Miocene unroofing of the Canyon Range during extension along the Sevier Desert Detachment, west central Utah

Apatite fission track results from Neoproterozoic and Lower Cambrian quartz ites collected from the Canyon Range in west central Utah reveal a signific ant early to middle Miocene cooling event (similar to 19-15 Ma). Preextensi onal temperatures estimated from multicompositional apatite fission track d ata suggest similar to4.5 to >5.6 km of unroofing during the early to middl e Miocene, assuming a geothermal gradient of similar to 25 degreesC/km. The spatial distribution of these preextensional temperatures indicates simila r to 15 degrees -20 degrees of eastward tilting of the Canyon Range during rapid extensional unroofing along a moderately west dipping detachment faul t (similar to 35 degrees -40 degrees). We interpret this fault to be the br eakaway of the Sevier Desert Detachment fault (SDD), the existence of which has been contested. The new thermochronologic data presented in this study provide compelling evidence for the existence of the SDD and thus the gene ral viability of low-angle detachment faulting. The data directly date the onset of extensional faulting along the SDD starting at similar to 19 Ma an d constrain the fault slip rate in the SDD breakaway zone at 2.4-2.1 mm/yr between similar to 19 and 15 Ma. An early Miocene apatite fission track age obtained from a Proterozoic clast from the Tertiary Oak City Formation con firms that these conglomerates were deposited in a synextensional basin in the hanging wall of the SDD. The timing of tectonic unroofing of the Canyon Range in response to faulting along the SDD appears to be synchronous with large-magnitude extension along the Snake Range decollement and with early extension along the Cave Canyon detachment exposed in the Mineral Mountain s, pointing to widespread east-west extension in the eastern Great Basin in the early and middle Miocene.