PETROCHRONOLOGICAL DISCRIMINATION OF SOURCES FOR CAMBRIAN DETRITAL ZIRCONS IN LATE PALEOZOIC STRATA OF THE CENTRAL COLORADO TROUGH DURING ANCESTRAL ROCKY MOUNTAIN OROGENESIS

The Central Colorado Trough (CCT), an Ancestral Rocky Mountain (ARM) basin provides a case example in which multivariate geochemical analyses of detrital zircons refines sediment source attribution, reconciling previously incompatible observations. Previous work attributed the immature, arkosic character of Upper Pennsylvanian CCT strata to local derivation, consistent with isolation of ARM basins from external sediment sources. However, detrital zircon U-Pb ages show that these strata were dominated by Cambrian zircons, the most common source of which is the Oklahoma Aulacogen (OA). The appearance of detritus from the OA in CCT strata would suggest a westward sediment dispersal pathway that could also explain provenance records in Paleozoic strata farther west, but which is at odds with the model of ARM basin isolation.

We examine this question through petrochronologic analysis (U-Pb, εHf, and REE) of detrital and igneous zircons from the CCT and potential source areas in OK, NM, and CO. Results from potential source areas suggest that εHf values from igneous zircons decrease from east to west (medians of 8.5-1.4, respectively). Conversely, REE abundances do not systematically vary with respect to location but track source lithology and can discriminate igneous sources within the CCT’s catchment during the late Paleozoic.

Provenance and geologic data suggest local sourcing by Cambrian igneous rocks exhumed in the Apishapa Uplift (AU) and support a model of multi-phase exhumation and drainage reorganization. Relatively low εHf values of Cambrian detrital zircons (medians from 1.9-5.0) are consistent with dominant sediment sourcing from the AU, which bounds the basin to the east. However, changes in dominant age population and REE abundances from Cambrian detrital zircons, as well as paleocurrent direction and sandstone composition provide insight into the evolution of the basin drainages. Based on paleocurrent direction and the predicted location of the late Paleozoic AU, we propose that a Cambrian igneous rock body, ~30 km north of the modern-day exposure of the McClure Mountain Syenite, sourced the Upper Pennsylvanian-lower Permian CCT. Presently, this hypothesized Cambrian igneous source is not exposed and has either been completely eroded or is mantled by Tertiary volcanic rocks.