Journal of South American Earth Sciences xxx (xxxx) xxx

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Journal of South American Earth Sciences

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Geology and geochronology of the Jurassic magmatic arc in the Magdalena quadrangle, north-central Sonora, Mexico

Carlos M. Gonzalez-Le´ on´ a,*, Michelle Vazquez-Salazar´ b,1, Teresita Sanchez´ Navarro c,2, Luigi A. Solari d, Jonathan A. Nourse e, Rafael Del Rio-Salas a, Rufino Lozano-Santacruz f, Ofelia P´erez Arvizu d, Juan Carlos Valenzuela Chacon´ b a Estacion´ Regional del Noroeste, Instituto de Geología, Universidad Nacional Autonoma´ de M´exico, Hermosillo, 83000, Mexico b Universidad Estatal de Sonora, Ingeniería en Geociencias, Hermosillo, 83140, Mexico c Universidad de Sonora, Departamento de Geología, Hermosillo, 83000, Mexico d Centro de Geociencias, Universidad Nacional Autonoma´ de M´exico, Campus Juriquilla, Santiago de Quer´etaro, QRO, 76001, Mexico e Department of Geological Science, California State Polytechnic University, Pomona, 3801 West Temple Ave, Pomona, CA, 91768, USA f Universidad Nacional Autonoma´ de M´exico, Instituto de Geología, Laboratorio Nacional de Geoquímica y Mineralogía, Ciudad Universitaria, Ciudad de M´exico, 04510, Mexico

ARTICLE INFO ABSTRACT

Keywords: This work reports on the geology and U–Pb LA-ICPMS zircon geochronology of a crustal section that is part of the Continental jurassic magmatic arc Jurassic magmatic arc in the Magdalena quadrangle of north-central Sonora, Mexico. This rock succession is – U Pb igneous Geochronology variably metamorphosed and strained as it was affected by Late Cretaceous shortening, intruded by early Tertiary Detrital zircon geochronology granitoids, and further exhumed in the lower plate of the early Miocene Magdalena metamorphic core complex. Geochemistry The older and more extensively exposed Jurassic unit is the >3.5 km thick Sierra Guacomea rhyolite that is Sonora Mexico composed of massive to poorly bedded rhyolite, bedded quartz-phyric rhyolitic ignimbrite and interbedded ash- fall tuffs and quartz-rich sandstone beds. Three rhyolite samples collected at different localities of its outcrops yielded concordia ages of 175.2 ± 0.9, 171.7 ± 0.6, and 171.4 ± 0.7 Ma. The quartz-phyric Rancho La Víbora, Los Vallecitos, and the Agua Caliente rhyolitic domes that are associated with the Sierra Guacomea rhyolite yield concordia ages of 176 ± 0.8, 174.4 ± 0.9 and 173.1 ± 0.8 Ma, respectively. The Rancho Los Pozos unit composed of interbedded rhyolitic ash-fall tuff and flows, sandstone, siltstone and subordinate limestone beds has an estimated thickness of 600 m and yielded a crystallization concordia age of 170.7 ± 0.6 Ma from a rhyolite bed. The porphyritic El Rincon´ granite that intrudes into the Sierra Guacomea rhyolite yields crystallization ages of 167.43 ± 0.42 and 164.4 ± 0.7 in samples from different localities. The La Jojoba metasandstone that consists of foliated, quartz-rich to arkosic strata of fluvial origin is at least 900 m thick; detrital zircon grains dated from three sandstone samples yielded dominantly Jurassic ages with peaks at 172, 170, and 163.7 Ma, and a combined maximum depositional age of ca. 163 Ma. The younger plutons are the porphyritic El Nopalito granite that has an interpreted crystallization age of 160.8 ± 0.6 Ma, and the leucocratic, two-mica, garnet-bearing La Cebolla granite that yielded a concordia age of 158.1 ± 1 Ma. These granitic intrusions record the waning magmatic pulses of the arc, in the study quadrangle, but their volcanic equivalents were not identified. Inherited zircon grains in the reported volcanic and plutonic units are only of Jurassic age, except by two Proterozoic zircon grains yielded by the El Nopalito granite. The El Salto granite augen gneiss is a xenolith dated at 1071.9 ± 5 Ma that indicates the presence of Grenvillian basement in the study area. Major- and trace-element geochemical data indicate that the volcanic and plutonic units are silica-rich, mostly high K calc-alkaline to shoshonitic rocks associated with a continental margin arc setting. The plutons are mostly

* Corresponding author. E-mail addresses: [email protected] (C.M. Gonzalez-Le´ on),´ [email protected] (M. Vazquez-Salazar),´ [email protected] (T.S. Navarro), solari@ unam.mx (L.A. Solari), [email protected] (J.A. Nourse), [email protected] (R. Lozano-Santacruz), [email protected] (J.C. Valenzuela Chacon).´ 1 Present address: Programa de Maestría en Ciencias, Departamento de Geología, Universidad de Sonora, Hermosillo, M´exico 83000. 2 Present address: Posgrado en Ciencias de la Tierra, Estacion´ Regional del Noroeste, Instituto de Geología, Universidad Nacional Autonoma´ de Mexico,´ Hermosillo, Mexico´ 83000. https://doi.org/10.1016/j.jsames.2020.103055 Received 31 March 2020; Received in revised form 21 September 2020; Accepted 19 November 2020 Available online 28 November 2020 0895-9811/© 2020 Elsevier Ltd. All rights reserved.

Please cite this article as: Carlos M. González-León, Journal of South American Earth Sciences, https://doi.org/10.1016/j.jsames.2020.103055 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

peraluminous, and in conjunction with trace element geochemistry data, they suggest crustal assimilation of magmas emplaced in a probably thickened continental crust. Chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams also suggest partial melting and fractional crystallization processes. The ages obtained indicate that the arc in the study area developed from ca. 176 to 158 Ma, encompassing a 17 m.y. interval of magmatism and associated sedimentation. Regional correlation and geochronologic published data indicate that the arc crustal section of the Magdalena quadrangle is part of the Jurassic magmatic arc that regionally lasted from ca. 190 to 158 Ma.

Author contribution cratonal Mazatzal province (Whitmeyer and Karlstrom, 2007) is inferred to be delimited from the Caborca block of Mojave crustal affinity Carlos M. Gonzalez-Le´ on.´ Conceptualization, Investigation, Writing (Farmer et al., 2005; Nourse et al., 2005) by a NW-SE structure whose – original draft, Visualization, Funding acquisition. Michelle Vazquez-´ tectonic nature and age has not been well resolved (Fig. 1). This struc­ Salazar. Investigation, Visualization, Writing, Review, Editing. Teresita ture that was first recognized as the Late Jurassic Mojave-Sonora meg­ Sanchez´ Navarro. Investigation, Visualization, Writing, Writing – review ashear by Silver and Anderson (1974) and Anderson and Silver (2005), it & editing, Luigi A. Solari. Conceptualization, Methodology, Writing, was later interpreted to be Proterozoic (Whitmeyer and Karlstrom, Writing – review & editing, Funding acquisition. Jonathan A. Nourse. 2007), or Pennsylvanian-Permian age (Dickinson and Lawton, 2001; Conceptualization, Investigation, Writing, Writing – review & editing, Lawton et al., 2017). An alternative explanation is that this structure Funding acquisition. Rafael Del Rio-Salas. Investigation, Writing, corresponds to the Proterozoic suture zones between the Yavapai and Writing – review & editing. Rufino Lozano-Santacruz. Writing, Meth­ Mazatzal provinces, a hypothesis that requires two megashear structures odology, Writing – review & editing. Ofelia P´erez Arvizu. Writing, (Arvizu and Iriondo, 2015). Methodology, Writing – review & editing. Juan Carlos Valenzuela Rock outcrops corresponding to the basement of the Mazatzal Chacon.´ Investigation, Writing – review & editing. province in Sonora are only known in the northeastern and north­ western parts of the state. In the northeastern part, they consist of the 1. Introduction Pinal Schist that has been dated at ca. 1.6 Ga and by intruding granites of ca. 1.4 and 1.1 Ga (Anderson et al., 2005; Solari et al., 2018). In the The region of northern Sonora that belongs to the Proterozoic region of northwestern Sonora, around Sonoita and El Pinacate,

Fig. 1. Location of the study quadrangle (red rect­ angle) within the southeast extent of the Jurassic magmatic arc of southwestern North America (indi­ cated by gray pattern, taken from Tosdal et al., 1989 and Haxel et al., 2005), and northwest extent of the Nazas arc (Lawton and Molina-Garza, 2014). Also shown are approximate location of reported Jurassic rocks (black outcrops), boundaries of Paleoproter­ ozoic crustal provinces (dashed lines, inferred from Pb isotopes by Wooden and DeWitt, 1991), approxi­ mate trace of the disputed Mojave-Sonora megashear (MSM), the Magdalena detachment fault (Mdf, taken from Nourse et al., 1994) and location of cities and towns mentioned in the text. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

2 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx juxtaposition of basement rocks of the Mazatzal and Caborca blocks is (Haxel et al., 2005) that includes an ~8 km thick interlayered succession documented (Iriondo et al., 2004; Nourse et al., 2005). The Mazatzal of mostly alluvial, fluvial, eolian, calc-alkaline rhyolitic, dacitic and basement of northeastern Sonora is overlain by an incomplete Cambrian subvolcanic rocks which accumulated in continental basins from ~170 to Permian sedimentary succession of marine origin (Gonzalez-Le´ on,´ to 165 Ma. Similarly, in southeastern California and southwestern Ari­ 1986), which in turn is overlain by volcanic and sedimentary strata of zona, dacitic, rhyolitic and hypabyssal rocks of the Dome Rock sequence Jurassic age that is intruded by co-magmatic plutons (Anderson and were emplaced between 190 and 185 Ma, and later intruded by felsic Silver, 2005). The Upper Jurassic to Lower Cretaceous formations of the plutons of 173 to 158 Ma (Tosdal and Wooden, 2015). In the eastern and Bisbee Group are present in northeastern Sonora, with outcrops central Mojave Desert, Jurassic magmatism initiated with the high-K extending through most of northern and central Sonora overlapping calc-alkalic Fort Irwin sequence at ca. 183-172 Ma and the Bullion along with the Upper Jurassic Cucurpe Formation (Mauel et al., 2011) sequence of 167–164 Ma, which was followed by a shoshonitic, the two different basements. Younger rocks in northern Sonora include alkali-calcic waning pulse in the range of 164–161 Ma (Barth et al., the Upper Cretaceous conglomerate succession of the Cocospera´ For­ 2017). mation (Gonzalez-Le´ on´ et al., 2017a), volcanic and plutonic rocks of the Considering that few systematic studies on the Jurassic rocks of Upper Cretaceous-Eocene Laramide magmatic arc (Gonzalez-Le´ on´ et al., Sonora are known, the present work intends to characterize an area that 2000; McDowell et al., 2001; Gonzalez-Le´ on´ et al., 2011; Gonzalez-Le´ on´ may record in part the evolution of the continental arc in the northern et al., 2017b) and Oligocene-Miocene volcanic and sedimentary rocks of part of the State (Fig. 1). For this purpose, we conducted cartography at the Sierra Madre Occidental with its transition to the extensional Basin the scale of 1:50,000 of a quadrangle located north of the town of and Range sedimentary fill. Magdalena, and used U–Pb LA-ICPMS to date zircons from most of the In north-central Sonora (Fig. 1) the oldest rocks reported from the recognized units. We also present herein U–Pb and geochemical data for Mazatzal block are volcanic, sedimentary and granitic rocks of Jurassic the Mesoproterozoic El Salto granite augen gneiss whose age is reported age that are typically metamorphosed and have also been included in abstracts, as it testifies in part to the Mazatzal and Grenville base­ within the Papago terrane (Haxel et al., 1984). Within this region, a ments in north-central Sonora. Whole-rock geochemical analyses of single, tens of meter outcrop of a ca. 1.07 Ga granite augen gneiss occurs major- and trace-elements of the plutonic and volcanic rocks were also as a xenolith in sheared Cenozoic plutons of the Sierra Magdalena conducted to further document the nature of the Jurassic magmatism. (Nourse, 1989; Nourse et al., 2018; Zapata Martínez et al., 2018), establishing the presence of Proteozoic basement, although Farmer and 2. Geologic setting DePaolo (1984) reported Nd and Sr evidence of a Paleoproterozoic crust underlying the Papago terrane in southern Arizona. The study quadrangle is located north of the town of Magdalena in The Jurassic rocks in the Mazatzal block in Sonora have been dated the north-central part of the state of Sonora (Figs. 1 and 2), and it is part (by conventional U–Pb TIMS analyses) at several scattered localities, of the lower plate of the Magdalena metamorphic core complex that was mostly by Anderson and Silver during the late 1960’s and early 1970’s. firstrecognized by Davis et al. (1981), and later studied in detail by J.A. ´ Anderson et al. (2005) assigned them to the continental magmatic arc Nourse (1989). The area includes the sierras El Alamo Viejo and Las recognized by Busby-Spera (1988) and Busby-Spera et al. (1990) Jarillas-Potrero in the western part, and sierras Magdalena, La Jojoba extending from California to southwestern Arizona and northern and Guacomea (Fig. 1) in the central and eastern part of the quadrangle. Sonora. Busby-Spera (1988) postulated that the thick arc successions of These correspond to NNW-elongated ranges typical of the Basin and sedimentary and mostly calc-alkalic volcanic rocks accumulated in Range Province, and their bounding faults are mostly covered by alluvial extensional to transtensional graben depressions and were intruded by sediments. high-level plutons. Bartolini et al. (2003), Dickinson and Lawton (2001) Previous works describing the geology of the study area and sur­ and Lawton and Molina-Garza (2014) extended outcrops of the Jurassic roundings (Fig. 1) include cartography at 1:250,000 scale and partially arc through northern Mexico, assigning them to the Nazas arc (Fig. 1). at 1:50,000 by the Servicio Geologico´ Mexicano (see maps at Others authors that reported volcanic, plutonic and metamorphic https://www.sgm.gob.mx/CartasDisponibles). The oldest rocks they Jurassic rocks with ages from 186 to 153 Ma in northern Sonora, include reported are metasedimentary, metavolcanic and plutonic rocks of Calmus and Sosson (1995), Poulsen et al. (2008), Quintanar- Ruiz presumably Jurassic age. Younger rocks include outcrops of the Upper (2008), Izaguirre-Pompa (2009), Arvizu and Iriondo (2015) and García Jurassic-Lower Cretaceous Bisbee Group, Upper Cretaceous sedimentary Flores (2019). A stratigraphic column reported from the Cucurpe region rocks of the Cocospera´ Formation, volcanic successions of the Tarahu­ by Mauel et al. (2011) and Leggett (2009) (Fig. 1) is the most complete mara Formation, Paleogene granites, Oligocene-Miocene volcanic and part of the arc described from northern Sonora. Strata of this column sedimentary rocks and Pliocene basalts. have ages from ca. 190 to 170 Ma and are intruded by a quartz porphyry A cartographic and petrologic work by Salas (1968) interpreted the of 180.6 ± 1.3 Ma (Leggett, 2009). Similarly, in the Nacozari-Cananea metamorphic rocks of this area to have a Precambrian age, while some region of northeastern Sonora (Fig. 1) a crustal section of the arc ex­ of the granites and rhyolitic rocks were considered late Mesozoic. poses the leucocratic granite of Sierra Buenos Aires of ca. 184 Ma, other Similarly, Morales Montano˜ (1984) assigned the igneous and meta­ younger granites with ages from 170 to 160 Ma, and a rhyolitic and morphic rocks to the “complejo ígneo-metamorfico´ Santa Ana” of pre­ sedimentary succession with ages from 174 to 160 Ma (Anderson and sumably Middle to Late Jurassic age. A detailed cartographic and Silver, 2005; Gonzalez-Le´ on´ et al., 2009; Gonzalez-Le´ on,´ unpublished structural work conducted by Nourse (1989) describes the Magdalena U–Pb ages). The Upper Jurassic marine succession of the Cucurpe For­ metamorphic core complex in the study area, which was later summa­ mation that unconformably overlies the arc assemblage in the Cucurpe rized in Nourse (1990, 1995) and Nourse et al. (1994). According to region yielded U–Pb zircon ages from 158 to 149 Ma (Mauel et al., Nourse (1989), the type section of the lower plate of the core complex in 2011), similar to its Oxfordian-early Tithonian biostratigraphic age the sierras Magdalena, La Madera, La Jojoba and Guacomea consists (Villasenor˜ et al., 2005) and is considered to be a post-arc succession mostly of Jurassic rhyolite porphyry, granite porphyry, conglomerate that accumulated during rifting and incursion of the Gulf of Mexico and quartzarenite, Upper Jurassic-Lower Cretaceous sedimentary rocks, waters into Sonora (Mauel et al., 2011). and at least three generations of leucocratic, two-mica granites and Supracrustal sections of the Jurassic Cordilleran arc neighboring biotite granitoids, presumably of Late Cretaceous to middle Tertiary age. Sonora have been studied in detail in southern Arizona and the Mojave Nourse (1989) recognized that rocks in these sierras record intense Desert of California (Riggs and Busby-Spera, 1990, 1991; Riggs and metamorphism and ductile strain, assigning them to a “central high Blakey, 1993; Schermer et al., 2002; Haxel et al., 2005). One repre­ strain belt” located beneath the zone of detachment that characterizes sentative example is the Topawa Group in the Bavoquivari Mountains the core complex (Fig. 2). Nourse (1989) recognized two ductile strain

3 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 2. Geologic map of the study quadrangle simplified from our cartography at 1:50,000 scale. Gray color areas in valleys between the mountains correspond to Oligocene to Quaternary sedimentary and volcanic rocks and alluvial sediments. Cartography for the sierras El Pinito and La Madera is not included. Trace of the Magdalena detachment fault is taken from Nourse et al. (1994). Digital elevation map elaborated from the 1:50,000 scale, INEGI digital charts La Arizona (H12A49, 2004), Cibuta (H12B41, 2002), El Carrizo (H12B59, 2004), Imuris (H12B51, 2001), Magdalena (H12B61, 2000), and Santa Ana (H12A69, 2001). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) events. The earliest event is characterized by regional metamorphism northeast of Imuris (Fig. 2). This sample yielded two near-concordant and ductile deformation and by at least two generations of granitic zircon fractions with 206Pb/238U ages of 174 Ma (Fig. 2). The Jurassic plutons that occurred during the Late Cretaceous to early Cenozoic ages assigned by Nourse (1990; 1995) to lower plate rocks of the Mag­ Laramide orogeny. The second event is characterized by a dalena core complex were based on similarities to the El Tunel quartz southwest-vergent mylonitic fabric imposed on the Late Cretaceous and porphyry and correlation with rhyolitic rocks dated in southern Arizona Tertiary granites and their Mesozoic hosting rocks. The SW-dipping (Busby-Spera, 1988; Tosdal et al., 1989; Riggs and Busby-Spera, 1991) Magdalena detachment fault (Fig. 2) separates the lower plate from an and northern Sonora (Anderson and Silver, 2005). Supporting this upper plate composed of Cretaceous to Cenozoic sedimentary and vol­ interpretation was the common occurrence of interstratified rhyolite canic rocks. Two U–Pb datings of Eocene age for the granites of the and quartz arenite, a widespread characteristic of the Jurassic arc Magdalena metamorphic core complex were published by Herrera (Busby-Spera, 1988). Part of the motivation of our current study is to Urbina et al. (2006), and Gonzalez-Le´ on´ et al. (2017a, 2017b) recog­ confirm the existence and distribution of Jurassic arc rocks in the nized the Upper Cretaceous Cocospera´ Formation in the lower plate of Magdalena quadrangle through systematic application of modern U–Pb the core complex. zircon geochronology methods. The closest dated Jurassic rocks to our study area is the “El Tunel The more recent works in the western part of the study area were quartz porphyry” (Anderson et al., 2005), collected from a tunnel conducted by Sanchez´ Navarro (2018) and Vazquez´ Salazar (2018), who entrance near the pass along Highway 2 in the southern Sierra El Pinito, reported the cartography, stratigraphy, U–Pb geochronology, and

4 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx whole-rock geochemistry of Jurassic and Paleocene-Eocene volcanic and For the geochemical analyses, we collected 15 samples of about 1 kg ´ granitic rocks of sierras El Alamo Viejo, Las Jarillas and Potrero. In this of centimeter-sized fragments that were hammer-cut from the freshest work, we focus on description of the Jurassic rocks while the geology of and unweathered rock outcrops in the field,and these were then crushed the Paleocene-Eocene granites will be published elsewhere. and ground in the LPM-ERNO. Major elemental concentrations of the prepared powders were analyzed in fused beads by X-ray fluorescenceat 3. Methods the Laboratorio Nacional de Geoquímica y Mineralogía (LANGEM) of the UNAM following procedures indicated in Gonzalez-Le´ on´ et al. Cartography for this work was conducted at 1:50,000 scale in several (2017a, 2017b), while the trace element contents were determined by field campaigns during the period from 2017 to 2019, and a general inductively coupled plasma mass spectrometry (ICP-MS) at the Centro geologic map from this work is presented in Fig. 2. Samples for petro­ de Geociencias (CGEO), UNAM, usig a ICAP-Qc instrument. Sample graphic, geochronologic and geochemical analyses were collected from preparation for determining trace element contents was done in a clean the freshest outcrops of most of the recognized lithologic units. lab and trace elements were determinated on 50 mg of powdered sample For the U–Pb geochronologic analyses we collected up to 5 kg for that was digested in 1 mL HF plus 0.5 mL HNO3 in closed screw-top ◦ rock samples, which were crushed and pulverized in the Laboratorio de Savillex (®) Teflon bakers and put on a hot plate overnight at 100 C. Preparacion´ de Muestras of the Estacion´ Regional del Noroeste, Instituto Acids were evaporated to dryness and further fluxedtwice with 15 drops de Geología, UNAM (LPM-ERNO). Zircon separation, mounting and of 16 M of HNO3 in order to break down the fluorides.Once the acid was dating was performed at the Laboratorio de Estudios Isotopicos´ (LEI) of evaporated to dryness, 2 mL desionized water plus 2 mL 8 N HNO3 were ◦ the Centro de Geociencias, UNAM. U–Pb analyses were conducted by added, and the samples were left closed overnight on a hot plate 100 C. laser ablation inductively-coupled plasma mass spectrometry (LA- All samples were then diluted to 1:2000 to provide adequate concen­ ICPMS) using a Resonetics M050 (now, Applied Spectra) 193 nm exci­ trations within the instruments detection limits and yield the strong mer laser workstation, coupled to a Thermo ICap Qc quadrupole mass signals required for high precision data. All samples diluted with in­ spectrometer, according to the methods recently reported by Solari et al. ternal standard solution made of Ge (10 ppb), In (5 ppb), Tm (5 ppb) and (2018). A 23 μm spot was employed during this whole study for all the Bi (5 ppb) to monitor instrumental drift. Calibration and data reduction U–Pb analyses, alternating unknown zircon crystals with several stan­ were based on the digestion of four international rocks standards dards. Standard reference material 91500 was employed as external (AGV_2, BHVO-2, JB-2, BCR-2 and JR-1), two blanks that followed the reference zircon (ca. 1062 Ma, Wiedenbeck et al., 1995), whereas Ple­ same chemical procedure as the samples (Mori et al., 2007). Tables 2 ˇsovice standard zircon acted as secondary (control) standard (ca. 337 and 3 report the results of these analyses. Ma, Slama´ et al., 2008). Raw data were reduced offline using Iolite 3.5 software (Paton et al., 2011), including all the error calculations and 4. Field relationships and geochronology propagation, and employing the VizualAge data reduction scheme of Petrus and Kamber (2012). The secondary Pleˇsovice standard zircon Below we describe the recognized lithologic units and their field yielded a mean 206Pb/238U age of 338.9 ± 1.4 Ma, in agreement with the relationship, and U–Pb results from 13 samples in the study area, from accepted age. Table 1 summarizes the age and UTM location of samples older to youngest. Fig. 2 shows sample locations on a generalized and data results are reported in Table A Data Repository. geologic map of the Magdalena quadrangle. Corresponding concordia diagram and weighted mean plots are presented in Figs. 3–5.

Table 1 4.1. Mesoproterozoic El Salto granite augen gneiss Summary of U–Pb ages of Proterozoic and Jurassic rocks dated from the Mag­ dalena quadrangle. MDA = maximum depositional age. A single small outcrop of this granite is located at the southern Sierra Sample Unit Age Error UTM location MDA de Magdalena, in arroyo El Salto, just in the outer northwest limits of the (Ma) (Ma) (Ma) town. Nourse (1989) described this rock as a “coarse grained biotite 3-24-17-1 El Salto granite 1071.9 5 500634; granite augen gneiss” with “…pink augen shaped microcline crystals up augen gneiss 3390048 10 cm long that are deformed with a sheared matrix of coarse quartz, 5-28-19-2 Sierra Guacomea 175.2 0.9 504398; rhyolite 3424182 shredded biotite, and comminuted plagioclase. The rock is strongly 5-27-19-5 Rancho La Víbora 176 0.8 501268; foliated and lineated, and displays a well-developed S–C structure”. This rhyolitic dome 3421223 exposure forms a large xenolith within sheared Paleocene and Eocene 10-14-18- Los Vallecitos 174.4 0.9 506700; granites (Nourse et al., 2018). Several smaller elongated xenoliths occur 1 rhyolitic dome 3414061 1-22-19-1 Agua Caliente 173.1 0.8 512741; along the same stratigraphic horizon in the southern Sierra Magdalena. rhyolitic dome 3425475 Nourse et al. (2018) reported SHRIMP-RG analyses from a sample 12-9-17-1 Sierra Guacomea 171.7 0.6 482940; collected in 2005. Much of the data set was discordant but subsets of 10 rhyolite 3428029 total analyses yielded a concordia age of 1043 ± 4 Ma (N = 4) and a 8-5-18-3 Sierra Guacomea 171.4 0.7 498618; weighted mean 206Pb/238 U age of 1037 ± 10 Ma (N = 7). Upper rhyolite 3414711 12-8-17-1 Rancho Los Pozos 170.7 0.6 475252; intercept ages ranged from 1050 to 1084 Ma. We also dated sample unit 3433166 3-24-17-1 (Table 1), from this outcrop with the LA-ICPMS technique, MX-1347 El Rincon´ granite 167.4 1 497087; and yielded a weighted mean 206Pb/238 U age of 1071.9 ± 5 Ma (N = 18) 3418023 ± = ´ (Fig. 3A), with a significantinherited population at 1392 21 Ma (N 8-3-18-1 El Rincon granite 164.4 0.7 493066; ´ ´ 3422147 9) (Gonzalez-Leon et al., 2018; Nourse et al., 2018). 3-25-17-5; La Jojoba 493913; ca. Despite the slightly different analytical results between the two 3-25-17- metasandstone 3402794 163 laboratories, this sample is important because it documents the presence 2; 1-23- 496468; of autochthonous Grenville-age granitic basement in north-central 17-2 3408900 Sonora. The only other known occurrences of such basement crops out 474677; 3424440 in allochthonous thrust sheets farther south. A micrographic granite 8-5-18-4 El Nopalito 160.8 0.6 498706; described by Anderson and Silver (2005) at Rancho Santa Margarita granite 3414825 Ranch yielded a conventional ID-TIMS upper intercept age of 1104 ± 21 7-8-16-4 La Cebolla 158.1 1 479661; Ma, while a similar rock near Cucurpe yielded two zircon fractions with granite 3400109 207Pb/206Pb ages of 1098 Ma and 1039 Ma. The Cucurpe granite was

5 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

re-analyzed with similar methods by Amato et al. (2009), yielding a concordia upper intercept age of 1072 ± 20 Ma and a weighted mean 207Pb/206Pb age of 1076 ± 14 Ma.

Sierra Guacomea rhyolite 5-28-19-2 75.54 0.15 13.19 1.40 0.00 0.10 0.34 3.19 5.59 0.03 0.46 100.00 4.2. Jurassic rocks La rhy The Jurassic rocks in the study quadrangle consist of variably foli­ ated and recrystallized volcanic, plutonic and sedimentary rocks among Rancho Víbora dome 5-27-19-5 74.80 0.17 13.95 1.76 0.01 0.18 0.15 3.89 4.62 0.02 0.45 100.00 which, from older to younger we recognize the following lithologic units: 1) Sierra Guacomea rhyolite, 2) Rancho La Víbora rhyolitic dome, 3) Agua Caliente rhyolitic dome, 4) Rancho Los Pozos unit, 5) Los Val­ lecitos rhyolitic dome, 6) El Rincon´ granite, 7) La Jojoba metasandstone, El Rincon granite 4-26-19- 4 74.22 0.30 14.16 1.17 0.05 0.75 1.17 4.68 2.93 0.07 0.50 100.00 8) El Nopalito granite, and 9) La Cebolla granite (Fig. 2).

4.2.1. Sierra Guacomea rhyolite

El Rincon granite 4-25-19- 3 72.33 0.33 14.64 1.02 0.02 0.67 1.56 3.70 4.44 0.09 1.20 100.00 This is the most extensively exposed unit in the study quadrangle with outcrops in the southern part of the Sierra Cibuta, in the Sierra Guacomea and in the eastern low hills of the sierra Los Chinos where it was informally named as “riolita Jotaiqui” by Sanchez´ Navarro (2018). dome The least metamorphosed outcrops occur in the southern Sierra Cibuta, Los Vallecitos rhy 10-14-18-2 74.05 0.23 13.66 2.00 0.01 0.19 0.21 2.71 6.20 0.05 0.69 100.01 where a poorly stratified to massive rhyolitic succession with an esti­ mated thickness of 800 m (Fig. 2) dips homoclinally to the northeast ◦ with values less than 25 . These rocks are consistently composed of

dome phenocrysts (20–30% of the rock volume) of quartz and feldspar in a

Los Vallecitos rhy 10-14-18-1 76.37 0.13 12.55 1.29 0.02 0.30 0.21 2.27 6.08 0.01 0.76 100.00 fluidalfelsitic groundmass slightly altered to sericite. Quartz crystals are subhedral, up to 6 mm long and have resorbed borders. Feldspar consists mostly of fragmented plagioclase and subordinate K-feldspar, up to 3 indicated. mm long, partly altered to sericite and clays and with minor replacement are

El Nopalito granite 8-5-18-4 65.40 0.57 15.48 4.75 0.13 1.77 2.26 3.73 4.62 0.18 0.90 99.80 of microcrystalline quartz. Subordinate grains that have strong

units replacement by iron oxide and epidote might be rock fragments. Biotite is scarce and commonly altered to iron oxide, while patches and euhe­ dral iron oxides grains are also present.

lithologic Outcrops of this unit at sierra Los Chinos form a gently folded suc­ Sierra Guacomea rhyolite 8-5-18-3 72.55 0.36 13.70 2.60 0.04 0.21 1.36 3.54 4.82 0.09 0.63 99.90 cession of foliated, quartz-phyric rhyolite igimbrite in beds up to 20 m the

of thick that are interlayered with massive, tuffaceous mudstone/siltstone in beds up to 5 m thick. In some outcrops the ignimbrite preserves eutaxitic texture with cm-long fiamme fragments. In thin section it is porphyritic with quartz eyes and glass shards, up to 3 mm long that are Sierra Guacomea rhyolite 12-9-17-1 65.38 0.53 15.96 4.01 0.05 1.65 1.67 3.30 6.21 0.17 1.03 99.97 embedded in a fine-grained, recrystallized, felsic groundmass of quartz nomenclature and biotite. A moderate

and continuous foliation is defined by laminations of oriented muscovite,

El Rincon granite 8-25-17- 2 71.47 0.41 15.15 2.25 0.04 0.41 3.09 5.96 0.43 0.12 0.47 99.79 biotite and epidote. At this locality, a minimum thickness of 500 m is estimated as it is in fault contact with Los Pozos unit and is intruded by numbers an Eocene granite (Sanchez´ Navarro, 2018). In the sierra Guacomea (Fig. 2) a strongly metamorphosed and El Rincon granite 8-25-17- 1 75.16 0.26 13.35 0.45 0.04 0.48 0.62 3.29 5.69 0.05 0.41 99.80 ◦

Sample recrystallized section dips to the northeast with values less than 40 , and has an estimated thickness of 3.5 km. It consists of metamorphosed

study. rhyolitic beds that alternate with ash-fall tuffs and quartz-rich sandstone

La Cebolla granite 7-30-17-1 71.83 0.35 14.18 2.11 0.03 0.04 0.89 3.03 7.15 0.05 0.16 99.80 beds. Rhyolitic ash flowsbeds in sierra Guacomea are up to 20 m thick this and extend hundreds of meters laterally as observed in cliff exposure. in Petrographic characteristics of the rhyolite are similar to those in the sierra Los Chinos area. The foliated sandstone is medium-to coarse-

analyzed grained with quartz and K-feldspar grains and have laminations of fine-

Sierra Guacomea rhyolite 9-22-16-1 69.18 0.41 15.52 3.43 0.12 0.40 0.19 4.45 5.09 0.10 1.01 99.90 grained quartz ≪ sericitized feldspar and parallel-oriented biotite

rocks crystals (<1 mm in diameter) that define a continuous foliation. Meta­ morphic crystals that occur include fine-grained microcline along with subordinate albite and tourmaline. The original composition of this Salto igneous

El granite augen gneiss 3-24-17-1 73.23 0.28 13.97 2.11 0.05 0.43 1.68 3.41 3.87 0.06 0.90 99.98 sandstone most probably was a medium-to coarse-grained subarkose. the We analyzed three rhyolite samples that were collected at different of localities of its outcrop area (Table 1). Sample 5-28-19-2 was collected in

data the southern part of the Sierra Cibuta (Fig. 2) and yielded 26 zircon

La Cebolla granite 7-8-16-4 MV 74.28 0.19 12.91 1.91 0.03 0.09 0.26 2.25 7.64 0.05 0.37 99.98 grains with 206Pb/238 U ages between 182 and 170 Ma. A concordia age of 175.2 ± 0.9 Ma (MSWD = 1.4; N = 22) (Fig. 3B) is interpreted as the 2 elements time of zircon crystallization. Sample 8-5-18-3 was collected from near rancho El Nopalito (Fig. 2), in the southern Sierra Guacomea and yielded UNIT Sample number SiO2 TiO2 Al2O3 Fe2O3t MnO MgO CaO Na2O K2O P2O5 LOI Total

Table Major a concordia age of 171.4 ± 0.7 Ma (MSWD = 1.6) (Fig. 3C) from 23

6 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx Sierra Guacomea rhyolite 5-28-19-2 39.38 77.47 8.74 29.58 5.23 0.50 4.41 0.70 4.30 0.92 2.83 3.29 0.52 177.86 0.32 8.59 12.60 613.25 173.98 52.94 5.36 17.92 4.07 188.00 13.76 26.90 4.92 5.21 0.51 3.84 5.41 1.02 La rhy Rancho Víbora dome 5-27-19-5 50.76 97.65 12.15 39.49 7.53 0.77 6.71 1.09 6.70 1.37 4.03 4.21 0.62 233.08 0.33 8.64 16.74 754.96 210.51 86.71 5.35 18.56 2.91 181.01 14.88 41.37 3.10 5.44 0.55 2.52 5.46 1.12 ´ on El Rinc granite 4-26-19- 4 21.32 47.16 6.13 21.74 4.31 0.61 3.98 0.64 4.00 0.86 2.68 3.27 0.51 117.19 0.45 4.67 55.99 662.51 130.31 134.05 6.77 38.69 4.75 137.05 18.22 25.72 3.96 25.35 0.78 6.41 4.38 1.86 ´ on El Rinc granite 4-25-19- 3 37.76 70.99 7.90 27.42 5.20 0.91 4.60 0.71 4.19 0.88 2.66 3.01 0.47 166.69 0.57 8.99 56.69 712.01 169.27 201.88 14.43 27.01 4.23 160.61 12.79 25.53 3.37 15.82 0.99 5.95 4.81 1.06 dome Los Vallecitos rhy 10-14-18-2 51.68 88.59 10.40 32.38 4.71 0.84 3.84 0.56 2.93 0.57 1.62 1.72 0.27 200.11 0.60 21.54 15.67 1223.58 220.99 68.55 17.70 18.76 2.92 128.16 10.72 17.63 3.77 12.45 1.13 2.10 3.59 0.88 dome Los Vallecitos rhy 10-14-18-1 36.65 69.33 8.13 24.62 4.29 0.44 3.54 0.55 3.22 0.68 2.10 2.61 0.41 156.56 0.34 10.09 31.32 655.78 220.75 47.49 38.34 26.51 4.40 98.07 12.23 20.92 3.23 6.35 1.00 4.93 3.34 1.19 indicated. are El Nopalito granite 8-5-18-4 48.66 90.59 10.46 36.96 6.77 1.40 5.89 0.89 5.17 1.05 3.03 3.13 0.47 214.48 0.68 11.15 42.47 1336.73 195.67 192.97 25.82 22.04 5.23 202.27 14.32 30.89 12.03 84.92 5.46 10.95 5.35 1.11 units lithologic Sierra Guacomea rhyolite 8-5-18-3 25.23 44.80 5.57 20.03 3.87 0.92 3.62 0.59 3.85 0.83 2.45 2.59 0.39 114.75 0.75 6.98 13.55 1445.55 181.72 151.43 7.27 12.34 2.66 184.89 10.61 23.83 4.01 26.34 1.00 2.72 5.06 0.79 the of Sierra Guacomea rhyolite 12-9-17-1 39.93 78.95 8.46 28.65 5.23 1.15 4.54 0.69 4.08 0.83 2.39 2.47 0.37 177.74 0.72 11.58 44.93 1004.18 251.19 131.83 17.91 21.54 2.35 225.68 13.45 23.40 7.72 88.72 3.75 43.78 5.92 0.98 nomenclature ´ on and El Rinc granite 8-25-17- 2 31.28 57.83 6.58 22.95 4.34 0.91 3.94 0.61 3.73 0.79 2.31 2.52 0.39 138.18 0.67 8.92 26.40 46.72 11.83 230.45 7.35 13.18 4.54 186.47 9.92 22.66 4.22 39.41 1.36 0.66 4.94 0.70 numbers ´ on El Rinc granite 8-25-17- 1 24.19 53.44 4.94 16.07 2.91 0.57 2.65 0.45 3.00 0.66 2.05 2.43 0.37 113.73 0.62 7.14 68.11 824.03 214.89 141.91 20.86 28.45 3.80 90.44 13.65 19.77 4.22 18.69 1.20 6.47 2.92 1.21 Sample study. La Cebolla granite 7-30-17-1 36.91 73.81 8.52 29.99 6.02 1.19 5.39 0.83 5.02 1.04 3.09 3.43 0.53 175.78 0.64 7.71 3.96 1343.64 232.00 56.33 20.77 24.18 6.49 299.17 15.59 30.82 3.79 19.33 1.35 1.81 8.08 1.06 this in analyzed Sierra Guacomea rhyolite 9-22-16-1 31.11 58.01 6.66 23.43 4.33 1.04 3.87 0.62 3.77 0.79 2.32 2.52 0.39 138.86 0.78 8.85 18.87 1392.78 189.21 102.61 21.87 13.49 3.12 177.02 9.71 22.27 6.00 15.73 1.84 4.60 4.67 0.73 rocks Salto igneous El granite augen gneiss 3-24-17-1 13.93 27.70 3.30 12.74 2.76 0.94 2.57 0.39 2.30 0.47 1.29 1.33 0.21 69.94 1.08 7.52 28.56 1255.29 139.21 258.38 28.80 4.58 1.32 218.15 14.32 12.16 1.99 14.57 2.76 4.89 5.22 0.83 the of data La Cebolla granite 7-8-16-4 MV 43.87 83.50 10.54 37.68 7.39 0.72 6.70 1.10 7.05 1.48 4.39 4.50 0.68 209.60 0.31 6.99 8.36 694.14 265.52 39.95 20.55 21.04 2.62 258.21 15.07 43.59 6.55 5.12 0.37 5.32 7.56 1.02 3 elements YbN REE UNIT Sample number La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb Lu Σ Eu/Eu* LaN/ Mg# Ba Rb Sr Pb Th U Zr Nb Y Sc V Ni Cs Hf Ta Table Trace

7 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 3. A) Concordia and histogram diagrams of U–Pb age of El Salto granite augen gneiss. B-D) Concordia diagrams of U–Pb ages of the Sierra Guacomea rhyolite, and Concordia diagrams of U–Pb ages of samples of the E) Rancho La Víbora and F) Agua Caliente rhyolitic domes. MSWD — mean square of weighted deviates. Key number of the dated samples are indicated. concordant zircon grains. Also, sample 12-9-17-1 was collected near 4.2.2. Rancho La víbora rhyolitic dome rancho El Jotaiqui (Fig. 2) and yielded 28 zircon grains with ages be­ This is a local intrusion found in the northern part of the study area tween ca. 177 to 167 Ma, with two younger ages at 157 and 133.6 Ma that is truncated by the San Antonio fault (Moreno Ibarra and Martínez that were discarded. A concordia age of 171.7 ± 0.6 Ma (MSWD = 2.3; Cuevas, 2019). It intrudes the Sierra Guacome rhyolite and consists of a N = 26) (Fig. 3D) is interpreted as the crystallization age for this sample. massive rhyolitic body that has phenocrysts of feldspar and quartz in a

8 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 4. Concordia diagrams of U–Pb ages of samples dated of the A) Rancho Los Pozos unit, B) Los Vallecitos rhyolitic dome, C) El Rincon´ granite, E) La Jojoba metasandstone, F) El Nopalito granite, and D) Concordia and histogram U–Pb age for sample MX-1347 of the El Rincon´ granite. MSWD — mean square of weighted deviates. microcrystalline felsitic groundmass. Phenocrysts compose 40% of the dome, we dated 33 zircon grains that yielded only Jurassic ages. A volume of the rock and consist of commonly broken crystals of K-feld­ concordia age of 176 ± 0.8 Ma (MSWD = 1.6, N = 29) (Fig. 3E) is spar and plagioclase altered to sericite and clays. Quartz crystals are up interpreted as its crystallization age. to 6 mm long and some are subhedral with resorbed borders. For sample 5-27-19-5, collected from the Rancho La Víbora rhyolitic

9 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

sample 12-8-17-1 that was collected from a rhyolitic tuff. This sample yielded 28 zircon grains of Jurassic age, and one grain of ca.145 Ma. A concordia age of 170.7 ± 0.6 Ma (MSWD = 1.1, N = 25) is the best approximation for the crystallization age of this unit (Fig. 4A).

4.2.5. Los Vallecitos rhyolitic dome This unit crops out in the eastern part of the sierra Guacomea (Fig. 2), where it is intruding the Sierra Guacomea rhyolite with poorly defined contacts. It is also in fault contact with the Upper Cretaceous Cocospera´ Formation (Gonzalez-Le´ on´ et al., 2017a, 2017b) and is intruded by a Paleocene granite. The Los Vallecitos rhyolitic dome is a light gray, foliated, porphyritic rock that characteristically bears recrystallized quartz eyes up to 6 mm long. The felsitic matrix of this rock is abundant and composed of equigranular, very fine-grained quartz with subordi­ nate intergrowths of oriented biotite and muscovite, scarce small crys­ tals of plagioclase and microcline. Occasionally, the quartz and subordinate K-feldspar and plagioclase porphyroclasts are broken, the quartz has resorbed borders and these crystals are weakly oriented by flow. The feldspars are altered to clay minerals, biotite and muscovite. Sample 10-14-18-1 collected from Los Vallecitos rhyolitic dome yielded 25 zircon grains of Jurassic age ranging from 187 to 160 Ma and two younger grains of ca. 133 Ma and 126 Ma that were discarded from Fig. 5. Concordia diagram of U–Pb age of sample dated of the La Cebolla age calculation because of Pb loss, probably due to fluidcirculation. The granite. MSWD — mean square of weighted deviates. nine concordant zircon grains yield a concordia age of 174.4 ± 0.9 (MSWD = 2.1; Fig. 4B) that is considered here as the probable crystal­ 4.2.3. Agua Caliente rhyolitic dome lization age. The local outcrop of this unit intrudes the Sierra Guacomea rhyolite in the southeastern part of the Sierra Cibuta. It is composed of ca. 50% of 4.2.6. El Rincon´ granite quartz, plagioclase and K-feldspar phenocrysts that are embedded in a The El Rincon´ granite is part of the “granite porphyry” unit reported fluidal, vitric to felsitic groundmass that is altered to sericite. Quartz by Nourse (1989; 1990) in the northwestern part of the Sierra Guaco­ crystals are up to 5 mm long and some have resorbed borders. Feldspar mea. This unit is named after outcrops near Rancho El Rincon´ (Fig. 2), crystals are commonly broken, up to 3 mm long and show alteration to where it occurs as intrusive sheets into the Sierra Guacomea rhyolite. It sericite and iron oxide. Other minerals include subordinate cloritized is a coarse-grained, well-foliated, porphyritic biotite granite with biotite up to 2 mm long that is also altered to iron oxides. No K-feldspar crystals up to 4 cm long. Foliation is formed by elongate geochemistry was performed in samples from this unit because of bands of K-feldspar, subordinate plagioclase and undulose, commonly evident alteration. polycrystalline quartz grains up to 2 cm long that alternate with bands of Sample 1-22-19-1 collected from the Agua Caliente rhyolitic dome finer-grained, recrystallized quartz and feldspar. Partially chloritized yielded 28 zircon grains of only Jurassic ages, and a concordia age of brown biotite occurs in crystals up to 4 mm long forming continuous 173.1 ± 0.8 Ma (MSWD = 1.3, N = 25) (Fig. 3F). laminations. Other accessory minerals are hornblende, titanite, and epidote. 4.2.4. Rancho Los Pozos unit Exposures of the El Rincon´ granite occur as concordant layers 1 m to Outcrops of this unit are restricted to the central part of sierras El tenths of meters thick within the finer grained recrystallized Sierra ´ Alamo Viejo and Los Chinos, where it is faulted with the Sierra Guaco­ Guacomea rhyolite. The El Rincon´ granite is intruded near its base by a mea rhyolite. In its southern part it is faulted against La Jojoba meta­ 500–1000 m thick sill of medium grained, porphyritic biotite granodi­ sandstone and is intruded by a Paleogene granite (Fig. 2) (Sanchez´ orite (the 78 ± Ma “Guacomea gneiss” reported by Anderson et al., Navarro, 2018). Although this unit is affected by low-grade meta­ 2005; see also Nourse, 1989 and 1990). A strong north-to-N20E linea­ ◦ ◦ morphism, it is generally well-bedded and dips 10 –58 NE, or SW, as it tion is preserved in the Jurassic rocks and Late Cretaceous granodiorite, is folded and affected by a reverse fault that suggests NE vergence of and a pervasive amphibolite facies metamorphic fabric that probably shortening. It is composed of interbedded rhyolitic ash-fall tuff and records Laramide deformation, diminishes in intensity eastward into the flows,sandstone, siltstone and subordinate limestone beds that together Sierra Guacomea rhyolite. make up an estimated thickness of 600 m. Ash-fall tuffs are laminated to We collected two samples of the El Rincon´ granite for U–Pb massive, up to 20 m thick, and the rhyolitic flows commonly present geochronologic analysis. Sample 8-3-18-1, collected from the Rancho El flow-banding. Interbedded sandstone and siltstone are tuffaceous and Rincon´ locality (Fig. 2), yielded three older zircon grains with 206Pb/238 occur in beds of 0.1–1.5 m-thick, composing intervals up to 15 m thick. U ages between 171 and 176 Ma, four grains with disparate ages be­ Also, present there is an 80-m thick package of recrystallized sandy tween 158 and 138 Ma, and a coherent population of 22 grains with limestone in beds 10- to 40-cm thick with subordinate quartz-rich Jurassic ages between 160 and 169 Ma that were used to obtain a sandstone in beds up to 1 m thick. concordia age of 164.4 ± 0.7 (MSWD = 1.8; Fig. 4C). Sample MX 1347 Petrographically, the rhyolite has a moderately-oriented recrystal­ was collected from outcrops about 1 km west of Rancho La Sopalpía by lized matrix of fine-grainedpolygonal quartz grains with discontinuous J. Nourse during his thesis mapping in November 1987. We analyzed 35 laminations of parallel oriented muscovite and epidote, or muscovite- zircons grains from this foliated granite porphyry sample that yielded biotite-epidote that define a continuous to locally spaced foliation. Jurassic 206Pb/238 U ages between 164 and 179 Ma, and one grain of Some samples show recrystallized quartz eyes, and others have pre­ Cretaceous age. When considering the younger ages, a weighted mean served glass-shards. Scarce metamorphic minerals observed in some thin 206Pb/238 U age of 167.4 ± 0.4 (MSWD = 2.2, N = 10) (Fig. 4D) is ob­ sections include titanite, amphibole, staurolite, allanite, albite and tained for this sample. According to these data, we interpret the crys­ mirmekite. tallization age of the El Rincon´ granite between 167 and 164 Ma. The Rancho Los Pozos unit is dated by zircon grains separated from

10 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

4.2.7. La jojoba metasandstone with common, cm-to m-large enclaves of metasedimentary rocks. Parts This is a foliated unit that crops out in the western part of sierra La of this pluton are pegmatitic with K-feldspar crystals up to 5 cm long and Jojoba where it is intruded by Paleocene granites, but its most extensive subordinate quartz. Petrographically it has a hypidiomorphic granular ´ outcrops are in sierra El Alamo Viejo (Fig. 2). Strata of this unit in Sierra texture and it is dominantly composed of K-feldspar (orthoclase and ◦ La Jojoba dip in average 30 SE and have an estimated thickness of 900 microcline) > plagioclase > quartz. Subordinate minerals include bio­ m. In this locality, this unit consists of light-gray, foliated quartz-rich tite, muscovite, garnet, iron oxides, epidote and sericite. Biotite shows sandstone in beds that range from 5 cm to 1.5 m thick that preserve minor alteration to chlorite, the muscovite crystals are smaller than no primary sedimentary structures and commonly are intruded by fol­ biotite, and garnet occurs as euhedral crystals. ded pegmatitic and aplitic dikes of leucocratic granite. Some of the least Sample 7-8-16-4 from La Cebolla granite yielded 32 Jurassic zircon deformed samples that were observed in thin section reveal an arkosic grains. The most coherent group of 18 analyses yields a concordia age of composition with abundant quartz and feldspar. The most deformed 158.1 ± 1 Ma (MSWD = 2.8) interpreted as the crystallization age for samples show dynamically recrystallized bands of coarse grained quartz this granite (Fig. 5). and feldspar that alternate with bands of fine-grained quartz where development of muscovite, biotite and epidote occurs. 4.3. Inherited zircon grains ´ In the Sierra El Alamo Viejo we measured an incomplete 445-m thick stratigraphic column that is intruded by a Paleogene granite (Sanchez´ The Jurassic intrusive and volcanic rock samples dated in this work Navarro, 2018). It is composed of superposed, up to 50 m-thick fluvial dominantly have zircon grains (N = 265) with U–Pb ages that range successions that commonly start with a basal, stretched-clast conglom­ from ca. 194 to 150 Ma, and show a peak age at 172 Ma (Fig. 6A). erate that grades upwards into light gray sandstone and siltstone with Inherited zircon grains in these samples are only of Jurassic age, except local interbedded rhyolitic beds up to 15 m thick. The conglomerate for the El Nopalito granite, which yielded two Proterozoic zircon grains. beds are base erosive and clast-supported, up to 18 m thick and Eight other zircon grains in these samples yielded disparate ages from composed of poorly sorted, up to 20 cm long clasts of quartzarenite and 124 to 146 Ma and they might indicate Pb loss (data not included in rhyolite, minor granite and chert clasts in a sandy matrix. The least Fig. 6). Detrital zircon grains dated from three samples collected from deformed sandstone samples are composed of quartz, K-feldspar, sub­ the La Jojoba metasandstone also show dominantly Jurassic ages, except ordinate lithic fragments and plagioclase to classify as arkose and sub­ sample 1-23-17-2 that yielded 35 out of 84 grains with dispersed ages arkose. The deformed samples commonly show continuous schistosity from Triassic to Neoarchean. When the detrital zircon grains with formed by alternating laminations of subparallel oriented botite ≫ Permian to Jurassic ages dated from the three samples of the La Jojoba muscovite and finely recrystallized quartz. Occasionally some samples metasandstone are included in the probability density curve of Fig. 6A, a preserve unoriented hornblende crystals intergrowths. similar peak age is obtained (Fig. 6B) and only three of these grains are Maximum depositional age for the La Jojoba metasandstone was of Triassic and Permian ages. obtained by dating detrital zircon grains separated from sandstone samples of three different localities; one hundred grains were analyzed 5. Geochemistry from each sample. Sample 3-25-17-5 was collected in sierra La Jojoba, in the central part of the area, and sample 3-25-17-2 was collected in hills We collected 14 rock samples from the Jurassic igneous units, except located 7 km to the north of this sample (Fig. 2). Both of these samples from the Los Pozos unit, the Agua Caliente rhyolitic dome and the La yielded dominantly Jurassic zircon grains with peak ages of ca. 172 and Jojoba metasandstone. The rock samples were analyzed to constrain 170 Ma, respectively. On the other hand, sample 1-23-17-2 that was concentrations of major and trace elements. One sample of the Meso­ ´ collected from the Sierra El Alamo Viejo yielded zircon grains with an proterozoic El Salto granite augen gneiss was also analyzed and all these important peak age of 164 Ma, although nearly half of the analyzes geochemical results are reported in Tables 2 and 3 preserve inherited ages from Triassic to Neoarchean. Considering the large number of zircon grains that are younger than 167 Ma (Fig. 4E) 5.1. Major and trace elements and that render the most consistent ages in the three samples, a maximum depositional age of ca. 163 Ma is inferred herein for the La The analyzed samples have a loss on ignition (LOI) values lower than Jojoba metasandstone (Fig. 4E, inset). 1.2%, with an average value of 0.68%. Major oxides values were recalculated to 100% on an anhydrous basis, and results were plotted on 4.2.8. El Nopalito granite proper diagrams (Fig. 6) to determine the geochemical characteristics of This unit crops out as small stocks that intrude the Sierra Guacomea the igneous rocks of the study area. rhyolite at a few localities in the southern part of the sierra with the The SiO2 content of four samples of the Sierra Guacomea rhyolite same name. The sizes of the outcrops are exaggerated in Fig. 2 to indi­ varies from 66 to 75.9 wt% and in a variation diagram of Zr/TiO2 versus ´ cate the observed locations. Similar to the El Rincon granite, this unit is SiO2 of Winchester and Floyd (1977) and Floyd and Winchester (1978) composed by coarse-grained porphyritic rock with K-feldspar as large as (not shown), these rocks are classified as rhyolite to rhyodacite. Simi­ 4 cm and polycrystalline quartz-grains up to 3 cm long in a matrix of larly, the SiO2 content of the Jurassic granites range from 66 to 76 wt % finely recrystallized quartz. This granite contains oriented biotite crys­ while the rhyolitic dome rocks range from 75 to 77 wt %. In a R1-R2 tals up to 1 mm long and also subordinate titanite. multicationic classification diagram of De la Roche et al. (1980) From sample 8-5-18-4 collected from El Nopalito granite we dated 33 (Fig. 6A), the intrusive rocks are classified granites, except for the El zircon grains, of which, three have disparate ages between ca. 150 and Rincon´ granite that varies into granodiorite, and two samples of the La 134 Ma, two are inherited zircon of 540 and 1035 ± 24 Ma. The Cebolla unit are classified as alkaline granite straddling into syenog­ remaining grains form a coherent age population between 165 and 156 ranite. The rhyolitic dome rocks are classifiedas alkaline rocks and the Ma, except for one zircon grain that has an age of 171 Ma. A mean Proterozoic El Salto granite augen gneiss is classified as monzogranite interpreted crystallization age of 160.8 ± 0.6 Ma (MSWD = 2, N = 23) is (Fig. 7A). calculated for El Nopalito granite (Fig. 4F). The geochemical data also indicate that the rocks vary from high-K calc-alkaline to shoshonitic, including the El Salto granite augen 4.2.9. La cebolla granite gneiss (Fig. 7B). Moreover, according to the Ta vs. Yb diagram of Pearce This is a N–S elongated intrusive body that crops out in the eastern et al. (1984), the studied rock units are restricted within the field of middle part of the sierra El Potrero where it is crosscut by a Paleogene volcanic arc environment (Fig. 7C). In a Shand’s alkali index diagram of granite. It is a weakly mylonitized, medium-grained leucocratic granite A/(NK) vs. A/(CNK) to characterize tectonic environments (Maniar and

11 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 6. A) Probability density plot for the zircon grains dated from the Jurassic intrusive and volcanic rocks of the study area (n = 265). Main peak age is 172 Ma. B) Same probability density plot graph with added zircon grains of Permian to Jurassic age from the detrital zircon grains in the three samples dated from the La Jojoba metasandstone (N = 512); the resultant peak age is 171 Ma.

Piccoli, 1989), the intrusive rocks of the study area are mostly per­ in this region, and they have been associated with the Jurassic Cordil­ aluminous, and are located within the fields of continental arc and leran magmatic arc (Haxel et al., 2005, Fig. 1) that was built on the post-orogenic granitoids (Fig. 7D). southwestern continental margin of North America (Tosdal et al., 1989; The Jurassic rocks show total REE values that vary from 114 to 254 Busby-Spera et al., 1990; Saleeby et al., 1992; Riggs and Blakey, 1993; ppm and lanthanum concentrations from 90 to 218 times the chondrite. Schermer et al., 2002), and that continues into northern Mexico as the In a chondrite-normalized REE diagram (Fig. 8A), these rocks are Nazas arc (Bartolini et al., 2003; Dickinson and Lawton, 2001; Lawton enriched in light REEs with respect to the heavy REEs, as indicated by and Molina-Garza, 2014). their (La/Yb)N ratios that vary from 21 to 7, except for one sample of the In the study quadrangle, the Jurassic rocks are volcanic, plutonic and ´ El Rincon granite, whose (La/Yb)N value is 4.7. These rocks also have sedimentary units that are herein recognized as named, informal litho­ negative europium anomalies with Eu/Eu* (McLennan, 1989) values logic units (Fig. 1). They are part of an exhumed crustal section of the that range from 0.31 to 0.78. The El Salto granite augen gneiss, however, Jurassic arc and were affected by low- to medium-grade metamorphism is depleted in REE, and show a smoother pattern compared to those of (Nourse, 1989). They also constitute the lower plate of the Madgalena the Jurassic rocks, and it is characterized by a subtle Eu positive metamorphic core complex and their exhumation and metamorphism anomaly. may be related to development of this structure whose rapid cooling and Trace element diagrams normalized to primitive mantle values extension is constrained between 25 and 22 m.y. by Ar/Ar thermo­ (Fig. 8B), indicate enrichments in the large-ion lithophile elements Rb, chronology (Wong et al., 2010). Nevertheless, and as Nourse (1989) Ba, K and Pb, compared to the high field strength elements, while they recognized, these rocks were also affected by older fabrics, prior to show negative anomalies for Nb–Ta, Sr, P, and Ti. In general, the undergoing mylonitic deformation of the core complex. Jurassic intrusive and volcanic rocks have fairly uniform normalized The oldest unit is the Sierra Guacomea rhyolite that was geochro­ REE, and trace element patterns (Fig. 8). nologically contrained in three samples from different localities with ages from 175.2 ± 0.9 to 171.4 ± 1.1 Ma. Its widespread outcrops occur 6. Discussion in the northern part of the study quadrangle, where we infer a composite thickness of at least 3.5 km. In the Sierra Guacomea this unit is domi­ The study quadrangle located in north-central Sonora lies in the nated by rhyolitic flowswith subordinate interbeds of ash-fall tuffs and Mazatzal cratonic block of North America and is also part of the quartz-rich sandstone, while in the southern Sierra Cibuta the rhyolites southern Papago terrane (Haxel et al., 1984; 1988; or southern Papago are massive to poorly stratified and have subordinate quartz-rich sand­ domain of Anderson et al., 2005), which extends into this region from stone interbeds. southern Arizona. As defined the Papago terrane in south-central Ari­ Nourse (1989) named this rhyolite unit in the Sierra Guacomea zona (Haxel et al., 1984, 1988; Riggs and Haxel, 1990), it differs in “schistose quartz porphyry” and recognized it as derived from a geology and geologic evolution from adjoining areas and is character­ porphyritic volcanic protolith that represents the deepest known strat­ ized by sparse to absent rocks older than Jurassic, the greater abundance igraphic levels of the Magdalena metamorphic core complex. Because of Jurassic magmatic arc-related rocks, and by a relative paucity of Late outcrops of the Sierra Guacomea rhyolite are not strained in the Sierra Cretaceous arc-related rocks relative to adjacent areas (Riggs and Haxel, Cibuta, Nourse et al. (1994) and Nourse (1995) proposed that a north­ 1990; Riggs and Busby-Spera, 1991). In the region of north-central west trending structure, the “Imuris Lineament”, separates the Sierra Sonora the Proterozoic basement rocks do not crop out, except for a Cibuta outcrops from its strained outcrops in the neighboring Sierra hundred meters large gneissic granite xenolith that occurs in a sheared Guacomea to the south, interpreting that this lineament defines the Cenozoic pluton of the study quadrangle, as reported by Nourse et al. northeast limit of the middle Tertiary ductile deformation (Nourse, (2018). This xenolith corresponds to the El Salto granite augen gneiss 1995). whose U–Pb age of 1071.9 ± 5 Ma reported herein, demonstrates the The Rancho Los Pozos unit with a U–Pb zircon age of 170.7 ± 0.6 Ma existence of Grenville basement in the study area. is slightly younger than the Sierra Guacomea rhyolite, and composi­ Although the central part of northern Sonora is mostly covered by tionally is dominated by interbedded rhyolitic ash-fall and ash-flow geologic cartography to the scale of 1:250,000 and 1:50,000 by the beds, sandstone, quartz-rich sandstone and siltstone and subordinate Servicio Geologico´ Mexicano (https://www.sgm.gob.mx/CartasDis limestone beds with an estimated thickness of 600 m. Its age and ponibles/), most of the inferred ages for the reported lithologic units composition indicate that it was part, along with the Sierra Guacomea in these charts are constrained by scarce geochronologic data. The most rhyolite, of an abundant continental volcanism and clastic sedimenta­ complete dataset for this region was published by Anderson et al. tion that occurred from ca. 176 to 170 Ma, while the intercalated quartz- (2005), who reported nearly a dozen ID-TIMS U–Pb ages for granitic and rich sandstone might be reworked eolianites that were introduced to the rhyolitic rocks that ranged from ca. 180 to 150 Ma. Outcrops of these arc from the Colorado Plateau (Busby-Spera et al., 1990; Schermer et al., late Early to Late Jurassic rocks represent the most abundant and oldest 2002; Lawton and Molina-Garza, 2014). The Rancho La Víbora, Los

12 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 7. Geochemical discrimination plots for the Jurassic rocks of the study area, including the Proterozoic El Salto granite augen gneiss. A) Chemical classificationof the Jurassic granites and rhyolitic domes according to the R1-R2 diagram of De la Roche et al. (1980). B) (K2O vs. SiO2)N diagram showing the fieldsof Peccerillo and Taylor (1976). C) Ta vs. Yb diagram of Pearce et al. (1984) that discriminate the tectonic environment for the Jurassic rocks of the study area (VAG: volcanic arc, WPG: within plate, ORG: ocean ridge, and Syn-COLG: syn-collision granites). D) Shand’s index diagram A/(NK) vs. A/(CNK) from Maniar and Piccoli (1989) distinguish alkali index and tectonic environments (IAG: island arc, CCG: continental collision, CAG: continental arc and POG: post-orogenic granitoids). E) Zr/Nb vs. Zr diagram of Allegre and Minster (1978) showing that Jurassic magmas were probably controlled by partial melting and fractional crystallization processes.

Vallecitos and Agua Caliente rhyolitic domes that have ages from 176 to for the Sierra El Pinito (El Tunel quartz porphyry, Fig. 2). Also, from the 173 Ma, intrude the Sierra Guacomea rhyolite and are considered to be Las Borregas area located 15 km to the north of the study area, Riggs and part of the older magmatic event in the area. Busby-Spera (1991) recognized strata similar to the tuff of Pajarito, The volcanic succession represented by the Sierra Guacomea rhyolite which belongs to strata of the Cobre Ridge caldera complex of the border and Rancho Los Pozos unit extends to the north into the adjacent sierra region in south-central Arizona. This ca. 3 km thick rhyodacite ignim­ Las Avispas (Escamilla Torrres and Gú zman Espinoza, 2008), from brite tuff is ~170 Ma, about the same age as the Los Pozos unit, and where Segerstrom (1987) reported the at least 1 km thick Las Avispas extends south of the border into the Pajarito Mountains of Sonora, north formation composed of silicic welded tuff and intercalated eolian of the study quadrangle. According to Riggs and Busby-Spera (1991), sandstone of interpreted Early to Middle Jurassic age. Farther east, this tuff is underlain by silicic ignimbrites, tuffs, and eolian and fluvial Anderson et al. (2005) reported two concordant zircon ages of 174 Ma sandstones in the Las Borregas area, and may represent precursor

13 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

Fig. 8. A) Chondrite-normalized rare earth element (REE) diagram, and B) primitive mantle-normalized multi-element diagram of the Jurassic rocks of the study area. Normalizing values are from McDonough and Sun (1995). eruptions of the tuff of Pajarito. The association of the mostly silicic which is composed by volcaniclastic sandstone and conglomerate, volcanic rock successions and domes from 176 to 170 Ma in the study eolian quartzarenite, lacustrine limestone, andesitic flows,and dacitic to area might represent part of a disorganized caldera complex that was rhyolitic ash-flowtuffs that yielded ages of ca. 170 to 168 Ma (Leggett, contemporaneous to the Cobre Ridge complex of southern Arizona. 2009), may correlate with the Rancho Los Pozos unit reported here. The next Jurassic event of the arc is represented by the intrusion of Also, from the San Francisco mine located 25 km south of study quad­ the 167-164 Ma El Rincon´ granite into strata of the Sierra Guacomea rangle, Poulsen et al. (2008) reported metarhyolites dated at ca. 180 Ma, rhyolite. No volcanic rocks of this age were identified in the study and from the Sierra Buenos Aires granite in northeastern Sonora we quadrangle. Anderson et al. (2005), however, reported ages of four obtained an U–Pb age of ca. 184 Ma (G-L. unpublished data), while an concordant zircon analyses of 166 Ma from El Plomo porphyritic U–Pb age of 180 Ma was reported by Anderson et al. (2005) from their granite, located ~ 50 km to the northwest, and two analyses of 165 Ma Sonora pophyritic rhyolite near Sonoita, in northwestern Sonora. and 152 Ma from the Canon˜ Las Planchas rhyolite in Sierra Las Avispas, The studied rocks correlate in age with the Middle Jurassic Topawa located 20 km north of the study area. The El Rincon´ granite is about Group of the Baboquivari Mountains in southern Arizona (Haxel et al., same age as the 165 ± 2 Ma Kitt Peak granodiorite of the northern 2005) which is composed from base upwards of the largely rhyolitic Ali Bavoquivari Mountains, in southern Arizona (Haxel et al., 2005). Molina Formation, the mostly sedimentary Pitoikam Formation, and by Middle Jurassic arc magmatism was closely followed by basin for­ the Mulberry Wash Formation composed of rhyolite, breccia, mation and detritus accumulation of the La Jojoba metasandstone that conglomerate and subordinate alkali basalt and comendite in its upper occurred at least near 163 Ma. The ca. 1.5 km thick succession of vol­ part (Haxel et al., 2005). The Ali Molina Formation is the only dated unit caniclastic and epiclastic sediments with intercalated rhyolitic ignim­ (170 ± 3 Ma, U–Pb), and the group is intruded by the Kitt Peak Plutonic brite flows of the La Jojoba metasandstone, were deposited in local Suite that includes the Aguirre Peak Quartz Diorite (ca. 170 to 165 Ma), basins of the arc, as indicated by unimodal detrital zircon populations of the Kitt Peak Granodiorite (ca. 165 Ma) and the Pavo Kug Granite (159 Jurassic age yielded by the dated sandstone samples of this unit, except ± 2 Ma) (Haxel et al., 2008a). Regional correlation of the Topawa Group by sample 1-23-17-2. The dominant Jurassic detrital zircons in samples in southern Arizona is discussed by Haxel et al. (2005), who suggest 3-25-17-2 and 3-25-17–5 may indicate that fluvialstrata of the La Jojoba broad similarities with rocks of the lower Colorado River region, where metasandstone were derived from local sources in the arc. The sandstone evolution of the Jurassic arc is recorded by silicic volcanic rocks of the ´ from the Sierra El Alamo Viejo (sample 1-23-17-2) yielded zircon grains Dome Rock sequence (190-185 Ma) and the Kitt Peak-Trigo Peaks with a significant peak age of ca. 164 Ma, but nearly half are inherited plutonic suite (173-158 Ma) (Tosdal and Wooden, 2015). The youngest zircon grains of Triassic to Paleoproterozoic ages that may indicate in­ unit of this suite corresponds to the Gold Rock Ranch granite (163-158 fluence to the arc from neighboring source areas. Although the age Ma) (Tosdal and Wooden, 2015). herein assigned to the La Jojoba metsandstone is interpreted as its The La Cebolla granite in the study area has similar age to the Pavo maximum depositional age, its intercalated rhyolites flows might Kug and Gold Rock Ranch granites. The Gold Rock Ranch granite is correspond to volcanic products derived from the El Rincon´ granite considered to indicate regional ending of arc activity (Tosdal and magma chamber. Wooden, 2015) before inception of younger, Late Jurassic alkalic mag­ The younger Jurassic magmatic events in the quadrangle are recor­ matism that occurred in southern Arizona and northern Sonora related ded by the intrusion of the nearly contemporaneous El Nopalito and La to intra-arc extension (Haxel et al., 2008b), or transtension (Anderson Cebolla granites that occurred at ca. 160 and 158 Ma, respectively; et al., 2005). The magmatism that records intra-arc extension in although no equivalent volcanic rocks are recorded in the study area. southern Arizona include the 158 ± 3 Ma Mount Devine Quartz Syenite, These plutons might represent the roots of waning activity of the the 146 ± 3 Ma Baboquivari Peak Perhite Granite and other plutons Jurassic arc that is thus constrained from ca. 176 to 158 Ma, repre­ reported by Haxel et al. (2008b), while the Pavo Kug granite intrudes the senting a 17 m.y. interval of magmatism and associated sedimentation in early bimodal magmatism of the Mulberry Wash Formation. In Sonora, the study area. near the Mexico-US border, Anderson et al. (2005) describe the San The earlier Jurassic arc in Sonora is recorded by a crustal section Moises alkaline granite that yielded a concordant zircon age of 149 Ma, reported by Mauel et al. (2011) and Leggett (2009) from the Cucurpe and also reported ages of 153 and 152 Ma from a quartz monzonite at region (Fig. 1). It is composed of the basal Rancho Basomari and the Estacion Sahuaro, northwest of Caborca. Despite its alkalic composition, overlying Rancho San Martin formations. The fluvial and alluvial we consider that the La Cebolla granite might be related to the waning Rancho Basomari has intercalated dacitic tuffs that were dated at 189.2 Late Jurassic arc magmatism as indicated by its similar REE and trace ± 1.1 Ma (U–Pb zircon SHRIMP), and is intruded by a rhyolite porphyry element patterns to the other Jurassic arc rocks in the study area (Fig. 8). of 180.6 ± 1.3 Ma (Leggett, 2009). The Rancho San Martin formation The marine Cucurpe Formation in north-central Sonora also records

14 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx younger rift basin formation and sedimentation in the Altar-Cucurpe et al., 2008a, 2008b; Fig. 6A). They also show a REE-pattern of enriched basin of northern Sonora during Oxfordian-Tithonian time (Villasenor˜ LREE relative to HREE and Eu anomaly (Haxel et al., 2008a, 2008b, et al., 2005; Mauel et al., 2011). Fig. 12A) that overlaps the REE-pattern of our studied rocks. The REE Life span of the Jurassic arc in northern Sonora, if constrained from pattern of our studied rocks also overlaps with that shown by the ca. 190 to 158 Ma, is similar to the ~30 m.y. duration recorded in Jurassic granites and rhyolites reported from the Caborca region (Iza­ southwestern Arizona (Tosdal and Wooden, 2015) and in the eastern guirre Pompa, 2009), while the REE pattern of the El Salto granite augen Mojave Desert (Barth et al., 2017); this arc is considered as a long-lived gneiss overlaps that of the North America (Mazatzal) granites reported arc related to subduction of either the Farallon (Engebretson et al., 1985; by Iriondo et al. (2004, Fig. 7D) from that same region. The REE and Matthews et al., 2016), or the Mezcalera (Dickinson and Lawton, 2001) multielement patterns of the studied Jurassic rocks are also very similar plates below the western continental margin of North America. The ca. to patterns that characterize the Laramide arc rocks of central and 172 Ma peak age yielded by the zircon grains dated from the Jurassic northern Sonora (Valencia-Moreno et al., 2001; Gonzalez-Le´ on´ et al., igneous and sedimentary rocks reported in this study (Fig. 4B), suggests 2011; Gonzalez-Becuar´ et al., 2017; Gonzalez-Le´ on´ et al., 2017a, that it records an important flare of magmatism in northern Sonora, 2017b). which is similar to the 170 Ma most important magmatic episode re­ ported by Tosdal and Wooden (2015, Fig. 17B) for arc rocks of the lower 7. Conclusions Colorado River region in Arizona and California. Moreover, it is sur­ prising that rocks of the study quadrangle do not show inherited zircons 1. Extensive exposures of Jurassic volcanic, hypabyssal, plutonic, and that record the Permian-Triassic magmatic arc, which is well repre­ volcano-sedimentary rocks are documented throughout the 1:50,000 sented by plutonic and volcanic rocks with ages from 284 to 221 Ma in scale map of the Magdalena quadrangle in the lower plate of a the Sonoita region (Fig. 1) (Arvizu et al., 2009; Riggs et al., 2012; Arvizu regional metamorphic core complex. This rock association is part of and Iriondo, 2015). The relationship of the magmatic events of northern Cordilleran magmatic arc transitional to the Nazas arc of northern Sonora with Triassic and Jurassic magmatic pulses (249–241, 213–203, Mexico. Most of these rocks preserve Laramide and/or middle Ter­ and 161 - 150 Ma) reported by Sarmiento-Villagrana et al. (2016) from tiary metamorphic fabrics, and structural thickness of the mapped the Sonobari Complex in southernmost Sonora is not yet clearly un­ section exceeds 3.5 km in Sierra Guacomea. derstood, although these authors suggest that magmatism may be 2. According to U–Pb LA-ICPLMS geochronology, the volcanic, volca­ related to the Cordilleran arc. nosedimentary and sedimentary strata of the Sierra Guacomea The suggested continental magmatic arc setting for the Early-Middle rhyolite and Los Pozos units range in age from ca. 176 to 170 Ma and Jurassic igneous rocks of northern Sonora is supported by geochemical are intruded by the Rancho La Víbora, Agua Caliente and Los Val­ data in this study. Rocks of the study area are highly evolved, silica-rich, lecitos rhyolitic domes constrained between ca. 176 and 173 Ma. mostly high-K calc-alkaline to shoshonitic granite and rhyolites, which is 3. The younger, quartzose and arkosic La Jojoba metasandstone records typical of active continental margins (Pearce et al., 1984). A continental mostly fluvial sedimentation while its intercalated rhyolitic beds margin arc setting is further suggested by the trace element discrimi­ may be related to El Rincon´ granite that has an age from 167 to 164 nation diagrams of Pearce et al. (1984), like the Ta vs. Yb (Fig. 7C) and Ma. Detrital zircon grains dated from three sandstone samples from the Ta/Yb vs. Th/Yb (not shown) diagrams. The geochemical nature of La Jojoba metasandstone preserve dominant middle Jurassic peak the plutons is mostly peraluminous, which may indicate crust assimi­ ages suggesting derivation from the local magmatic arc, but the ´ lation of arc-related magmas that were emplaced in a probably thick­ sample from the Sierra El Alamo Viejo locality shows significant ened continental crust. provenance of Triassic to Neoarchean basements of southwestern The normalized REE and trace element patterns (Fig. 8), which are North America. Maximum depositional age for La Jojoba meta­ very homogeneous for the plutonic and volcanic Jurassic rocks, also sandstone is ~163 Ma for all the three dated samples. suggest arc related signatures. The chondrite-normalized REE pattern 4. Two other younger plutons are recognized with ages at 160.8 ± 0.6 show (La/Yb)N ratios from 21 to 7 indicating enriched light REEs with Ma and 158 ± 1 Ma. They record waning of the Jurassic arc in the respect to the heavy REEs, and negative europium anomalies (Fig. 8A). Magdalena quadrangle, whose age is constrained from ca. 176 to The multielement diagram (Fig. 8B) indicates relative enrichments in 158 Ma. The major and trace element geochemistry of the recognized REE, Rb, Ba, Th, U, K and Pb and negative anomalies for Nb–Ta, Sr, P, igneous rock units indicate that their high-K, calc-alkaline, mostly and Ti, suggesting involvement of crustal sources. Magma differentia­ peraluminous magmas were emplaced in a continental margin arc tion are also supported by a low Mg# that averages 30 (Gill, 2010) setting with important crustal assimilation. Similarly, REE pattern, (Table 3), while a positive tendency observed by increasing the Zr/Nb trace element variation and Mg numbers suggest partial melting and and La/Sm ratio with Zr (Fig. 7E) and La (not shown) contents (Allegre fractional crystallization processes. and Minster, 1978), respectively, indicates that the Jurassic magmas 5. A small outcrop of biotite granite augen gneiss (1072 ± 5 Ma) in were probably controlled by partial melting and fractional crystalliza­ Arroyo El Salto of the southern Sierra Magdalena is the first recog­ tion processes. nized Grenville basement in this area that is part of the Mazatzal The REE pattern of the El Salto Augen gneiss is depleted respect to province. This rock also preserves a significantinherited component the Jurassic rocks and although it does not show the Eu negative at 1392 ± 21 Ma. anomaly it is high-K calc-alkaline, slightly peraluminous and plot within the volcanic arc granites field (Fig. 7C and D). The contribution of the Declaration of competing interest basement rocks during the petrogenetic evolution of the Jurassic magmas will need further studies to find more outcrops and to obtain The authors declare that they have no competing financial interests isotope information from the Proterozoic rocks. or personal relationships that could have appeared to influencethe work Trace element and isotope composition of the mostly rhyolitic rocks reported in this paper. of the Ali Molina Formation of the Topawa Group of southern Arizona indicate they are calc-alkaline orogenic rocks (Haxel et al., 2005) that Acknowledgments geochemically compare with rhyolitic rocks of the study area, although no maficrocks like those present in the Mulberry Wash Formation were Results of this contribution were obtained through financialsupport identified in our study. Compositions of The Kitt Peak Plutonic Suite of project CONACYT No. 253545 granted to Gonzalez-Leon. We thank vary from diorite to granite and are mostly high-K calc-alkaline to and acknowledge valuable support from Aim´e Orci and Elizard Gonzalez´ slightly shoshonitic, and metaluminous to weakly peraluminous (Haxel Becuar of ERNO who provided sample thin sectioning, and sample

15 C.M. Gonzalez-Le´ on´ et al. Journal of South American Earth Sciences xxx (xxxx) xxx

´ powdering and mineral separation. Angel Zapata Martínez participated De la Roche, H., Leterrier, J., Grandclaude, P., Marchal, M., 1980. A classification of in earlier stages of the project and we thank him for support during field volcanic and plutonic rocks using R1R2-diagram and major element analyses: its relation with current nomenclature. Chem. Geol. 29, 183–210. https://doi.org/ and laboratory work. Valuable help of the following persons is also 10.1016/0009-2541(80)90020-0. greatly appreciated for allowing us the permit to do field work in their Dickinson, W.R., Lawton, T.F., 2001. Carboniferous to Cretaceous assembly and ´ “ ” fragmentation of Mexico. Geol. Soc. Am. Bull. 113, 1142–1160. https://doi.org/ ranches: Alonso Portillo and ejidatarios of El Coyotillo, Hector Tito < > “ ” 10.1130/0016-7606(2001)113 1142:CTCAAF 2.0.CO;2. Gerlach, Arturo Gerlach, Arnulfo Montijo, Enrique Jorique Noriega, Engebretson, D.C., Cox, A., Gordon, R.G., 1985. Relative Motions between Oceanic and Javier “El Carrillero” Cruz, Manuel Lafontaine, “Chuchi” Esquer, Jorge Continental Plates in the Pacific Ocean, vol. 206. Geological Society of America ´ “ Special Paper, p. 61. https://doi.org/10.1130/SPE206. Valenzuela, Oscar Fontes, Omar Quihuis and Jesús and Jose María Los ´ ” Escamilla Torrres, T.R., Gúzman Espinoza, J.B., 2008. Carta geologico-minera el correo Cuates Gastelum. J.A. Nourse is grateful to the Leon T. Silver and H12-A49. Servicio Geologico´ Mexicano, scale 1, 50, 000. Caltech for logistical support during many field seasons of the 1980s. Farmer, G.L., DePaolo, D.J., 1984. Origin of Mesozoic and Tertiary granite in the western Discussions with Tom Anderson, Gordon Haxel, and Nancy Riggs were United States and implications of pre-Mesozoic crustal structure. 2. Nd and Sr isotopic studies of unmineralized and Cu- and Mo-mineralized granite in the very helpful in establishing regional correlations of the Jurassic rocks in Precambrian craton. J. Geophys. Res. 89, 141–160. the study area. This paper was benefited by helpful and insightful re­ Farmer, G.L., Bowring, S.A., Matzel, J., Espinosa Maldonado, G., Fedo, C., Wooden, J., views of Roberto Molina Garza and an anonymous reviewer that we 2005. Paleoproterozoic Mojave province in northwestern Mexico? Isotopic and U-Pb greatly appreciate. zircon geochronologic studies of Precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora. In: Anderson, T.H., Nourse, J.A., McKee, J.W., Steiner, M.B. (Eds.), The Mojave-Sonora Megashear Hypothesis: Development, Appendix A. Supplementary data Assessment, and Alternatives, vol. 393. Geological Society of America Special Paper, pp. 183–198. https://doi.org/10.1130/2005.2393(05. Floyd, P.A., Winchester, J.A., 1978. Identification and discrimination of altered and Supplementary data to this article can be found online at https://doi. metamorphosed volcanic rocks using immobile elements. Chem. Geol. 21, 291–306. org/10.1016/j.jsames.2020.103055. https://doi.org/10.1016/0009-2541(78)90050-5. García Flores, J.R., 2019. Control temporal de los eventos magmaticos´ en la Sierra Los Tanques, NW de Sonora; evidencia de asimilacion´ de basamento en la generacion´ de References magmas. B.Sc. thesis. Universidad Estatal de Sonora. Gill, R., 2010. Igneous Rocks and Processes: A Practical Guide. Wiley-Blackwell, p. 428. Allegre, C.J., Minster, J.F., 1978. Quantitative models of trace element behavior in Gonzalez-Becuar,´ E., Perez-Segura,´ E., Vega-Granillo, R., Solari, L., Gonzalez-Le´ on,´ C.M., magmatic processes. Earth Planet Sci. Lett. 38, 1–25. Sole,´ J., Lopez´ Martínez, M., 2017. Laramide to Miocene syn-extensional plutonism Anderson, T.H., Silver, L.T., 2005. 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