Research Paper GEOSPHERE Paleoproterozoic orogenesis and quartz-arenite deposition in the Little Chino Valley area, Yavapai tectonic province, central GEOSPHERE; v. 12, no. 6 Arizona, USA doi:10.1130/GES01339.1 Jon E. Spencer1, Mark E. Pecha1, George E. Gehrels1, William R. Dickinson1,*, Kenneth J. Domanik2, and Jay Quade1 14 figures; 3 supplemental files 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA 2Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA CORRESPONDENCE: jklmspenc@ dakotacom .net CITATION: Spencer, J.E., Pecha, M.E., Gehrels, ABSTRACT strata in the area, and it is probably significantly younger. We infer that the G.E., Dickinson, W.R., Domanik, K.J., and Quade, J., 2016, Paleoproterozoic orogenesis and quartz- arenite physically immature but chemically super-mature Del Rio Quartzite was de- deposition in the Little Chino Valley area, Yavapai New field mapping and laboratory studies of Paleoproterozoic rock units posited during a time of extreme weathering during a hot, humid climate with tectonic province, central Arizona, USA: Geosphere, around Little Chino Valley in central Arizona clarify the timing of magmatism, exceptionally high atmospheric CO concentrations and associated corrosive v. 12, no. 6, p. 1–21, doi:10.1130/GES01339.1. 2 deformation, and sedimentation in part of the Yavapai tectonic province and rainwater rich in carbonic acid. yield new insights into sources of sands and weathering environments. Mafic Received 29 March 2016 Revision received 22 July 2016 lavas, calc-silicate rocks, and pelitic and psammitic strata in the Jerome Can- Accepted 24 August 2016 yon area west of Little Chino Valley were deposited, deformed, and intruded INTRODUCTION by the 1736 ± 21 (2σ) Ma Williamson Valley Granodiorite. U-Pb geochronologic analysis of detrital zircons from a sample of psammitic strata yielded a maxi- Laurentia is the Paleoproterozoic ancestor of the North American continent. mum depositional age of ca. 1738 Ma. Approximately 25% of the detrital- Much of it formed by 1.8 Ga as a result of tectonic assembly of Paleoprotero- zircon grains were derived from a ca. 2480 Ma source, as previously identified zoic and Archean cratonic elements into the Hudsonian craton (Hoffman, 1988). in Grand Canyon schist units. Kolmogorov-Smirnov statistical comparison of Over the following 200 million years, magmatism, sedimentation, and tec- the Jerome Canyon detrital-zircon analyses with Grand Canyon schist analy- tonic accretion added the Transcontinental Proterozoic provinces to its (now) ses indicates that three of the 12 samples analyzed by Shufeldt et al. (2010) southern margin (Condie, 1982; Karlstrom and Bowring, 1993; Van Schmus and are statistically indistinguishable from the Jerome Canyon sample at the 95% Bickford, 1993; Karlstrom et al., 2001; Whitmeyer and Karlstrom, 2007). These confidence level and supports the concept that the Jerome Canyon sequence tectonic provinces represent genesis of much of the continental crust beneath and Paleoproterozoic schists in the eastern and western Grand Canyon are the United States, including that beneath all of Arizona and New Mexico (Fig. 1). part of the same tectonostratigraphic terrane. Genesis of continental crust, and changes to crustal genesis processes over The Del Rio Quartzite on the northeast side of Little Chino Valley, previously geologic time, are major topics of geologic interest. Earth’s greater radiogenic considered an outlier of Mazatzal Quartzite, consists of poorly sorted quartz heat production in the past has been identified as the likely cause of different arenite, pebbly quartz arenite, and conglomerate deposited in a braided- tectonic and magmatic processes associated with crustal genesis (e.g., Ham- stream environment. Microscope examination of 32 thin sections stained for ilton, 2007), including rates of accretion in forearcs (Condie, 2007). The Chino potassium and calcium failed to identify any feldspar, mica, or mafic silicate Valley area in central Arizona is in the Yavapai tectonic province, which was grains. Similarly, conglomerate clasts consist entirely of vein quartz and less created by magmatic activity, sedimentation, and tectonic accretion at ca. 1.7– abundant argillite and jasper. A rock unit interpreted as a paleosol beneath the 1.8 Ga (Fig. 2; Karlstrom and Bowring, 1988, 1993) and perhaps modified by rift- Del Rio Quartzite contains no surviving minerals except quartz, some of which ing and related magmatism (Duebendorfer et al., 2006; Bickford and Hill, 2007). is embayed and rounded as in corrosive saprolitic soils. U-Pb geochrono logic Two 7 ½′ quadrangles in the Chino Valley area, mapped in detail as part of analyses of detrital zircons from the 1400-m-thick Quartzite indicate maxi- the STATEMAP program (a component of the National Geologic Mapping Act mum depositional ages of ca. 1745 Ma for the base and ca. 1737 Ma for the of 1992), encompass areas of Paleoproterozoic magmatism, sedimentation, top. The unit is folded but is unaffected by the penetrative deformation and and deformation. This new mapping and associated U-Pb geochronologic, metamorphism that affected other Paleoproterozoic volcanic and sedimentary geochemical, and petrographic analyses yielded insights into Yavapai prov- For permission to copy, contact Copyright ince genesis. A folded section of quartzite and quartz-cobble conglomerate in Permissions, GSA, or [email protected]. *Published posthumously the same area has been mapped as an outlier of the Mazatzal Quartzite. The © 2016 Geological Society of America GEOSPHERE | Volume 12 | Number 6 Spencer et al. | Orogenesis and quartzite deposition, Yavapai tectonic province 1 Research Paper quartzite is not affected by the metamorphism and penetrative deformation that affected other Paleoproterozoic strata in the area and is likely younger. The quartz-rich composition of the quartzite and a deeply weathered paleosol at its base support previous interpretations of extreme chemical weathering during latest Paleoproterozoic quartz-arenite deposition across the Transcontinental Paleoproterozoic provinces. Background Since genesis, the Transcontinental Proterozoic tectonic provinces have been greatly modified and largely buried, but they are fairly well preserved and exposed in a 500-km-long, northwest-southeast belt across Arizona that is perpendicular to the dominant structural and lithologic fabric of the prov- inces (Fig. 1). This belt is within a part of Arizona known as the Transition Zone. Unlike the Colorado Plateau to the northeast, its Paleozoic cover has been mostly removed by erosion, and unlike the Basin and Range province to the southwest, it is not severely affected by Phanerozoic tectonism and magmatism. Paleoproterozoic rocks of the Transition Zone consist largely of granitoids and weakly to strongly metamorphosed volcanic and clastic sedimentary rocks (Fig. 2; Wrucke and Conway, 1987; Karlstrom and Bowring, 1988; DeWitt et al., 2008). Geochronologic studies suggest that assembly of the Proterozoic tectonic provinces occurred from northwest to southeast (Condie, 1982; Karl- strom et al., 1987, 2001; Van Schmus et al., 1993; Eisele and Isachsen, 2001; Meijer, 2014), although in detail, igneous-rock ages are only weakly correlated with position in the orogen. Isotopic studies indicate that the newly formed Paleoproterozoic crust was largely juvenile, with little incorporation of older material (Bennett and DePaolo, 1987; Wooden and DeWitt, 1991; Iriondo et al., 2004). Central Arizona Paleoproterozoic rocks are notable for their prominent north- to northeast-striking shear zones that separate multiple tectonic blocks, as identified by Karlstrom and Bowring (1993). The well-developed Shylock shear zone, a north-south–striking zone of strong, subvertical foliation that is exposed over ~60 km, bounds the Chino Valley area on the east (Fig. 2). The steep, planar fabric in the shear zone (S2 of Darrach et al., 1991), with steeply plunging lineations and fold axes, is interpreted to represent shortening with dip-slip displacement. The fabric is both intruded by, and affects, a 1699 Ma pluton (Karlstrom, 1989; Darrach et al., 1991). The Mesa Butte shear zone, a feature that includes a fault on the west side of Chino Valley, was proposed to be part of the tectonic boundary between the Hualapai block to the northwest and the Green Gulch block to the southeast (Bergh and Karlstrom, 1992; Karl- strom and Bowring, 1993). The geologic histories of each block have been used to infer the approximate timing of juxtaposition of the blocks, with a plausi- ble interpretation of juxtaposition indicated by synchronous deformation and Figure 1. Geologic map of the interior of southwestern North America showing location of Precambrian bedrock including Mazatzal and Uncompahgre quartzites and similar units. Also shown are named shear zones in central Arizona and extrapolated boundaries from Arizona magmatism in adjacent blocks (Karlstrom and Bowring, 1988, 1993). to the Rocky Mountains. Modified from Karlstrom and Bowring (1993) and Jones et al. (2009). Note that the Mojave, Yavapai, and Mazatzal Upper Paleoproterozoic to lower Mesoproterozoic quartz-rich clastic rocks provinces are part of the Transcontinental Proterozoic provinces, whereas the Wyoming province is part of the Hudsonian craton. are present in widely scattered exposures across the Transcontinental Protero- GEOSPHERE | Volume 12 | Number 6 Spencer et al. | Orogenesis and quartzite deposition,