ROBERTS RIFT, CANYONLANDS, UTAH, A NATURAL HYDRAULIC FRACTURE CAUSED BY COMET OR ASTEROID IMPACT

The impact that created Upheaval crater in Canyonlands National Park, Utah, is invoked here as the source for energy that simultaneously cau sed Roberts rift. However, no temporal linkage has been proven between the impact and rifting events. Roberts rift lies between 22 and 32 km northeast of the Upheaval impact crater on a subradial trend. The fis sure contains clasts that were carried as much as 1,000 m upward from Paleozoic sources into the Mesozoic section. A plausible model for bot h the rifting and clast movement involves incremental loading of overp ressured fluid compartments in the Pennsylvanian Paradox section and a ttendant hydraulic fracturing of the overlying confining strata during the impact event. The clasts were proppants entrained in upward movin g fluids that originated from overpressured aquifers in the Pennsylvan ian section or materials eroded from the fissure walls. Alteration hal os and mineralization along the fissure reveal that there was upward l eakage of reducing fluids from the overpressured zones following openi ng of the fissure. The fissure infillings became cemented with time, t hus reducing fissure permeabilities to negligible.