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  • Thumbnail for Along-Strike Variations in Detrital Zircon Provenance of the Tava Sandstone Injectites, Colorado Front Range
    Along-Strike Variations in Detrital Zircon Provenance of the Tava Sandstone Injectites, Colorado Front Range by Shatford, Sally Mae

    An assemblage of massive remobilized sandstone bodies and subsidiary sedimentary dikes, hosted by Pikes Peak Granite and older Proterozoic rocks, exists in the Colorado Front Range (CFR). Detrital zircon (DZ) zircon provenance analysis reveals the Tava sandstone is Neoproterozoic (800-680 Ma). Tava contains multiple DZ ages including a broad ‘Grenville’ age plateau (Gehrels and Pecha, 2014) and sharp, narrow age peaks at ~1400 Ma and ~1700 Ma (Figure 2) correlating to known Neoproterozoic age samples. There are no other non-metamorphosed sedimentary rocks of Proterozoic age known in Colorado, excluding the Uintah Mountains. Field-based research, U-Pb DZ geochronology and scanning electron microscope (SEM) imaging of quartz grains were the research methods used. Field-based research entailed observation of Tava sandstone sedimentology and variation in sandstone characteristics at sites along the Ute Pass Fault. U-Pb DZ geochronology produced minimum ages of deposition for Tava sandstone sediment. SEM imaging determined if some quartz and zircon grains were a result of aeolian transport. U-Pb DZ geochronology produced DZ spectra for the eleven sample sites. Within these sites that are ~11 km apart, the DZ spectra varied in its major peaks. Differences in DZ age abundances between Tava sample sites are reflected in varying P-values that are used to assess statistical probability of correlation among Tava samples (Siddoway and Gehrels, 2014). These variations in sedimentary and vii DZ provenances indicate the presence of topographic relief at the time of Tava sandstone formation. Evidence of extensive river systems in the Neoproterozoic provides a mechanism for zircon transport and a paleoenvironment to transport zircons to Colorado from the opposite side of Laurentia (Figure 4, Yonkee et al., 2014; Dehler et al., 2010; Rainbird et al., 2012). The Tava sandstone is a test for existing hypotheses about the region’s paleogeography. Comparing the weighted means of the detrital zircon populations in each Tava sample to the age of igneous sources and detrital zircon populations of Proterozoic igneous rocks of Colorado, reveals potential local igneous sources for the zircons. Cross cutting relationships indicate a generation younger than the Tava parent bodies. The ~1.4 Ga and ~1.7 Ga aged peaks from bedrock exposure suggests potential erosion of uplifted bedrock caused by tectonism. These differences in DZ spectra provide evidence for the presence of an intracontinental rift across Colorado.