed deformation corresponds to the central uplift and the encircling ring structural depression seen in complex impact craters.