Framework and Petrogenesis of the Northern Peninsular Ranges Batholith, Southern California

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Geological Society of America Memoirs

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California

D.M. Morton, F.K. Miller, R.W. Kistler, W.R. Premo, C-T.A. Lee, V.E. Langenheim, J.L. Wooden, L.W. Snee, B.L. Clausen and P. Cossette

Geological Society of America Memoirs 2014;211;61-143 doi: 10.1130/2014.1211(03)

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Notes

The Geological Society of America Memoir 211 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California

D.M. Morton U.S. Geological Survey and Department of Earth Sciences, University of California, Riverside, California 92521, USA

F.K. Miller U.S. Geological Survey, Spokane, Washington 99201, USA

R.W. Kistler U.S. Geological Survey, Menlo Park, California 94025, USA

W.R. Premo U.S. Geological Survey, Denver, Colorado 80225, USA

C-T.A. Lee Department of Earth Sciences, Rice University, Houston, Texas 77005, USA

V.E. Langenheim U.S. Geological Survey, Menlo Park, California 94025, USA

J.L. Wooden Department of Geological and Environmental Sciences, Stanford University, California 94305, USA

L.W. Snee Global Gems and Minerals, Denver, Colorado 80235, USA

B.L. Clausen Geoscience Research Institute and Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, California 92350, USA

P. Cossette U.S. Geological Survey, Spokane, Washington 99201, USA

Morton, D.M., Miller, F.K., Kistler, R.W., Premo, W.R., Lee, C-T.A., Langenheim, V.E., Wooden, J.L., Snee, L.W., Clausen, B.L., and Cossette, P., 2014, Frame- work and petrogenesis of the northern Peninsular Ranges batholith, southern California, in Morton, D.M., and Miller, F.K., eds., Peninsular Ranges Batholith, Baja California and Southern California: Geological Society of America Memoir 211, p. 61–143, doi:10.1130/2014.1211(03). For permission to copy, contact editing@ geosociety.org. © 2014 The Geological Society of America. All rights reserved.

61 Downloaded from memoirs.gsapubs.org on March 25, 2014

62 Morton et al.

ABSTRACT

The Peninsular Ranges batholith north of latitude 33°N consists of fi ve distinctive longitudinal batholith zones. Four zones are autochthonous—a western zone, western transition zone, eastern transition zone, and an eastern zone. The fi fth zone, the upper-plate zone, is allochthonous. The western zone, western transition zone, eastern transition zone, and eastern zone are contiguous products of Cretaceous subduction transitioning from a Mesozoic oceanic-arc setting to continental margin arc setting. Within the autochthonous zones, the nature and geochemistry of plutons record changes refl ecting subduction proceeding from west to east over a 35 m.y. period. The allochthonous upper-plate zone is structurally located above the regional Eastern Peninsular Ranges mylonite zone. Host rocks for the western zone, western transition zone, and eastern transition zone are mostly Mesozoic, and host rocks of the eastern zone are Paleozoic. The composition of the plutons refl ects changes in magma originating in shallow oceanic crust in the western zone to a deeper continental marginal setting in the eastern zone and upper-plate zone. Several aspects of the upper-plate zone rocks set them apart from the autochthonous batholithic rocks. Western zone magmatism occurred during an extensional subduction phase that involved Mesozoic oceanic crust. Plutons were emplaced passively from 126 Ma to 108 Ma, forming 47.9% of the area of the autochthonous batholith at a rate of 2.7% per million years. Geochemical variation is greater in the western zone than it is in

the other zones. Rock compositions range from gabbro to high-SiO2 granites; plutons in this zone contain magnetite as an accessory mineral. Most plutonic rocks have ini- 87 86 206 204 δ18 tial Sr/ Sr (Sri) values <0.7045, initial Pb/ Pb (Pbi) <19, O <9‰, and positive ε initial epsilon Nd ( Ndi). By 111 Ma, conditions for pluton emplacement began to change radically from extensional to compressional as subduction encountered older continental crust. The boundary between the western zone and western transition zone is marked clearly by a change in the magnetic properties, which are highly magnetic in the western zone to weakly magnetic in the transition zones. Western transition zone plutons, which have afﬁ nities with the western zone plutons, constitute 13.5% by area of the autochthonous batholith and formed over 13 m.y. at a decreased rate of batholith formation,

1% per million years. Plutons of the western transition zone are characterized by Sri δ18 ε values of 0.7045–0.7050, O <9‰, and positive Ndi. Deformation of the prebatholithic rocks was intense at 100 Ma, as the plutonism of the western transition zone ended and emplacement in the eastern transition zone began. From 99 to 93 Ma, the rate of magma emplacement accelerated, forming 2.4% per million years by area of the northern part of the autochthonous batholith. The eastern transition zone plu-

tons, having afﬁ nities with the eastern zone plutons, have Sri values of 0.7051–0.7057, δ18 ε O >9‰, and negative Ndi. Most eastern transition zone plutons were emplaced in a less dynamic setting than the western transition zone plutons. By 98 Ma, subduction had transitioned eastward as plutons were emplaced in continental crust. The rate of magma emplacement increased to form the eastern zone over 7 m.y., or a rate of batholith growth of 3.4% per million years by area. There is considerable temporal overlap in the magma emplacement of the eastern transition zone and the eastern zone. Combined eastern transition zone and eastern zone magmatism produced 39% (by area) of the autochthonous batholith in 8 m.y. at a rate of ~5% per million years. The 102 Ma gabbro body is not considered in this

analysis. Eastern zone plutons are characterized by Sri >0.7060, mostly in the range δ18 ε of 0.7061–0.7076, Pbi >19, O >9‰, and a large negative Ndi. The allochthonous granitic sheets that constitute the upper-plate zone include batholithic rocks ranging in age from 92 to 75 Ma; most are in the range of 86–75 Ma. These granitic rocks have a more restricted range of geochemistry than those in the other zones; they are magnetite-bearing rocks, unlike the ilmenite-bearing granitic Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 63

ε rocks of the transition zones and eastern zone, and they have large negative Ndi, and

Sri in the range of 0.7076–0.7084. During the Late Cretaceous, the Eastern Penin- sular Ranges mylonite zone developed in the eastern part of the Peninsular Ranges Province, deforming granitic rocks of the eastern part of the eastern zone. Following mylonitization, westward displacement on a series of low-angle thrust faults placed sheets of metamorphic and plutonic rock above the Eastern Peninsular Ranges mylonite zone, forming the upper-plate zone. Compatible elements decrease west to east across the batholith, and incompatible elements increase. Geochemical variation shows that magma forming the western part of the batholith had a shallow and primitive source compared with the eastern part, which had a deeper and more-evolved continental component. The frequency

distribution of Sri in the batholith is bimodal, having a peak of 0.7038 in the western zone, reﬂ ecting the oceanic crustal source, and a peak of 0.7072 in the eastern zone, reﬂ ecting increased incorporated continental crust sources. Only a small part of

the batholith has Sri values between 0.7055 and 0.7065, indicating a relatively sharp boundary between oceanic and continental crust. Linear arrays on Harker diagram indicate that geochemical variation within the batholith is from magma mixing and not magmatic differentiation. Our data are most simply explained by the Cretaceous arc transitioning from a Mesozoic oceanic-arc setting to a continental margin setting.

INTRODUCTION cally collected samples of the late A.K. Baird and E.E. Welday, Pomona College, California (Baird et al., 1974, 1979; Baird and The Mesozoic Sierra Nevada and Peninsular Ranges batho- Miesch, 1984), augmented with 60 samples from selected parts liths of California and Baja California are considered stereotypic of the batholith where greater detail was needed. The Baird sam- examples of subduction-related magmatism. Large numbers ples are all composite samples collected on a predesigned and of papers have interpreted various segments of the Cretaceous tested grid to mitigate heterogeneity and sampling bias at individ- batholiths in plate-tectonic models (e.g., Bateman, 1992; Busby, ual sample sites; the augmented samples are single rock samples. 2004; papers in Johnson et al., 2003; Lackey et al., 2012; Sil- The sampling method used by Baird and Welday is described in ver and Chappell, 1988; Wenner and Coleman, 2004). Here, the Appendix. These systematically collected samples allow an detailed fi eld and analytical data are presented for a geologic transect across the northern part of the Cretaceous Peninsular Ranges batholith, primarily for the area north of latitude 33°30′Ν 119° W 115° W 34° N (Fig. 1). In addition to fi eld and analytical data, the transect Approximate study includes descriptions of both prebatholithic and batholithic area of study rocks. Regional geochemical and potential fi eld data extend N south to 33°N (Fig. 2 [available on the CD-ROM accompanying this volume and in the GSA Data Repository1), coinciding with 30° N G the northern boundary of the geologic transect described by Todd u l Peninsular ′Ν f et al. (2003). Our isotopic data set south of latitude 33°30 is Ranges

o Batholith not as complete as it is to the north. In addition to the general f

C features of the batholith, several individual plutons, considered a 0 100 l i Km f characteristic of various parts of the batholith, are described. The o r n various data sets are interpreted in a subduction magmatic model. 26° N i Unless otherwise cited, detailed geologic maps of prebatho- a lithic rock bodies and individual plutons are by D.M. Morton. Regional geochemical and isotope data are from systemati-

1GSA Data Repository Item 2014040—Table 2: Major oxides and trace elements of Northern Peninsular Ranges batholith; Table 5: Major oxides and trace 111° W 107° W elements of Box Springs plutonic complex; and detailed, enlargeable versions of Figures 2, 3, 18, and 68—is available at www.geosociety.org/pubs/ft2014 Figure 1. Index map of the Peninsular Ranges batholith; cross-ruled .htm, or on request from [email protected] or Documents Secretary, area shows outline of the northern part of the batholith covered in GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA. this paper. Downloaded from memoirs.gsapubs.org on March 25, 2014

64 34°N Morton et al. 33° 116° 116°W Kam QTc QTc ppb UPZ mu Kam ppb QTc Kam QTc QTc QTc Kam Kam Kgdt mu Kam EZ mu Ktmm Kqd Kqd Kam 33° 30’ ppb QTc Klog ppb mu ppb Kcv + Kt Kgdt ppb QTc mu QTc QTc mu QTc Kam ppb Kgpm ppb msmg mu Kgdt Kgm QTc mu Kgm mu Kcs ppb ppb mu Kbc Kcv + Kt Kgm UPZ Kgb Kbm Kgm QTc ppb Kgdt Kam ppb QTc Kbm ppb Kbt ppb ppb ppb Kgbh Klog msmg Kam Kgp Kgp mu Ktg EZ Kbc ppb ppb Kgm Kgu Kog Kt ppb QTc gm 116° 30’ 116° 30’ ppb Klog Kt ppb myl QTc Kt msg QTc Kcv + Kt msmg gm Kgu Kgu gm Kt Kgu gm QTc ETZ Kgdt Kcv + Kt ppb Kgu Kpc Ktg Kqd Kgb Kbt gm QTc ppb EZ ppb Kqd Kcv + Kt ppb QTc ppb ppb ppb Kgu Kgb 2 gm QTc QTc Ksj gm Kgdt ppb QTc Ksjm QTc

ppb Kgd ? Areas shown Kgu

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Kt Q Ki Kdl Kqbd QTc ppb Kgb Kgb Kgd Ki WZ Kgd Krm Kdvg ppb QTc Krct Kcc Klmt ppb Kls Km Kmm Kdvg ppb Kmm Kdvg Kr Kt Kgb ppb Kjd Kgb Kmm Klh Kgb Kt Kgd Kgb Khg Kmm Ki Kgb Kgb Kjd ppb ppb ppb Ktbh Kbpg Kt Kmm Kgu ppb QTc Kt Klmt Kgb Khg Kgb Kgb Kgb Kmp ppb Kt Kgb ppb Kmgt Kdvg Kgb Kt QTc Kbft Kt Kbgg Kpvg Klh ppb Kt Kbfgi Kbhg Kts Kt Kt Kbgg Kbgr Kbt Khg Kgb Kgb WTZ Kgt Kbfg Kgd Khg Kgd Kgd Kgct Kt Kbt Kgd Kbft ppb Kbht ppb Kgb Kgg Kvt ppb 1 Kgu Kbft Kbgg Khg Kght 20 km Kgb ppb Katg Kt Kbhg QTc Khg Ksmg Kbgg Kgh Kt Kgti Kbgr ppb Krg Kgtf Kgb Khg Kbft Kgu ppb Krg Kgu Kgu Krg ppb Kgd Kht Kgb Kgb Kgt Kmrg Kt Kgd ppb Khg Kt ppb Krg ppb ppb QTc Kht Kcg 10 Kgd Kgb Kht Kqd Kgu Khg Kdqd ppb N Kgu ppb ppb Kt Kgbh Kqd ppb Kt ppb Krg Khg Kqd 5 Khg ppb Kgbh ppb Kgb Khg 117° 30’ Klst 117° 30’ 33° QTc Kcg Kd Kmhg Kcg Kd QTc 0 Kmp 33° 30’N Klst WZ Kcg ppb gp K Keh Figure 2. Generalized geologic map for the northern Peninsular Ranges batholith showing boundaries for the ﬁ ve batholith zones. Detailed version of this map and list units are on batholith zones. Detailed version ve boundaries for the ﬁ Figure 2. Generalized geologic map for the northern Peninsular Ranges batholith showing transition zone; ETZ—eastern WTZ—western WZ—western zone; footnote 1). Compilation sources for the map are on list of units. (see text CD-ROM the accompanying zone. zone; EZ—eastern UPZ—upper-plate Downloaded from memoirs.gsapubs.org on March 25, 2014

h Framework and petrogenesis of the northern Peninsular Rangesg batholith, southern California 65 u o r T n o l t a S

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S A P 118° 00' 33° 30' Figure 3. Map of the northern Peninsular Ranges showing locations and place names mentioned in the text. An enlargeable version is on accompanying CD-ROM (see text footnote 1). (see text CD-ROM is on accompanying version An enlargeable locations and place names mentioned in the text. Figure 3. Map of the northern Peninsular Ranges showing Res—Reservoir. Cyn—canyon; Vly—valley; base; AFB—Air Force 34° 00' Downloaded from memoirs.gsapubs.org on March 25, 2014

66 Morton et al.

87 86 accurate quantitative estimation of the composition of this part of All Sr, Rb, Nd, Pb, and O isotopes and initial Sr/ Sr (Sri) val- the Peninsular Ranges batholith. We know of no other batholith ues are whole-rock values. The 40Ar/39Ar data, unless otherwise that has been sampled in such a complete and systematic fashion indicated, are from L.W. Snee. Conventional K/Ar ages are from as the northern Peninsular Ranges batholith, thanks to the Baird- F.K. Miller, who gives detailed descriptions and analytical data in Welday collection. this volume (Miller et al., this volume). Conventional K/Ar, and All samples were analyzed in U.S. Geological Survey 40Ar/39Ar ages of hornblende, biotite, and K-feldspar, with one (USGS) laboratories, Denver, Colorado, using standard tech- exception, are interpreted as cooling ages. Also, unless otherwise niques. Major elements were analyzed by X-ray fl uorescence indicated, hornblende geobarometry data are from D.K. Smith analysis, and trace elements were analyzed by inductively (Smith et al., 1991; Smith, 1991, written commun.). Locations of coupled plasma mass spectrometry (ICP-MS) analysis. Major- place names mentioned in the text are given in Figure 3. element analyses were done by Dave Siems, and trace-element We have subdivided the batholith into fi ve zones. The sub- analyses were done by Fred Lichte and Jim Budahn. divisions are defi ned on the basis of fi eld characteristics, geo- U/Pb zircon and monazite ages, unless otherwise cited, were chemistry, age, stable and radiogenic isotopes, and geophys- determined by W.R. Premo and J.L. Wooden. Isotope dilution ics. Specifi c features and properties characterizing the zones U-Pb ages on zircons are indicated by the subscript “id,” and are summarized in Figure 4. From west to east, these zones are ion probe ages are indicated with the subscript “ip.” Premo et (1) western zone, (2) western transition zone, (3) eastern transi- al. (this volume, Chapter 4) provide a detailed description and tion zone, (4) eastern zone, and (5) upper-plate zone. The fi rst four analytical data for ages cited here. Additional U-Pb zircon ages zones are autochthonous, and the fi fth is allochthonous. Although from gabbroic rocks are from D.L. Kimbrough, San Diego State each of these batholith zones is distinct from the others based on University (2010, written commun.). Sr, Rb, Pb, and O isotope the above combination of properties, because of the transitional data are from R.W. Kistler, and J.L. Wooden (Kistler et al., 2003, nature of the processes controlling batholith emplacement, in this volume). Kistler et al. (2003, this volume) provide detailed some cases there is overlap and/or gradation between zones. For analytical descriptions for Sr, Rb, Nd, Pb, and O isotopes and example, north of 33°22′Ν, rock fabric is a key element used to 87 86 initial Sr/ Sr (Sri). Additional Sr and Rb isotopic data are from distinguish the western zone from the western transition zone. R.J. Fleck, U.S. Geological Survey (2011, written commun.). Although most measured properties discussed in this report and

Western Zone Western Transition Zone Eastern Transition Zone Eastern Zone Upper Plate Zone (WZ) (WTZ) (ETZ) (EZ) (UPZ) Characteristic range of em- 126-108 Ma 109-98 Ma 96-93 Ma 98-91 Ma 85-75 Ma placement ages

Average emplacement age 115 Ma 103 Ma 95 Ma 96 Ma 84 Ma

Mode of emplacement Passive Dynamic Dynamic Dynamic Unknown

Characteristic fabric Isotropic Well foliated Moderately well foliated Moderately well foliated Well foliated Mafic enclaves Equidimensional Thin discoidal to plate-like Thin discoidal Thin discoidal Thin discoidal Range of characteristic 0.7032-0.7040 0.7045-0.7050 0.7050-0.7054 0.7060-0.7075 0.7077-0.7082 Sri Average 0.7039 0.7049 0.7053 0.7070 0.7079 Sri Range of characteristic 18.650-18.980 18.760-18.870 18.830-18.900 19.045-19.300 19.220-19.450 206Pb/204Pb Average 206Pb/204Pb 18.783 18.841 18.880 19.198 19.336 Range of characteristic δ18O 6.0-8.0 7.6-8.6 9.0-10.9 9.2-12.0 8.6-9.1

Average δ18O 6.97 8.11 9.74 10.22 8.73

Average εNd 2.9 1.7 -2.6 -2.8 -6.65 Potential field Intensely magnetic Nonmagnetic Nonmagnetic Nonmagnetic Moderately magnetic Depth of emplacement (kb) 2 to 3 4 to 6 4 to 5 4 to 4.5 6 to 6.5

Figure 4. Comparison of selected zone characteristics, listing features and properties that typify the ﬁ ve batholith zones. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 67

used to defi ne the zone boundaries are surface properties, some In the Santa Monica Mountains, which are the southwestern properties refl ect depth within the batholith (e.g., aeromagnetic); part of the Transverse Ranges, both the plutonic and metamor- this leads to some differences between the surface zone boundary phic rocks have affi nities with Peninsular Ranges batholith rocks and a parameter that refl ects the boundary at depth (e.g., surface but not with plutonic and metamorphic rocks elsewhere in the rock textures at the western zone–western transition zone bound- Transverse Ranges (e.g., Miller and Morton, 1980). These Santa ary compared with aeromagnetic data that refl ect conditions at Monica Mountains basement rocks were probably detached dur- 10 km depth). ing the mid-Tertiary from the western Peninsular Ranges Prov- In reporting results of their geochemical studies, Baird et ince basement. Although they were probably originally part of al. (1979) subdivided the northern part of the batholith into three the Peninsular Ranges batholith, our fi eld and analytical data are Pleistocene postbatholith structural blocks, which are, from insuffi cient to evaluate them, and therefore they are not consid- west to east, the Santa Ana Mountains block, the Perris block, ered further here. and the San Jacinto Mountains block. The Santa Ana Moun- Host rocks for the Cretaceous batholith range in age from tains and Perris blocks are separated by the Elsinore fault zone, Jurassic to probably early Paleozoic and, in general, are increas- and the Perris and San Jacinto Mountains blocks are separated ingly older eastward across the Peninsular Ranges Province. by the San Jacinto fault zone. For descriptive and locational Jurassic batholithic rocks, well documented farther south (e.g., purposes, we recognize and utilize this structural subdivision Shaw et al., 2003), have not been confi dently documented in this scheme, which is independent of the fi vefold scheme described area by geochronology. However, based on high initial 87Sr/86Sr herein based on geochemical, isotopic, and geophysical batho- ratios and foliated fabric, some deformed plutonic rocks north of lith criteria. the city of San Jacinto in the central part of the northern Penin- sular Ranges are undoubtedly Jurassic. These rocks are shown BATHOLITH SETTING as gr-m on the Santa Ana 1:250,000 scale quadrangle (Rogers, 1965). Farther south, in the Palomar Mountain area (Fig. 3), two Introduction samples from the south-central part of the batholith have high 87 86 initial Sr/ Sr (Sri) values of 0.7120 and 0.7133 (Kistler et al., The boundaries and the nature of the boundaries of the 2003) and are undoubtedly Jurassic granitic rocks (Shaw et al., northern part of the Peninsular Ranges batholith, chiefl y north 2003). Even though Jurassic granitic rocks are well documented of latitude 33°30′Ν, are extremely varied and complex, being by isotopic dating south of the area sampled for this study, only in places intrusive, depositional, and structural. The Peninsular the Cretaceous batholith is considered in this paper. Ranges Province, and the included Peninsular Ranges batholith, Foliation in prebatholithic metamorphic rocks is oriented is structurally terminated on the north by the Transverse Ranges northwest, except at the northern edge of the batholith and except Province (Fig. 3). At the present level of erosion, boundaries of for local defl ections around some western transition zone, east- the western part of the batholith in and west of the Santa Ana ern transition zone, and eastern zone plutons. In the northern San Mountains are both intrusive and depositional by overlapping Jacinto Mountains and the Jurupa Mountains–Riverside areas, younger sedimentary rocks. The eastern limit of batholith expo- foliation is oriented east-west. In the Jurupa Mountains, granitic sures includes intrusive contacts with metamorphic rocks in the rocks have two planar fabrics, an older northwest foliation and eastern San Jacinto Mountains, and overlapping Quaternary and Tertiary sedimentary deposits of the western Coachella Valley and Salton Trough (Fig. 3). The northwesternmost exposures of the batholith consist of a few isolated outcrops surrounded by sedimentary materials in the Pomona area (Fig. 3), 3 km south of an isolated exposure of Transverse Ranges Province granitic rocks (see Premo et al., this volume, Chapter 4). East of Pomona, in the Jurupa Moun- tains and Slover Mountain areas (Fig. 3), batholithic rocks occur in isolated but more extensive exposures. East of Riverside, the northern part of the batholith is covered by extensive Tertiary and Quaternary sedimentary deposits of the San Timoteo Badlands (Fig. 5) and San Gorgonio Pass. In the San Gorgonio Pass area, the northern part of the Peninsular Ranges batholith is structurally overridden by Transverse Ranges Province basement by displacement on the reverse San Gorgonio Pass faults (Morton and Matti, 1993). South and southeast of San Gorgonio Pass, Penin- sular Ranges batholith rocks core the San Jacinto and Santa Rosa Figure 5. Tonalite of Lamb Canyon and overlying Pliocene sediments Mountains (Fig. 3). of the San Timoteo Badlands, north end of Lamb Canyon. Downloaded from memoirs.gsapubs.org on March 25, 2014

68 Morton et al. a younger east-striking foliation (Morton, 2003a). The younger ered from these rocks due to the high degree of metamorphism east-striking planar fabric lacks brittle or protoclastic textures and penetrative deformation. and appears to have formed when the granitic rocks were still Most occurrences of these metasedimentary rocks in the ductile. South of Riverside, tonalite in the northern part of the Val Riverside-Colton area consist of two marble layers and an inter- Verde pluton (Fig. 2) commonly has an older northwest-oriented vening silicate layer. Two thick marble layers separated by a planar fabric and a younger east to northeast planar fabric. Based section of schist occur at Slover Mountain (Fig. 6), Crestmore on the widespread eastward-oriented planar fabrics in both pre- (Burnham, 1959), Jensen, and the Old City (Riverside) Quar- batholithic and batholithic rocks of the north-central and north- ries (Morton, 2003a; Morton and Cox, 2001a, 2001b), suggest- eastern parts of the Peninsular Ranges batholith, these areas may ing that the same sequence of rocks may occur at each locality. be approaching the northern termination of the entire batholith. Although the marble and schist appear to be structurally simple, they are pervasively deformed (Figs. 7 and 8). At Slover Moun- Paleozoic Prebatholithic Rocks tain, marble blocks occur in tonalite near a marble-tonalite contact, and locally tonalite has been emplaced along layering in the Metasedimentary rocks that include thick sections of marble marble. The uniform orientation of lineations within the marble and quartzite occur in the San Jacinto and Santa Rosa Moun- extends to the contact with the tonalite, indicating deformation tains in the eastern part of the Peninsular Ranges batholith, and was synchronous with the emplacement of the tonalite. at the north end in the Riverside-Colton area. These rocks are At the New City (Riverside) Quarry (Fig. 9), marble lay- considered to be Paleozoic based on general lithologic afﬁ nities ers are separated by a section of meta-quartzite and pyroxenite. with dated Paleozoic rocks further to the south in the Peninsu- Boudins are common in the pyroxenite layers (Fig. 10), and lar Ranges (Morton and Miller, 2006). The size and thickness of discontinuous lenticular biotite-hornblende tonalite bodies are marble bodies are considerably greater than those in the Jacumba interleaved with the metasedimentary units. The marble con- Mountains sequence. Ordovician conodonts have been recovered sists of massive, coarse-grained to extremely coarse-grained from similar carbonate rocks in the Coyote Mountains in west- calcite, calcite-dolomite, and predazzite marble. A wide variety ern Imperial County (Dockum, 1982; Dockum and Miller, 1982; of skarns is found in the contact zones between marble and plu- Miller and Dockum, 1983); in northern Baja California, Permian tonic rocks, including ludwigite-paigeite magnetite skarn. Oxy- fossils have been found in similar carbonate rocks (Gastil and gen isotope analyses of garnet and clinopyroxene skarn show Miller, 1981). All of these marble and quartzite sections appear to high δ18O values (7‰–11‰) in the New City Quarry skarns, differ in various ways from Paleozoic sections found north of the indicating that magmatic ﬂ uids driving formation of the skarns Peninsular Ranges in the Great Basin, Mojave Desert, and San were buffered to high-δ18O values by the surrounding carbonates Bernardino Mountains. (J.S. Lackey, 2012, written commun.). Other examples of mar- In the northern San Jacinto Mountains, west of the Eastern ble and thick quartzite units occur in the central Jurupa Moun- Peninsular Ranges mylonite zone, marble, quartzite, and schist tains and the Glen Avon area (Fig. 3) (Morton, 2003a; Morton sequences are commonly termed the Windy Point group, and in and Cox, 2001b). the southern San Jacinto Mountains, they are termed the Desert In the Santa Rosa Mountains and southern and eastern San Divide group (e.g., Brown, 1968; Hill, 1984). These two groups Jacinto Mountains areas, the Paleozoic metasedimentary rocks of rocks are probably correlative; both include thick sections of strike northwest, but in the northern San Jacinto Mountains, they quartzite and marble, interlayered with amphibolite-grade biotite veer westward. In the Jurupa Mountains and Glen Avon area, schist and gneiss. Sillimanite-biotite schist is common, and gar- the foliation strikes west. Paleozoic rocks in the Santa Rosa and net-sillimanite-biotite schist is less common. Corundum-biotite San Jacinto Mountains are located within the eastern part of the gneiss occurs very locally in the northern San Jacinto Mountains batholith, whereas those in the Jurupa Mountains and Glen Avon (Murdoch and Webb, 1942). Chemical analyses of both Desert areas are located in the western part of the batholith. Restora- Divide and Windy Point samples are given in Hill (1988b). East tion of strike-slip displacement on the San Jacinto fault closely of the Eastern Peninsular Ranges mylonite zone, Erskine (1986a), aligns the Paleozoic rocks of the northern San Jacinto Mountains following the usage of Miller (1946), termed metasedimentary with those of the Riverside-Colton area. This alignment suggests rocks the Palm Canyon Complex for allochthonous rocks in the major pre–105 Ma deformation and bending of the Paleozoic Palm Springs area. The intensely deformed metasedimentary rocks from northwest to west orientation in this area. rocks of the Palm Canyon Complex include marble bodies but appear to lack the quartzite sections of the Windy Point–Desert Mesozoic and Paleozoic(?) Prebatholithic Rocks Divide groups. Probable Paleozoic metasedimentary rocks in the Riverside- Rocks of Jacumba Mountains Colton area include biotite schist, gneiss, quartzite, calc-silicate West of the Paleozoic rocks, there are discontinuous masses rocks, and marble. Mineral assemblages are of mostly pyroxene of schist and gneiss, minor quartzite, and marble containing local hornfels facies, but include hornblende hornfels facies assem- small masses of skarn, and amphibole- and pyroxene-bearing blages at Slover Mountain (Fig. 2). No fossils have been recov- rocks. We interpret this assemblage to be the northward extension Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 69 68 Kt 20 Ks 20 40 Kt 75 75 pKm pKm Marble Pegmatite Skarn Schist Tonalite Kt Ks Kp pKs pKm 36

31 N pKs 42 Kt Kt 44 Kt pKm 47 pKs Kt Inclined Vertical Accurately located Accurately located Approximately Lineation Joint Foliation Contacts Fault of quarry face Top of quarry face Toe pKm 34 62 62 0 10 20 30 40 meters pKm pKm 47 28

pKm

117 ° 20’ 29” 20’ ° 50 pKm

34 ° 3’ 37” 3’ ° pKs 32 pKm 41 33 42 32 45 32 23 24 32 40 pKs pKs 40 42 42 82 44 30 42 Kp pKm 34 44 pKs 44 40 pKs 30 33 44 pKs 40 62 pKs pKs 55 40 35 Kp 36 42 72 46 32 pKs Kp pKs 45 pKs 55 70 Kp pKm 80 Ks pKs 39 32 Kt 56 pKm 34 35 57 54 45 55 Kp 62 48 36 pKs 60 pKs 32 40 41 pKm pKs 45 38 Kp 32 33 44 Kt 52 47 pKs 75 38 36 Kp 30 38 pKm 42

24 ? pKs

Kt ? ? 52

Kt ? Figure 6. Geologic map of Slover Mountain, Colton. Two intensely deformed Paleozoic(?) marble layers separated by a biotite schist layer are intruded by biotite-hornblende intensely deformed Paleozoic(?) Two Mountain, Colton. Figure 6. Geologic map of Slover included in the marble. isolated schist bodies are part of the tonalite, and a few tonalite. Some detached blocks of marble are included in the marginal Downloaded from memoirs.gsapubs.org on March 25, 2014

70 Morton et al.

Qaf Artifical fill MPs Magnetite-paigeite skarn Qaf Is Idocrase skarn Pmp SPs Scapolite-pyroxene skarn Uds Uds Undifferentiated skarn Kt Pmp Kqf Quartz-feldspar rock Kqf Pqp 940 Kt Biotite-hornblende tonalite Pqp Quartzite-pyroxenite Kt 950 Pqp Pmp Marble and predazzite Pmp

Pmp

Kqf 960 Qaf Is Kt 60

70 Pmp 60 Kt Pqp

Kt 65

70 SPs Pmp

Kt 60 Kt 60 Kt 55Uds

Kt Uds 65 80 SPs 45 9 Kt N Pmp 65 Kt 60 Pmp 60

Kt 60

65 MPs Figure 7. Intensely slip-folded, metamorphosed siliceous calcareous 970 Pqp metasedimentary rocks containing diopside and wollastonite, Old City 85 Qaf SPs Quarry, Riverside. Light-colored layers are discontinuous layers of 50 quartzite and wollastonite. Pick for scale. Contacts 65 SPs Faults Approximately located Concealed N Quarry head Qaf Quarry toe 950 Lineation 45 Quarry waste dump Mean lineation vector Kqf 65 91 Number of lineations SPs 65 Foliation, inclined 117 Mean lineation azimuth Kt 36.5 Mean lineation plunge 65 Uds 65 Pqp 60 Pmp 70 Kt 930 Pqp Uds Uds 55 Pmp Pqp SPs 55 75 Kqf Kt Qaf 0 50 100 150 200 feet Contour interval 10 feet 117° 21’ 29” Datum assumed 33° 56’ 57”

Foliation pole Best fit great circle to foliation Figure 9. Geologic map of the New City Quarry, Riverside. Paleozo- 69 Number of foliations 201 Great circle azimuth ic(?) marble-predazzite (Pmp) layers are separated by an intervening 54.3 Great circle plunge quartzite-pyroxenite layer (Pqp); both units are intruded by biotite- hornblende tonalite (Kt). Nature of contacts indicates that tonalite Figure 8. Stereoplot of minor folds and lineations in marble and schist, was forcefully emplaced mostly along contact between the marble- Slover Mountain, Colton. Foliation is penetrative planar fabric in mar- predazzite and quartzite-pyroxenite layers. ble and mineral foliation in schist. Lineations are penetrative mineral orientation and minor folds in marble and schist. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 71

view Mountains and in the hills north of Lakeview. In the Mount Eden–Soboba Hot Springs area, predominant sillimanite-biotite schist and gneiss commonly contain marble bodies and sparse amphibolite and rare gabbro. Within this unit north of the town of San Jacinto, gneissic biotite monzogranite and biotite- hornblende tonalite are widespread. Based on the nature and intensity of deformation, the monzogranite and tonalite are probably Juras- sic. The metamorphic rocks are intruded by a distinctive garnet- bearing granitic rock, the granite of Mount Eden (Morton and Miller, 2006). Similar schist and gneiss, the Bautista complex of Sharp (1967), extend from the mouth of Bautista Canyon to Anza. Within the Bautista complex, there are bodies of garnet-bearing monzogranite that resemble the Mount Eden monzogranite, as well as foliated biotite monzogranite and gabbro. East of Anza, the Burnt Valley complex of Sharp (1967) is the continuation of the Bautista complex offset by the San Jacinto fault. South of 33°30′Ν, the large Tule Canyon complex of Sharp (1967) is probably also part of the Jacumba Mountains sequence. The widespread sillimanite indicates all metamorphism is in excess Figure 10. Boudinaged pyroxenite layers in the interlayered quartzite- of 500 °C and therefore at least amphibolite facies. pyroxenite unit, New City Quarry, Riverside. Pencil for scale. Triassic Prebatholithic Rocks of the Mesozoic and Paleozoic(?) rocks of the Jacumba Moun- Rocks of Menifee Valley tains of Todd (2004). Larsen (1948) considered the metasedimentary rocks east of Included in the schist and gneiss are relatively thin, dis- the Santa Ana Mountains, in the western part of the Perris block, continuous marble layers that occur as discontinuous bodies on to be part of the Bedford Canyon Formation, and those in the the east side of the Lakeview Mountains, in the area between eastern part of the Perris block to be Paleozoic in age. Schwarcz Mount Eden and Soboba Hot Springs (Figs. 3 and 11), and as (1969) interpreted the rocks Larsen assigned to the Paleozoic to a large heterogeneous body from the mouth of Bautista Canyon be Mesozoic and named them the French Valley Formation. He south to Anza (Sharp, 1967). These rocks are dominantly bio- retained Larsen’s terminology of Bedford Canyon Formation for tite schist and gneiss, containing minor amphibolite and variable the rocks in the western Perris block. Both Larsen and Schwarcz small amounts of marble and skarn. A few pod-like and variable noted lithologic differences between the Bedford Canyon Forma- (but small in amount) marble and calc-silicate rock bodies occur tion on the Perris block and the Bedford Canyon Formation at its with sillimanite-biotite schist and gneiss in the easternmost Lake- type locality in the Santa Ana Mountains. Schwarcz’s Mesozoic age was based on his observations that “….The French Valley Formation interﬁ ngers with the Bedford Canyon Formation at their contact….” (Schwarcz, 1969, p. 22). Based on mapping in the Winchester area, Morton (2003b; Morton et al., this volume)

interpreted this as structural interﬁ ngering of S1 fabric rocks. Because of this, all of Larsen’s and Schwarcz’s Bedford Can- yon Formation on the Perris block and all but the easternmost part of Schwarcz’s French Valley Formation are here included in rocks of Menifee Valley as deﬁ ned by Morton and Miller (2006). The easternmost part of Schwarcz’s French Valley Formation is here interpreted as the northward extent of the metavolcanic and metasedimentary unit of Todd (2004). Schwarcz (1960, 1969) described a remarkable Buchan-type metamorphic gradient of greenschist to upper amphibolite facies within the rocks of the eastern part of his French Valley Formation. Age. Larsen’s (1948) Paleozoic age assignment for the Figure 11. Thick (1–4 m) marble layers in sillimanite-biotite schist Perris block rocks was based upon a report (Webb, 1939a) of and gneiss, Lamb Canyon; unit is interpreted to be part of rocks of a single Mississippian coral from the waste dump of the Hemet Jacumba Mountains of Todd (2004). (Winchester) magnesite mine (Fig. 3). Larsen (1948, p. 16) Downloaded from memoirs.gsapubs.org on March 25, 2014

72 Morton et al.

characterized the coral as “Carboniferous (Mississippian) fossils interlayered quartzite and phyllite (Morton, 2003b, 2003c). Sedi- in the interbedded limestone near the old magnesite quarry ….” mentary structure in sporadically occurring 8- to 24-cm-thick Schwarcz (1969), however, clearly showed that the coral speci- quartzite beds in fold hinges is interpreted as relic bedding, con-

men cited by Larsen, which was found as fl oat by a mineral col- trasting with 5- to 7-cm-thick S1 quartzite layers on the fl anks of lector, could not have originated where it was found. the folds (Fig. 12). M.A. Murphy (1966, personal commun.) collected poorly On Searl Ridge (Fig. 3), the eastern 4.5 km of the rocks of preserved deformed fossils from a calc-silicate rock included Menifee Valley are within the transition zones of the northern in the rocks of Menifee Valley, east of Menifee (previously Sun batholith (for details of the structure and mineralogy of these City). Included in the collection were large crinoid stems and metamorphic rocks, see Morton et al., this volume). Metamor- pelecypods. A latex impression of a pelecypod was examined phism of this 5-km-thick section increases from west to east, by G.E.G. Westerman (personal commun.), who reported “… from greenschist grade to lower granulite grade. Schwarcz This is a poorly preserved, obviously distorted specimen which (1969) and Morton et al. (this volume) give detailed descrip- cannot be identifi ed at the generic or specifi c level. I dare only tions of the mineralogy of the metamorphic gradient; Premo the following: Right valve of the Bivalvia family Aviculepectini- and Morton (this volume) give Ar-Ar ages, and temperature and dae; possible ?? Claraia ex. gr. C. himaica (Bittner) and C.(?) occidentalis (Whiteaves) which would be late Lower Triassic. However, almost any age within the Triassic or even Permian is possible….” Based on Westerman’s comments, Morton and Miller (2006) considered the rocks of Menifee Valley as Triassic. Samples from the western part of the rocks of Menifee Valley on Searl Ridge contain no post–210–205 Ma detrital zircons (Premo and Morton, this volume). Lithology. Almost all bedding in the rocks of Menifee Val-

ley was pervasively transposed to S1 foliation before 134 Ma, the age of the oldest dated undeformed volcanic rocks in the region (Anderson, 1991). The structural transposition producing the S1 fabric was probably Jurassic in age. Bedding is locally preserved in the hinges of folds, in addition to thin, mostly subcentimeter layers that contain relic cross-bedding showing alternating top directions. Phyllite, containing some discontinuous sequences of metagraywacke, dominates in the western part of the rocks of Menifee Valley. Metagraywacke, impure quartzite, and interlayered quartzite and phyllite are increasingly abundant eastward. Thick sequences of impure quartzite, including calcareous quartzite, form extensive sections in the Quail Valley and Menifee City areas (Morton, 2003b; Morton and Weber, 2003)(Fig. 3). East of

Elsinore, a 9-km-thick section of S1 foliated phyllite, containing some interlayered metagraywacke, and minor tremolite-bearing marble and manganese-bearing siliceous rocks, locally contains small tabular aggregates of white mica that appear to be pseudo- morphs after chiastolite. Tremolite-bearing marble, which is dis- similar to the block-like limestone bodies in the Bedford Canyon Formation, occurs as a few thin elongate layers in this sequence (Morton, 2003b). Manganese-bearing siliceous rocks are sparse but widespread in the Railroad Canyon area and also occur in a single layer in the Winchester area. Rhodonite is common, as are manganese oxides and hydroxides in these manganese-bearing siliceous rocks. Metagraywacke forms thick S layers, many of which con- Figure 12. Interlayered quartzite and phyllite of the Triassic(?) rocks 1 of the Menifee Valley (Morton and Miller, 2006) and relic bedding, S , tain small phyllite fragments. Many of these phyllite fragments 0 in hinges of slip folds (arrows) in the upper left and upper center of the are deformed into irregularly to uniformly oriented tabular bod- photograph. Dominant layering is ﬁ rst-generation transposed bedding, ies. Some metagraywacke sections contain discontinuous phyl- S1. For scale, arrows are ~33 cm long. Hill east of the city of Menifee lite layers, and some in the Menifee and Winchester areas contain Valley. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 73

pressure data are provided by Miggins et al. (this volume). Meta- from ﬁ ne-grained lithologies within the Bedford Canyon Forma- morphic zircon rims on detrital zircons from these rocks have an tion, interpreted two ages of deposition: a Jurassic age of 175.8 ± age range of 103–97 Ma, which dates the time of deformation 3.2 Ma and a Triassic age of 228 ± 4.3 Ma. The ages were based and metamorphism. Structures related to deformation within the on analysis of 14 samples collected between Silverado and Ladd transition zones include, west to east, three progressive structural Canyons near Bedford Canyon (Fig. 2). The Bedford Canyon transpositions. In the western part of Searl Ridge, the regional Formation is unconformably overlain by the Cretaceous Santiago

S1 layering and schistosity were transposed to S2, which in turn Peak Volcanics (see Herzig et al., this volume). was transposed to S3; in turn, S3was transposed to S4. Mineral- Lithology. Exposures of the Bedford Canyon Formation are ogic changes are evident over a 3.5-km-wide zone on the ridge, commonly thoroughly fractured, complexly folded sequences of as thermal effects of the structural transitions produced a low- brown to black and gray interbedded shale or mudstone (argil- pressure–high-temperature, Buchan-type metamorphic gradient. lite), graywacke, conglomerate, impure quartzite, and minor scat- Progressive changes in mineral assemblages containing andalu- tered limestone (Fig. 13). At the type locality, the Bedford Can- site, cordierite, sillimanite, garnet, and K-feldspar refl ect changes yon Formation consists of well-indurated lithologies containing from greenschist facies to lower granulite facies. a variety of sedimentary structures including ripple marks and In the eastern part of the multiply deformed rocks of Menifee cross-bedding. Exposures of the unit are generally nonexistent in Valley, several meta-serpentinite and related rock bodies are dis- the chaparral-covered slopes of the Santa Ana Mountains, except continuously exposed over a strike length of 14 km. These ultra- along roads and in scoured canyon bottoms. Most limestone mafi c and related rocks are most abundant on Searl Ridge, where bodies are blocky and have no appreciable length. Brachiopods the least-altered meta-serpentinite is composed of olivine-talc identifi ed as Anarhynchia gabbi Ager collected from one of these rock, in which some talc crystals are more than 5 cm in diam- limestone bodies are interpreted to typify a cold-seep paleoenvi- eter. Several bodies of meta-serpentinite are thoroughly altered ronment (Sandy and Campbell, 2003). Dark-gray conglomerate to a mixture of clay minerals containing numerous veinlets of layers are massive and contain subangular clasts of a wide variety magnesite. At and near the outer margins of most of the meta- of lithologies. Massive graywacke, lithic graywacke, and arkosic serpentinite bodies, there is a layer consisting mostly of enstatite, arenites consist of subangular quartz, feldspar, and rock frag- which in some places grades outward to a few-centimeter-thick ments. Some gray-colored beds appear to be tuffaceous. Impure layer of spinel (Table 1). quartzite consists of fi ne- to medium-grained, subrounded to subangular quartz and a small amount of feldspar. Thickness of most Jurassic Prebatholithic Rocks beds is on the order of a few centimeters, but locally, beds are up to about 1 m thick. Bedford Canyon Formation West of Lake Elsinore, the southern part of the Bedford Can- The name Bedford Canyon Formation has been loosely yon Formation is mostly massive quartz-rich metasandstone and applied to a wide variety of metasedimentary rocks in the north- impure quartzite (Morton and Miller, 2006). West of Murrieta- ern Peninsular Ranges Province. At the type locality in Bedford Temecula (Fig. 3), a large area is underlain by unnamed metasedi- Canyon, northern Santa Ana Mountains, it consists of a thick mentary rocks that include thick sections of black, impure quartz- and structurally complex metasedimentary section of mostly ite commonly containing disseminated pyrite. These rocks are well-indurated lithologies. For a history of the nomenclature unlike the rocks of the Bedford Canyon Formation to the north. used for the Bedford Canyon Formation, see Morton and Miller Although most of the Bedford Canyon Formation is (2006). Here, the name Bedford Canyon Formation is restricted intensely deformed, primary sedimentary features are commonly to the rocks contiguously exposed in the northern Santa Ana preserved (e.g., Gray, 1961; Schoellhamer et al., 1981). Bed-

Mountains (Fig. 3). ding (S0) in parts of the formation is incipiently to moderately

Age. Based on fossil evidence, the Bedford Canyon Forma- transposed to S1 layering; many outcrops show mixed bedding tion is considered to be Jurassic (Imlay, 1963, 1964, 1980; Silber- and transposed S1 layering. Typically, in the northern part of the ling et al., 1961), but a Triassic age for some of the unit cannot unit, primary sedimentary structures are pristine, and the rocks be ruled out. Criscione et al. (1978), based on Rb-Sr isotopes appear as a folded section of indurated sedimentary rocks. South

TABLE 1. MAJOR OXIDES (%) AND SELECTED TRACE ELEMENTS (PPM) OF WINCHESTER MAGNESITE MINE MAFIC ROCKS

SiO2 Al2O3 Fe2O3* MgO CaO Na2O K2O TiO2 P2O5 MnO Cr Ni MM-109 Metaserpentinite 31.4 24 10.37 29.3 0.27 0.15 0.03 1.08 0.19 0.193 140 90 MM-110 Metaserpentinite 31.9 16.75 8.81 30.29 0.26 0.18 0.03 0.9 0.18 0.13 430 550 MM-111 Metaserpentinite 33.7 15.5 8.34 31.16 0.19 0.15 0.02 0.88 0.11 0.078 100 330 MM-108 Spinel-rich metaserpentinite 19.67 40.7 10.34 18 5.78 0.75 0.15 1.99 0.58 0.221 210 140 MM-112 Pyroxenite 55.25 1.76 7.11 32 0.09 0.12 0.02 0.07 0.02 0.093 2810 2200 MM-113 Pyroxenite 55.23 0.88 6.58 32.84 0.15 0.1 0.11 0.05 0.06 0.071 2970 1560 MM-114 Pyroxenite 50.21 1.06 7.29 36.52 0.2 0.1 0.01 0.05 0.02 0.088 2450 1970

*Total Fe expressed as Fe2O3. Downloaded from memoirs.gsapubs.org on March 25, 2014

74 Morton et al.

Figure 14. Discontinuous black amphibolite layers in Cretaceous– Jurassic metavolcanic and metasedimentary unit of Todd (2004). Peak metamorphism is inferred to be in the upper amphibolite facies. Loca- Figure 13. Interbedded argillite and graywacke, Jurassic Bedford Can- tion is near east end of Searl Ridge. yon Formation, near the mouth of Silverado Canyon, northern Santa Ana Mountains. Argillite beds are recessive and do not show well in the photograph. Unit also includes immature, poorly sorted pebble conglomerate beds. in length. Sillimanite-biotite gneiss is common, and, although present, garnet-sillimanite-biotite gneiss is subordinate. Much of the gneiss is anatectic, containing thin rheomorphic stringers of and east from Bedford Canyon, primary sedimentary structures quartz and feldspar (Fig. 15). This unit is distinct from the Tri- appear to be progressively obliterated, largely by structural trans- assic rocks of Menifee Valley in that it lacks the thick sections position. Bedding in many places is transposed, and the extent of of pelitic rocks that are abundant in the latter, and it generally transposition ranges from slight to intense. Flexural slip folds are lacks thick sections of graywacke, which are also characteris- common in the areas where bedding is intact (e.g., Gray, 1961; tic of that unit. In addition, the numerous and widespread black Schoellhamer et al., 1981). amphibolite bodies within the metavolcanic and metasedimentary unit do not occur in the rocks of Menifee Valley. Rocks of Jurassic and Cretaceous Prebatholithic Rocks the metavolcanic and metasedimentary unit contain Mesozoic inherited and metamorphic zircons having ages of 200–250 Ma Metavolcanic and Metasedimentary Unit of Todd (2004) and 103–123 Ma, respectively (Premo et al., 2002; Premo and South from the Hemet-Winchester area through the Magee Morton, this volume). Hills (Fig. 3), and extending to at least 30°30′Ν, there is a sequence of schist, gneiss, and amphibolite. These rocks are interpreted to Cretaceous Rocks Coeval with the Batholith be the northward extension of the Cretaceous–Jurassic metavolcanic and metasedimentary unit (KJvs) of Todd (2004). Early Cretaceous Sedimentary Rocks It is assumed that the age of the prograde metamorphism Sedimentary rocks coeval with the batholith are locally exposed producing the schist and gneiss is the same as the pre–134 Ma within the Gavilan plutonic ring complex (Fig. 2). In the southern regional metamorphism of the Triassic rocks of Menifee Valley part of the Gavilan ring complex, there is a sequence of volcanic, unit, which is described later herein. Rims on detrital zircons interbedded volcanic and sedimentary, and sedimentary rocks. The from this unit, where it is adjacent to younger deformed and sedimentary rocks are well indurated and undeformed and include metamorphosed rocks north of 30°30′Ν, give ages of 100 Ma granitic pebble conglomerate, quartzite, and black, thin-bedded (Premo and Morton, this volume), which are interpreted as the siliceous rocks (Fig. 16). The volcanic rocks are part of the Estelle age KJvs was metamorphosed. Older detrital zircons from the Mountain volcanics of Herzig (1991; Herzig et al., this volume). KJvs unit range in age from 250 Ma to ca. 120 Ma, and 1710 Ma West of Lake Mathews (Fig. 3), siliceous sedimentary rocks also to ca. 1040 Ma (Premo and Morton, this volume). On Searl Ridge associated with the Estelle Mountain volcanics are considered to be

(Fig. 3), the eastern 600 m section of rocks with S4 fabrics was of Early Cretaceous age (Morton and Weber, 2001).

derived from this unit. The S4 fabric rocks there grade eastward into older prograde gneissic foliation. Cretaceous Volcanic and Hypabyssal Rocks The metavolcanic and metasedimentary unit is dominantly A large area of the Santa Ana Mountains and adjacent parts biotite schist and gneiss that contains numerous elongate bodies of the Perris block are underlain by Cretaceous volcanic rocks and layers of black amphibolite (Fig. 14). The amphibolite bodies and related shallow intrusive rocks. The volcanic rocks include range in size from a few centimeters to several hundred meters some volcaniclastic and sedimentary rocks. In the Santa Ana Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 75

Figure 16. Well-indurated Cretaceous conglomeratic quartzite interbedded with Estelle Mountain volcanics of Herzig (1991), Arroyo del Toro Canyon. Clasts include leucogranite.

exposures, siliceous layered rocks, some of which have primary folds (Morton and Weber, 2003) (Fig. 17). A U-Pb zircon age from the Estelle Mountain volcanics just west of Lake Mathews is 125.8 Ma (Anderson, 1991). Figure 15. Upper-amphibolite-grade anatectic gneiss of the Cretaceous– Interlayered volcanic and well-indurated sedimentary rocks Jurassic metavolcanic and metasedimentary unit of Todd (2004). Loca- along the southwest and south sides of the Arroyo del Toro pluton tion is near east end of Searl Ridge. (Fig. 2) are not included in the Estelle Mountain volcanics. The sedimentary rocks of this sequence, in which primary bedding features are well preserved, consist of conglomerate and thinly Mountains, these volcanic rocks were originally termed the bedded, very ﬁ ne-grained sedimentary rocks. Black Mountain volcanics by Hanna (1926), but the name was preempted, and Larsen (1948) renamed them the Santiago Peak volcanics for exposures in the vicinity of Santiago Peak, northern Santa Ana Mountains (Fig. 3). The Santiago Peak volcanics, which range in composition from basaltic andesite to rhyolite, rest unconformably on the Jurassic Bedford Canyon Formation. Zircon ages range from 134 to 123 Ma, indicating they are at least partly coeval with older granitic rocks of the Peninsular Ranges batholith (Anderson, 1991). Included in the Santiago Peak volcanics in the Santa Ana Mountains block is a small serpentinite body and associated carbonate-silicate rock (Gray, 1961). Cretaceous volcanic rocks of the Perris block are in general more silicic than those of the Santa Ana Mountains block and were named the Temescal dacite-porphyry by Dudley (1935) and Temescal Wash quartz latite porphyry by Larsen (1948). Based on a more recent detailed study, Herzig (1991) described and named these rocks the Estelle Mountain volcanics after their extensive distribution in the Estelle Mountain area in the western part of the Perris block (Fig. 3). Included in the Estelle Mountain Figure 17. Fold in volcanic rocks, Estelle Mountain volcanics of Her- volcanics is relatively homogeneous rhyolite, and in southeastern zig (1999), east side of Arroyo del Toro Canyon. Pen for scale. Downloaded from memoirs.gsapubs.org on March 25, 2014

76 Morton et al.

Early descriptions of the Santiago Peak volcanics and Based on sparsely spaced samples, Taylor and Silver (1978) Estelle Mountain volcanics suggested they had been subject to described a linear step of δ18O from +8.5‰ to +9‰ from latitude low-grade metamorphism. Herzig (1991), in a thorough exami- 31°30′Ν to the north end of the batholith. Baird and Miesch (1984) nation at the Santiago Peak “type” area, determined that mineral developed a mixing model having four end members the northern assemblages previously considered to be the result of low-grade part of the batholith, based on major-element geochemistry. They regional metamorphism were produced by hydrothermal activity interpreted the western part of the batholith to have been largely associated with the volcanism; see also Wetmore et al. (2003). To derived from oceanic crust and the eastern part largely from con- the south, in San Diego County, sedimentary rocks interbedded tinental crust. As determined by Baird and Miesch (1984), the with volcanic rocks, which had been correlated with the Santiago boundary between the two is essentially coincident with the δ18O Peak volcanics, have yielded Late Jurassic fossils (Fife et al., step of Taylor and Silver (1978). Gromet and Silver (1987) divided 1967; see Kimbrough et al., this volume). The San Diego County the batholith into three zones based on rare earth elements. Similar Jurassic volcanic rocks may be related to the Jurassic batholithic to Baird and Miesch (1984), they interpreted the western part of rocks south of 33°30′Ν. These volcanics obviously do not cor- the batholith as being derived from largely oceanic materials and relate with the Cretaceous Santiago Peak volcanics. the eastern part from continental materials. Kistler et al. (2003) 87 86 recorded a major step in initial Sr/ Sr ratio (Sri) that does not NORTHERN PART OF THE PENINSULAR coincide with the δ18O step of Taylor and Silver (1978). Based on a RANGES BATHOLITH combination of geochemistry and age, Silver and Chappell (1988) divided the batholith into six, mostly longitudinal, zones. Five of Previous Work their zones occur in the area north of 33°N. Todd et al. (1988) summarized the various subdivisions of the batholith. While conduct- Early descriptions of portions of the northern part of the batho- ing paleomagnetic studies in the batholith, Erskine (1982) noted lith include those by Dudley (1935), Osborn (1939), Merriam systematic variation in magnetic properties, which led to subdi- (1946), Miller (1946), and Engel (1959). An early and very detailed viding the batholith into a magnetically high western part and a investigation of the modal mineralogy and structure of the tonalite magnetically low eastern part (Gastil et al., 1990). This difference of Val Verde pluton was done by Osborn (1939). The fi rst major in magnetic properties between the western and eastern parts of the synthesis of the batholith was by Larsen (1948), who conducted batholith shows as a marked change on aeromagnetic maps (e.g., fi eld work discontinuously from 1906 to 1938 in the central and Langenheim et al., this volume). western parts of the batholith. Jahns (1954) provided an overview of The fi ve batholith zones we have established are based on the entire southern California part of the batholith. Recently, Todd a combination of fi eld and analytical data. Field data consist et al. (2003) provided an excellent analysis of the batholith imme- chiefl y of fabric, structure, enclave shape and confi guration, diately south of the area considered here. Most recent batholithic mode of emplacement, and to some degree, contrasting rock investigations have centered largely on topical aspects (e.g., Baird types. Analytical data include geochemistry, age, stable and et al., 1974, 1979; Krummenacher et al., 1975; Taylor and Silver, radiogenic isotopes, and geophysics. Specifi c features and prop- 1978; Baird and Miesch, 1984; Gromet and Silver, 1987; Silver and erties characterizing the zones are summarized in Figure 4. The Chappell, 1988; DePaolo, 1981; Premo et al., 1998), and on indi- fi ve batholith zones are distinct from one another, but because vidual plutons (e.g., Hill, 1988a, 1988b; Jenney, 1968; Joshi, 1967; of the transitional nature of the processes controlling batholith Menzie, 1962; Miesch and Morton, 1977; Morton, 1969; Morton et emplacement, and a combination of surface and subsurface mea- al., 1969; Morton and Baird, 1976; Sims, 1960). sured properties, in some cases there is overlap and/or gradation Because systematic variations across the Peninsular Ranges between the zones. Chemistry of the fi ve batholith zones is given batholith were recognized very early, previous workers have in Table 2 (on CD-ROM accompanying this volume and in the subdivided it into various longitudinal zones based on a variety GSA Data Repository [see footnote 1]). of parameters, including age, chemistry, isotopes, and potential fi eld data, (e.g., Baird et al., 1974, 1979; Taylor and Silver, 1978; General Features Baird and Miesch, 1984; Gromet and Silver, 1987; Silver and Chappell, 1988; Todd et al., 1988; Gastil et al., 1990; Langen- Relatively shallowly emplaced western zone plutons have heim et al., 2004). Most agree on a basic twofold subdivision of sharp, discordant contacts and passively intrude Mesozoic-age the batholith, generally termed the western and eastern zones. rocks. Pluton compositions range from olivine gabbro to high- This twofold subdivision has been variously attributed to (1) a silica monzogranite. Typically, mafi c enclave shapes are equidi- change in plate motions, (2) two magmatic arcs, or (3) a single mensional, not exhibiting the dynamically modifi ed shapes com- arc transitioning from oceanic to continental crust. Kimbrough et mon in varying degrees in zones to the east. Except for some al. (2001) calculated, for the 800 km length of the batholith north rocks in the northern part of the western zone, Sri values are of 28°N, that the western half constitutes 53% of the batholith typically between 0.7032 and 0.7040. In the northern Santa Ana and the eastern half 47%. Their western half ranged in age from Mountains and the northwestern Perris block, most Sri values ca. 140 to 105 Ma, and their eastern half from 99 to 92 Ma. are between 0.7044 and 0.7047, except for seven samples that Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 77

range from 0.7052 to 0.7075. Samples from the Jurupa Moun- eastern transition zone and eastern zone are less obvious than

tains, including the sample having a Sri of 0.7075 (sample DMM those between the western transition zone and eastern transition 94–13), are in an area of Paleozoic (?) metasedimentary rocks. zone, but the presence of megascopically noticeable sphene in Some of these samples may be anomalous due to interaction with eastern zone rocks is highly distinctive. The range in rock com- these metasedimentary host rocks. positions is more narrowly restricted in eastern zone plutons than Aeromagnetic data clearly show a major twofold division of in those of the western part of the batholith. Gabbro is sparse and the autochthonous batholith consisting of an intensely magnetic is found in only the western part of the zone. The eastern zone western part, essentially coincident with the western zone, and a is terminated on the east by the regional Late Cretaceous East- mildly magnetic part to the east (Fig. 18 [available on the CD-ROM ern Peninsular Ranges mylonite zone, which is bounded almost accompanying this volume and in the GSA Data Repository]). The everywhere on its east side by younger east-dipping thrust faults. upper-plate zone is more magnetic than the eastern zone. This two- These thrust faults place the easterly derived allochthonous fold magnetic division of the autochthonous part of the Peninsular upper-plate zone rocks above the Eastern Peninsular Ranges Ranges batholith extends for the length of the batholith (Gastil et mylonite zone and the eastern zone. al., 1990). As the aeromagnetic data refl ect magnetic properties to a Upper-plate zone plutons are distinctly younger and more depth of ~10 km, deviation between surface-collected data and the magnetic than those in the eastern zone. Major-element chemistry aeromagnetic data is to be expected. See Langenheim et al. (this of upper-plate zone rocks has a narrower range, and the average volume) for a geophysical overview of the batholith. silica value is lower than that of eastern zone rocks, disrupting the The boundary between the western zone and western transi- trend of higher silica values from west to east in the allochthonous tion zone in the northern Peninsular Ranges batholith is marked zones. Sri also has a narrow range, averaging 0.7079, which is con- by a change in rock fabric from isotropic to foliated. In the west- siderably higher than the 0.7067 average of the eastern zone. δ18O ern transition zone, pluton emplacement is dynamic, producing values are decidedly lower than in the eastern zone. concordant, in places gradational, contacts with the Mesozoic Based on collective structural, chemical, and isotopic data, host rocks. Where detailed mapping exists, the change from the western zone, western transition zone, eastern transition zone, western zone discordant pluton contacts to concordant western and eastern zone are interpreted to have developed as subduc- transition zone contacts is very obvious (e.g., Morton and Miller, tion transitioned from oceanic-arc setting to a continental margin 2006). In contrast to the equidimensional mafi c enclaves in west- arc setting. Western zone plutons were emplaced into Mesozoic ern zone plutons, mafi c enclaves in the western transition zone oceanic crust. Western transition zone and eastern transition zone are ellipsoidal- to pancake-shaped. All but the northern part of plutons were emplaced at the interface between oceanic and con- western zone–western transition zone boundary coincides with tinental crust. The eastern zone plutons were emplaced into older ε the Sri 0.7045 isopleth. Most initial epsilon Nd ( Ndi) values are continental crust, and granitic rocks, originating east of the east- slightly positive. Magnetite-bearing plutons of the western zone ern zone, were subsequently thrust westward on low-angle faults contrast with ilmenite-bearing plutons in the western transition to form the upper-plate zone. zone; the contrast is especially noticeable in aeromagnetic data. In general, our western transition zone corresponds to the A few zoned ilmenite-magnetite plutons occur in the western “…older, western static arc…” of Silver et al. (1979), the western transition zone (e.g., Lakeview Mountains pluton; Fig. 3). West- Peninsular Ranges batholith of Silver and Chappell (1988), and ern transition zone plutons have a range of chemistry similar to the western plutonic zone of Kimbrough et al. (2001) and Todd

that of the western zone but with Sri consistently greater than et al. (2003). Our combined western transition zone, eastern tran- ε 0.7045, and positive Ndi values. sition zone, eastern zone, and upper-plate zone corresponds in Host rock for the eastern transition zone is largely Meso- general to the “…younger migrating arc…” of Silver et al. (1979, zoic, but it includes some probable Paleozoic rocks. The eastern p. 92), the eastern Peninsular Ranges batholith of Silver and transition zone plutons, mostly larger than those of the western Chappell (1988), and the eastern zone of Kimbrough et al. (2001) transition zone, have less-well-developed planar fabrics than the and Todd et al. (2003). Our upper-plate zone may be included in typical western transition zone plutons. Sri values are more uni- the eastern part of the eastern zone of Kimbrough et al. (2001) and form and slightly higher in the eastern transition zone than they the eastern batholith of Todd et al. (2003), and it appears to be the are in the western transition zone. Similar to those in the east- same as the chemical domain F of Silver and Chappell (1988). ern zone, rocks in the eastern transition zone have more negative The upper-plate zone granitic rocks are exposed only north of ε δ18 ′Ν ′Ν ′Ν Ndi, and O >9‰. The eastern transition zone has geochemical 33°22.5 . South of 33°22.5 to 33°15 , any upper-plate zone similarities to the eastern zone, just as the western transition zone rocks are covered by postbatholithic sedimentary rocks (Fig. 2). has geochemical similarities to the western zone. All four zones collectively show an irregular, but distinct gradation of properties Some Batholith-Wide Rock Types across the batholith. Eastern zone plutons, emplaced into Paleozoic rocks, have Pegmatites 206 204 initial Pb/ Pb (Pbi) > 19 and Sri > 0.7060, with most Sri val- The northern Peninsular Ranges batholith is well known ues in the range of 0.7076–0.7084. Textural changes between the for a large number of complex pegmatites that include a number Downloaded from memoirs.gsapubs.org on March 25, 2014

78 Morton et al. of world-class gem- and lithium-bearing pegmatites. With one layers of garnet and tourmaline (Jahns and Wright, 1951). The exception, all of these complex pegmatites are located within 50-m-thick Stewart pegmatite, the largest complex pegmatite in the western zone, western transition zone, and eastern transi- the area, contains a complex of multiple zones. At the roof of the tion zone. Essentially all complex pegmatites in the northern Coahuila Valley pluton, in the Chihuahua Valley area, a greisen- Peninsular Ranges occur within plutonic rocks of the Peninsular like lithium-bearing rock contains lithium-bearing gem minerals. Ranges batholith. The largest and best-known gem- and lithium- The northernmost pegmatite district, Lakeview Mountains, con- bearing pegmatite districts are Pala (Jahns and Wright, 1951), sists of complex, rare-earth–bearing pegmatites (see Morton et Mesa Grande (Jahns, 1979), and Rincon (Hanley, 1951). Smaller al., this volume). districts include Aguanga Mountain, Chihuahua Valley, and Red Based on isotopic data from two plutons that host complex Mountain, and the single occurrence in the eastern zone, Thomas pegmatites, the Pala gabbro and the Lakeview Mountains pluton, Mountain (Fig. 3). An overview of the gem-bearing pegmatites the pegmatites and mafi c host rocks are essentially the same and in San Diego County was given in Weber (1963) and Foord et al. have essentially the same Sri. At Pala, western zone gabbro that (1991). Most of the complex pegmatites, including the gem- and hosts the lithium-bearing Stewart pegmatite has a U-Pb zircon age lithium-bearing pegmatites, are hosted by mafi c plutonic rocks, of 104 Ma, and muscovite from the pegmatite has a 40Ar/39Ar age gabbro, diorite, and mafi c tonalite (e.g., Jahns, 1979; Foord et of 100.4 Ma. Sri of the Pala Stewart pegmatite is 0.7040, simi- al., 1991). lar to the host gabbro value of 0.7034. Three tonalite samples Thin pegmatite dikes, many with planar-sided walls, are from the western transition zone Lakeview Mountains pluton, ubiquitous throughout the northern part of the batholith. They collected from the oldest to youngest parts of the pluton, have consist of symmetrical border and wall zones composed of bio- zircon ages of 97.4–100.6 Ma; monazite from a complex rare tite, sodic plagioclase, K-feldspar, and quartz. Graphic textures earth element (REE) pegmatite in the pluton has a sensitive high- within these dikes are common. Larger dikes have an interme- resolution ion microprobe (SHRIMP) age of 103 Ma and an iso- diate zone that includes schorl, garnet, muscovite, sodic plagio- tope dilution–thermal ionization mass spectrometry (ID-TIMS) clase, K-feldspar, and quartz, and, where present, a core zone consists of quartz and K-feldspar. The productive gem- and lithium-bearing pegmatites have miarolitic cavities in the core zone, or less commonly, in intermediate zones (Fig. 19), both of which are crystal-lined and contain loose euhedral crystals in the interior of the pockets (Fig. 20). Most shallow-dipping Pala district pegmatites have a low K-feldspar, aplitic-textured foot- wall rock, termed “line rock” that generally includes alternating

Figure 19. Core zone of the Stewart pegmatite, Pala, containing abundant lath-shaped crystals of converted spodumene that now consists Figure 20. Metasomatic chimney containing miarolitic cavities in an of petalite, spodumene, quartz, tridymite, heulandite, and stilbite in a intermediate zone of the Stewart pegmatite, Pala. The upward-tapering matrix of albite, petalite intergrown with heulandite, altered elbaite, chimney replaces perthite and consists of an outer zone of albite, quartz, and amblygonite-montebrasite. and muscovite and a core of albite that contains miarolitic cavities. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 79

age of 99.6 (Morton et al., this volume). Sri values for the Lake- the host rock (e.g., Larsen, 1948). The parentage for most maﬁ c view Mountains tonalite range from 0.7045 to 0.7051 and have enclaves is either unclear or undetermined, although earlier

an average value of 0.7048. Sri values for perthite from two peg- workers invoked a gabbroic parentage for many of them (e.g., matites are both 0.7049. The complex pegmatites appear to be the Larsen, 1948; Schwarcz, 1960). This interpretation is probably products of immiscible residues from mafi c host rock, and not in large part due to an early study by Hurlbut (1935), who clearly products of foreign fl uids derived from some nearby fertile gran- demonstrated that mafi c xenoliths in a tonalite pluton in San ite as generally interpreted (e.g., Jahns and Wright, 1951; Hanley, Diego County were derived from gabbro. In a few places, enclave 1951; Jahns, 1979; Foord et al., 1991; Walawender, 2003). parentage is recognizable. Larsen (1948, p. 162) noted that “… The typical inclusions were in almost perfect equilibrium with Gabbro the magma, and they would probably persist a very long time Gabbro bodies, originally called the San Marcos Gabbro by in a stagnant magma without mixing with the magma to give a Larsen (1948), occur in all zones except the upper-plate zone, homogeneous rock…” decreasing in volume from west to east. A few small gabbro bod- Mixing of magmas having distinctly different compositions ies occur in the western part of the eastern zone, but they are not has been described from granitic rocks of the Bernasconi Hills present in the eastern part. Most of our chemical and isotopic data area (Mason and Cohen, 1990), the San Jacinto pluton (Hill,

are from gabbro in the western zone. The Sri values of 18 gabbro 1984), and by Todd et al. (2003) for granitic rocks farther south samples from the western zone range from 0.7031 to 0.7043 and in the batholith. have an average of 0.7037, which is slightly less than the 0.7039 It appears that, regardless of initial composition, maﬁ c average value for all samples from the western zone. A troctolite enclaves attain a composition in equilibrium with the enclos- from the western transition zone, the Green Acres gabbro, has ing host rock, probably through grain-boundary advection of

a Sri value of 0.7046. Two samples from an eastern transition magmatic ﬂ uids because a positive correlation exists between zone gabbro body, collected only 100 m apart, have Sri values the silica content of an enclave and that of the enclosing host of 0.7034 and 0.7050. The eastern zone easternmost gabbro, an rock. Within the western zone Domenigoni Valley pluton, stoped olivine gabbro from a small body adjacent to the San Jacinto plu- calcareous quartzite xenoliths are progressively transformed to ton, has a Sri value of 0.7057. Based on these few samples from the composition of typical maﬁ c enclaves. The silica content of the western transition zone, eastern transition zone, and eastern the country rock of the Domenigoni Valley pluton is consistently

zone, a systematic increase in Sri from the western zone into the greater than that of the transformed maﬁ c xenoliths. In an apo- eastern zone is apparent, just as is true for granitic plutons. Rb/Sr phasis of the Domenigoni Valley pluton, the transformation of

ratios are very similar; all samples have Rb under 12 ppm, except calcareous quartzite xenoliths (SiO2 = 80%), derived from the

for one containing 36 ppm Rb. Gabbros from all four zones in country rock, to typical maﬁ c enclaves (SiO2 = 57%) within

which gabbro occurs have REE patterns that are similar to each the apophasis tonalite (SiO2 = 65%) clearly demonstrates that the other (Fig. 21) and to those reported by Todd et al. (2003) farther initial silica content of the xenolith is not the controlling factor to the south. Most of the gabbros have a positive Eu anomaly. Early workers in the northern Peninsular Ranges batholith 100 stated or implied that gabbro was the oldest component of the 99PT-8 Rice Canyon batholith (e.g., Jahns, 1954, 1979; Larsen, 1948). Zircon ages B 362 by David Kimbrough (D. Kimbrough, 2009, personal commun.) clearly demonstrate that gabbro bodies are not the oldest part of 10 the batholith but are of varying ages, which, in general, decrease from west to east. In the northern part of the Peninsular Ranges Rock/Chondrites

batholith, the westernmost gabbro of the western zone has a U-Pb 1 zircon age of 110.5 ± 0.7 Ma. The U-Pb zircon age of gabbro La Ce Pr Nd Sm Eu TbGd Dy Ho Er Tm Yb Lu from Rice Canyon, just west of Pala, is 112 ± 0.6 Ma, and at 100 Pala, the gabbro is 104 Ma (both localities are also in the western B483 zone). Gabbro at Thomas Mountain, adjacent to the 94 Ma San B379 DM94-98 Jacinto pluton, yields a U-Pb zircon age of 101.4 ± 1.7 Ma. Todd et al. (2003) described commingling of gabbroic and granitic 10 rocks indicating coexisting gabbroic and granitic magmas. Rock/Chondrites Maﬁ c Enclaves 1 Maﬁ c enclaves having relatively uniform mineralogic La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu composition are moderately abundant to very abundant in most Figure 21. Chondrite-normalized rare earth element (REE) spi- northern Peninsular Ranges batholith granitic rocks of all zones. der diagrams for representative gabbro bodies. Note the relatively Most enclaves have a higher biotite and hornblende content than strong positive Eu anomalies in B379 and B483. Downloaded from memoirs.gsapubs.org on March 25, 2014

80 Morton et al.

regarding the ﬁ nal silica content of the enclave, but rather the ﬁ nal Xenoliths in the Domenigoni Valley pluton typify morphology

silica content is a function of the silica content of the host rock. of fi rst-generation enclaves, E0 (Fig. 23). In western transition In the northern part of the batholith, the relationship between the zone, eastern transition zone, eastern zone, and upper-plate zone silica content of mafi c enclaves and host rock holds for the west- plutons, mafi c enclaves were dynamically shaped during pluton ern transition zone Lakeview Mountains pluton (Morton et al., emplacement, refl ecting movement in the host magma. These

1969) and the western transition zone Box Springs Mountains enclaves are referred to as transposed enclaves, E1. The degree pluton (Morton et al., this volume) (Fig. 22). The parentage of of enclave attenuation is a function of several variables, includ- maﬁ c enclaves in these two plutons is not known, but adjacent ing, but not limited to, the amount of movement within the host older rocks suggest it was not gabbro. The average silica content rock and its viscosity. Enclaves in the Lakeview Mountains and of enclaves increases with an increase in silica content of the host Val Verde plutons, and the Bernasconi monzogranite are typical

rock. For a host rock of 60% silica, the average silica content of E1 enclaves.

the enclaves is 10% less. This difference increases to an average E1 enclaves that have undergone deformation after pluton

of 13% for enclaves in a 75% silica host rock. emplacement are termed E2 enclaves. Shape alone cannot be

To determine the chemical variability of enclaves at the out- used to deﬁ ne whether an enclave is E1 or E2. The clearest case 2 crop scale, eight enclaves were collected from a 1 m outcrop in of transposition of E1 to E2 enclaves occurs when E1 enclaves the Lakeview Mountains pluton. The silica content of the host are only partly transposed to E2 or in outcrops that show alter- tonalite is 58%. The silica content of the enclaves ranged from nating E1and E2 enclave zones. Enclaves in the mixed granitic 46.7% to 50.8%, or 7.2%–11.3% less than the silica content of rocks south of the Lakeview Mountains pluton are examples of the tonalite; enclave silica average is 48.8%, or 9.2% less than the E1 enclaves partly transposed to E2 (Figs. 24 and 25). Lacking silica content of the tonalite. the presence of partly transposed E1 enclaves, the determination

Enclaves appear to be passive participants in the structural of whether extremely attenuated enclaves are E1 or E2 is ques- evolution of the granitic plutons. Shape, orientation, and fabric tionable. The uniform attenuated maﬁ c enclaves in the Reinhardt of most enclaves are dependent on the mode of pluton emplace- Canyon pluton (Fig. 26), which are interpreted as deformed by ment. Enclaves in passively emplaced western zone plutons are an expanding Lakeview Mountains pluton (see Morton et al., this mainly angular and commonly equant. Borrowing terminol- volume), are an example of E2 enclaves. ogy for structural designation of metamorphic tectonites, these enclaves are referred to as primary, or ﬁ rst-generation enclaves, Western Zone Plutons

E0. Xenoliths that retain or largely retain their initial composition (e.g., quartzite, phyllite, and schist) have more angular shapes Most western zone plutons are moderate sized, have discor- than those that have reached, or largely reached, equilibrium with dant contacts, are exposed at shallow levels, and were passively the host rock (Fig. 23). Some E0 enclaves may show some degree emplaced into Jurassic and Triassic metasedimentary rocks. The of alignment, but they are not physically (dynamically) shaped. plutons were emplaced from 126 to 108 Ma in an early extensional phase of subduction in a back-arc setting (e.g., Lee et al., 2007). Exposed levels of plutons crystallized at pressures of

68 1.5–3 kbar (Ague and Brimhall, 1988; Smith et al., 1991; Ham- 66 marstrom, 1992). Included in the western zone north of 33°N are three distinct ring complexes: the Paloma Valley ring complex 64 (Morton and Baird, 1976), the Gavilan ring complex described 62 here, and the Ramona ring complex, described in detail by Todd 60 et al. (this volume). These ring complexes are commonly inter- 58

(percent) preted to be roots of calderas. The location of the ring structures

2 56 in the western part of the Peninsular Ranges batholith is similar 54 to the location of ring structures in the westernmost part of the 52 Sierra Nevada batholith (e.g., Lackey et al., 2008). Enclave SiO Enclave 50 Lithologies of western zone plutons range from olivine gab- 48 bro to monzogranite. Granitoids that make up the western zone 46 55 60 65 70 75 plutons are visually characterized by isotropic fabric and equidimensional maﬁ c enclaves. These plutons have a broader range of Host rock SiO2 (percent) compositions than found in the plutons of the other four batholith

Figure 22. SiO2 value in host rocks compared to SiO2 values in the zones. Silica content averages 64.8% and ranges from 42.5% to mafi c enclaves within the host rocks. As the SiO value of host rock 18 2 76.8%. Most Sr values are between 0.7034 and 0.7040. The δ O increases, the SiO value of mafi c enclaves likewise increases. Analy- i 2 values range from +2.3‰ to +9.0‰ and average +6.9‰. Pb val- ses are of representative host rock and mafi c enclaves from the western i ε zone Domenigoni Valley pluton and western transition zone Lakeview ues have an average of 18.753. Based on 14 samples, Ndi values Mountains pluton and Box Springs Mountains plutonic complex. average +2.8, with ranges between +0.3 and +5.6, except for a Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 81

Quartzite Schist Mafic Mafic Mafic Gabbro xenoliths

Domenigoni Valley Pluton xenoliths Paloma Ring Complex xenoliths

Eo enclaves, Western Zone

E1 enclaves, Transition Zone

Figure 23. Maﬁ c enclaves, northern Peninsular Ranges batholith, showing characteristic enclave shapes related

to passive emplacement (E0), dynamic emplacement (E1), and late and post em- E2 enclaves placement deformation (E2).

Partly transposed E1 to E2 enclaves, Transition Zone E1

E1 and E2 enclaves

ε − single negative Ndi of –0.97 or 1.0 at the contact of a granodio- have been mapped as undifferentiated granitic rocks (e.g., Mor- rite pluton at Hot Springs Canyon on the west side of the northern ton and Miller, 2006). Pluton compositions range from gabbro to Santa Ana Mountains (Fig. 3). A sample from the same pluton monzogranite. Granitic rocks are mostly isotropic-textured bio- ε 500 m away from the contact has a Ndi of + 2.7 (see Premo et tite granodiorite containing various amounts of equidimensional ε al., this volume, Chapter 4). The negative Ndi sample also has an maﬁ c enclaves. Although most plutonic rocks have typical hypid-

anomalously high Pbi value of 19.092. iomorphic-granular textures, some hypabyssal granitic rocks are located in the Santiago Peak area (Fig. 3). Northern Santa Ana Mountains The westernmost sample from Hot Springs Canyon (Fig. 3.) Detailed studies of plutonic rocks in the northern Santa Ana near the contact of granodiorite and Bedford Canyon Formation

Mountains have not been undertaken due to a combination of has a U-Pb zircon age of 119.2 Maid and 117.4 Maip; a sample col-

exceedingly poor exposure and thick brush. Much of the area has lected 1 km east of the contact has a U-Pb zircon age of 119.9 Maip. been mapped only in reconnaissance, and many plutonic rocks In the vicinity of Elsinore Peak (Fig. 3), a large area is underlain by Downloaded from memoirs.gsapubs.org on March 25, 2014

82 Morton et al.

Figure 24. E1 enclaves transposed and others partly transposed to E2 enclaves, western transition zone tonalite from mixed granitic rock unit south of the Lakeview Mountains pluton, central Perris block.

homogeneous granodiorite that has a U-Pb zircon age of 125 Maip. Figure 26. Attenuated maﬁ c enclaves in the western transition zone

South of Elsinore Peak, intermixed gabbro, granodiorite-tonalite, Reinhardt Canyon pluton are interpreted to be E2 enclaves. Attenua- and monzogranite plutons are common. Within these intermixed tion is interpreted to be the result of upward and outward expansion plutonic rocks, there is the Squaw Mountain pluton (Fig. 3), a of the adjacent Lakeview Mountains pluton. Note pair of postenclave 2 deformation shears extending to the left from the central-upper part of well-deﬁ ned, small (5 km ), equant-shaped monzogranite pluton. the outcrop to the middle of the left side of outcrop. The Squaw Mountain pluton has an age similar to the Elsinore

Peak granodiorite, with U-Pb zircon ages of 120.4 Maid and

122.8 Maip. It consists of isotropic biotite monzogranite, some of which is semiporphyritic. East of the Squaw Mountain pluton, on the Santa Rosa Plateau, a hornblende tonalite pluton has U-Pb

zircon dates of 122.0 Maid and 126.0 Maip. In the northern Santa Ana Mountains, most REE patterns for generic granodiorite, commonly referred to as Woodson Mountain granodiorite (e.g., Larsen, 1948), have moderate negative Eu anomalies and have slight increases in heavy REEs (Fig. 27).

Perris Block Western zone plutons are much better exposed on the Perris block than those in the Santa Ana Mountains. Three western zone

100

10 472 479 Rock/Chondrites 476 489

1 Figure 25. Tonalite outcrop showing both E1 and E2 enclaves. Tonalite LaNdPrCe Sm Eu Gd Tb HoDy Er Tm Yb with extremely attenuated E2 enclaves in central part of photograph (area with narrow light streaks of quartz) is bordered by a zone in the Figure 27. Chondrite-normalized rare earth element (REE) spider tonalite that contains noticeably less-attenuated E1 enclaves. Mixed diagrams for western zone Woodson Mountain granodiorite, showing western transition zone granitic rocks south of the Lakeview Moun- consistent negative Eu anomalies, particularly strong for sample 489. tains pluton, central Perris block. All samples are from the Baird-Welday collection. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 83 ppm Kgb Kgb Kgb

Qal

33 ° 37’ 30” 37’ ° Kgb

Qal

117 ° 07’ 30” 07’ ° Kpvt Qal ppm Kpvt Kpvt ppm Qal Kpvt Kgb uids. Tvh Kpvt Kpvg Kpvt Kpvt Kpvg Kgb Kgb Kgb Qal Qal Tvh Kpvg ppm Qal Kgb Kpvg Kgb Kt Kgb Kpvg Kgb Kgb Kpvgr Kgb Kgb N Km Kpvg Kgb Kdvg Kpvg Kpvgr Qal Kgb 012 Kpvgr Kpvg Kpvg Kpvg Kgb Kdvg Qal Kpvgb Kgb Kpvg Qal ppm Kpvgr Kpvp Kpvgr

Kpvg

33 ° 37’ 30” 37’ ° Kgb

Kpvg ° 15’ 15’ ° Kgb Qal

Kgb 117 Kgb Kgb Kpvg Kgb Kpvg Kgd Alluvium Pegmatite dikes Pegmatite Ranges Batholith metamorphic rocks Pre-Peninsular Estelle Mountain volcanics of Herzig (1991) Mountain volcanics Estelle Basalt of Hogbacks Granophyre and monzogranite Granodiorite Tonalite undivided and gabbro, Granodiorite undivided Granodiorite, undivided Tonalite, undivided Gabbro, Granodiorite and monzogranite of Dominigoni Pluton and monzogranite Granodiorite Kt

Qal Tvh Kgd Kgb Kpvt

ppm Kdvg Kpvg Kpvp Kvem Kpvgr Kpvgb

Complex Kgd Ring Valley Paloma Kvem Figure 28. Generalized geologic map of the western zone Paloma Valley ring complex, Paloma Valley area, Perris block. The older outer ring dike of granodiorite outer ring dike The older area, Perris block. Valley Paloma ring complex, Valley Figure 28. Generalized geologic map of the western zone Paloma lls domal-shaped fractures that resulted from ﬁ complex ring dike The younger inner pegmatitic emplaced by magmatic stoping of gabbro. and monzogranite was ﬂ are products of pressure-quenched pegmatitic Aphanitic granophyre bodies in the center of complex cauldron subsidence. Downloaded from memoirs.gsapubs.org on March 25, 2014

84 Morton et al. plutons have been studied in detail: the Paloma Valley ring com- diorite of the unit, from the eastern part of the outer dike, has a plex (Morton and Baird, 1976), the Domenigoni Valley pluton U-Pb zircon age of 119.3 Maip. (Morton et al., this volume), and the Ramona ring dike (Todd et The inner and younger part of the ring dike complex con- al., this volume). sists of hundreds of thin, relatively short-arc granitic pegmatite Paloma Valley ring complex. The Paloma Valley ring com- and interlayered pegmatitic-textured and coarse-grained granite plex (Fig. 28) is a composite ring complex consisting of an outer dikes. These dikes defi ne a domal structure composed of steeply granodiorite ring dike, emplaced by magmatic stoping in gab- dipping outer dikes that shallow progressively to subhorizontal bro, and an inner set of slightly younger pegmatitic and granit- in the center of the complex (Fig. 28). Most pegmatite dikes oid dikes, most of which were emplaced in the gabbro core of are 30 cm to 1 m thick and are texturally and compositionally the older dike (Morton and Baird, 1976). The outer granodiorite zoned. Mineralogy of the dikes is simple: Outer zones of coarse- ring dike is composed of massive granodiorite and monzogran- grained granite are composed of quartz, perthite, and sodic pla- ite that grade to tonalite in the eastern part of the complex. In gioclase, and, locally, biotite and minor amounts of magnetite. some places, a faintly developed planar fabric, produced by ori- Pegmatite inner zones consist of pegmatitic perthite, sodic pla- ented biotite crystals, parallels the geometry of the ring dike. The gioclase, quartz, biotite, and/or muscovite. Some pegmatite dikes elliptical in plan outer ring dike, and several subsidiary short-arc have accessory magnetite, schorl, garnet, and epidote, and some dikes, are steep walled. Continuity of the outer dike is interrupted larger dikes contain small miarolitic cavities lined with quartz in its northwest part for 0.5 km by the southeast end of a mass of crystals. Graphic intergrowths of quartz and perthite are common metasedimentary rock that was apparently more resistant to stop- in rock transitional between coarse-grained granite and pegma- ing than the gabbro. titic granite. Dikes that lack pegmatitic cores consist entirely of The outer granodiorite dike was emplaced into gabbro by coarse- to extremely coarse-grained granitoid textured rock, with ring fracturing and magmatic stoping. Stoped masses of gab- or without graphic intergrowths. Based on their domal arrange- bro are common to abundant in much of the dike; locally, the ment, the dikes of the younger ring complex dikes are interpreted amounts of granodiorite dike rock and stoped gabbro are sub- as products of volatile-charged magma that fi lled a domal set of equal (Fig. 29). Based on the low magnesium content of the fractures developed during cauldron subsidence attendant to the granodiorite, however, only a few percent of gabbro could have emplacement of the outer dike. been assimilated by the granodiorite magma (Morton and Baird, Horizontal and near-horizontal fl oored masses of grano- 1976). The larger, stoped gabbro blocks are up to 3 km in length. phyre occur in the central part of the ring complex. Where fresh, Many of these large stoped gabbro blocks are plate-like or ellip- the granophyre is pale gray, but it typically weathers to form tical. Most of the elliptically shaped blocks are oriented with reddish-brown outcrops due to oxidation of pyrite, a ubiquitous the long axes vertical, although a few are oriented with the long accessory mineral. The very fi ne-grained porphyritic granophyre axes near horizontal. U-Pb zircon ages of atypical hornblende- consists of phenocrysts of altered plagioclase in a groundmass of bearing granodiorite from the western part of the outer dike are granophyric intergrowths of quartz within K-feldspar and sodic 40 39 121.3 Maid and 121.2 Maip. The Ar/ Ar ages of hornblende and plagioclase. A network of pegmatitic stringers averaging 2.5 cm biotite are 117.7 and 118.8 Ma, respectively. More typical grano- thick cuts much of the granophyre. These pegmatitic stringers are compositionally and texturally zoned and have fi ne-grained margins and coarse-grained interiors. Vertically and steeply dipping pegmatite stringers are symmetrically zoned, whereas horizontal or gently dipping stringers are asymmetrically zoned. The asymmetrically zoned pegmatite stringers have plagioclase crystals growing upward from the base and K-feldspar crystals growing and increasing in size downward from the top of the dike. The granophyre is interpreted as the product of pressure- quenched granitic pegmatite magma. The potassium content of the granophyre is lower than that of the granitic pegmatites, and the calcium content is higher. The lower potassium content is interpreted as due to a loss of volatiles, including potassium, accompanied by the decrease in pressure during cauldron subsidence. Less-mobile calcium remained in the pressure-quenched granophyre (Fig. 30). Gavilan ring complex. The discontinuously exposed, elliptical-in-plan, composite Gavilan ring complex consists Figure 29. Stoped gabbro blocks in the granodiorite of the older outer of granitic rocks ranging from hypersthene monzogranite to ring dike, Paloma Valley ring complex, north side of the ring dike where biotite-hornblende tonalite (Morton, 2001; Morton and Weber, it is exposed in road cuts on Scott Road, west of U.S. Interstate 215. 2003). Located in the core of the ring complex, but not part of Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 85

5.0 dimensional mesocratic-to-melanocratic enclaves. The northeast- 4.5 ern part of the complex consists of hypersthene monzogranite. 4.0 This black monzogranite weathers to form slopes covered with distinctive dark-brown outcrops. The monzogranite contains 3.5 hypersthene, clinopyroxene, hornblende, and biotite, as well as 3.0 sparse small maﬁ c enclaves that are commonly lighter colored O (percent) 2 Dike K 2.5 than the fresh monzogranite. This part of the complex, with its Granophyre widely spaced joints, has been quarried for stone, marketed as 2.0 black granite (Fig. 32). 1.5 Medium-grained biotite-hornblende tonalite and moder- 1.0 ately ﬁ ne-grained tonalite in the northern part of the complex 77 77.5 78 78.5 79 have a faint, poorly developed foliation and contain abundant, SiO (percent) 2 small platy mesocratic enclaves. In the northeastern part of the complex, a relatively small body of coarse-grained, relatively 1.2 light-colored biotite-hornblende tonalite resembles a schlieren- free tonalite in the western transition zone Lakeview Mountains 1.0 pluton. This tonalite weathers to form giant core stones. Chemi- 0.8 cal analyses of the major rock types of the complex are given in Table 2 (on CD-ROM accompanying this volume and in the GSA 0.6 Data Repository [see footnote 1]). Several gold mines in the Gavilan ring complex comprise

CaO (percent) CaO 0.4 the Pinacate mining district (Sampson, 1935). The largest pro- Dike ducer was the Goodhope Mine, located in the southeastern part 0.2 Granophyre of the complex. The gold occurred in arsenopyrite-bearing quartz 0 veins that are spatially restricted to the complex. 77 77.5 78 78.5 79 SiO (percent) U-Pb zircon ages for the complex have a spread of 5.3 m.y., 2 ranging from 112.9 to 107.6 Ma. U-Pb zircon ages of the hypersthene tonalite are 112.9 Ma and 112.7 Ma . The 40Ar/39Ar age Figure 30. Comparison of K2O and CaO values of younger ring dike id ip rocks and granophyre of the Paloma Valley ring complex. Lower value of biotite and K-feldspar in the same rock is 106.2 Ma and of K2O in the granophyre is interpreted to be the result of potassium 95–103.5 Ma, respectively. U-Pb zircon ages for the black leaving the young ring dike magma when pressure was reduced during hypersthene monzogranite are 109.0 Ma and 107.6 Ma . The caldron subsidence. id ip 40Ar/39Ar age of biotite is 104.5 Ma, and the age of K-feldspar is 98–100.5 Ma. U-Pb zircon ages for the ﬁ ne-grained tonalite in

the northern part of the complex are 108.5 Maid and 109.1 Maip, 40 39 it, is the near-circular Arroyo del Toro pluton (Fig. 31). Interlay- and the U-Pb age of sphene is 103.9 Maid. The Ar/ Ar ages of ered Estelle Mountain volcanics and well-indurated sedimentary hornblende, biotite, and K-feldspar from this rock are 106.4 Ma, rocks are the country rocks on the west side of the complex; rocks 103.1 Ma, and 101–97 Ma, respectively. of Menifee Valley are the host rocks in the eastern part. Arroyo del Toro pluton. Located in the center of the Gavilan In the southeastern part of the complex, the level of expo- ring complex, the nearly circular Arroyo del Toro pluton geo- sure is at the complex roof, giving rise to irregular traces of con- metrically resembles a resurgent dome (Fig. 31). The pluton tacts with the rocks of Menifee Valley. Textures within the ring intrudes Estelle Mountain volcanics and well-indurated Creta- complex grade from hypabyssal in the west to hypautomorphic- ceous sedimentary rocks on the west and rocks of Menifee Valley granular in the central and eastern parts. Based on textural dif- on the east. The pluton is spatially related to the Gavilan ring ferences and country rock relations, the ring complex was tilted complex, but because its chemistry and mineralogy are so differ- up on the east, and the near-horizontal erosion surface exposes ent from those of the ring complex units, it is not considered to be progressively deeper levels of the complex from west to east. related petrogenetically to the complex. Chemically, the Arroyo

The hypabyssal rocks in the western part of the body grade topo- del Toro pluton is higher in Na2O and SiO2 and lower in MgO graphically upward into volcanic-textured rocks that were pre- and Fe2O3 than the Gavilan ring complex. The pluton is com- viously mapped as intrusive rocks related to the Santiago Peak posed of light-gray, medium-grained, very homogeneous iso- volcanics (Weber, 1976). tropic biotite-hornblende granodiorite. Where exposed, the con- Hypersthene is a characteristic mineral for most of the com- tact with surrounding rocks is very sharp (Fig. 33). Some of the plex. A feature restricted to the northern part of the complex is a granodiorite in the western part of the pluton is subporphyritic. distinctive brown weathering, massive, hypautomorphic-granular Small equidimensional maﬁ c enclaves are rare. The granodiorite hypersthene-bearing biotite-hornblende tonalite. It contains equi- typically weathers to form large boulders (Fig. 34). Based on the Downloaded from memoirs.gsapubs.org on March 25, 2014

86 Morton et al.

Kop

Kop Kgb Kgb Kop Kop QTs Kgtf QTs TRmv

Kgtf TRmv Kop Kgct Kgt Kgb

TRmv QTs

Kgti Kght Kgg TRmv QTs Kop

TRmv QTs QTs Kgt Kv Kop

33° 45’ Arroyo del Toro Pluton TRmv 117° 22’ 30”

Kgt

Kv TRmv

TRmv Kgh TRmv

Kop QTs

TRmv QTs Quaternary and Tertiary sediments

Kga Arroyo del Toro Pluton

Kgg Hypersthene monzogranite

Kgt Hypersthene tonalite Kgh Hypabyssal tonalite N Kgtf Foliated tonalite

Kgti Tonalite containing abundant mesocratic inclusions

Kgct Coarse-grained biotite-hornblende tonalite Gavilan Ring Complex Kght Heterogeneous tonalite 0 1 2 Other granitic rocks of the Peninsular Ranges Batholith Kop Km Kgb Gabbro, undivided Some map labels in dark areas are shown in white Kv Estelle Mountain volcanics of Herzig (1991)

TRmv Rocks of Menifee Valley

Figure 31. Generalized geologic map of the western zone Gavilan ring complex and the Arroyo del Toro pluton, Perris block. Despite its locational and temporal coincidence with the Gavilan ring complex, on the basis of geochemical and isotopic properties, the Arroyo del Toro pluton is considered to be petrogenetically unrelated to the Gavilan complex. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 87

Figure 32. Quarry in massive-textured, hypersthene-bearing monzogranite (Kgg unit); Kgg is cut by widely spaced joints, northeastern part of the Gavilan ring complex. Kgg was quarried and marketed under the name “Black Granite.” Figure 34. Boulder-covered slopes underlain by the Arroyo del Toro pluton stand in contrast to the rubbly, brush-covered slopes underlain by the Estelle Mountain volcanics of Herzig (1991). Southwestern contact of the Arroyo del Toro pluton. speciﬁ c gravity of 20 samples collected across the pluton, it is very homogeneous, with values ranging from 2.621 to 2.66, and a mean value of 2.647. The speciﬁ c gravity range of 0.039 is considerably less than the 0.191 range in the Lakeview Mountains ring complex. Chemical analysis of granodiorite of the pluton is tonalite or the 0.07 range in the Domenigoni Valley pluton. The given in Table 2 (on CD-ROM accompanying this volume and in emplacement age of the Arroyo del Toro pluton is the same as the GSA Data Repository [see footnote 1]). that of the Gavilan ring complex. U-Pb zircon ages are 108.6 Maid Domenigoni Valley pluton. At the present level of expo- 40 39 and 113.4 Maip. The Ar/ Ar age of biotite is 104.3 Ma, and sure, the pluton consists of two roughly elliptical in plan, non- K-feldspar age is 94–102.5 Ma. Although apparently not sharing contiguous bodies separated by a septum composed of Trias- a petrogenetic relationship to the Gavilan ring complex, because sic (?) metasedimentary rocks, Cretaceous gabbro, and minor of its location and similarity in age, the Arroyo del Toro pluton Cretaceous granitic rock (Fig. 35). The eastern body, which is almost certainly shares an emplacement history with the Gavilan ~11 km long and 8 km wide, underlies an area of ~88 km2; the western body underlies an area of ~24 km2. Subsurface, beneath the intervening septum, the two parts of the pluton are inferred to be joined and have a combined areal extent of ~160 km2. Two small apophyses of Domenigoni Valley–type granitic rocks intrude calcareous quartzite within the septum; one apophysis is well exposed in a highway cut on Interstate 215. Several irregularly shaped apophyses, with very discordant contacts, are poorly exposed within quartzite west of the pluton (Fig. 35). The pluton contact is steeply dipping, except where the eastern extent of the pluton is within the western transition zone. Displacement in the western transition zone has deformed and elevated the eastern edge of the pluton, forming a shallow-dipping contact with rocks of Menifee Valley. The degree of deformation in the tonalite ranges from closely spaced fractures to gneissic-textured tonalite (Morton et al., this volume). The pluton was passively emplaced into low- to intermediate- metamorphic-grade metasedimentary rocks of the Triassic-age (?) rocks of Menifee Valley (Morton and Miller, 2006). The metasedimentary rocks consist mainly of impure quartzite, calcareous quartzite, phyllite, interlayered quartzite and Figure 33. Hand sample showing sharp contact between the Estelle Mountain volcanics of Herzig (1991) and granodiorite of the Arroyo phyllite, and metagraywacke. Where seen, the contact with coun- del Toro pluton. Where seen, western zone pluton contacts are typi- try rock is extremely sharp with little or no observable chemical cally very sharp. or textural change in the country rock at the contact (Fig. 36). The Downloaded from memoirs.gsapubs.org on March 25, 2014

88 Morton et al. pluton contact is conspicuously discordant in all but the southern pluton. In the apophasis exposed on I-215, xenoliths range from part of the pluton, where it is structurally concordant with folia- thermally metamorphosed metasedimentary xenoliths to those tion in phyllite. The contact between this part of the pluton and in all stages of transformation into the maﬁ c xenoliths that are the phyllite is not exposed. typical of the pluton. The pluton is composed of massive, isotropic, gray, Two relatively consistent, steeply dipping joint sets are medium-grained, biotite-hornblende tonalite, minor granodio- present throughout the pluton; one strikes northeast, and the rite, and some faintly foliated rock in the southeastern part of other strikes northwest. A dacite-quartz latite dike swarm was the pluton. Biotite in the northeastern part of the pluton consists emplaced along these northwest-striking joints. Most of the dikes of felted aggregates. Common accessory minerals include zir- are located in the eastern part of the pluton, but a few extend con, sphene, apatite, and magnetite-ilmenite. Minute, oriented into the surrounding metasedimentary country rock or occur rutile crystals impart a faint blue opalescence to the quartz. entirely within the metasedimentary rock pendant separating the Small masses of epidote and/or tourmaline rock occur locally two halves of the pluton. Almost all of the dikes are foliated and and replace the granodiorite-tonalite. The tonalite-granodiorite lineated. The foliated texture of the dikes contrasts sharply with contains common-to-abundant equidimensional maﬁ c xenoliths the massive texture of the enclosing tonalite. Some dike rocks (Fig. 37). Xenoliths are rare or lacking around the margins of the contain small needle-like hornblende prisms. Streaks of biotite,

117° 07′ 30′ W 33° 45’45 ′ N

80 85

Kdv 70 McCall Blvd 70 70 52 70 80 32 65 75 85 Kdv 45 Kgb 75 DB sample site TRmv 80 TRmv I-215 apophysis 60 65 75 50 TRmv 70 50 Kql 60 Kql 70 55 62 60 Kdv 56 80 TRmv Kob Kql 54 Kdv 58 70 75

Kdv 60 68 TR mv 80

TR mv 80 80 Kob 80 65 75 75 Kql Kgb 70 Kgb Kdv 72 Kdv TRmv 75 55

70 82 55 60 80 60 Kdv 50 Kob 65 70 45 TRmv 60 65 75 65 KgbKgb Kgb 65 65 70 50 80 Kql Quartz latite dikes 65 Kql Kdv Domenigoni Valley Pluton Foliation N Kob Other batholithic rocks 55 Primary igneous 55 Metamorphic Kgb Gabbro 33° 37’ 30” 012 Lineation 117° 07’ 30” Km TRmv Rocks of Menifee Valley 50Primary igneous

Figure 35. Generalized geologic map of the western zone Domenigoni Valley pluton, Perris block. The McCall Boule- vard, I-215 apophasis, and DB sample site localities are discussed in text. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 89

Figure 37. Typical equant- to irregular-shaped maﬁ c xenoliths in isotropic biotite-hornblende tonalite, central part of the western zone Domenigoni Valley pluton, Perris block.

3.3 3.6 4.2 N

3.8 5.0 3.4 3.7 3.03.0 4.8 3.6 3.2 4.2 3.7 2.8 3.7 3.2 3.6 012 4.4 Figure 36. Contact between the Domenigoni Valley pluton and the in- 4.3 2.9 3.5 Km terlayered quartzite and biotite schist of the rocks of Menifee Valley 3.0 3.4 (Morton and Miller, 2006). No contact effects, structural or chemical, 3.4 3.6 3.8 are visible at the contact. Photograph was taken on McCall Boulevard 4.3 on the east side of the city of Menifee Valley. Keys for scale. 3.9 4.0 3.7 4.4 3.8 4.2 4.0 4.2 4.0 4.3 4.4 4.0 4.4 and less commonly, oriented hornblende crystals give rise to a 4.0 4.0 4.1 4.2 4.1 4.3 2.8 33° 41’ 15” 4.0 pronounced lineation plunging to the southeast. 4.0 4.1 4.1 3.8 4.8 4.0 4.3 Zircons from the western part of the pluton have U-Pb 117° 07’ 30” 40 39 3.8 4.3 4.1 4.3 ages of 117.8 Maid and 123.3 Maip. The Ar/ Ar ages of horn- 3.4 blende, biotite, and K-feldspar from this sample are 122.6 Ma, 3.6 4.1 4.1 3.7 103.7 Ma, and 95.5 Ma, respectively. A sample from the north- 4.0

eastern part of the pluton, adjacent to the 100 Ma western transi- 3.5 3.9 4.2 4.3 3.9 3.4 3.5 tion zone metasedimentary rocks and the 100 Ma, dynamically 3.6 3.4 3.8 3.6 3.5 emplaced Lakeview Mountains pluton, has U-Pb zircon ages of 4.2 5.4 4.2 4.6 119 Ma and 124 Ma (Premo et al., this volume, Chapter 4). 4.0 id id 3.5 4.4 Hornblende and biotite from this sample have 40Ar/39Ar ages of 3.6 3.9 4.04.2 101.3 Ma and 93.7 Ma, respectively. The young 40Ar/39Ar ages Figure 38. Fifth-degree trend surface map of percent Fe O vari- of hornblende and biotite in the northeastern part of the pluton 2 3 ation in the Domenigoni Valley pluton. Fe2O3 is low in the north- are interpreted as reset ages along the western part of the west- east part of the pluton, which is the least δ18O- contaminated part ern transition zone. of the pluton (Turi and Taylor, 1971). Downloaded from memoirs.gsapubs.org on March 25, 2014

90 Morton et al.

90 5.0 85 AAB4.5 B 4.0 80 3.5 75 3.0 70 2.5 Contact (percent) 2 65 2.0 MgO (percent)

SiO 1.5 60 1.0 Contact 55 0.5 50 0 -10 06010 20 30 40 50 -10 06010 20 30 40 50 Meters Meters

Figure 39. Variation in SiO2 (A) and MgO (B) at the outer part of the Domenigoni Valley pluton, McCall Boulevard, on the east side of the city of Menifee Valley. Tonalite of the pluton is shown as open circles. The three solid circles outside the pluton contact are rocks of Menifee

Valley; the solid circles within the pluton are maﬁ c xenoliths. Note the higher SiO2 and lower MgO values of the tonalite near the contact.

Like the majority of western zone plutons, the Domenigoni location as one of Turi and Taylor’s sample traverses, determined Valley pluton is relatively primitive, with relatively low initial the pluton composition to be quite uniform at distances >25 m 87 86 Sr/ Sr ratios (Sri). Sri values of six samples from the pluton from the contact. Tonalite at the contact of the pluton has higher

range from 0.7037 to 0.7045, and average 0.7041 (Kistler et al., SiO2 and Al2O3 contents and a lower contents of CaO, Fe2O3, and 2003, this volume). MgO than tonalite 1 m inside the pluton (Fig. 38). The ﬁ rst xeno- Turi and Taylor (1971) found that the eastern body of the lith encountered (7 m inside the host rock contact) has slightly pluton has undergone pronounced oxygen and hydrogen iso- higher silica and alumina contents than xenoliths farther from the topic exchange affecting at least 70% of the body. They inter- contact (Fig. 39). Based on detailed chemistry at and near the plu- preted elevated isotopic values as evidence of contamination ton contact, the pluton magma chamber chemically homogenized by the metasedimentary country rock. In contrast to the wide- within ~25 m of the outer contact, i.e., very different from the spread isotopic exchange, major elemental variation shows oxygen and hydrogen isotope exchange that affects at least 70% only the northeastern part of the eastern body having slightly of the pluton. more silicic and less maﬁ c tonalite than the rest of the pluton Cajalco pluton. The Cajalco pluton extends from south of (Fig. 38). This northeastern area is within a low-δ18O zone of Lake Mathews, northwest to the Norco–La Sierra area (Figs. 2 Turi and Taylor (1971). and 3). The pluton was emplaced by magmatic stoping of Estelle A detailed examination of the outer 51.5 m section of the Mountain volcanics and volcaniclastic rocks in the western part eastern body exposed on McCall Boulevard (Fig. 35), the same of the pluton and gabbro in the central and eastern parts. Areas in

TABLE 3. MAJOR OXIDES (%) AND TRACE ELEMENTS (PPM) OF GRANITIC AND TOURMALINIZED ROCKS, CAJALCO PLUTON

Sample Rock type SiO2 Al2O3 Fe2O3* MgO CaO Na2OK2OTiO2 P2O5 MnO Sc V Co Rb Sr Y DMM-94-71 Granodiorite 72.9 13.7 2.47 0.54 2.18 3.49 3.31 0.30 0.11 0.03 4.07 25.16 4.67 157.84 135.23 20.13 DMM-94-72 Granodiorite 72.9 13.7 2.48 0.57 2.16 3.52 3.40 0.30 0.12 0.04 4.13 24.8 3.99 187.9 137 18.55 DMM-94-75 Granodiorite 72.7 13.8 2.61 0.52 1.85 3.51 3.41 0.30 0.12 0.07 4.54 28.29 2.22 178.78 142.78 13.58 DMM-94-78 Monzogranite 75.4 12.9 1.54 0.24 1.45 3.18 4.20 0.19 0.08 0.02 2.98 13.81 1.62 173.58 98.47 33.13 Caj-1 Least 74.3 13.4 2.07 0.35 1.71 3.44 3.79 0.24 0.04 0.03 6 20 2.1 137 116 29.6 tourmalinized Caj-2 Least 75.2 12.9 1.96 0.43 1.7 3.13 3.89 0.23 0.03 0.03 <5 15 2.2 138 124 26.6 tourmalinized Caj-3 Slightly 74.6 13.3 2.1 0.42 1.59 3.59 3.41 0.24 0.04 0.05 <5 18 2.1 118 118 40.3 tourmalinized Caj-4 Slightly 73.7 13.3 1.99 0.41 1.83 3.45 3.64 0.24 0.04 0.02 <5 18 3.4 138 132 24 tourmalinized Caj-5 Moderately 71.8 12.5 8.73 0.32 0.49 0.79 0.04 0.22 0.04 0.03 <5 15 1.5 1.4 52 7.2 tourmalinized Caj-6 Moderately 75.7 11.3 6.83 0.57 0.32 0.6 0.03 0.19 0.04 0.02 <5 14 2.2 1.2 48.5 9.7 tourmalinized Caj-7 Tourmaline 65.6 17.1 6.16 2.23 0.55 0.81 0.31 0.63 0.07 0.03 12 101 7.2 17.3 53.5 41 Caj-8 Tourmaline 36 27.7 17 4.28 1.25 2.06 0.51 0.3 <0.01 0.05 14 56 5.8 38.9 193 33.6

*Total Fe expressed as Fe2O3. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 91

from fi ne to coarse grained. Northwest of Lake Mathews, much of the pluton consists of fi ne-grained leucocratic monzogranite. In the subporphyritic and porphyritic rocks near the pluton roof, quartz phenocrysts have a beta quartz habit. Locally, the subporphyritic and porphyritic rocks contain small miarolitic cavities. In the eastern part of the pluton, monzogranite is subordinate to granodiorite. The granodiorite is mainly medium grained, equigranular, hypautomorphic-granular and contains variable amounts of angular mafi c enclaves. Within the pluton, there are a few hypabyssal porphyritic dikes composed of distinctive feldspar phenocrysts in a dark-gray, very fi ne-grained groundmass (Fig. 40). Autometamorphic tourmalinized rock is widespread near the pluton roof in the western part of the pluton. Tourmaliniza- Figure 40. Hypabyssal-textured porphyritic dike that intrudes grano- tion extends into overlying volcanic and volcaniclastic rocks. The diorite of the western zone Cajalco pluton, south of Lake Mathews, tourmalinized rock ranges from incipient fracture-fi lling fi lms to northern Perris block. large masses up to hundreds of meters in length, both consisting of essentially only tourmaline and accessory minerals. These large tourmaline bodies, locally termed “tourmaline blow-outs,” consist of very fi ne-grained to aphanitic schorl that is more ero- the western part of the pluton are underlain by subequal amounts sionally resistant than surrounding granodiorite and stands out as of granodiorite and stoped quartz latite porphyry of the Estelle small, bold black hills. Northeast-striking joints are preferential Mountain volcanics. Small to mappable (1:24,000 scale) stoped sites for the most tourmalinized rock. In the areas of most intense blocks of gabbro are abundant north of Lake Mathews, where the tourmalinization, the host monzogranite has subporphyritic and pluton consists of about equal volumes of gabbro and granodio- porphyritic textures. rite (Morton and Weber, 2001). The chemistry of the various stages and degree of tourma- The pluton is composed mostly of biotite and biotite- linization are given in Table 3 and shown in Figure 41. The fi rst hornblende monzogranite and granodiorite. Textures in the plu- stage of tourmalinization is fracture fi lling by paper-thin layers of ton change from porphyritic and subporphyritic in the shallower tourmaline (Fig. 41A). Tourmalinization progressively extends western part of the body to hypautomorphic granular in the cen- beyond fracture fi lling to replace minerals adjacent to the frac- tral and eastern parts. Porphyritic textures are common in the ture, fi rst replacing mafi c minerals (Fig. 41B) and then feldspar. granodiorite near the pluton roof. The west-to-east variation in In moderate tourmalinization, quartz content increases with the texture suggests that the pluton, like the Gavilan ring complex, increase in tourmaline (Fig. 41C). With further tourmalinization, was tilted up on the east. Grain size is quite variable, ranging quartz is progressively replaced by tourmaline. Where quartz

Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Hf Ta W Th U 106.88 4.42 5.55 631.18 16.61 32.23 3.49 15.97 2.95 0.61 3.16 0.64 3.32 0.73 2.33 0.35 2.12 3.41 0.66 0.76 10.61 2.3 106.02 5.04 5.67 662.37 19.45 38.94 3.94 15.31 3.07 0.7 2.71 0.5 3.22 7 2.14 0.24 1.78 3.24 0.6 0.25 14.56 1.33 116.29 4.52 8.12 717.22 15.67 34.14 3.25 14.94 2.84 0.87 2.49 0.36 2.5 0.47 1.64 0.28 1.45 3.72 0.35 1.06 14.87 4 117.02 5.09 3.76 676.79 32.47 66.92 7 26.43 5.97 0.66 4.73 0.9 5.56 1.19 3.45 0.53 3.35 4.36 0.73 0.58 23.33 3.28 177 6 4.8 863 18.1 33.8 4.32 16.7 3.9 0.77 4.29 0.82 5.18 1.15 3.49 0.54 3.5 6 0.7 0.7 17.9 4.12

142 5 5.2 804 29.6 59.5 6.75 24.7 4.8 0.58 4.66 0.76 5.08 0.98 2.93 0.44 2.9 5 0.6 0.6 20.6 5.49

145 6 2.7 800 29 59 6.77 25.1 5.3 0.75 5.7 1.15 7.53 1.61 4.73 0.74 4.8 5 0.7 0.7 17.1 13.7

160 5 3.8 832 18.9 37.8 4.34 16.4 3.6 0.64 3.45 0.63 4.28 0.88 2.52 0.4 2.9 5 0.5 0.5 14.5 5.16

147 3 0.7 7.2 4.3 8.4 1.03 3.9 0.9 0.12 1.11 0.17 1.05 0.28 0.8 0.11 0.9 5 <0.5 <0.5 15.6 1.91

147 3 0.5 2.4 7.6 15.2 1.83 7 1.3 0.15 1.56 0.26 1.67 0.39 1.03 0.18 1.5 5 <0.5 <0.5 22.3 3.08

93.1 15 0.5 41.5 8.2 12.3 1.99 8.6 2 0.31 3.14 0.67 4.9 1.29 4 0.7 4.1 3 0.8 0.8 6.9 2.98 114 4 1.2 22.3 1.9 3.1 0.4 1.7 0.4 0.12 0.89 0.28 3.46 1.22 5.21 1.07 8.9 4 0.5 0.5 26.8 2.44 Downloaded from memoirs.gsapubs.org on March 25, 2014

92 Morton et al. is the only remaining mineral of the original rock, the resulting tacts of western zone plutons. The clearest distinction between tourmalinized rock is a very distinctive, white-dappled black western zone and transition zone plutons is seen in the western rock resembling porphyry (Fig. 41D). Brecciated tourmalinized transition zone plutons, which have intense and well-developed ε rock is common and occurs in zones as thin as 0.5 cm to tens of planar foliations, slightly positive Ndi, and Sri >0.7045. West- meters. Monzogranite clasts in breccia zones show various stages ern transition zone plutons are ilmenite bearing, in contrast to of tourmalinization. Some clasts are zoned, indicating breccia- the magnetite- bearing western zone plutons. This difference tion occurred during tourmalinization (Fig. 41E). produces a marked change in the aeromagnetic expression of Completely tourmalinized rock contains small amounts of the highly magnetic western zone against the weakly magnetic pyrite, and very locally, cassiterite. Cassiterite occurs as branch- western transition zone (Fig. 18 [available on the CD-ROM ing and anastomosing light-brown veinlets (Fig. 41F) and as accompanying this volume and in the GSA Data Repository ε small dark-brown masses of zoned crystals (Fig. 41G). Most (see footnote 1)]). The slightly positive Ndi that characterizes of the extensively tourmalinized rock has been prospected for the western transition zone plutons extends to the western tran- tin, which was discovered ca. 1853 within a large body of tour- sition zone Lakeview Mountains pluton, which is magnetite and ε malinized rock in the Eagle Valley area west of Lake Mathews ilmenite bearing and has a slightly positive Ndi, (+0.4). Values (Sampson, 1935). of δ18O are <9‰ in the western transition zone and >9‰ in the Average silica content of typical Cajalco pluton rock in the eastern transition zone, and eastern transition zone plutons have ε western part of the pluton is 73%; moderately tourmalinized rock distinctively negative Ndi values. The eastern transition zone has slightly higher silica, 74%–75%. Silica content decreases includes large plutons of the La Posta–type that do not occur in to a range of between 65.6% and 36% in completely tourma- the western transition zone but are typical of the eastern zone. linized rock. With progressive tourmalinization, CaO and K2O La Posta–type plutons of the eastern transition zone are distin- decrease with replacement of feldspar, and Al2O3, MgO, and guished from those of the eastern zone in having Sri < 0.7060

Fe2O3 increase with increases in tourmaline (Table 3). and, except for a few samples, Pbi of <19. Locally, dumortierite rather than tourmaline occurs, most commonly as large sprays of pink-to-violet acicular to pris- Western Transition Zone Plutons matic radiating crystals. An exceptionally large tabular body of dumortierite located in Temescal Canyon (Fig. 3) has been Western transition zone plutons occur in an irregular zone described as a dumortierite dike (Larsen, 1948). Cobbles of up to 25 km wide in the northern part of the Perris block. South- tourmalinized rock are locally abundant in the Miocene Lake eastward, the western transition zone abruptly narrows south of Mathews Formation and in Quaternary fl uvial deposits in the 33°22′Ν, where a 5 km width of intensely deformed metamor- area south of Lake Mathews. phic rocks, devoid of western transition zone plutons, separates U-Pb zircon ages from the coarse-grained monzogran- the western zone from the eastern transition zone (Fig. 2). This ite of the Cajalco pluton are 109.5 Maid and 111.5 Maip. REE patterns for the Cajalco pluton (Fig. 42) are similar to (1) the generic granodiorite of the western zone plutons, (2) the patterns of Gromet and Silver (1987) for granodiorite of their western Figure 41. Tourmalinized monzogranite, Cajalco pluton, Eagle Valley, region, and (3) the Las Bancas and East Mesa plutonic suites of northern Perris block. (A) Incipient tourmalinization of semiporphyritic monzogranite containing beta habit quartz. Introduction of tour- Todd et al. (2003). maline and quartz is largely restricted to fractures in the monzogranite. Some outward progression of tourmalinization formed the thicker Transition Zone Plutons tourmalinized fracture in the center of the photograph. Note development of breccia along the vertical tourmalinized fracture on the right The western and eastern transition zones formed (Fig. 2) side of the photograph. (B) Pervasive tourmalinization has replaced all mafi c minerals in semiporphyritic monzogranite as well as expanding as subduction transitioned from beneath a Mesozoic oce- into the monzogranite along fractures. Breccia in thicker tourmalin- anic arc to beneath a continental marginal setting overlain ized rock is visible below the quarter. (C) Monzogranite in which tour- by thicker and older continental crust (e.g., Lee et al., 2007). malinization ranges from incipient to complete. Left side of sample Western transition zone plutons have some geochemical simi- is essentially unaltered monzogranite that grades into silica-enriched larities with plutons of the western zone, and similarly, some quartz tourmaline rock, and progressively increases in tourmaline passing into breccia zone on right side of sample. (D) Uniformly tour- eastern transition zone plutons are zoned La Posta–type plu- malinized monzogranite. All mafi c minerals and feldspars have been tons common in the eastern zone. La Posta–type plutons have replaced by tourmaline, leaving only quartz of the original monzogran- tonalite outer parts and granodiorite-monzogranite cores, the ite. This sample is from a 100-m-wide tourmalinized body. (E) Brec- latter of which are commonly muscovite bearing. Transition ciated tourmalinized monzogranite. Light areas are breccia clasts, not zone plutons were emplaced mostly in Mesozoic rocks, but phenocrysts, that are in various stages of tourmalinization. Nolan pick for scale. (F) Vein-like masses of cassiterite in massive aphanitic tour- some intruded Paleozoic metamorphic rocks in the eastern part maline. (G) Zoned cassiterite crystals in massive aphanitic tourmaline. of the eastern transition zone. Pluton contacts are concordant The two largest, prominently zoned crystals just below the center of with enclosing country rock, in contrast to the discordant con- the photomicrograph are approximately 0.5 mm across. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 93

E F

G Downloaded from memoirs.gsapubs.org on March 25, 2014

94 Morton et al.

belt of deformed metamorphic rocks, wholly within the western Extensive alluvial cover in the Riverside–Jurupa Mountains area transition zone, continues southward for ~10 km, to the point obscures much of the geometry and intrusive relationships of the where it is intruded by a massive to foliated tonalite body, the plutons at the north end of the western transition zone. Chemical Tucalota Valley pluton, which may be part of, or related to, a analyses for all western transition zone units are given in Table 2 large body of the tonalite of Coahuila Valley to the east. The (on CD-ROM accompanying this volume and in GSA Data western transition zone widens around the Tucalota Valley pluton Repository [see footnote 1]). and a kilometer-wide metamorphic screen along its eastern side, Granitic rocks at the northern edge of the batholith. The and then narrows again to about a width of 2 km just south of the northwesternmost Peninsular Ranges batholith exposures are a pluton. To the southeast, the western transition zone widens to, few isolated outcrops of biotite-hornblende tonalite in the Ele- and maintains, an average width of ~10 km to at least latitude phant Hill area west of Pomona (Fig. 3), only 3 km south of an 33°N. Plutons of the western transition zone south of 33°N have exposure of Transverse Ranges granitic rock (see Premo et al., only been mapped in reconnaissance, and although tonalite pre- this volume, Chapter 2). The tonalite at Elephant Hill has U-Pb

dominates, the western transition zone consists of a wide range zircon ages of 98.3 Maid and 100 Maip. The Sri of the tonalite is ε of granitic lithologies that are mixed with large areas of meta- 0.7055, and Ndi is 0.4. morphic rocks. To the east, exposures of granitic rocks in the Jurupa Moun- Western transition zone plutons are eroded at mid- to lower- tains (Fig. 3) include gabbro, tonalite, and granodioritic bodies, crustal depths, as indicated by pressures of crystallization rang- and common granitic pegmatite dikes, emplaced in probable ing from 4.5 to 6.5 kbar (Ague and Brimhall, 1988; Smith et al., Paleozoic metasedimentary rocks. Some bodies are elongate in a 1991). In contrast to the isotropic textured western zone granitic western Transverse Ranges orientation, while others are in a more plutons containing equidimensional enclaves, western transition typical northwest Peninsular Ranges orientation. The gabbro is zone plutons consist of well-foliated rock containing ellipsoidal typical medium- to coarse-grained hornblende-pyroxene gabbro. to pancake-shaped enclaves. Locally, some of these enclaves Biotite-hornblende tonalite is relatively heterogeneous, foliated, have undergone two periods of deformation (Figs. 22 and 23). and medium- to coarse-grained hypautomorphic-granular tonal- Silica content of the western transition zone rocks ranges from ite. Many outcrops of tonalitic rocks have two different planar 42.9% to 77.1%, and averages 63.8%. fabrics, a northwest-striking fabric and an east-striking fabric. Plutons range in composition from olivine gabbro to mon- Most outcrops of biotite granodiorite appear relatively homo-

zogranite and are characterized isotopically by moderate Sri geneous. U-Pb zircon ages for the tonalite are 104 Maid, 104.1 δ18 (0.7045–0.7055), O (+7‰ to +10‰), and Pbi average 18.744. Maid, and 101.7 Maip. Sri of the tonalite is 0.7044 and 0.7047. ε The Ndi values are positive +0.4 to +2.9. Pluton emplacement age Granodiorite U-Pb zircon age is 111 Maip. The granodiorite has ranges from 111 to 98 Ma. an abnormally high value Sri of 0.7076. In addition to discrete plutons, the western transition zone Granites of the Riverside area. Discontinuous bodies of includes signifi cant expanses of heterogeneous granitic rocks, biotite granite and local hypersthene and fayalite granite occur which are commonly gneissic rocks consisting mostly of biotite- in the Riverside area. Although located within the western tran- hornblende granodiorite and tonalite. These heterogeneous gra- sition zone and having mostly western transition zone proper- nitic rocks have moderately well-developed planar fabrics and are ties, some of these bodies are more typical of western zone more mineralogically heterogeneous in close proximity to meta- plutons based on texture and age. Most of the granitic rocks in morphic country rock. Northeast of Lakeview (Fig. 3), where they the Riverside area are leucocratic, medium- to coarse-grained, are in contact with the rocks of Jacumba Mountains, these rocks massive- to faintly foliated biotite granite that averages 1%–3% contain abundant thin mafi c enclaves. The heterogeneous rock biotite. Mafi c enclaves are sparse, except locally in some western unit bordering the Lakeview Mountains pluton in many places contains complex, composite irregular-to-planar shear zones that appear to be protoclastic. Ellipsoidal mafi c enclaves are partly 100 B330 to completely transposed and attenuated where cut by the shear B332 zones. These shear zones are interpreted to have resulted from the B333 outward expansion of the Lakeview Mountains pluton (Morton et al., this volume). 10 Gabbro is less common in the western transition zone than in the western zone, but this contrasts with the near absence of Rock/Chondrites gabbro farther east in the batholith. Most of the gabbro in the 1 western transition zone is hornblende gabbro with lesser amounts LaNdPrCe GdEuSm Tb ErHoDy Tm Yb of olivine gabbro. Three plutons, the Val Verde, the Lakeview Figure 42. Chondrite-normalized rare earth element (REE) spider Mountains, and the Box Springs Mountains plutonic complex, diagram for Cajalco pluton, showing relatively uniform, moderate- comprise most of the northern part of the western transition zone, ly strong negative Eu anomalies. All samples are from the Baird- in addition to some small plutons in the Bernasconi Hills (Fig. 3). Welday collection. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 95

exposures, where the granite contains 2%–8% biotite and sparse contains abundant light-green chlorite. Locally, the rocks con- to abundant xenoliths of quartz diorite, granodiorite, and fi ne- sist of nematoblastic hornblende gabbro, which is typically 46% grained mafi c rock. At Mount Rubidoux (Fig. 3), granite con- brown hornblende, 7% green hornblende, 9% clinopyroxene, 2% tains sparse hypersthene and fayalitic olivine and has a higher olivine, 34% calcic plagioclase, and 2% opaque minerals. A vari- concentration of dark-gray, fi ne-grained enclaves. Also at Mount ety of small gabbroic dikes cut the olivine gabbro. These dikes Rubidoux, a second body, informally named the granite of Mount consist of equigranular fi ne- to coarse-grained mesocratic to Rubidoux (Morton and Miller, 2006), is a coarse-grained granite melanocratic hornblende gabbro, porphyritic hornblende-olivine phase that is also characterized by fayalite and hypersthene. This gabbro, and porphyritic anorthite-olivine gabbro. latter granite is massive and heterogranular, with an average grain Two small elliptical masses of distinctive troctolite (Fig. 44)

size of 5 mm, and contains some K-feldspar crystals up to 12 mm in the southern part of the unit contain ~45% anorthite (An90),

in length. Biotite and hornblende aggregate to ~5%, and fayalite 36% olivine (Fo85), 11% clinopyroxene, 3% orthopyroxene, 2% and hypersthene are scarce constituents. U-Pb zircon ages are hornblende, 2% spinel, and 5% iddingsite. Kelyphytic rims man- 40 39 109.1 Maid and 106.1 Maip. The Ar/ Ar ages of biotite and of tle most olivine crystals, and large subhedral anorthite crystals K-feldspar are 98.2 Ma and 95–91 Ma, respectively. impart a slightly porphyritic texture to the troctolite. Clinopyrox- Green Acres gabbro. The Green Acres gabbro is a hetero- ene and hornblende occur as large poikilitic crystals enclosing geneous gabbroic body, the northern half of which consists of large areas of plagioclase and olivine crystals. Locally, masses intermingled olivine, pyroxene, and hornblende gabbros intruded of leucocratic gabbro consist largely to entirely of labradorite- by biotite-hornblende quartz diorite and tonalite (for a thorough anorthite with small quantities of olivine and/or pyroxene. This description of the Green Acres gabbro, see Berger, this volume). anorthitic gabbro weathers to form gray slopes. Within the unit, quartz diorite and tonalite decompose more read- Pegmatite dikes are common in the Green Acres gabbro. ily than gabbro, giving rise to slopes covered by gabbro rubble, Euhedral garnet and tourmaline (schorl) are common accessory which in most places masks the presence of the quartz diorite minerals; some pegmatite dikes contain andalusite, apparently and tonalite. Locally, the unit contains small masses of orbicular produced by chemical interaction between pegmatite and gab- gabbro (Fig. 43). bro. One pegmatite dike contains a mass of gabbro altered to bio- The southern half of the body is mainly olivine gabbro, con- tite, hydrobiotite, and vermiculite enclosing individual andalusite taining olivine (Fo75 to Fo87) that ranges from a few percent to crystals up to 6 cm in length. Euhedral dark-blue corundum crys- about one third of the rock. Anorthite (An90) makes up 30%–90% tals, up to 1 cm in length, occur in the core of some andalusite of the gabbro as anhedral to subhedral, complexly twinned crys- crystals. Webb (1943) interpreted this relationship as resulting tals. Hypersthene and augite are widespread; commonly, augite is from the incorporation of metasedimentary rock into the pegma- mantled with brown and/or green hornblende. Light-green horn- tite, but we interpret it to be the result of interaction between the blende occurs primarily in kelyphytic reaction rims intergrown pegmatite and included masses of olivine gabbro. Some of the with spinel around olivine. Thin, planar, vein-like hornblende- pegmatite dikes are mylonitic with very planar fabric and pro- spinel masses are common in gabbro that contains abundant oliv- nounced mineral lineation. ine. Protoclastic olivine gabbro (ﬂ aser gabbro) occurs locally and

Figure 44. Isotropic-textured troctolite containing large crystals of an- Figure 43. Orbicular gabbro, northeast part of the western transition orthitic plagioclase, southern part of the Green Acres gabbro, central zone Green Acres gabbro, central Perris block. Perris block. Downloaded from memoirs.gsapubs.org on March 25, 2014

96 Morton et al.

Mixed granitic rocks at the south end of the Lakeview Val Verde pluton. The Val Verde pluton, located along the Mountains pluton contain several small bodies of metamor- west side of the western transition zone, extends from south phosed gabbro apparently derived from the Green Acres gabbro. of Perris northward to the Riverside area (Figs. 2 and 45). The This metagabbro contains abundant masses of chlorite and blue- pluton is steep walled, exposed at a midcrustal depth, and com- green hornblende. posed of relatively homogeneous, foliated, medium- to coarse-

35 10 35 35 20 25 Kdg 30 40 20 Kvv 35 30 45 40 25 Kg 30 Figure 45. Generalized geologic map Qal 35 20 Kdg 25 of the western transition zone Val Verde 15 Km 75 30 20 25 pluton. In contrast to the isotropic-tex- 45 30 Kvv 75 55 55 35 50 60 45 tured western zone plutons, abundant 35 45 70 60 Kdg foliation attitudes reﬂ ect the structure 25 40 30 40 30 40 Kg 40 60 40 35 typically developed in western transi- 50 55 60 tion zone plutons. Note the northeast- 55 50 50 45 60 35 35 70 70 45 50 striking foliations in the northern part 80 45 50 40 60 70 70 80 80 45 25 80 30 50 of the pluton. These foliations postdate 80 80 50 45 25 20 80 70 30 55 10 60 50 60 15 8 65 70 65 40 the northwest-striking foliations. Some 60 20 6070 65 60 55 60 60 70 60 50 outcrops in the northern part of the plu- 50 60 45 45 30 50 45 55 65 ton contain northwest- and northeast- 55 70 45 Qal 60 85 70 60 60 55 80 striking foliations. 60 50 75 80 70 65 55 60 70 55 60 65 70 75 65 45 65 75 65 50 70 75 60 40 55 50 20 80 40 75 50 60 70 70 55 75 75 50 50 55 50 Kvv 60 Kvv 60 50 60 55 55 50 70 45 60 37 60 75 Qal 65 45 25 117° 15’ 40 45 10 65 35 35 Qal 60 Km 35 50 50 70 33° 52’ 30” 40 60 70 40 25 50 60 40 35 35 40 35 60 70 30 40 45 50 47 50 Kgb 50 50 40 50 Km 30 30 40 45 50 40 25 20 20 50 45 50 50 50 20 20 Kdg 30 40 27 55 Kg 35 25 35 30 20 35 75 70 45 70 10 70 30 70 30 20 70 30 Kg 20 50 30 15 55 13 30 10 20 75 60 Kg Kgb 55 10 50 40 80 40 25 85 40 30 25 4550 35 25 N 80 85 55 55 20 50 30 40 15 40 30 10 70 12 15 55 45 1515 15 8 7 10 10 Qal 30 pKm 15 25 35 Kdg 45 45 25 45 60 60 70 80 55 65 55 70 25 55 012 50 30 12 60 55 45 45 80 85 55 45 70 Km 50 45 40 70 55 60 20 70 pKm Kvv 60 60 40 75 85 55 35 15 70 50 70 35 75 10 85 60 40 40 40 60 70 70 60 60 25 Qal Quaternary alluvium 85 20 75 Kgb 55 60 40 8580 45 65 70 Km Migmatite Kgb 60 85 55 40 60 40 85 50 70 70 Kg Leucocratic granitic rocks 45 65 75 54 75 70 75 55 50 60 40 pKm 65 57 Kvv Val Verde Pluton 60 75 65 60 35 30 65 50 65 40 60 55 10 45 45 Kdg Mixed granodiorite and diorite 65 70 40 70 30 45 55 40 30 Kvv Kgb Gabbro 50 65 60 40 35 40 50 50 50 20 72 67 pKm 25 15 Pre-Cretaceous metamorphic rocks 55 45 40 25 50 Qal 35 pKm 40 45 50 50 65 Inclined foliation 45 48 40 70 45 50 Vertical foliation 65 42 40 Horizontal foliation 60 60 45 65 50 Lineation 60 50 60 55 42 65 75 Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 97 grained hypautomorphic-granular biotite-hornblende tonalite. ated. In this part of the pluton, there are segregation masses of The K-feldspar content is less than 2% for most of the tonal- mesocratic-to-melanocratic tonalite. ite, except along the west margin of the pluton, where it ranges The Val Verde pluton is slightly older than the adjacent from 2% to 10%. A number of gabbro and migmatitic bodies and Box Springs and Lakeview Mountains plutons. U-Pb zircon 40 39 one elongate heterogeneous granodiorite-quartz diorite body are ages are 105.7 Maid and 107.8 Maip. The Ar/ Ar ages of enclosed within the pluton; all of these bodies appear to be older hornblende, biotite, and K-feldspar are 100.5 Ma, 94.7, and than the Val Verde pluton. Pegmatite dikes are rare, contrasting 90.3–86.5 Ma, respectively. with the adjacent Box Springs Mountains plutonic complex and Lakeview Mountains pluton. The Lakeview Mountains the Lakeview Mountains pluton. However, one tabular-shaped pluton is a steep-walled, in plan view, teardrop-shaped pluton pegmatite has a length of 2 km and contains basal aplitic line- (Morton, 2003c, 2003d; Morton and Matti, 2001a) exposed at rock layering. midcrustal depth (Fig. 47). Emplacement of the pluton is inter- Most of the foliation in the tonalite strikes northwest, par- preted to have been largely forceful. The body is located at a allel to the regional structural grain of the batholith, and dips major defl ection of the regional northwest structural grain within moderately to steeply to the northeast (Fig. 45). In the northern the batholith. This defl ection is interpreted to have been caused 3 km of the central part of the pluton, east-to-northeast–striking by outward growth of the pluton. For a more complete descrip- foliations are dominant. To the south, some tonalite outcrops tion and chemistry of this pluton, see Morton et al. (this volume). include two planar fabrics, an older northwest-striking foliation Mineralogically, the pluton is characterized by extreme cut by a younger east-striking foliation. An elegant investigation heterogeneity produced by ubiquitous schlieren. The pluton of the modal mineralogy and structure of the tonalite through consists of foliated biotite-hornblende tonalite, virtually devoid the central part of the pluton, along the Colorado River aqueduct of K-feldspar, which occurs only as rare antiperthite. Schlieren tunnel, was conducted by Osborn (1939). Based on petrofabric range in composition from leucocratic plagioclase-quartz rock analysis, Osborn determined the tonalite had two different pla- to melanocratic biotite-hornblende rock; in most of the pluton, nar mineral orientations. these schlieren range from a few centimeters to several meters in The tonalite contains abundant elliptical to pancake-shaped length (Fig. 48). Typically, schlieren are near-planar, but some are mafi c enclaves parallel to the foliation plane (Fig. 46). Where wispy and folded. Locally, alternating sheet-like concentrations measured in the northern part of the pluton, the long axes of elon- of plagioclase-quartz rock and biotite-hornblende rock produce gate mafi c enclaves are oriented northeast and plunge at moder- a pronounced layering commonly consisting of juxtaposed leu- ate angles to the northeast. In the central and southern parts of cocratic quartz-plagioclase and melanocratic hornblende-biotite the pluton, elongate enclaves strike east to southeast and plunge layers. Some hornblende is cored with colorless cummingtonite. at low to moderate angles to the southeast. In the south-central Ellipsoidal to pancake-shaped mafi c enclaves are common. part of the pluton, much of the rock is massive or has only faint, Plagioclase-quartz rock and biotite-hornblende rock form commonly horizontal, foliation, and the enclaves are less attenu- mappable-sized (1:24,000 scale) bodies. Except for form and scale, the composition of these bodies is similar to that of the schlieren. Leucocratic rock masses consist of andesine and quartz that have minor amounts of poikilitic biotite and hornblende. Muscovite occurs in these rocks as a rare accessory mineral interstitial to plagioclase. Melanocratic rock masses range in composition from ~50% biotite-hornblende to entirely biotite-hornblende. An elliptical body of comb-layered gabbro is located along the southwest margin of the pluton. Layering in the gabbro consists of alternating layers of labradorite gabbro and hornblende or augite gabbro. Labradorite crystals are oriented normal to the layering and branch upward from the base of a layer to form feather-like crystals. Folded layering, having fold amplitudes of 1 cm, is common. Concentrated near the center of the pluton are masses of hypersthene gabbro. Numerous granitic pegmatite dikes are also concentrated in the center of the pluton. Most of the dikes are tabular, steeply dipping, and strike northeast and southwest. A few dikes are bulbous (Jahns, 1955), and a few are thickened at a roll in Figure 46. Crudely, but pervasively, foliated biotite-hornblende tonal- the dip of the dike. Almost all dikes are symmetrically zoned, ite of the Val Verde pluton, Perris block. Tonalite breaks along foliation compositionally and texturally. Many contain rare earth miner- that includes elongate E1 mafi c enclaves. als, both oxides and phosphates. Downloaded from memoirs.gsapubs.org on March 25, 2014

98 Morton et al.

80 73 80 Khg Khg 75 75 78 85 80 83 73 85 80 87 80 82 80 85 85 65 80 85 75 Klmt 75 80 75 Qal 75 80 80 Klmt 85 80 80 80 81 80 85 85 85 72 85 Qal 85 65 76 75 60 85 60 85

52 80 80 80 Klmt 60 55 80 64 60 65 50 80 70 80 70 50 64 75 56 80 55 15 70 65 40 40 61 65 35 70 Klmt 60 85 55 40 60 80 60 40 83 30 82 77 40 55 40 85 87 70 64 80 82 75 52 84 65 46 55 70 40 60 64 45 80 65 60 55 50 80 70 75 75 75 75 80 62 55 65 70 84 86 78 50 60 60 65 75 65 50 70 70 82 70 50 50 75 75 65 75 82 82 64 58 80 74 7865 75 70 85 80 80 65 75 70 80 80 85 82 50 80 80 80 60 80 85 85 80 46 67 70 85 65 7580 77 85 65 65 75 80 60 80 85 Khg 70 75 80 Klmt 55 78 85 N 75 70 79 75 67 72 75 83 72 65 75 80 80 80 60 82 68 70 72 70 70 82 80 65 55 55 66 80 Klmt 82 65 87 65 80 70 55 80 80 45 75 75 80 77 80 10 70 50 70 80 85 70 70 80 50 75 8277 75 80 83 80 78 82 87 77 65 70 75 80 55 55 60 65 70 68 87 87 80 74 60 80 72 60 85 60 85 82 80 85 80 80 65 55 50 75 85 7585 8588 70 70 57 72 75 87 Qal Quaternary alluvium 55 72 83 65 75 65 70 55 72 82 70 Khg 68 80 65 80 Klmt Lakeview Mountains pluton Khg 60 75 88 80 65 82 Qal 82 75 78 Khg Heterogeneous granitic rocks 46 65 82 Qal 80 70 75 77 77 70 70 80 85 75 Attitude of schlieren 65 80 70 70 75 65 50 65 33° 45’ 70 70 70 70 70 65 72 65 Inclined, showing dip Khg 80 70 70 75 75 70 Vertical 117° 07’ 30” 75 78 66 65 85 Inclined, showing dip direction 80 78 012 Khg 65 Strike only 78 80 Km 75 Khg

Figure 47. Generalized geologic map of the western transition zone Lakeveiw Mountains pluton showing concordant and discordant northwest- and northeast-oriented schlieren.

Although masked by extreme outcrop-scale chemical varia- Mountains pluton, has a well-developed planar fabric parallel to tion produced by schlieren, the pluton is chemically and miner- the outline of the body, and contains abundant mafi c enclaves that alogically zoned (Morton et al., 1969, this volume). Even though in places are rod-shaped and vertical (Fig. 26). A more exten- the Lakeview Mountains pluton is located in a relatively low- sive description of the pluton is included in the discussion of the magnetic part of the Peninsular Ranges batholith, the center part Lakeview Mountains pluton (Morton et al., this volume). of the pluton is more magnetic than any other part of the western Box Springs Mountains plutonic complex. The Box Springs transition zone (Langenheim et al., 2004). Mountains plutonic complex is elliptical in plan view, fl at fl oored,

U-Pb zircon ages from two samples are 100 Maid, 97.4 Maip and compositionally, isotopically, and texturally zoned. It is made

and 99.3 Maid and 98 Maip. A third sample has an age of 100.2 Maip. up of ﬁ ve major and two minor units (Fig. 49). The core of the The 40Ar/39Ar age of hornblende is 98.6 Ma, and the conventional complex consists of massive isotropic, high-silica biotite tonalite. K/Ar age of biotite is 92.4 Ma. The pressure of crystallization of Foliated biotite tonalite and granodiorite surround this core, and hornblende is 5–5.5 kbar (Smith et al., 1991). they are in turn surrounded by a variety of foliated tonalite and Reinhardt Canyon pluton. An arcuate-shaped tonalite plu- granodiorite. Based on a combination of geometry and fabric, ton, the Reinhardt Canyon pluton, borders the east side of the the plutonic complex is interpreted as an elongate balloon-like Lakeview Mountains pluton. Most tonalite of the Reinhardt Can- mass having a tapering inﬂ ation point near its north end. The yon pluton lacks the ubiquitous schlieren of the adjacent Lakeview outer parts of the complex are in contact with biotite-hornblende Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 99

produced by variation in biotite content. Modal mineralogy of this and other units of the Box Springs Mountains plutonic complex is given in Table 4. The tonalite contains scattered, equant subrounded maﬁ c enclaves. The morphology of these enclaves is markedly different from the discoidal to platy maﬁ c enclaves that are common throughout the rest of the complex. U-Pb zircon

ages from the core unit are 98.6 Maid and 98 Maip, and the core

rocks have a high Pbi of 19.016. The massive biotite tonalite (Kbt) is in contact with a biotite granite (Kbgr) on the east and north, a heterogeneous biotite- hornblende tonalite (Kbht) on the west, and appears to grade southward to light-gray, medium- to coarse-grained, foliated biotite tonalite and granodiorite (Fig. 51, Kbfg). The biotite granite (Kbgr) has steeply dipping foliation and occurs north of the core Kbt on Blue Mountain, where it is intruded by Kbt. In the La Loma Hills, in the northwestern part of the complex, the biotite granite is located between two older units, a porphyritic granodiorite and granite (Kbgg) and foliated hornblende tonalite (Kft). Kbht, which is a light-gray, nonequigranular, medium- to coarse-grained, foliated granitic rock, is restricted to the west Figure 48. Typical melanocratic biotite-hornblende schlieren, south- side of the core in the northwestern part of the Box Springs western Lakeview Mountains pluton. Mountains, where it intrudes a foliated biotite-hornblende tonalite (Kbft). The dominant rock type is leucocratic tonalite containing a few percent biotite, which occurs as thin irregular plates that are randomly distributed but crudely aligned to produce a tonalite. All of the units include abundant mafi c enclaves, most of wispy, swirling foliation. Within the leucocratic tonalite, pods which are discoidal to platy in shape. and lenses of more mafi c tonalite contain ~15% large ragged The southern part of the complex was included by Larsen crystals of biotite. Both the leucocratic and more mafi c tonalite (1948) in his general Bonsall tonalite unit, but the northern part contain 30%–40% quartz. Sparse potassium feldspar makes up is located north of his map area. In addition to Larsen’s work, 1% or less of the rocks. The tonalite contains dispersed, discoidal the complex has been the subject of several theses (Menzie, mesocratic enclaves. Simple granitic pegmatite dikes are abun- 1962; Joshi, 1967; Stock, 1992) and is included in its entirety dant within the unit. on a series of detailed 7.5′ quadrangle geologic maps (Morton, The contact between foliated Kbfg and the nonfoliated com- 1978; Morton and Cox, 2001a; Morton and Matti, 2001b). The plex core unit Kbt is drawn on the basis of foliation development major units of the complex are described here from the core to because the compositional difference between the two units is the outer margin and are shown on Figure 49. In general, this not obvious in some places. The inner part of unit Kbfg is tonal- sequence is interpreted as representing the youngest to oldest ite containing minor hornblende and K-feldspar. K-feldspar is parts of the complex. extremely variable in the unit, ranging from 1% to 21%, progres- The center of the complex is composed of light-gray, fi ne- sively increasing outward, grading from tonalite to granodiorite. to medium-grained equigranular biotite tonalite (Fig. 50; Kbt Mafi c, discoidal enclaves are common but not abundant. The on Fig. 49). Unlike other rocks of the complex, the center is Kbfg unit thins and pinches out along the west side of the core. massive-textured, and only in the outer part has a crude folia- On the east side of the complex, biotite granodiorite and tonalite tion developed. Lithologically identical tonalite occurs as a are bounded by a unit of similar lithology (Fig. 49, Kbfgi), which small elliptical-shaped body on the summit of Blue Mountain contains very abundant discoidal mafi c enclaves. north of the complex core. Compositional layering in the cen- Surrounding Kbfg and the enclave-rich Kbfgi unit, there is ter of the complex is shallow-dipping to horizontal, defi ning a a heterogeneous porphyritic granodiorite that locally grades to shallow basin that is horizontally fl oored. Unlike the core of tonalite (Kbhg). This unit is thickest in the southeast part of the the complex, the biotite tonalite body on the summit of Blue complex, pinches out along the southwest side, and reappears

Mountain has steeply inward-dipping foliation, geometrically west of the core in conjunction with Kbhg1, a layered version deﬁ ning a funnel-shaped body. Based on the funnel-shaped of the porphyritic granodiorite. The porphyritic granodiorite is structure, this body is interpreted as the feeder for the core of light gray, medium to coarse grained, and has a well-developed the complex. foliation. Heterogeneity in the unit is the result of unevenly Much of the center biotite tonalite, the most homogeneous distributed maﬁ c minerals. Subhedral tabular K-feldspar phe- part of the complex, has faint to well-developed primary layering nocrysts are up to 2.5 cm in length. Widespread and common Downloaded from memoirs.gsapubs.org on March 25, 2014

100 Morton et al.

75 Kbfg Kbgr 65 60 Kbft 40 60 65 85 80 65 50 50 Kbft 60 50 85

85 65 80 70 65 80 65 80 Kbgg Kbt 70 80 40 80

80 80 Kbgr 80

85 75

80 80 Kbgr 80 75 75 80 80 Kbfg Kbhg 20 65 Kbgr 55 117° 15’ 45 Kbht 15 40 60 Kgb 34° 00’ Kbhg 55 60 30 60 15 65 45 30 Kbt 80 Kprb Kbgg 30 80 45 Kbft 40 10 80 80 45 35 15 Kbfgi 75 60 35 80 75 75 30 30 75 80 35 70 45 Kbft 80 Kbhg1 Kbft 75 Kbft 40 75 75 35 40 80 70 Kbgg 55 65 75 Kbgg 40 65 45 65 45 50 45 55 50 60 60 60 Kbt 50 60 60 60 40 Kgb 75 45 Kbfg 60 Kbgr Kbht 45 45 60 65 60 60 Kbfg Kbfgi Kba 35 60 65 55 55 50 Kbhg Kbhg1 50 55 55 60 60 50 60 55 Kbgg 50 55 35 30 60 Kbhg Kbft 55 60 30 55 Kprb Kgb Kba Kprb Kbgg 40 50 55 55 25 45 75 Kbt Biotite tonalite 55 55 Kbgr Heterogeneous granite 25 45 50 N Kbht Heterogeneous biotite tonalite Kbfg Biotite granodiorite and tonalite Kbfgi Biotite granodiorite and tonalite containing abundant mafic enclaves Kbhg Heterogeneous porphyritic granodiorite Layered heterogeneous porphyritic granodiorite Kbhg1 Kbgg Porphyritic granodiorite and granite 0 1 2 Kbft Biotite-hornblende tonalite Kprb Granitic rocks not part of Box Springs Complex Km Kgb Gabbro Some map labels in dark Kba Amphibolitic gabbro areas are shown in white

Figure 49. Generalized geologic map of the western transition zone Box Springs Mountains plutonic complex, northern Perris block. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 101

TABLE 4. MODES OF MAJOR ROCK UNITS, BOX SPRINGS MOUNTAINS PLUTONIC COMPLEX Sample Map Kspa. Plag. Qtz. (%) Mafics unit (%) (%) (%) BX-1A kprb 17 41 27 15 BX-1E kprb 19 39 28 14 BX-1H kprb 19 41 27 13 BX-2F Kbgg 15 45 35 5 BX-2C Kbgg 18 38 38 6 BX-2I Kbgg 15 41 40 4 BX-3C Kbgg 28.5 36.5 27 8 BX-3G Kbgg 4 52 33 11 BX-4D Kbhg 17 41 32 10 BX-4G Kbhg 18 42 29 11 BX-5A Kbhg 1 50 34 15 Figure 50. Scattered rounded outcrops and boulders of massive BX-5B Kbhg 2 51 34 13 BX-6A Kbfg 19 40 29 12 isotropic-textured biotite tonalite (Kbt), which forms the core of BX-6B Kbfg 16 38 34 12 the Box Springs Mountains plutonic complex. View looking east BX-7A Kbfg 1 52 37 10 from Riverside. BX-7B Kbfg 17 43 30 10 BX-8A Kbfg 4 49 34 13 BX-8B Kbfg 3 57 26 14 BX-9A Kbfg 2 54 21 23 BX-9B Kbfg 1 54 23 22 discoidal-shaped mesocratic enclaves are oriented parallel to the BX-10A Kbt 2 50 39 9 foliation. In the west-central part of the complex, this unit has BX-10B Kbt 1 52 37 10 a pronounced layering resulting from systematic layer-by-layer BX-11A Kbt 2 47 42 9 variation in grain size. BX-11B Kbt 1 51 36 12 BX-12A Kbft 0 51 24 25 The outer part of the Box Springs Mountains plutonic com- BX-12B Kbft 0 49 24 27 plex consists of a zone of heterogeneous porphyritic biotite BX-13A Kbfg 5 55 28 12 granodiorite, lesser amounts of granite, and some biotite tonalite BX-13B Kbfg 21 38 32 9 BX-14A Kbfgi 12 45 35 8 (Kbgg). The biotite granodiorite and subordinate biotite tonalite BX-14B Kbfgi 16 44 32 8 are light gray, coarse grained, and well foliated. Biotite is the BX-15A Kbhg 22 42 27 9 common mafi c mineral, but sparse hornblende is present. Mafi c BX-15B Kbhg 15 33 41 11 minerals are quite evenly distributed, unlike the uneven distri- BX-16A Kbgg 2 54 34 10 BX-16B Kbgg 17 39 32 12 bution in the adjacent heterogeneous porphyritic granodiorite. BX-17A Kbft 4 48 26 22 Subhedral K-feldspar phenocrysts are up to 2.5 cm in length. BX-17B Kbft 4 59 18 19 Discoidal mafi c enclaves are oriented parallel to foliation. The BX-18A Kprb 14 43 32 11 porphyritic granodiorite grades inward into the heterogeneous BX-18B Kprb 21 36 34 9 BX-19J Kprb 6 54 25 15 porphyritic granodiorite. BX-20A Kbft 4 48 28 20 Foliated biotite-hornblende tonalite containing minor granite BX-20B Kbft 3 49 30 18 (Kbft) occurs as several discontinuous bodies (1) near the center BX-21A Kbgr 27 35 34 4 BX-21B Kbgr 28 23 46 3 of the complex, (2) in the northwesternmost part of the complex BX-22A Kbgg 25 33 41 1 in the La Loma Hills, and (3) on the east side of the complex. BX-22B Kbgg 29 32 36 3 These separate bodies were probably not derived from a single BX-23A Kbft 0 53 23 24 magma source. The tonalite contains 20%–25% quartz and ~25% BX-23B Kbft 0 44 34 22 BX-24A Kbht 0 52 44 4 hornblende and biotite in subequal amounts. Hornblende and BX-24B Kbht 1 51 44 4 biotite occur as ragged crystals. K-feldspar is a sparse constitu- BX-25A Kbht 0 53 30 17 ent, and anhedral interstitial sphene is a conspicuous accessory BX-25Z Kbht 0 49 17 34 mineral. The tonalite contains abundant fi ne-grained ellipsoidal BX-26G Kbht 1 55 41 3 BX-27A Kbt 3 53 38 6 to extremely thin, platy mafi c enclaves that are aligned within BX-27B Kbt 4 54 36 6 foliation in the enclosing tonalite (Fig. 52). BX-1Z1 kprb 14 26 16 44 Thin elongate bodies of dark-gray to black foliated amphibo- BX-1Z3 kprb 19 32 6 43 BX-2Z Kbgg 1 53 33 13 litic gabbro occur within biotite granodiorite and tonalite (Fig. 49, BX-4Z1 Kbhg 0 58 11 31 unit Kbfg). Only the larger masses are shown on Figure 49, and on Note: BX-1Z1 and BX-1Z3 feldspars are concentrated in streaks. the geologic map of the Riverside East 7.5′ quadrangle (Morton Kspa—K-feldpsar; Plag—plagioclase; Qtz—quartz. Refer to text for and Cox, 2001a). Foliation within the amphibolitic gabbro is par- map units. allel to that in the adjacent granodiorite. On the basis of compo- Downloaded from memoirs.gsapubs.org on March 25, 2014

102 Morton et al.

Figure 51. North-dipping foliated tonalite-granodiorite (Kbfg, Kbhg, and Kbgg) of the intermediate part of the Box Springs Mountains plutonic complex. View looking west from Moreno Valley. Figure 52. Well-foliated biotite-hornblende tonalite (Kbft) containing very attenuated E2 mafic enclaves, southwestern Box Springs Mountains. sition, the amphibolitic bodies are interpreted to be hornblende varies little from the biotite tonalite core to biotite-hornblende gabbro that was deformed and metamorphosed within the grano- tonalite on the outer margin of the complex. Silica content of the diorite. In addition to amphibolitic gabbro, several small, less- granitic host rock is ~10%–12% greater than the silica content deformed hornblende gabbro masses occur within biotite grano- of the maﬁ c enclaves (Fig. 53). Average alumina correlates posi- diorite and tonalite. These small gabbro masses retain a primary tively between host rock and maﬁ c enclaves. Average alumina gabbroic fabric. In plan view, they are elongate, with the direction content in the host rock ranges from ~12% in the core to 14% in of elongation lying within the planar fabric of the enclosing rock. the outer tonalite. Average alumina content in the enclaves is 4% In addition to the simple granitic-pegmatite dikes found higher than host rock in the core and decreases progressively to within the heterogeneous Kbht unit, granitic pegmatite dikes 2% higher than host rock in the outer tonalite. Likewise, iron cor- occur in the outer parts of the complex. Most dikes are less than relates positively between host rock and enclaves (Fig. 53). Iron a meter thick, and most are less than 10 m in length. Larger dikes content in the host rock ranges from ~7.5% in the core to a low of are compositionally and texturally zoned. Outer border-wall 5.5% in Kbg, but rises to 8% in the outer tonalite. Calcium shows zones include graphic granite and biotite. Intermediate zones a pattern similar to iron, having a 1.75% core, increasing to 3% contain schorl, almandine garnet, and muscovite. Giant perthite in the granodiorite surrounding the core, decreasing to nearly 1% and quartz crystals occur in the inner part of the intermediate in the outer granodiorite of the complex, and rising to 2.5% in the zone. Monazite and columbite-tantalite are accessory minerals. outer tonalite.

Rarely, the basal area of radiating crystal groups of columbite- The Na2O content of enclaves, 3.5% to nearly 4%, correlates tantalite crystals consists of yttrocolumbite-tantalite. negatively with the Na2O content of the host rock. K2O progres- Modes, calculated from point counts on stained slabs, for the sively increases from 1% in the core to 2.75% in the outer part major rock units are given in Table 4. To estimate the mineralogic of the complex. In general, the K2O content of enclaves is great- variation at the scale of an outcrop, multiple samples were col- est in the core, decreases regularly to the outer granodiorite, and lected from some outcrops. All of the units, except for the mas- increases slightly in the outer tonalite. There is no systematic cor- sive tonalite core, are quite heterogeneous. The foliated grano- relation in K2O variation between the host rocks and enclaves. diorite beyond the massive tonalite core is extremely variable in The relative ages for four of the major units of the complex K-feldspar and quite variable in the other mineral contents. are reasonably certain. Of the four, Kbt is youngest, Kbfg is older Twenty-seven granitic rock samples, representative of the than Kbt and younger than Kbhg, and Kbgg is oldest. The age map units, and their included mafi c enclaves, and two amphibo- relations of Kbfg to Kbht and to Kbgr are not clear from intrusive litic gabbros were analyzed (Table 5 [on CD-ROM accompany- relationships or fi eld exposures. Within the overall complex, Sri ing this volume and in GSA Data Repository (see footnote 1)]). values range from 0.7048 to 0.7055 (table 6) and have an aver- For six host rock samples, two mafi c enclaves were collected age value of 0.7051. This 0.0007 range is slightly greater than and analyzed. Silica content of the mafi c enclaves systematically the 0.0006 range of Sri for the Lakeview Mountains pluton. Sri correlates with the silica content of the host rock (Fig. 53). A values for the constituent units of the complex indicate that it similar systematic correlation is seen in the comparison of the is systematically zoned with respect to Sri. Sri values for Kbt,

Fe2O3, MgO, and CaO contents of host rocks and their included Kbfg, Kbhg, and Kbgg correspondingly increase with age from maﬁ c enclaves. youngest to oldest (Fig. 54A). This progressive increase in Sri Averaging the values for each map unit produces a much with age is interpreted to be the result of more interaction of smoother variation diagram (Fig. 53). Average silica content the complex’s magmas with older continental materials through Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 103 70 5.0 68 4.5 66 4.0 64 3.5 (percent) 62 2 60 3.0

58 2.5 56

Enclave SiO Enclave 2.0 54

52 MgO (percent) Enclave 1.5 50 1.0 64 66 68 70 72 74 76 78 80 0 0.5 1.0 1.5 2.0 Host rock MgO (percent) Host rock SiO2 (percent) 10 14 9 13 8 1 2 11 7 10 (percent)

6 3 O

2 9 5 8 4 7 3 6 Enclave Fe Enclave Enclave CaO (percent) CaO Enclave 2 5 1 4 123456123456 Host rock CaO (percent) Host rock Fe2O3 (percent) 70 12 68 Kbgg Kbt 11 66 Kbhg Kbgg 10 Kbt 64 Kbfg (percent)

(percent) Kbhg 3 2 Kbft

62 O 9 Kbfg 2 Kbft 60 8 58 7 56 54 6 52 5 Enclave average SiO average Enclave

50 Fe average Enclave 68 70 72 74 76 78 4 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Host rock average SiO (percent) 2 Host rock average Fe2O3 (percent) 3.0 4.0 2.8 3.5 2.6 Kbgg 3.0 Kbt 2.4 Kbhg

O (percent) 2.5 Kbfg

2 2.2 Kbft 2.0 Kbgg 2.0 Kbt 1.8 Kbhg 1.5 1.6 Kbfg Kbft 1.0 1.4 0.5 1.2 Enclave average K average Enclave 1.0 MgO (percent) average Enclave 0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Host rock average K2O (percent) Host rock average MgO (percent)

Figure 53. Plots of selected oxides of mafi c enclaves and their respective host rock for the major map units, Box Springs Mountains plutonic complex. The upper four plots are all mafi c enclaves and their respective host rocks. The lower four plots are the average oxide value for mafi c enclaves and their respective host rocks for the major map units of the complex. Downloaded from memoirs.gsapubs.org on March 25, 2014

104 Morton et al.

TABLE 6. Rb, Sr, AND 87Sr/86Sr DATA FOR THE BOX SPRINGS MOUNTAINS PLUTONIC COMPLEX Specimen Rb (ppm) Sr (ppm) Rb/Sr 87Rb/86Sr 87Sr/86Sr (87Sr/86Sr) 99 Ma 833B 5.59 582 533.0 969.0 93607.0 1507.0 BX-1 80.7 195 0.414 1.198 0.70668 0.7050 2-XB 7.15 412 242.0 007.0 73607.0 4507.0 BX-3 80.2 152 0.527 1.525 0.70749 0.7054 4-XB 8.68 271 405.0 854.1 02707.0 2507.0 BX-5 55.3 239 0.231 0.668 0.70611 0.7052 6-XB 5.07 571 404.0 961.1 05607.0 9407.0 BX-7 65.3 224 0.292 0.845 0.70626 0.7051 8-XB 8.57 952 292.0 548.0 52607.0 1507.0 BX-9 45.2 350 0.129 0.373 0.70597 0.7055 BX-10 33.0 403 0.082 0.237 0.70516 0.7048 BX-11 22.9 405 0.057 0.163 0.70501 0.7048 BX-12 43.8 378 0.116 0.336 0.70587 0.7054 BX-13 67.0 237 0.283 0.819 0.70620 0.7051 BX-14 79.7 185 0.432 1.250 0.70676 0.7050 BX-15 62.9 178 0.353 1.021 0.70659 0.7052 BX-16 81.2 183 0.443 1.282 0.70684 0.7050 BX-17 75.1 279 0.269 0.778 0.70653 0.7054 BX-18 68.7 171 0.402 1.163 0.70664 0.7050 BX-19 59.6 226 0.264 0.764 0.70595 0.7049 BX-20 63.9 242 0.263 0.761 0.70628 0.7052 BX-21 97.1 183 0.530 1.533 0.70706 0.7049 BX-22 61.2 196 0.313 0.906 0.70660 0.7053 BX-23 30.2 429 0.070 0.203 0.70574 0.7055 BX-24 12.4 434 0.029 0.083 0.70506 0.7049 BX-25 45.7 373 0.123 0.385 0.70568 0.7051 BX-26 22.6 415 0.055 0.158 0.70521 0.7050 BX-27 26.9 352 0.076 0.221 0.70520 0.7049

0.70535 time. Figure 54B shows Sri for Kbrg, Kbht, and Kbft in addition 0.70530 to Kbt, Kbfg, Kbhg, and Kbgg. Applying Occam’s razor, the ages 0.70525 of Kbgr and Kbht, based on their Sr values, should fall between 0.70520 i 0.70515 those of Kbt and Kbfg, and Kbft, containing extremely attenuated maﬁ c enclaves, should be the oldest unit of the complex.

i 0.70510

Sr 0.70505 Granitic rocks in the Bernasconi Hills area. A wide variety 0.70500 of granitic rocks occurs in the Bernasconi Hills, located between 0.70495 the Lakeview Mountains pluton and the Box Springs Mountains 0.70490 plutonic complex. The monzogranite of Bernasconi Pass (Figs. 2 0.70485 A and 3) underlies the area from the southern part of the Bernasconi 0.70480 Kbt Kbfg Kbhg Kbgg Hills to north of Bernasconi Pass. North of Bernasconi Pass, the monzogranite is slightly foliated, contains few maﬁ c enclaves, and weathers to form bold outcrops. South of Bernasconi Pass, 0.7054 porphyritic biotite and biotite-hornblende monzogranite weather to form extremely large outcrops (Figs. 55A and 55B). Unlike the 0.7053 monzogranite north of Bernasconi Pass, much of the latter mon-

0.7052

i 0.7051 Sr

Figure 54. (A) Average Sri for the four Box Springs Mountains plu- 0.7050 tonic complex units with known relative ages; Sri systematically increases with age. (B) Age of Kbrg and Kbht, relative to each other, is 0.7049 not known. Kbrr and Kbht are older than Kbt and younger than Kbfg. Based on Sr values relative to those of Kbt, Kbfg, Kbhg, and Kbgg, B i 0.7048 Kbrg is interpreted as older than Kbht. Based on its Sri value, the rela- KbtKbrg Kbht Kbfg Kbhg Kbgg Kbft tively older Kbft is considered the oldest unit of the complex. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 105 zogranite contains large quantities of ellipsoidal mafi c enclaves. commonly massive, and has common-to-abundant, small, ellip- Most of this monzogranite has moderately well-developed pla- soidal mafi c enclaves. nar fabric and includes masses of migmatitic-appearing rock in which the volume of mafi c enclaves commonly exceeds the vol- Eastern Transition Zone ume of enclosing granitic rock (Fig. 56). On the south side of Bernasconi Pass, a migmatitic zone, mappable at 1:24,000 scale, Plutons of the eastern transition zone occur primarily south occurs within the monzogranite and extends both west and east of 33°40′Ν, but a few relatively sparse exposures are present at of the Bernasconi Hills. The enclave-rich mafi c rocks appear to the north end of the batholith in the northwestern San Jacinto be the same age as the monzogranite, based on a case of back- Mountains, east of the San Jacinto fault zone (Fig. 2). The present veining of a mafi c body by the host monzogranite. The relation- level of exposure of eastern transition zone plutons is shallower ships among the mafi c rocks, mafi c enclaves, and granitic rocks than western transition zone plutons, as indicated by crystalliza- have been described by Mason and Cohen (1990). tion pressures of 4.5–6.5 kbar (Ague and Brimhall, 1988; Smith North of the monzogranite of Bernasconi Pass, brown- et al., 1991). The eastern transition zone is dominated by the weathering sillimanite-cordierite, schist correlated with the rocks large La Posta–type Coahuila Valley pluton, but unlike other La of Jacumba Mountains, is intruded by heterogeneous granitic Posta–type plutons of the eastern zone, it has Sri <0.7060 and Pbi rocks (Khg) and by a series of tonalite plutons comprising the <19. Biotite-hornblende tonalite, characterized by large euhedral tonalite of Bernasconi Hills (Fig. 2). The tonalite weathers to biotite and hornblende crystals, is the dominate rock type. Within form distinctive gray bold outcrops; it is relatively fi ne grained, the eastern transition zone, granodiorite is distinctly subordinate to tonalite, and hornblende gabbro and olivine gabbro are sparse. In contrast to western transition zone plutons, eastern transition zone plutons are noticeably less foliated, and the mafi c enclaves less attenuated. Plutonic rocks of the eastern transition zone are generally more homogeneous than those of the western transition zone. Silica content ranges from 42.9% to 77.1% and averages 64.2%. Moreover, pluton emplacement occurred from 99 to

93 Ma. Pluton compositions are isotopically characterized by Sri values of 0.7050–0.7054, δ18O of +7‰ to +10‰, and an average ε − − Pbi value of 18.744. The Ndi values are negative ( 0.6 to 5), ε similar to Ndi in the eastern zone. Coahuila Valley pluton. The Coahuila Valley pluton was the name given by Sharp (1967) for a large area underlain by biotite- hornblende and hornblende-biotite tonalite. Within his Coahuila Valley pluton, he distinguished ﬁ ve variations of tonalite. The northern part of the pluton as originally deﬁ ned by Sharp was

Figure 55. (A) Western transition zone monzogranite of Bernasconi Pass, south of Lake Perris. Rock contains abundant ellipsoidal-shaped

E1 maﬁ c enclaves. (B) Monzogranite of Bernasconi Pass containing Figure 56. Migmatitic zone within the monzogranite of Bernasconi abundant E1 maﬁ c enclaves. Pass, west of Lake Perris. Downloaded from memoirs.gsapubs.org on March 25, 2014

106 Morton et al.

subsequently subdivided into two plutons: the heavily sphene- tonalite at the head of Lamb Canyon yields U-Pb ages of 94 Maid

bearing eastern zone Hemet pluton (Morton and Matti, 2008) and and 92.8 Maip, and the sphene U-Pb age is 92.8 Maid. the eastern transition zone Tucalota Valley pluton (Morton and Granite of Mount Eden. The granite of Mount Eden is a Kennedy, 2005) (Fig. 2). The remaining Coahuila Valley pluton, small elongate pluton of garnet-muscovite granite that under- shown in Figure 2 as the large undifferentiated Kcv + Kt body, lies Mount Eden (Fig. 3). Fresh rocks of this pluton are nearly probably consists of other discrete plutons. Most of this as-yet- white, but they weather to form very pale-brown bold outcrops. undifferentiated remainder is biotite-hornblende and hornblende- Bright pink garnets impart a distinctive appearance to the oth- biotite tonalite that contains numerous ellipsoidal-shaped maﬁ c erwise white rock. Grain size in the rock ranges from ﬁ ne to enclaves. At least some of the southeastern part of the Coahuila coarse grained. Adjacent to the pluton, metamorphic rocks con- Valley pluton, where it extends into Coyote Canyon (Fig. 3), is tain a number of sills and dikes of the granite. Most of the sills a distinctive tonalite characterized by large euhedral biotite and and dikes are foliated, and the foliation is oriented parallel to

hornblende crystals. This tonalite has a Sri >0.7060 and, based on the enclosing metamorphic rock foliation. Similar, small garnet-

the Sri, is here included in the eastern zone. muscovite granite plutons occur at several localities in the Bau- The southwestern part of Sharp’s Coahuila Valley pluton, tista complex of Sharp (1967). Except for pegmatite dike rocks, in the Chihuahua Valley area, is a classic mineralogically zoned garnet-muscovite–bearing granitic rocks are sparse in the north- La Posta–type pluton. The outer part of the pluton exposed in ern Peninsular Ranges batholith. Chihuahua Valley consists of biotite-hornblende tonalite containing large euhedral biotite plates and stout euhedral hornblende crystals (Figs. 57A and 57B), and the central part includes a muscovite-biotite granodiorite-tonalite. Abundant schorl-bearing granitic pegmatite dikes are located in the intermediate parts of the pluton and are particularly abundant just west of Chihuahua Valley. Locally, the uppermost part of the pluton is in contact with metasedimentary roof rock where the roof of the pluton includes vuggy greisen composed of muscovite, lepidolite, albite, and minor rubellite tourmaline. Farther south in the metamorphic roof rocks, there is a lithium-bearing pegmatite; a second discrete lithium-bearing pegmatite, the Anita pegmatite, is located in the northern part of the pluton west of Red Mountain (Fig. 3). The pocket-bearing part of the Anita pegmatite is located at a roll in the dip of the dike. The central part of the Coahuila Valley pluton (Fig. 2) has 40 39 zircon U-Pb ages of 96.5 Maid and 95.5 Maip. The Ar/ Ar ages of hornblende and biotite are 94.4 Ma and 91.9 Ma, respectively. ε − Sri is 0.7052, and Nd is 5.0. A sample from the northwest part of the pluton has zircon ages of 96.5 Maid and 92.6 Maip, and a sphene age of 93.8 Ma. Tucalota Valley pluton. West of Sharp’s Coahuila Val- ley pluton, the Tucalota Valley pluton (Morton and Kennedy, 2005) is separated from the Coahuila Valley pluton by a septum of amphibolite-facies metamorphic rocks including sillimanite- garnet-biotite schist (Fig. 2). The Tucalota Valley pluton consists of relatively homogeneous biotite-hornblende tonalite that weathers to relatively large core stones. Most of the tonalite is massive to very crudely foliated. Ellipsoidal mafi c enclaves are sparse or lacking in much of the pluton. Tonalite of Lamb Canyon. The Tonalite of Lamb Canyon (Morton and Miller, 2006) is a distinctive sphene-bearing biotite- hornblende tonalite exposed in several noncontiguous exposures surrounded by Tertiary sedimentary rocks in the La Borde and Lamb Canyons area (Fig. 5). Most of the unit is homogeneous- Figure 57. (A) Typical tonalite of the eastern transition zone Coahuila appearing, massive to slightly foliated biotite and hornblende- Valley pluton, containing sparse E1 mafi c enclaves, Chihuahua Valley. biotite tonalite that in most places contains large euhedral sphene (B) Euhedral plates of biotite and stubby euhedral hornblende char- crystals. Ellipsoidal mafi c enclaves are uncommon. Zircon from acterize the tonalite of the Coahuila Valley pluton, Chihuahua Valley. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 107

Eastern Zone Plutons zone near the Eastern Peninsular Ranges mylonite zone, pressures of crystallization increase to 5.6 kbar (A. Bern, 2010, per- δ18 The eastern zone of the batholith is characterized by large sonal commun.). Most Sri values are 0.7060 to 0.7075, most O tonalitic plutons, most having foliation that is not as well devel- values are +9‰ to +12‰, and Pbi values average 19.19. Values ε oped as in western transition zone or eastern transition zone of Ndi range between –2.2 and –3.9. plutons. The eastern zone is structurally terminated on the east The compositionally zoned San Jacinto pluton is the largest by the Eastern Peninsular Ranges mylonite zone, and it pinches pluton in the eastern zone north of 33°30′Ν. Sphene is a char- out at the southeast end of the Buck Ridge pluton located in the acterizing accessory mineral in the San Jacinto pluton, as it is southeastern Santa Rosa Mountains. At Coyote Mountain, north in most tonalite plutons in the eastern zone. Sphene commonly of Borrego Springs (Fig. 3), eastern zone rocks are in contact occurs as readily visible large euhedral crystals; megascopically with the Eastern Peninsular Ranges mylonite zone (Fig. 2). West visible sphene is uncommon to absent in plutonic rocks of the of Borrego Springs, the eastern zone rocks reappear as the Pin- western zone, western transition zone, and eastern transition zone. yon Ridge pluton (Wagner, 2006), located within an eastern zone Sphene commonly occurs as small groups of crystals in maﬁ c- inlier on the southeast side of the eastern transition zone; the depleted areas of quartz and feldspar, giving rise to a speckled eastern part of the pluton is deformed by the Eastern Peninsular appearance. In the eastern zone, there are a few garnet and white Ranges mylonite zone. mica–bearing granitic plutons, a rock type essentially lacking in Plutons in the eastern zone are generally larger than those of the western zone and western transition zone. A relatively large the western zone and western transition zone and are character- body of garnet-bearing granite, the granite of Penrod Canyon, is ized by what is commonly termed La Posta–type plutons (e.g., located in the southern part of the San Jacinto Mountains (Fig. 3). Walawender et al., 1990; Kimbrough et al., 2001). The compo- Extensive granodiorite is located in the northernmost part of the sitional range of these rocks is narrower than in plutons of the eastern zone, and east of the San Jacinto pluton, there is a large western zone and western transition zone. Sparse occurrences of area of undifferentiated granodiorite and tonalite (Fig. 2). Biotite- gabbro occur only in the western part of the eastern zone. Ellip- hornblende tonalite just west of the Eastern Peninsular Ranges soidal enclaves are generally less abundant and less attenuated mylonite zone has U-Pb zircon ages of 97.5 Maid and 91.3 Maip, a ε − than those in western transition zone and eastern transition zone U-Pb sphene age of 92 Ma, Sri of 0.7074, and Ndi of 3.9. plutons (Fig. 58). Silica content ranges from 46.8% to 75.8% Gabbro is sparse and limited to the western part of the east- and averages 67%. Most eastern zone plutons were emplaced ern zone, where several olivine-hornblende and hornblende gab- between 98 and 91 Ma, with a U-Pb zircon age from an olivine bro bodies are located within the Bautista Canyon and Thomas gabbro of 102 Ma. The exposed level of the plutons is shallower sills of Sharp (1967). An olivine gabbro from Bautista Canyon than the western transition zone, with most eastern zone plutons has a Sri of 0.7035. Zircon from olivine gabbro of the Thomas crystallizing at pressures of ~4.5 kbar (Ague and Brimhall, 1988; Mountain sill in the southern Thomas Mountains (Fig. 3) has Smith et al., 1991). However, in the eastern part of the eastern a U-Pb age of 102 Ma (D.L. Kimbrough, 2009, personal commun.). Lithium-bearing pegmatites in the Thomas Mountain gabbro were the source of the ﬁ rst recorded lithium gem tourmaline in California. In the southeastern part of the pluton, located between the northern part of Coyote Canyon and the Coyote Creek fault (Fig. 3), there is a very distinctive hornblende-biotite tonalite containing large euhedral biotite and hornblende crystals. This distinctive tonalite was included by Sharp (1967) within his Coa- huila Valley pluton. Four samples of this tonalite yield U-Pb zir-

con ages of 96.6, 97.7, 97.8, and 98.2 Maip. Sri values for the four dated samples have a restricted range of 0.7062–0.7063. San Jacinto pluton. The San Jacinto pluton (Fig. 59) is an elongate body with a somewhat bulbous northern part, and it consists of three major biotite-hornblende tonalite units. Hill (1984, 1988a, 1988b) provided an in-depth description of the San Jacinto δ18 pluton, including chemistry and internal Sri and O variations. All three of his tonalite units, unit I, unit II, and unit III, ranged from mafi c tonalite to low-potassium granodiorite. The relatively older units I and II are slightly more mafi c than the youngest unit Figure 58. Typical rock of an undifferentiated tonalite unit in the east- III. Unit I was intruded by unit II before unit I had crystallized completely. The bulbous unit III was emplaced between units I ern zone containing E1 mafi c enclaves, west of Pinyon Flats, southeastern San Jacinto Mountains. and II before unit II had crystallized completely. Much of unit Downloaded from memoirs.gsapubs.org on March 25, 2014

108 Morton et al.

III consists of massive to faintly foliated tonalite with few mafi c unit III as defi ning a funnel-shaped pluton. Unit III is systemati- enclaves (Fig. 60). Unit I is in contact with unit II only south cally zoned compositionally, grading from mafi c tonalite at the of unit III. Mineral layering, foliation, and schlieren are concor- margins to low-potassium granodiorite at the center. Variation in dant with the plutons external and internal contacts. Schlieren δ18O, caused by contamination from surrounding metamorphic commonly occur as isolated masses within homogeneous tonal- rocks, is limited to a narrow zone at the pluton margin. Synplu- ite (Figs. 61A and 61B). Hill (1984) interpreted foliation in his tonic mafi c dikes within the pluton are commonly disaggregated

ppb ppb 15 10 Ksj3 72 22 ppb 8 20 Kgd Black 34 Mountain San 11 Jacinto 17 Peak Ksj3 Ksjm 31 Ksjm 33 6 3

17 22 2 N 4 26 Ksj1 20

Ksj2 31 22 33° 45’N 012 5 Km 116° 37’W 25 Ksj3 San Jacinto Pluton, Unit 3

Ksj2 San Jacinto Pluton, Unit 2

Ksj1 San Jacinto Pluton, Unit 1 7 Ksjm San Jacinto Pluton, mixed units 40 15 5 Ksj1 Kgd Granodiorite 9 34 ppb 8 Pre-Cretaceous metamorphic rocks 5 8 28 2 3 Foliation 11 16 12 11 Ksj2 Inclined 27 25 5 Vertical . Lake Ksj . Xenolith orientation 19 1 Inclined Vertical 7 31 6 Schlieren 43 2 Inclined 41 Vertical 33 4 Mineral lineation Geology from Hill (1984) 12 Thomas Mountain

Figure 59. Generalized geologic map of the eastern zone San Jacinto pluton, San Jacinto Mountains. Geology from Hill (1984). Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 109

to form linear trains of dike fragments (Fig. 62). Minor felsic tonalite differentiates are of granodioritic composition. U-Pb zir-

con ages from Hill’s unit I are 95.3 Maid and 93.9 Maip; U-Pb sphene age is 93.2 Ma. The 40Ar/39Ar ages of hornblende and biotite are 91.6 Ma and 92.2 Ma, respectively. Penrod Canyon pluton. A garnet-bearing granite pluton is located in the southern part of the Garner Valley area, south of the San Jacinto pluton. This body was termed Penrod quartz monzonite by Brown (1968), and granite of Penrod Canyon by Hill (1984). The pluton is ~4 by 9 km and consists of medium- grained, leucocratic biotite-garnet-muscovite granite. Crudely oriented biotite imparts a subtle foliation to the granite. Dark-red garnet occurs in some rocks in amounts up to several percent. Chemistry of the granite is given in Table 2 (on CD-ROM accompanying this volume and in GSA Data Repository [see footnote Figure 60. Typical biotite-hornblende tonalite of unit 3, San Jacinto 1]; B270 and B271). These samples have a Sr of 0.7061, which pluton. Tonalite commonly contains few mafi c enclaves. i is considerably lower than typical eastern zone plutons. Hemet pluton. Hornblende-biotite tonalite containing large sphene crystals at the north end of Sharp’s (1967) Coahuila Val- ley pluton has been differentiated as the Hemet pluton (Morton and Matti, 2008). It consists of massive to relatively well-foliated biotite-hornblende tonalite and biotite tonalite, which is noticeably more heterogeneous than the adjacent Coahuila Valley pluton. This tonalite contains only sparse ellipsoidal mafi c enclaves. Most of the tonalite contains readily visible subhedral and euhedral sphene. The biotite tonalite is subporphyritic with euhedral biotite up to 1 cm. The texture of biotite tonalite ranges from massive to crudely foliated; however, in many places, the foliation is so indistinct that accurate measurements are not possible. The crude foliation defi nes a semicircular confi guration, apparently the southern part of an elliptical pluton, the northern part of which is covered by alluvium of San Jacinto Valley. The unit contains some layers of brown weathering tonalite that contrasts with typical gray-weathering tonalite. A few simple-mineralogy

Figure 61. (A) Isolated mass of mafi c schlieren-like tonalite within faintly foliated weathered tonalite, unit 3 of the San Jacinto pluton. Figure 62. Abundant irregularly shaped mafi c enclaves, interpreted to (B) Close-up of an isolated mass of mafi c schlieren-like tonalite; all be from disaggregated synplutonic mafi c dike. Deeply weathered unit rock here is deeply weathered unit 3 of the San Jacinto pluton. 3 of the San Jacinto pluton. Downloaded from memoirs.gsapubs.org on March 25, 2014

110 Morton et al.

granitic pegmatite dikes are found in the western part of the pluton. One large dike was mined for quartz and K-feldspar. Tonalite from the north-central part of the pluton has U-Pb

zircon ages of 95.9 Maid and 91.6 Maip. Sphene has a U-Pb age of 93.8 Ma. The 40Ar/39Ar ages of hornblende and biotite are 92 Ma and 90 Ma, respectively. Pinyon Ridge pluton. West of Borrego Springs (Fig. 3), in the southeasternmost part of the geologic map shown in Figure 2, there is the eastern zone Pinyon Ridge pluton. The pluton is bordered on the west by western transition zone rocks, on the north by eastern transition zone rocks, and is structurally terminated on the east by the Eastern Peninsular Ranges mylonite zone. Outliers of the pluton occur within metamorphic rocks that enclose it. The 0.7062 value at B450 falls on the small unnamed granite (Kgu) outcrop west of the main Pinyon Ridge body that is probably Figure 64. Biotite-hornblende tonalite in the eastern part of the eastern Pinyon Ridge rock (Fig. 2). The Pinyon Ridge pluton, termed the zone Pinyon Ridge pluton, showing an older, faintly foliated fabric

Pinyon Ridge granodiorite by Wagner (2006), consists mostly of containing E1 mafi c enclaves (upper part of photograph), and younger medium-grained biotite-hornblende tonalite, biotite tonalite, and well-foliated fabric containing E2 mafi c enclaves (lower part of photograph). Tonalite having well-foliated fabric with E mafi c enclaves is lesser hornblende-biotite tonalite. Some biotite tonalite has small 2 spatially related to the Eastern Peninsular Ranges mylonite zone. amounts of fi ne-grained primary muscovite. Accessory minerals are sphene, apatite, zircon, and opaque minerals. Sphene occurs as relatively large euhedral crystals. Common epidote and sparse calcite are secondary minerals. Typical hypautomorphic textured (Fig. 65). Mylonitic textures are common close to the Eastern

tonalite with common ellipsoidal-shaped mafi c enclaves occurs Peninsular Ranges mylonite zone. Sri values in the pluton ranges in the western part of the pluton (Fig. 63). In the eastern part, the from 0.7062 to 0.7072, but most values are around 0.7062. texture progressively changes near the Eastern Peninsular Ranges mylonite zone, as quartz is intensely undulated, kinks appear in Upper-Plate Zone plagioclase, and biotite is highly deformed into kinked and wispy crystals. Moderately strained quartz commonly has fractures that Allochthonous granitic rocks, assigned to the Santa Rosa are fi lled with very fi ne-grained quartz. Outcrops in the eastern allochthon of Erskine (1986b), constitute the upper-plate zone part of the pluton commonly have both an older moderate folia- of the batholith (Fig. 2). The feature separating the eastern zone tion accompanied by ellipsoidal mafi c enclaves, and a younger from the upper-plate zone is a major regional mylonite zone that intense foliation accompanied by extremely attenuated mafi c has been variably termed the Eastern Peninsular Ranges mylonite enclaves (Fig. 64). Near the Eastern Peninsular Ranges mylonite zone, foliated tonalite weathers to form shingle-like slopes

Figure 65. Shingle-like slopes developed from uniformly foliated to-

nalite containing E2 maﬁ c enclaves; macroscopic characteristic of Pin- Figure 63. Typical biotite-hornblende tonalite containing ellipsoidal- yon Ridge pluton rocks near the Eastern Peninsular Ranges mylonite

shaped E1 maﬁ c enclaves in the western part of the eastern zone Pinyon zone, west of Borrego Springs. Field of view across center of photo- Ridge pluton. graph is approximately 150 m. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 111 zone (Sharp, 1967, 1979; Todd et al., 1988), Santa Rosa mylonite between granitic sheets within the upper-plate zone. The granitic zone (e.g., Erskine and Wenk, 1985; Wenk and Pannetier, 1990; rocks above the Haystack Mountain fault form a klippe in the Goodwin and Wenk, 1995), and Borrego Springs–Santa Rosa Pinyon Flats area. The Asbestos Mountain–Haystack Mountain mylonite zone (Simpson, 1984); see also Girty et al. (1993). Here, fault complex is exposed discontinuously southeastward to the we use the terminology of Sharp, i.e., the Eastern Peninsular end of the Santa Rosa Mountains. For a detailed description and Ranges mylonite zone. Within the mylonite zone, shear indica- analysis of the upper-plate zone, see Erskine (1986a), Erskine tors have been interpreted as showing evidence of east-over-west and Wenk (1985), and Todd et al. (1988). Upper-plate granitic displacement. Geochemistry and isotopic data also indicate that rocks are not exposed south of the southeastern end of the Santa the upper-plate zone originated east of the autochthonous Penin- Rosa Mountains. The Eastern Peninsular Ranges mylonite zone sular Ranges batholith. Inception of mylonitic deformation has is offset by branches of the San Jacinto fault zone and is exposed been interpreted to have begun as early as 87 Ma (Cecil, 1990; between faults at Coyote Mountain (Theodore, 1967, 1970) north cited in Wenk, 1998). Goodwin and Renne (1991) interpreted of Borrego Springs, and south of the San Jacinto fault zone west that mylonitization began ca. 80 Ma, and extended to ca. 62 Ma; of Borrego Springs. Detailed petrography and structure of the see also Dokka (1984). The western, structurally lowest, part Eastern Peninsular Ranges mylonite zone at Coyote Mountain of the upper-plate zone is dominated by mylonitic fabrics that were given by Theodore (1967, 1970). If upper-plate zone gra- include pseudotachylyte. nitic rocks extend south into the Borrego Springs area, they are East of the Eastern Peninsular Ranges mylonite zone, the covered by sedimentary deposits. upper-amphibolite-metamorphic-grade Palm Canyon Complex is Foliated biotite-hornblende granodiorite and tonalite separated from the mylonite zone by the east-dipping low-angle (Fig. 66) containing abundant accessory sphene are the dominant Palm Canyon fault (Erskine, 1986a, 1986b). Brittle deformation lithologies of the upper-plate zone. Much of the tonalite in the of the Palm Canyon fault contrasts with the ductile deformation Asbestos Mountain area contains large euhedral sphene crystals of the underlying mylonite zone. The Palm Canyon fault extends (Webb, 1939b). Crude gneissic fabric and ellipsoidal to pancake- from just south of Palm Springs to the southeast end of the Santa shaped maﬁ c enclaves are common throughout the upper-plate Rosa Mountains. It borders the Palm Canyon complex, which zone (e.g., Wenk, 1998) (Fig. 67). Epidote is a common acces- consists of anatectic gneiss, orthogneiss, and mylonitic gneiss. sory mineral. Magnetite is the common opaque mineral, in con- In this complex, relatively abundant mylonitic garnet-bearing trast to the ilmenite-bearing granitic rocks of the eastern zone. anatectic gneiss is interlayered with metasedimentary gneiss and Ages of most dated upper-plate zone granitic rocks are dis- orthogneiss. Anatectic metamorphism is interpreted as beginning tinctly younger than those of the eastern zone plutons. Tonalite ca. 110 Ma (Wenk et al., 1998). Structurally above the Palm Can- from the Pinyon Flats area has U-Pb zircon ages of 84.2 Maid and 40 39 yon complex, there is a second low-angle east-dipping fault, the 85.7 Maip, and U-Pb sphene age is 76.9 Ma. The Ar/ Ar ages Asbestos Mountain fault. Above the Asbestos Mountain fault, of hornblende, biotite, and K-feldspar are 75.3 Ma, 69.8 Ma, granitic rocks comprise the allochthonous upper-plate zone of and 68–62 Ma, respectively. Pinyon Flats rocks yield Sri of δ18 ε the batholith (Erskine, 1986a; Todd et al., 1988). 0.7078, O 8.3 ‰, and Ndi of –6.0. Farther east, a tonalite

In the Pinyon Flats area of the eastern San Jacinto Mountains, sample yields a U-Pb zircon age of 92.5 Maip; the reason for a third low-angle fault, the Haystack Mountain fault, is located this distinct age reversal is not understood. A sample from Point

Figure 66. Foliated tonalite of the upper-plate zone, east of Pinyon Figure 67. Well-foliated gneissose-textured upper-plate zone grano- Flats, southeastern San Jacinto Mountains. diorite. East of Pinyon Flats, southeastern San Jacinto Mountains. Downloaded from memoirs.gsapubs.org on March 25, 2014

112 Morton et al.

Happy (Fig. 2), the easternmost exposure of the upper-plate Based on the grid of systematically collected samples, the

rocks, gives U-Pb ages of 83 Maid and 84.5 Maip for zircon, and western zone constitutes 43.7% by area of the northern Peninsu- 75.9 Ma for sphene. The 40Ar/39Ar ages of hornblende, biotite, lar Ranges batholith, western transition zone 12.3%, eastern tran- and K-feldspar are 71.2 Ma, 63.9 Ma, and 62.5–59 Ma, respec- sition zone 13.3%, eastern zone 22%, and the upper-plate zone ε tively. A Sri value for this rock is 0.7080, and Ndi is –7.3. Ague 9.7%. Normalized for only the autochthonous part of the batho- and Brimhall (1988) reported an 87 Ma age for the tonalite. A lith, the western zone constitutes 47.9% by area, western transi- biotite-hornblende tonalite sample collected south of La Quinta tion zone 13.5%, eastern transition zone 14.6%, and the eastern (Fig. 3) has a U-Pb zircon age of 84.4 Ma (D. Kimbrough, zone 24%. (Note: In both normalizing calculations, the number 2010, personal commun.). of eastern zone samples was reduced from 74 to 68 because of Upper-plate granitic rocks crystallized at pressures of ~6.0– the difference in sampling interval in the northern part of the east- 6.9 kbar (Ague and Brimhall, 1988). The silica range for these ern zone.) Alluvial cover in much of the Riverside area, the Perris granitoids is 60.9%–72.4%, which is a considerably narrower block, and the Temecula area precludes collection of batholith range than that of the other batholith zones. This is, at least to samples. In spite of the areas of alluvial cover, we consider the some degree, due to the absence of gabbro in the upper-plate systematically collected samples to be a reasonably quantitative zone. Average silica content of 64.7% is signifi cantly lower than representation of the part of the batholith sampled. Several sam- the average of 66.1% for the eastern zone, but it is close to the ples shown on Figure 68 that appear to fall within metamorphic average of 64.2% for the eastern transition zone. Most Sri values units or alluvium actually fall on granitic outcrops too small to are in the range of 0.7077–0.7082, δ18O values average +8.73‰, show at the scale of the map. and the average Pbi is 19.336. Based on relatively few samples, ε ε − all Ndi values are negative. At Point Happy, our Ndi value is 7.3. Previous Regional Geochemistry ε − DePaolo (1981) reported Ndi of 5.9 for the Point Happy rock, but ε his Ndi value was calculated at 100 Ma(?). The Sri and Pbi ratios Systematic west-to-east dichotomy in chemical and isoto- indicate incorporation of greater amounts of more-evolved conti- pic composition of the batholith has long been recognized (e.g., nental crust in the pluton-forming magma than the other zones of Baird et al., 1974; Gromet and Silver, 1987; Taylor and Silver, the batholith (Kistler et al., this volume). Although granitic rocks 1978; Todd et al., 1988, 2003), and Peninsular Ranges batho- of the upper-plate zone are magnetite-bearing rocks like those of lith workers now appear to agree on a basic twofold division of the western zone, their ages and Sri values are entirely different. the batholith into western and eastern zones (e.g., Taylor and Silver, 1978; Baird and Miesch, 1984; Todd et al., 1988; and REGIONAL GEOCHEMISTRY various papers in Johnson et al., 2003). The twofold division of the Peninsular Ranges batholith has been variously attributed to Most of our regional geochemical data are from composite be the result of (1) a change in plate-tectonic motions during the samples systematically collected by E.E. Welday and A.K. Baird, Cretaceous (Walawender et al., 1990), (2) two Cretaceous mag- Pomona College (Baird et al., 1974, 1979; Baird and Miesch, matic arcs (Silver and Chappell, 1988; Johnson et al., 1999), 1984), from the northern 120 km of the batholith (Fig. 68). These and (3) a single Cretaceous arc transitioning from Mesozoic systematically collected samples allow an accurate quantita- oceanic to continental crust (Thomson and Girty, 1994; Todd tive estimation of the composition of this part of the Peninsu- et al., 1988, 2003). lar Ranges batholith. The sample-collection procedure is given Another chemical division of the Peninsular Ranges in the Appendix. An additional 60 samples were collected in batholith is based on rare earth element patterns that divide selected areas where greater detail was needed. Chemical analy- the batholith into three longitudinal zones (Gromet and Silver, ses are given in Table 2 and Baird-Welday sample locations are 1987). Later, Silver and Chappell (1988) divided the Penin- given in Figure 68; locations of additional samples are given in sular Ranges batholith into a western batholith and an eastern Table 2 (on CD-ROM accompanying this volume and in GSA batholith and recognized six chemical domains within the two Data Repository [see footnote 1]). All newly collected samples batholiths. Their chemical domains were “…recognized on the were analyzed, and the Welday-Baird samples reanalyzed, in basis of a regular linear covariation of Rb and Sr concentra- USGS laboratories, Denver, Colorado, using standard tech- tions.…” (Silver and Chappell, 1988, p. 110). The northern niques. Major elements were analyzed by X-ray fl uorescence, Peninsular Ranges batholith considered here includes fi ve of and trace elements were analyzed by ICP analysis. Whole- rock the six chemical domains of Silver and Chappell (1988). Except Rb-Sr, U-Pb, and O isotopes were measured in USGS isotope for their chemical domain F, a direct comparison of the chemi- laboratories in Menlo Park, California. Chemistry of the fi ve cal domains of Silver and Chappell to our zones is not possible batholith zones is given in Table 2. Zircon geochronology was due to their generalized small-scale chemical domain map and obtained in USGS laboratories in Denver, Menlo Park, and Stan- lack of sample locations. However, despite the different scale ford University. Details of analytical procedures are given in the of their study, signifi cant differences are apparent, most notably Appendix, in Kistler et al. (this volume), and in Premo et al. (this in some trace elements, and in the average chemistry of their volume, Chapter 4). domains, particularly their domain F as compared to our results Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 113 34˚ 33° 116° 116˚ Kam QTc QTc ppb

0 UPZ

291 mu

289 Kam 94 ppb

2 QTc Kam

292 QTc 293 QTc QTc

288

285 Kam Kam Kgdt

2 mu Kam EZ

296 4

297

299 mu

298

28 Ktmm Kqd

286

13 Kqd Kam

33° 30’ 314

3 ppb QTc Klog ppb

328

300 mu ppb Kcv + Kt

28 Kgdt ppb

301 QTc mu QTc QTc mu QTc Kam ppb Kgpm ppb msmg mu Kgdt

02 Kgm QTc mu Kgm mu

431 Kcs

441

280

451 ppb

308 ppb mu Kbc

311 282 4

281

327 Kcv + Kt Kgm 312 UPZ Kgb Kbm Kgm 307 QTc

305

430 ppb Kgdt

452 Kam ppb

278 10 QTc Kbm

03 ppb Kbt ppb ppb

3 ppb

309

3 Kgbh Klog msmg Kam

32 456 Kgp Kgp

304

79 mu

432 Ktg EZ 53 Kbc

2 ppb ppb

306 4 Kgm Kgu

75 55

426 Kog Kt ppb QTc gm

425 116° 30’

2 4 116° 30’

433 ppb Klog Kt ppb myl QTc Kt msg QTc Kcv + Kt msmg

277 gm

276

0 Kgu

74 Kgu

4 gm Kt

424 Kgu

454 gm

2 QTc ETZ

Kgdt 273

450 Kcv + Kt ppb

421

262 Kgu Kpc Ktg Kqd

434

70 Kgb

271

3 Kbt gm

272

2 QTc

438

2 ppb

417

5 26 EZ ppb .7034 Kqd

422 Kcv + Kt

266 ppb

253 QTc

261

264

437

45 ppb ppb

435

397 ppb

447

2 Kgu Kgb

268 9 2

423

324 gm QTc QTc Ksj

323 gm .7050

416 Kgdt ppb

94 QTc

406

408 Ksjm

254 QTc

244

415

269

ppb 436 265 ? Kgd .7063 Areas shown

2 Kgu

260

321 Kig ? gm are reconnaissance-

255 2 WTZ units are not subdivided. Kgb Kgu as

247 Ksj Kgu

322 1 98

mapped. Mixed Mesozoic granitic mapped. Mixed

409 546

414 QTc 243 ? units and pre-Mesozoic metamorphic gm Ksj

320

557

93 Kgdt

257

256 405

56 3

395

258 1 gm 2 Kgb Kgu

13 ppb

251

Ksj g

246 ppb

248

J b

24 p ppb 3

Kcv

Kjv p

410 Klb

318

Kcv + Kt

Kcm + Ksj Kgdt

Kgd

v T

Kgb

Klb Kj

Kgb Q QTc

319 Kpc

396

400

547 555

545

533 b

399 Kgb

249

ppb p

317 411 Klb

401 p 232 24

Kgb +

ppb v Kgu Kgu

234 Kj

241 p Kgb

250 QTc

.7060

Ka Kl

QTc m

91 Kgd

548

Kgd Kg

390

9 c

226 Kgd

31 Klp

83 QTc T

8 Kcv + Kt 3 Ksjm

412 Q QTc ppb 2 ppb

3 Klb .7051

532

34 Klp Kgd EZ 544 gm

448

are recon- v Kgu Kbt

5 b

225

naissance-

Kj p

v 553 3

Kgu p ppb

Areas shown as Areas shown

Klp Kj

402

404 units are undivided 449

82 Ka Ksj

230 Kcm

3 Kgb Kgd mapped. Cretaceous granitic

42 Klp 2

237 Kgd Kgb 543 Ksjm

5 ppb

535 ppb

381

385

403

8 QTc 3

389 ppb

531 p .7047

384 Klb

Ksj Kc

ETZ

Kgb Kcp QTc

536

29 Kgd

549 ppb

541 ppb 22

373 3

3 c Kh

2 Klw Kh Kgu .7060 ppb

71 Kgb ppb Khg

Ksj

QT v

22 Kgd

Kri 530 Kgb

0 Kj Ksjm

376 550

3 Kgb Kgu

513

529

372 Kt ETZ Kgd 1

88 v 54

37 Kgd Kri

QTc Kj

80 Ksj

70 Ka

3 .7062 5

522 QTc Kqd Ktv

3 Khg .7057

28 2 wm

551

538

Klw

Ka K Kgd . .7055

Kqd Kld Kgd

387 12

514

Kgb b Kt Kcv

369 Kat

ppb Kg

5 Khg

77 c Kt

QTc

v QT ETZ 3 .7057 ppb 117°

117° Kj Kdl

515 Khg

2 Kgb Kqbd Kbp Ktcg QTc

Kat 58

386

Kcgt 539

Kqbd 520 Kat

379 Kgd Kat Kdl Khg

Klct 3 Khg

50 Kthgd

510 Kmeg

378 Kgb

511 Kvc

5 Kgao ppb

16 Khg ppb Kvc

01 Khg

525 Kgd Kwm ppb Kt Kgd Kgb

5 .7058

5 Kdl Kgdf Kgb Kgb Krct Kgab Kgu Kwmt Kgd

Kbm c 524

519 Kgb

Kt QT Ki

367 Kqbd Kdl

365 QTc

509 ppb

517 Kgb Kgb Kgd

504 59 Ki WZ Kgd

492 Krm

Kdvg 353 ppb 500 QTc Krct Kcc Klmt

3 ppb Kls

366 490

357 Kmm Km 491 Kdvg ppb

361

356 Kmm

505 Kdvg Kr

Kt 64 Kgb 3

50 ppb Kjd

Klh Kgb 351

Kmm 3 Kgb Kt

488

489 499 Kgd Kgb Khg

49 Kmm Ki

482

360 352 Kgb Kgb Kjd

506

518 ppb ppb ppb

Ktbh 355 Kbpg Kt Kmm Kgu ppb

48 QTc Kt Klmt Kgb Khg Kgb

494 Kgb Kgb Kmp ppb

362 Kt Kgb

483

354 ppb

350 36 Kmgt

Kdvg 481 Kgb

498 Kt QTc Kbft Kt 0 Kbgg Kpvg Klh

344

48 ppb Kt

497

484 Kbfgi Kbhg

49 Kts

9 Kt Kt

495

3 348 Kbgg

486 Kbgr Kbt Khg 496

347 Kgb Kgb WTZ 47 Kgt Kbfg

468 Kgd Khg 475 Kgd

Kgd 345

Kgct Kt 343 Kbt Kgd

485

340

Kbft 472 ppb Kbht ppb Kgb Kgg

337 Kvt ppb

338

8 1 Kgu Kbft

341 Kbgg Khg Kght 20 Km Kgb ppb Katg Kt

Kbhg 476

45 469

QTc

339 346 Khg Ksmg Kbgg Kgh Kt

465 Kgti Kbgr ppb Krg Kgtf

478 Kgb

342 Khg Kbft

Kgu 71 ppb Krg

477

440 4 .7067 Kgu

Kgu 463 Krg ppb

Kgd 336 Kht Kgb 427 Kgb 466 Kgt Kmrg

70 334 Kgd ppb

335 467

Khg 4

Kt 428 ppb Krg ppb ppb .7050 QTc

464 .7047 Kht Kcg .7075 10

333

Kgd 418 Kgb Kht Kqd Kgu Khg Kdqd ppb N

462 Kgu ppb ppb Kt Kgbh Kqd ppb Kt

ppb 460 Krg

332

Khg 329

Kqd 461 5 Khg ppb .7046 Kgbh ppb Kgb Khg 117° 30’ Klst .7038 117° 30’ 33° .7040 QTc Kcg Kd Kmhg Kcg Kd QTc

330 0 Kmp 33° 30’

Klst 429 WZ .7039 Kcg ppb Kgp Keh Figure 68. Generalized geologic map of the northern Peninsular Ranges batholith showing Baird-Welday sample localities. An enlargeable version is on accompanying CD (see text CD (see text is on accompanying version An enlargeable sample localities. Baird-Welday Figure 68. Generalized geologic map of the northern Peninsular Ranges batholith showing footnote 1). Downloaded from memoirs.gsapubs.org on March 25, 2014

114 Morton et al.

for the upper-plate zone. These differences may be due to dif- thonous upper-plate zone rocks on autochthonous Peninsular ferences in sampling or variations in the Peninsular Ranges Ranges basement. batholith south of 33°N. Chemical averages for the ﬁ ve zones are summarized here Our western zone and western transition zone in general cor- and are given in Figure 69. The compatible elements Fe, Mg, respond to the western zone of Todd et al. (2003), and our eastern Ca, Sc, V, and Co decrease eastward in the autochthonous zones transition zone and eastern zone correspond to their eastern zone. and increase in the upper-plate zone. K, P, Rb, Sr, Nb, Ba, and Upper-plate zone rocks may not occur south of 33°N in the area light REEs increase from the western zone through the upper- of Todd et al. (2003). In general, our western zone corresponds plate zone. As noted by Baird et al. (1974), the increase in K

to domain B of Silver and Chappell (1988), our transition zones across the batholith is evident, with K2O increasing from an correspond to their domain C, our eastern zone corresponds to average of 1.9% to 2.9%. Silica is essentially the same in the their domains D and E, and the upper-plate zone correspond to western zone and western transition zone, increases slightly in their domain F. The western REE zone of Gromet and Silver the eastern transition zone, and shows signiﬁ cant increase in the

(1987) in general corresponds to our western zone, their interme- eastern zone, before decreasing in the upper-plate zone. Na2O diate zone corresponds to our transition zones, and their eastern increases slightly across the autochthonous batholith from the zone corresponds to our eastern zone and upper-plate zone. The western zone through the eastern zone and decreases to a low in western batholith zone of Baird and Miesch (1984) is essentially the upper-plate zone. our western zone and western transition zone, and their eastern As noted by Silver and Chappell (1988), some trace ele- batholith zone corresponds to the eastern transition zone, eastern ments have much greater variation across the batholith than zone, and upper-plate zone. major elements. For the autochthonous batholith, average values for Sc, V, Co, Ba, Sr, Nb, La, and Ce change by about a factor Regional Geochemistry of 2. Incompatible trace elements Zn, Rb, Sr, Nb, Ba, Th, and U increase from the western zone through the upper-plate zone Our batholith zones are based on a combination of ﬁ eld (Fig. 69). V, Co, and Mo decrease from the western zone through and analytical data. Field data include host rock, mode of plu- the eastern zone but increase in the upper-plate zone. REEs show ton emplacement, rock fabric, and mineralogy. Analytical data a systematic variation from light REEs to heavy REEs (Gromet ε include pluton emplacement age, Sri, Ndi, Pbi, whole-rock geo- and Silver, 1987). Light REEs La, Ce, Pr, Nd, and Eu increase chemistry, and aeromagnetic data. A summary of the character- from the western zone through the upper-plate zone, but Tm and istics of the batholith zones is given in Figure 4. The boundar- Yb decrease east of the western zone. ies between the western zone and the western transition zone, Harker diagrams for most major elements have a relatively and the western transition zone and the eastern transition zone linear pattern. Some dispersion is common for rocks having low

are based largely on rock fabric, mode of pluton emplacement, SiO2 and high Fe2O3, MgO, and CaO (Figs. 70A–70H). CaO is

aeromagnetic properties, the Sri <0.7045 isopleth, and positive especially linear, showing only a slight dispersion at the high ε Ndi values. The change from western zone passively emplaced, end of its range. The ratio of Al2O3 to SiO2 increases from the massively textured plutons to dynamically emplaced, concordant western zone to the eastern zone, but it decreases in the upper- foliated western transition zone plutons is very noticeable north plate zone to the same values seen in the two transition zones, ′Ν, of 33°22 but not to the south (e.g., Todd et al., 2003). Host producing an arcuate pattern. Both TiO2 and P2O5 have nonlinear rocks for the western zone and transition zones plutons are gen- patterns. Reﬂ ecting the distribution of apatite, the P2O5 pattern is erally quite different, marked by very low metamorphic grade, a relatively symmetrical convex arc, having maximum P2O5 in mostly below greenschist grade in the western zone, and higher intermediate-silica rocks and decreasing in both low-and high- amphibolite grade in the transition zones. silica rocks. Most low-silica rocks in the western zone have

Most rocks in western transition zone have Sri <0.7055 decreased TiO2, forming an asymmetric pattern. ε and a small positive Ndi, in contrast with the eastern transition ε zone, which has Sri mostly >0.7055, and a large negative Ndi. Rare Earth Elements The eastern transition zone includes large La Posta–type plutons Normalized REE patterns are similar to those described that are not present in the western transition zone. The boundary by Gromet and Silver (1987) and Todd et al. (2003). Normal- between the plutons of the western transition zone and eastern ized zone-average REE plots show a systematic enrichment in transition zone with the eastern zone plutons is less certain based the light REEs from west to east (Fig. 71). Average light REEs on textural changes, but it is generally more pronounced based are very similar for the western zone, western transition zone, on the widespread occurrence of large euhedral sphene in east- and eastern transition zone, but there is a signiﬁ cant difference

ern zone rocks. Most of the eastern zone has Sri >0.7060 and between patterns for these three zones and the eastern zone and

Pbi >19. Even though the eastern zone is structurally terminated upper-plate zone. Gabbros have two basic REE patterns, inde- on the east by the Eastern Peninsular Ranges mylonite zone, the pendent of location within the batholith. One pattern, displayed clear eastern zone boundary is the low-angle fault contact above mostly by hornblende gabbros, is nearly ﬂ at from light to heavy the Eastern Peninsular Ranges mylonite zone that places alloch- REEs, but slightly lower toward the heavy REE end (Fig. 21). Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 115

WZ WTZ ETZ EZ UPZ The second gabbro pattern, which includes most pyroxene and/or olivine gabbros, is similar, except for having a positive Eu anom- SiO * 64.0 63.8 64.3 67.1 64.7 2 aly. In general, there is less REE enrichment in olivine gabbro Al O * 15.6 16.2 16.4 15.7 15.8 2 3 than in hornblende gabbros. Fe O *+ 5.7 5.3 4.5 3.8 4.8 2 3 Many western zone granitoids are slightly enriched in light MgO* 2.5 2.2 2.0 1.1 1.7 REEs and have pronounced low Eu values, especially in what is CaO* 5.2 5.1 5.1 3.8 4.2 commonly termed the Woodson Mountain granodiorite (Fig. 27). 3.4 3.3 3.5 3.6 3.2 Most granitoids of the western transition zone and eastern tran- Na2O* K O* 1.9 2.0 1.9 2.6 2.9 sition zone have a relatively linear pattern, showing moderate 2 enrichment in light REEs, and, with the exception of gabbro, TiO * 0.56 0.67 0.68 0.62 0.73 2 little if any negative Eu. Typical eastern zone granitoids are more P O * 0.13 0.15 0.17 0.18 0.22 2 5 enriched in light REEs and more depleted in heavy REEs than MnO* 0.09 0.08 0.07 0.06 0.07 western transition zone and eastern transition zone granitoids. Sc 17 15 11 7.1 7.7 Some eastern zone plutons have a slight negative Eu anomaly. V 104 106 85 44 68 White mica– and garnet-bearing leucogranites at Mount Eden

Co 15.5 13 10 7 10 and Bautista Canyon have moderate-to-large negative Eu anomalies (Fig. 72). Upper-plate granitoids have patterns similar to the Cu 13 8.6 7.5 16 25 eastern zone granitoids, but they show greater enrichment in La. Zn 48 64 65 67 72 Scandium (Fig. 70G) and the heavy REEs decrease progres- Rb 59 74 65 89 110 sively from the western zone through the eastern zone, suggesting Sr 236 307 402 431 471 processes of relatively shallow fractionation in the west to much Y 23 18 12 17 18 deeper fractionation in the east, involving garnet and/or clinopy- Zr 148 125 130 163 214 roxene in the thick lower continental crust or upper mantle. Rb, Nb 5 569 15 Sr, Nb, Ba, Ta, Th, U, and the light REEs are not sequestered in garnet and/or clinopyroxene. The increase in these elements from Mo 2.6 2.0 2.0 2.1 2.8 the western zone through the upper-plate zone refl ects shallow Cs 2.4 2.6 3.2 2.6 2.3 crustal differentiation in the west and much deeper crustal dif- Ba 557 710 886 1017 1034 ferentiation in the east. La 14.6 15.9 18.7 28.8 44.0 Ce 32.8 34.4 39.2 61.6 90.8 Strontium Isotopes Pr 4.3 4.4 4.9 7.4 10.5 Our rubidium, strontium, lead, and oxygen isotope data are from the Welday-Baird samples augmented by 104 samples from Nd 17.8 18.0 19.6 28.7 38.1 selected locations. The Sr and Rb data and analytical methods Sm 4.6 4.2 4.2 6.0 7.3 are given in Kistler et al. (2003, this volume). Additional Sr data Eu 1.1 1.1 1.2 1.3 1.6 are given for the Lakeview Mountains pluton (Morton et al., this Gd 4.4 3.7 3.4 4.4 5.2 volume) and the Box Springs Mountains plutonic complex. Tb 0.82 0.70 0.51 0.69 0.76 Initial strontium isotope variation in the batholith was fi rst Dy 4.7 3.5 2.7 3.6 4.1 described by Early and Silver (1973) and Kistler et al. (1973). Both studies showed a southwest to northeast increase in Sr . Ho 1.1 0.8 0.6 0.7 0.8 i Samples in Kistler et al. (1973) were from the northern part of Er 3.1 2.1 1.5 2 2.1 the batholith. Early and Silver (1973, p. 494) gave no sample Tm 0.52 0.39 0.23 0.32 0.33 locations other than that the samples were from southern Cali- Yb 3.1 1.9 1.3 1.9 1.9 fornia and Baja California. Their Sri values ranged from 0.7033 Hf 4.7 3.8 3.9 4.7 5.8 to 0.7062, except for the “…extreme eastern side of the batho- Ta 0.54 0.60 0.61 0.90 1.40 lith, initial values are limited to less than 0.7045….” They noted W 0.45 0.36 0.34 0.36 0.43 that the “…east-west contrasts appear to relate to a major boundary between pre-batholithic host rocks…. Mesozoic metavol- Th 8.0 8.2 8.5 10.9 20.5 canics to the west and a metamorphic sedimentary complex of U 1.9 1.8 1.7 2.2 3.0 unknown age to the east.” A highly diagrammatic depiction of Zr/Hf 32.1 33.2 33.0 35.0 37.0 near-linear 0.7040 and 0.7060 Sri isopleths from the north end of the batholith southward for 600 km was given by Gromet and Figure 69. Comparisons of zone chemistry, showing major element and rare earth element (REE) averages for the fi ve batholith zones. As- Silver (1987). Silver and Chappell (1988), referring to the study terisk (*) denotes values expressed as percent, Zr/Hf as ratio, all others of Early and Silver (1973, p. 114), stated, “They found that the as parts per million (ppm). Total Fe expressed as Fe2O3. rocks of the batholith are characterized in general by a gradient Downloaded from memoirs.gsapubs.org on March 25, 2014

116 Morton et al.

14 14

12 12 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 10 10

8 8 (percent) (percent) 6 6 3 3 O O 2 2 4 4 Fe Fe

2 2

0 0 40 455055 60 65 70 75 80 40 455055 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

14 14 Western Zone 12 12 Western Transition Zone Upper Plate Zone Eastern Transition Zone 10 10 Eastern Zone Upper Plate Zone 8 8 (percent) (percent)

3 6 3 6 O O 2 2 4 4 Fe Fe

2 2

0 0 40 455055 60 65 70 75 80 40 455055 60 65 70 75 80 SiO (percent) SiO (percent) 2 . . 2

12 12

10 10 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 8 8

6 6 MgO (percent) MgO (percent) 4 4

2 2

0 0 40 4550 55 60 65 70 75 80 40 4550 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

12 12 Western Zone 10 10 Western Transition Zone Eastern Transition Zone Upper Plate Zone Eastern Zone 8 8 Upper Plate Zone

6 6 MgO (percent) 4 MgO (percent) 4

2 2

0 0 40 455055 60 65 70 75 80 40 455055 60 65 70 75 80

A SiO2 (percent) SiO2 (percent)

Figure 70 (Continued on following pages). Harker diagrams of selected major and trace elements. Diagrams show plots by zones and by all zones combined. Analyzed samples include all Baird-Welday samples, samples collected to augment the Baird-Welday collection, and samples collected primarily for U-Pb isotopes. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 117

5.0 5.0

4.5 4.5

4.0 4.0

3.5 3.5

3.0 3.0

2.5 2.5 O (percent) O (percent) 2 2.0 2 2.0 Na 1.5 Na 1.5 Western Zone Western Transition Zone 1.0 Eastern Zone 1.0 Eastern Transition Zone 0.5 0.5

0 0 40 455055 60 65 70 75 80 40 455055 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

5.0 5.0

4.5 4.5

4.0 4.0

3.5 3.5

3.0 3.0

2.5 2.5 O (percent) O (percent) 2 2.0 2 2.0 Western Zone Na 1.5 Na 1.5 Western Transition Zone Upper Plate Zone Eastern Transition Zone 1.0 1.0 Eastern Zone Upper Plate Zone 0.5 0.5

0 0 40 455055 60 65 70 75 80 40 455055 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

6 6

5 5 Eastern Zone Western Transition Zone Western Zone Eastern Transition Zone 4 4

3 3 O (percent) O (percent) 2 2 K K 2 2

1 1

0 0 40 4550 55 60 65 70 75 80 40 4550 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

6 6 Western Zone Western Transition Zone 5 5 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 4 4

3 3 O (percent) O (percent) 2 2 K K 2 2

1 1

0 0 40 4550 55 60 65 70 75 80 40 4550 55 60 65 70 75 80

B SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

118 Morton et al.

18 18

16 16

14 14 Western Transition Zone Western Zone Eastern Transition Zone 12 Eastern Zone 12

10 10

8 8

6 6 CaO (percent) CaO CaO (percent) CaO 4 4

2 2

0 0 40 4550 55 60 65 70 75 80 40 455055 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

18 18

16 16 Western Zone 14 14 Western Transition Zone Upper Plate Zone Eastern Transition Zone 12 Eastern Zone 12 Upper Plate Zone 10 10

8 8

6 6 CaO (percent) CaO CaO (percent) CaO 4 4

2 2

0 0 40 455055 60 65 70 75 80 40 4550 55 60 65 70 75 80 SiO (percent) 2 SiO2 (percent)

0.30 0.30

0.25 0.25 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 0.20 0.20

0.15 (percent) 0.15 5 O (percent) 2 5 P O 0.10 0.10 2 P

0.05 0.05

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80 SiO (percent) 2 SiO2 (percent)

0.30 0.30 Western Zone Western Transition Zone Eastern Transition Zone 0.25 0.25 Eastern Zone Upper Plate Zone Upper Plate Zone 0.20 0.20

0.15 0.15 (percent) 5 (percent) 5 O 2 O 0.10 0.10 2 P P

0.05 0.05

0 0 C 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80 SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 119

1.4 1.4

1.2 1.2 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 1.0 1.0

0.8 0.8 (percent) (percent) 2

2 0.6 0.6 TiO TiO 0.4 0.4

0.2 0.2

0 0 40 4550 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

1.4 1.4 Western Zone Western Transition Zone 1.2 1.2 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 1.0 1.0

0.8 0.8 (percent) (percent) 2 2 0.6 0.6 TiO TiO 0.4 0.4

0.2 0.2

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

24 24

22 22 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 20 20

18 18 (percent) (percent) 3 3 O 16 O 16 2 2 Al Al 14 14

12 12

10 10 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

24 24 Western Zone Western Transition Zone 22 22 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 20 20

18 18 (percent) (percent) 3 3 O O 16 16 2 2 Al Al 14 14

12 12

10 10 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

D SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

120 Morton et al.

3000 3000

2500 2500 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 2000 2000

1500 1500 Ba (ppm) 1000 Ba (ppm) 1000

500 500

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

3000 3000 Western Zone Western Transition Zone 2500 2500 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 2000 2000

1500 1500 Ba (ppm)

Ba (ppm) 1000 1000 .

500 500

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

60 60

50 50 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 40 40

30 30 La (ppm) La (ppm) 20 20

10 10

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

60 60 Western Zone Western Transition Zone 50 50 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 40 40

30 30 La (ppm) La (ppm) 20 20

10 10

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

E SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 121

250 250

200 200 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 150 150

100 100 Rb (ppm) Rb (ppm)

50 50

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

250 250

Western Zone 200 200 Western Transition Zone Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 150 150

100 100 Rb (ppm) Rb (ppm)

50 50

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

700 700

600 600 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 500 500

400 400

300 300 Sr (ppm) Sr (ppm)

200 200

100 100

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

700 700 Western Zone Western Transition Zone 600 600 Eastern Transition Zone Upper Plate Zone Eastern Zone 500 500 Upper Plate Zone

400 400

300 300 Sr (ppm) Sr (ppm)

200 200

100 100

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

F SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

122 Morton et al.

60 60

50 50 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 40 40

30 30 Sc (ppm) Sc (ppm) 20 20

10 10

0 0 4045 50 5560 65 70 75 80 4045 50 5560 65 70 75 80 SiO (percent) SiO2 (percent) 2

60 60 Western Zone Western Transition Zone 50 50 Eastern Transition Zone Upper Plate Zone Eastern Zone Upper Plate Zone 40 40

30 30 Sc (ppm) 20 Sc (ppm) 20

10 10

0 0 4045 50 5560 65 70 75 80 4045 50 5560 65 70 75 80 SiO (percent) 2 SiO2 (percent)

120 120 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 100 100

80 80

60 60 Zn (ppm) Zn (ppm) 40 40

20 20

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80 SiO (percent) 2 SiO2 (percent)

120 120

100 100 Upper Plate Zone 80 80

60 60 Zn (ppm) Zn (ppm) 40 40 Western Zone Western Transition Zone 20 20 Eastern Transition Zone Eastern Zone Upper Plate Zone 0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80 SiO (percent) G SiO2 (percent) 2

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 123

50 50

45 45 Western Zone Western Transition Zone 40 Eastern Zone 40 Eastern Transition Zone 35 35

30 30

25 25 Y (ppm) 20 Y (ppm) 20

15 15

10 10

5 5 0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

50 50 Western Zone 45 45 Western Transition Zone Upper Plate Zone Eastern Transition Zone 40 40 Eastern Zone Upper Plate Zone 35 35

30 30

25 25 Y (ppm) 20 Y (ppm) 20

15 15

10 10

5 5 0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

25.0 25.0

20.0 20.0 Western Zone Western Transition Zone Eastern Zone Eastern Transition Zone 15.0 15.0

10.0 10.0 Nb (ppm) Nb (ppm)

5.0 5.0

0 0 40 45 5055 60 65 70 75 80 40 45 50 55 60 65 70 75 80

SiO2 (percent) SiO2 (percent)

25.0 25.0 Western Zone Western Transition Zone 20.0 20.0 Eastern Transition Zone Eastern Zone Upper Plate Zone Upper Plate Zone 15.0 15.0

10.0 10.0 Nb (ppm) Nb (ppm)

5.0 5.0

0 0 40 45 50 55 60 65 70 75 80 40 45 50 55 60 65 70 75 80

H SiO2 (percent) SiO2 (percent)

Figure 70 (Continued). Downloaded from memoirs.gsapubs.org on March 25, 2014

124 Morton et al.

1000 The average Sr for the ﬁ ve zones of the Peninsular Ranges Western Zone i Western Transition Zone batholith increases systematically from west to east, with a mod- Eastern Transition Zone Eastern Zone Upper Plate Zone erate step between the eastern transition zone and the eastern zone (Fig. 75). For the northern Peninsular Ranges batholith, Sr 100 i is bimodal, with peaks at 0.7038 and 0.7072 (Fig. 76). Only a

minor part of the batholith has Sri between 0.7056 and 0.7064, with a minimum frequency of samples at 0.7059. Despite considerable sample density, this dearth of samples of Sr >0.7056 and

Rock/Chondrites 10 i <0.7064 and peaks at 0.7038 and 0.7072 clearly defi ne a bimodal character for the batholith. We interpret this bimodal distribution to refl ect a relatively sharp boundary between Mesozoic oceanic crust and older continental crust; it is essentially coincident with La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb the western zone and western transition zone boundary, and it is Figure 71. Average chondrite-normalized rare earth elements (REEs) one of the criteria used to establish the boundary. for the fi ve batholith zones. Average light REE values are similar for Sri values for western zone samples have an average of the western zone, western transition zone, and eastern transition zone, 0.7039, with most in the mid-0.7030s and a few in the 0.7040s. and the eastern zone and upper-plate zone are distinct from each other The uniformly low Sr that characterizes the western zone is nota- and from the other zones of the batholith. i bly independent of pluton composition. The Sri = 0.7045 isopleth is mostly coincident with the western zone–western transition zone boundary, and at its southern extent also separates highly from very low values of initial 87Sr/86Sr (<0.703) at the western magnetic rocks on the west from less magnetic rocks on the east. limits, to values as high as 0.7080 at the eastern margin.” Kistler However, in the northern Santa Ana Mountains and the north-

and Morton (1994) and Morton and Kistler (1997) discussed pre- western Perris block, the Sri 0.7045 isopleth deviates southwest

liminary results of investigations of Sri variation in the northern away from the zone boundary. This deviation is caused by the Peninsular Ranges batholith between 33°N and 34°N. western zone Gavilan ring complex, which has relatively wide

Our extensive Sri data set for the northern Peninsular Ranges variation in Sri ranging from 0.7041 to 0.7062. In the western batholith (see also Kistler et al., 2003, this volume) shows con- zone Paloma Valley ring complex, just south of the Gavilan ring

siderable geometric complexity in Sri isopleths, rather than a complex, most Sri values range from 0.7036 to 0.7046, except

uniform gradient. Geometric Sri complexities of the 0.7045 and for one anomalous value of 0.7058. The Sri = 0.7045 isopleth

0.7060 isopleths (Fig. 73) are in part inherent pluton Sri varia- bisects the northwest part of the Paloma Valley ring complex tion and in part from offsets on the Neogene Elsinore and San mainly because of the anomalous 0.7058 value; lower values

Jacinto fault zones (see also Miller et al., this volume). The Sri typify the southeastern 80% of the complex, and the lone higher

variation shown in Figure 74 is after 29 km of lateral displace- value represents the northwestern 20%. The Sri heterogeneity of ment on the San Jacinto fault zone and 12 km of displacement the Gavilan and the Paloma Valley ring complexes is interpreted on the Elsinore fault zone have been restored, so that sample as a reﬂ ection of heterogeneity in the magma sources along the localities have the positions relative to each other that they had interface between oceanic and continental crust.

at the time of pluton emplacement. For most western transition zone plutons, Sri values range from 0.7045 to 0.7050 and average 0.7049. In the Riverside area, a few western transition zone granodiorite and granite samples

1000 have Sri >0.7060, and in the Jurupa Mountains area, Sri is quite

Mount Eden pluton variable, with one value of 0.7075. The relatively high Sri values 94-91 Two-mica monzogranite in the Riverside–Jurupa Mountains area likely reﬂ ect contamina- 94-90 Fine-grained muscovite granite dike tion of the magma by abundant Paleozoic(?) prebatholithic rocks 100 in these areas.

Sri values of eastern transition zone samples range from 0.7050 to 0.7055 and average 0.7053. The eastern transition zone is dominated by the Coahuila Valley and Tucalota Valley 10 Rock/Chondrites plutons, which have relatively uniform Sri values of 0.7048– 0.7052. The white mica eastern transition zone Mount Eden

granite has Sri values of 0.7058 and 0.7059, and a ﬁ ne-grained

1 leucocratic granite dike of the pluton has Sri of 0.7069. Sri val- La Ce Pr Nd Sm Eu TbGd Dy Ho Er Tm Yb ues of relatively few eastern transition zone gabbros range from

Figure 72. Chondrite-normalized rare earth element (REE) plots for 07035 to 0.7050. This range in Sri values in eastern transition Mount Eden leucogranite and associated ﬁ ne-grained leucocratic dike. zone plutons shows a deﬁ nite link to plutonic rock type, unlike Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 125

Box Springs Plutonic Complex ′ 50 116° 30′ W 117° 30 75 45 46 52 34° 00′ 55 34° 00′ N 45 51 47 49 47 67 48 ETZ 48 43 57 44 45 45 WTZ 109 52 60 58 85 60 85 70 39 62 57 46 48 57 40 38 47 70 66 71 71 70 73 74 48 70 44 55 45 55 72 66 76 45 46 47 51 67 ETZ 61 70 71 69 44 47 60 71 68 67 73 45 50 71 44 45 48 WTZ 69 70 66 65 88 74 44 49 50 73 70 41 52 49 72 67 44 63 70 59 63 84 45 46 71 73 70 70 EZ 83 80 40 52 70 75 62 71 69 77 WZ 39 41 74 70 77 76 50 68 73 77 47 67 74 77 77 78 58 45 42 37 52 52 69 72 61 78 78 46 48 65 83 80 36 76 78 UPZ 38 52 52 61 80 44 36 37 36 74 77 82 52 52 31 60 34 78 83 54 36 66 47 50 61 61 76 35 43 46 81 43 51 54 55 80 81 36 70 81 66 81 46 34 51 55 55 82 40 EZ 74 79 46 51 50 55 74 81 ′ 38 52 66 78 33° 30 36 43 41 WZ 55 ETZ 66 74 80 55 57 73 73 41 49 49 117° 30′ 49 44 51 41 36 60 73 49 51 36 36 36 32 54 54 50 41 36 WTZ 49 36 36 53 85 52 36 32 32 49 45 36 38 46 50 54 35 36 32 43 49 48 47 38 38 53 38 38 36 37 40 43 49 36 32 42 38 36 37 67 40 WTZ 58 38 37 46 36 38 42 62 36 36 62 62 37 38 47 62 38 38 36 37 36 38 47 72 62 38 37 36 38 38 46 47 36 36 38 66 EZ 62 36 36 36 Sr 36 43 47 i 36 36 41 (all numbers shown are 36 43 36 36 38 preceded by 0.70) 36 36 43 45 43 36 36 WZ 40 36 36 42 Zone boundaries 36 36 36 36 36 33° 00′ 36 36 N Sri 0.7045 116° 30′ 36 36 36 Sri 0.7060 δ18O 9.0 line

Pb 19.0 line i 0 10 20 30 km Eastern Peninsular Ranges Mylonite Zone

Figure 73. Generalized map showing Sri 0.7045 and 0.7060 isopleths and all Sri values. Total offset of the Eastern Peninsular Ranges mylonite zone by San Jacinto fault zone is diagrammatically shown as having occurred on a single strand. Major offsets of the Eastern Peninsular Ranges mylonite zone are actually across two stands of the San Jacinto fault zone that are separated by ~7 km at the latitude of the offsets. WZ—western zone; WTZ—western transition zone; ETZ—eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone. Downloaded from memoirs.gsapubs.org on March 25, 2014

126 Morton et al.

Box Springs Plutonic Complex 57 ETZ 109 ′ 50 70 116° 30′ W 117° 30 75 45 58 57 85 60 85 46 52 57 55 70 66 71 71 70 73 74 34° 00′ N 34° 00′ 45 70 51 66 47 49 55 67 72 76 47 67 48 61 70 71 69 71 68 67 73 71 48 66 88 43 45 45 WTZ 69 70 65 74 44 52 60 73 70 39 62 67 46 70 72 40 38 48 47 84 48 71 73 70 70 EZ 83 80 44 55 75 45 71 69 77 77 45 46 47 51 74 70 76 ETZ 68 73 77 44 47 60 67 74 77 77 78 45 50 69 72 44 45 48 61 78 83 44 49 50 76 65 78 80 41 52 49 61 80 44 74 77 82 63 60 34 83 59 46 63 61 76 78 45 40 52 61 62 70 80 81 81 39 41 70 81 66 81 50 82 WZ 79 58 45 42 52 74 81 37 52 74 78 46 48 74 80 36 52 52 78 36 37 36 73 73 47 52 52 31 UPZ 36 66 47 50 46 73 51 54 55 44 38 46 34 51 55 55 EZ 54 43 WZ 46 51 50 55 66 33° 30′ 35 43 52 55 66 36 ETZ 55 40 49 57 ′ 49 49 117° 30 60 44 51 43 38 41 49 36 54 54 50 51 32 WTZ 49 41 53 85 32 32 49 45 52 41 36 46 50 54 41 36 36 36 32 43 49 48 47 N 36 53 36 36 36 40 43 49 36 32 42 36 WTZ 58 67 35 36 38 40 38 38 42 46 38 62 62 38 37 47 62 36 62 38 36 37 47 38 37 72 62 36 38 0 10 20 30 km 36 36 47 37 38 66 EZ 62 38 38 36 37 36 38 47 46 38 37 36 38 38 Sr 36 36 38 i 36 36 36 43 36 36 (all numbers shown are 36 36 41 43 preceded by 0.70) 36 36 36 38 ′ WZ 36 43 45 43 33° 00 Zone boundaries 36 36 40 36 36 42 36 116° 30′ Sr 0.7045 36 36 i 36 36 36 36 Sri 0.7060 36 36 δ18O 9.0 line 36

Pbi 19.0 line Note: Latitude/longitude ticks are relative to the Perris Block. Restoration of movement on the San Eastern Peninsular Ranges Jacinto and Elsinore Fault Zones causes true Mylonite Zone localities in the Santa Ana and San Jacinto Blocks to not correspond to the latitude/longitude ticks.

Figure 74. Generalized map showing Sri 0.7045 and 0.7060 isopleths and all Sri values after restoration of 12 km displacement on the Elsinore fault zone and 29 km displacement on the San Jacinto fault zone. WZ—western zone; WTZ—western transition zone; ETZ—eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 127

0.7090 206 ing Pb from west to east, with Pbi values of 18.5–18.7 in the 0.7080 western part of the batholith. In the central part of the batholith,

at their age step of 105 Ma, Pbi values were in the range of 18.8– 0.7070 18.9. Values as high as 19.4–19.5 were recorded at the eastern i 0.7060 margin of the batholith. Kistler et al. (2003) reported Pb values Sr i for the northern Peninsular Ranges batholith and gave values as 0.7050 low as 18.4 in the western zone and as high as 19.5 in the upper- 0.7040 plate zone. The Pb = 19.0 isopleth is coincident with the Sr = 0.7060 0.7030 i i WZ WTZ ETZ EZ UPZ isopleth (Fig. 77), both of which are generally coincident with the San Jacinto fault zone. All western zone, western transition Figure 75. Plot of average Sr for the ﬁ ve batholith zones. i zone, and eastern transition zone samples have Pb <19 (Fig. 77), Note the step between the eastern transition zone and i eastern zone. WZ—western zone; WTZ—western tran- with the exception of two samples from the eastern transition sition zone; ETZ—eastern transition zone; EZ—eastern zone, one sample of the western transition zone Box Springs zone; UPZ—upper-plate zone. Mountains pluton, and one sample from the northern Santa Ana δ18 Mountains that has an aberrant O value. Average Pbi increases systematically from west to east, with a pronounced step between

western zone plutons, which show little correlation between Sri the eastern transition zone and the eastern zone (Fig. 78). Similar

and pluton composition. to Sri, the frequency distribution of Pbi is bimodal, with a mini-

For most of its length, the eastern transition zone–eastern mum number of samples having Pbi of 19.05 (Fig. 79). The pro-

zone boundary is essentially coincident with the San Jacinto fault nounced step (Fig. 78) and the bimodal minimum at Pbi of 19.05

zone (Langenheim et al., 2004), the Sri = 0.7060 isopleth, and the are interpreted to reﬂ ect the transition of subduction from largely

Pbi = 19.0 isopleth. Most eastern zone granitic rocks have Sri val- beneath oceanic crust to beneath continental crust. ues ranging from the mid-0.7060s to the low 0.7070s, but aver- At ~33°45′Ν, the eastern transition zone pinches out, and age close to 0.7070, i.e., considerably greater than the average the Pbi = 19.0 isopleth separates the western transition zone from 0.7049 of the western transition zone and 0.7053 of the eastern the eastern zone; at ~34°N, the eastern transition zone reappears transition zone. At the north end of the batholith, the Sri = 0.7060 between the western transition zone and eastern zone. The Pbi isopleth is located just east of the San Jacinto fault zone in the = 19 isopleth is one of the criteria used to establish the eastern northwestern part of the San Jacinto Mountains (Fig. 74). Control transition zone–eastern zone boundary. at the northern end of the Sri = 0.7060 isopleth is poor, with only two samples from the Lamb Canyon pluton having Sri values of Oxygen Isotopes

0.7056 and 0.7057. Upper-plate zone granitic rocks have Sri val- Turi and Taylor (1971) published an early detailed oxy- ues in the range of 0.7076–0.7084, and they have an average of gen isotope study on the Domenigoni Valley pluton, but the 0.7079, which is considerably greater than the average of 0.7070 ﬁ rst detailed investigation of regional oxygen isotope variation for eastern zone samples. of the batholith was by Taylor and Silver (1978). Their work showed a systematic change of δ18O from 6.0‰ to 7.0‰ in Lead Isotopes the west to 12.8‰ in the east. They emphasized a near-linear Silver (1987) and Silver and Chappell (1988) summarized step in δ18O from 8.5‰ to 9.0‰ isopleths striking southward 206 204 the variation of initial Pb/ Pb (Pbi) across the Peninsular from the north end of the batholith for over 300 km, well into Ranges batholith. They described a general gradient of increas- Baja California. Additional δ18O data are given in Taylor (1986, 1988). Kistler et al. (2003) showed oxygen isotope variation across the northern part of the batholith and discussed the rela- 80 δ18 tionship between O and Sri. 70 Our oxygen isotope database consists of only 100 samples, 60 38 from the western zone, 14 from the western transition zone, 50 9 from the eastern transition zone, 27 from the eastern zone, and 40 δ18 30 12 from the upper-plate zone. Variation of O across the north- 20 ern Peninsular Ranges batholith is depicted in Figure 80, which 10 shows sample locations after restoration of displacement on the Number of samples 0 Elsinore and San Jacinto fault zones. The average δ18O values are 0.703 0.704 0.705 0.706 0.707 0.708 0.709 7‰ for the western zone, 8.3‰ for the western transition, 10.2‰ (87Sr/86Sr) 0 for the eastern transition zone, 10.3‰ for the eastern zone, and Figure 76. Bimodal frequency distribution of initial 87Sr/86Sr for the 8.7‰ for the upper-plate zone, showing a gradual rise in δ18O northern Peninsular Ranges batholith. values across the autochthonous zones and a notable drop in the Downloaded from memoirs.gsapubs.org on March 25, 2014

128 Morton et al.

Box Springs Plutonic Complex ETZ 18.809 ′ 116° 30′ W 117° 30 19.161 19.399 18.900 19.244 ′ 19.092 34° 00′ N 34° 00 18.756 19.016 WTZ 19.144 EZ 19.296 18.868 19.183 18.667 18.814 19.243 19.573 18.977 18.790 19.300 19.158 18.826 19.228 19.402 18.746 19.189 18.869 18.784 19.197 19.452 19.125 19.476 19.414 18.782 18.747 18.876 ETZ 19.120 19.092 19.410 18.767 19.182 19.343 18.773 18.874 UPZ 19.069 19.340 19.153 19.126 WZ 18.907 19.473 18.924 18.831 19.172 19.223 18.792 19.278 18.776 19.014 18.990 18.890 18.768 18.704 19.335 18.977 18.933 18.980 18.837 18.860 19.118 18.785 18.843 18.836 ETZ EZ 33° 30′ 19.045 18.904 18.931 18.910 18.887 18.960 18.835 18.803 18.476 WZ WTZ 18.829 18.999 N 18.923 18.686 18.689 18.970 18.943 18.446 19.119 18.818 18.868 18.747 18.863 18.897 0102030 km 18.813 18.788 18.699 WTZ EZ 18.532 18.654 18.654 18.611 18.882 18.597 18.744 Pbi Zone boundaries 18.730 18.676 18.684 18.758 18.557 Sri 0.7045 18.656 WZ 18.798 33° 00′ Sr 0.7060 18.628 i 116° 30′ 18.686 18.842 δ18O 9.0 line 18.596 18.793 Note: Latitude/longitude ticks are relative to the Pbi 19.0 line Perris Block. Restoration of movement on the San Jacinto and Elsinore Fault Zones causes true Eastern Peninsular Ranges localities in the Santa Ana and San Jacinto Blocks to Mylonite Zone not correspond to the latitude/longitude ticks.

Figure 77. Generalized map showing distribution of lead isotope samples, and initial 206Pb/204Pb 19.0 isopleth after restoration of 12 km displacement on the Elsinore fault zone and 29 km displacement on the San Jacinto fault zone. WZ—western zone; WTZ—western transition zone; ETZ—eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 129

19.40 interpreted δ18O randomness in the central part of the Cretaceous Sierra Nevada batholith as principally due to variation in the orig- 19.30 inal magma composition and not due to alteration. Most of the western zone and western transition zone have 19.20 δ18O <9‰, and the δ18O = 9‰ isopleth is essentially coincident

i 19.10 with the western transition zone–eastern transition zone bound- Pb ary, except in the southern part of the area. There, the isopleth 19.00 diverges from the zone boundary, making a near right-angle turn across the western transition zone, and then follows the western Average Average 18.90 zone–western transition zone boundary to the southern edge of the map. The δ18O is <9‰ for the western zone, except for a 18.80 single value of 9.3‰ for the westernmost sample in the northern Santa Ana Mountains (sample HSCZ). The δ18O values in the 18.70 WZ WTZ ETZ EZ UPZ eastern transition zone and eastern zone fall between 9.0‰ and 12.8‰, with most between 9.6‰ and 10.6‰. 206 204 Figure 78. Plot of average Pbi ( Pb/ Pb) for the fi ve batholith zones. There is a much greater step in initial Pbi values between the eastern transition zone and eastern zone than for initial 87Sr/86Sr. Geochemical Interpretation WZ—western zone; WTZ—western transition zone; ETZ— eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone. Nearly all current work on the northern part of the Peninsu- lar Ranges batholith appears to substantiate the proposal that relatively uniform west-to-east geochemical and isotopic variations upper-plate zone (Fig. 81). The lower δ18O values in the upper- across the batholith refl ect a change in magma derivation from plate zone appear coincident with the area of low-δ18O values in oceanic-type lithosphere in the west to derivation from a mix the San Jacinto block reported by Taylor and Silver (1978). The of oceanic-type lithosphere and more-evolved continental litho- δ18O map of Taylor and Silver (1978) is reproduced in Silver et sphere in the east (e.g., Baird and Miesch, 1984; DePaolo, 1981; al. (1979). Gromet and Silver, 1987; Kistler et al., 2003; Silver and Chap- The distribution of δ18O values within the western zone does pell, 1988; Todd et al., 2003). Baird and Miesch (1984) arrived not show an even progression from lower values in the western at this interpretation based on studies of major-element chemis- part of the zone to higher values in the eastern part. In places, try. Gromet and Silver (1983) based their interpretation on the there are signifi cant reversals or a near randomness to the values. REE chemistry. Kistler et al. (2003) based their interpretation on δ18 The same absence of an even value-progression is apparent within a combination of Sri, O, and Pbi isotopes. Silver and Chappell the combined transition zones, although slightly less pronounced (1988), summarizing various chemical and isotopic data, as did than in the western zone. The internal value distribution within Todd et al. (2003), both arrived at basically the same conclusion. the eastern zone appears to have about the same degree of ran- Uniquely comprehensive geochemical and isotopic data sets domness as the combined transitions. Although it may be partly are presented here to substantiate and augment the prevailing a result of the limited number of samples, δ18O values within the consensus interpretation for the origin of the northern Peninsu- ε upper-plate zone show a regular eastward progression from low lar Ranges batholith. West-to-east variations in Sri, Pbi, and Ndi to high values. Lackey and coworkers (Lackey et al., 2008, 2112) and some elements (e.g., Sr, and Ba) support the interpretation of magma emplacement progressing from oceanic to continental lithosphere and forming the fi ve zones of the northern Peninsular 25 Ranges batholith (Figs. 75, 78, and 82). This variation is similar to recent work in the Fine Gold intrusive suite of the central 20 Sierra Nevada batholith (Lackley et al., 2012). The reversal in trend in average values between the eastern 15 δ18 zone and upper-plate zone for O, SiO2, Fe2O3, MgO, and V 10 and the step between the eastern zone and upper-plate zone for other elements (e.g., Th and Ta; Figs. 81and 82) suggest that the

Number of samples 5 magma source for the upper-plate zone was farther east than our designated eastern zone, because its isotopic characteristic sug- 0 gest greater input of aged North American crust. We are uncertain 18.4 18.6 18.8 19.019.2 19.4 19.6 Pb whether interpretations based on this very detailed data set are i applicable to the entire Peninsular Ranges batholith. Our interpretations are linked to the four autochthonous zones of the north- Figure 79. Bimodal frequency distribution of initial Pbi for the northern Peninsular Ranges batholith. ern Peninsular Ranges batholith and the criteria used to deﬁ ne Downloaded from memoirs.gsapubs.org on March 25, 2014

130 Morton et al.

Box Springs Plutonic Complex ETZ ′ 117° 30′ 116° 30 10.1 10.6 34° 00′ 7.6 34° 00′ 8.6 10.4 8.5 10.3 10.0 8.6 EZ WTZ 9.5 10.8 9.8 9.2 10.0 7.6 10.6 9.9 8.8 9.1 9.1 ETZ 9.9 9.0 11.2 8.6 7.7 9.8 8.9 7.1 8.6 8.7 7.2 9.6 10.5 8.3 7.1 11.1 9.6 8.3 8.9 8.2 7.2 9.7 8.8 7.9 9.7 9.3 8.6 8.9 7.4 WZ 9.7 UPZ

8.3 ETZ 9.0 10.1 11.0 12.8 WZ 9.2 10.9 8.2 EZ ′ 9.3 8.0 9.0 33° 30 10.5 12.3 7.4 9.6 N 5.9 8.0 WTZ8.6 10.8 8.6 10.9 9.7 ETZ 8.4 8.2 10.2 7.2 WZ 7.4 12.3 0 10 20 30 km 8.5 8.1 9.0 EZ WTZ 10.8 δ18O 6.4 6.2 6.6 Zone boundaries 6.9 6.5 6.6 5.9 6.8 4.4 2.3 Sri 0.7045 6.4 6.6 7.2 5.8 6.7 Sri 0.7060 6.7 WZ 33° 00′ δ18O 9.0 line 6.3 ′ 6.1 116° 30 Pb 19.0 line i 6.3 7.0 Note: Latitude/longitude ticks are relative to the Perris Block. Restoration of movement on the Eastern Peninsular Ranges San Jacinto and Elsinore Fault Zones causes true Mylonite Zone localities in the Santa Ana and San Jacinto Blocks to not correspond to the latitude/longitude ticks.

Figure 80. Generalized map showing distribution of oxygen isotope samples, and δ18O isopleth after restoration of 12 km displacement on the Elsinore fault zone and 29 km displacement on the San Jacinto fault zone. WZ—western zone; WTZ—western transition zone; ETZ—eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 131

crust are used in the calculations. Basaltic crust is assumed to 10.5 have consisted of juvenile island-arc material similar to that in 10.0 the Marianas and the Fiji-Tonga island arcs. For the Marianas 9.5 island arc, Sri ranges from 0.70263 to 0.70432, averaging 0.7036

9.0 (Meijer, 1976). For the Fiji arc, the average Sri is 0.7041 (Gill, 1981). There is greater variability for reported Sr values of the 8.5 i O older continental crust, but a Sr of 0.714 appears to be a reason- 18 8.0 i δ able average. The western zone batholithic rocks in the northern 7.5 Peninsular Ranges batholith have an average calculated Sri of 7.0 0.7039, which is in keeping with oceanic island crust. However, 6.5 the Sri 0.7045 isopleth (Fig. 74) crosses the northern part of the 6.0 western zone, and that part of the western zone northwest of the WZ WTZ ETZ EZ UPZ isopleth has an average Sri of 0.7045, indicating ~93% juvenile Figure 81. Plot of average δ18O for the ﬁ ve batholiths zones component. The bulk of the western zone, southeast of the mean-

showing major differences between the eastern zone and upper- dering part of the <0.7045 isopleth, has an average Sri of 0.7037, plate zone. WZ—western zone; WTZ—western transition zone; indicating no involvement of ancient continental crust. ETZ—eastern transition zone; EZ—eastern zone; UPZ— upper- The other four batholith zones show a systematic decrease plate zone. in the island-arc component from west to east (Fig. 83). The

western transition zone has an average Sri of 0.7049, indicating 91% juvenile component, and the eastern transition zone has an

those zones. Variations in major-element chemistry materially average Sri of 0.7053, indicating an 87% juvenile component. As support progressively increasing chemical differentiation from expected, the composition of the eastern zone reﬂ ects a major west to east. Across the entire autochthonous part of the northern increase (17%) in the ancient continental crust component, hav- Peninsular Ranges batholith, both major- and trace- element spa- ing an average 0.7070, which requires 70% juvenile component.

tial distributions refl ect progressive changes from near-juvenile The upper-plate zone has an average Sri of 0.7079, which indi- to much more-evolved source materials, refl ecting subduction cates a 61% juvenile component. If, however, any juvenile com- transitioning from oceanic lithosphere to more-evolved subcon- ponent was derived from anomalously enriched mantle sources, tinental lithosphere. Major-element chemistry for plutons in both the calculated contributions of evolved crustal components transition zones refl ects an intermediate stage of chemical dif- would be smaller. Regardless of these assumptions, some amount ferentiation, as does trace-element distribution. of isotopically evolved component (crust or enriched mantle) is This chemical progression, however, does not appear to have required to explain the isotopic signatures of the plutons. been a smooth, even process, but in places it shows abrupt changes As expected, this west-to-east progression also shows an that, at least in part, are associated with dynamic changes in mode increase in the incompatible elements (e.g., K, P, Nb, La, Nd, of emplacement and possibly rate of emplacement. In particular, Rb, Ba, Th, U, and Zr) and a decrease in compatible elements the sharp transition in chemistry, isotopic and magnetic signa- (e.g., Ca, Mg, Fe, and Sc). Harker diagrams clearly indicate that, tures, and rock fabrics from the western zone to western transi- despite the relatively uniform chemistry of the subducting plate tion zone marks a change consistent with a shift to derivation component, the magma generated for the eastern granitoids is of magma from more-evolved subcontinental lithosphere in the notably different than that for the western granitoids. This is well

western transition zone compared with that derived from oceanic illustrated by the Harker diagrams for MgO, Fe2O3, TiO2, Al2O3, lithosphere in the western zone. The notably increased rate of CaO, and V (Fig. 70). magma emplacement in the eastern part of the Peninsular Ranges The discrimination diagram of Ta plotted against Yb batholith, beginning in the eastern transition zone, but especially (Fig. 84) (Pearce et al., 1984) shows that most of the batholith evident in the eastern zone, as indicated by the size and narrow plots within the volcanic-arc granite fi eld. There is a progressive age range of La Posta–type plutons, does not appear to have any shift from the western zone to the eastern zone toward the syn- obvious refl ection in the major element or REE chemistry. collisional granite fi eld. Most of the upper-plate zone falls within the syncollisional granite fi eld. A progressive deepening of the Source for Granitoids magma source from the west to the east is refl ected in the shift in values from the western zone to the eastern zone upward through

Sri values increase from west to east, refl ecting a decrease the volcanic-arc granite fi eld and into the syncollisional granite in mantle component and an increase in continental crustal com- fi eld in the upper-plate zone.

ponent. Based on Sri values, and assumptions outlined here, an Based on the correlation of increased alkalinity with depth estimate can be made for the proportions of oceanic and conti- of magma generation, several variation diagrams indicate that nental crust contributions for the ﬁ ve batholith zones. Sri values the magma source for the Peninsular Ranges batholith increases of 0.7040 for juvenile basaltic crust and 0.7140 for continental in depth from west to east. The Rb (ppm) versus Sr (ppm) plot Downloaded from memoirs.gsapubs.org on March 25, 2014

132 Morton et al.

19.4 0.7980 19.3

0.7970 19.2 of zones of zones

i 19.1 i 0.7960

Eastern Transition Zone Eastern Transition 19.0 Western Transition Zone Transition Western Upper Plate Zone Average Sr Average Average Pb Average Eastern Zone Eastern Transition Zone Eastern Transition 0.7950 18.9 Eastern Zone Western Transition Zone Transition Western Upper Plate Zone Western Zone Western 18.8 Zone Western 0.7940

18.7 43.7% 12.3% 13.3% 22.0% 8.7% 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone 12.0 4.0

10.0 2.0

8.0 0 O of zones 18 Nd of zones 6.0 ε -2.0 Eastern Transition Zone Eastern Transition Eastern Zone Western Zone Western Average Average δ Average 4.0 -4.0 Upper Plate Zone Eastern Transition Zone Eastern Transition Upper Plate Zone Western Zone Western 2.0 -6.0 Zone Transition Western Eastern Zone Western Transition Zone Transition Western

0 43.7% 12.3% 13.3% 22.0% 8.7% -8.0 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone 6.0

5.0 66 (percent) of zones (percent) Eastern Transition Zone Eastern Transition 3 (percent) of zones (percent) Eastern Zone O 2 Upper Plate Zone 2

65 Eastern Zone 4.0 Eastern Transition Zone Eastern Transition Western Transition Zone Transition Western Upper Plate Zone Western Zone Western Western Zone Western Western Transition Transition Zone Western Average SiO Average 64 Fe Average

3.0 43.7% 12.3% 13.3% 22.0% 8.7% 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone

3.0 500

450 2.6

of zones 400 2.2 (ppm) 350 Eastern Transition Zone Eastern Transition 1.8 Upper Plate Zone Western Transition Transition Zone Western 300 Average Sr Average Upper Plate Zone Eastern Zone 1.4 Zone Western Average MgO (percent) of zones MgO (percent) Average Western Zone Western 250 Eastern Transition Zone Eastern Transition Eastern Zone Western Transition Zone Transition Western 1.0 200 43.7% 12.3% 13.3% 22.0% 8.7% 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone

δ18 ε Figure 82 (Continued on following page). Plots showing averages of Sri, Pbi, O, Ndi, and selected oxides for the ﬁ ve batholith zones. Width of the bars representing each zone is proportionate to its percentage of the batholith based on its areal extent. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 133

1200 120

100 1000 80

800 60 Western Transition Zone Transition Western Eastern Zone 40 Eastern Zone Upper Plate Zone

600 Zone Transition Western Average Ba (ppm) of zones Average Average V (ppm) of zones Average Western Zone Western Western Zone Western Upper Plate Zone 20 Eastern Transition Zone Eastern Transition Eastern Transition Zone Eastern Transition

400 0 43.7% 12.3% 13.3% 22.0% 8.7% 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone

1.4 1.4

1.2 1.2

1.0 1.0 Eastern Zone

0.8 0.8 Upper Plate Zone Upper Plate Zone Eastern Zone Average Th (ppm) of zones Average Western Transition Zone Transition Western Western Zone Western Average Ta (ppm) of zones Ta Average Eastern Transition Zone Eastern Transition Western Transition Zone Transition Western 0.6 Zone Eastern Transition 0.6 Western Zone Western

0.4 0.4 43.7% 12.3% 13.3% 22.0% 8.7% 43.7% 12.3% 13.3% 22.0% 8.7% Volume percent of northern part of batholith by zone Volume percent of northern part of batholith by zone

Figure 82 (Continued).

(Fig. 85) and a MALI (modiﬁ ed alkali-lime index) plot (Fig. 86) show that the western part of the batholith is calcic when com- 100 WZ pared to the eastern, more alkaline part, which is similar to the more alkaline Sierra Nevada batholith (Bateman, 1992). K O WTZ 2 90 and Na2O increase from west to east as the depth of the magma ETZ source increases (Fig. 70B). A QAP (quartz, alkali feldspar, and

80 plagioclase feldspar) diagram (Fig. 87) indicates a more calcic differentiation trend for the western part of the batholith than for the eastern part, whereas the differentiation trend for the eastern EZ arc component 70 part of the batholith is similar to that of the Sierra Nevada batho- Percent juvenile island- juvenile Percent UPZ lith (Lameyre and Bonin, 1991). 60 Nb/Yb values systematically increase from the western 0.7039 0.7050 0.7060 0.7070 0.7079 Average Sr for each zone zone to the upper-plate zone (Fig. 88). For the western zone, i Nb/Yb values are quite uniform, mostly 2 or less (Fig. 89; see

Figure 83. Plot comparing average Sri for the ﬁ ve batholith zones also Clausen et al., this volume), and they show no increase in with calculated percentage of juvenile island-arc component in values with increase in SiO2. Nb/Yb values are somewhat less the batholith melt. Plot shows progressive decrease in island-arc uniform in the western transition zone than in the western zone, component from western zone to upper-plate zone, and a major decrease between the eastern transition zone and eastern zone. WZ— with all but seven values in the 1–3 range (Fig. 89). In contrast, western zone; WTZ—western transition zone; ETZ—eastern tran- most Nb/Yb values in the eastern transition zone and eastern sition zone; EZ—eastern zone; UPZ—upper-plate zone. zone are fairly dispersed, mostly ranging in value from 2 to 10, and generally, they show an increase in Nb/Yb with an increase

in SiO2 (Fig. 90). In the upper-plate zone, the values are quite Downloaded from memoirs.gsapubs.org on March 25, 2014

134 Morton et al.

4.0 10 Western Zone 3.5 Western Zone Western Transition Zone Western Transition Zone Eastern Transition Zone Eastern Transition Zone 5 Eastern Zone 3.0 Eastern Zone Upper Plate Zone Upper Plate Zone 2.5 syn-COLG WPG i c 0 a l l k 2.0 - A O-CaO l c i c 2 a c C a l 1.5 C Ta (ppm) Ta VAG -5 O+K 1.0 2

ORG Na 0.5 -10

0 0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Yb (ppm) -15 4045 50 55 6065 70 75 80 SiO (percent) Figure 84. Discrimination diagram of Ta plotted against Yb, northern 2 Peninsular Ranges batholith, showing progression from volcanic-arc granite fi eld (VAG) toward syncollisional granite (syn-COLG) from Figure 86. MALI (modifi ed alkali-lime index) plot for northern Penin- the western zone to eastern zone. Most of the upper-plate zone is with- sular Ranges batholith rocks. The autochthonous zones of the batholith in the syncollisional granite fi eld. WPG—within-plate granite fi eld; are mostly calcic, and most of the allochthonous upper-plate zone is ORG—ocean-ridge granite fi eld. calc-alkalic. uniform, with only one aberrant value less than 6 (Fig. 89). changes by three orders of magnitude between the lightest and This west-to-east dichotomy, due to interaction with continental heaviest REEs for crystallization below the garnet stability pres- lithosphere, is also evident from Sr/Y, La/Yb, and Ta/Yb values. sure of 10–12 kbar (Carroll and Wyllie, 1990; Tepper et al., 1993; Similar to Nb/Yb, average values for La/Yb, Ta/Yb, and Zr/Yb Moyen and Stevens, 2006). The gentle slope for the western zone increase from the western zone to upper-plate zone. This increase granitoids (Fig. 71) indicates that crystallization occurred at is interpreted as being due to progressive interaction with conti- depths less than 30–35 km. Eastern zone plutons have a relatively nental lithosphere (Figs. 88 and 89). steeper slope, indicating greater depths.

Garnet REE spidergrams can be used to estimate the depth at which Q magma generation occurred. Gromet and Silver (1987) used REE spidergrams to deﬁ ne three north-south–trending depth zones in the batholith, showing that magma was generated at increasingly greater depths eastward. The partition coefﬁ cient for garnet Western Zone Western Transition Zone Eastern Transition Zone

700 Eastern Zone G Western Zone Upper Plate Zone ranodiorite Western Transition Zone 600 Eastern Transition Zone Tonalite Eastern Zone Upper Plate Zone 500

Monzogranite 400 Quartz diorite 300 Quartz monzonite Sr (ppm) A P 200 Gabbro

100 Figure 87. Q-A-P (quartz–alkali feldspar–plagioclase) plot for northern Peninsular Ranges batholith rocks. Because the plot is based on 0 calculated normative values, most rock compositions fall in the grano- 0 50 100 150 200 250 diorite fi eld. Mineralogically, many northern Peninsular Ranges batho- Rb (ppm) lith rock compositions fall within the granodiorite fi eld, but the majority are in the tonalite fi eld. Even though many of the Peninsular Ranges Figure 85. Rubidium plotted against strontium for northern Peninsular batholith rocks contain almost no K-feldspar, they do contain biotite. Ranges batholith rocks, showing progressive enrichment in Sr from the In the normative calculation, potassium from the biotite is partitioned western zone to upper-plate zone. to K-feldspar, biasing the plots toward the alkaline corner. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 135

25 8 20 6 15

4 10 La/Yb Nb/Yb 2 5

0 0 WZ WTZ ETZ EZ UPZ WZ WTZ ETZ EZ UPZ

0.8 120

100 0.6 80

0.4 60 Ta/Yb Zr/Yb 40 0.2 20

0 0 WZ WTZ ETZ EZ UPZ WZ WTZ ETZ EZ UPZ

Figure 88. Average Nb/Yb, La/Yb, Ta/Yb, and Zr/Yb values for the ﬁ ve batholith zones showing increases in values from the western zone to the upper-plate zone. The eastern transition zone and eastern zone values are similar, with a step between eastern zone and upper-plate zone values. WZ—western zone; WTZ—western transition zone; ETZ—eastern transition zone; EZ—eastern zone; UPZ—upper-plate zone.

Values for the HREE and LREE ratios, Gd/Yb and La/Sm, depth of differentiation (e.g., Tulloch and Kimbrough, 2003). respectively, can also be used to estimate depth; Gd/Yb values Shallow differentiation produced granitoids in the western zone increase with increasing magma source depth, and La/Sm values with low Sr/Y values that average 13.6 (Fig. 92). In contrast, the increase with fractionation. Most Gd/Yb values are less than 2 deeper level of differentiation that produced rocks of the more for western zone rocks (Fig. 91), but almost all ratios from the easterly batholithic zones resulted in more than double the Sr/Y eastern transition zone, eastern zone, and upper-plate zone are value, which averages 27.3 for the western transition zone, 41.1 greater than 2, indicating a relatively deeper source. La/Sm val- for the eastern transition zone, 33.8 for the eastern zone, and 28.5 ues average ~3.5 for western zone rocks, and, although there is for the upper-plate zone. greater scatter for the eastern zone rocks, their average is ~5. With respect to lithology, La/Sm values for western zone plutons Magma Mixing increase from an average of ~2.3 for gabbro, to ~2.9 for tonalite, The western zone plutons are interpreted as being derived from and to ~3.6 for granodiorite. three magma groups (see Clausen et al., this volume): (1) gabbros, Sr/Y values summarize the effect of garnet and plagioclase formed from partial melting of the mantle, (2) granodiorites, formed fractionation in a subduction zone. Fractional crystallization from partial melting of oceanic crust, and (3) tonalities, interpreted at depth in the garnet stability zone, where plagioclase is less to be the product of mixing of gabbro and granodiorite magmas. stable, separates garnet, Y, and the HREEs from the melt resi- This model is discussed in detail by Clausen et al. (this volume) for due, effectively depleting the melt of Y. In the northern Peninsu- the low-Sri Escondido granitoids. lar Ranges batholith, Y averages 23 ppm in the shallow western For granitic rocks, a plot of compatible trace elements against zone, decreases to 18 in the western transition zone and to 13 incompatible trace elements on a log base is linear if the rocks in the eastern transition zone, and increases slightly to 16 in the were produced by fractional crystallization, and it is concave eastern zone. Fractional crystallization at shallower depths where downward if the rocks were produced by magma mixing (Coche- plagioclase is stable and garnet is unstable separates plagioclase, rie, 1986). Plots on a log base of Co versus Ba (Fig. 93), Sr against Sr, and Eu from the melt residue and depletes the melt of Sr. Sr Rb, and V against Ce are all concave downward, indicating that concentrations average 227 ppm in the shallow western zone and the chemical variation in the northern Peninsular Ranges batholith increase to 283 in the western transition zone, 375 in the eastern is a result of magma mixing. Partial melting would yield a plot transition zone, and 428 in the eastern zone. Sr/Y values reﬂ ect with inverse concavity for the magma mixing curve. Downloaded from memoirs.gsapubs.org on March 25, 2014

136 Morton et al.

16 16 14 14 Western zone Western Transition zone 12 12 10 10 8 8 Nb/Yb Nb/Yb 6 6 4 4 2 2 0 0 0 20 40 60 80 100 120 140 015 10 520 2530 35 40 Samples evenly spaced, plotted in sequence calculated Samples evenly spaced, plotted in sequence calculated

16 16 14 14 Eastern Transition zone Eastern zone 12 12 10 10 8 8 Nb/Yb Nb/Yb 6 6 4 4 2 2 0 0 0610 20 30 40 50 00620 40 080 100 Samples evenly spaced, plotted in sequence calculated Samples evenly spaced, plotted in sequence calculated

16 16 14 14 Upper Plate zone All zones 12 12 10 10 8 8 Nb/Yb Nb/Yb 6 6 4 4 2 2 0 0 015 10 520 25 30 35 0 50 100 150 200 250 300 350 Samples evenly spaced, plotted in sequence calculated Samples evenly spaced, plotted in sequence calculated

Figure 89. Nb/Yb plots by batholith zones. Nb/Yb plots show progressive increase in value from the western zone to upper-plate zone with very constant values in the western zone, and relatively constant values in the upper-plate zone.

Eichelberger (1978) showed that igneous rocks tend to can be trapped and have time to mix and form magmas of inter- display a bimodal SiO2 composition during tectonic extension, mediate composition. whereas intermediate compositions dominate during compression. During tectonic extension in a thin crust, dense basal- SUMMARY tic magma from the mantle should have less to inhibit ascent toward the surface, but low-density silicic magma from crustal The northern Peninsular Ranges batholith includes both melting easily ascends with little time for mixing. During tec- autochthonous and allochthonous rocks. Most of the northern tonic compression and thickening crust, maﬁ c magma from the Peninsular Ranges batholith is autochthonous, with the allochtho- mantle and felsic magma from partial melting of the lower crust nous rocks restricted to the easternmost part. The autochthonous Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 137

16 160 Western Zone 14 Western Zone 140 Western Transition Zone Western Transition Zone Eastern Transition Zone Eastern Transition Zone 12 120 Eastern Zone Eastern Zone Upper Plate Zone Upper Plate Zone 10 100

8 80 Sr/Y Nb/Yb 6 60

4 40

2 20

0 0 40 45 50 55 60 65 70 75 80 01020 30 40 50 60 70 80 Y (ppm) SiO2 (percent)

Figure 90. Nb/Yb plotted against SiO2 showing relatively uniform Nb/Yb Figure 92. Sr/Y ratio plotted against Y for the northern Peninsular values in the western zone, independent of SiO2 values. Nb/Yb values Ranges batholith rocks. The average decrease in Y from the western progressively increase in the western transition zone to upper-plate zone, zone to the eastern zone reﬂ ects progressively deeper depth for the with a general increase in Nb/Yb values with increasing SiO2. batholith melt.

batholithic rocks were emplaced between 126 Ma and 91 Ma. nature, the upper-plate zone rocks were derived from east of the Based on a variety of parameters, the autochthonous northern eastern zone. Peninsular Ranges batholith is divided into four longitudinal The four autochthonous batholith zones were formed over zones, a western zone, western transition zone, eastern transition a 35 m.y. period as subduction progressively transitioned from zone, and an eastern zone. In an extensional phase of subduction, under oceanic lithosphere to under continental lithosphere. From highly magnetic western zone plutons were passively emplaced 126 to 108 Ma, pluton emplacement was passive in an exten- into oceanic Jurassic and Triassic metasedimentary rocks of low sional phase of subduction, forming the western 47.6 areal per- metamorphic grade. The western transition zone and eastern tran- cent of the autochthonous batholith at a rate of 2.6% per million sition zone plutons were dynamically emplaced into Mesozoic years. By 111 Ma, the subducted plate began to underride conti- and Paleozoic (?) rocks of amphibolite facies, and the eastern nental lithosphere. At this time, the mode of pluton emplacement zone plutons were emplaced into Paleozoic (?) metasedimentary changed radically from passive to dynamic in a compressional rocks. Rocks of the allochthonous upper-plate zone were thrust tectonic regime. Dynamically emplaced plutons characterize the into position in the Late Cretaceous. Based on their geochemical two transition zones. The western transition zone formed over a

100

7 Western Zone Western Transition Zone 6 Eastern Transition Zone Eastern Zone 10 5 Upper Plate Zone Western Zone Western Transition Zone 4 Eastern Transition Zone Eastern Zone Upper Plate Zone 3 (ppm) Co

Gd/Yb 1.0 2

0 0.1 0 2 4 6 8 10 12 10 100 1000 10000 La/Sm Ba (ppm)

Figure 91. Gd/Yb ratios plotted against La/Sm ratios. The low Gd/Yb Figure 93. Co plotted against Ba on a log base for the northern Pen- ratios, mostly less than 2, for the western zone indicate a relatively insular Ranges batholith rocks. Concave-downward distribution shallow source. The higher Gd/Yb ratios in the other zones indicate an is interpreted to reﬂ ect magma mixing. Fractional crystallization increase in source depth. would produce a linear array. Downloaded from memoirs.gsapubs.org on March 25, 2014

138 Morton et al.

period of 11 m.y. and constitutes 13.5% by area of the northern the east. Based on the linearity of Harker diagrams and plots of Peninsular Ranges batholith. The western transition zone plu- Ba against Co, chemical variation in the batholith is a product tons have geochemical affi nities with the western zone plutons. of magma mixing. Our data for the northern Peninsular Ranges Growth of the northern Peninsular Ranges batholith progressed batholith are best explained by a model involving a single Creta- at a rate of ~1% per million years, with most magma emplace- ceous arc that transitioned from Mesozoic oceanic to continental ment occurring from 106 to 99 Ma. The 99–93 Ma plutons of the lithosphere. Island arcs and their accretion to continental cratons eastern transition zone have geochemical affi nities more closely provide the simplest geochemistry for understanding crust for- associated with the eastern zone plutons than with the western mation (e.g., Leat and Larter, 2003). transition zone plutons. The eastern transition zone plutons form 15% by area of the batholith, with pluton emplacement increas- ACKNOWLEDGMENTS ing the size of the northern Peninsular Ranges batholith at a rate of 2.5% per million years. Eastern zone pluton emplacement, The regional geochemistry study would not have been possible 98.5–91 Ma, occurred when the subducted plate was under older if the late Alex Baird had not had the foresight to develop a continental crust and temporally overlapped plutonism of the thorough and systematic regional sampling plan for the northeastern transition zone. The eastern zone constitutes 25% by area ern Peninsular Ranges batholith. The samples would not have of the northern Peninsular Ranges batholith, as pluton emplace- been collected except for the sheer tenacity of Ed Welday. The ment increased the northern Peninsular Ranges batholith at a rate sampling arguably remains the most exhaustive and systematic of 3.3% per million years. Both the eastern transition zone and of any Cordilleran batholith. Many thanks go to U.S. Geological eastern zone are dominated by La Posta–type plutons. The com- Survey (USGS) analysts Jim Budahn, Fred Lichte, Dave Siems, bined eastern transition zone and eastern zone formed 40% by Jaime Azain, and Dave Detra, for the high quality of chemical area of the batholith in 8 m.y., at a rate of 5% per million years. analysis. Dave Kimbrough, San Diego State University, Bob This rate of magma emplacement from 99 to 91 Ma is similar to Fleck, USGS, and Jade Star Lackey, Pomona College, kindly the 47% of other parts of the Peninsular Ranges batholith form- made available unpublished isotopic data. Thanks also go to ing in the interval 99–92 Ma calculated by Ortega-Rivera (2003). Bret Cox, USGS, for the modal analysis of the Box Springs In the Late Cretaceous, 92–84 Ma granitic rocks were thrust from Mountains plutonic complex. Many thanks go to Victoria Todd the east on low-angle faults to form the allochthonous upper-plate for numerous conversations regarding the batholith and improv- zone of the batholith. ing the text of this paper. The paper was greatly improved by Major- and trace-element chemistry shows multiple sys- thoughtful reviews by Bob Fleck and Jade Star Lackey. tematic west-to-east variations across the northern Peninsular Ranges batholith. Compatible elements decrease from west to APPENDIX east, and incompatible elements increase, with some trace ele- Batholith Sampling ments changing by more than a factor of 2. Geochemical evolution of the northern Peninsular Ranges batholith refl ects a shal- More than 300 Northern Peninsular Ranges batholith samples low and primitive source for the western part of the batholith and were systematically collected by E.E. Welday and A.K. Baird (Baird a more-evolved, deeper source for the eastern part. Based on geo- et al., 1974b, 1979). The resulting sample set is the most systematic chemistry, the upper-plate zone rocks are distinct from those of geochemical sample set for Cordilleran batholiths assembled to date. The purpose of the sampling was to extract unbiased representative the structurally adjacent autochthonous eastern zone. composition of the northern part of the northern Peninsular Ranges Three isotopic systems likewise show systematic west- batholith that could be used to determine spatial chemical distribu- to-east variation. Initial 87Sr/86Sr ratios refl ect the progressive tions. The sampling method was basically megascale point counting. change in subduction magmatism transitioning from oceanic A combined large- and small-scale pattern for sampling the lithosphere in the west to continental lithosphere in the east. northern Peninsular Ranges batholith was developed after a series of sampling studies (Baird et al., 1964, 1967; Morton et al., 1969). Sr is bimodal, with most values between 0.7034 and 0.7040 in i Sample localities were spaced ~5 km apart on a grid, and at each local- the western zone, and slightly higher values of 0.7045–0.7055 ity, eight specimens were collected, two at each of the four corners in the transition zones. Eastern zone rocks have Sri values of of a square, 400 ft (120 m) on a side. These eight specimens were separately crushed, and a split was taken from each sample and com- 0.7065–0.7080, and the upper-plate zone has Sri values of 0.7075–0.7090. Only a very minor part of the batholith has Sr bined to generate a homogeneous composite sample representative of i the sample site. Most sample sites included a single rock type; a few >0.7055 and <0.7065, refl ecting a relatively abrupt change from sample sites included multiple rock types. The sampling technique was pluton emplacement in oceanic lithosphere to emplacement in tested by using a grid offset of half a sample-spacing, and the results continental lithosphere. The 206Pb/204Pb ratio likewise increases were similar. One additional “typical” sample per locality was sec- from west to east, with a major step from the transition zones to tioned and used to determine rock classifi cation (Baird et al., 1979). the eastern zone. The 206Pb/204Pb 19.0 isopleth is coincident with This determination was based on an older classifi cation system (Bate- man et al., 1963). the Sr 0.7060 isopleth. i Note that Ni trace-element concentrations were measured but not Scandium and REE distributions refl ect a shallower magma tabulated in this paper because of contamination with hardened steel source in the western part of the batholith and a deeper source in when the samples were plate-pulverized in a ball mill. Downloaded from memoirs.gsapubs.org on March 25, 2014

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California 139

Rare Earth Elements: Chondrite Normalization Values for Rare Todd, V.R., eds., Mesozoic Crystalline Rocks: San Diego, California, Cal- Earth Elements ifornia State University, Department of Geological Sciences, p. 111–132. Bateman, P.C., 1992, Plutonism in the Central Part of the Sierra Nevada Batho- lith, California: U.S. Geological Survey Professional Paper 1483, 186 p. Rare earth elements were normalized using the following chon- Bateman, P.C., Clark, L.D., Huber, N.K., Moore, J.G., and Rinehart, C.D., 1963, The drite values. Sierra Nevada Batholith—A Synthesis of Recent Work across the Central Part: U.S. Geological Survey Professional Paper 414-D, p. D1–D46. La = 0.311 Tb = 0.047 Berger, B.R., 2014, this volume, Petrology and chemistry of the Green Acres Ce = 0.813 Dy = 0.323 gabbro complex near Winchester, Riverside County, California, in Mor- Pr = 0.123 Ho = 0.0722 ton, D.M., and Miller, F.K., eds., Peninsular Ranges Batholith, Baja Cali- Nd = 0.603 Er = 0.211 fornia and Southern California: Geological Society of America Memoir Sm = 0.196 Tm = 0.0326 211, doi:10.1130/2014.1211(10). Eu = 0.074 Yb = 0.21 Brown, A.R., 1968, Geology of a Portion of the Southeastern San Jacinto Gd = 0.26 Lu = 0.0323 Mountains, Riverside County, California [M.S. thesis]: Riverside, Cali- fornia, University of California, 95 p. Burnham, C.W., 1959, Contact metamorphism of magnesian limestones at CIPW Norm Calculations Crestmore, California: Geological Society of America Bulletin, v. 70, p. 879–920, doi:10.1130/0016-7606(1959)70[879:CMOMLA]2.0.CO;2. Busby, C., 2004, Continental growth at convergent margins facing large ocean basins: To plot the granitoid samples on the IUGS (International Union of A case study from Mesozoic convergent-margin basins of Baja California, Geological Sciences) quartz-feldspar (QAP) system, it was necessary Mexico: Tectonophysics, v. 392, p. 241–277, doi:10.1016/j.tecto.2004.04.017. to perform CIPW norm calculations on the major-oxide data. Because Carroll, M.R., and Wyllie, P.J., 1990, The system tonalite-H2O at 15 kbar and the oxide data include only Fe O total, whereas the norm calculations the genesis of calc-alkaline magmas: The American Mineralogist, v. 75, 2 3 p. 345–357. require both Fe2O3 and FeO, the Fe2O3/FeO ratios had to be estimated. From Larsen’s (1948) data for the eastern Peninsular Ranges batholith, Cecil, J.D., 1990, A Study of the Palm Canyon Complex and Related Rocks, a ratio of 0.3 can be estimated for the gabbros, 0.4 for the tonalites, Riverside County, California [Senior thesis]: Berkeley, California, Uni- versity of California–Berkeley. and 0.5 for the granodiorites. Using the total alkali–silica diagram for Clausen, B.L., Morton, D.M., Kistler, R.W., and Lee, C.-T.A., 2014, this vol- volcanic rocks, Middlemost (1989) suggested a ratio of 0.2 for basalt, ume, Low initial-Sr felsic plutons of the northwestern Peninsular Ranges 0.35 for andesite, 0.4 for dacite, and 0.5 for rhyolite. These two esti- batholith, southern California, and the role of mafi c-felsic magma mixing mates were combined, and the unrealistic discontinuity in ratio at fi eld in continental crust formation, in Morton, D.M., and Miller, F.K., eds., boundaries was removed by using the following equation to estimate Peninsular Ranges Batholith, Baja California and Southern California: Geological Society of America Memoir 211, doi:10.1130/2014.1211(08). the iron-oxide ratio: Fe2O3/FeO = 0.011 × SiO2 – 0.31. The sum of the albite and anorthite norms was used for the plagioclase composition. Cocherie, A., 1986, Systematic use of trace element distribution patterns in The resulting norms are plotted on the QAP diagram in Figure 87. log-log diagrams for plutonic suites: Geochimica et Cosmochimica Acta, The gabbro samples fall in the gabbro and quartz diorite fi elds; the tonal- v. 50, p. 2517–2522, doi:10.1016/0016-7037(86)90034-7. Criscione, J.J., Davis, T.E., and Ehlig, P., 1978, The age of sedimentation/ ite samples fall in the granodiorite, quartz monzodiorite, quartz diorite, diagenesis for the Bedford Canyon Formation and the Santa Monica For- and tonalite fi elds; and the granodiorite samples fall in the granodiorite mation in southern California: A Rb/Sr evaluation, in Howell, D.G., and and granite fi elds. This paper uses the generic terms gabbro, tonalite, and McDougall, K.A., eds., Mesozoic Paleogeography of the Western United granodiorite for the three groups, although the samples do not fi t exactly States: Sacramento, California, Pacifi c Section, Society of Economic into the corresponding fi elds in the QAP diagram. Paleontologists and Mineralogists, Pacifi c Coast Paleogeography Sym- The classifi cation used for these granitoids by Baird et al. (1979) posium 2, p. 385. was based on an older QAP system (Bateman et al., 1963). 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