IMPACT CRATER EXPLORATIONS
by: Charles O'Dale
UPHEAVAL DOME IMPACT CRATER, Utah
The structure had been interpreted as a crypto volcanic feature, a salt diapir*, a pinched-off salt diapir, and an eroded impact crater. Recent structural mapping, modeling, and analyses of deformation mechanisms strongly support an impact origin. Deeply eroded by Upheaval Canyon, it is one of the best exposed impact craters on this planet offering excellent views of its structural features in both plan and profile. The deformed zone which defines the Upheaval Dome Impact Crater is about 5.5 km (3.4 mi) in diameter. A prominent central peak dominates the structure and is ringed by a syncline (Huntoon 2000).
The precise age of Upheaval crater has not been determined. The problem is that the crater is deeply eroded so that crucial melt rocks and post-impact crater-filling sediments are missing. One certainty is that the crater is younger than the Jurassic Navajo Sandstone which was deformed by the impact and is the youngest unit exposed in the vicinity.
*A diapir is a type of intrusion in which a more mobile and ductily-deformable material is forced into brittle overlying rocks.
Geological Evidence for Impact
The original impact origin hypothesis for Upheaval Dome is based on the following criteria (Buchner, 2008):
- There isn’t a salt diapir anyplace in the vast Paradox basin with a structure remotely similar to Upheaval Dome, although many classical diapirs are present;
- The structural character of Upheaval Dome is identical to that of proven impact craters;
- The temporal relationship between different classes of strain features and the strain orientations that can be deduced from them at Upheaval Dome are consistent with the different stages of crater growth, whereas they are inconsistent with those of diapirs. When meteorites collide with the earth, they leave impact craters like the well-known one in Arizona. Some geologists estimate that roughly 60 million years ago, a meteorite with a diameter of approximately 0.5 km hit at what is now the Upheaval Dome. The impact created a large explosion, sending dust and debris high into the atmosphere. The impact initially created an unstable crater that partially collapsed. As the area around Upheaval Dome reached an equilibrium, the rocks underground heaved upward to fill the void left by the impact. Erosion since the impact has washed away any meteorite debris, and now provides a glimpse into the interior of the impact crater, exposing rock layers once buried thousands of metres underground. Structures produced during the three stages of cratering are preserved at Upheaval Dome. The conclusion of the contact and compression stage and earliest part of the crater excavation stage are represented by pseudo-shattercones and clastic dikes. Mechanical thickening of the stratigraphic section by conjugate thrust faults and ductile crowding structures adjacent to the opening transient crater remain from the crater excavation stage. A record of the gravity-driven modification stage is preserved as:
- listric normal faults that carried material back into the transient crater;
- imbricated thrust sheets piled against the central peak representing the material that slid back into the transient crater;
- a ring syncline produced by mechanical thinning associated with the listric normal faulting;
- outwardly plunging anticlines which reveal shortening of the circumferences of the ring-shaped hanging wall blocks as they contracted toward the center, and;
- a prominent central peak caused by rebound.
- There are no remnants of Paradox or Hermosa strata, some of which are insoluble, either in the core or around Upheaval Dome to reveal that salt moved through the structure, and;
- The energies required to produce many of the classes of structures observed in Upheaval Dome, to cause the shattering of sand gains in the clastic dikes in the core of the crater, and to possibly cause the hydraulic fracturing at Roberts rift and the soft-sediment deformation of the Carmel Formation far exceed those available in diapirism.
- The Roberts rift is a unique northeast-striking, circa 10 kilometer-long fracture located approximately 25-30 kilometers northeast of Upheaval Dome and hypothesized to be the result of impact at the dome (Shoemaker, 1998).
For terrestrial craters larger than 2.4 km in diameter in crystalline rocks, the rim diameter is related to the impact energy. Assume that the energy for sedimentary rocks is 20% less that the energy for crystalline rocks (Dence et al., 1977), and the kinetic energy of the impactor that formed Upheaval Dome had an impact velocity of 20 km/sec. For a crater of 5 km diameter, the expected uplift is approximately 350 meters. Hence, the observed structural uplift at Upheaval Dome is consistent with the scaling relationship derived from other terrestrial impact craters (Shoemaker 1998).
Compactional deformation bands found within the Wingate Sandstone at Upheaval Dome require between 0.7 GPa and 4.6 GPa to nucleate. These magnitudes of mean stress are consistent with numerical model predictions of a meteoritic impact. These deformation bands are additional evidence of an impact event at Upheaval Dome. This finding also supports a post-Wingate (post-Early Jurassic) age for this impact (Okubo 2007).
Planar Deformation Features (PDF) Confirmation of impactMIAC).
Planar deformation features, in quartz grains have been documented from within the Upheaval Dome Impact Crater, Utah, USA. Quartz is a mineral which retains particularly well the memory of the extreme pressures induced during impact. TEM analyses revealed that the lamellae are dislocation bands with extremely high dislocation densities that contain numerous fluid inclusions precipitated on the dislocations. The original amorphous material of the lamellae was devitrified by thermal annealing.
Documentation of planar deformation features provides the definitive evidence for the impact origin of Upheaval Dome. Experiments have concluded that such lamellae are impact diagnostic as they can only be produced by a rapid pressure change of > 10,000 atmospheres and cannot form in any other geological environment. The documented planar deformation feature lamellae discovered at Upheaval Dome suggest an impactor contact causing shock pressures of ~10 GPa at a distance of <1.3 km from the crater center (Buchner 2008).
One of the great benefits of this crater documenting hobby of mine is I get to meet and correspond with many interesting people with a common interest.
Buchner, E., Kenkmann, T., Upheaval Dome, Utah, USA: Impact Origin Confirmed. Geology, v 36, no 3, p 227-230. 2008.
Dence M. R., Grieve R. A. F., and Robertson P. B., Terrestrial impact structures: Principal characteristics and energy considerations. In Impact and Explosion Cratering: Planetary and Terrestrial Implications. D. J. Roddy, R. O. Pepin, and R. B. Merrill, eds., pp. 247–275. Pergamon, 1977.
Peter W. Huntoon, Upheaval Dome, Canyonlands, Utah: Strain Indicators that Reveal an Impact Origin. Utah Geological Association, 2000.
Kenkmann, T., Jahn, A. Scherler, D. and Ivanov,B.A., Structure and formation of a central uplift: a case study at the Upheaval Dome impact crater, Utah. In Kenkmann, T., Hörz, F. and Deutsch, A. (eds.) Large Meteorite Impacts. Geological Society of America Special Paper 384 Chapter 6. 2005.
Chris H. Okubo ,Richard A. Schultz, Compactional deformation bands in Wingate Sandstone; additional evidence of an impact origin for Upheaval Dome, Utah. Lunar and Planetary Laboratory, University of Arizona, 2007
Eugene M. Shoemaker, Bryan J. Kriens, Ken E. Herkenhop, GEOLOGY OF THE UPHEAVAL DOME IMPACT STRUCTURE, SOUTHEAST UTAH. Journal of Geophysical Research--Planets, April 16, 1998
Additional References for the Impact Hypothesis (pre shock metamorphic discovery)
Arguments in favor of an impact origin are based on Upheaval Dome’s structure:
Kanbur, Z., Louie, J.N., Chavez-Perez, S., Plank,G.and D.Morey., Seismic reflection study of Upheaval Dome, Canyonlands National Park, Utah, Journal of Geophysical Research, v 105, E4, p 9489-9505. 2000.
Kenkmann, T., Scherler, D., New structural constraints on the Upheaval Dome impact crater. Lunar and Planetary Science Conference 33, Houston: CD-ROM 1037. 2002.
Kenkmann, T., Ivanov, B. A., The Upheaval Dome impact crater, Utah: Combining structural and numerical data to constrain age, diameter, and amount of erosion. Lunar and Planetary Institute Third International Conference on Large Meteorite Impacts, August 5-7th, 2003, Nordlingen, Germany. 2003.
Kriens, B. J., Herkenhoff, K.E. and Shoemaker,E.M., Structure and kinematics of a complex crater: Upheaval Dome, southeast Utah (abstract). Large Meteorite Impacts and Planetary Evolution,. 1997.
Louie, J. N., Chávez-Pérez, S. and Plank,G., Impact Deformation at Upheaval Dome, Canyonlands National Park, Utah, Revealed by Seismic Profiles. (abstract), Fall AGU, p. F337. 1995.
Scherler, D., Kenkmann, T. , Jahn, A., Structural record of an oblique impact, Earth and Planetary Science Letters, 248, P. 43 - 53. 2006.
Scherler, D., Jahn, A. Kenkmann,T., Structural investigations in the central uplift of the Upheaval Dome impact crater, Utah, Lunar and Planetary Institute Third International Conference on Large Meteorite Impacts, August 5-7th, 2003, Nordlingen, Germany. 2003.