Evolution of Granitoids in the Catalina Metamorphic Core Complex, Southeastern Arizona: U–Pb, Nd, and Hf Isotopic Constraints

Home , Santa Catalina Mountains, Sill (geology)

Contrib Mineral Petrol DOI 10.1007/s00410-013-0859-4

ORIGINAL PAPER

Evolution of granitoids in the Catalina metamorphic core complex, southeastern Arizona: U–Pb, Nd, and Hf isotopic constraints

Katherine F. Fornash • P. Jonathan Patchett • George E. Gehrels • Jon E. Spencer

Received: 31 August 2012 / Accepted: 31 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013

Abstract The Santa Catalina Mountains, SE Arizona, respectively. Our Nd results agree with limited results from was one of the first metamorphic core complexes to be Farmer and DePaolo (89:10141–10160, 1984). Although described. Despite its status as a type example, relatively the Catalina Granite seems to have a significant juvenile little is known about precise ages and origins of the component based on Nd and Hf, most of the Laramide and intrusive rocks that make up most of the crystalline core. Wilderness intrusions contain Nd and Hf compositions U–Pb and Hf isotopic data by laser ablation–inductively lying close to the evolution of 1.44-Ga Oracle Granites, a coupled plasma–mass spectrometry from zircons and Nd fact that is confirmed by the U–Pb data, which show both isotopic results from whole rocks were obtained for 12 1.7- and 1.4-Ga zircon cores in these samples, with 1.4 Ga granitoids ranging from 1,440 to 26 Ma. Results confirm as the dominant core age. In order to become the dominant that the 1.44-Ga Oracle Granite extends through the Cat- source of most of the 72–45-Ma magmas, the Oracle pluton alina Range as variably mylonitic granite and banded must not only extend across the whole Catalina region, but gneiss. Laramide intrusions (67–73 Ma) display initial eNd also have abundant deep-seated equivalents to provide values -5to-8 and eHf from -7.5 to -9. Magmatic ages magma sources. for the prominent white granite sills of the Wilderness suite are 46–57 Ma, in agreement with Terrien (2012), and these Keywords Santa Catalina metamorphic core complex granites have initial eNd values -8to-10 and eHf from -7 Granite origins U–Pb ages Hafnium isotopes to -14. Lastly, the undeformed Catalina Granite has an age Neodymium isotopes of 26 Ma, with an initial eNd and eHf of -6 and -8,

Introduction Communicated by J. Hoefs.

Electronic supplementary material The online version of this The Santa Catalina metamorphic core complex (Fig. 1), article (doi:10.1007/s00410-013-0859-4) contains supplementary part of a chain of NW-trending metamorphic core com- material, which is available to authorized users. plexes stretching across Arizona (Banks 1980; Davis 1980), is among the ﬁrst occurrence to have been recog- K. F. Fornash P. J. Patchett G. E. Gehrels Department of Geosciences, University of Arizona, nized as a ‘‘metamorphic core complex’’ (Davis and Coney Tucson, AZ 85721, USA 1979). The Santa Catalina Mountains became the focus of further study, which tended to reinforce their status as a Present Address: type example of Cordilleran metamorphic core complex K. F. Fornash (&) Department of Earth Sciences, University of Minnesota, formation (Dickinson 1991; Force 1997). As is typical of Minneapolis, MN 55455, USA most metamorphic core complexes in the western North e-mail: [email protected] American Cordillera, the Catalina Mountains have a gently dipping mylonitic foliation and lineation, intrusive igneous J. E. Spencer Arizona Geological Survey, 416 West Congress Street, rocks ranging from Precambrian to Cenozoic in age, mid- Suite 100, Tucson, AZ 85701, USA Tertiary K–Ar cooling ages, and a detachment fault 123 Contrib Mineral Petrol

Fig. 1 Geologic map of the Catalina metamorphic core complex, not differentiated from mixed gneissic rocks in this map. Figure 2 Arizona, showing the locations of samples. Note that the ‘‘leucog- (area of box) shows the different leucogranite units. Sources of map ranites (Eocene)’’ near the center of the range are part of the data include Banks (1974), Force (1997), Dickinson (1999), Spencer Wilderness suite granites, but the main leucogranite occurrences are et al. (2000), Spencer and Pearthree (2004)

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Fig. 2 Geologic map of the Wilderness suite sills (after Force 1997), showing the locations of most Wilderness samples, and the sample of foliated granite (KJJ09-1) taken to test whether this material in the Catalina core complex is deformed Oracle Granite separating faulted and tilted syn-extensional sedimentary plasma–mass spectrometry (LA–ICP–MS), we present U– rocks in the hanging wall from plastically deformed mid- Pb and Hf data from zircons, combined with whole-rock crustal rocks in the footwall (Coney 1980; Davis 1980; Nd analyses of granites from the Catalina Mountains in Keith et al. 1980; Armstrong 1982). order to determine the origins and evolution of the volu- Although the Santa Catalina metamorphic core complex minous granitoid magmas that were closely tied to the has been studied since the early 1900s, relatively little is development of this metamorphic core complex in late known about the ages and origins of the deformed footwall Mesozoic and Tertiary time. plutons in the region as much of the previous work focused on structural mapping of the region (Creasey 1965; 1967; Banks 1974) and interpreting the origins of the pervasive Geologic history and previous work low-angle mylonitic fabric. Furthermore, much of the early geochronological work was difﬁcult to interpret as a result The Santa Catalina Mountains, together with the Rincon of the mylonitic overprint, reset mid-Tertiary K–Ar ages, and Tortolita Mountains, forms a granitic-gneissic crys- and complex zircon growth histories, namely the presence talline complex within the Basin and Range province, a of older inherited cores and younger magmatic rims (Banks region of fault block mountains and down-dropped valleys 1980; Keith et al. 1980; Force 1997; Shakel 1978). (Fig. 1). The crystalline core is generally fault bounded, Until the recent advent of microbeam analytical tech- with intrusive contacts only to the north and northeast niques, separating the various phases of crystallization was (Keith et al. 1980). The Catalina fault, the low-angle difﬁcult, thus preventing the accurate dating of many detachment surface that separates rocks with brittle defor- granitoids. Using laser ablation–inductively coupled mation in the hanging wall from ductilely sheared rocks in

123 Contrib Mineral Petrol the footwall, lies along the south flank of the complex Intrusion of seven peraluminous granitic sills (Figs. 1, 2, (Dickinson 1991). This detachment fault is interpreted to 3) inflated the supracrustal sequence and its immediately have accommodated extension and tectonic denudation underlying basement by *4 km (Force 1997). These sills, during the mid-Tertiary which resulted in mylonitization of termed the ‘‘Wilderness suite’’ by Keith et al. (1980), range the structurally lower rocks (Naruk and Bykerk-Kauffman in thickness from a few tens of meters to over 1 km in the 1990; Spencer 2006). The core of the Catalina complex is case of the Wilderness sill itself. The sequence is capped composed of both undeformed and deformed plutons by an eighth body, the Mt. Lemmon Pegmatite–Aplite ranging from Precambrian to Cenozoic in age, as well as intrusion, exposed near the summit of the range. The sills sedimentary and metasedimentary rocks ranging from mid- are all peraluminous, although only two (Wilderness and Proterozoic to Mesozoic in age. These plutons and any Thimble Peak) have relatively abundant muscovite and relevant geochronology are discussed in greater detail below. contain garnet (Keith et al. 1980; Coney and Reynolds The oldest unit exposed in the region is the mid-Protero- 1980). Each of the sills has a distinct composition, and all zoic Pinal Schist (Ransome 1903; Cooper and Silver 1964; are variably foliated, with the Catnip Sill displaying a Silver 1978). It consists of both metasedimentary and meta- banding structure that may be cumulate in origin (Force volcanic rocks, which underwent a major deformational 1997). Estimates of the emplacement depths for the Wil- event at *1.65 Ga (Karlstrom and Bowring 1988; Silver derness suite based on stratigraphic reconstructions and 1978). In neighboring ranges to the south, much of the vol- contact aureole assemblages range from 3 to 6 km (Banks canism is also close to 1.65 Ga in age (Eisele and Isachsen 1980; Palais and Peacock 1990). Previous radiometric age 2001). The Pinal Schist is only exposed in very limited areas determinations of the Wilderness suite sills range from 43 of the Santa Catalina Mountains, but forms the basement into to 57 Ma (Terrien 2012; Shakel et al. 1977; Reynolds et al. which the 1.4-Ga Oracle Granite (Peterson 1938) was em- 1986). placed. Oracle granite accounts for *80 % of the exposed The final plutonic event in the Santa Catalina Mountains basement rock in the Catalina Range. These Precambrian was intrusion of the Catalina Granite (DuBois 1959; crystalline basement rocks are unconformably overlain by a McCullough 1963). The Catalina Granite is mineralogi- 1.1-km-thick sequence of mid-Proterozoic Apache Group, cally distinct from the Precambrian, Laramide, and Eocene dominantly clastic sedimentary rocks, and Cambrian to plutons in the region and is characterized by differences in Devonian carbonate and clastic sedimentary units. the modal abundances of quartz, K-feldspar, and biotite, This sequence of rocks was thickened by thrust faulting and by the accessory minerals hornblende and sphene during the Late Cretaceous–early Tertiary Laramide (Keith et al. 1980). The Catalina Granite is a roughly orogeny (the regional name for the main phases of Meso- semicircular pluton at the western edge of the mountain zoic–Cenozoic Cordilleran tectonism), as well as a series of range (Fig. 1), and its western continuation lies deeply intrusive events of Laramide, Eocene, and Oligocene age. buried beneath gravels following basin-and-range faulting. The Laramide intrusions (‘‘Leatherwood suite’’) are pre- Radiometric age determinations for the Catalina Granite dominantly calc-alkaline granodiorite, granite, and diorite, are all mid-Tertiary and range from 23.5 to 28 Ma (Keith characterized by abundant biotite (15–25 %) and several et al. 1980; Reynolds et al. 1986). A U–Pb age of 27 Ma textural varieties of epidote (Keith et al. 1980; Creasey was obtained from concordant zircon analyses (Shakel 1967). The presence of epidote has led to significant dis- et al. 1977). cussion of the depth of emplacement of the Laramide Figure 3 is a representative cross section, along a tra- intrusions, with estimates ranging from 7.5 to 14 km (Pa- verse line indicated in Fig. 1, showing the approximate lais and Peacock 1990) to in excess of 20 km (Anderson relations of the granitoid bodies. The relations of Oracle et al. 1988). The assignment of a Laramide (75–55 Ma) age Granite, Wilderness suite sills, Rice Peak Porphyry, granite to these plutons is based primarily on geologic relation- of Alamo Canyon, and surface exposures of Leatherwood ships observed in the field and an age of 68.5 Ma from a Granodiorite are more or less as observed in the field, Rb–Sr whole-rock isochron of the type pluton (Keith et al. whereas the deeper occurrences of Leatherwood and Cat- 1980; Reynolds et al. 1986). Zircons from the San Manuel alina plutons are less well constrained, and are included in Porphyry to the immediate north of the Santa Catalina Fig. 3 for diagrammatic reasons. What is evident from Mountains yield ages of 68.1 ± 3.0 and 67.8 ± 2.3 Ma Fig. 3, as well as Figs. 1 and 2, is how the granitoids (Unruh in Force 1997). No reliable radiometric ages have collectively form the majority of the mass of the Santa been published for the Rice Peak Porphyry, although Catalina Mountains, making their characterization and attempts to date it using U–Pb on zircon have suggested a origin of great importance to the evolution of this meta- roughly Laramide (71 ± 8 Ma) age (Unruh in Force 1997). morphic core complex.

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Fig. 3 Cross section along line A–A0 (shown in Figs. 1, 2) illustrating the relationships between the granitoid units sampled in this study. Note that the core complex consists almost entirely of presumed deformed Oracle Granite or younger granitoids emplaced into it

Samples in the present study Of the seven Eocene Wilderness suite sills identified by Force (1997), five were sampled for this study. The topo- In order to determine the ages and evolution of the rocks in graphically lowest (Seven Falls Sill) and highest sill the Catalina metamorphic core complex, twelve granitoids (Spencer ‘‘Lens’’ of Force 1997), as well as three inter- were sampled from Precambrian basement rocks and vening sills (Wilderness, Catnip, and Gibbon Mountain) intrusions emplaced during each of the three main mag- were chosen to evaluate correlations between age, isotopic matic episodes. Zircon separates from samples previously values, and topographic position and to shed light on the collected and analyzed by Spencer and Gehrels were used thermal evolution of the region. All of the sills are variably for the U–Pb and Hf analyses for four samples, with the foliated, peraluminous granites. whole-rock Nd samples collected from the same outcrop One granite from high along the Catalina Highway where possible. For the purposes of this study, all samples (KJJ09-4) was mapped as Knagge Granite by Force (1997), were treated as being igneous in origin. Representative another example of peraluminous Eocene granite in the modes and more detailed petrography, as well as sample upper part of the topographic sequence. Our sample, from a locations, are provided in Online Resource 1. Figures 1 and new quarried outcrop area not available before the publi- 2 show map locations of all samples. cation of Force (1997), was taken from close to the mapped The most widely exposed basement rock in the Catalina contact between Knagge Granite and the Wilderness Sill Mountains is the Oracle Granite, and two samples (foliated (Fig. 1). We show our sample as Knagge Granite in Fig. 1 and non-foliated) were collected. The non-foliated sample and in data tables. KJJ09-9 (Fig. 1), from near the town of Oracle and beyond The Catalina Granite was sampled at the western foot of any Laramide or core complex deformation zones, was the Santa Catalina range, at a location close to the center of previously collected and analyzed for Sr, Nd, and Hf iso- the semicircular exposed part of the pluton (Fig. 1). topes by Farmer and DePaolo (1984) and Barovich (1991). From further south within the Catalina Core Complex, we collected the foliated rock KJJ09-1 (Figs. 1, 2) presumed to Analytical methods be Oracle Granite, in order to evaluate whether the banded gneissic rocks present over wide areas of the Catalina Zircon preparation frontal range are in fact Oracle Granite. Three intrusions from the Laramide (Cordilleran) tec- Zircon crystals were extracted from samples using tradi- tonic episode were sampled: the Rice Peak Porphyry, the tional methods of crushing and grinding, followed by Leatherwood Granodiorite, and the granite of Alamo heavy mineral separations with a Wilfley table, heavy Canyon (Fig. 1). Apart from minor variants within the liquids, and a Frantz magnetic separator. Samples were sampled intrusions, and the small Little Hill stock in the processed such that all zircons were retained in the final northwestern Santa Catalina Mountains (Fig. 1; Spencer heavy mineral fraction. Of these, *40 grains from each et al. 2003), these three samples represent both the com- sample were incorporated into a 100 epoxy mount together positional and geographic range of exposed Laramide with fragments of our Sri Lanka zircon standard for U–Pb intrusive rocks in the area. Compositions for the intrusions analysis (Gehrels et al. 2008), and by R33, Temora, 91500, range from granite to granodiorite and often contain epi- Plesovice, Mud Tank, and FC 1 zircon standards for Hf dote as an accessory mineral. analysis (Woodhead and Hergt 2005; Slama et al. 2008).

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The mounts were polished down to a depth of *20 l with measurements were made in static mode, using Faraday 2,500 grit sandpaper and 9 l lapping film to expose grain detectors with 3 9 1011 ohm resistors for 238U, 232Th, interiors. Cathodoluminescence (CL) images were acquired 208Pb–206Pb, and discrete dynode counters for 204Pb and for all samples to identify complexities (e.g., zonation, 202Hg. Ion yields were approximately 0.8 mv per ppm. overgrowths, and high-U domains) and to provide navi- Each analysis consists of one 15-s integration with the laser gational aids for placement of laser pits. All CL images are off (for instrumental backgrounds), 15 1-s integrations with presented in Online Resource 2, and selected examples the laser firing, and a 30-s delay to remove the previous appear in Fig. 4 here. sample and prepare for the next analysis. The ablation pit is For samples where imaging revealed major heteroge- *15 l in depth. neities in the zircon crystals, a U–Pb analysis spot was For each analysis, the errors in determining 206Pb/238U taken in both the interior (core) and exterior (rim) portions and 206Pb/204Pb result in a measurement error of *1–2 % of the grain (Fig. 4). In the case of the Hf isotopic analyses, (at 2-r level) in the 206Pb/238U age. The errors in mea- the analysis spots were taken directly over the pits where surement of 206Pb/207Pb and 206Pb/204Pb also result in the U–Pb ages had been determined or in some cases *1–2 % (at 2-r level) uncertainty in age for zircon grains adjacent to the U–Pb pit but in the same CL zone. that are [1.0 Ga, but errors are substantially larger for All Pb and Hf isotopic data were acquired at the Arizona younger grains due to the low intensity of the 207Pb signal. Laserchron Center on a Nu Plasma HR ICP–MS, coupled Common Pb correction was accomplished by using the to a New Wave 193 nm ArF laser ablation system equip- measured and Hg-corrected 204Pb and assuming an initial ped with a New Wave SuperCell. Details specific to each Pb composition from Stacey and Kramers (1975). Absolute analysis are provided below and in Gehrels et al. (2008) for uncertainties of 1.5 for 206Pb/204Pb and 0.3 for 207Pb/204Pb U–Pb analyses and in Cecil et al. (2011) for Lu–Hf anal- are applied to these compositional values based on varia- yses. CL images were acquired with a Hitachi 3400 N SEM tion in Pb isotopic composition in modern crystalline rocks equipped with a Gatan Chroma CL detector system (https:// and sediments. sites.google.com/a/geoarizonasem.org/semsite). In-run analyses of fragments of a Sri Lankan zircon standard (generally every fifth measurement), with a U–Pb geochronology of zircons known age of 563. 5 ± 3.2 Ma (2-r error, Gehrels et al. 2008), were used to correct for interelement fractionation The U–Pb analyses involve ablation of zircon, using a spot of Pb/U. The uncertainty resulting from the calibration diameter of 30 l. The ablated material is carried in helium correction is generally 1–2 % (2-r) for both 206Pb/207Pb into the plasma source of the mass spectrometer, which is and 206Pb/238U ages. equipped with a flight tube of sufficient width that U, Th, The reported ages of samples are determined from the and Pb isotopes are measured simultaneously. All weighted mean (Ludwig 2008) of the 206Pb/238Uor

Fig. 4 Cathodoluminescence images of representative zircons from the Wilderness suite (1–3) and Laramide (4–6) granites 1. 3. 5. 1419.2 Ma showing analysis spots and ages 1448.7 Ma 55.6 Ma for older inherited cores and younger magmatic rims. 67.7 Ma Photographs are from intrusions as follows: 1 Catnip Sill, 2 and 3 51.1 Ma Spencer Sill, 4 Rice Peak 1320.9 Ma Porphyry, 5 and 6 granite of Alamo Canyon 68.8 Ma 2. 4. 6.

1426.2 Ma 1414.8 Ma 1687.7 Ma

58 Ma 72.9 Ma

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206 207 Pb/ Pb ages of the concordant and overlapping anal- were used for the calculation of eHf values, and the inter- yses. The systematic error, which includes contributions preted age of crystallization is based on the U–Pb analyses. from the standard calibration, age of the calibration stan- In the following sections, eHf (Tmag) is used to denote the dard, composition of common Pb, and U decay constants, eHf values at the time of crystallization of the unit. Hafnium is generally *1–2 %. This systematic error is added qua- model ages are not calculated because the Lu/Hf of the dratically to the weighted mean error to determine the final source material is unknown. uncertainty of the age, which is reported at 2-r. Whole-rock Nd isotopic analysis Hf isotopic analysis Whole-rock Sm–Nd separations followed the procedure The Lu–Hf isotopic data were acquired using 10 fixed and analytical conditions outlined in Patchett and Ruiz Faraday detectors, equipped with 3 9 1011 ohm resistors, (1987), and mass spectrometry was performed on a VG- measuring masses 171Yb–180Hf. In situ data were collected 354 thermal mass spectrometer with six collectors. using a 40-l-diameter spot size and a laser pulse frequency Samarium concentrations were measured by multicollector of 7 Hz. The laser was run in constant energy mode with an in static mode, while Nd concentrations were measured by output energy of 8 mJ, which corresponds to an energy multicollector in dynamic (peak-jumping) mode. The density of about 5 J/cm2 and an estimated drill rate of average 143Nd/144Nd for three La Jolla standards measured 0.7 lm/s. Under these conditions, total Hf beams range during the analytical sessions was 0.511869 ± 3. from 2 to 7 V for standard zircons. The analytical routine starts with 40 s of background measurement (on peaks) followed by 60 s of laser ablation with a 1-s data integration time. Results Correction for the isobaric interference of 176Yb and 176Lu with 176Hf follows the procedure of Woodhead et al. New U–Pb age, Nd, and average Hf isotopic data are (2004). Correction for the interference of 176Yb is deter- summarized in Tables 1, 2, and 3. For U–Pb age and Hf mined by monitoring 171Yb and assuming a 176Yb/171Yb isotopic results for each analysis pit, see Online Resources ratio of 0.901691 (Vervoort et al. 2004). Before the inter- 4 and 5. Nd and Hf isotopic information is summarized in ference corrections are applied, the expected contributions Figs. 5 and 6. CL images for each zircon grain are provided from 176Yb to 176Lu are corrected for mass fractionation in Online Resource 2. using 173Yb/171Yb as a monitor ratio (Vervoort et al. 2004), With the exception of the non-foliated Oracle Granite unless 171Yb has a very low signal intensity (\5 mV), in and the Catalina Granite, all samples yield a cluster of which case a fractionation factor derived from Hf is used. young ages that reflect the age of magmatic crystallization Correction for the interference of 176Lu is determined by and older ages from zircon cores inherited from source or monitoring 175Lu and using 176Lu/175Lu = 0.02653 country rocks. The younger ages record latest Cretaceous (Patchett 1983). All of the above corrections are done on a or early Tertiary crystallization, whereas nearly all inher- line-by-line basis, meaning the interference-corrected ited components are *1.4 or 1.6–1.7 Ga in age. The non- 176Hf/177Hf is determined for each integration. The repor- foliated Oracle Granite and the Catalina Granite yield only ted 176Hf/177Hf is based on the average and standard error a single set of ages that reflect the age of magmatic of all integrations from an analysis (with a 2-r filter crystallization. applied to remove outliers). Zircon U–Pb ages from the samples of foliated and non- The accuracy of Hf–Lu–Yb isotopic measurements is foliated Oracle Granite yield ages of 1,440 ?20/-20 and ensured by analysis of both solutions of JMC 475 doped 1,440 ?20/-21 Ma, respectively. These ages are broadly with varying amounts of Yb and Lu and by analyses of the consistent with those reported for the Oracle Granite in Hf standards mounted with each set of unknowns. Online Reynolds et al. (1986) and are similar to ages of resource 3 shows the results of these measurements. 1,434.5 ± 3.4 and 1,433.5 ?2.1/-1.2 Ma determined by Because all solutions and standard zircons yield values that U–Pb TIMS (thermal-ionization mass spectrometry) for are statistically indistinguishable from the known values, Oracle Granite in nearby ranges to the northwest and west no correction factors were applied to the unknowns. (Spencer et al. 2003). The eNd (t) values obtained for the The 176Hf/177Hf at the time of crystallization is calcu- foliated and non-foliated Oracle Granite also show little lated from measurement of present-day 176Hf/177Hf and variation and are ?1.0 and ?0.4, respectively. These val- 176Lu/177Hf and using the decay constant of 176Lu ues generally agree with the Nd values obtained for the (k = 1.867 9 10-11, from Scherer et al. 2001;So¨derlund non-foliated Oracle Granite by Farmer and DePaolo (1984) et al. 2004). The chondritic values of Bouvier et al. (2008) and Barovich (1991). 123 Contrib Mineral Petrol

Table 1 Sample of U–Pb ages Sample Unit Magmatic 2r Metamorphic 2r Inherited components age (Ma) age (Ma) Age (Ma) 2r Age (Ma) 2r

Catalina Granite KJJ 10-1 Catalina Granite 25.8 ?0.4/-0.5 Wilderness suite (in ascending topographic sequence) KGJ 10-3 Seven Falls Sill 55.2 ?4.6/-3.2 45.1 ?1.5/-2.0 1,438 ±19 1,664 ±25 KGJ 09-2 Gibbon Mtn. Sill 57.2 ?1.2/-3.0 46.0 ?1.2/-1.2 1,451 ±9 KJJ 09-3 Catnip Sill 56.6 ?2.4/-3.3 48.4 ?2.9/-1.2 1,431 ±24 KJJ 09-5 Wilderness Sill 45.8 ?0.9/-2.0 1,442 ±5 KJJ 09-4 Knagge Granite 49.1 ?4.8/-2.5 1,439 ±10 1,723 ±17 KJJ 09-6 Spencer Sill 56.4 ?2.8/-1.2 1,428 ±17 1,702 ±22 Laramide intrusives KJJ 09-8 Rice Peak Porphyry 73.0 ?1.5/-1.1 1,446 ±14 KJJ 10-2 Granite of Alamo Canyon 67.2 ?1.1/-2.4 1,443 ±8 1,675 ±51 KJJ 09-7 Leatherwood granodiorite 69.1 ?1.2/-2.9 1,443 ±6 1,709 ±29 Precambrian Oracle Granite KJJ 09-9 Oracle Granite 1,440 ?20/-20 KJJ 09-1 Oracle Granite, foliated 1,440 ?20/-21 1,642 ±15

In contrast to the U–Pb and Nd data, Hf values differ cores and returned magmatic U–Pb ages of 69.1 ?1.2/-2.9 between the non-foliated and foliated samples of the Oracle and 67.2 ?1.1/-2.4 Ma, respectively. Little difference is

Granite. Zircons from the non-foliated sample of Oracle observed between the initial eNd (-7.7 and -7.6, respec- Granite lack inherited cores and have an average eHf tively) and eHf (Tmag)(-8.1 ± 1.3 and -9.3 ± 1.2) values (1.44 Ga) of 4.2 ± 1.2 (2-r), close to the values measured (Figs. 5, 6) of the two samples, suggesting that the two for whole rocks by Barovich (1991). However, the foliated units are genetically related. The Rice Peak Porphyry also sample of Oracle Granite contains 1.7-Ga inherited cores contains 1.7- and 1.4-Ga cores, but has a slightly older and appears to have two distinct 1.4-Ga zircon populations: magmatic age of 73.0 ?1.5/-1.1 Ma. With the exception those with a present-day eHf value \-16 and those with a of the Precambrian basement rocks, the Rice Peak Por- present-day eHf value [-16. The zircon grains with pres- phyry has the most radiogenic eNd (t)(-4.9) and one of the ent-day eHf values \-16 are interpreted here as reﬂecting most radiogenic eHf (Tmag)(-7.5 ± 2.3) values. It also the magmatic eHf values and yield an eHf (1.44 Ga) of contained the oldest inherited zircon cores of any sample, 5.8 ± 2.7. The eHf (1.44 Ga) for the zircon grains with with two cores returning ages of [2,000 Ma. elevated present-day eHf values is quite variable, ranging Zircons from all samples of the Wilderness suite sills from ?16.3 to ?46.2. The two 1.7-Ga cores yield an contained inherited cores; however, only three (Knagge average eHf (Tmag) value of ?11.5. Granite, Spencer Sill, and Seven Falls Sill) contained older These apparently disturbed Hf isotopic values are not 1.6–1.7-Ga cores. We list the age and isotopic results in discussed further because we do not have concrete data that ascending topographic sequence for the sills. The struc- constrain an interpretation. However, our best hypothesis turally lowest sill, the Seven Falls Sill, returned a magmatic 176 177 to explain elevated Hf/ Hf in zircon of the gneissic age of 55.2 ?4.6/-3.2 Ma and has an eNd (t) value of 1.4-Ga granite is that Tertiary mylonitization caused -10.2 and an eHf (Tmag) value of -13.9 ± 3.8. The Gibbon mobilization of chemical components from rare earth ele- Mountain Sill has a magmatic age of 57.2 ?1.2/-3.0 Ma ment-rich minerals such as apatite, leading to redistribution and has an eNd (t) value of -9.0 and an eHf (Tmag) value of of radiogenic Hf grown over the 1.4-billion-year life span -12.6 ± 3.1. The Catnip Sill has a magmatic age of 56.6 of the granite. Once mobilized from phases like apatite, ?2.4/-3.3 Ma and an eNd (t) value of -9.7 and an eHf uptake of Hf by zircon, even under modest metamorphic (Tmag) value of -12.6 ± 2.1. The foliated Wilderness sill conditions, might be probable. has an age of 45.8 ?0.9/-2.0 Ma and an eNd (t) value of Zircons from the Leatherwood Granodiorite and the -9.4 and an eHf (Tmag) value of -6.7 ± 1.5. The Knagge granite of Alamo Canyon contained both 1.7- and 1.4-Ga Granite has an age of 49.1 ?4.8/-2.5 Ma and an eNd

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Table 2 Sm–Nd isotopic data

147 144 b 143 144 c Sample Unit Description Age Sm Nd Sm/ Nd Nd/ Nd eNd(0) eNd T (DM) (t) (Ma) (ppm) (ppm) (t)d (Ma)

Catalina Granite KJJ 10-1 Catalina Granite Granite 25.8 9.06 51.30 0.1067 0.512311 ± 7 -6.4 -6.1 1,045 Wilderness suite (in ascending topographic sequence) KGJ 10-3 Seven Falls Sill Peraluminous 55.2 2.96 21.25 0.0841 0.512074 ± 9 -11 -10.2 1,141 granite KJJ 09-2 Gibbon Mtn. Sill Peraluminous 57.2 3.27 22.33 0.0885 0.512136 ± 11 -9.8 -9 1,106 granite KJJ 09-3 Catnip Sill Peraluminous 56.6 4.76 32.85 0.0876 0.512099 ± 9 -10.5 -9.7 1,141 granite KJJ 09-5 Wilderness Sill Peraluminous 45.8 2.92 14.79 0.1193 0.512133 ± 8 -9.9 -9.4 1,466 granite KJJ 09-4 Knagge Granite Peraluminous 49.1 2.62 12.92 0.1225 0.512102 ± 8 -10.5 -10 1,568 granite KJJ 09-6 Spencer Sill Peraluminous 56.4 3.39 18.62 0.1099 0.512177 ± 9 -9 -8.4 1,271 granite Laramide intrusives KJJ 09-8 Rice Peak Porphyry Hypabyssal granite 73.0 3.70 19.83 0.1129 0.512349 ± 11 -5.6 -4.9 1,052 KJJ 10-2 Granite of Alamo Granite 67.2 4.69 25.75 0.1101 0.512210 ± 7 -8.4 -7.6 1,226 Canyon KJJ 09-7 Leatherwood Granodiorite 69.1 5.44 30.24 0.1088 0.512208 ± 9 -8.4 -7.7 1,212 granodiorite to granite Precambrian Oracle Granite KJJ 09-9 Oracle Granite Granite 1,440 9.24 44.82 0.1246 0.512004 ± 11 -12.4 1 1,772 KJJ 09-1 Oracle Granite, Granite 1,440 9.33 43.43 0.1298 0.512025 ± 9 -12 0.4 1,845 foliated Pinal Schist CAT-3 Pinal Schista Schist 1,700 – 41.63 0.1163 0.511789 ± 9 -16.6 1 2,000 a Eisele and Isachsen (2001), sampled at Locality 1 from Force (1997) b 2-r error is 0.5 % or better c 143Nd/144Nd error is 2-r d 2-r error is 0.2 epsilon units

(t) value of -10 and an eHf (Tmag) value of -9.9 ± 2.0. In addition to the presence of inherited cores, zircons The Spencer Sill has an age of 56.4 ?2.8/-1.2 Ma and from the three lowest Wilderness sills (Seven Falls Sill, an eNd (t) value of -8.4 and an eHf (Tmag) value of Gibbon Mountain Sill, and Catnip Sill) also contained a -10.6 ± 2.8. The U–Pb ages are in close agreement with younger, *45-Ma rim overgrowth. These rims generally those obtained by Terrien (2012). Because there are appear bright in CL images (Data Repository Fig. 1) and reversals in age through the ascending topographic have average U concentrations ranging from 243 to sequence, these data suggest that there is no rigorous cor- 439 ppm and average U/Th ratios ranging from 2.6 to 17.8. relation between the age of emplacement and the structural These U concentrations and U/Th ratios are generally position of the sill. This lack of a simple progression in lower than those measured for the portions of the zircon value is also true for eNd (t) and eHf (Tmag). that crystallized at *55 Ma (average U concentrations Although Sample KJJ 09-4 was mapped as the Knagge 498–1,597 ppm, average U/Th ratios 5.1–19.4) and appear Granite by Force (1997), our inability to ﬁnd any pluton-to- as darker ‘‘mantles’’ in CL images (Data Repository pluton contact in the large new exposure, the petrographical Fig. 1). Little to no difference is observed between the similarities of the Knagge sample to Wilderness Granite, as initial eHf values of the *45-Ma portions and the *55-Ma well as the very similar age and Nd, Hf isotopic data obtained portions of the zircon. Terrien (2012) also documented for the two samples may well indicate that the Knagge younger zircon growth in zircons from the Gibbon Granite and Wilderness Granite are genetically related. Mountain and Seven Falls Sill; however, the average age

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Table 3 Lu–Hf isotopic data

176 177 c 176 177 d Sample Unit Age 1.7 1.4 Lu/ Hf Hf/ Hf eHf eHf (t) (t) (Ma) core core (0)

Catalina Granite KJJ 10-1 Catalina Granite 25.8 0.001233 ± 0.00021 0.282549 ± 0.000026 -8.3 -7.8 ± 0.9 Wilderness suite (in ascending topographic sequence) KGJ 10-3 Seven Falls Sill 55.2 990.001329 ± 0.00039 0.282359 ± 0.000106 -15.1 -13.9 ± 3.8 KJJ 09-2 Gibbon Mtn. Sill 57.2 9 0.001632 ± 0.00031 0.282395 ± 0.000087 -13.8 -12.6 ± 3.1 KJJ 09-3 Catnip Sill 56.6 9 0.001133 ± 0.00015 0.282394 ± 0.000059 -13.8 -12.6 ± 2.1 KJJ 09-5 Wilderness Sill 45.8 9 0.002193 ± 0.00067 0.282568 ± 0.000043 -7.7 -6.7 ± 1.5 KJJ 09-4 Knagge Granite 49.1 990.002339 ± 0.00062 0.282476 ± 0.000057 -10.9 -9.9 ± 2 KJJ 09-6 Spencer Sill 56.4 990.001953 ± 0.00048 0.282453 ± 0.000081 -11.7 -10.6 ± 2.8 Laramide intrusives KJJ 09-8 Rice Peak Porphyry 73.0 990.001284 ± 0.00041 0.282530 ± 0.000064 -9.0 -7.5 ± 2.3 KJJ 10-2 Granite of Alamo 67.2 990.000890 ± 0.00038 0.282480 ± 0.000033 -10.8 -9.3 ± 1.2 Canyon KJJ 09-7 Leatherwood 69.1 990.000742 ± 0.00054 0.282514 ± 0.000036 -9.6 -8.1 ± 1.3 granodiorite Precambrian Oracle Granite KJJ 09-9 Oracle Granite 1,440.4 0.001559 ± 0.00023 0.282030 ± 0.000031 -26.7 4.2 ± 1.2 KJJ 09-1 Oracle Granite, foliated 1,439.7 9 0.001552 ± 0.00029 0.282075 ± 0.000075 -25.1 5.8 ± 2.7 KB Oracle Granitea 0.014410b 0.282446 ± 0.000016 -1.2 6.5 ± 0.8 90-110 KB Oracle Granitea 0.016110b 0.282520 ± 0.000026 -9.4 7.5 ± 1.1 90-111

9 Core present in population of analyzed zircons, blank absent in analyzed zircons a Whole-rock data from Barovich (1991) b 2-r error is 1 % or better c Reported 176Lu/177Hf values are the average of several analysis spots for each granite, with error derived from statistics on that average d176 Hf/177Hf error is 2-r

for the young zircon growth in their sample of the Gibbon and using eNd and eHf values in studies of magmatic and Mountain Sill was younger, at *38 ± 2 Ma. crustal evolution, the determination of accurate ages for the The U–Pb age obtained for the Catalina Granite (25.8 plutons in this region was an important ﬁrst step in con- ?0.4/-0.5 Ma) is in close agreement with the previous age straining the sources of granites in this region. determinations of 23–28 Ma (Reynolds et al. 1986). None Previous studies (e.g., Farmer and DePaolo 1983, 1984) of the zircons contained inherited cores. The eNd(t) value have suggested that the source regions of granites can be for the granite is -6.1, and the eHf (Tmag)is-7.8 ± 0.9 determined if the isotopic compositions of both the granites (Figs. 5, 6). and their potential mantle and crustal sources are known. In the Catalina region, one potential source for the granites is the exposed Precambrian basement. The most widely Discussion exposed basement rock is the 1.4-Ga Oracle Granite, which

has an initial eNd value around ?1 and an initial eHf value Background for the origin of granitoids of ?4to?6. The *1.7-Ga Pinal Schist is also exposed in parts of the Catalinas (Fig. 1), as part of a N–S trending The ages of the intrusive rocks in the Catalina metamorphic belt offset by the Geesaman and Mogul faults (Force 1997). core complex prior to this study were only known from No hafnium data presently exist for the Pinal Schist, but an

K–Ar, Rb–Sr, and sparse U–Pb dates, and for many of the eNd (t) value of ?1 at 1.7 Ga was obtained by Eisele and units, no radiometric dating had ever been attempted. Isachsen (2001). Although not large in number nor ideal in Because the crystallization age is important in calculating geographical coverage, these data from Oracle and Pinal

123 Contrib Mineral Petrol

10 Figs. 5 and 6, along with the initial Nd and Hf isotopic values for the younger granitoids. 5 Figure 6, showing the Hf isotopic relations, requires additional explanation. The Hf isotopic evolution lines

0 shown for Oracle Granite are based on total-rock data (Barovich 1991). These evolution trends begin at the points labeled ‘‘TR’’ (total rock) at 1.44 Ga. In any much younger -5 Nd(t) melting or assimilation events, the total-rock Lu–Hf sys- Pinal Schist tematics should control the Hf isotopic composition of the -10 Oracle Granite magma. However, zircon of the Oracle Granite (labeled Laramide intrusives ‘‘Zr’’ at 1.44 Ga in Fig. 6) that is not melted, but never- Wilderness Suite -15 Catalina Granite theless entrained in the new magma, will retain its original DM evolution Hf isotopic composition (as well as 1.4-Ga U–Pb age -20 information). The original Hf isotopic composition is 1600 1200 800 400 0 retained because the Lu/Hf ratio of zircon is so low that Age (Ma) little to no Hf isotopic change occurs. By the time of Mesozoic-Tertiary magmatism, the unmelted zircon will Fig. 5 Initial eNd values of granites versus crystallization age. The depleted mantle (DM) evolution curve is from DePaolo (1981), and have very negative eHf values simply because it has been the Pinal Schist evolution is derived from the data of Eisele and left behind by 1.3–1.4 billion years of chondritic evolution. Isachsen (2001). The evolution trend for Oracle Granite is from this Hence, the points labeled ‘‘1.4-Ga cores’’ in Fig. 6, with paper, but agrees closely with determinations from the same outcrop by Farmer and DePaolo (1983) and Barovich (1991) Mesozoic and Tertiary eHf values of -20 to -25, represent broadly the same actual Hf isotopic ratio as the initial Oracle Granite zircon at 1.44 Ga. The same relationship 10 would be true for 1.7-Ga zircon cores, except that no Hf

TR isotopic data are available for 1.7-Ga rocks in order to 5 Zr make the comparison.

0 Because all of the Mesozoic and Eocene granites have 1.4-Ga cores within a signiﬁcant fraction of their zircon -5 crystals, and because the initial Nd and Hf isotopic compositions of the magmas lie close to the evolutionary lines

Hf -10 Oracle Granite Magmatic zircon for 1.44-Ga Oracle total-rock granites (Figs. 5, 6), it is Laramide intrusives -15 growth clear that Oracle Granite and possible deeper-seated Wilderness Suite equivalents must represent the dominant contributor to the -20 Catalina Granite Inherited young granitoids. This inference is the background for the 1.4 Ga zircon cores zircon -25 remaining discussion. We will ﬁrst deal with particulars for 1.7 Ga zircon cores each rock unit and then discuss broader issues about -30 magma and heat sources, the constitution of the crust under 1600 1200 800 400 0 the Catalina Mountains, the relation or non-relation of Age (Ma) leucogranite emplacement to core complex extension, as

Fig. 6 eHf values at the time of magmatism (Tmag) versus the well as the extent of Oracle Granite and any deep-seated crystallization age for granites. Evolution trends for total-rock Oracle equivalents. Granite are from the data of Barovich (1991), with eHf values recalculated using our U–Pb zircon age (1.44 Ga) and the chondritic values of Bouvier et al. (2008). For 1.44-Ga samples TR total-rock Origin of individual magmatic units Lu–Hf analyses from Barovich (1991), Zr U–Pb concordant zircon from this paper; all these initial ratios for Oracle Granite overlap, or The Laramide intrusions (67–73 Ma) have initial eNd and almost overlap, within 2-r error. Also shown are eHf values for inherited cores in the younger samples. ‘‘1.4-Ga cores’’ have eHf values that are generally higher than those obtained for essentially the same Hf isotopic composition as the initial Hf for the Eocene Wilderness granites (Figs. 5, 6, 7), with the Oracle zircon, with the different eHf values due solely to chondritic Rice Peak Porphyry having one of the most radiogenic eNd evolution since 1.4 Ga (-4.9) and eHf (-7.5) values of any sample. The Leath- erwood Granodiorite and the granite of Alamo Canyon lithologies can be used as a reference for discussion of the have eNd values that are *4 epsilon units above the evo- isotopic systematics of Cretaceous and Tertiary granitoids. lution curve for the Oracle Granite, but have eHf values that The bulk-rock evolution lines for these units are plotted in plot on the evolution curve for the Oracle Granite (Figs. 5, 123 Contrib Mineral Petrol

6). The results indicate that these granites were likely -6.7 to -12.7 (Figs. 5, 6, 7). These values all lie on or derived from sources dominated by Oracle Granite or very close to evolution trends for Oracle Granite, suggesting material coeval with it. This conclusion is supported by the that these granites were derived primarily from this Pre- presence of abundant 1.4-Ga cores in the zircon separates cambrian crystalline basement. Farmer and DePaolo (1983, that yield eHf (1,400) values within the observed range of 1984) and Wright and Haxel (1982) reached similar conclu- initial eHf for the Oracle Granite. sions for peraluminous granites in southern Arizona, the The Rice Peak Porphyry, which is largely conﬁned to northern Rocky Mountains, and the northern Great Basin. the area between the Geesaman and Mogul faults (Fig. 1) The mid-Tertiary Catalina Granite has initial eNd (-6.1) (Force 1997), has eNd and eHf values that are almost cer- and eHf (-7.8) values that are higher than the Precambrian tainly too high for the magma to have been derived entirely basement rocks, Laramide intrusions, and the Wilderness from the Oracle Granite, even when uncertainties about suite granites; only the Rice Peak Porphyry has comparable Oracle equivalents at depth are considered. Although the values (Figs. 5, 6, 7). While this suggests that the Catalina porphyry contains 1.4-Ga Precambrian cores which have Granite had more juvenile input than most other granitoids an average eHf (1,400) of ?6.6, close to the initial Hf value in the study, it is difﬁcult to constrain the source region as for the Oracle Granite obtained by Barovich (1991), the eHf the zircon grains lack inherited cores. (Tmag) values for the oldest cores ([1.6 Ga) in the sample For both the Laramide and Eocene intrusions, there is a range from -4.0 to -54.2. This large range of eHf values small discrepancy between the averages of the Nd and Hf for the oldest cores in this sample are likely a result of the results such that the Hf isotopic data appear to allow the fact that the Rice Peak Porphyries are enclosed within Mesozoic and Eocene granitoids to have been derived sedimentary rocks that contain detrital zircons from a essentially 100 % from Oracle Granite (Fig. 6), whereas variety of sources. These observations suggest that the Rice the Nd isotopic data seem to suggest a juvenile compo- Peak Porphyries are at least partially derived from the nent, because the Mesozoic and Eocene results lie 1–6 Oracle Granite, but with both more juvenile input than epsilon units above the Oracle Granite evolution trends either the Leatherwood Granodiorite or the granite of (Fig. 5). Deriving young granite 100 % from old granite is Alamo Canyon, plus a probable input from sedimentary not very plausible, because mass balance would require a rocks near or below the present exposure level. high degree of melting. A more realistic origin would The Eocene Wilderness suite granites, emplaced over a have the younger granites derived from deep-seated, less period of 11 million years (46–57 Ma), have initial eNd felsic equivalents of Oracle Granite, where the degree of ranging from -8.4 to -10.2 and initial eHf ranging from melting would not be implausible. The Sm/Nd ratios of possible deep-seated 1.4-Ga equivalents would be expected to be higher than the exposed Oracle Granite, gener- 8 Oracle Granite 1.4 Ga ating higher eNd values by Mesozoic time. Alternatively, if Laramide intrusives 72-67 Ma heat budgets for melting require a mantle-derived magma, 4 Wilderness Suite 57-45 Ma then the higher eNd values of Mesozoic and Eocene Catalina Granite 26 Ma granitoids could simply be due to admixing of a juvenile 0 mantle-derived component into the magmas. The fact that

eHf values do not appear to track either such a juvenile -4

Hf(t) input or deep-seated cumulates with higher Lu/Hf can be attributed to two factors. First, knowledge of the behavior -8 of Lu/Hf ratios in crustal differentiation is much less well Magmatic understood than for Sm/Nd ratios (e.g., Vervoort et al. -12 Nd + Hf 2000), so that we cannot predict with any conﬁdence what ratios deep-seated cumulate or residual equivalents of 1.4-Ga -16 magmas might look like in terms of Lu/Hf. Second, the -16 -12 -8-4 0 4 8 fact that zircon, the main carrier of Hf, did not melt Nd(t) anywhere close to completely in the Laramide and Eocene events (evidenced by the abundant 1.4-Ga cores), but then Fig. 7 Initial Nd and Hf epsilon values for the granitoids in the study. Samples are plotted at the respective time of their magmatism, so the was at least partially entrained in the magma, makes the Oracle point represents Nd and Hf at 1.44 Ga, whereas the points for Lu/Hf behavior quite complex. It would be difﬁcult to younger granites represent Mesozoic and Tertiary isotopic values. predict what Lu–Hf total-rock systematics would be seen Values for Laramide and Wilderness granitoids include only as a result of these complex processes, and the total-rock magmatic zircon, with inherited zircon and its Hf being excluded. Nd and Hf isotopic values are positively correlated with an expected Nd results are thus a better guide to bulk magmatic terrestrial array contributions. 123 Contrib Mineral Petrol

Basement of the Catalina region and extent of Oracle Melting from Oracle-dominated sources generates a Granite and equivalents very interesting question about the nature and disposition of Oracle Granite and materials related to it. Including the The close correspondence of U–Pb ages from samples of deformed Oracle lithologies of the Catalina Mountains the foliated and non-foliated Oracle Granite, as well as the together with the generally undeformed Oracle Granite to Nd isotopic results for these samples, confirms that the the north (Fig. 1) gives the pluton or plutons a batholithic widespread dark, melanosome component of augen gneis- dimension of [50 km horizontally. Classically, such a ses present in the Catalina front range consists largely of pluton might have been expected to represent the upper deformed Oracle Granite, as previously suggested by the part of a continuous mass extending upward from the very U–Pb and Rb–Sr data of Shakel et al. (1977) and Keith deep crust. Present-day views of plutonic geometries, et al. (1980). If this is the case, then deformed Oracle however, are much more along the lines of wide tabular Granite lithologies occupy a large volume of the Catalina– granitoid bodies without large extensions to depth. This Rincon Core Complex. would be a problem for our Catalina dataset, because 1.4- In addition, the conclusion that Oracle Granite and Ga materials are so dominant in the magma sources. Our lithologies of equivalent age and character dominated preliminary conclusion is that there must exist either one or magma sources for Mesozoic and Eocene granitoids more additional bodies of Oracle Granite at greater depth suggests that the crystalline massif can be regarded, from or that deeper-seated equivalents of the exposed Oracle a crustal evolutionary point of view, as 1.4-Ga felsic Granite do in fact occupy a volume extending many kilo- material in bulk composition and constitution, with the meters below the present exposure level. We do not have younger granitoids just representing mainly reprocessing any constraint on the depth of the granitoid magma sour- of the 1.4-Ga material. The result is that the whole mid- ces, but the coherent sets of magmatic Nd and Hf isotopic crustal section represented by the exposed lower plate of values suggest that sources would have lain more than just the core complex (Fig. 3) is to first order a 1.4-Ga crustal a few kilometers below the present level. The impression segment, a perception that generally accords with the created is that around 1.4 Ga, Oracle and related magma- concepts outlined in prior isotopic studies of southwest tism pervaded the crust over a large range of depth and USA continental crust and younger granites (e.g., Farmer represented very significant crustal addition. and DePaolo 1984; Bennett and DePaolo 1987). These If preexisting 1.4-Ga crustal material dominated the results are in contrast to recent studies of Mesozoic and source of the younger granitoids, then there is a question of Cenozoic plutonic rocks in the Sierra Nevada and the the origin of the heat for melting. If heat was provided by Coast Mountain Batholith where Nd, Sr, and Hf isotopes emplacement of mantle-derived magmas into the deep suggest greater production of young crust from accreted crust, then most of the mantle-derived material did not mix arc terranes (Cecil et al. 2011; Lackey et al. 2012a; Gir- into the felsic magmas and remained solidified in the deep ardi et al. 2012). crust (Hildreth 1981). On the other hand, it is possible, Although 1.4-Ga material was dominant in the source of given the large time span from 1.44 Ga to late Mesozoic, younger magmas, and in the case of Wilderness suite that self-heating (by radioactivity) of the deep crust was a intrusions, there were many thin dikes, sills, and veins of factor (Patinõ-Douce et al. 1990). felsic magma emplaced along with the larger sills, in no case were any Mesozoic or Tertiary granitoids derived Relation of magmatism to core complex formation from their immediate country rocks. No Catalina gneisses are true migmatites, grades of metamorphism are green- As with many other metamorphic core complexes, the schist to lower amphibolite facies (Force 1997 and refer- Santa Catalina Mountains include heterogeneous, com- ences therein), and there is no evidence of in situ melting. monly pegmatitic leucogranite with likely crustal sources. The Wilderness suite granites, while peraluminous, some- This has given rise to a persistent question about the times muscovite- and garnet-bearing, and carrying very relation (if any) between leucogranite emplacement and the large amounts of inherited zircon, do not display the iso- ductile extension that characterizes the core complex. In topic heterogeneity often shown for S-type granites (e.g., one interpretation, core complexes were elevated to surface Villaros et al. 2012; Lackey et al. 2012b). Instead, the levels by buoyant crustal roots inherited from earlier sequence of Wilderness Suite intrusions shows a remark- crustal thickening (Coney and Harms 1984; Spencer and ably consistent set of magmatic initial Nd and Hf ratios Reynolds 1990), with thrust burial of upper crustal rocks, (Fig. 7), suggesting a coherent magma genesis process and perhaps radiogenic self-heating of overthickened crust, from a consistent mixture of source rocks at greater depth. leading to in situ melting and leucogranite magmatism The Mesozoic and Tertiary intrusions must have been before uplift and tectonic exhumation (e.g., Haxel et al. derived from lower crustal levels. 1984). It has also been proposed that intrusion of individual 123 Contrib Mineral Petrol middle-Tertiary magma chambers provided the buoyant the post-tectonic Catalina Granite was emplaced at force for core complex uplift (Lister and Baldwin 1993). In *26 Ma. those views, the production and ascent of leucogranite 3. All Laramide and Wilderness suite granitoids contain magmas is closely associated with the doming and exten- abundant zircon cores derived from 1.4-Ga sources, sion process. It is unknown, however, whether core com- and several also contain 1.7-Ga cores. plexes contain more leucogranite than other, still concealed 4. Whole-rock Nd isotopes and zircon Hf isotopes also regions of the middle crust that were not uplifted and suggest that 1.4-Ga sources related to the Oracle exhumed by large-displacement normal faulting. Granite dominated the petrogenesis of Laramide and Crustal extension in southeastern Arizona, and pre- Wilderness granitoids. Substantial Oracle-related (but sumably extensional exhumation of the Catalina core probably more mafic) materials must exist at depth complex, began at about the same time as late Oligocene below the range, and the whole region represents to magmatism, but continued well after the main magmatic first order a 1.4-Ga crustal segment, partially reworked pulse had ended (Dickinson 1991). In the shear zone model in all subsequent events. for core complex mylonitization, mylonitic shearing occurred down-dip from a large-displacement normal fault Acknowledgments U–Pb geochronologic and Hf isotopic analyses and therefore was fundamentally related to tectonic were conducted in the Arizona LaserChron Center, with support from extension (e.g., Davis et al. 1986). Fission track dates from NSF EAR-0732436 and EAR-1032156. CL images were acquired the Santa Catalina Mountains record cooling through ages with instruments supported by NSF EAR-0929777. We thank D. Coleman and J.S. Lackey for their thorough and constructive reviews. as young as *20 Ma during continued tectonic uplift and exhumation of the range (Fayon et al. 2000). Tilted and faulted Miocene conglomerates at the southern edge of the core complex contain mylonitic clasts derived from the References footwall (Dickinson 1991), which indicates that the mylonitic core complex was tectonically exhumed and Anderson JL, Barth AP, Young ED (1988) Mid-crustal roots of exposed to erosion late during detachment faulting (Dick- Cordilleran metamorphic core complexes. Geology 16:366–369 inson 1999). Oligo-Miocene exhumation of the core com- Armstrong RL (1982) Cordilleran metamorphic core complexes— from Arizona to Southern Canada. Annu Rev Earth Planet Sci plex thus occurred 20–40 million years after intrusion of 10:129–154 the Wilderness suite peraluminous granites. As a result, it Banks NG (1974) Reconnaissance geologic map of the Mount is not apparent that peraluminous magmatism had any Lemmon quadrangle, Arizona. US Geol Surv Misc Field Stud relationship to core complex mylonitization and exhuma- Map MF 747, scale 1:62,500 Banks NG (1980) Geology of a zone of metamorphic core complexes tion other than to have formed much of the middle crust in southern Arizona. Geol Soc Am Mem 153:177–215 that was incidentally exhumed by much younger exten- Barovich KM (1991) Behavior of Lu–Hf, Sm–Nd, and Rb–Sr isotopic sional detachment faulting. systems during processes affecting continental crust. PhD dissertation, University of Arizona Bennett VC, DePaolo DJ (1987) Proterozoic crustal history of the western United States as determined by neodymium isotopic Conclusions mapping. Geol Soc Am Bull 99:674–685 Bouvier A, Vervoort JD, Patchett PJ (2008) The Lu–Hf and Sm–Nd isotopic composition of CHUR: constraints from unequilibrated A systematic examination of the ages and sources of chondrites and implications for the bulk composition of terres- granitoids in the classic Santa Catalina metamorphic core trial planets. Earth Planet Sci Lett 273:48–57 complex using U–Pb, Nd, and Hf isotopes yields better Cecil MR, Gehrels GE, Ducea MN, Patchett PJ (2011) U–Pb–Hf characterization of the central Coast Mountains batholith: constrained ages than previous studies and indicates: implications for petrogenesis and crustal architecture. Lithos 1. Oracle Granite was emplaced at 1.44 Ga, with this 3:247–260 Coney PJ (1980) Cordilleran metamorphic core complexes: an result obtained both for an undeformed lithology and overview. Geol Soc Am Mem 153:7–31 for the widespread gneissic rock of the Catalina Core Coney PJ, Harms TA (1984) Cordilleran metamorphic core com- Complex. Most of the dark component of gneissic plexes: Cenozoic extensional relicts of Mesozoic compression. rocks in the core complex has been assumed to be Geology 12:550–554 Coney PJ, Reynolds SJ (1980) Cordilleran metamorphic core complexes deformed Oracle Granite, and this is now demon- and their uranium favorability (final report and appendices). US strated. The Oracle intrusion(s) occupies a very large Dep Energy, Open-file Rep GJBX-268(80), p 627 area more than 50 km across. Cooper JR, Silver LT (1964) Geology and ore deposits of the 2. Mesozoic granitoids of the Laramide tectonic episode Dragoon quadrangle, Cochise county, Arizona. US Geol Surv Prof Paper No. 416 are dated between 67 and 72 Ma, leucogranites of the Creasey SC (1965) Geology of the San Manuel area, Pinal County, Wilderness suite have ages between 46 and 57 Ma, and Arizona. US Geol Surv Prof Paper 471, p 64

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