NEOPROTEROZOIC ORIGIN OF THE UTE PASS FAULT (SOUTHERN FRONT RANGE) AND STRUCTURAL CONTROL UPON THE PRESERVATION OF A SNOWBALL EARTH SEDIMENTARY RECORD IN COLORADO

The Ute Pass Fault (UPF) transects the 1080 Ma Pikes Peak Batholith and is a high-angle, NW-striking fault along most of its length. Phanerozoic activity on the UPF and neighboring faults is indicated by plutonic detritus in Pennsylvanian Fountain Formation (Ancestral Rockies Orogeny) and Paleogene D1 Sequence (Laramide Orogeny) fanglomerates. Steeply inclined Mesozoic strata of the Front Range monocline are cut and deflected by left-oblique translation. Less widely known is the association of circa 675 Ma Tavakaiv sandstone with the UPF. The sandstone of Cryogenian age forms sandstone ridges and injectites along >60 km of the fault. At intervals, the “Tava” and rock bordering the UPF host hematite-quartz and barite veins.

Tava consists of structureless diamictite formed of granules and pebbles of polycrystalline quartz and fragmented granite in a quartz sand matrix. Detrital zircon U-Pb data for 14 specimens, sampled at intervals along the UPF, define distinct populations of ca. 1440 and 1700 Ma. Probability density plots display the sharp narrow peaks indicative of proximal sources, considered to be the Silver Plume and Boulder Creek plutonic suites. A broad 1230–970 Ma ‘Grenville’ distribution is superimposed by an ~1100 Ma peak. Among the ca. 1100 Ma grains are prismatic, oscillatory-zoned zircons attributed to a Pikes Peak extrusive phase (Fonseca Teixiera et al. 2023, 10.5194/egusphere-egu23-5447). The zircon populations signify that Proterozoic bedrock was exhumed and undergoing erosion as Tava sandstone accumulated in depocenters spatially associated with the UPF, suggesting a structural control upon the sedimentary or tectonic burial that enabled the preservation of the Tava sediments. The Fe-oxides and sulfate indicate circulation of crustal and/or basinal fluids. Given the contemporaneity of UPF with ca. 675 Ma Tava sandstone, UPF initiation can be best understood within the context of Rodinia paleogeography and tectonics at the time of the Sturtian Snowball Earth glaciation (717–660 Ma).