Polyphase Proterozoic Deformation in the Four Peaks Area, Central Arizona, and Relevance for the Mazatzal Orogeny GEOSPHERE; V

Research Paper

GEOSPHERE Polyphase Proterozoic deformation in the Four Peaks area, central Arizona, and relevance for the Mazatzal orogeny GEOSPHERE; v. 11, no. 6 Calvin A. Mako1, Michael L. Williams1, Karl E. Karlstrom2, Michael F. Doe3, David Powicki1, Mark E. Holland2, George Gehrels4, and Mark Pecha4 1Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, 233 Morrill Science Center, Amherst, Massachusetts 01003, USA doi:10.1130/GES01196.1 2Department of Earth and Planetary Science, MSCO3-2040, University of New Mexico, Albuquerque, New Mexico 87131, USA 3Department of Geology and Geologic Engineering, Berthoud Hall, Room 221, 1516 Illinois Street, Colorado School of Mines, Golden, Colorado 80401, USA 9 figures; 2 tables; 3 supplemental files 4Arizona LaserChron Center, Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA

CORRESPONDENCE: [email protected] ABSTRACT growth. They are defined by crystallization age of exposed rocks, and the Nd and Hf isotopic character of plutons, which provides an indication of the bulk CITATION: Mako, C.A., Williams, M.L., Karlstrom, For more than 25 yr, the Mazatzal orogeny has been a central component crustal age. These provinces include the 1.80–1.70 Ga Yavapai Province, the K.E., Doe, M.F., Powicki, D., Holland, M.E., Gehrels, G., and Pecha, M., 2015, Polyphase Proterozoic of virtually all tectonic models involving the Proterozoic rocks of the south- 1.70–1.60 Ga Mazatzal Province, and the 1.50–1.35 Ga Granite-Rhyolite Prov- deforma tion in the Four Peaks area, central Arizona, western United States. Recent recognition that some sedimentary sequences ince. The assembly of each crustal age province is thought to correspond to and relevance for the Mazatzal orogeny: Geosphere, and some major structures are Mesoproterozoic rather than Paleoproterozoic distinct orogenic episodes, referred to as the Yavapai (1.71–1.68 Ga), Mazatzal v. 11, no. 6, p. 1975–1995, doi:10.1130/GES01196.1. has led to new questions about the nature, even the existence, of the Mazatzal (1.66–1.60 Ga), and Picuris orogenies (1.49–1.45 Ga), respectively. The com- orogeny. This study aims to clarify the relationship between Mazatzal (ca. bined provinces have been interpreted to document punctuated episodes Received 21 April 2015 Revision received 28 July 2015 1.65 Ga) and Picuris (ca. 1.45 Ga) orogenic activity. New U-Pb geochronology within a long-lived convergent plate margin along southern Laurentia (Karl- Accepted 28 August 2015 of variably deformed igneous and metasedimentary rocks constrains sev- strom et al., 2001) that culminated with the ca. 1.2–1.0 Ga Grenville orogeny Published online 2 October 2015 eral periods of deformation at ca. 1.68 Ga, 1.66 Ga, and 1.49–1.45 Ga in the and the final assembly of the supercontinent Rodinia. Four Peaks area of central Arizona. Detrital zircon analyses and field relation- Several new data sets provide major challenges to elements of this model ships indicate the deposition of a rhyolite-sandstone-shale assemblage at ca. for sequential southward continental growth, particularly, the timing of accre- 1.660 Ga with renewed deposition at 1.502–1.490 Ga and a significant discon- tion and major orogenic events. New U-Pb-zircon ages (detrital and ash layers) formity, but no recognized angular unconformity, between these episodes. from New Mexico (Jones et al., 2011; Daniel et al., 2013) and Arizona (Doe Three populations of monazite growth at 1.484 ± 0.003 Ga, 1.467 ± 0.004 Ga, et al., 2012a, 2012b, 2013; Bristol et al., 2014) have identified younger (1.502– and 1.457 ± 0.005 Ga indicate prolonged Mesoproterozoic metamorphism. The 1.45 Ga) depositional successions within the Mazatzal and southern Yavapai ca. 1.485 Ga population is associated with the formation of the Four Peaks syn- Provinces. These rocks form the upper parts of sequences previously thought cline during Mesoproterozoic orogenesis and subsequent amphibolite-facies to be entirely Paleoproterozoic (i.e., the Hess Canyon Group of Arizona and contact metamorphism. Rocks in the Four Peaks area record polyphase defor Hondo Group of New Mexico) and part of the cover sequence interpreted to mation, sedimentation, and plutonism from the Paleoproterozoic to Meso separate the Yavapai and Mazatzal orogenies (i.e., the Hondo Group of New proterozoic. Hf-isotopic data suggest the involvement of older, nonjuvenile Mexico). Thus, the upper parts of at least some “Mazatzal-age” sedimentary crust. In this area, effects of the Mazatzal (ca. 1.65 Ga) and Picuris orogenies successions are actually Mesoproterozoic (1.50–1.48 Ga) in age. Importantly, (ca. 1.49–1.45 Ga) are entwined and involved sedimentation, deformation, plu- no angular unconformities have yet been recognized, and some regional struc- ton emplacement, and pluton-enhanced metamorphism. tures involve both the lower (Paleoproterozoic) and upper (Mesoproterozoic) parts of the sections. This has been interpreted to suggest that some, and perhaps much, of the deformation and metamorphism previously attributed INTRODUCTION to the Mazatzal orogeny is Mesoproterozoic in age and may correspond with the newly named Picuris orogeny (Daniel et al., 2012a, 2012b, 2013). These re- Proterozoic orogenic belts (1.8–1.0 Ga) define a 1000-km-wide swath across cent data raise questions about the extent of 1.7–1.6 Ga juvenile crust (Mazatzal southern North America and underlie much of the lower 48 United States. For crustal province), 1.70–1.60 Ga sedimentary sequences (Mazatzal basins), and more than 25 yr, the southward growth of the Laurentian continent has been the nature of the ca. 1.68–1.60 Ga Mazatzal deformation and metamorphism interpreted in terms of successive accretionary orogenic events, incrementally (Mazatzal orogeny) and the way in which Mesoproterozoic orogenesis over- adding juvenile (and some continental) material to the long-lived plate margin prints these. For permission to copy, contact Copyright (Fig. 1; Karlstrom and Bowring, 1988; Karlstrom et al., 2001; Whitmeyer and Models for the growth of Laurentia and paleogeographic reconstructions Permissions, GSA, or [email protected]. Karlstrom, 2007). Three main crustal age provinces account for much of the critically depend on a clarified understanding of the relative importance of

GEOSPHERE | Volume 11 | Number 6 Mako et al. | Polyphase Proterozoic deformation in the Four Peaks area Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/6/1975/4333614/1975.pdf 1975 by guest on 26 September 2021 Research Paper

Laurentia

Figure 1. Proterozoic provinces of North T. Z. America, modified after Whitmeyer and S. L. Karlstrom (2007). Belt e Cheyenne

Yavapai Provinc e e

Mazatzal Provinc 1.55–1.35 Ga juvenile crust

1.70–1.65 Ga quartzites Four Peaks 1.70–1.60 Ga crust Granite - Rhyolite Provinc 1.45–1.35 Ga intrusions

(Modified from Whitmeyer and Karlstrom, 2007)

the Mesoproterozoic and Paleoproterozoic tectonism (Picuris, Mazatzal, and tigraphy and Mazatzal tectonism. The Four Peaks area (Fig. 2) is south of the Yavapai orogenies). Proterozoic crustal age provinces have been correlated proposed boundary of the Yavapai and Mazatzal crustal provinces, the Slate across Laurentia (Holm et al., 1998, 2005; Whitmeyer and Karlstrom, 2007; Creek shear zone (Labrenze and Karlstrom, 1991), in central Arizona. Our new Jones et al., 2013) and are used as pinning points for supercontinent recon- data show that, at Four Peaks, an ~1.5-km-thick section of Proterozoic meta structions (Karlstrom et al., 1999, 2001; Burrett and Berry, 2000; Betts et al., sediments includes a lower Paleoproterozoic and an upper Mesoproterozoic 2008; Li et al., 2008; Betts et al., 2011). The spatial and temporal transitions component. The metasedimentary section is folded into a kilometer-scale, among the Yavapai, Mazatzal, and Picuris orogenies are particularly important overturned, north-verging syncline (Estrada, 1987; Fig. 3) similar to other folds (Shaw and Karlstrom, 1999), as are the extent and significance of older crustal and thrusts of the Mazatzal Group and related successions (Wilson, 1939). The components within what have been considered to be dominantly juvenile metasedimentary and metavolcanic rocks are presently surrounded by a sea of crustal provinces (Bickford and Hill, 2007; Karlstrom et al., 2007). variably deformed plutonic rocks, which we use to place constraints on the age The purpose of this paper is to summarize relationships and constraints of sedimentation and tectonism. New detrital and igneous zircon geochrono- from one of the classic, but now questionable, exposures of Mazatzal stra- logic data, coupled with field relationships, show components of both Meso-

3730 A C13-073 C13-056a

K13-FPKS-14 C13-011 C13-012

K13-4PKS-5 C14-013a C13-036 C13-029a K13-4PKS-3,4 K13-FPKS-15 Figure 2. Geologic map of the Four Peaks C13-035 area. This map is modified after Skotnicki (2000) map of the Four Peaks Quadrangle 3726 and a simplified regional map provided by S. Skotnicki. The locations of relevant samples are shown, and the domain that was determined to be cylindrically folded A′ for structural analysis is marked by a box. Note the zones of more intense deformation east and southwest of the syncline. The grid is a 1 km spaced Universal Trans- verse Mercator grid (zone 12S) with north- C13-082a ing and easting as shown. 66 70 3722 75 04 04 04 Supracrustal Rocks Intrusive Rocks Symbols Upper Pelite El Oso Related Granite The Four Peaks Four Peaks Quartzite (FPQ) El Oso Granite Structural Analysis Area Lower Pelite granites of Soldier Camp C13-073 Sample Locations Lower Quartzite Buckhorn Granodiorite Mylonites Four Peaks Rhyolite

proterozoic and Paleoproterozoic tectonism. In addition, new Hf isotopic data BACKGROUND from Mazatzal-age (1.70–1.60 Ga) plutons from this area suggest the granites were derived from an underlying pre-Mazatzal-age (pre–1.7 Ga) crust. Our ul- Paleoproterozoic and Mesoproterozoic tectonism has been documented timate goal is to build a new model for Proterozoic accretionary orogenesis in across the North American continent. Beginning at ca. 1.8 Ga, the Laurentian Arizona that accommodates both the new and the long-standing constraints craton rapidly grew southward by the addition of juvenile crust and older crustal and, thus, can serve as a template for a refined understanding of North Amer- components in a series of orogenic events. The rocks that record this growth ican continental growth. are divided into several provinces on the basis of age and isotopic characteris-

v=h Samples Photographs A′ 500 meters A upper pelite C13-082a tzite eaks Quar Four P F C13-029a

09162013-1 C13-012 B E A,D C13-011 C13-073 C13-035 lower pelite C13-056a K13-FPKS-15 El O El Oso Granite Buck K13-FPKS-14 so related intrusio horn GranodioritK13-4PKS-3,4 lower qtzt C e K13-4PKS-5 rhyolit granites of Soldier Camp e n

Figure 3. Interpretive cross section of the geology of the Four Peaks area (A-A′ on Fig. 2). This figure uses the same unit color scheme as Figure 2. Topography is designated by a white line. The effective stratigraphic locations of relevant samples and photographs in Figure 5 are also shown. There is no vertical exaggeration; qtzt—quartzite.

tics (Fig. 1; Condie, 1986; Reed et al., 1987; Karlstrom et al., 1987; Bennett and termed the Pinwarian orogeny (1.5–1.45 Ga; Wasteneys et al., 1997). A volumi- DePaolo, 1987; Hoffman, 1989). The Penokean Province represents terrane ac- nous suite of ferroan granites intruded across the older Laurentian provinces cretion from 1.875 to 1.835 Ga and is exposed in the midcontinent, Great Lakes at 1.48–1.35 Ga (Anderson and Morrison, 2005; Goodge and Vervoort, 2006; region (Van Schmus, 1976; Holm et al. 2005, 2007). The 1.80–1.70 Ga Yavapai Bickford et al., 2015) and was associated with regional metamorphism and lo- Province formed by the accretion of largely juvenile materials, although the calized deformation in the southwestern United States (Grambling et al., 1989; presence of some older crust in the subsurface is suggested by isotopic stud- Grambling and Dallmeyer, 1993; Nyman et al., 1994; Kirby et al., 1995; Williams ies (Bennett and DePaolo, 1987) and inherited zircon (Hill and Bickford, 2001). and Karlstrom, 1996; Shaw et al., 2005). The associated Yavapai orogeny peaked at 1.71–1.68 Ga (Whitmeyer and Karl- The Mazatzal orogeny is thought to represent the 1.66–1.60 Ga amalgama- strom, 2007). The 1.7–1.6 Ga Mazatzal Province includes granitic plutons as tion and deformation of the Mazatzal Province. It was originally proposed by well as supracrustal successions and is also considered to be dominantly juve- Silver (1965) after Wilson’s (1939) “Mazatzal revolution,” which ascribed all of nile (Bennett and DePaolo, 1987; Wooden and DeWitt, 1991). Thick rhyolite and the penetrative deformation of Proterozoic rocks, including older greenstone quartzite sequences are characteristic (Whitmeyer and Karlstrom, 2007) and successions, to a single event (Karlstrom and Bowring, 1988). This orogeny is are interpreted as fill basins built on existing accreted crust via mechanisms of characterized by fold-and-thrust–style deformation, penetrative shortening, and upper-plate extension due to slab roll back (Jones et al., 2009). The Mazatzal low- to medium-grade metamorphism (Wilson, 1939; Puls, 1986; Doe and Karl- crustal province is correlated with crust of similar age in northeastern Canada, strom, 1991; Williams, 1991a, 1991b; Williams and Karlstrom, 1996; Williams known as the Labradorian Province (Fig. 1; Gower et al., 1997; Whitmeyer and et al., 1999). The timing of deformation has been constrained to 1.660–1.600 Ga Karlstrom, 2007; Hynes and Rivers, 2010). The ca. 1.5–1.35 Ga Granite-Rhyo- based on data from across Arizona and New Mexico (Silver, 1978; Labrenze and lite Province includes potentially large domains of juvenile crust south of the Karlstrom, 1991; Bauer and Williams, 1994; Brown et al., 1999; Shaw et al., 2001; Missouri Line (Van Schmus et al., 1993, 1996; Slagstad et al., 2009; Whitmeyer Eisele and Isachsen, 2001; Amato et al., 2008), with some variation therein. and Karlstrom, 2007; Bickford et al., 2015). Evidence for ca. 1.45 Ga crust forma- These constraints are based primarily on dated 1.66–1.60 Ga intrusions cross- tion and tectonism also exists in the Grenville Province of Ontario and is there cutting deformation structures and fabrics. Deformation and magmatism far-

ther north in the Rockies (Jones et al., 2013) and across the midcontinent and against older (pre–1.7 Ga), lower-grade crust to the NW. Significant work has into Ontario are also correlated with the Mazatzal orogeny (Romano et al., 2000; been done on the stratigraphy, sedimentology, and structural geology of the Bailey et al., 2004; Holm et al., 2007; Craddock and McKiernan, 2007). Proterozoic metasedimentary rocks of the Tonto Basin from 1.729 Ga Payson The current model for the timing and nature of the Mazatzal orogeny has Ophiolite through the ca. 1.330 Ga Apache Group (Darton, 1925; Wilson, 1939; been complicated by the recognition of younger sedimentary sequences Gastil, 1958; Ludwig, 1974; Cuffney, 1977; Trevena, 1979; Anderson and Wirth, within the Mazatzal Province of Arizona and New Mexico (Jones et al., 2011; 1981; Hall-Burr, 1981; Vance, 1983; Alvis, 1984; Puls, 1986; Sherlock, 1986; Doe et al., 2012a; Daniel et al., 2013; Doe, 2014). For example, metatuffs inter Roller, 1987; Wrucke and Conway, 1987; Brady, 1987; Bayne, 1987; Bayne and layered with siliciclastics from the lower Yankee Joe Group of the upper Salt Middleton, 1987; Conway and Silver, 1989; Doe and Karlstrom, 1991; Doe, 1991, River Canyon, Arizona, are dated at 1.502–1.479 Ga (Bristol et al., 2014). Depo- 2014; Labrenze and Karlstrom, 1991; Labrenze, 1990; Sherlock and Karlstrom, sition and deformation of the Yankee Joe Group were previously interpreted 1991; Wessels and Karlstrom, 1991; Dann, 1991, 1997, 2004; Stewart et al., 2001; as Paleoproterozoic (Trevena, 1979). In the northern Mazatzal Mountains, the Cox et al., 2002; Doe et al., 2012a, 2012b, 2013). The Mazatzal quartzite of the Hopi Springs Shale is deposited on the Mazatzal Peak Quartzite (Doe, 1991; for upper Tonto Basin Supergroup is broadly correlated with the Ortega Quartzite alternative interpretation, see Puls, 1986; Cox et al., 2002). New detrital zircon of northern New Mexico and the Uncompahgre Quartzite of Colorado. Most data collected from lower Hopi Springs Shale suggest a maximum deposi- recently, significant sequences of deformed Mesoproterozoic sediments have tional age of ca. 1.571 Ga (Doe, 2014). The Hopi Springs Shale appears to be been recognized within folded bedding beneath thrust sheets in the northern folded and thrusted beneath Mazatzal Peak Quartzite, and this is interpreted to Mazatzal Mountains and folded beds along the Salt River Canyon, ~50 km east be Mazatzal deformation. In north-central New Mexico, metatuff layers from of the Four Peaks (Doe et al., 2012a, 2012b; Doe, 2014), raising questions about the Pilar Formation in the Picuris Mountains yielded similar, near-concordant the timing of regional deformations. U-Pb zircon ages ranging from 1.504 to 1.479 Ga (Daniel et al., 2013). The geology of the Four Peaks area (Fig. 2) consists of a kilometer-scale, Tectonism at ca. 1.45 Ga has largely been thought to consist of widespread doubly inward-plunging syncline of Proterozoic metasedimentary rocks metamorphism (Karlstrom et al., 1997) and deformation localized around (Fig. 3) that are interpreted as members of the Mazatzal Group (Estrada, 1987; plutons (Nyman and Karlstrom, 1997; Karlstrom and Humphreys, 1998). Al- Powicki, 1996). The syncline is interpreted as a roof pendant in a large volume though ca. 1.4 Ga plutons were initially considered anorogenic (Anderson and of granitic rocks (Wilson, 1939; Estrada, 1987). A major, 12-km-wide, thrust- Bender, 1989), it was later shown that regionally significant deformation oc- sense shear zone was proposed adjacent to the southern limb of the syncline curred during the Mesoproterozoic (Grambling and Dallmeyer, 1993; Nyman (Powicki, 1996), although subsequent work (Skotnicki, 2000) has questioned et al., 1994; Kirby et al., 1995; Karlstrom and Humphreys, 1998; Daniel and Pyle, the regional significance of the shear zone. Previous workers have attributed 2006). Additionally, Daniel and Pyle (2006) found no evidence of ca. 1.65 Ga the major structures present in the Four Peaks area to Mazatzal-age deforma- deformation in the Picuris Mountains. The recognition of large-scale structures tion (Estrada, 1987; Powicki, 1996). in Mesoproterozoic metasedimentary rocks, but not in 1.45 Ga plutons, constrains Picuris orogenesis to 1.49–1.45 Ga (Daniel et al., 2013). Some models proposed the Picuris orogeny to represent significant ca. 1.45 Ga intracratonic METHODS metamorphism (Shaw et al., 2005) and deformation (Whitmeyer and Karl- strom, 2007) well inboard from a 1.5–1.4 Ga accretionary boundary. Others Previous geologic mapping and stratigraphic analysis of rocks in the Four (Daniel et al., 2013, their fig. 10C) suggested that the 1.49–1.46 Ga Mesoprotero Peaks area were carried out by Estrada (1987), Powicki (1996), and Skotnicki

Supplemental Table 1. Isotope ratiosApparent ages (Ma) zoic strata were deposited above undeformed Paleoproterozoic sediments, (2000). Our new field research focused on key contact relationships between Analysis U 206Pb U/Th 206Pb* ±207Pb* ± 206Pb* ±error 206Pb* ±207Pb*± 206Pb* ±Best age±Conc (ppm) 204Pb 207Pb* (%)235U*(%) 238U(%) corr.238U* (Ma) 235U (Ma) 207Pb* (Ma) (Ma) (Ma) (%) Four Peaks RhyoliteStandard Error = 0.8 C13-082B-14 72 392011.1 9.9624 1.84.0888 2.80.2954 2.10.761668.631.01652.122.71631.133.71631.133.7102.3 and then both were deformed at 1.46–1.40 Ga during final suturing of Mazatzal supracrustal and intrusive rock units, and on structural analysis. C13-082B-4 91 157378 1.09.9201 0.84.0502 3.90.2914 3.90.981648.556.11644.332.11639.014.61639.014.6100.6 C13-082B-10 70 102851 0.99.8961 1.34.0268 3.30.2890 3.10.931636.644.61639.627.11643.523.41643.523.499.6 C13-082B-2 1241287830.7 9.8936 0.44.0432 1.10.2901 1.00.921642.114.61642.98.9 1643.9 7.71643.97.7 99.9 C13-082B-12 69 877490.8 9.8795 1.33.9668 3.00.2842 2.70.911612.638.41627.424.11646.623.41646.623.497.9 Province crust to the southern margin of Laurentia. In the former model, the U-Pb dating of detrital and igneous zircon was carried out at the Univer- C13-082B-27 74 113276 1.09.8690 1.24.0887 4.20.2927 4.10.961654.859.11652.034.41648.621.81648.621.8100.4 C13-082B-3 1142239580.8 9.8659 0.84.0803 1.10.2920 0.70.661651.310.71650.49.1 1649.1 15.5 1649.1 15.5 100.1 C13-082B-11 72 469151.0 9.8627 1.04.0765 1.70.2916 1.30.791649.519.21649.613.61649.719.01649.719.0100.0 C13-082B-19 88 107522 0.89.8494 1.34.0774 1.80.2913 1.20.681647.917.71649.814.61652.224.21652.224.299.7 Mazatzal crustal province was already part of Laurentia by 1.6 Ga; in the latter sity of Arizona LaserChron Center using a laser ablation–inductively coupled C13-082B-5 137118184 0.79.8443 0.84.0643 1.90.2902 1.70.911642.424.41647.215.11653.214.31653.214.399.3 C13-082B-26 99 886290.9 9.8368 0.94.0765 1.80.2908 1.50.861645.721.91649.614.31654.616.61654.616.699.5 C13-082B-6 131 941650.9 9.8279 0.64.0378 1.20.2878 1.10.851630.615.31641.910.11656.312.01656.312.098.4 C13-082B-23 95 100698 0.99.8274 0.84.1041 1.60.2925 1.40.881654.121.01655.113.41656.414.71656.414.799.9 model, the Mazatzal crustal province (Fig. 1) could have been exotic to North plasma–multicollector mass spectrometer (LA-ICP-MS). Analytical methods C13-082B-8 1472154140.7 9.8248 0.74.1064 1.20.2926 1.00.831654.614.41655.69.7 1656.9 12.4 1656.9 12.4 99.9 C13-082B-22 88 228749 1.39.8225 1.03.8467 2.30.2740 2.10.911561.329.21602.618.61657.317.71657.317.794.2 C13-082B-21 87 604900.9 9.8224 0.84.1533 1.70.2959 1.50.891670.822.71664.914.21657.314.61657.314.6100.8 C13-082B-28 86 959870.9 9.8198 1.04.1535 5.70.2958 5.60.991670.582.11664.946.41657.818.01657.818.0100.8 C13-082B-7 150115505 0.89.8083 0.64.1385 3.00.2944 2.90.981663.542.61661.924.31660.011.81660.011.8100.2 America until 1.46 Ga. followed that of Gehrels et al. (2008). U-Th-Pb isotopic data were manually C13-082B-15 100 845231.1 9.8068 0.94.1454 2.20.2948 1.90.901665.728.61663.317.61660.317.21660.317.2100.3 C13-082B-1 83 127796 1.29.7986 1.34.11611.7 0.2925 1.20.691654.117.21657.514.11661.823.21661.823.299.5 C13-082B-17 1421445740.7 9.7893 0.74.2297 3.80.3003 3.80.981692.856.31679.831.61663.612.61663.612.6101.8 C13-082B-23 137 258940.8 9.7893 0.94.0191 2.20.2853 2.10.921618.229.61638.118.31663.616.41663.616.497.3 The Tonto Basin area of central Arizona, where the Four Peaks Wilderness filtered based on U concentration, U/Th ratio, and concordance using the Age- C13-082B-18 1972141921.2 9.7618 0.54.1919 1.30.2968 1.20.931675.418.41672.411.01668.88.9 1668.8 8.9100.4 C13-082B-9 99 528900.8 9.7559 1.04.0668 2.30.2878 2.00.901630.329.51647.718.51669.917.91669.917.997.6 C13-082B-25 250 586610.8 9.7491 0.64.0903 4.60.2892 4.50.991637.665.51652.437.31671.210.51671.210.598.0 C13-082B-20 103 262281.1 9.7428 1.84.1940 2.30.2964 1.50.631673.221.61672.919.01672.433.31672.433.3100.0 of the southern Mazatzal Mountains is located, is an important location for Pick program (Gehrels, 2009). Only zircon grains that were 80%–105% concor- C13-082B-16 82 258151.1 9.6145 3.44.2300 3.60.2950 1.20.341666.317.91679.929.71696.962.71696.962.798.2 studying the Proterozoic tectonism of southern Laurentia. The nearby northern dant were included in final age calculations. Crystallization ages for igneous 1Supplemental Table 1. Isotopic data and calculated Mazatzal Mountains expose a fold-and-thrust system that is interpreted as the samples were interpreted from a weighted mean of ages determined to be ages for all zircon grains dated during this study. foreland system of the Mazatzal orogeny (Doe and Karlstrom, 1991). The Slate cogenetic based on these parameters. All uncertainties are given at 2s and Please visit http://dx .doi .org /10 .1130/GES01196 .S1 1 or the full-text article on www.gsapubs.org to view Creek shear zone, exposed in this area, has been proposed as a major crustal include all internal and external errors (the ages in Supplemental Table 1 are Supplemental Table 1. boundary, juxtaposing younger (1.66–1.63 Ga), higher-grade crust in the SE reported at 1s). Detrital zircon age peaks were also determined with the Age-

Pick program, with peak ages defined by groups of greater than three ages RESULTS that overlap at 2s (Table 1). All zircon data are in Supplemental Table 1 and the Supplemental File.2 Stratigraphic Relationships Hf isotopic analysis of selected zircon grains was also carried out at the Uni- versity of Arizona LaserChron Center, following the methods detailed in Geh- Supracrustal rocks in the Four Peaks area include a basal rhyolite over- rels and Pecha (2014). Grains were selected for Hf isotopic analysis on the basis lain by four metasedimentary units (Fig. 4; Powicki, 1996; Skotnicki, 2000). The

of concordance and uncertainty in their U-Pb ages. The eHf(t) values were deter- rhyolite is exposed in two large bodies southwest and southeast of the Four mined using the 176Lu decay constant of Scherer et al. (2001), the depleted man- Peaks syncline (Fig. 2). Smaller bodies of the rhyolite are consistently found tle array of Vervoort and Blichert-Toft (1999), and the bulk silicate earth compo- below the lowermost sedimentary unit (lower quartzite), particularly on the sition of Bouvier et al. (2008). All Hf isotope data are in Supplemental Table 2.3 northern limb of the syncline (smaller than map scale). The rhyolite consists Monazite was analyzed at the University of Massachusetts by electron of fine-grained quartz, muscovite, and plagioclase with minor oxides. Quartz probe microanalysis (EPMA). Monazite was identified from full thin section “eyes” and, more rarely, plagioclase phenocrysts occur as porphyroclasts. It wavelength-dispersive spectrometry (WDS) compositional maps of Ce-La is strongly foliated in most localities, but unfoliated, low-strain exposures, are X-ray intensity on a Cameca SX-50 electron microprobe. Individual monazite also present. The stratigraphically higher units are interpreted to be deposited Timing of deformation in the Four Peaks area, central Arizona, and grains were then mapped at high resolution for U, Th, Y, Ca, and Nd to identify on top of the rhyolite based on the consistent presence of rhyolite below the relevance for the Mazatzal orogeny compositional domains that might relate to generations of monazite growth. lower quartzite (Powicki, 1996; Skotnicki, 2000). Calvin A. Mako, Michael L. Williams, Karl E. Karlstrom, Michael F. Doe, David Powicki, Mark E. Holland, George Gehrels, Mark Pecha Selected monazite domains were analyzed on the Ultrachron electron micro- The lowermost metasedimentary unit is a thin (0–60 m), extremely pure

DR3- Zircon Age Data Plots probe using the methods of Williams et al. (2006) and Dumond et al. (2008). (up to 99% quartz), basal quartzite (Powicki, 1996), referred to as the lower Below are shown the zircon age distributions and histograms foreach sample in Monazite ages reported herein do not include systematic uncertainties from quartzite. Overlying the lower quartzite, there is a pelitic to psammitic unit, this study. Plots were made in the Isoplot 4.1 macro for Microsoft Excel (Ludwig, 2008). the electron probe microanalysis. ~450 m thick, (Estrada, 1987; Powicki, 1996), referred to as the lower pelite. On Data for the K13- series samples and sample C13-067b can be retrieved on the Arizona

Laserchron Center website under “Current Projects” in the Karlstrom, March, 2014 run.

Figure DR3-1: Sample K13-4PKS-4- Buckhorn granodiorite.(collected by Karlstrom, Powicki, Doe, 2014) TABLE 1. DETRITAL AND IGNEOUS ZIRCON GEOCHRONOLOGY OF THE FOUR PEAKS AREA Age range Max. depositional UTM NAD 83 Min Max Peak age coordinates (Ga) (Ga) age(s) (Ga) Sample no. Unit name Zone: 12S Ntotal ±2σ ±2σ (Ga) Npeak ± 2σ Nmax depo MSWD C13-029a Four Peaks Quartzite 0469674 E, 91 1.635± .075 3.498± .008 1.685 7 1.684± .016 31.3 3724354 N 1.742 37 1.766 39 1.855 4 2.732 3 20130916-1 Upper pelite 0470789 E, 94 1.553± .017 3.288± .019 1.579 8 1.566± .014 70.83 3726723 N 1.784 18 2Supplemental File. Plots of all detrital and igneous 1.831 5 zircon data for each sample. Please visit http://dx 2.462 3 .doi.org /10 .1130/GES01196 .S2 or the full-text article 2.696 3 on www.gsapubs.org to view the Supplemental File. Crystallization age

Sample no. Unit name UTM NAD 83 coordinates Ntotal Note (Ga) MSWD

Supplemental Table 2. Hf isotopic data from the Four Peaks region. 176 176 176 /177 ( Yb + Lu) / Volts Hf Hf E-Hf (0) ± Age Sample Analysis 176 Hf (%) Hf 176 Hf /177Hf ± (1s) 176 Lu /177Hf (T)E-Hf (0) (1s) E-Hf (T) (Ma) K13-4PKS-4 Buckhorn granodiorite 0472773E, 3727262N 30 1.677± .014 0.39 K13-4PKS-4 - Buckhorn Granodiorite K13-4PKS-4-2918.62.3 0.281931 0.000038 0.001099 0.281896 -30.21.3 5.91666 K13-4PKS-4-2 14.8 2.20.2819220.000043 0.000886 0.281894 -30.51.5 6.31686 K13-4PKS-3 Post-tectonic rhyolite dike 0472773E, 3727262N 16 1.675± .015 1.9 K13-4PKS-4-4 25.6 2.10.2819600.000038 0.001472 0.281913 -29.21.3 6.71671 K13-4PKS-4-2812.32.4 0.281886 0.000032 0.000736 0.281862 -31.81.1 5.01677 K13-4PKS-4-9 23.3 2.20.2819000.000039 0.001399 0.281855 -31.31.4 4.81682 C13-067b Young granite 0501728E, 3779024N 18 1.664± .017 0.28 K13-4PKS-4-8 19.1 2.30.2820560.000031 0.0011410.282020 -25.81.1 10.4 1669 K13-4PKS-4-2414.02.2 0.281962 0.000041 0.000844 0.281936 -29.11.5 7.51675 K13-4PKS-4-2311.72.4 0.281944 0.000035 0.000736 0.281921 -29.71.2 7.11681 K13-FPKS-14 Granite at Soldier Camp 0468118E, 3729121N3015m below 1.658± .015 0.45 K13-4PKS-4-1122.62.2 0.281983 0.000050 0.001322 0.281941 -28.41.8 7.81679 K13-4PKS-4-1026.71.9 0.281960 0.000044 0.001636 0.281908 -29.21.6 6.41667 C13-082b Basal rhyolite 0467242E, 3723969N 27 1.657± .014 0.44 K13-4PKS-4-2715.82.2 0.281964 0.000042 0.000983 0.281933 -29.01.5 7.31670 K13-4PKS-4-1515.92.0 0.281920 0.000045 0.000957 0.281889 -30.61.6 5.91677 K13-4PKS-4-2111.12.4 0.281976 0.000035 0.000671 0.281954 -28.61.2 8.51689 K13-4PKS-5 Megacrystic granite–Chillicut Tr.0472760E, 3727509N 22 1.652± .014 0.36 K13-4PKS-4-1714.72.3 0.281975 0.000034 0.000898 0.281947 -28.61.2 8.11684 K13-4PKS-4-1919.71.8 0.282006 0.000046 0.001243 0.281966 -27.51.6 9.11694 C13-073 El Oso granite 0468720E, 3729545N 27 1.449± .013 0.71 3Supplemental Table 2. Hafnium isotopic data for K13-FPKS-15 Ygm granite dike 0468739E, 3727229N 10 1.437± .015 0.4 each analyzed zircon grain. Please visit http://dx .doi 41.651 ± .021 1.8 .org/10 .1130/GES01196 .S3 or the full-text article on Note: MSWD—mean square of weighted deviates; UTM NAD 83—Universal Transverse Mercator North American datum 1983. www.gsapubs.org to view Supplemental Table 2.

? ? ? 600–1000 m of the Four Peaks Quartzite are distinctively rusty weathered, and the quartz Upper Pelite 1.502–1.490 Ga grain size is larger (1–3 mm). The upper pelite is easily distinguishable from the quartzite by its tan-gray weathered appearance, more finely bedded nature, and well-defined slatey cleavage. The contact between the quartzite and the upper pelite is poorly exposed and was not observed directly during this study. Four However, the contact is interpreted to be sharp because it occurs over a narrow Peaks interval (as little as 1 m), and no evidence for a gradational contact was seen Quartzite either above or below the contact region.

ca. 1.660 Ga Figure 4. Stratigraphic section of the Four Peaks metasedimentary package, Intrusive Rocks modified after Estrada (1987), Powicki (1996), and Skotnicki (2000). Inter- preted timing of deposition for each Three intrusive igneous units were distinguished by Powicki (1996) and unit is shown on the right. See text for Skotnicki (2000). The Buckhorn granodiorite (Fig. 5A) is exposed southeast of discussion. Lw. Qtzt—lower quartzite. Lower Pelite the Four Peaks syncline (Fig. 2). The granodiorite has two unpublished ages of 1.685 ± 0.004 Ga (Skotnicki, 2000 citing Isachsen, unpublished data) and 1.669 ± 0.007 Ga (Powicki, 1996). Spencer and Richard (1999) reported that the Buckhorn granodiorite is gradational with other granitic rocks, which are in- Lw. Qtzt cluded in the more regionally extensive Buckhorn Creek complex. The contact between Buckhorn granodiorite and the lower quartzite was not observed di- Four Peaks 1.657 ± 0.014 Ga Rhyolite rectly during this study. However, the supracrustal package is interpreted to be deposited on top of the Buckhorn granodiorite because the metasedimentary 0 meters ? ? ? rocks were deposited on top of the rhyolite, which is younger than the grano Modi ed from Estrada (1987), Powicki (1996), Skotnicki (2000) diorite (see later herein). Skotnicki (2000) interpreted the granites exposed west of Four Peaks (his units Xg and Xgm) to be equivalent to the Beeline Granite (1.632 ± 0.003 Ga; the north side of the Four Peaks syncline, a large area of this unit experienced Isachsen et al., 1999) of the southwest Mazatzal Mountains (Fig. 5B). However, intense contact metamorphism from the adjacent El Oso Granite and is now new data, presented here, suggest that the granite at Four Peaks has an age of a gneissic, and commonly migmatitic, rock. The (200–400-m-thick) Four Peaks ca. 1.660 Ga and thus is probably older than the Beeline Granite. This granite Quartzite occurs conformably above the lower pelite. It makes up the resistant intrudes the lowermost sedimentary units in several places (for example, near ridge and topography of the Four Peaks. The quartzite is an extremely mature, Universal Transverse Mercator (UTM NAD 83, zone 12S) 0468165E, 3729082N; gray to purple, fine-grained and finely cross-bedded quartzite with rare layers see also Skotnicki, 2000). Further, a large block of what appears to be lower of pelitic phyllite to schist (Wilson, 1939; Estrada, 1987; Powicki, 1996). The syn- quartzite is included in the granite (Mako, 2014). Various granitic rocks occur west cline is cored by an upper pelitic to argillaceous unit, referred to as the upper and northeast of Four Peaks, probably a greater variety than described in the pre- pelite. This unit has a strong slatey cleavage parallel to the axial plane of the vious works or this study. For this study, these granites are collectively termed the Four Peaks syncline. Estrada (1987), Powicki (1996), and Skotnicki (2000) pro- granites of Soldier Camp. It is possible that the Beeline Granite is represented in vided detailed descriptions of these units. These rocks were metamorphosed the Four Peaks area; however, this remains unsubstantiated by our dating efforts. to at least chlorite and andalusite grade within the study area (Williams, 1991b; The youngest major igneous unit is the El Oso Granite, which is also ex- Powicki, 1996). posed over a large area of the southern Mazatzal Mountains and is similar The contact between the Four Peaks rhyolite and the lower quartzite is sharp to the ca. 1.4 Ga suite of ferroan granites that extend across North America (although poorly exposed) and is interpreted to be depositional in nature. Con- (Fig. 5C; Whitmeyer and Karlstrom, 2007). The granite is distinguishable by tacts between the lower three metasedimentary units (quartzite-pelite-quartzite) the pervasive occurrence of 2–3 cm potassium feldspar megacrysts, a general are gradational. The lower quartzite becomes intercalated with pelitic beds to- lack of penetrative foliation, and its crumbly weathered appearance. There is ward its top as it transitions to the lower pelite. The lower pelite becomes more a fine-grained phase of this granite that occurs as dikes and small isolated quartzite-rich up section, with increasing interbeds of quartzite as it transitions bodies across the study area. This generation of granite crosscuts all of the into the Four Peaks Quartzite. Thus, the lower quartzite, lower pelite, and Four other rocks in the Four Peaks area (Skotnicki, 2000; Powicki, 1996). The El Oso Peaks Quartzite appear to be stratigraphically continuous. The top few meters Granite exhibits local, meter-scale shear zones, but it is largely undeformed.

A B

Figure 5. Relevant field photographs. C D (A) Typical appearance of foliation in the

Buckhorn granodiorite (S1). (B) Typical appearance of foliation in the granites of Sol-

dier Camp (S2) defined by the alignment of biotite. The tip of the pen (bottom center) is aligned with the foliation. (C) The typical texture and appearance of the El Oso Granite. (D) Rhyolitic dikes cutting across foliations in the Buckhorn granodiorite with pen parallel to foliation trace. (E) Iso- clinal, intrafolial folds common in the metasedimentary rocks close to the granites of Soldier Camp. These features are suggestive of a bedding-parallel foliation

(S3). (F) Folded migmatitic leucosomes. These might indicate that migmatization

occurred prior to D4 and during crustal thickening, or that minor folding post- dated granite emplacement. E F

Structural Geology blages include quartz, biotite, and sillimanite, with migmatitic leucosomes locally present in rocks nearest the granite. The zone of migmatitic, silli- The Four Peaks area is dominated by a kilometer-scale syncline, the Four manite-grade rocks extends consistently ~1 km away from the El Oso Granite Peaks syncline (Fig. 3). It is a tight, doubly plunging (sheath-like) fold verging to (see map by Skotnicki, 2000). Calculated isochemical phase diagrams for two the northwest. The stratigraphy on the southern limb is locally overturned and rocks across the gradient indicate that temperatures ranged from <500 °C to thin relative to the northern limb (Fig. 2; Estrada, 1987; Powicki, 1996). The fold >700 °C, at pressures of 0.3–0.4 GPa, equivalent to 11–15 km depth (Mako, 2014). has an axial surface striking 050 and dipping 60°–70°S (Estrada, 1987; Powicki, It is difficult to constrain the Paleoproterozoic metamorphic character of the 1996). The fold is distinctly doubly plunging; the axis plunges to the southwest Four Peaks area. No contact metamorphic effects associated with the Paleo (55° → 210°) in the northeast and plunges to the northeast (47° → 030°) in the proterozoic granites of Soldier Camp have been recognized. In places where southwestern parts of the area. Axial plane cleavage is generally not present in a direct contact between the granites of Soldier Camp and the metasedi the quartzite units, but it is present in the more pelitic units. Slatey axial plane ments was observed (further from the El Oso Granite), contact metamorphic cleavage dominates the upper pelite. The orientations of bedding, foliation, porphyroblasts are notably absent (see also map in Skotnicki, 2000). The lack and minor structures are similar from the lowest to the youngest sedimentary of significant contact metamorphism may suggest that the Paleoproterozoic units, although the minor fold axes in the upper pelite have a shallower plunge granites were emplaced at relatively shallow depth at cooler ambient tempera- and a more northeasterly trend (14° → 057°, n = 4; Fig. 6A) than that of the tures. Rocks in the southernmost parts of the area, farthest from the El Oso Four Peaks Quartzite (22° → 074°, n = 9; Fig. 6B; Mako, 2014). The orientation Granite, may preserve Paleoproterozoic greenschist-facies conditions, consis- of minor folds and beta axes of bedding from the upper pelite and Four Peaks tent with regional conditions (Williams, 1991b). There is no evidence against Quartzite are all similar and lie nearly within the axial planar foliation of the Paleoproterozoic metamorphism, but contact metamorphism from the El Oso Four Peaks syncline (Fig. 6C). This is relevant to the nature of an unconformity Granite generally obscures any earlier metamorphism. between these units (see later herein). Mylonitic and locally ultramylonitic fabric is present in a 100–200-m-wide Zircon Geochronology and Hf Isotopic Data zone along the southern limb of the Four Peaks syncline (see also Powicki, 1996). Lineations in the mylonites plunge moderately east to southeast. Kine New U-Pb and Hf zircon data were obtained from eight samples from the matic indicators (mainly sigma porphyroclasts and locally S-C-C′ fabrics) sug- Four Peaks area and one from near Young, Arizona. Seven key igneous rocks gest oblique, right-lateral, thrust displacement, best developed in the rhyolite that constrain stages of the deformation history were dated. Detrital zircon (Powicki, 1996; this study). Powicki (1996) interpreted the mylonitic fabric along data from two samples are also reported to constrain the timing of sedimen- with localized fabrics in the Buckhorn granodiorite as a regionally significant tation (see also Doe, 2014). Samples and results are summarized next and in shear zone associated with the Four Peaks syncline. In contrast, Skotnicki Table 1. Hf isotopic data from five igneous samples provide insight into the age (2000) found little evidence for shearing and questioned the significance of and isotopic character of the lower-crust melt-source regions for the Paleopro- shearing or thrusting. Field observations during this study suggest that there terozoic and Mesoproterozoic intrusions in the Four Peaks region. Results for is indeed a zone of more intense, thrust-sense, shearing heterogeneously ex- each analysis are shown in Figure 7 and are given in Supplemental Table 2. posed along the southeast margin of the syncline. The presence of both rhyo- Descriptions of each analyzed sample are given next. It should be noted that lite and Buckhorn granodiorite on either side of the shear zone suggests that the apparently short time spans between uplift, sedimentation, and emplace- the offset may be relatively small. ment of the various units are not well resolved given the uncertainties in our geochronology techniques (usually ~15 m.y.). Metamorphism Isotopic Results Williams (1991b) concluded that regional metamorphism in the Sunflower tectonic block, including the Four Peaks area, ranged from greenschist to am- K13-4PKS-4 is a sample of the Buckhorn granodiorite, crosscut by post-tec- phibolite facies and that metamorphism occurred at 1.66–1.60 Ga (during the tonic rhyolitic dikes (Fig. 5D; Powicki, 1996). (Samples K13-4PKS-3, 4, and 5 Mazatzal orogeny). As discussed later herein, the metamorphic signature of were collected along the Chillicut Trail.) This sample is composed of plagio the Four Peaks area is dominated by a Mesoproterozoic field gradient increas- clase, quartz, hornblende, and biotite and is pervasively deformed. Thirty zir- ing northward toward the El Oso Granite (Powicki, 1996; Skotnicki, 2000; Mako, con grains yield an age of 1.677 ± 0.014 Ga (mean square of weighted devi- 2014). Pelitic rocks in the southern parts of the area have assemblages with ates [MSWD] = 0.4). This is within the error of both unpublished dates of this quartz, muscovite, biotite, chlorite, andalusite, and cordierite. Andalusite and granodiorite, 1.685 ± 0.004 Ga and 1.669 ± 0.006 Ga (Skotnicki, 2000; Powicki,

cordierite are rarely preserved; typically, the rocks contain muscovite-rich or 1996, respectively). Hf isotopic analysis of 15 zircon grains yielded eHf(t) values

chlorite-rich pseudomorphs, respectively. Near the El Oso Granite, assem- ranging from +10.4 to +4.8. All eHf(t) values overlap with each other within 2s

A B C

D E F

Figure 6. Stereograms of foliation orientations in the Four Peaks area. Data are taken from Skotnicki (2000) geologic map of the Four Peaks Quadrangle. Additional data were gathered during this study. (A) A pi diagram of bedding in the upper pelite (measurements restricted to the domain of cylindrical folding; see Fig. 2). The beta axis is represented by an open cross with a 95% confidence small circle (Holcombe, 2011). The mean orientation of minor fold axes (n = 4) is plotted as an open circle. (B) A pi diagram of bedding in the Four Peaks Quartzite. The beta axis is represented by a black cross with a 95% confidence small circle (Holcombe, 2011). The

mean orientation of minor fold axes (n = 9) is plotted as a black circle. (C) A summary of the beta axes and minor folds plotted with the average orientation of S4 in

the cylindrically folded domain. (D) The foliations in the Buckhorn granodiorite, thought to represent a composite of S1, S2, and S4. (E) The foliations in the granites

of Soldier Camp, striking distinctly east-west and thought to represent S2. (F) The foliations in the rhyolite including high-strain zones. These orientations probably

represent a composite of S2 and S4. In D–F, the average orientation is shown by an open circle and corresponding great circle.

uncertainty. One grain yielded a value of +10.4. Others grains are 2–5.5 epsilon of these grains were assimilated from the Buckhorn granodiorite; however, units more negative than the depleted mantle array value of +10.3 at 1.677 Ga. because the grains are not distinct in size, internal texture, morphology, U con- Sample K13-4PKS-3 is from a post-tectonic, rhyolitic dike that cuts folia- centration, or U/Th ratios, and both age determinations are within 2s uncer-

tions (S1) in the Buckhorn granodiorite (Fig. 5D). Dikes at this locality are also tainty of each other, the final age calculation includes all of the analyzed grains.

deformed by small shear zones but clearly cut the S1 fabric in the host grano Powicki (1996) reported an age of 1.660 Ga for this dike. Hf isotopic analysis

diorite. Sixteen zircon grains yielded a weighted mean crystallization age of of 10 zircon grains yielded eHf(t) values ranging from +9.8 to +3.3. The oldest

1.675 ± 0.015 Ga (MSWD = 1.9). If four of the oldest grains are excluded, the grains mentioned here did not yield distinct eHf(t) values; five grains ranging

weighted mean is 1.670 ± 0.014 Ga (MSWD = 0.6). It is possible that some in age from 1.695 to 1.668 Ga yielded a tight cluster of eHf(t) values ranging

Avg. 2σ 176 Hf = 0.015 177 Hf

176 Hf = 0.0093 177 Hf

Figure 7. U-Pb-Hf isotopic data for igneous zircons in the Four Peaks area. Each point represents a zircon for which we have a paired U-Pb crystallization age, and a 176Hf/177Hf value. DM—depleted mantle array of Vervoort and Blichert-Toft (1999); CHUR—chondritic uniform reservoir of Bouvier et al. (2008). The average uncertainty in U-Pb ages is shown in the bottom left, as well as the average 2σ uncertainty in 176Hf/177Hf ratios expressed as epsilon units. The dashed and dotted line represents average crustal evolution paths assuming 176Hf/177Hf = 0.0093 (Vervoort and Patchett, 1996), and 176Hf/177Hf = 0.015 (GERM, 2001), respectively.

from +6.9 to +6.1. The eHf(t) values of all grains overlap with each other at the contact with the lower pelite. The quartzite consists of ~95% quartz with acces- 2s confidence level, with the exception of the grains K13-4PKS-3-10 and K13- sory sericite, oxides, monazite, and zircon. Zircon grains in this sample were

4PKS-3-11, which yielded eHf(t) values of +3.3 and +9.6, respectively. Two of the small (50–150 µm long) and commonly fragmental. In cathodoluminescence grains plot within error of the depleted mantle array at 1.670 Ga (+10.3), but the (CL) images, oscillatory zoning and dark cores were very common. Ninety-one

rest of the zircons, with the exception of K13-4PKS-10, yielded eHf(t) values that detrital zircon ages were obtained. The distribution is dominantly unimodal

are 2–4.1 epsilon units less positive than the +10.3 eHf(t) value of the depleted with peaks at 1.742 and 1.766 Ga (Table 1), and with subsidiary peaks at 1.685 mantle at 1.67 Ga. and 1.855 Ga, and ~13 grains in the range 2.5–2.8 Ga. According to Dickinson C13-082b is a sample of the rhyolite that is interpreted to be the base of the and Gehrels (2009), the most robust maximum depositional age that can be stratigraphic section in the Four Peaks area. The sample exhibits mylonitic to determined from detrital zircon age data is determined by the weighted mean ultramylonitic, northeast-striking fabrics and steeply plunging lineations. Zir- of at least the three youngest ages that overlap at 2s. The weighted mean of con grains were 100–200 µm and tabular to irregular in shape. Twenty-seven the three youngest grains in the population is 1.684 ± 0.016 Ga (MSWD = 1.3); zircon grains yielded a crystallization age of 1.657 ± 0.014 Ga (MSWD = 0.4). No however, not all of these grains overlap at 2s. The weighted mean of the two Hf isotopic data were collected for this sample. youngest grains that overlap at 2s is 1.659 ± 0.039 Ga (MSWD = 0.6), which C13-067B is a sample from the Young granite from near Young, Arizona. is more consistent with depositional constraints from the underlying rhyolite This granite is from within the Slate Creek shear zone and was interpreted to (see following). Neither of these maximum depositional ages meet the crite- be syn- to post-tectonic because it crosscuts strongly foliated metasedimen- rion of Dickinson and Gehrels (2009) exactly, but given that the former esti- tary rocks (Labrenze and Karlstrom, 1991). No foliation or deformation struc- mate includes more grains, the methodologically best maximum depositional tures were observed in this particular sample or in the immediate area from age estimate is taken to be 1.684 ± 0.016 Ga. The Four Peaks Quartzite uni- which it was taken. A weighted mean of 18 zircon ages yields an age of 1.664 ± modal age spectra are typical of many Proterozoic quartzites in the southwest,

0.017 Ga (MSWD = 0.3). Hf isotopic analysis of 10 zircon grains yielded eHf(t) including the Ortega Quartzite (New Mexico), and White Ledges Formation and

values ranging from +6.9 to +3.7. All eHf(t) values overlap with each other at 2s, Mazatzal Peak Quartzite (Arizona; Jones et al., 2009; Doe, 2014). and they are between 3 and 7 epsilon units below the depleted mantle array Sample K13-FPKS-14 is from the granites of Soldier Camp (Fig. 2). This

value of +10.3 at 1.667 Ga. sample was from a foliated (S2), biotite-bearing granite. It was mapped close C13-029a is a sample of the Four Peaks Quartzite. This sample was col- to a contact between the lower quartzite and granites of Soldier Camp by Skot- lected from the base of the Four Peaks Quartzite, several meters above the nicki (2000) and was correlated with the 1.632 ± 0.003 Ga (Isachsen et al., 1999)

Beeline Granite. Zircon from this sample yielded an age of 1.667 ± 0.016 Ga (32 Twenty-eight zircon grains yielded a crystallization age of 1.449 ± 0.013 Ga grains, MSWD = 2.1). Two grains yielded older ages of 1.715 ± 0.014 Ga and (MSWD = 0.7). Three zircon grains yielded older Paleoproterozoic ages, rang- 1.788 ± 0.304 Ga, outside the 2s error of the population, which we interpret ing from 1.616 to 1.663 Ga, which are likely assimilated from country rocks. as inherited. If these grains are eliminated, a weighted mean age of 1.658 ± These grains were eliminated from the final age calculations. No Hf isotopic 0.015 Ga (30 grains) is calculated (MSWD = 0.5). Based on these data, this sam- data were collected for this sample. ple of the granites of Soldier Camp, in the Four Peaks area, is distinctly older Sample K13-FPKS-15 is from a muscovite-bearing granitic dike that is un-

than the Beeline Granite. Hf isotopic analysis of 19 zircon grains yielded eHf(t) deformed and cuts across all other units. This granite was mapped as Ygm values ranging from +10.3 to +2.4. This sample yields the greatest spread of (Mesoproterozoic medium-grained granite) by Skotnicki (2000). It is relatively

eHf(t) values of the Paleoproterozoic igneous samples. A cluster of four grains fine grained and commonly contains dispersed 2–4 cm feldspar megacrysts. In-

yield eHf(t) values between +4.3 and +3.8 at ca. 1.66 Ga, as many as 8.0 epsilon trusions of this kind are interpreted to be related to the El Oso Granite. Zircon units below the depleted mantle array value of +10.4. Zircon K13-FPKS-14-7, analysis yielded distinct Mesoproterozoic and Paleoproterozoic age populations.

with an age of 1.715 ± 0.014 Ma, yielded an eHf(t) value of 6.3. Notably, this Ten Mesoproterozoic grains yielded a weighted mean age of 1.437 ± 0.015 Ga

grain and K13-4PKS-5-1 (see following) yielded U-Pb ages and eHf(t) values (MSWD = 0.4), interpreted as the crystallization age, and four Paleoproterozoic that overlap at 2s. It should be noted that this sample was taken close to the grains yielded a weighted mean age of 1.651 ± 0.021 Ga (MSWD = 0.4). The metasedimentary rocks, so it is possible that the final age is dominated by older grains may have been assimilated from the granites of Soldier Camp or assimilated grains, making the granites appear older. However, most zircon possibly the lower sedimentary units. Finally, one additional Paleoproterozoic from this sample appears euhedral and igneous, not rounded. grain yielded an age of 1.716 ± 0.022 Ga. The Paleoproterozoic zircon grains are K13-4PKS-5 is a sample of megacrystic granite from the Chillicut trail, east interpreted to have been inherited from country rocks during dike emplacement.

of the Four Peaks syncline. This granite is very similar in appearance to the Hf isotopic analysis of 14 zircon grains yielded eHf(t) values ranging from Mesoproterozoic El Oso Granite and is weakly foliated. It was interpreted by +7.8 to +2.0; however, due to the bimodal age population of this sample, the Hf Powicki (1996) to be Paleoproterozoic in age, while Skotnicki (2000) consid- isotopic composition of each population must be addressed separately. Meso-

ered it Mesoproterozoic. Twenty-two zircon grains yielded an age of 1.655 ± proterozoic zircon grains yielded eHf(t) values ranging from +5.6 to +2.0. Five

0.015 Ga (MSWD = 2.0). One grain (K13-4PKS-5-1) yielded an age of 1.727 ± Paleoproterozoic zircon grains yielded eHf(t) values ranging from +7.8 to +2.5.

0.024 Ga, well outside of the 2s range of the rest of the population and prob- Interestingly, the oldest grain, K13-FPKS-15-28, yielded an eHf(t) value of +2.5 at ably inherited from an older source. If this grain is removed, a final age of 1.716 Ga, one of the oldest and most-evolved grains in our data set. 1.652 ± 0.014 Ga (MSWD = 0.4) is calculated. The older grain has a distinct CL-dark overgrowth, which was too small to be analyzed by a 30 mm beam. Fabric Relationships As shown by Powicki (1996), there are two bodies of Paleoproterozoic granite on either side of the Four Peaks syncline, cut by the large, Mesoproterozoic, El Four distinct structural fabrics were identified in the Four Peaks area based

Oso pluton. Hf isotopic analysis of 11 zircon grains yielded eHf(t) values ranging on their orientation and probable age, although overprinting relationships

from +10.4 to +6.2. Two grains gave values of +8.7 and +10.4 and are within among some of the fabrics are not evident. The oldest structural fabric (S1) error of the depleted mantle array at 1.655 Ga (+10.4). Nine grains plotted in a occurs in the Buckhorn granodiorite, the oldest unit in the study area (ca. tight cluster with values of +7.5 to +6.2 and hence are 3–4 epsilon units below 1.680 Ga). It is a heterogeneous, moderate to strongly developed foliation that the depleted mantle array. K13-4PKS-5 and K13-FPKS-14 are petrologically, iso- generally strikes northeast and dips 85–90°SE with a steeply plunging lineation topically, and chronologically similar, so they are both regarded as members (Fig. 6D; Powicki, 1996; Skotnicki, 2000). The foliation is defined by ribbons of of the granites of Soldier Camp. dynamically recrystallized feldspar, aligned biotite, and elongate quartz grains, Sample 20130916-1 is a sample of the upper pelite collected by coauthor indicating deformation temperatures of greater than 500 °C (Fig. 5A). Localized

Doe and was analyzed at the Arizona LaserChron Center (Doe, 2014). The sam- protomylonitic to mylonitic shear zones, generally parallel to the S1 foliation, ple was taken from the stratigraphically highest point available in the Four exist throughout the granodiorite, alternating with areas of less intense fab-

Peaks area in the upper pelite. A probability density plot of detrital zircon ages ric. S1 foliation formation preceded the intrusion of crosscutting rhyolitic dikes (94 grains) shows peaks at 1.580 and 1.785 Ga. Minor peaks occur at 1.730 Ga (Fig. 5D; 1.675 ± 0.015 Ga). and 1.830 Ga, and several grains yielded Archean ages. The maximum deposi- The granites of Soldier Camp (1.660–1.655 Ga) contain a relatively weak to

tional age of the upper pelite, based on the seven youngest zircon grains in the moderately strong fabric, here termed S2. Most commonly, S2 is defined by the analyzed population, is 1.566 ± 0.014 Ga (Doe, 2014). alignment of biotite with a lesser component of aligned quartz and feldspar C13-073 is a sample of the El Oso Granite. This sample contains large porphyroclasts. The presence of dynamically recrystallized quartz, observed in 1–3 cm feldspar phenocrysts, along with quartz and biotite. Zircon grains thin section, suggests that the fabric is a solid-state rather than synmagmatic were 200–300 µm and elongate, with some fractured cores (not analyzed). fabric. As noted already, several different granite bodies are present in the Sol-

dier Camp area, and the S2 fabric is extremely weak or absent in some and titic lower quartzite (C13-056a-1). All of these samples are very close to the con-

present in others. The S2 foliation has a distinctive and tightly clustered east- tact with the El Oso Granite (<1 km) except for the sample of Four Peaks Quartz- west orientation (269°, 76°N; Fig. 6E). This is atypical for the Four Peaks area, ite, which was collected ~2 km from the granite. Dated monazite grains range

where the majority of fabrics strike northeast-southwest. No S2-S1 overprinting in age from ca. 1.380 to ca. 1.78 Ga, but most dates are 1.49–1.45 Ga (Table 2).

has been recognized to date. However, S2 must be younger than S1 given the Three different monazite populations can be distinguished within migma- geochronologic constraints. titic lower pelite and lower quartzite based on composition and texture. Many The earliest fabric recognized in the metasedimentary rocks is a bed- grains display high-Th and high-Y cores (population 1) with lower-Th and

ding-parallel foliation (S3). It generally has a northeast-oriented strike (i.e., slightly lower-Y rims (population 2). A third population of grains is character- parallel to the strike of the units themselves) and is typically observed close ized by consistently low Th and low Y. Nine dated population 1 domains give to the contact with the granites of Soldier Camp. Intrafolial folds within sedimentary layers suggest local transposition of bedding (Fig. 5E). Such features TABLE 2. MONAZITE GEOCHRONOLOGY DATA have not been recognized in areas of the Four Peaks syncline further away Age from the granites. The S2 foliation in the adjacent granites of Soldier Camp Monazite domain (Ma)2σ MSWDCategory has a distinctly different orientation (steeply dipping and east-west–striking) C13-012_m14 hi Th core 1480 7.4 1.2Core compared to the northeast strike of S in the metasediments. The timing rela- 3 C13-012_m8_core 1480 7.2 2.6Core tionship between the S2 foliation in the granites of Soldier Camp and S3 in the C13-012_m15 core 1480 9.2 1.2Core metasediments is not clear at present. C13-012 m1 lw Th sect 14818 0.5Core

The fourth foliation (S4) is axial planar to the Four Peaks syncline. This fab- C13-012 m2 hi Th 14847 0.8Core ric is steeply dipping and northeast striking, averaging 066°, 86°SE within the C13-012 m4 hi Th core 1487 7.2 2.1Core

area of structural analysis (Fig. 6A). S4 is defined by the alignment of biotite C13-012_m9_hi Th 14878 4.1Core and muscovite and is strongly developed in the upper pelite and rhyolite. In C14-013a-1_m1-bot-rim 1489 9.4 2.4Core the upper pelite, it is a strong slatey cleavage. In several parts of the Four Peaks C13-012_m9_lw_Th 1493 10.4 2.2Core Monazite cores 1484 2.6 1.14 area, S4 forms a crenulation cleavage as it overprints the nearly bedding-par- C13-012_m14_lwYrim 1465 7.8 0.7 Rim allel S3 foliation (see also Powicki, 1996). The ultramylonitic fabrics of the high- strain zones to the southwest and east of the syncline are also correlated with C14-013a-1_m7-rim-PbP 1466 10.8 0.9 Rim C13-012_m11 1468 7.4 1.2 Rim S4. Generally, foliations in the rhyolite (too young to be S1) are a composite of C13-012_m15 rim 14708 0.5 Rim S and S (Fig. 6F), and foliations in the Buckhorn granodiorite in areas away 2 4 Monazite rims 1467.4 40.3 from the crosscutting rhyolitic dikes may be a composite of S1, S2, and S4. Migmatitic leucosomes tend to form parallel to bedding along the contact C13-011-1_m7 1454 12.8 0.5Young core C13-011-1_m2 1457 10.4 0.4Young core with the El Oso granites. Leucosomes are folded similar to the regional Four C14-013a-1_m4-core 1457 8.4 0.4Young core Peaks syncline and associated axial planar fabrics defined by the growth of bio C13-011-1_m7rim 1459 13.4 0.1Young core tite. In the field, it is not clear whether partial melting occurred before, during, Young monazite cores 1456.8 5.2 0.101 or after folding. Leucosomes may have formed preferentially along favorable C13-056a-1_m8light 1386 7.6 1.2Other sedimentary layers that had already been folded, or they may have been folded C13-056a-1_m4 1410 5.4 1.8Other after formation (Fig. 5F). Additionally, it is possible that anatexis preceded large- C13-056a-1_m4light 1416 4.4 1.8Other scale folding in the area. Finally, very local shear zones of the style described by C13-056a-1_m8 1418 9.2 1Other Ramsay and Graham (1970) and minor foliations are found in the young El Oso C13-036-1_m2-1 1445 39.2 0.5Other Granite. These clearly record some local deformation after the emplacement of C13-056a-1_m3 1458 6.4 1.3Other Mesoproterozoic granites, but the magnitude of the strain is relatively small. C13-036-1_m1.7-core 1464 39.2 0.1Other C14-013a-1_m1-core 1475 12.4 0.4Other Monazite Geochronology C13-012_m5lowall 1483 10.4 1.6Other C14-013a-1_m7-core 1483 28.8 1.3Other C13-012 m2 lw Th 1490 10.2 0.6Other Monazite was identified in many of the metasedimentary rocks of the Four C13-012 m1 hi Th sect 1510 8.8 1.5Other Peaks area. Much of the monazite was heavily altered, very small, and unsuit- C13-036-1_m7-core 1736 14.6 0.2Other able for dating. Monazite was successfully mapped and dated in five samples: C13-036-1_m3-1-right-core 178111.6 0.5Other three samples of migmatitic lower pelite (C13-011-1, C13-012, and C13-013a-1), Note: MSWD—mean square of weighted deviates. one sample of Four Peaks Quartzite (C13-036-1), and one sample of the migma-

a weighted mean date of 1.484 ± 0.003 Ga (2 , MSWD = 1.14). Four popula- A All Dated Monazite B s 1.350 1.350 Similar Domains tion 2 (rim) domains were analyzed and give a weighted mean age of 1.467 ± 0.004 Ga (MSWD = 0.30). Four population 3 domains give a weighted mean

age of 1.457 ± 0.005 Ga (4 domains, MSWD = 0.10). These results are summa- e (Ma) rized in Figure 8. 1.500 Dates from population 1 domains are significantly older than the age of the 1.450 El Oso Granite (1.449 ± 0.013 Ga), while population 2 just overlaps the granite 1.700 Monazite Ag at 95% confidence. We interpret grains in populations 1 and 2 to have grown during prograde metamorphism before the intrusion of the El Oso Granite. The 1.800 drop in Th and Y in rocks with little or no garnet may suggest an early phase C Weighted Averages of partial melting prior to granite intrusion. Population 3 grains overlap in age 1.375 1.550 with the El Oso Granite. We interpret these grains to be the result of crystalliza- D Explanation Young Cores tion of injected granite melt or fluids related to the El Oso Granite. 1.457 ± .005 Ga Samples Domain Types Rims As noted already, most of the monazite-bearing samples are very close to e (Ma) C13-036-1 Population-3 1.467 ± .004 Ga

Ag 1.450 the El Oso Granite contact. Monazite grains further away from the granite tend C13-012 Population-2 to be heavily altered, have patchy complex compositional zonation, and give C14-013a-1 Population-1 inconsistent dates. It is possible that monazite was preserved in higher-tem- Monazite 1.484 ± .003 Ga C13-011 “Other” Domains perature rocks near the El Oso Granite but was more extensively altered by Cores C13-056a-1 1.525 late-stage fluids in cooler rocks more distant from the granite (Harlov et al., 2011; Williams et al., 2011). Figure 8. Plots of monazite geochronology data and interpretation. Each bell-curve represents Two monazite grains from the Four Peaks Quartzite (sample C13-036-1) analyses from a single compositional domain and is centered on the mean age with a distribution reflecting analysis uncertainty. (A) Monazite age with each analyzed domain colored give Paleoproterozoic ages (1.736 Ga and 1.781 Ga). The rocks also yielded by sample of origin. (B) Interpreted analysis association with generations of monazite growth grains and rims in the younger populations (see above). These older domains (core, rim, and young core) on the basis of X-ray mapping. Monazite domains that did not fit are interpreted to be detrital monazite cores present within the original quartz well within an age-composition category are designated “other.” (C) Weighted mean ages of cores, rims, and young cores plotted with 2σ uncertainty. (D) Explanation of the color scheme. sandstone. These are consistent with detrital zircon ages from the same rocks. More extensive detrital monazite analyses from these sediments may provide additional insight into the depositional age and provenance of the sediments rhyolite deposition at ca. 1.660–1.655 Ga. This is broadly compatible with re- and also into possible Paleoproterozoic metamorphism. gional constraints on the timing of Mazatzal Group sedimentation (Doe, 2014). Early workers (Conway and Silver, 1989) interpreted the deposition of the entire Tonto Basin Supergroup to have been 1.710–1.675 Ga. Cox et al. (2002) DISCUSSION constrained the age of the Lower Deadman Quartzite (a.k.a. Pine Creek Con- glomerate) to ca. 1.70 Ga by dating an overlying rhyolite. Many of the rocks in Timing of Deposition the Tonto Basin now appear much younger. The youngest unit in the stratigraphic section (upper pelite) has a maxi- Our new data provide improved constraints on the age of supracrustal mum depositional age of 1.566 ± 0.014 Ga, based on detrital zircon ages (Doe, rocks in the Four Peaks area with implications for the timing of tectonism. 2014). If only data from Four Peaks are considered, the sediments must have The whole stratigraphic package, including a basal rhyolite, was deposited been deposited 1.566–1.449 Ga, with the younger constraint being the intru- on top of the older Buckhorn granodiorite (ca. 1.680 Ga). The rhyolite (1.657 ± sion of the El Oso Granite (1.449 Ga), but based on regional correlations (see 0.014 Ga) represents the base of the stratigraphic section, bracketing the onset following), the upper limit may be closer to 1.502 Ga. Importantly, if the lower of deposition to younger than 1.657 ± 0.014 Ga. The lower two sedimentary units are older than 1.650 Ga and the upper unit is younger than 1.502 Ma, a units (lower quartzite and lower pelite) are intruded by and included within the significant unconformity or disconformity exists at the upper contact of the granites of Soldier Camp (1.658 ± 0.015 Ga and 1.652 ± 0.014 Ga). Therefore, Four Peaks Quartzite with a time gap of 100–140 m.y. No angular relationship the lower sediments were deposited immediately after the rhyolite. The Four was observed between the Four Peaks Quartzite and the upper pelite. How- Peaks Quartzite has a maximum depositional age of 1.659 ± 0.039 Ga or 1.684 ± ever, work to date does not preclude the possibility of a subtle angular uncon- 0.016 Ga based on detrital zircon data, and the lower quartzite and lower pelite formity between the Four Peaks Quartzite and upper pelite. If there is such an are stratigraphically continuous with the Four Peaks Quartzite. Thus, the three unconformity, the angular difference is relatively minor and may have been lower sedimentary units were conformably deposited relatively soon after diminished during folding (Mako, 2014).

Regional Correlations voir (Fig. 7). Combined with the presence of >1.7 Ga xenocrystic zircons in our data set, and Nd isotopic data from Paleoproterozoic gneisses in the southern Strata at Four Peaks can be directly correlated with rocks of the surrounding Mazatzal Province that show similar evidence for 2.0–1.78 Ga crustal compo- Tonto Basin, including the Paleoproterozoic Redmond Formation, Hess Canyon nents (Amato et al., 2008), these data may suggest that lower crust older than Group, and the Mesoproterozoic Yankee Joe Formation. The 1.657 ± 0.003 Ga 1.7 Ga is present in the Mazatzal Province.

Redmond Formation is correlated with the Four Peaks rhyolite. The Four Peaks The evolved eHf(t) values of zircon grains from the Mesoproterozoic granitic Quartzite is likely correlative with the White Ledges Formation (quartzite) of dike (K13-FPKS-15) suggest that they were derived primarily from recycling the Hess Canyon Group and with the Mazatzal Peak Quartzite in the northern of a Paleoproterozoic crust. These results are in line with previous studies of Mazatzal Mountains (1.660–1.630 Ga; Doe, 2014). However, it is somewhat prob- 1.48–1.35 Ga Laurentian granites (Frost and Frost, 1997; Goodge and Vervoort, lematic that the Maverick Shale, beneath the Mazatzal Peak Quartzite, has a 2006; Bickford et al., 2015). The apparent 1.85–1.75 Ga model ages of the source maximum depositional age of 1.631 ± 0.022 Ga. This is younger than, but still region for many of the grains do not fit well with other interpreted crustal ages within error of, the constraints at Four Peaks. The lowermost White Ledges For- in Arizona, such as the 1.75 Ga crustal model age for the Jerome region of the mation is intercalated with the Redmond Formation (Livingston, 1969), a rela- Yavapai crust (Doe, 2014), or the Archean model ages seen beneath Mojave tionship that was not observed at Four Peaks but is expected to exist given the crust (Holland et al., 2015). However, the apparent 1.85–1.75 Ga crustal age strength of the correlation. Doe (2014), studying the Proterozoic stratigraphy of is compatible with the observed ca. 1.8 Ga Nd model ages obtained from the the Hess Canyon Group in the nearby Salt River Canyon, correlated the upper Payson ophiolite (Dann, 1992) farther north in the Tonto Basin area. pelite at Four Peaks with the Yankee Joe Group and interpreted a depositional age of 1.502–1.490 Ga. The uppermost units of the Yankee Joe Formation have Timing of Deformation detrital zircon as young as ca. 1.470 Ga (Doe et al., 2013), while the lower units have interbedded ash layers dated at ca. 1.502 Ga (Bristol et al. 2014). Thus, Four distinct deformation fabrics are recognized in the Four Peaks area.

the upper pelite at Four Peaks is probably equivalent to lowermost Yankee Joe The first deformation event (D1) occurred ca. 1.680–1.675 Ga and formed north-

Group (Doe, 2014). The contact between the Paleoproterozoic White Ledges east-striking S1 foliations that are present in the Buckhorn granodiorite. The Formation and the Yankee Joe Group is a well-exposed disconformity for age of this event is constrained by the crystallization age of the granodiorite ~20 km along the upper Salt River Canyon ~50 km to the east of Four Peaks. The (1.677 ± 0.014 Ga, 1.685 ± 0.004 Ga) and the age of a rhyolitic dike (1.675 ±

apparent lack of an angular unconformity between the Mazatzal and Yankee 0.015 Ga) that crosscuts the solid-state S1 foliation (Figs. 5A and 5D).

Joe Groups appears to be a regional feature of that contact. The second episode (D2) formed weak to moderate east-west–striking foli-

ation (S2) in the granites of Soldier Camp, the rhyolite, and the Buckhorn gran-

Magmatic Source and Crustal Evolution odiorite. The age of D2 is partially constrained by the ages of a deformed sample K13-FPKS-14 (1.658 ± 0.015 Ga) and low-strain sample K13-4PKS-5 (1.652 ± The Mazatzal Province has previously been defined as composed of 1.70– 0.014 Ga) of granite. Because of the significant variation in fabric intensity from 1.60 Ga juvenile arc rocks (Whitmeyer and Karlstrom, 2007, and references granite to granite, it seems likely that the suite was emplaced syntectonically

therein). However, our new Hf isotopic data suggest some involvement of at ca. 1.660–1.655 Ga. The dates that constrain both D1 and D2 are within uncer- older crustal material in the petrogenesis of Paleoproterozoic rocks in the Four tainty of one another, but crosscutting relationships clearly separate these fab- Peaks region (Fig. 7). Ideally, juvenile contributions would be represented by rics in time. It is possible that the rhyolitic dikes in the granodiorite are related

rocks that yield eHf(t) values equal to the depleted mantle array at the time of to the larger rhyolite body, and such a relationship would permit that D1 and

crystallization. From our data, 33% (20 zircon grains) of all Paleoproterozoic zir- D2 were a single progressive event. However, the high temperature (feldspar

con grains yielded eHf(t ) values that overlap with the depleted mantle array at ductility) of S1 and the probably extrusive nature of the rhyolite suggest that

the time of crystallization. The remaining two thirds of Paleoproterozoic zircon there was a period of time (exhumation) between D1 and D2.

grains yielded eHf(t) values that may suggest the involvement of 2.0–1.75 Ga The Young granite brackets deformation in the Slate Creek shear zone crust (Fig. 7). The nature of older crustal contributions is ambiguous in the 50 km to the northeast of the Four Peaks area. Labrenze and Karlstrom (1991) data, and results from modern oceanic arcs, which show substantial variability noted that penetrative fabrics in the Slate Creek zone shear are crosscut by in epsilon Hf space (Dhuime et al., 2011), may not preclude formation of these the granite, suggesting intrusion was late or postdeformation. Our new Young rocks in a juvenile arc setting. Thus, a conservative interpretation of the data granite date brackets Slate Creek shear zone deformation to after 1.700 Ga (the is that the Paleoproterozoic rocks of the Four Peaks region were derived in age of the deformed Red Rock Rhyolite; Conway and Silver 1989) and before part from a juvenile source that experienced some mixing with crustal com- 1.664 ± 0.017 Ga (the crystallization age of the Young granite). The timing and

ponents as old as 2.0 Ga. However, eHf(t) values from the Mesoproterozoic orientation of the Slate Creek shear zone deformation correlate well with D1 in granite dike (K13-FPKS-15) suggest derivation from a ca. 1.75 Ga crustal reser- the Four Peaks area.

The absolute age of S3 (bedding-parallel fabric; Fig. 5E) is difficult to re- part of this event and, if so, could reflect a period of thrusting and tectonic

solve because S3 occurs in sedimentary rocks intruded by the granites of Sol- burial. The coarse-grained nature of the granite and the ductile penetrative

dier Camp. It is not clear from field evidence whether the granites crosscut nature of S2 suggest at least some amount of burial, probably greater than

S3. Because the lower sedimentary units were deposited by ca. 1.660 Ga, S3 the currently exposed 600–800 m Paleoproterozoic metasedimentary package. can broadly be constrained to 1.650–1.450 Ga. We entertain three possibilities: We suggest that burial of at least several kilometers would be required for

(1) S3 may have been roughly synchronous with S2 and reflect deformation emplacement of the generally medium-grained granites of Soldier Camp. Be-

partitioning between the granitic and metasedimentary packages. (2) S3 may tween ca. 1.655 Ga and ca. 1.570 Ga (or possibly 1.502 Ga), the Four Peaks area

have been synchronous with S4 and large-scale folding as strain was parti- was once again exhumed to the surface. The lack of a recognizable angular tioned around the rheologically stiff granites of Soldier Camp. This would unconformity at this time is puzzling. provide an explanation for the absence of northeast-striking fabrics in the The third tectonic cycle involved deposition of the (1.502–1.490 Ga) up-

granites. (3) S3 may represent penetrative deformation at ca. 1.660–1.655 Ga per pelite, deformation and burial to midcrustal (petrologically constrained, associated with a regional Mazatzal orogeny. 11–15 km) depths, emplacement of the 1.450 Ga El Oso Granite, and regional The youngest and most significant regional deformation event recorded in metamorphism to at least greenschist facies, with higher temperatures asso

the Four Peaks area (D4) occurred 1.490–1.450 Ga and resulted in the kilome- ciated with plutons. The Four Peaks syncline was developed at this time, pre-

ter-scale Four Peaks syncline. D4 is bracketed between the deposition of the sumably associated with regional thrusting and tectonic burial. The rocks at upper pelite (1.502–1.490 Ga) and the intrusion of the El Oso Granite (1.449 ± Four Peaks were exhumed by ca. 1.33 Ma, when the regional deposition of

0.013 Ga). S4 foliations, spaced cleavage, and slatey axial plane cleavage, espe- the flat-lying Apache Group sediments occurred (Cuffney, 1977; Stewart et al., cially in the uppermost unit, were formed during this folding event. In the past, 2001). However, the growth of monazite as young as 1.400 Ga suggests that this fold was considered a classic Mazatzal (i.e., Paleoproterozoic) structure. The the rocks remained at some depth after 1.450 Ga granite emplacement. new age constraints from the upper pelite require that the slatey cleavage in the upper units is a Mesoproterozoic fabric. Zones of intense shear south of the Four Peaks syncline probably formed during this event and were related to folding. Testing Alternative Models

Mesoproterozoic (D4) deformation was accompanied by crustal thickening and monazite growth. By the time of intrusion of the El Oso Granite (ca. There are a few alternative possibilities to this tectonic history that war- 1.450 Ga), the metasedimentary rocks in the Four Peaks area had been buried rant examination. First, because the contact relationships among the rhyolite, to a depth of 11–15 km, and significant anatexis had occurred in rocks within lower quartzite, and Buckhorn granodiorite have not been documented in ~1 km of the El Oso Granite (Mako, 2014). At least one phase of monazite detail, we consider whether the Paleoproterozoic sedimentary package was growth preceded the intrusion of the El Oso Granite and thus is attributed to actually intruded by the granodiorite. This would make the sedimentary rocks crustal thickening and orogenesis. Small, meter-scale shear zones are pres- older than the Mazatzal Group (>1.68 Ga), and it would remove one of the ent in the El Oso Granite, and monazite growth continued on to ca. 1.400 Ga. “tectonic cycles” from the history. However, the maximum depositional age of Significant tectonism generally ceased in the Four Peaks area by ca. 1.450 Ga. the Four Peaks Quartzite is 1.684 ± 0.016 Ga, which would still make the deposition of the sedimentary package rapid. Additionally, rocks of this depositional age are unknown in the Tonto Basin area; the Mazatzal Group was deposited Tectonic History—Three Orogenic Cycles Recorded 1.66–1.63 Ga, and the next older Alder Group was deposited 1.72–1.70 Ga (Doe, in the Four Peaks Area 2014). The fact that the younger granites of Soldier Camp (1.658 ± 0.015 Ga) intrude the sedimentary package, that the rhyolite (1.657 ± 0.014 Ga) under- Three cycles of burial–pluton emplacement–deformation–exhumation are lies the sedimentary package, and the reasonable correlation with the Hess recorded in the Four Peaks area. The first cycle involved the emplacement of Canyon Group to the south argue against this alternative model. Additionally,

the ca. 1.680 Ga Buckhorn granodiorite and the production of the S1 foliation. the sedimentary package would have been deformed during D1 at ~500 °C No older host rocks have been recognized, but the medium-grained nature of (feldspar plasticity), if the diorite intruded the sediments. High-temperature,

the granodiorite and the ductile nature of S1 (~500 °C) suggest some significant localized deformation structures or microstructures (S1; Fig. 5A) in the lower depth of burial, probably on the order ~10 km. The rocks were exhumed by ap- sedimentary units have not been recognized. proximately ca. 1.660 Ga, when the rhyolite and lower three metasedimentary We also consider whether the entire sedimentary package at Four Peaks units were deposited. may be Mesoproterozoic in age. Such a situation is permissive based on the The second cycle involves burial, emplacement of the granites of Soldier detrital zircon data. It is conceivable that during the deposition of the lower

Camp (1.658 ± 0.015 Ga), and development of the S2 foliation. D2 is interpreted sedimentary units, the basin received little or no 1.660–1.490 Ga detritus.

to have occurred at ca. 1.655 Ga. The formation of S3 foliations may have been Again, however, the granites of Soldier Camp (1.658 ± 0.015 Ga) appear to

intrude the lower parts of the sedimentary section, and the rhyolite appears rocks were buried to middle-crustal levels during the Mazatzal orogeny and to form the base of the stratigraphic section. Given the critical nature of this possibly remained in the midcrust until at least 1.400 Ga (Williams and Karl- contact relationship, future work should focus on the granites of Soldier Camp. strom, 1996). Based on detrital zircon data, the region was exhumed by 1.57– The conundrum of the present data is that there is an apparently continuous 1.50 Ga, when new sediments were deposited. Regional metamorphic grades stratigraphic section that contains Paleoproterozoic strata (1.66 Ga) at the bot- were probably in the greenschist facies during the Mazatzal orogeny, with tom and Mesoproterozoic strata at the top, with the lower parts of the section higher grades possible near some syntectonic plutons (Williams, 1991b). Our intruded by Paleoproterozoic granites. new U-Pb-Hf isotopic data suggest that the Four Peaks region may be under Readers may notice that the lower sedimentary package is deposited on lain by a component of 1.75–2.0 Ga crust that is not directly related either to a 1.657 ± 0.014 Ga rhyolite and intruded by 1.658 ± 0.015 Ga granite, which is juvenile Yavapai (1.8–1.7 Ga) or juvenile 1.7–1.6 Ga crust. The age of the crustal problematic if the mean ages are taken as absolute. The relatively large uncer- source region for the Four Peaks granites is similar to that of granitoids in- tainty (95% confidence) on these ages (~15 m.y.) must be taken into account. truded by the Payson ophiolite further north in the Tonto Basin area. The Slate Additionally, if the granites of Soldier Camp sample includes a significant num- Creek shear zone, which runs between these two locales, has previously been ber of assimilated detrital zircon grains, this could make the age of the granites proposed as a crustal age boundary (Wessels and Karlstrom, 1991), but the appear older (and given the presence of ca. 1.75 Ga grains, this is certainly similarity in crustal age across the shear zone casts doubt on this interpretation possible). A correlation with the Beeline Granite may in fact be valid. Clearly, and suggests a need for more detailed “mapping” of the Hf characteristics of better age constraints are needed for this suite of granites. Additionally, Brady lower-crustal source regions. (1987) documented caldera-related rhyolites in the nearby Sheep Basin Moun- Jones et al. (2009) concluded that thick rhyolite-quartzite packages of north- tain area, which might explain the similar age of granite plutons and rhyolites. ern New Mexico and Colorado were deposited in relatively short-lived syntectonic basins during regional collisional orogenesis. This type of model is consistent with ca. 1.65 Ga Mazatzal orogenesis in the Four Peaks area, where Regional Implications: The Mazatzal and Picuris Orogenies and sedimentary deposition appears to have been rapid and closely followed by the Mazatzal Province in Southwestern Laurentia granite emplacement and deformation. We suggest that the cycles of deposition and tectonism in the Four Peaks area reflect syncollisional basin formation Deformation in central Arizona, including the Tonto Basin region and more and basin closure events. The fact that no clear angular unconformity has been specifically the northern Mazatzal Mountains, has generally been associated recognized between Paleoproterozoic and Mesoproterozoic sediments in the with the ca. 1.65 Ga Mazatzal orogeny (Karlstrom and Bowring, 1988; Labrenze Four Peaks or throughout the Tonto Basin area remains an unresolved chal- and Karlstrom, 1991; Eisele and Isachsen, 2001). Recent detrital U-Pb zircon lenge for models of crustal dynamics in this long-lived accretionary margin. data from both New Mexico and Arizona have suggested that previously un- Significant Mesoproterozoic tectonism has been recognized for several recognized Mesoproterozoic rocks, disconformably deposited on Paleoprotero- decades as evidence for the age of structures, fabrics, and metamorphic events zoic successions, were deformed by northwest-directed folding and thrusting has emerged throughout southwest Laurentia (Grambling and Dallmeyer, during Mesoproterozoic time, previously thought to be ca. 1.660 Ga (Labrenze 1993; Nyman et al., 1994; Nyman and Karlstrom, 1997; Williams et al., 1999; and Karlstrom, 1991; Conway and Silver, 1989). Taken to the extreme, these Shaw et al., 2001; Amato et al., 2011; Daniel et al., 2013). The Four Peaks area is results led some workers to cast doubt on the very existence of the Mazatzal another example of the importance of more recently recognized Mesoprotero orogeny (Daniel et al., 2013; Daniel and Pyle, 2006). The large syncline in the zoic sedimentation. The classic fold-and-thrust belt in the Barnhart Canyon Four Peaks area is one such structure, and indeed, data presented here suggest area further north in the Mazatzal Mountains (Doe and Karlstrom, 1991) was that it formed during the Mesoproterozoic (ca. 1.490–1.450 Ga). Rocks in the Four originally interpreted to have deformed at 1.66–1.65 Ga synchronous with the Peaks area, however, also preserve evidence for two periods of Paleoprotero Slate Creek shear zone (Karlstrom and Bowring, 1991). Based on similarities zoic deformation, one at ca. 1.680 Ga and another at ca. 1.660 Ga, or perhaps a in the stratigraphy and structural style, this fold-and-thrust belt may also be continuum of tectonism during this broader time frame. Both of these events primarily or partly of Mesoproterozoic age. fall into the window of Mazatzal tectonism and may represent two stages in a An additional challenge for understanding the Proterozoic growth of Lau-

progressive Mazatzal orogeny. D1 (1.680–1.675 Ga) also overlaps in time with rentia revolves around determining the nature and location of crustal prov- the end of the Yavapai orogeny in the Grand Canyon (Karlstrom et al., 2003). At ince boundaries. The term Mazatzal orogeny has been used in the literature least two, and possibly three, tectonic foliations in the Four Peaks area are con- as a 1.7–1.6 Ga crustal age province, as well as a magmatic and deformational sistent with the Mazatzal orogeny. There is only one foliation generation at Four event. Our new results are in agreement with published geochronologic Peaks that definitively fits within the current 1.660–1.600 Ga Mazatzal orogeny. boundaries (e.g., Karlstrom and Humphreys, 1998) that show no pre–1.7 Ga Our results require that some elements of the model for Paleoproterozoic rocks south of the Slate Creek shear zone. However, the new Hf data show that tectonism in central Arizona be revised. Classically, it was suggested that the the deep crust involves rocks older than 1.8–2.0 Ga, such that the deep crust

does not conform to published notions of progressive addition of juvenile cleavage. Thus, the Four Peaks syncline reflects Mesoproterozoic crustal short- 1.75 Ga “Yavapai” crust followed by addition of juvenile 1.7–1.6 Ga Mazatzal ening, probably associated with the Picuris orogeny (Daniel et al., 2013). Meta- crust (e.g., Whitmeyer and Karlstrom, 2007). Instead, this crustal block differs morphic analysis indicates that the rocks were buried to middle-crustal levels from both, and additional Hf and Nd data are needed to understand the extent (11–15 km) during Mesoproterozoic orogenesis (Mako, 2014). The crust of the of older crustal substrates within different parts of the orogen. Four Peaks area may include pre–1.750 Ga, nonjuvenile crust, which suggests These new results, highlighting the importance of Mesoproterozoic tec that the supposed juvenile nature of the Mazatzal Province may be compli- tonism in southwestern Laurentia, call into question the nature of previously cated by the incorporation of older material. Thus, both Mazatzal and Picuris proposed province boundaries. It is clear from our results that at least in cen- deformation at Four Peaks involved the reworking of older continental mate- tral Arizona, deformation related to the Picuris orogeny overprints Mazatzal rial. The deformation, metamorphism, and sedimentation in this part of the deformation of even older crust (Fig. 9). Examples across the southwestern Mazatzal Province reflect a complex combination of both Paleoproterozoic and United States are similar (Grambling and Dallmeyer, 1993; Williams et al., Mesoproterozoic tectonism, possibly imprinted on a component of slightly 1999; Amato et al., 2011; Daniel et al., 2013; Jones et al., 2011). Mesoproterozoic older basement. deformation in the southwestern United States tends to rework older crust. Given that there may be a component of older basement in the Four Peaks area (pre–1.7 Ga), Mazatzal deformation might also rework older (Yavapai or slightly ACKNOWLEDGMENTS older) crust in this area. Field work for this research was funded by a Graduate Student Research Grant from the Geological Society of America to Mako. U-Pb zircon work at the University of Arizona LaserChron Center was funded by National Science Foundation grant EAR-1145247 to Karl Karlstrom and George Gehrels. We thank Michael Jercinovic for assistance with microprobe analysis at the University of Massa- CONCLUSIONS chusetts and Dominique Geisler for assistance at the Arizona LaserChron Center. Comments by Daniel Holm and an anonymous reviewer improved the manuscript. Rocks in the Four Peaks area record evidence for a polyphase history

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