Zircon U-Pb Ages and Petrologic Evolution of the English Peak Granitic Pluton: Jurassic Crustal Growth in Northwestern California GEOSPHERE; V

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Research Paper THEMED ISSUE: Active Margins in Transition—Magmatism and Tectonics through Time: An Issue in Honor of Arthur W. Snoke

GEOSPHERE Zircon U-Pb ages and petrologic evolution of the English Peak granitic pluton: Jurassic crustal growth in northwestern California GEOSPHERE; v. 12, no. 5 W.G. Ernst1, Eric S. Gottlieb1, Calvin G. Barnes2, and Jeremy K. Hourigan3 1Geological Sciences, Stanford University, Building 320, Stanford, California 94305-2115, USA doi:10.1130/GES01340.1 2Geosciences, Texas Tech University, MS 1053, Science Building 125, Lubbock, Texas 79409-1053, USA 3Earth and Planetary Sciences, University of California–Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA 6 figures; 1 table; 1 supplemental file

CORRESPONDENCE: wernst@stanford.edu ABSTRACT incorporated into the evolving Jurassic continental crust. It took place prior to the earliest Cretaceous onset of westward transport of the stack of Klamath CITATION: Ernst, W.G., Gottlieb, E.S., Barnes, In the central Klamath Mountains, the English Peak plutonic complex (EPC) allochthons relative to the active Jura-Cretaceous Sierran calc-alkaline arc. C.G., and Hourigan, J.K., 2016, Zircon U-Pb ages and petrologic evolution of the English Peak granitic invaded the faulted contact between the outboard Eastern Hayfork and inboard pluton: Jurassic crustal growth in northwestern North Fork terranes of the Western Paleozoic and Triassic Belt (WTrPz). This California: Geosphere, v. 12, no. 5, p. 1422–1436, calc-alkaline igneous complex is composed of two small, ~1–2-km-diame INTRODUCTION TO THE REGIONAL GEOLOGY doi:10.1130/GES01340.1. ter, relatively mafic satellitic plutons peripheral to the younger, much larger, ~10–15-km-diameter English Peak zoned granitic pluton. The EPC magmas The iconic Klamath Mountains Province provides a classic example of the Received 30 March 2016 Revision received 8 July 2016 were mantle derived and reflect temporary residence and mixing at various Phanerozoic growth of transitional continental crust. Its imbricated lithotec- Accepted 23 August 2016 depths in the overlying crust, with initial storage and modification near the tonic belts testify to successive (1) arrival of far-traveled oceanic crust and Published online 9 September 2016 Moho, and uppermost crustal emplacement at 5–10 km depths. Phase assem- overlying deep-sea sediments, (2) underflow and off-loading along the conver- blages suggest pre-emplacement magma storage at a depth of ~20–25 km gent plate junction, (3) suprasubduction-zone arc generation, and (4) erosional for the early satellitic plutons, versus ~15–20 km for samples from the larger supply of arc debris to the accreting ophiolitic basement terranes. This late zoned granitic pluton. We obtained zircon U-Pb geochronologic results (re- Paleozoic–Mesozoic development of northern California was typified by chiefly ported as internal and external weighted-mean 207Pb-corrected 206Pb/238U ages, margin-parallel slip, episodic suturing of ophiolitic complexes and their spa- 95% confidence level) from seven samples in the complex via laser ablation– tially associated chert-argillite terranes, concurrent construction of volcanic- inductively coupled plasma–mass spectrometry (LA-ICP-MS). The 172.3 ± 2.0 plutonic arcs, plus the aprons of derived clastic sediments (Saleeby, 1981, [3.7] Ma Uncles Creek and 166.9 ± 1.6 [3.4] Ma Heiney Bar satellitic plutons 1982, 1983; Ernst et al., 2008). range from gabbro–quartz diorite to granodiorite in bulk-rock composition. The The terrane assembly of the Klamath Mountains has been correlated with main English Peak pluton consists of an early stage of gabbro-tonalite (three the northern Sierran Foothills based on similar rock types, structures, terrane samples: 160.4 ± 1.1 [3.1] Ma, 158.1 ± 1.1 [3.1] Ma, and 158.0 ± 1.2 [3.1] Ma) ages, the oceanward assembly of successively younger geologic units, and and a late stage (two samples: 156.3 ± 1.3 [3.1] Ma and 155.3 ± 1.2 [3.0] Ma) their times of orogeny (Davis, 1969; Davis et al., 1980; Wright and Fahan, 1988; passing inward from tonalite through granodiorite to a central zone of granite. Wright and Wyld, 1994; Irwin, 2003). However, the accreted Sierran Foothill The 172 Ma age of the Uncles Creek pluton makes it coeval with Middle Ju- terranes stand nearly vertically, whereas the Klamath thrust sheets root gently rassic Western Hayfork arc magmatism. In contrast, Heiney Bar and the main to the east. Scattered, chiefly calc-alkaline igneous activity characterized the English Peak igneous ages overlap some of the oldest and youngest compo- Late Triassic margin, but most lithologic sections of late Paleozoic–early Meso- nents, respectively, of the Middle to Late Jurassic Wooley Creek plutonic suite. zoic age are oceanic in their genesis. However, a major Andean arc began to Study of this multiple-intrusion complex provides an illuminating example of form in the Sierra Nevada and Klamath Mountains by ca. 175 Ma during trans- the gradual intermediate-to-felsic modification of the upper crust in the central pressive eastward underflow of oceanic lithosphere (Dunne et al., 1998; Irwin, Klamath Mountains. Inherited zircon ages of ca. 172 Ma in two other EPC sam- 2003; Dickinson, 2008). This magmatic arc shed clastic detritus into the realm ples indicate potential Middle Jurassic crustal sources or contaminants. Geo- of the accreting ophiolitic basement terranes of both the Klamath Mountains chronologic correlation of the EPC with geologic histories of other Klamath ter- and Sierran Foothills (Miller and Saleeby, 1995; Scherer et al., 2006). ranes provides fresh insights for understanding spatial and temporal elements Figure 1 presents the regional geology of the Klamath Mountains Province, of Middle to Late Jurassic arc magmatism in the Klamath Mountains sector of as well as published geochronology of various mafic-to-felsic plutons. The For permission to copy, contact Copyright the Cordilleran margin. This igneous activity illuminates some petrotectonic orogen is a terrane collage consisting of four major lithotectonic zones. From Permissions, GSA, or [email protected]. processes whereby accreted ophiolitic basement terranes were modified and east to west, these are the Eastern Klamath Belt, the Central Metamorphic Belt,

GEOSPHERE | Volume 12 | Number 5 Ernst et al. | U-Pb ages of the English Peak pluton Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/5/1422/3335013/1422.pdf 1422 by guest on 30 September 2021 on 30 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/5/1422/3335013/1422.pdf Research Paper

42 those indicated by t (U-Pb on titanite), tonalite-trondhjemite-granodiorite plutons. Numbers associated with each pluton indicate ages (Ma) determined by U-Pb zircon analyses except for Jones terrane is also termed the Stuart Fork terrane. Plutons are color coded according to age group. In the key, “ttg suite” refers to earliest Cretaceous Figure 1. Lithotectonic divisions of the Klamath Mountains, after Irwin and Wooden (1999) and with additions from Snoke and Barnes (2006). The Fort respectively).

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GEOSPHERE | Volume 12 | Number 5 Ernst et al. | U-Pb ages of the English Peak pluton 1423 Research Paper

the Western Paleozoic and Triassic Belt, and the Western Jurassic Belt (Irwin, STATEMENT OF THE PROBLEM 1960). Individual allochthons that constitute each belt are dominantly upright. Most are bounded by gently east-dipping, mid-Paleozoic to Late Jurassic thrust Multiple, discrete phases of arc magmatism built the English Peak plutonic faults (Irwin, 1994). Most Klamath terranes contain mafic-intermediate volcanic complex in the central Klamath Mountains. The EPC is one of a large group of and plutonic oceanic rocks as well as aprons of arc- and continent-derived Jurassic composite plutons emplaced in a broadly arc setting active from late clastic sedimentary rocks. Thin layers of deep-sea chert ± limestone cap some Middle Jurassic to Late Jurassic time (Allen and Barnes, 2006; Barnes et al., of the tectonically dismembered ophiolitic allochthons. The west-vergent ter- 2006). Seyfert (1965) and Schmidt (1994) showed that the English Peak plu- ranes accreted progressively outboard (westward in modern coordinates), re- tonic complex was emplaced in several distinct pulses. Integrated mineralogic, flecting a component of eastward oceanic plate underflow from Permo-Triassic petrologic, and geochemical investigations by Barnes et al. (2016) described through Cretaceous time (Irwin, 1981; Ando et al., 1983; Mankinen et al., 1996; the petrochemical evolution of various pluton stages of the EPC. Based on Scherer and Ernst, 2008; Saleeby and Dunne, 2015). Al-in-hornblende barometry, pseudosection P-T studies, and oxygen + Sr iso- The WTrPz is the largest of the four major lithotectonic belts and hosts the topic analyses, Barnes et al. (2016) concluded that generation of the EPC mag- EPC. The belt consists of regionally metamorphosed sedimentary, volcanic, and mas reflected the arrival of mantle-derived mafic magmas in the deepest part ultramafic rocks intruded by numerous plutons, some of which are metamor- of the crust, followed by mixing, assimilation, storage, and homogenization phosed. In the southern Klamath Mountains, Irwin (1972) divided the WTrPz (MASH), during which magmas were contaminated by older meta-igneous from east to west into the North Fork, Hayfork, and Rattlesnake Creek terranes. and metasedimentary rocks. Fractional crystallization of these mantle-derived Later, the inboard Stuart Fork high-pressure (HP) metamorphic terrane was de- calc-alkaline magmas occurred near Moho depths. Magmas that formed the fined (Hotz et al., 1977; Goodge, 1989), and the Hayfork terrane was divided oldest satellitic plutons were sequestered and underwent partial crystallization into distinct eastern and western terranes (Wright, 1982; Goodge, 1989). Hacker at mid-crustal levels (~600 MPa). Younger magmas were stored in a large, re- et al. (1993, 1995) and Donato et al. (1996) demonstrated that many of the WTrPz charged magma chamber, or chambers in the upper middle crust (~400 MPa), terranes extend through a broad region of the Klamath Mountains. Mesozoic then rose to form the composite pluton in the upper crust (~200 MPa). amalgamation of WTrPz terranes involved a series of accretion events, at least We summarize results of these and prior investigations (e.g., Donato et al., one of which was accompanied by regional, locally high-grade metamorphism. 1982; Ernst, 1998, 1999) to provide a geologic framework for our geochrono- The late Middle Jurassic Siskiyou orogeny (Coleman et al., 1988) involved ex- logic study of the English Peak plutonic complex. Our goal is to determine tinction of the Middle Jurassic arc (Western Hayfork terrane), thrusting of out- the longevity and crystallization history of the EPC, to characterize potential board Western Hayfork and Rattlesnake Creek terranes beneath inboard Eastern source and/or contaminant rocks, and to describe the subsequent geochemi- Hayfork terrane, and metamorphism that reached granulate-facies conditions cal evolution of the derived magmas. We show that the EPC grew episodically 75 km north of the EPC, and greenschist- to lower amphibolite–facies conditions by amalgamation of several compositionally and temporally distinct magma immediately north of the EPC (Barnes et al., 2006; Garlick et al., 2009; Medaris batches, that magmatism spanned the important orogenic Siskiyou event, et al., 2009). In addition to terrane amalgamation, Barnes et al. (1992) and Allen and that magma storage and crystallization occurred in multiple levels of and Barnes (2006) argued that the Siskiyou orogeny resulted in reorganization the middle and upper crust. Considering the modern and inferred ancient of the lower crust, resulting in chemical and isotopic modification of sources regional plate-tectonic settings, the central Klamath Mountains and its asso- and contaminants of arc magmas. Figure 1 depicts the presently recognized di- ciated plutons provide instructive examples of processes whereby accreted visions of the Klamath Province into map units (Harper and Wright, 1984; Irwin oceanic terranes were modified and incorporated into the continental crust and Wooden, 1999; Snoke and Barnes, 2006). during Middle and Late Jurassic time. Numerous broadly calc-alkaline plutons intruded the WTrPz and older belts during Middle Jurassic to earliest Cretaceous time (Lanphere et al., 1968; Hotz, 1973; Barnes et al., 1992, 2006; Irwin and Wooden, 1999; Allen and Barnes, LOCAL GEOLOGY 2006). These intrusions, along with the coeval outboard Josephine ophiolite (Harper et al., 1994) and the yet further outboard Rogue-Chetco magmatic Geology of the Sawyers Bar Area fringing arc (Garcia, 1979, 1982), occupy transtensional, arc, and backarc settings. Nevadan- and post-Nevadan uplift exposed a crustal section that en- Figure 2 presents the local geology of the Sawyers Bar area including the compasses upper- to lower-crustal environments (Coleman et al., 1988; Gar- English Peak plutonic complex. The mapped bedrock (Irwin, 1960, 1972, 1994; lick et al., 2009). Consequently, plutons occur over a range of crustal levels. Seyfert, 1965; Ernst, 1998) consists of three tectonically juxtaposed supracrustal One, the Wooley Creek batholith (WCB), lies directly to the west and northwest units of oceanic and ocean-continental arc margin affinities. (1) On the east, of the EPC (Fig. 1). Exposure of the WCB involves >12 km of structural relief the Stuart Fork HP metabasalt-metachert-metagraywacke terrane lies above (Barnes, 1983; Barnes et al., 1986a, 1986b). the low-angle, east-dipping Soap Creek Ridge thrust fault (Goodge, 1995).

Shelly Lake pluton

Twin Sisters fault U Eastern

h Hayfork A terrane B 172.3 ± 2.0Ma o

Border unit U

Uncles Creek

Wooley Creek batholit Late Stage Chimney Rock o 156.3 ± 1.3Ma North Fork terrane Yellow Jacket RidgeEnglish Peak pluton o Early Stage 155.3 ± 1.2Ma Forks of Soap Creek English Peak plutonic complex Salmon Ridge thrust Figure 2. General geologic map of the pluton 156.2 ± 158.1 ± 1.1Ma Sawyers Bar map area, after Schmidt Border unit 1.0Ma o o (1994), Ernst (1998), and Barnes et al.

160.4 ± U Russian * (2016). Sample sites and U-Pb zircon ages Heiney Bar 1.1Ma Peak 158.0 ± 1.2Ma in Ma are indicated for the seven granitic

o pluton U rocks studied in this report (Table 1). In 166.9 ± addition, a U-Pb zircon age previously re- 1.6Ma o ported by Allen and Barnes (2006) is also

U located (black asterisk). An early precursor

U to the Siskiyou contractional event involved nearly tangential suturing (ca. 174 Ma?) of the Eastern Hayfork and North Fork terranes U e prior to intrusion of the Uncles Creek satel-

litic pluton. U Black Stuart Fork terran W E Bear Summit 0 2 4 6 km S

pluton U SF Twin Sisters fault Feet 6000 4000 2000 0 North Fork terrane A B

Eastern Hayfork metaclastics Salmon River (IAT) greenstone St. Clair Creek metasedimentary strata cherts greenstones North Fork (OIB) flow breccia Serpentinized peridotite ± metagabbro

o 158.1 ± 1.1Ma New ziron U-Pb ages (this work) 156.2 ± 1.0Ma Published zircon U-Pb age (Allen and Barnes, 2006)

(2) The North Fork ophiolitic terrane occupies a medial zone and consists of the The main English Peak pluton consists of early and late stages (Seyfert, Lower Jurassic (Scherer and Ernst, 2008) St. Clair Creek laminated metacherts 1965; Schmidt, 1994; Barnes et al., 2016). The early stage crops out in the and fine-grained siliciclastic, feldspar-poor meta-argillites interstratified with southern and southeast part of the complex and comprises gabbro, diorite, and overlain by a pair of sparsely pillowed, mafic metavolcanic suites—the quartz diorite, tonalite, quartz monzodiorite, and granodiorite (Fig. 2). The amygdaloidal, Fe + Ti–rich North Fork mildly alkaline basalts and the Mg-rich most common mafic phase assemblage is hornblende + biotite, but various mid-Jurassic (Hacker et al., 1993, 1995) Salmon River basaltic-diabasic-gab- combinations of hornblende, biotite, augite, and orthopyroxene occur. This broic arc tholeiites. (3) On the west, the Eastern Hayfork terrane lies in tectonic heterogeneity is clear at the outcrop scale, and as a result, Barnes et al. were contact beneath the North Fork terrane along the high-angle Twin Sisters re- unable to detect a map-scale zoning pattern in terms of rock types or mineral verse fault. The Eastern Hayfork map unit consists of chert-argillite, broken assemblages. formation, and micrograywacke mélange hosting various locally derived and Late-stage intrusions underlie the central, western, and northeastern parts exotic blocks (Wright, 1982; Goodge and Renne, 1993; Scherer et al., 2010). The of the pluton (Fig. 2). They include biotite-hornblende quartz monzodiorite, EPC rose and at its present level, stitches the juxtaposed terranes and locally tonalite, granodiorite, and granite. The late-stage body is zoned, with a gradual obliterates the Twin Sisters fault. inward increase in modal quartz + K-feldspar, and a parallel decrease in color Mesozoic plutonism began at ca. 174 Ma in the Sawyers Bar area with in- index (Seyfert, 1965). Schmidt (1994) subdivided late-stage units based on min- trusion of the small, NW-trending Forks of Salmon pluton (Wright and Fahan, eralogy and bulk-rock compositions; Barnes et al. (2016) further modified these 1988; Allen and Barnes, 2006) and continued through emplacement of the EPC zones using a larger data set. The border unit underlies the northern part of and adjacent WCB until as late as 159–156 Ma. The English Peak composite the pluton and forms a km-wide zone along the southwest edge of the late- pluton is the largest plutonic complex in the Sawyers Bar map area. Contact stage units. Lithologically the most variable part of the late-stage pluton suite, metamorphism in the narrow EPC aureole reached maximum temperatures the border unit ranges from quartz monzodiorite to granodiorite. The adja of ~500–600 °C at pressures of 200–300 MPa (Hacker et al., 1992; Ernst, 1999). cent Yellow Jacket Ridge map unit is chiefly biotite-hornblende granodiorite. Fluid exchange with the EPC and heated metasedimentary country rocks re- The central Chimney Rock unit consists of hornblende-biotite granodiorite and sulted in local increase in bulk-rock d18O values to >15‰ in North Fork mafic granite. The Chimney Rock body contains aplitic dikes, some reaching 50 m in metavolcanic rocks (Ernst and Kolodny, 1997). In the Sawyers Bar map area, width. Aplites are sparse elsewhere in the EPC. Late Jurassic granitic plutons include the small, 159.1 ± 1.3 Ma Shelly Lake plu- Contacts between EPC plutons and their host rocks are mostly sharp (Sey- ton (Dorais, 1983; Allen and Barnes, 2006), the tiny Black Bear Summit body, fert, 1965; Donato et al., 1982; Schmidt, 1994; Ernst, 1998), but lit-par-lit injec- a suite of microdiorite dikes injected before and during EPC magmatism, and tion of the country rocks occurs along the northern contact of the main pluton a group of alaskitic dikes emplaced after intrusion of the English Peak pluton and on the east side of the Uncles Creek pluton (Seyfert, 1965; Schmidt, 1994). (Ernst, 1993, table 3). Near the northern contact of the English Peak pluton and locally within the Uncles Creek pluton, xenoliths and screens of country rocks ≥10 m long are Geology of the English Peak Plutonic Complex present, some locally fragmented (Gates, 2015). Xenoliths are rare elsewhere in the complex but occur in all pluton units (Seyfert, 1965; Schmidt, 1994; Irwin (1960) reported the EPC as broadly granitic. His reconnaissance map Barnes et al., 2016). showed the plutonic complex continuous with the Wooley Creek batholith on the west. Later mapping by Seyfert (1965) demonstrated that these two plutons are separated by more than 3 km of metasedimentary rocks of the Eastern GEOCHRONOLOGIC STUDY Hayfork terrane (Donato et al., 1982; Barnes, 1983). Seyfert also showed that the EPC consists of three plutonic units. The main English Peak pluton is nearly Sample Description circular in outcrop, with a diameter of ~10–15 km (Fig. 2). It invaded the Eastern Hayfork–North Fork tectonic contact adjacent to two small satellite plutons— We selected seven large, unweathered granitic rocks for zircon U-Pb geo- the Uncles Creek pluton to the northeast and the Heiney Bar pluton to the chronology from samples collected during the 2014 field season as well as from south. All igneous bodies are essentially undeformed. suites of EPC samples (>300 specimens) previously studied by Schmidt (1994) The Uncles Creek pluton, containing distinctive elongate hornblende and by Ernst (1998). The investigated specimens are: Heiney Bar, RBEP-005; prisms, consists of quartz diorite, tonalite, and minor granodiorite. Based on Uncles Creek, 180M; early stage, RBEP-010, RBEP-011, and 687M; Yellow Jacket similar bulk-rock compositions and textures, Barnes et al. (2016) identified the Ridge–Chimney Rock contact zone, 906M; Chimney Rock, RBEP-022. These small northern appendage of the EPC (Fig. 2) as part of the Uncles Creek body. are all medium- to coarse-grained, massive rocks devoid of mafic inclusions The Heiney Bar pluton exhibits a roughly concentric arrangement of gabbro and schlieren. Table 1 lists petrographically estimated modes and U-Pb zircon through granodiorite. crystallization ages (see next section). Barnes et al. (2016) provided detailed

TABLE 1. VISUALLY ESTIMATED MODES OF U-Pb DATED ENGLISH PEAK PLUTONIC COMPLEX ROCKS Sample number 180M RBEP-005 687M RBEP-010 RBEP-011 RBEP-022 906M Mineral (vol%) Quartz 14 26 11 11 10 23 22 Na-plagioclase 25 40 43 47 48 44 36 K-feldspar 211 86515 14 Ca-clinopyroxene0 tr 5330 0 Ca-clinoamphibole 24 81615127 14 Biotite 0111514105 6 White mica 51 Trace Trace4 23 Chlorite 10 1Trace Trace4 22 Epidote-clinozoisite 15 1Trace 111 1 Titanite 3tr 1121 2 Opaque minerals 11 121TraceTrace Totals 99 100 100 100100 100100 Total maﬁcs 53 23 38 36 37 18 28 Rock type Uncles Creek Heiney Bar Early stageEarly stage Early stage Chimney Rock Yellow Jacket Ridge–Chimney Rock U-Pb age (Ma) 172.3 ± 2.0 [3.7] 166.9 ± 1.6* [3.4] 160.4 ± 1.1 [3.1] 158.1± 1.1 [3.1]158.0 ± 1.2 [3.1]156.3 ± 1.3** [3.1]155.3 ± 1.2 [3.0] *Age ignoring six grains average: 176.5 ± 2.4 [4.0] Ma. **Age ignoring three grains average: 172.2 ± 3.2 [4.5] Ma.

mineralogic, textural, and geochemical data and inferred genetic relationships LA-ICP-MS Zircon U-Pb Analysis among the wide range of intergradational rock types. Zircons were separated and purified from four rocks at GeoSep Services, LLC, Moscow, Idaho, and About 50–70 zircon grains from each sample along with zircon age stan- from the other three at Texas Tech University. Both facilities employed conven- dards (Temora2 as primary; R33 as secondary) were arranged in 1 × 0.1 cm tional grinding, magnetic, and heavy-liquid separation techniques. rows on double-sided tape, encased in transparent epoxy, and polished ~30 mm through grain surfaces to expose their interiors. After polishing, mounts were gold coated and imaged at the Stanford–U.S. Geological Survey (USGS) Micro Zircon Cathodoluminescence (CL) Imagery Analysis Center using secondary electron and cathodoluminescence detectors on a JEOL LV5600 scanning electron microscope equipped with a Hamamatsu A Zircon CL textures vary in the relative broadness or narrowness of discrete photomultiplier tube. The images allowed distinction of zircon crystals from growth zones (e.g., Corfu et al., 2003), with a general correlation observable other minerals and guided the placement of analytical ablation pits into parts between higher modal proportion of biotite and broader growth zones (Fig. of grains devoid of cracks and non-zircon inclusions. 3A). The broadest growth zones are present in zircon from Heiney Bar and Zircon U-Pb geochronology analyses were performed at University of early-stage samples (RBEP-005, RBEP-010, RBEP-011, and 687M), all of which California–Santa Cruz by laser ablation–inductively coupled plasma mass contain ≥10% modal biotite. However, a few grains in RBEP-010, RBEP-011, and spectrometry (LA-ICP-MS) in a single session during November 2015 using 687M display indistinct zonation (Supplemental Fig. S1)1. RBEP-005, which has methodology described by Sharman et al. (2013). To minimize the effects of the least modal amount of calcic pyroxene of these samples, contains zircon instrument drift during the analytical session, the seven unknowns and R33 crystals that typically exhibit sector-zoned cores and narrow, oscillatory-zoned secondary standards were analyzed in a “round robin” pattern. Analyses of

1Supplemental Materials. LA-ICP-MS zircon U-Pb data, outer domains that are dark in CL. Zircon from late-stage samples RBEP-022 five Temora2 standards bracketed the beginning and ending of the session, cathodoluminescence images of zircons analyzed, and 906M, which contain 5% and 6% modal biotite, respectively, and lack and Temora2 was analyzed after every five analyses of unknowns and/or sec- and plots used for age determination of intrusions calcic pyroxene, more commonly exhibit oscillatory zoning (Fig. 3A). Uncles ondary standards in the routine. Cathodoluminescence images annotated with and inheritance. Please visit http://dx.doi.org/10 .1130 /GES01340.S1 or the full-text article on www.gsapubs Creek sample 180M, possessing neither modal biotite nor clinopyroxene laser pit locations for zircons analyzed from the seven investigated samples .org to view the Supplemental Materials. but significant volumes of amphibole and secondary epidote, contains the are shown in Supplemental Figure 1 (see footnote 1). smallest zircons of any sample; these grains typically are rimmed by dark CL Sample introduction was performed by ablation of 28-mm-diameter pits domains (Fig. 3A). using a Photon Machines Analyte 193 excimer laser. Ablated material was

A RBEP-005 (inh.) RBEP-022 180M RBEP-005 687M RBEP-011 906M RBEP-010 RBEP-022 (inh.) 6 14 20 27 17 26 26 26 9 8 16 3 9 3 30 24 9 Figure 3. (A) Cathodoluminescence images 29 8 of representative zircon grains analyzed 22 from each of the seven English Peak 30 26 5 28 25 granitic samples; numbers overlain on 29 pit area zircon images indicate laser pit positions on analyzed grains. Circle symbol next to Early Jr.Middle Jr. Late Jr. scale bar in lower left shows approximate B laser pit diameter. Images of all zircons ana lyzed annotated with pit locations shown in Supplemental Figure 1 (see footnote 1). RBEP-005-inheritance (B) Sample-by-sample geochronology re-

g sults, summarized from text. Individual RBEP-022-inheritance plots and age results generated using Isoplot 3.75 (Ludwig, 2012) from data sets -bearin are shown in Figure 4A and Supplemental 180M Figure 2 (see footnote 1). Symbols are according to age type shown in key at bot-

pyroxene early main stage tom right. Uncertainty shown at 95% con- t RBEP-005 fidence level as intra-session precision of calculated age results (denoted by hashes, 687M i.e., black horizontal lines) and total uncer- eek tainty including 1.8% systematic error (full biotite + hornblende late stage RBEP-010 error bars). Divisions of Jurassic (Jr.) Period into Early, Middle, and Late are from Walker et al. (2012). RBEP-011 rich Uncles Cr e- RBEP-022

≥ 175 Ma inherited componen Age type (95% conf.) 207 206 238

biotite + hornblende Heiney Bar Pb(c) Pb/ U hornblend 906M weighted average Age (Ma) common Pb 180 175 170 165 160 155 150 isochron

transported by helium carrier gas into the plasma source of an Element XR ICP was due to surficial contamination and can be subtracted using 0.836 ± 0.005 MS, from which a positively charged ion beam was extracted and manipulated for upper 207Pb/206Pb intercept as modern terrestrial common Pb ratio (Stacey to measure the intensities of atomic masses 202Hg, 204Pb, 206Pb, 207Pb, 208Pb, 232Th, and Kramers, 1975). The 207Pb-based approach is preferred over a 204Pb-based 235U, and 238U in single-collector mode. Raw data were reduced using the Iolite method to mitigate for low signal and poor precision of 204Pb measurements add-on for IgorPro to correct for down-hole fractionation and instrument back- because internal uncertainties (at 2SE) of measured 204Pb count rates overlap ground and to propagate associated random errors (Paton et al., 2010, 2011). negative values in 94 of 236 unknown measurements (without accounting for Reduced ratios and error-propagated uncertainties of 206Pb/238U, 207Pb/235U, isobaric Hg interference) and exceed 50% of the measured count rates in 201 of and 207Pb/206Pb (uncorrected for common Pb) from individual analyses were 236 measurements. Thus, precisions of any ratios calculated using 204Pb results exported from Iolite and used for age calculations (Supplemental Table S1 [see would be greatly impacted by propagation of these uncertainties. Analyses footnote 1]). A 207Pb correction–based approach was used to subtract nonradio- with significant common Pb are easily discernable in Supplemental Table S1 genic Pb from isotopic ratios, under the assumption that common Pb measured (see footnote 1) on the basis of higher 207Pb/206Pb ratios.

Isoplot 3.75 (Ludwig, 2012) was used to calculate 207Pb-corrected 206Pb/238U define a common Pb intercept at 176.5 ± 2.4 [4.0] Ma (Fig. 4A). The zircons that ages and 207Pb/206Pb ages (uncorrected for common Pb) for individual analy- yielded these ages lack distinct cores in CL images (Fig. 3A). Most of the grains ses and inverse concordia (uncorrected for common Pb) and 207Pb-corrected that yield older ages exhibit minimally sloped time-series age spectra on LA- 206Pb/238U weighted-mean age results. The weighted-mean 207Pb-corrected ICP-MS analysis, consistent with a wholly xenocrystic origin to explain their 206Pb/238U age (418.6 ± 2.3 Ma) and inverse concordia age (419.5 ± 2.6 Ma) older ages (e.g., grain 3 from RBEP-005 and grain 30 from RBEP-022; Fig. 4B). results (95% confidence level) from R33 secondary standard (419 Ma, Black Conversely, two of the nine analyses with apparent inheritance exhibit a step et al., 2004) demonstrate the effective accuracy of the Temora2 primary stan- function in the time-series age spectra (Fig. 4B), suggesting that a slightly older dard. As a gauge of systematic error, the reproducibility (stated as % error) of core domain was ablated during these two analyses. In both of the latter exam- downhole-corrected 206Pb/238U, 207Pb/235U, and 207Pb/206Pb ratios measured in the ples, the age of the base of the step function is identical to the crystallization age R33 secondary standard was calculated from the (internal only) standard error determined for the sample. However, the spectrum of each older domain shows and mean square of weighted deviates of each ratio category, yielding preci- progressively increasing age to an upper plateau, suggesting that the plateau sions of 1.7%, 1.8%, and 1.0% for the respective ratios at 95% confidence prior represents an inherited component and the slope between base and plateau to propagation of excess error in the Temora2 standard. The 207Pb-corrected results from mixing of these components (Fig. 4B). In both cases, the age de- 206Pb/238U weighted-mean age results from each sample are reported in Table 1 termined from the plateau is older than the 207Pb-corrected 206Pb/238U age of the and are shown alongside inverse concordia plots as Supplementary Materials older results in each sample (Fig. 4). Based on these observations, the 176.5 ± (see footnote 1). All uncertainties in text and figures are shown at the 95% 2.4 [4.0] Ma and 172.2 ± 3.2 [4.5] Ma pre-magmatic ages shown in Figure 4A confidence level, and as a conservative measure, we propagate a systematic may accurately represent the ages of some inherited material, but inheritance 1.8% error (based on the poorest reproducibility of R33 analyses during the of additional older material (likely Early Jurassic >185 Ma; time scale of Walker analytical session), with the total uncertainty shown in square brackets after et al., 2012) is also possible. Background-corrected 204Pb and 206Pb signal inten- the analytical uncertainty. sities from each of the analyses shown in Figure 4B indicate nominal amounts of nonradiogenic Pb but relatively elevated 206Pb count rates in the analyses U-Pb Zircon Ages and Interpretations that yield older results. The latter observation, qualitatively suggesting higher U content in inherited zircon, is consistent with those domains having previously The crystallization ages determined for the sampled intrusions indicate that crystallized from relatively small volume melts (e.g., Claiborne et al., 2010). they were emplaced over a 15–20 m.y. span (Fig. 3B, Table 1, and Supplemental At least four tectonic explanations for these older zircons can be proposed. Fig. S2 [see footnote 1]). The Uncles Creek (180M) and Heiney Bar (RBEP-005) (1) They could be xenocrysts derived from host rocks of the North Fork terrane, intrusions yield the oldest ages at 172.3 ± 2.0 [3.7] Ma and 166.9 ± 1.6 [3.4] Ma, metasediments of which contain a suite of Early Jurassic zircons (Scherer respectively (Fig. 3B). Zircons from both rocks commonly are rimmed by dark and Ernst, 2008) or from the Uncles Creek pluton. (2) Alternatively, they could CL domains (Fig. 3A). Samples that contain the most modal calcic pyroxene represent detrital zircons from the Western Hayfork terrane (WHT). Figure 5 (RBEP-010, RBEP-011, and 687M) are all from the early stage of the main presents a diagrammatic scenario for magmatic emplacement, differentiation, English Peak pluton and yield overlapping ages of 158.1 ± 1.1 [3.1] Ma, 158.0 ± and rearrangement of the chiefly oceanic terrane amalgam in the Sawyers Bar 1.2[3.1] Ma, and 160.4 ± 1.1 [3.1] Ma, respectively (Fig. 3B). The youngest ages area, modified from Barnes et al. (2016). If our reconstruction of the crustal are from two late-stage samples, one (RBEP-022) from the core Chimney Rock section is correct, then it is probable that mid-crustal reservoirs for EPC mag- unit, the other (906M) from the Yellow Jacket Ridge unit straddling the grada- mas were hosted in the WHT. However, petrographic examination of >200 sam- tional contact with the Chimney Rock unit. These samples yield overlapping ples of the WHT has failed to identify detrital zircons (C.G. Barnes, personal ages of 156.3 ± 1.3 [3.1] Ma and 155.3 ± 1.2 [3.0] Ma, respectively (Fig. 3B). commun., 2016), suggesting that this possibility is unlikely. (3) A third expla- Allen and Barnes (2006) obtained a LA-ICP-MS U-Pb age for one EPC sam- nation is that the older zircons reflect inheritance from a lower-crustal source. ple, FPE-288, a quartz diorite from the early stage of the main English Peak Such a contaminant could represent the deep plutonic underpinnings of the pluton. Their reported age of 156.2 ± 1.0 Ma is younger than any of the three Middle Jurassic arc. (4) Instead, the source could be arc-derived clastic rocks early-stage rocks reported here; but among all four samples, FPE-288 lies clos- that were relaminated (Hacker et al., 2011) to the base of the crust during the est to the late-stage intrusions (Fig. 2). Assuming that different laboratory ana ca. 170–168 Ma Siskiyou orogenic event (Coleman et al., 1988). It is noteworthy lytical results are comparable, it seems possible that early and late stages of that some samples of the coeval WCB to the west and northwest of the EPC the main pluton are compositionally and temporally intergradational. also contain inherited and/or xenocrystic zircons with Middle Jurassic ages Two samples investigated in this study appear to contain inherited or xeno (N. Coint and C.G. Barnes, personal commun., 2016). Inasmuch as Wooley crystic zircon. Of the 30 zircons analyzed from the Chimney Rock specimen, Creek magmas did not intrude rocks of the North Fork terrane, the possibility three have concordant, statistically older ages that define a common Pb inter- exists that Middle Jurassic inheritance from deep crustal levels may be wide- cept at 172.2 ± 3.2 [4.5] Ma; and of 30 Heiney Bar analyses, six concordant ages spread among post-Siskiyou plutons in the Klamath Mountains.

A Figure 4. Details of geochronologic analy ses from inheritance-bearing samples RBEP-005 Weighted mean ages RBEP-022 REBP-005 and RBEP-022. (A) Tera-Wasser 0.12 data-point error ellipses are 2 172.2 ± 3.2 [4.5] Ma data-point error ellipses are 2 burg concordia plots (uncorrected for com- 0.07 mon Pb) with error ellipses color coded to 156.3 ± 1.3 [3.1] Ma show interpreted inheritance-influenced age results (black) versus pluton age re- Weighted mean ages sults (red). Common Pb chords (dashed 176.5 ± 2.4 [4.0] Ma lines) shown with upper concordia inter- 0.10 Pb cept set at 0.836 ± 0.005 (modern terres-

166.9 ± 1.6 [3.4] Ma 20 6 trial common Pb, Stacey and Kramers, 0.06 1975). Age results are 207Pb-corrected Pb 206 238

Pb / Pb/ U weighted means. Total uncer- 206 tainty includes 1.8% systematic error dis- 20 7 0.08 cussed in methods. (B) Waveform spectra Pb / of down-hole fractionation-corrected 206 238 20 7 Pb/ U age results in Ma (y-axis) plotted versus time (x-axis) from selected analy 0.05 ses. Zircon cathodoluminescence (CL) 0.06 180 170 160 images of these grains are shown in Figure 150 3A. Each waveform shows ~20 seconds of data. Rectangles show time-integration windows used to calculate ages. Ages shown at top of each plot under analysis 190 180 170 160 150 238U/206Pb 0.04 labels are those reported in Supplemental 0.04 238 206 Table 1 (see footnote 1). Far left plots from 32 34 U/ Pb 38 40 42 34 36 38 40 42 44 each sample show examples of waveforms from analyses that appear older than the crystallization age determined for 300 the respective sample. Center plots show RBEP-005 (inheritance, no step) RBEP-005 (inheritance with step) RBEP-005 (crystallization age) waveforms with “step-function” character, B suggesting mixing of two discretely aged Grain 3 (179.1±3.1 [6.0] Ma) Grain 6 (177.2±3.1 [6.0] Ma) Grain 30 (166.0±3.4 [5.9] Ma) components (see text). Black filled rectangle in center plots shows the average of the entire integration, whereas the open 190±5 [7] Ma rectangles and ages labeled on center plots show model ages resulting from 200 3 6 30 breaking integrations into multiple components. Far right plots are example waveforms from zircon analyses that yield ages 168±3 [6] Ma overlapping the determined crystallization ages of the samples. Gray filled horizon- 204Pb: 6 ± 31 cps 206Pb: 18510 ± 580 cps 204Pb: 31 ± 32 cps 206Pb: 30800 ± 1900 cps 204Pb: 43 ± 36 cps 206Pb: 9560 ± 210 cps tal rectangles provide comparisons of the 100 crystallization age spectra to the spectra from inherited zircons, illustrating over- 300 RBEP-022 (inheritance, no step) RBEP-022 (inheritance with step) lap of crystallization ages with younger RBEP-022 (crystallization age) components in “step-function” spectra Grain 30 (173.4±2.2 [5.5] Ma) Grain 26 (172.1±3.0 [5.8] Ma) Grain 9 (159.7±2.0 [5.0] Ma) shown in center, but younger than ages of inherited components. Age errors (2σ) calculated by Iolite as internal and prop- 186±3 [6] Ma agated errors shown with propagated er- FinalAge206_238 ror in brackets and displayed as rectangle 26 200 30 heights. Age uncertainty shown does not 9 include propagation of 1.8% systematic error discussed in Methods section. Back- 157±3 [5] Ma ground-subtracted 204Pb and 206Pb signal intensities shown with 2σ internal uncer- 204Pb: 54 ± 36 cps 206Pb: 47200 ± 2700 cps 204Pb: 28 ± 32 cps 206Pb: 107800 ± 5500 cps 204Pb: 24 ± 29 cps 206Pb: 35800 ± 1100 cps tainties. 100

160.4 ± 1.1 to 158.0 ± 1.2 Ma 156.3 ± 1.3 to 155.3 ± 1.2 Ma Figure 5. Schematic cross section through episodic emplacement of early- development of mid-crustal the WTrPz showing evolution of the km stage magmas late-stage magma reservoir(s) English Peak plutonic complex over time, 0 with episodic mixing/mingling. modified after Barnes et al. (2016, fig. 13). Crystal-rich magmas rise to Initial activity involved emplacement of NFT upper crust. dioritic to tonalitic Uncles Creek magmas in the mid crust (~600 MPa). These magmas differentiated and rose to upper crustal levels (~200 MPa) to form the Uncles Creek pluton. This activity was fol- EHT lowed by thrusting along the Wilson Point 10 thrust, such that the Uncles Creek pluton Wilson Point thrust was detached from its mid-crustal roots. This earliest post-thrusting magmatism resulted in emplacement of Heiney Bar WHT 172.3 ± 2.0 Ma magmas, first in a mid-crustal reservoir mid-crustal storage of and then in the upper crust. By 160 Ma, Uncles Creek magmas influx of ferromagnesian magmas into 20 followed by emplacement the lower crust resulted in a deep crustal RCT in the upper crust MASH (i.e., mixing, assimilation, storage, and homogenization) zone in which mafic 166.9 ± 1.4 Ma magmas hybridized with lower crustal mid-crustal storage/fractionation rocks and melts. These hybrid magmas of Heiney Bar magmas followed rose episodically to form the early stage by rise to upper of the English Peak pluton. Full development of this lower crustal zone produced 30 diapiric plutons that rose to a mid-crustal reservoir (~400 MPa), where localized magma mixing occurred. Progressively evolved magmas from the mid-crustal res- MASH zone ervoir ascended into the upper crust (~200 MPa), forming the late stage of the English 160–156 Ma MOHO Peak pluton. The depth to the Moho is after Barnes and Allen (2006); Barnes et al. (2016) 40 determined terrane boundary depths by projection from outcrop patterns. Abbrevi- ations are: NFT—North Fork terrane; EHT— Eastern Hayfork terrane; WHT—Western Hayfork terrane; RCT—Rattlesnake Creek SSW NNE terrane.

MAGMATIC EMPLACEMENT SEQUENCE with any stage of the main English Peak pluton. In addition, despite the overlap in ages among early- and late-stage samples of the EPC, neither bulk-rock As noted above, both cathodoluminescence and LA-ICP-MS analyses failed geochemical nor isotopic data suggest that the latter evolved from the former to identify distinct, old cores in any of the analyzed zircons from the seven (Barnes et al., 2016). The contrast in CL appearance between zircon from early- dated English Peak rocks. The overall U-Pb zircon age relations support the versus late-stage samples (Fig. 3A) also suggests contrasts in the zircon crys- petrologic history summarized in previous sections. The magmas that formed tallizing environments of the respective magmatic suites. the Uncles Creek and Heiney Bar satellitic plutons rose from mid-crustal reser- An interesting outcome of our study is the unexpectedly old age of the voirs and solidified ca. 172 and ca. 167 Ma, respectively. About 7–12 m.y. later, Uncles Creek pluton. At ca. 172 Ma, this body is coeval with magmatism in a series of magmatic pulses built the concentrically zoned English Peak plu- the outboard Western Hayfork terrane (Hacker et al., 1995; Donato et al., 1996) ton during the interval ca. 160–155 Ma, beginning with the early mafic stages and potentially with magmatism associated with detrital zircons derived from and ending with development of the concentrically zoned late stages. Judging the North Fork terrane. It is also coeval with the Forks of Salmon pluton, which from the substantial time gap reported here, as well as contrasting bulk-rock crops out directly to the west and southwest of the EPC (Fig. 2). In contrast, geochemistry detailed by Barnes et al. (2016), it is virtually impossible that the the 167 Ma Heiney Bar pluton is too young to be related to the WHT, but it Uncles Creek and Heiney Bar plutons were comagmatic with each other, or is coeval with the oldest plutons of the Wooley Creek suite—specifically the

Vesa Bluffs and Castle Crags plutons (Fig. 1; Allen and Barnes, 2006). The time 125°W 120°W gap between emplacement of Uncles Creek and Heiney Bar magmas coin- Canada cides with regional thrusting and metamorphism termed the Siskiyou orog- pre-140 Ma: eny (Coleman et al., 1988). Thus the pervasive low-temperature alteration of Uncles Creek rocks may be due to Siskiyou-age metamorphism. In contrast, the main English Peak pluton was emplaced during the peak of Wooley Creek suite magmatism, and its extended compositional range, from gabbro to gran- 45°N ite, exemplifies this group of plutons (Allen and Barnes, 2006). Washington

(thick oceanic Blue Oregon

CRUSTAL EVOLUTION OF THE CENTRAL KLAMATH MOUNTAINS plate) Mountains

These new insights on igneous geochronology and petrology of the 45°N Sawyers Bar area and relationships to the geologic history of the Klamath Mountains Province help support a tectonic model for this sector of the North American Cordillera. Ernst (1999) proposed a speculative petrotectonic his- (thin tory for the Sawyers Bar area and adjacent parts of the WTrPz, here updated oceanic Klamath Idah slightly. During late Paleozoic–early Mesozoic time, paleo-Pacific oceanic crust plate) o approached and was subducted beneath the Klamath margin during long pe- 40°N Mountains

riods of transpression. Concomitantly, clastic debris eroded from the accreting, west-facing arc was supplied seaward and came to rest on the incoming ophiolitic basement. Eastward underflow of the oceanic lithosphere resulted in formation, accretion, and HP recrystallization of the Stuart Fork blueschist ±

eclogite complex, followed by its exhumation at ca. 227 Ma (Hotz et al., 1977; W E 40° Goodge, 1989, 1995). Arc tholeiite lavas, alkaline basalt flows, and distal tur- N bidites were deposited and progressively accreted outboard of the Stuart Fork S lithotectonic unit in deep marine (Eastern Hayfork) and marginal arc (North Fork) settings during end-of-Permian to earliest Jurassic time (Wright, 1982; (thick oceanic Ernst et al., 1991; Scherer and Ernst, 2008). Suturing of the North Fork–Eastern plate) Hayfork terrane amalgam against the yet farther outboard Western Hayfork Sierra Nevada Californ calc-alkaline arc rocks and their Rattlesnake Creek oceanic mélange basement 35°N Nevada probably occurred by ca. 170–168 Ma. In the Sawyers Bar area, this accretion Range ia (Siskiyou orogeny) was attended by regional folding, granitic pluton intru-

sions, and prehnite-pumpellyite to biotite-grade greenschist-facies metamorphism at 300–425 °C and 300 ± 100 MPa (Donato, 1989; Hacker et al., 1992; Wright and Wyld, 1994; Ernst, 1999; Allen and Barnes, 2006; Barnes et al., 2006). 35°N The arcuate Klamath Mountains stack of allochthons is now sited ~100– 0 80 160 km 150 km west of the trend of the Sierra Nevada Range of northern California, Arizona and still farther outboard from the Blue Mountains (Schwartz et al., 2011; John- son et al., 2015; LaMaskin et al., 2015) of eastern Oregon. A left-lateral offset of the Klamath salient seems required by the spatial disposition of Upper Juras- Mexico sic on-lap strata resting on the western Sierran Foothills and western Klamath 120°W 115°W Mountains, whereas Cretaceous Great Valley strata lie inboard of the Klamaths and outboard of the Sierran arc (Ernst, 2012). Palinspastic reconstruction com- Figure 6. Palinspastically restored Sierran-Klamath-Blue Mountains active continental margin bined with clockwise back-rotation of 20° of the Klamath salient, as shown in arc prior to inferred Early Cretaceous offset, including ~20° clockwise rotation of the Klamath salient, after Ernst (2012, 2015). The restoration does not undo accumulated strain caused by Figure 6, would restore the complex to an end-of-Jurassic, curvilinear Andean- frictional drag during the conjectured thrusting that produced the curvature of the salient. type margin (Ernst, 2012). A 20° back-rotation also would minimize the large Correlation of the Klamaths with the Blue Mountains is somewhat speculative.

apparent offset between the Klamath Mountains and, speculatively, correla- study, Middle to Late Jurassic igneous activity preceded earliest Cretaceous tive units in the Blue Mountains. This restoration does not remove the arcu- onset of westward displacement of the crustal stack of Klamath allochthons, ate bulge (i.e., eastern concavity) reflecting ~50 km of additional deformation thereby abandoning the upper mantle site of magma genesis fueling the active induced by differential slip of the Klamath Mountains salient along ENE-trend- Cordilleran arc. ing transform faults relative to the adjacent lithospheric plate segments of the formerly continuous, broadly calc-alkaline arc (Ernst, 2015; fig. 3). How relative displacement of the Klamath lithotectonic stack took place SUMMARY is obscure, but areal disposition of the sedimentary overlap strata indicates a mainly earliest Cretaceous (ca. 140–136 Ma) westward transportation and The inferred magmatic intrusion, differentiation, and terrane accretion of minor counterclockwise rotation of the salient relative to the active Sierran the dominantly oceanic assemblage in the Sawyers Bar area is summarized in arc. A CCW rotation of ~20° would also account for the more westerly trend of Figure 5. As the WTrPz accreted due to the episodic arrival of outboard ophio the Jurassic Andean arc relative to its Cretaceous NNW trend. Thermochrono litic units, terrigenous debris was sourced and shed from landward Klamath logic research in the Western Klamath terrane by Batt et al. (2010) has docu- lithotectonic belts, forming clastic sedimentary wedges interdigitating with mented an episode of 40Ar/39Ar-based cooling-degassing of rocks and min- the allochthonous oceanic crust and overlying deep-sea sediments. Continu- erals at ca. 135–126 Ma, compatible with an earliest Cretaceous oceanward ing transpressive plate underflow, low-grade regional recrystallization (300– transport of the Klamath Mountains salient away from the Sierra Nevada arc. 425 °C, ~300 MPa), and later contact metamorphism (500–600 °C, ~250 MPa) Combined with fission-track ages, Batt et al. (2010) interpreted their data to re- accompanied the sequential intrusion of granitic plutons (172 + 167 Ma and flect thermal annealing-recrystallization attending exhumation of the Klamath 160–155 Ma) derived from the upper mantle and basal parts of the accreting Mountains and erosional stripping of a widespread cover sequence (see also arc crust. Ascent of crystallizing plutons gradually enriched the intermediate Sliter et al., 1984). bulk-compositional nature of the upper crust in sialic components, not only This outboard extrusion of the Klamath Mountains stack of allochthons in the Sawyers Bar map area, but regionally throughout the central Klamath may have been a tectonic consequence of the arrival and subduction of a seg- Mountains. Modification of the crust by magma-driven differentiation and em- ment of thin, young, hot oceanic lithosphere (Wang et al., 2013). Bordered on placement declined abruptly in earliest Cretaceous time as the west-vergent both north and south across ENE-trending sinistral faults by old, cold, much Klamath stack of thrust sheets gradually moved off the upper mantle realm of thicker oceanic lithosphere (e.g., Sager et al., 1999; Wells et al., 2014), the calc-alkaline magma production. Klamath slab must have been largely decoupled from the superjacent stack of gently east-rooting crustal allochthons. Collision of the thick oceanic litho sphere on both north and south could have produced contraction and east- ACKNOWLEDGMENTS ward displacement of the continental margin relative to the Klamath Moun- Our initial field research was part of a U.S. Geological Survey wilderness resource evaluation project (Donato et al., 1982). Partial support was also provided by National Science Foundation tains, which would thus assume its outboard location. Moreover, shortening grants EAR-8720141 and EAR-9117103 to C.G. Barnes. In addition to our work, results reported in the Sierran arc might have caused rotation of the Foothills terrane collage here utilize the detailed mapping, sampling, and petrographic descriptions in Ph.D. dissertations to the present near-vertical stack of imbricate sheets. As the Klamath salient by Seyfert (1965) and Schmidt (1994). We thank Melanie Barnes, Ken Johnson, and Katie Gates for was displaced relatively westward from the trend of the active Cordilleran vol- assistance in the field and David Atwood for logistical support. J.J. Schwartz, Jason Saleeby, and an anonymous reviewer provided detailed, constructive journal reviews of the original version of canic-plutonic arc during earliest Cretaceous time, it evidently moved off the our manuscript. deep-seated magmagenic zone and failed to participate in the massive Sierra Nevada igneous flare-up at ca. 125–85 Ma (Ernst, 2012, 2015). Various pulses of magmatic activity in the Klamath Mountains attest to the REFERENCES CITED progressive construction of the Jurassic arc along this part of the Cordilleran Allen, C.M., and Barnes, C.G., 2006, Ages and some cryptic sources of Mesozoic plutonic rocks margin. English Peak plutonic complex magmatism exemplifies the gradual in the Klamath Mountains, California, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the Klamath Mountains Province, California and Oregon: A Volume in Honor of intermediate-to-felsic modification of the upper crust in the central Klamath William P. Irwin: Geological Society of America Special Paper 410, p. 223–245. Mountains. The much larger Sierra Nevada and Peninsular Range batholiths Ando, C.J., Irwin, W.P., Jones, D.L., and Saleeby, J.B., 1983, The ophiolitic North Fork terrane exhibit an outboard, NW-trending belt composed chiefly of Jurassic mafic plu- in the Salmon River region, central Klamath Mountains, California: Geological Society of America Bulletin, v. 94, p. 236–252, doi:10.1130/0016-7606(1983)94<236:TONFTI>2.0.CO;2. tons, whereas the voluminous inboard, NNW-trending zone of mainly Creta- Barnes, C.G., 1983, Petrology and upward zonation of the Wooley Creek batholith, Klamath ceous plutons is more felsic in bulk-rock chemistry (e.g., Kistler and Peterman, Mountains, California: Journal of Petrology, v. 24, p. 495–537, doi:10 .1093 /petrology /24.4.495. 1973, 1978; Silver et al., 1979; Todd and Shaw, 1985; Ernst et al., 2009, fig. 6). Barnes, C.G., and Allen, C.M., 2006, Depth of origin of late Middle Jurassic garnet andesite, southern Klamath Mountains, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the Overall, the Klamath salient shows little evidence of this Andean-type arc evo- Klamath Mountains Province, California and Oregon: A Volume in Honor of William P. Irwin: lution, perhaps reflecting post-Siskiyou tectonic unrest. As documented in this Geological Society of America Special Paper 410, p. 269–286, doi:10 .1130 /2006 .2410(13) .

Barnes, C.G., Allen, C.M., and Saleeby, J.B., 1986a, Open- and closed-system characteristics of Ernst, W.G., 1993, Chemically distinct mafic dike/sill sequences of contrasting age ranges,Sawyers a tilted plutonic system, Klamath Mountains, California: Journal of Geophysical Research, Bar area, central Klamath Mountains, northern California: Journal of Petrology, v. 34, p. 63– v. 91, p. 6073–6090, doi:10.1029/JB091iB06p06073. 75, doi:10.1093/petrology/34.1.63. Barnes, C.G., Rice, J.M., and Gribble, R.F., 1986b, Tilted plutons in the Klamath Mountains of Ernst, W.G., 1998, Geology of the Sawyers Bar area, Klamath Mountains, northern California: California and Oregon: Journal of Geophysical Research, v. 91, p. 6059–6071, doi:10.1029 California Division of Mines and Geology, Map Sheet 47, scale 1:48,000, accompanying text /JB091iB06p06059. 59 p. Barnes, C.G., Peterson, S.W., Kistler, R.W., Prestvik, T., and Sundvoll, B., 1992, Tectonic implica- Ernst, W.G., 1999, Mesozoic petrotectonic development of the Sawyers Bar suprasubduc- tions of isotopic variation among Jurassic and Early Cretaceous plutons, Klamath Moun- tion-zone arc, central Klamath Mountains, northern California: Geological Society of Amer- tains: Geological Society of America Bulletin, v. 104, p. 117–126, doi:10 .1130 /0016 -7606 ica Bulletin, v. 111, p. 1217–1232, doi:10.1130/0016-7606(1999)111<1217:MPDOTS>2.3.CO;2. (1992)104<0117:TIOIVA>2.3.CO;2. Ernst, W.G., 2012, Earliest Cretaceous Pacificward offset of the Klamath Mountains salient, NW Barnes, C.G., Mars, E.V., Swapp, S., and Frost, C.D., 2006, Petrology and geochemistry of the California-SW Oregon: Lithosphere, v. 5, p. 151–159, doi:10 .1130 /L247 .1. Middle Jurassic Ironside Mountain batholith: Evolution of potassic magmas in a primitive Ernst, W.G., 2015, Mid-Jurassic to early Miocene clastic deposition along the northern California arc setting, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the Klamath Moun- margin: Provenance and plate-tectonic speculations, in Anderson, T.H., Didenko, A.N., John- tains Province, California and Oregon: A Volume in Honor of William P. Irwin: Geological son, C.L., Khanchuk, A.I., and McDonald, J.H., Jr., eds., Late Jurassic Margins of Laurasia—A Society of America Special Paper 410, p. 199–221. Record of Faulting Accommodating Plate Rotation: Geological Society of America Special Barnes, C.G., Ernst, W.G., Berry, R., and Tsujimori, T., 2016, Petrology and geochemistry of an Paper 513, p. 359–376, doi:10.1130/2015.2513(09). upper crustal retro-arc pluton: A view into crustal-scale magmatism: Journal of Petrology, Ernst, W.G., and Kolodny, Y., 1997, Submarine and superimposed contact metamorphic oxygen v. 57, p. 1361–1388, doi:10.1093/petrology.egw043. isotopic exchange in an oceanic arc, Sawyers Bar area, central Klamath Mountains, Cali- Batt, G.E., Harper, G.D., Heizler, M., and Roden-Tice, M., 2010, Cretaceous sedimentary blanket- fornia, USA: Geochimica et Cosmochimica Acta, v. 61, p. 821–834, doi:10.1016 /S0016 -7037 ing and tectonic rejuvenation in the western Klamath Mountains: Insights from thermochro- (96)00371-7. nology: Central European Journal of Geosciences, v. 2, p. 138–151. Ernst, W.G., Hacker, B.R., Barton, M.D., and Sen, G., 1991, Igneous petrogenesis of magnesian Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R., Camp- metavolcanic rocks from the central Klamath Mountains, northern California: Geological bell, I.H., Korsch, R.J., Williams, I.S., and Foudoulis, C., 2004, Improved 206Pb/238U micro- Society of America, v. 103, p. 56–72, doi:10.1130/0016-7606(1991)103<0056:IPOMMR>2.3 probe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, .CO;2. ID-TIMS, ELA-ICP-MS, and oxygen isotope documentation for a series of zircon standards: Ernst, W.G., Snow, C.A., and Scherer, H.H., 2008, Contrasting early and late Mesozoic petro- Chemical Geology, v. 205, p. 115–140, doi:10.1016/j.chemgeo.2004.01.003. tectonic evolution of northern California: Geological Society of America Bulletin, v. 120, Claiborne, L.L., Miller, C.F., and Wooden, J.L., 2010, Trace element composition of igneous zircon: p. 179–194, doi:10.1130/B26173.1. A thermal and compositional record of the accumulation and evolution of a large silicic Ernst, W.G., Saleeby, J.B., and Snow, C.A., 2009, Guadalupe pluton–Mariposa Formation age batholith, Spirit Mountain, Nevada: Contributions to Mineralogy and Petrology, v. 160, relationships in the southern Sierran Foothills: Onset of Mesozoic subduction in northern p. 511–531, doi:10.1007/s00410-010-0491-5. California?: Journal of Geophysical Research, v. 114, B11204, doi:10 .1029 /2009JB006607 . Coleman, R.G., Mortimer, N., Donato, M.M., Manning, C.E., and Hill, L.B., 1988, Tectonic and Garcia, M.O., 1979, Petrology of the Rogue and Galice formations, Klamath Mountains, Oregon: regional metamorphic framework of the Klamath Mountains and adjacent Coast Ranges, Identification of a Jurassic island arc sequence: The Journal of Geology, v. 87, p. 29–41, doi: California and Oregon, in Ernst, W.G., ed., Metamorphism and Crustal Evolution of the West- 10.1086/628389. ern United States: Englewood Cliffs, New Jersey, Prentice-Hall, p. 1061–1097. Garcia, M.O., 1982, Petrology of the Rogue River island-arc complex, southwest Oregon: Ameri- Corfu, F., Hanchar, J.M., Hoskin, P.W.O., and Kinny, P., 2003, Atlas of zircon textures, in Hanchar, can Journal of Science, v. 282, p. 783–807, doi:10.2475 /ajs .282.6.783. J.W., and Hoskin, P.W.O., eds., Zircon: Reviews in Mineralogy and Geochemistry, v. 53, Garlick, S.R., Medaris, L.G., Jr., Snoke, A.W., Schwartz, J.J., and Swapp, S.M., 2009, Granulite- p. 469–500. to amphibolite-facies metamorphism and penetrative deformation in a disrupted ophiolite, Davis, G.A., 1969, Tectonic correlations Klamath Mountains and western Sierra Nevada, Cali- Klamath Mountains, California: A deep view into the basement of an accreted oceanic arc, in fornia: Geological Society of America Bulletin, v. 80, p. 1095–1108, doi:10 .1130 /0016 -7606 Miller, R.B., and Snoke, A.W., eds., Crustal Cross Sections from the Western North American (1969)80[1095:TCKMAW]2.0.CO;2. Cordillera and Elsewhere: Implications for Tectonic and Petrologic Processes: Geological Davis, G.A., Ando, C.J., Cashman, P.H., and Goullaud, L., 1980, Geologic cross section of the Society of America Special Paper 456, p. 151–186. central Klamath Mountains, California: summary: Geological Society of America Bulletin, Gates, K., 2015, A quantitative analysis of xenolith fragmentation and incorporation in magma v. 91, p. 139–142, doi:10.1130/0016-7606(1980)91<139:GCSOTC>2.0.CO;2. [M.S. thesis]: Lubbock, Texas Tech University, 210 p. Dickinson, W.R., 2008, Accretionary Mesozoic–Cenozoic expansion of the Cordilleran conti- Goodge, J.W., 1989, Polyphase metamorphic evolution of a Late Triassic subduction complex, nental margin in California and adjacent Oregon: Geosphere, v. 4, p. 329–353, doi:10 .1130 Klamath Mountains, northern California: American Journal of Science, v. 289, p. 874–943, /GES00105.1. doi:10.2475/ajs.289.7.874. Donato, M.M., 1989, Metamorphism of an ophiolitic tectonic mélange, northern California Klamath Goodge, J.W., 1995, Pre-Middle Jurassic accretionary metamorphism in the southern Klamath Mountains, U.S.A: Journal of Metamorphic Geology, v. 7, p. 515–528, doi:10 .1111 /j.1525 -1314 Mountains of northern California: Journal of Metamorphic Geology, v. 13, p. 93–110, doi:10 .1989.tb00614.x. .1111/j.1525-1314.1995.tb00207.x. Donato, M.M., Barnes, C.G., Coleman, R.G., Ernst, W.G., and Kays, M.A., 1982, Geologic map Goodge, J.W., and Renne, P.R., 1993, Mid-Paleozoic olistoliths in eastern Hayfork Terrane of the Marble Mountains Wilderness, Siskiyou County, California: U.S. Geological Survey mélange, Klamath Mountains: Implications for late Paleozoic–early Mesozoic cordilleran Miscellaneous Investigations Map, MF-1452, scale 1:48,000. forearc development: Tectonics, v. 12, p. 279–289, doi:10 .1029 /92TC01325 . Donato, M.M., Barnes, C.G., and Tomlinson, S.L., 1996, The enigmatic Applegate Group of Hacker, B.R., Ernst, W.G., and Barton, M.D., 1992, Metamorphism, geochemistry and origin of southwestern Oregon: Age, correlation, and tectonic affinity: Oregon Geology, v. 58, magnesian volcanic rocks, Klamath Mountains, California: Journal of Metamorphic Geol- p. 79–91. ogy, v. 10, p. 55–69, doi:10.1111/j.1525-1314.1992.tb00071.x. Dorais, M.J., 1983, The geology and petrology of the Shelly Lake pluton, central Klamath Moun- Hacker, B.R., Ernst, W.G., and McWilliams, M.O., 1993, Genesis and evolution of a Permian– tains, California [M.S. thesis]: University of Oregon, Eugene, 147 p. Jurassic magmatic arc/accretionary wedge, and reevaluation of terranes in the central Dunne, G.C., Garvey, T.P., Osborne, M., Schneidereit, D., Fritsche, A.E., and Walker, J.D., 1998, Klamath Mountains: Tectonics, v. 12, p. 387–409, doi:10 .1029 /92TC02250 . Geology of the Inyo Mountains Volcanic Complex: Implications for Jurassic paleogeography Hacker, B.R., Donato, M.M., Barnes, C.G., McWilliams, M.O., and Ernst, W.G., 1995, Timescales of the Sierran magmatic arc in eastern California: Geological Society of America Bulletin, of orogeny: Jurassic construction of the Klamath Mountains: Tectonics, v. 14, p. 677–703, v. 110, p. 1376–1397, doi:10.1130/0016-7606(1998)110<1376:GOTIMV>2.3.CO;2. doi:10.1029/94TC02454.

Hacker, B.R., Kelemen, P.B., and Behn, M.D., 2011, Differentiation of the continental crust by Correlation and Klamath Mountains provenance: Journal of Geophysical Research, v. 100, relamination: Earth and Planetary Science Letters, v. 307, p. 501–516, doi:10.1016 /j .epsl.2011 p. 18,045–18,058, doi:10.1029/95JB00761. .05.024. Paton, C., Woodhead, J., Hellstrom, J., Hergt, J.M., Greig, A., and Maas, R., 2010, Improved laser Harper, G.D., and Wright, J.E., 1984, Middle to Late Jurassic tectonic evolution of the Klamath ablation U-Pb zircon geochronology through robust downhole fractionation correction: Mountains, California-Oregon: Tectonics, v. 3, p. 759–772, doi:10 .1029 /TC003i007p00759 . Geochemistry Geophysics Geosystems, v. 11, doi:10.1029 /2009GC002618 . Harper, G.D., Saleeby, J.B., and Heizler, M., 1994, Formation and emplacement of the Josephine Paton, C., Hellstrom, J., Paul, B., Woodhead, J., and Hergt, J., 2011, Iolite: Freeware for the visual- ophiolite and the Nevadan orogen in the Klamath Mountains, California-Oregon: U/Pb zir- ization and processing of mass spectrometric data: Journal of Analytical Atomic Spectrom- con and 40Ar/39Ar geochronology: Journal of Geophysical Research, v. 99, p. 4293–4321, doi: etry, v. 26, p. 2508–2518, doi:10 .1039 /c1ja10172b . 10.1029/93JB02061. Sager, W.W., Kim, J., Klaus, A., Nakanishi, M., and Khankishieva, L.M., 1999, Bathymetry of Hotz, P.E., 1973, Blueschist metamorphism in the Yreka–Fort Jones area, Klamath Mountains, Shatsky Rise, northwest Pacific Ocean: Implications for ocean plateau development at a California: U.S. Geological Survey Journal of Research, v. 1, p. 53–61. triple junction: Journal of Geophysical Research, v. 104, B4, p. 7557–7576, doi:10.1029 Hotz, P.E., Lanphere, M.A., and Swanson, D.A., 1977, Triassic blueschist from northern Califor- /1998JB900009. nia and north-central Oregon: Geology, v. 5, p. 659–663, doi:10 .1130 /0091 -7613(1977)5 <659: Saleeby, J.B., 1981, Ocean floor accretion and volcano-plutonic arc evolution of the Mesozoic TBFNCA>2.0.CO;2. Sierra Nevada, California, in Ernst, W.G., ed., The Geotectonic Development of California: Irwin, W.P., 1960, Geologic reconnaissance of the northern Coast Ranges and the southern Englewood Cliffs, New Jersey, Prentice-Hall, p. 132–181. Klamath Mountains, California, with a summary of the mineral resources: California Divi- Saleeby, J.B., 1982, Polygenetic ophiolite belt of the California Sierra Nevada: Geochronologi- sion of Mines Bulletin, v. 179, 80 p. cal and tectonostratigraphic development: Journal of Geophysical Research, v. 87, p. 1803– Irwin, W.P., 1972, Terranes of the western Paleozoic and Triassic belt in the southern Klamath 1824, doi:10.1029/JB087iB03p01803. Mountains, California: U.S. Geological Survey Professional Paper 800-C, p. C103–C111. Saleeby, J.B., 1983, Accretionary tectonics of the North American Cordillera: Annual Review of Irwin, W.P., 1981, Tectonic accretion of the Klamath Mountains, in Ernst, W.G., ed., The Geo- Earth and Planetary Sciences, v. 15, p. 45–73, doi:10.1146/annurev.ea.11.050183.000401. tectonic Development of California: Englewood Cliffs, New Jersey, Prentice-Hall, p. 29–49. Saleeby, J.B., and Dunne, G., 2015, Temporal and tectonic relations of early Mesozoic arc mag- Irwin, W.P., 1994, Geologic Map of the Klamath Mountains, California and Oregon: U.S. Geologi- matism, southern Sierra Nevada, California, in Anderson, T.H., Didenko, A.N., Johnson, C.L., cal Survey Miscellaneous Investigations Series Map I-2148, scale 1:500,000. Khanchuk, A.I., and MacDonald, J.H., Jr., eds., Late Jurassic Margin of Laurasia—A Record Irwin, W.P., 2003, Correlation of the Klamath Mountains and the Sierra Nevada: Sheet 1—Map of Faulting Accommodating Plate Rotation: Geological Society of America Special Paper showing accreted terranes and plutons of the Klamath Mountains and Sierra Nevada, 513, p. 223–268, doi:10.1130/2015.2513(05). scale 1:1,000,000; Sheet 2—Successive accretionary episodes of the Klamath Mountains Scherer, H.H., and Ernst, W.G., 2008, North Fork terrane, Klamath Mountains, California: Geo- and northern part of the Sierra Nevada: U.S. Geological Survey Open-File Report 01-490, logic, geochemical, and geochronologic evidence for an early Mesozoic forearc, in Wright, 2 sheets. J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Irwin, W.P., and Wooden, J.L., 1999, Plutons and accretionary episodes of the Klamath Moun- Geological Society of America Special Paper 438, p. 289–309. tains, California and Oregon: U.S. Geological Survey Open-File Report 99-374, 1 sheet. Scherer, H.H., Snow, C.A., and Ernst, W.G., 2006, Geologic-petrochemical comparison of early Johnson, K., Schwartz, J.J., Zak, J., Verner, K., Barnes, C.G., Walton, C., Wooden, J.L., Wright, Mesozoic oceanic terranes: western Paleozoic and Triassic Belt, Klamath Mountains, and Jura- J.E., and Kistler, R.W., 2015, Composite Sunrise Butte pluton: Insights into Jurassic–Creta- Triassic arc, Sierran Foothills, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the ceous collisional tectonics and magmatism in the Blue Mountains Province, northeastern Klamath Mountains Province, California and Oregon: Geological Society of America Special Oregon, in Anderson, T.H., Didenko, A.N., Johnson, C.L., Khanchuk, A.I., and MacDonald, Paper 410, p. 377–392. J.H., Jr., eds., Late Jurassic Margin of Laurasia—A Record of Faulting Accommodating Plate Scherer, H.H., Ernst, W.G., and Wooden, J.L., 2010, Regional detrital zircon provenance of exotic Rotation: Geological Society of America Special Paper 513, p. 377–398, doi:10.1130 /2015 metasandstone blocks, Eastern Hayfork terrane, Western Paleozoic and Triassic belt, Klamath .2513(10). Mountains, California: The Journal of Geology, v. 118, p. 641–653, doi:10.1086/656352 . Kistler, R.W., and Peterman, Z.E., 1973, Variations in Sr, Rb, K, Na, and initial 87Rb/ 86Sr in Mesozoic Schmidt, B.L., 1994, The petrology and geochemistry of the English Peak pluton suite, Klamath granitic rocks and intruded wall rocks in central California: Geological Society of America Mountains, California [Ph.D. dissertation]: Lubbock, Texas Tech University, 216 p. Bulletin, v. 84, p. 3489–3512, doi:10.1130/0016-7606(1973)84<3489:VISRKN>2.0.CO;2. Schwartz, J.J., Snoke, A.W., Cordey, F., Johnson, K., Frost, C.D., Barnes, C.G., LaMaskin, T.A., Kistler, R.W., and Peterman, Z.E., 1978, Reconstruction of crustal blocks in California on the basis and Wooden, J., 2011, Late Jurassic magmatism, metamorphism, and deformation in the of initial strontium isotopic compositions of Mesozoic granitic rocks: U.S. Geological Survey Blue Mountains Province, northeast Oregon: Geological Society of America Bulletin, v. 123, Professional Paper 1071, 17 p. p. 2083–2111, doi:10.1130/B30327.1. LaMaskin, T.A., Dorsey, R.J., Vervoort, J.D., Schmitz, M.D., Tumpane, K.P., and Moore, N.O., Seyfert, C., Jr., 1965, Geology of the Sawyers Bar area, Klamath Mountains, northern California 2015, Westward Growth of Laurentia by Pre-Late Jurassic Terrane Accretion, Eastern Ore- [Ph.D. dissertation]: Stanford, California, Stanford University, 227 p. gon and Western Idaho, United States: The Journal of Geology, v. 123, p. 233–267, doi:10 Sharman, G.R., Graham, S.A., Grove, M., and Hourigan, J.K., 2013, A reappraisal of the early slip .1086/681724. history of the San Andreas fault, central California, USA: Geology, v. 41, p. 727–730. Lanphere, M.A., Irwin, W.P., and Hotz, P.E., 1968, Isotopic age of the Nevadan orogeny and older Silver, L.T., Taylor, H.P., Jr., and Chappell, B., 1979, Some petrological, geochemical and geo plutonic and metamorphic events in the Klamath Mountains, California: Geological Soci- chronological observations of the Peninsular Ranges batholith near the International Border ety of America Bulletin, v. 79, p. 1027–1052, doi:10 .1130 /0016 -7606(1968)79 [1027: IAOTNO]2 of the U.S.A. and Mexico, in Abbott, P.L., and Todd, V.R., eds., Mesozoic Crystalline Rocks— .0.CO;2. Peninsular Ranges Batholith and Pegmatites, Point Sal Ophiolite: San Diego, California, Ludwig, K.R., 2012, Isoplot 3.75: A geochronological toolkit for Microsoft Excel: Berkeley Geo- Guidebook, Geological Society of America Annual Meeting, San Diego State University, chronology Center Special Publication, v. 5, 75 p. p. 83–110. Mankinen, E.A., Irwin, W.P., and Blome, C.D., 1996, Far-travelled Permian chert of the North Fork Sliter, W.V., Jones, D.L., and Throckmorton, C.K., 1984, Age and correlation of the Cretaceous terrane, Klamath Mountains, California: Tectonics, v. 15, p. 314–328, doi:10 .1029 /95TC03054 . Hornbrook Formation, in Nilsen, T.H., ed., Geology of the Upper Cretaceous Hornbrook Medaris, L.G., Jr., Lapen, T.J., Jicha, B.R., Singer, B.S., Ghent, E.D., and Garlick, S.R., 2009, formation, Oregon and California: Los Angeles, Society of Economic Paleontologists and 168 Ma granulite facies metamorphism and 154 Ma refrigeration in the Seiad metaophiolite Mineralogists, Pacific Section, p. 89–98. complex, Rattlesnake Creek terrane, Klamath Mountains: Geological Society of America Ab- Snoke, A.W., and Barnes, C.G., 2006, The development of tectonic concepts for the Klamath stracts with Programs, v. 41, p. 590. Mountains province, California and Oregon, in Snoke, A.W., and Barnes, C.G., eds., Geologi Miller, M.M., and Saleeby, J.B., 1995, U-Pb geochronology of detrital zircon from Upper Jurassic cal Studies in the Klamath Mountains Province, California and Oregon: Geological Society synorogenic turbidites, Galice Formation, and related rocks, western Klamath Mountains: of America Special Paper 410, p. 1–29.

Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived two-stage model: Earth and Planetary Science Letters, v. 26, p. 207–221, doi:10.1016 /0012 Yellowstone hotspot: Geosphere, v. 10, p. 692–719, doi:10 .1130 /GES01018 .1 . -821X(75)90088-6. Wright, J.E., 1982, Permo-Triassic accretionary subduction complex, southwestern Klamath Todd, V.R., and Shaw, S.E., 1985, S-type granitoids and an I-S line in the Peninsular Ranges Mountains, northern California: Journal of Geophysical Research, v. 87, p. 3805–3818, doi: batholith, southern California: Geology, v. 13, p. 231–233, doi:10 .1130 /0091 -7613(1985)13 10.1029/JB087iB05p03805. <231:SGAAIL>2.0.CO;2. Wright, J.E., and Fahan, M.R., 1988, An expanded view of Jurassic orogenesis in the western Walker, J.D., Geissman, J.W., Bowring, S.A., and Babcock, L.E., compilers, 2012, Geologic Time United States Cordillera: Middle Jurassic (pre-Nevadan) regional metamorphism and thrust Scale v. 4.0: Geological Society of America, doi:10.1130 /2012 .CTS004R3C . faulting within an active arc environment, Klamath Mountains, California: Geological Soci- Wang, Y., Forsyth, D.W., Rau, C.J., Carriero, N., Schmandt, B., Gaherty, J., and Savage, B., 2013, ety of America Bulletin, v. 100, p. 859–876, doi:10.1130 /0016 -7606(1988)100 <0859:AEVOJO>2 Fossil slabs attached to unsubducted fragments of the Farallon plate: Proceedings of the .3.CO;2. National Academy of Sciences of the United States of America, v. 110, p. 5342–5346, doi:10 Wright, J.E., and Wyld, S.J., 1994, The Rattlesnake Creek terrane, Klamath Mountains, California: .1073/pnas.1214880110. An early Mesozoic volcanic arc and its basement of tectonically disrupted oceanic crust: Wells, R., Bukry, D., Friedman, R., Pyle, D., Duncan, R., Haeussler, P., and Wooden, J., 2014, Geological Society of America Bulletin, v. 106, p. 1033–1056, doi:10 .1130 /0016 -7606(1994)106 Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast <1033:TRCTKM>2.3.CO;2.