PALEOPROTEROZOIC OROGENESIS AND QUARTZITE DEPOSITION IN THE LITTLE CHINO VALLEY AREA, CENTRAL ARIZONA, USA (Invited Presentation)

New field mapping and laboratory studies of Paleoproterozoic rock units around Little Chino Valley in central Arizona clarify the extent and history of previously outlined tectonic blocks and yield new insights into sources of sands and weathering environments. Mafic lavas, calc-silicate rocks, and pelitic and psammitic strata in the Jerome Canyon area west of Little Chino Valley were deposited, deformed, and intruded by the 1736 ± 21 Ma (2σ) Williamson Valley Granodiorite. U-Pb geochronologic analysis of detrital zircons from a sample of psammitic strata yielded a maximum depositional age of ~1738 Ma. Also, ~25% of the zircons were derived from a ~2480 Ma source, as previously identified by detrital-zircon analyses of Grand Canyon schists. Kolmogorov-Smirnoff statistical comparison of Jerome Canyon detrital-zircon analyses with Grand Canyon schist analyses indicates that three of twelve samples analyzed by Shufeldt et al. (2010) are not statistically distinguishable from the Jerome Canyon sample at the 95% confidence level, and supports the concept that the Jerome Canyon sequence is part of the Hualapai tectonic block as are Paleoproterozoic schists in the eastern and western Grand Canyon.

 

The Del Rio Quartzite on the northeast side of Little Chino Valley, previously considered an outlier of Mazatzal Quartzite, consists of poorly sorted quartz arenite, pebbly quartz arenite, and conglomerate deposited in a braided-stream environment. Microscope examination of 32 thin sections failed to identify any feldspar, mica, or mafic silicate grains. Similarly, conglomerate clasts consist entirely of vein quartz and less abundant argillite and jasper. U-Pb geochronologic analyses of detrital zircons from the 1400-m-thick Quartzite indicate maximum depositional ages of ~1749 Ma for the base and ~1740 Ma for the top. The unit is folded but is otherwise unaffected by the penetrative deformation and metamorphism that affected older Paleoproterozoic volcanic and sedimentary strata in the area, and is probably significantly younger. We infer that the physically immature but chemically super-mature Del Rio Quartzite was deposited during a time of hyperactive weathering with a hot, humid climate, exceptionally high atmospheric CO₂ concentrations, and corrosive rainwater rich in carbonic acid.