GEOLOGIC MAP OF THE GROUSE CREEK AND EAST PART OF THE JACKPOT 30' X 60' QUADRANGLES – A KEY ARCHIVE OF UTAH’S GEOLOGIC HISTORY

The geology of the northwest corner of Utah is arguably the most complicated in the state, and was recently mapped and compiled (1:62,500 scale) through a collaborative effort by the U.S. Geological Survey, Utah Geological Survey, and university geologists. The map area lies in the hinterland of the Sevier fold-thrust belt, the Raft River-Grouse Creek-Albion metamorphic core complex, and the northeastern Great Basin, thus leading to a complicated and protracted geologic history. The rock record includes: Archean crustal growth of the Grouse Creek block (2.6 Ga); deposition of Neoproterozoic siliciclastic and mafic volcanic rocks, which record sedimentation in evolving rift basins during Rodinia breakup following an ~1.9 b.y. hiatus; continued deposition on a passive margin reflected in structurally attenuated Ordovician and locally Devonian marble and quartzite; the inception of convergent-margin tectonism with deposition of Mississippian shale, sandstone, and conglomerate in the Antler foredeep basin; and intermittent disturbances related to continued plate convergence as recorded by Pennsylvanian to Triassic carbonate rocks, sandstone, and shale. Jurassic through Paleocene rocks are missing here, although Archean through Pennsylvanian rocks experienced Late Jurassic through Late Cretaceous metamorphism. Late Cretaceous, Eocene, Oligocene, and Miocene low-angle normal faults greatly attenuated the rock sequence. Eocene and Oligocene granitic intrusions and some extrusive rocks were emplaced between 41 and 25 Ma. Extensional basins developed in the Miocene, in which thick sections of sedimentary and volcanic rocks accumulated between 17 and 6 Ma, and bimodal volcanism continued into the Pleistocene (2.2 Ma). Part of the map area was covered by the extensive Pleistocene Lake Bonneville and now its smaller remnant, Great Salt Lake. Alluvial, eolian, glacial, and mixed surficial deposits veneer basins and bedrock. New gravity and aeromagnetic studies aided geologic interpretations and evaluation of mineral and geothermal resource potential. This map updates prior regional-scale maps with greater detail and geospatial accuracy, improved mapping of Quaternary-Tertiary surficial deposits, and new geochronologic, paleontologic, geochemical, and tectonic data.