Jurassic orogeny in the Klamath Mountains - Department of ...
Jurassic orogeny in the Klamath Mountains - Department of ...
Jurassic orogeny in the Klamath Mountains - Department of ...
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JURASSIC OROGENY IN THE KLAMATH MOUNTAINS: A GEOCHRONOLOGICAL ANALYSIS<br />
'-<br />
Bradley R. Hacker W. G. Ernst<br />
<strong>Department</strong> <strong>of</strong> Geology School <strong>of</strong> Earth Sciences<br />
Stanford University Stanford University<br />
Stanford, CA 94305-2115 Stanford, CA 94305-2110<br />
ABSTRACT o<strong>the</strong>rs, 1985; Mortimer, 1985; Zucca and<br />
o<strong>the</strong>rs, 1986; Fuis and o<strong>the</strong>rs, 1987).<br />
The <strong>Jurassic</strong> growth <strong>of</strong> <strong>Klamath</strong> <strong>Klamath</strong> terranes shown <strong>in</strong> Figure 1 generally<br />
cont<strong>in</strong>ental crust from oceanic materials has have east-dipp<strong>in</strong>g bedd<strong>in</strong>g and foliation and<br />
conventionally been considered <strong>the</strong> result <strong>of</strong> west-vergent folds; most are s~parated by<br />
two discrete orogenies, <strong>the</strong> "Siskiyou" and west-directed thrust faults. Terranes<br />
"Nevadan". Geochronologic data are now related to <strong>the</strong> ma<strong>in</strong> <strong>the</strong>me <strong>of</strong> this paper are<br />
numerous enough to beg<strong>in</strong> to recognize that described below.<br />
<strong>the</strong> metamorphic and deformational episodes<br />
are <strong>in</strong>stead a broad cont<strong>in</strong>uum <strong>of</strong> events whose The basis for this paper is <strong>the</strong><br />
characteristics varied <strong>in</strong> place and time and radiometric ages listed <strong>in</strong> Table 1 and Figure<br />
were closely l<strong>in</strong>ked with areas <strong>of</strong> active 2. All zircon ages summarized here for<br />
magmatism. Magmatism was widespread at -200 igneous rocks have been <strong>in</strong>terpreted as<br />
Ma, and by -170 Ma, led to <strong>the</strong> construction crystallization ages. On <strong>the</strong> o<strong>the</strong>r hand,<br />
<strong>of</strong> two enormous volcanoplutonic arcs, <strong>the</strong> K/Ar and 40Ar/39Ar ages generally are m<strong>in</strong>imum<br />
Western Hayfork and North Fork-Salmon River. ages for <strong>the</strong> crystallization cf plutonic<br />
Northwest-sou<strong>the</strong>ast extension <strong>in</strong> <strong>the</strong> nor<strong>the</strong>rn rocks because entrapment <strong>of</strong> argon <strong>in</strong> crystals<br />
<strong>Klamath</strong>s from 167-155 Ma was co<strong>in</strong>cident with occurs considerably below solidus<br />
<strong>the</strong> crystallization <strong>of</strong> volum<strong>in</strong>ous plutonic temperatures. Crystallization times <strong>of</strong><br />
and volcanic rocks <strong>of</strong> <strong>the</strong> Wooley Creek and rapidly cooled hypabyssal and volcanic rocks<br />
Western <strong>Klamath</strong> suites. Sudden cool<strong>in</strong>g <strong>of</strong> a are more closely reflected <strong>in</strong> K/Ar and<br />
large region <strong>of</strong> <strong>the</strong> central <strong>Klamath</strong> Mounta<strong>in</strong>s 40Ar/39Ar ages--provided that <strong>the</strong> rocks have<br />
to -300°C at -150 Ma may have occurred as <strong>the</strong> not undergone reheat<strong>in</strong>g sufficient to<br />
magmatic belt was ext<strong>in</strong>guished by subduction liberate argon. Closure temperatures, or <strong>the</strong><br />
<strong>of</strong> colder material at deeper structural temperature <strong>of</strong> a m<strong>in</strong>eral at <strong>the</strong> time<br />
levels. represented by its apparent age (Dodson,<br />
1973), are approximately 500-525uC (Harrison,<br />
INTRODUCTION 1981), 400-425°C (summary <strong>in</strong> Hodges, 1991),<br />
and 310-345°C (Harrison and o<strong>the</strong>rs, 1985),<br />
The <strong>Klamath</strong> Mounta<strong>in</strong>s provide a well- for rapidly cooled hornblende, muscovite, and<br />
studied archetype <strong>of</strong> cont<strong>in</strong>ental lithosphere biotite, respectively. Closure temperatures<br />
constructed largely from oceanic material. may be affected by factors such as cool<strong>in</strong>g<br />
S<strong>in</strong>ce <strong>the</strong> <strong>in</strong>ception <strong>of</strong> <strong>the</strong> terrane concept <strong>in</strong> rate (Dodson, 1973), composition (Harrison<br />
<strong>the</strong> <strong>Klamath</strong>s (Irw<strong>in</strong>, 1972), much debate has and o<strong>the</strong>rs, 1985; Scaillet and o<strong>the</strong>rs, 1992),<br />
centered on whe<strong>the</strong>r <strong>the</strong> terranes are exotic exsolution (Harrison and Fitz Gerald, 1986;<br />
with respect to <strong>the</strong> rest <strong>of</strong> western North Baldw<strong>in</strong> and o<strong>the</strong>rs, 1990), alteration<br />
America or formed more-or-less <strong>in</strong> situ (Davis (Onstott and Pr<strong>in</strong>gle-Goodell, 1988; Baldw<strong>in</strong><br />
and o<strong>the</strong>rs, 1978; Wright, 1982; Gray, 1986). and o<strong>the</strong>rs, 1990), and gra<strong>in</strong> size (Kelley,<br />
Hamilton (1978) suggested that <strong>Jurassic</strong> 1988). Of potential relevance to this study,<br />
magmatic belts <strong>in</strong> <strong>the</strong> <strong>Klamath</strong>s represent exsolution may reduce hornblende closure<br />
dist<strong>in</strong>ct far-traveled arcs, whereas Davis and temperature by more than 100°C (Baldw<strong>in</strong> and<br />
o<strong>the</strong>rs (1978) postulated that a s<strong>in</strong>gle o<strong>the</strong>rs, 1990). We have no~ detected<br />
<strong>Jurassic</strong> arc developed <strong>in</strong> situ. This paper exsolution <strong>in</strong> any <strong>Klamath</strong> hornblendes studied<br />
presents prelim<strong>in</strong>ary geochronology for by back-scattered electron microscopy, but<br />
<strong>Jurassic</strong> magmatic and related metamorphic this does not preclude its existence.<br />
rocks <strong>in</strong> <strong>the</strong> central <strong>Klamath</strong> Mounta<strong>in</strong>s that,<br />
coupled with extensive earlier geochronologic Western <strong>Klamath</strong> Terrane<br />
studies <strong>in</strong> <strong>the</strong> western <strong>Klamath</strong>s (Table 1),<br />
re<strong>in</strong>forces <strong>the</strong> latter model, and allows a The western <strong>Klamath</strong> terrane consists <strong>of</strong><br />
revised tectonic scenario for <strong>the</strong> <strong>Jurassic</strong> <strong>the</strong> Joseph<strong>in</strong>e ophiolite, Galice Formation,<br />
evolution <strong>of</strong> <strong>the</strong> <strong>Klamath</strong> Mounta<strong>in</strong>s. Rogue Formation, and Chetco complex. The<br />
Rogue Formation and Chetco complex are<br />
The overall structure <strong>of</strong> <strong>the</strong> <strong>Klamath</strong> <strong>in</strong>terpreted as a Middle to Late <strong>Jurassic</strong><br />
Mounta<strong>in</strong>s is a stack <strong>of</strong> gently east-dipp<strong>in</strong>g (Table 1, c15-c20) immature arc (Garcia,<br />
thrust sheets (Irw<strong>in</strong>, 1966; Blakely and 1979, 1982); plutonic rocks <strong>in</strong>clude <strong>the</strong><br />
. , "
Chetco River complex, Ill<strong>in</strong>ois River gabbro, been active dur<strong>in</strong>g <strong>the</strong> f<strong>in</strong>al stages <strong>of</strong> arc<br />
and Rum Creek metagabbro (Saleeby, 1990). volcanoplutonism (Harper and o<strong>the</strong>rs, 1993).<br />
The Joseph<strong>in</strong>e ophiolite (Harper, 1980) is The Joseph<strong>in</strong>e ophiolite and Rogue/Chetco arc<br />
Middle <strong>Jurassic</strong> <strong>in</strong> age (Table 1, c10-c14). are both depositionally overla<strong>in</strong> by <strong>the</strong><br />
It overlies <strong>the</strong> Rogue/Chetco arc along a Ga+ice Formation (Harper, 1980; Harper and<br />
regional thrust fault, <strong>the</strong> Madstone thrust, Wright, 1984), which consists <strong>of</strong> Oxfordian<br />
(Harper and o<strong>the</strong>rs, 1993) <strong>in</strong>terpreted to have radiolarian chert grad<strong>in</strong>g up'Nard <strong>in</strong>to<br />
Kimmeridgian flysch (pessagno and Blome,<br />
1990). The Galice Formation, Rogue<br />
Formation, and Joseph<strong>in</strong>e ophiolite are all<br />
Cretaceous cut by dikes/sills that yield ages as young<br />
wd as -150 Ma (Table 1, e6-e22). Sp<strong>in</strong>el,<br />
younger staurolite, garnet, and blue-amphibole<br />
rocks detritus <strong>in</strong> <strong>the</strong> Galice Formation suggests<br />
that Galice sediments were derived from<br />
sources <strong>in</strong> more easterly Kla.~ath terranes<br />
(Davis and o<strong>the</strong>rs, 1978; Saleeby and o<strong>the</strong>rs,<br />
1982). The Galice Formation and<br />
depositionally underly<strong>in</strong>g Rogue/Chetco arc<br />
and Joseph<strong>in</strong>e ophiolite <strong>the</strong>refore are not<br />
far-traveled with respect to <strong>the</strong> rest <strong>of</strong> <strong>the</strong><br />
<strong>Klamath</strong>s (Davis and o<strong>the</strong>rs, 1978; cf. Wright<br />
and Wyld, 1986).<br />
Preston Peak Ophiolite<br />
The Preston Peak ophiolite comprises<br />
greenschist-facies tholeiitic plutons, dikes,<br />
breccias and pillowed flows that <strong>in</strong>trude and<br />
unconformably overlie serpent<strong>in</strong>ized<br />
ultramafic tectonite with <strong>in</strong>cluded blocks <strong>of</strong><br />
amphibolite (Snoke, 1977; Snoke and o<strong>the</strong>rs,<br />
1981; Saleeby and o<strong>the</strong>rs, 1982). The<br />
ultramafic tectonite, and possibly <strong>the</strong><br />
amphibolite, are <strong>in</strong>ferred to be part <strong>of</strong> <strong>the</strong><br />
Rattlesnake Creek terrane (see below). A<br />
late-stage plagiogranite dike <strong>in</strong> diorite<br />
yielded a 164X1 Ma zircon age (Table 1, c21),<br />
F .<br />
C<br />
ranclscan<br />
I<br />
ompex<br />
and chert overly<strong>in</strong>g <strong>the</strong> flows conta<strong>in</strong>s<br />
J ' d . 1 ,<br />
urass~c ra ~o ar~ans (Sa 1ee by an d ot hers,<br />
1982). One contact-metamorphosed amphibolite<br />
block yielded a K/Ar hornblende age <strong>of</strong> 165x3<br />
Ma (Table 1, c22), whereas amphibolite<br />
distant from plutons produced 190 and 193 Ma<br />
ages (Table 1, a17-a18). Rocks possibly<br />
correlative with <strong>the</strong> Preston Peak ophiolite<br />
(near little Grayback Mounta<strong>in</strong>; Gorman, 1985)<br />
conta<strong>in</strong> <strong>Jurassic</strong> radiolarians (Saleeby and<br />
o<strong>the</strong>rs, 1982) and Late Triassic conodonts<br />
(Irw<strong>in</strong> and o<strong>the</strong>rs, 1983).<br />
Condrey Mounta<strong>in</strong> Terrane<br />
The Condrey Mounta<strong>in</strong> terrane is <strong>in</strong><br />
N f similar structural position to <strong>the</strong> Western<br />
<strong>Klamath</strong> terrane, but is a transitional<br />
greenschist-blueschist facies subduction<br />
Great complex with a greenschist facies overpr<strong>in</strong>t<br />
50km Valley (Helper, 1986). The protolith age <strong>of</strong> part <strong>of</strong><br />
Group <strong>the</strong> Condrey Mounta<strong>in</strong> terrane is bracketed to<br />
near 170 Ma by zircon ages (Table 1, b10-<br />
. ,b12). Rb/Sr and K/Ar ages <strong>in</strong>dicate that<br />
F~gure 1. <strong>Klamath</strong> ro~k un~ts (after cool<strong>in</strong>g <strong>of</strong> <strong>the</strong> Condrey Mounta<strong>in</strong> terrane below<br />
Blake and o<strong>the</strong>rs, 1982; Sm~th and o<strong>the</strong>rs, -350°C was delayed until Early Cretaceous<br />
1982; Ernst, 1990; Hacker and o<strong>the</strong>rs, 1993). time (125-132 Ma; Helper and o<strong>the</strong>rs 1989).<br />
Plutons discussed <strong>in</strong> text are shown. Ma<strong>in</strong> '<br />
portions <strong>of</strong> faults discussed <strong>in</strong> <strong>the</strong> text are Rattlesnake Creek Terrane<br />
named with italics; "Marble Mtn ft": Marble<br />
M~unta<strong>in</strong>s fau,lt. Low-angle fa~lts are shown The Rattlesnake Creek terrane, highw~th<br />
teeth, h~gh-angle faults w~thout. grade portions <strong>of</strong> which are also called <strong>the</strong><br />
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Marble Mounta<strong>in</strong> terrane, consists <strong>of</strong> mafic 1985; Wright and Wyld, 1985). Inasmuch as<br />
tectonite and ophiolitic melange overla<strong>in</strong> by <strong>the</strong> beg<strong>in</strong>n<strong>in</strong>g' <strong>of</strong> <strong>the</strong> Early <strong>Jurassic</strong> (201:i:2<br />
coherent, undeformed volcaniclastic rocks Ma; Hodych and Dunn<strong>in</strong>g, 1992) sign~ficantly<br />
(Wright, 1981; Petersen, 1982; Hill, 1984; postdates 212 Ma, <strong>the</strong>se reported age<br />
Rawson, 1984; Gorman, 1985; Gray, 1985; relationships are paradoxical.<br />
Wright<br />
(1972)<br />
and Wyld,<br />
<strong>in</strong>terpreted<br />
1986; Donato, 1987).<br />
<strong>the</strong> Rattlesnake<br />
Irw<strong>in</strong><br />
Creek The Rattlesnake Creek terrane served as<br />
terrane as a dismembered ophiolite. rift basement for <strong>the</strong> Rogue/Chetco arc<br />
(Harper and Wright, 1984; Saleeby, 1984),<br />
The melange conta<strong>in</strong>s blocks derived Joseph<strong>in</strong>e ophiolite (Wyld and Wright, 1988),<br />
from ophiolitic as well as cont<strong>in</strong>ental Preston Peak ophiolite (Saleeby and o<strong>the</strong>rs,<br />
sources. Ultramafic blocks reta<strong>in</strong> high- 1982), and possibly <strong>the</strong> Western Hayfork<br />
temperature fabrics that predate <strong>the</strong>ir (Wright and Fahan, 1988) and Salmon River<br />
<strong>in</strong>corporation <strong>in</strong>to <strong>the</strong> melange (Medaris, arcs (see below).<br />
1966;<br />
blocks<br />
Rawson,<br />
with<strong>in</strong><br />
1984; Donato,<br />
<strong>the</strong> melange<br />
1987).<br />
<strong>in</strong>clude<br />
Mafic<br />
massive Western Hayfork terrane<br />
amphibolite<br />
plutonic<br />
(Hill,<br />
complexes,<br />
1984)<br />
some<br />
and<br />
<strong>of</strong><br />
hypabyssal-<br />
which were The Western Hayfork terrane is a Middle<br />
deformed dur<strong>in</strong>g crystallization (Kle<strong>in</strong>, 1977; <strong>Jurassic</strong> (167-177 Ma; Table 1, b1-b7)<br />
Petersen, 1982). Zircons from plagiogranite immature <strong>in</strong>traoceanic arc that consists <strong>of</strong><br />
cutt<strong>in</strong>g one block <strong>of</strong> dikes at Ch<strong>in</strong>a Peak gave gabbroic to quartz-monzodioritic calcan<br />
age <strong>of</strong> 172:i:2 Ma (Table 1, b14). Trace alkal<strong>in</strong>e plutons <strong>in</strong>trud<strong>in</strong>g >6 km <strong>of</strong><br />
elements <strong>in</strong>dicate that mafic igneous rocks <strong>in</strong> consangu<strong>in</strong>eous volcaniclastic rocks and<br />
<strong>the</strong> Rattlesnake terrane have aff<strong>in</strong>ities with depositionally overly<strong>in</strong>g epiclastic rocks<br />
immature arc and mid-ocean ridge basalts (Fig 3; Kle<strong>in</strong>, 1975; Cashman, 1979; Charlton<br />
. '<br />
(FJ.g. 3). Chert blocks <strong>in</strong> <strong>the</strong> melange 1979; Hill, 1984; Rawson, 1984; Wright and<br />
conta<strong>in</strong> radiolarians rang<strong>in</strong>g from Middle Fahan, 1988). Fossils <strong>in</strong>clude Silurian coral<br />
Triassic to Early or Middle <strong>Jurassic</strong> age, and and Early Permian gastropods ir. limestone<br />
limestone blocks bear Devonian(?) coral to cobbles derived from <strong>the</strong> McCloud limestone <strong>of</strong><br />
Late Triassic conodonts (Irw<strong>in</strong>, 1972, 1985b; <strong>the</strong> Eastern <strong>Klamath</strong>s, and Triassic or<br />
Irw<strong>in</strong> and o<strong>the</strong>rs, 1977, 1982, 1983, 1985; <strong>Jurassic</strong> radiolarians <strong>in</strong> chert (Irw<strong>in</strong>, 1972,<br />
Gray, 1985). The Devonian(?) fossil coral is 1985b; Fahan, 1982; Irw<strong>in</strong> and o<strong>the</strong>rs, 1982;<br />
significant because it is similar to coral Wright, 1982). The McCloud fauna <strong>in</strong>dicates<br />
found <strong>in</strong> sedimentary strata <strong>in</strong> <strong>the</strong> Eastern that <strong>the</strong> Western Hayfork terrane formed near<br />
<strong>Klamath</strong>s, and thus ties provenance <strong>of</strong> <strong>the</strong> <strong>the</strong> eastern K1amaths, and hence is not exotic<br />
Rattlesnake Creek terrane to <strong>the</strong> Eastern (Harper and Wright, 1984).<br />
<strong>Klamath</strong> terrane (Irw<strong>in</strong>, 1972).<br />
Sawyers Bar terrane<br />
The coherent volcaniclastic unit<br />
overly<strong>in</strong>g <strong>the</strong> melange conta<strong>in</strong>s -350 m <strong>of</strong> Ernst (1990) and Hacker and o<strong>the</strong>rs<br />
conglomerate, arenite and tuff deposited (1993) reported that several <strong>Klamath</strong> units<br />
subaerially proximal to a volcano (Rawson, previously termed terranes, <strong>the</strong> Eastern<br />
1984; Gray, 1985, 1986). Trace element Hayfork, Salmon River, and North Fork, are<br />
abundances <strong>in</strong>dicate that <strong>the</strong> volcano was part not wholly fault-bounded units, and <strong>the</strong>refore<br />
<strong>of</strong> an immature arc (Fig. 3). The do not warrant terrane status. In addition,<br />
relationship between <strong>the</strong> melange and <strong>the</strong> well-bedded, coherent chert formerly <strong>in</strong>cluded<br />
coherent volcaniclastic suite is <strong>of</strong> as part <strong>of</strong> <strong>the</strong> North Fork unit was given a<br />
considerable tectonic import, yet it has not separate name, <strong>the</strong> St Claire Creek unit. All<br />
been well documented. Petersen (1982) and four units were grouped as <strong>the</strong> Sawyers Bar<br />
Gray (1985) state that <strong>the</strong> contact is not terrane (Ernst, 1990). Hacker and o<strong>the</strong>rs<br />
exposed. Moreover, although plutons rang<strong>in</strong>g (1993) provisionally <strong>in</strong>terpreted ~he Sawyers<br />
<strong>in</strong> age from 192 to 208 Ma <strong>in</strong>trude <strong>the</strong> Bar terrane to represent a vo1canop1utonic<br />
serpent<strong>in</strong>ite-matrix melange <strong>of</strong> <strong>the</strong> arc (North Fork and Salmon River units), and<br />
Rattlesnake Creek terrane <strong>in</strong> <strong>the</strong> Somes Bar associated fore-arc accretionary wedge<br />
area (Gray, 1985), plutons explicitly (Eastern Hayfork unit) and back-arc bas<strong>in</strong> (St<br />
<strong>in</strong>trud<strong>in</strong>g <strong>the</strong> volcaniclastic unit <strong>in</strong> that Claire Creek unit).<br />
area have not been dated. A prelim<strong>in</strong>ary<br />
report by Wright and Wy1d (1985) mentioned ~R~rprn HR~fork Unit<br />
that plutons as old as 212 Ma do cut<br />
volcaniclastic rocks that lie depositiona1ly The Eastern Hayfork unit vari~s from<br />
on melange <strong>in</strong> <strong>the</strong> sou<strong>the</strong>rnmost(?) K1amaths. broken formation to melange and is<br />
If depositional on melange, <strong>the</strong> <strong>in</strong>terpreted to represent an accretionary<br />
volcanic'astic rocks must be older than 212 wedge (Wright, 1981). The non-exotic<br />
Ma but must also postdate Late Triassic (plausibly <strong>in</strong>terbedded) component <strong>of</strong> <strong>the</strong><br />
limestone blocks <strong>in</strong> <strong>the</strong> melange (Gray, 1986). Eastern Hayfork <strong>in</strong>cludes rocks grad<strong>in</strong>g from<br />
Early <strong>Jurassic</strong> radiolarians must have been radiolarian chert to tuff, pillow lava, and<br />
mixed <strong>in</strong>to <strong>the</strong> Rattlesnake Creek melange at a quartzose turbidites (Cashman, 1979;<br />
later date, o<strong>the</strong>rwise <strong>the</strong> volcaniclastic Charlton, 1979; Fahan, 1982; Wright, 1982;<br />
rocks would have to postdate <strong>the</strong>m too (Gray, Hacker and o<strong>the</strong>rs, 1993). Tuffaceous<br />
- I<br />
;;'"J..""'"-"'."~) ,,'1"0' ",'" J,
-<br />
material and clastic volcanogenic rocks are Limestone blocks <strong>in</strong> <strong>the</strong> Eastern HayforK<br />
subord<strong>in</strong>ate to detritus derived from conta<strong>in</strong> Silurian or Devonian through Late<br />
cont<strong>in</strong>ental or plutonic provenances. Exotic Triassic shallow water fossils, <strong>in</strong>clud<strong>in</strong>g<br />
blocks <strong>in</strong>clude ultramafic rock, basalt, Late Permian Tethyan fusul<strong>in</strong>ids and coral<br />
gabbro, limestone, amphibolite, blueschist, (I~w<strong>in</strong>, 1972, 1974, 1985b; Cox and Pratt,<br />
quartz<strong>of</strong>eldspathic schist, recrystallized 1973; Irw<strong>in</strong> and o<strong>the</strong>rs, 1977, 1983; Gray,<br />
chert, and crenulated quartz-mica schist 1986; Miller and Wright, 1987; Stevens and<br />
(Cox, 1956; Cashman, 1979; Charlton, 1979; o<strong>the</strong>rs, 1987, 1991). Eastern Hayfork chert<br />
Burton, 1982; Fahan, 1982; Wright, 1982). conta<strong>in</strong>s Late Permian, Middle Triassic, Late<br />
Cashman and Wright suggested that <strong>the</strong> Triassic, and Late Triassic to Early <strong>Jurassic</strong><br />
metamorphic blocks were derived from <strong>the</strong> more radiolarians, and Middle Triassic and Late<br />
easterly Stuart Fork and Central Metamorphic Triassic conodonts, imply<strong>in</strong>g Late Permian to<br />
terranes; this suggestion has been Early <strong>Jurassic</strong> deposition (Irw<strong>in</strong> and o<strong>the</strong>rs,<br />
streng<strong>the</strong>ned by geochronologic work <strong>of</strong> Goodge 1982, 1983; Ando and o<strong>the</strong>rs, 1983; Irw<strong>in</strong>,<br />
and Renne (1991, 1993). 1985b).<br />
TiO2 Rattlesnake Creek Terrane Ti/100<br />
CAB<br />
0 amphibolite tectonite<br />
V mafic blocks<br />
OIB . volcaniclastic sequence<br />
. Ch<strong>in</strong>a Peak dikes<br />
£. Preston Peak diabase and<br />
6. mafic blocks <strong>in</strong> serpent<strong>in</strong>ite<br />
TiO Western Hayfork Terrane T'1<br />
T ' O Salmon River Unit<br />
1 T'100<br />
CAB<br />
018<br />
anic<br />
byss<br />
Figure 3. Tectonomagmatic discrim<strong>in</strong>ation diagrams after Pearce and Cann (1973) and Mullen<br />
(1983). Note that <strong>the</strong> hypabyssal and volcanic rocks <strong>of</strong> <strong>the</strong> Salmon River unit are similar to <strong>the</strong><br />
Western Hayfork and Rattlesnake Creek terrane, respectively. MORB: mid-ocean ridge basalt; OIB:<br />
ocean-island basalt; VAB: <strong>in</strong>traoceanic arc basalt; CAB: cont<strong>in</strong>ental arc basalt; WPB: with<strong>in</strong>plate<br />
basalt. Data from Charlton (1979), Wright (1981), Petersen (1982), Hill (1984), Donato<br />
(1985), Gorman (1985), Gray (1985), Wyld and Wright (1988), Ernst (1987), Ernst and o<strong>the</strong>rs<br />
(1991), Hacker and o<strong>the</strong>rs (1993), and Barnes (pers. comm., 1990). j<br />
""~:IiIi~ '~i.)' 1, !I. .i!I"' .,<br />
i
Quartzose blocks conta<strong>in</strong> detrital because <strong>of</strong> its ophiolitic rock types (Irw<strong>in</strong>,<br />
zircons with Pb/Pb ages <strong>of</strong> 2.0-2.1 Ga, 1972), and h'as s<strong>in</strong>ce been suggested to<br />
<strong>in</strong>dicat<strong>in</strong>g that some debris was ultimately represent a seamount complex (Ando, 1979).<br />
derived from a mature Precambrian cont<strong>in</strong>ental Hacker and o<strong>the</strong>rs (1993) presented an<br />
source (Miller and Saleeby, 1991). Trace- ai~ernative <strong>in</strong>terpretation--that <strong>the</strong> North<br />
element abundances <strong>of</strong> Eastern Hayfork Fork is an alkalic part <strong>of</strong> <strong>the</strong> Salmon River<br />
sedimentary rocks suggest that material was immature arc. The volcanic rocks are massive<br />
also derived from <strong>the</strong> adjacent North Fork- to amygdaloidal breccias with angular to<br />
Salmon River arc (Hacker and o<strong>the</strong>rs, 1993). subangular clasts, tuffaceous chert, pillowed<br />
The discovery <strong>of</strong> <strong>the</strong> same Late Permian _flows, _pill,Q~- breccias, a~Q--.h-Y~loclastites.<br />
Tethyan fossils <strong>in</strong> <strong>the</strong> Eastern <strong>Klamath</strong> Limestone beds or exotic(?) blocks conta<strong>in</strong><br />
terrane and Eastern Hayfork unit (Stevens and fusul<strong>in</strong>ids and foram<strong>in</strong>ifers <strong>of</strong> Carboniferous<br />
o<strong>the</strong>rs, 1987) implies that <strong>the</strong> limestone to Early Permian age (Irw<strong>in</strong>, 1972, 1974;<br />
blocks are olistoliths derived from eastern Irw<strong>in</strong> and o<strong>the</strong>rs, 1977).<br />
paleo-Pacific seamounts (Miller and Wright,<br />
1987) or from <strong>the</strong> Eastern <strong>Klamath</strong> terrane. The igneous crystallization age <strong>of</strong> <strong>the</strong><br />
North Fork volcanics may be as young as 165<br />
Salmon Rivpr Tln;r Ma, based on Ar/Ar ages obta<strong>in</strong>ed on<br />
hornblende from two dikes (Table 1, c24-c25).<br />
The Salmon River unit <strong>in</strong>cludes Sedimentary rocks <strong>of</strong> <strong>the</strong> Eastern Hayfork unit<br />
ultramafic rock, gabbro, diabase, and <strong>in</strong>terbedded with <strong>the</strong> North Fork range <strong>in</strong> age<br />
volcanic rock, and was <strong>in</strong>itially <strong>in</strong>terpreted from Late Permian to Late Triassic. Late<br />
as oceanic crust (Irw<strong>in</strong>, 1972; Blake and Permian fossils are present <strong>in</strong> limestone<br />
o<strong>the</strong>rs, 1982; Ando and o<strong>the</strong>rs, 1983; <strong>in</strong>tercalated with <strong>the</strong> North Fork volcanics,<br />
Mortimer, 1984). Recent field mapp<strong>in</strong>g, and <strong>the</strong> <strong>in</strong>terbedded St Claire Creek unit<br />
whole-rock analyses, and m<strong>in</strong>eral analyses conta<strong>in</strong>s Late Permian to Early <strong>Jurassic</strong><br />
provided <strong>the</strong> basis for Ernst and o<strong>the</strong>rs fossils. The oldest pluton <strong>in</strong>trud<strong>in</strong>g <strong>the</strong><br />
(1991) to propose genesis as an immature North Fork is <strong>the</strong> Vesa Bluffs pluton (~165 Ma<br />
<strong>in</strong>traoceanic arc <strong>in</strong>stead. Massive and Table 1, c9). Thus, eruption is poorly<br />
locally pillowed volcanic rocks with th<strong>in</strong> constra<strong>in</strong>ed to with<strong>in</strong> Late Permian to Middle<br />
volcaniclastic layers conta<strong>in</strong> igneous <strong>Jurassic</strong> time.<br />
cl<strong>in</strong>opyroxene, hornblende, and plagioclase,<br />
with m<strong>in</strong>or sp<strong>in</strong>el, apatite, and possibly St Clairp ~rppk Tln;r<br />
anorthoclase; carbonate and chert are present<br />
between pillows (Cox, 1956; Ando, 1979; This unit, <strong>in</strong>formally named by Hacker<br />
Mortimer, 1984; Ernst and o<strong>the</strong>rs, 1991). and o<strong>the</strong>rs (1993), is characterized by<br />
Metavolcanic rocks have trace element chiefly coherent, bedded chert with m<strong>in</strong>or<br />
abundances appropriate for immature argillite (this study; Ando, 1979; Wright,<br />
tholeiitic arc rocks, whereas younger, 1981; Mortimer, 1984) unlike <strong>the</strong> disrupted,<br />
recrystallized microdioritic dikes and sills argillite-dom<strong>in</strong>ated sequences <strong>of</strong> ~he Eastern<br />
tend to be calc-alkal<strong>in</strong>e (Fig. 3; Ernst, Hayfork unit. Previously this unit was<br />
1993). <strong>in</strong>cluded as part <strong>of</strong> <strong>the</strong> North Fork unit,<br />
which it overlies depositionally (Trexler,<br />
Fossil ages <strong>of</strong> <strong>in</strong>terbedded Eastern 1968; Ando and o<strong>the</strong>rs, 1983); earlier workers<br />
Hayfork sedimentary rocks suggest that postulated that this section t"epresented<br />
construction <strong>of</strong> <strong>the</strong> Salmon River suite began open-ocean sediments (Davis and o<strong>the</strong>rs, 1978;<br />
<strong>in</strong> Permian and extended through Late Triassic Ando, 1979; Wright, 1982). Hacker and o<strong>the</strong>rs<br />
time. Plagiogranite with<strong>in</strong> diabase yielded a (1993) separated this sedjment-dom<strong>in</strong>ated unit<br />
strongly discordant Pb/U zircon age from <strong>the</strong> alkalic volcanic rocks <strong>of</strong> <strong>the</strong> North<br />
<strong>in</strong>terpreted to <strong>in</strong>dicate crystallization <strong>in</strong> Fork unit. The new unit name emphasizes that<br />
<strong>the</strong> range 265-310 Ma (Pennsylvanian to <strong>the</strong> Salmon River and North Fork units<br />
Permian; Ando and o<strong>the</strong>rs, 1983). A gabbro <strong>in</strong>terf<strong>in</strong>ger and are <strong>in</strong>terbedded with two<br />
body that <strong>in</strong>trudes <strong>the</strong> diabase gave a dist<strong>in</strong>ctly different types <strong>of</strong> sedimentary<br />
40Ar/39Ar isochron age <strong>of</strong> 200 Ma on igneous rock: disrupted chert-argillite <strong>of</strong> <strong>the</strong><br />
hornblende (Table 1, a9). Two mafic outboard Eastern Hayfork and coherent wellhypabyssal<br />
rocks <strong>in</strong> <strong>the</strong> Salmon River unit bedded chert-argillite <strong>of</strong> <strong>the</strong> <strong>in</strong>board St<br />
yielded Ar/Ar hornblende ages <strong>of</strong> -174 Ma Claire Creek unit.<br />
(Table 1, b15-b16). These data are St Claire Creek chert conta<strong>in</strong>s Late<br />
<strong>in</strong>terpreted to <strong>in</strong>dicate <strong>the</strong> presence <strong>of</strong> an Permian through Early to Middle <strong>Jurassic</strong><br />
arc as young as Middle <strong>Jurassic</strong> built <strong>in</strong> radiolarians, and Middle Permian and Late<br />
oceanic basement as old as Permian. Triassic conodonts (Irw<strong>in</strong> and o<strong>the</strong>rs, 1977,<br />
1982; L<strong>in</strong>dsley-Griff<strong>in</strong> and Griff<strong>in</strong>, 1983;<br />
North Fork UniT Mortimer, 1984). It <strong>in</strong>cludes fragments <strong>of</strong><br />
plagioclase, quartz, cl<strong>in</strong>opyroxene, brown<br />
The North Fork unit comprises up to 2 hornblende, chlorite, muscovite, and<br />
km <strong>of</strong> amygdaloidal volcanic rocks with rare carbonaceous material (Cox and Pratt, 1973;<br />
limestone layers and massifs (Ando, 1979; Wright, 1981). Sandstone and argillite<br />
Wright, 1981; Mortimer, 1984). It was turbidites <strong>in</strong>terlayered with <strong>the</strong> chert<br />
<strong>in</strong>itially <strong>in</strong>terpreted as oceanic crust conta<strong>in</strong> crystals <strong>of</strong> quartz, plagioclase, rare<br />
"jt,.c';""~'"'M__""'"*,\.""",",,,"~C"""'cccc c<br />
.<br />
I
potassium feldspar, and clasts <strong>of</strong> argillite, Earliest,<strong>Jurassic</strong> Events (-200 Ma)<br />
chert, recrystallized chert, mica schist,<br />
volcanic rock, and Permian McCloud limestone Recognition that volcanoplutonism <strong>of</strong><br />
(Fahan, 1982; wright, 1982; Gray, 1986). The earliest <strong>Jurassic</strong> time (-200 Ma) was<br />
composition and m<strong>in</strong>eralogy <strong>of</strong> <strong>the</strong> detritus widespread <strong>in</strong> <strong>the</strong> <strong>Klamath</strong> Mounta<strong>in</strong>s is an<br />
<strong>in</strong>dicates that <strong>the</strong> St Claire Creek unit is important contribution <strong>of</strong> this paper. Most<br />
native to <strong>the</strong> <strong>Klamath</strong>s and was derived from plutons <strong>of</strong> this age crop out <strong>in</strong> <strong>the</strong><br />
sources similar to those provid<strong>in</strong>g sediment Rattlesnake Creek terrane (Fig. 4a), where<br />
'to <strong>the</strong> Eastern Hayfork unit (Wright, 1982). <strong>the</strong>y range <strong>in</strong> zircon age from 192 to 212 Ma-with<br />
somewhat younger K/Ar hornblende ages<br />
Stuart Fork Terrane (Table 1, a1-a8). Plutons <strong>of</strong> probable pre-<br />
Middle <strong>Jurassic</strong> age also crop out <strong>in</strong> <strong>the</strong><br />
The Stuart Fork terrane is a subduction Salmon River unit <strong>of</strong> <strong>the</strong> Sawyers Bar terrane<br />
complex composed <strong>of</strong> hemipelagic shale, chert, (Cox, 1956; Ando and o<strong>the</strong>rs, 198:i), and one<br />
and basaltic rocks metamorphosed to <strong>of</strong> <strong>the</strong>se bodies at Horse Mounta<strong>in</strong> (Fig. 4a)<br />
blueschist facies dur<strong>in</strong>g Late Triassic time has been dated as 200 Ma (Table 1, 39). This<br />
(Hotz, 1977; Hotz and o<strong>the</strong>rs, 1977; Goodge, is significant, for it z;aises <strong>the</strong> possibility<br />
1989). Detrital feldspars <strong>in</strong> <strong>the</strong> sedimentary that plutonic and volcanic rocks <strong>in</strong> <strong>the</strong><br />
rocks <strong>in</strong>dicate proximity to a craton or Salmon River unit might be equivalent to <strong>the</strong><br />
magmatic arc. Trace element abundances coherent volcaniclastic section and <strong>in</strong>trud<strong>in</strong>g<br />
suggest that <strong>the</strong> volcanic rocks are back-arc plutons <strong>in</strong> <strong>the</strong> Rattlesnake Creek terrane.<br />
bas<strong>in</strong> basalts (Goodge, 1990). Trace-element abundances shown <strong>in</strong> Figure 3<br />
support this possibility. !'he Lems Ridge<br />
Eastern <strong>Klamath</strong> Terrane olistostrome, spatially associated with <strong>the</strong><br />
Joseph<strong>in</strong>e ophiolite, also conta<strong>in</strong>s gabbro<br />
The Eastern <strong>Klamath</strong> terrane conta<strong>in</strong>s clasts <strong>of</strong> this age, and may rest<br />
>10 km <strong>of</strong> Devonian to <strong>Jurassic</strong> sedimentary depositionally on -200 Ma basement as well<br />
and volcanic strata formed chiefly <strong>in</strong> an (Table 1, zll-z17; Ohr, 1987; Harper and<br />
<strong>in</strong>tra-oceanic arc. Rocks <strong>of</strong> Late Permian and o<strong>the</strong>rs, 1993). Roughly 200 Ma wetaplutonic<br />
possibly Early Triassic age are absent rocks <strong>in</strong> <strong>the</strong> Rogue/Chetco arc and Preston<br />
(Miller and Harwood, 1990). The Pit Peak ophiolite support <strong>the</strong> presence <strong>of</strong><br />
Formation <strong>of</strong> Early (Noble and Renne, 1990) to Rattlesnake Creek terrane as rift basement to<br />
Late Triassic (Albers and Robertson, 1961) those units as well (Table 1, a17-a22).<br />
age is composed <strong>of</strong> flows and tuffaceous rocks<br />
overla<strong>in</strong> by shales and chert (Sanborn, 1960; Western Hayfork Age Events (177-167 Ma)<br />
Noble and Renne, 1990). Upper Triassic<br />
(Carnian) Hosselkus Limestone and Brock Shale The hallmark volcanoplutonism <strong>of</strong> early<br />
record shallow-water and bas<strong>in</strong>al Middle <strong>Jurassic</strong> age is <strong>the</strong> Western Hayfork<br />
sedimentation with distal volcanic <strong>in</strong>put terrane (Fig. 4b). As discussed earlier,<br />
(Sanborn, 1960), whereas <strong>the</strong> Upper Triassic plutons <strong>in</strong> <strong>the</strong> Western Hayfork terrane proper<br />
(Rhaetian) Mod<strong>in</strong> Formation records <strong>the</strong> (<strong>the</strong> Ironside Mounta<strong>in</strong> suite) yield<br />
resumption <strong>of</strong> <strong>in</strong>flux <strong>of</strong> proximal volcanic crystallization ages <strong>of</strong> 169-171 Ma, and<br />
detritus (Miller and Harwood, 1990). An volcaniclastic rocks have K/Ar hornblende<br />
unconformity may (Sanborn, 1960) or may not ages <strong>of</strong> 168-177 Ma (Table 1, b1-b7). Plutons<br />
(Renne and Scott, 1988) be present below <strong>of</strong> similar composition and age outside <strong>the</strong><br />
pyroclastic beds and m<strong>in</strong>or flows <strong>of</strong> <strong>the</strong> Lower Western Hayfork terrane <strong>in</strong>clude <strong>the</strong> Denny<br />
<strong>Jurassic</strong> (Pliensbachian-S<strong>in</strong>emurian) Arvison Complex and Forks <strong>of</strong> Salmon pluton (Table 1,<br />
Formation. The Mesozoic section ends with b8-b9). Two dikes with<strong>in</strong> <strong>the</strong> Salmon River<br />
argillite and tuffaceous sandstone <strong>of</strong> <strong>the</strong> unit also fall <strong>in</strong> this category (Table 1,<br />
Lower to Middle (Bajocian-Toarcian) <strong>Jurassic</strong> b15-b16). This is significant, because<br />
Potem Formation (Sanborn, 1960). Fault<strong>in</strong>g hypabyssal and volcanic rocks <strong>in</strong> <strong>the</strong> Western<br />
and fold<strong>in</strong>g <strong>in</strong> <strong>the</strong> Eastern <strong>Klamath</strong> terrane Hayfork and Salmon River suites might thus be<br />
postdated deposition <strong>of</strong> Bajocian strata and part <strong>of</strong> <strong>the</strong> same volcanoplutonic arc. Figure<br />
predated -164-170 Ma plutons (Renne and 3 <strong>in</strong>dicates that hypabyssal rocks <strong>in</strong> <strong>the</strong><br />
Scott, 1988). Salmon River unit are <strong>in</strong>dist<strong>in</strong>guishable from<br />
<strong>the</strong> Western Hayfork terrane <strong>in</strong> trace-element<br />
VOLCANOPLUTONIC AND RELATED METAMORPHIC abundances. The 172-Ma Ch<strong>in</strong>a Peak dike<br />
EVENTS complex <strong>in</strong> <strong>the</strong> older Rattlesnake Creek<br />
terrane lies on strike with <strong>the</strong> Western<br />
<strong>Klamath</strong> igneous rocks have been grouped Hayfork volcanics--although it tends to be<br />
<strong>in</strong>to suites <strong>of</strong> different ?ge and composition more tholeiitic than typical Western Hayfork<br />
(Irw<strong>in</strong>, 1985a; Barnes and o<strong>the</strong>rs, 1992). rocks (Fig. 3). Igneous activity <strong>of</strong><br />
Figures 2 and 4 divide magmatic and equivalent age also occurred <strong>in</strong> ~he Condrey<br />
associated metamorphic activity <strong>in</strong>to dist<strong>in</strong>ct Mounta<strong>in</strong> and Eastern <strong>Klamath</strong> terranes (Table<br />
time frames for ease <strong>of</strong> discussion. 1, b10-b13).<br />
_.,-~ 'c,"c~-]~-, "'..'::::::<br />
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Wooley Creek/Western <strong>Klamath</strong> Events crystallization ages. Igneous bodies <strong>of</strong> this<br />
(167-159 Ma) age are generally restricted to <strong>the</strong><br />
westernmost <strong>Klamath</strong>s, and consist exclusively<br />
The Wooley Creek <strong>in</strong>trusive suite <strong>of</strong> dikes and small plutons (Table 1, el-e24;<br />
(Irw<strong>in</strong>, 1985a; Barnes and o<strong>the</strong>rs, 1992) Fig. 4e). Near concordance <strong>of</strong><br />
constitutes a group <strong>of</strong> granitic to gabbroic crystallization (zircon) and cool<strong>in</strong>g<br />
calc-alkal<strong>in</strong>e plutons (Sl<strong>in</strong>kard, Wooley (hornblende and mica) ages <strong>in</strong>dicate rapid<br />
Creek, English Peak, Russian Peak, and Vesa cool<strong>in</strong>g <strong>of</strong> <strong>the</strong>se plutons to -300°C with<strong>in</strong> 5<br />
Bluffs) that range <strong>in</strong> igneous crystallization m.y. after emplacement (Fig. 2). Metamorphic<br />
age from 165-159 Ma (Table 1, c2-c9; Fig. cool<strong>in</strong>g ages <strong>of</strong> 148-152 Ma from amphibolite-<br />
4c). Coeval volcanic rocks have not been facies rocks occur <strong>in</strong> <strong>the</strong> Joseph<strong>in</strong>e sole and<br />
recognized, but may <strong>in</strong>clude parts <strong>of</strong> <strong>the</strong> throughout <strong>the</strong> Rattlesnake Creek terrane<br />
Salmon River unit. The Hea<strong>the</strong>r Lake pluton's (Fig. 4e; Table 1, e25-e57). Many hornblende<br />
167-Ma Ar/Ar hornblende age suggests that it and mica Ar/Ar and K/Ar ages from <strong>the</strong><br />
too is part <strong>of</strong> this suite (Table 1, cl). Rattlesnake Creek terrane are concordant,<br />
Dikes <strong>in</strong> <strong>the</strong> North Fork and Salmon River suggest<strong>in</strong>g rapid cool<strong>in</strong>g <strong>of</strong> <strong>the</strong> metamorphic<br />
units also have comparable Ar/Ar hornblende rocks to -300°C. K/Ar ages <strong>in</strong>dicate that<br />
ages (Table 1, c24-c26). Irw<strong>in</strong> (1985a) several plutons <strong>of</strong> <strong>the</strong> Wooley Creek suite<br />
<strong>in</strong>cluded <strong>the</strong> Ashland pluton <strong>in</strong> <strong>the</strong> Wooley also cooled through amphibolite-facies<br />
Creek suite, but Ar/Ar ages suggest it may be conditions at this time (Fig. 2).<br />
younger. Volcanoplutonism <strong>of</strong> similar age<br />
occurred far<strong>the</strong>r west <strong>in</strong> <strong>the</strong> <strong>Klamath</strong> Cretaceous Events<br />
Mounta<strong>in</strong>s, <strong>in</strong>clud<strong>in</strong>g formation <strong>of</strong> <strong>the</strong> Preston<br />
Peak and Joseph<strong>in</strong>e ophiolites and <strong>the</strong> Latest <strong>Jurassic</strong> and earliest Cretaceous<br />
Rogue/Chetco arc (Table 1, cl0-c22). Igneous time saw a return to widely distributed<br />
activity <strong>of</strong> this age is restricted to a NW- magmatism (Fig. 4f). Many weakly<br />
trend<strong>in</strong>g corridor. Plutons and volcanic metamorphosed dikes and plutons <strong>of</strong> this age<br />
rocks <strong>in</strong> <strong>the</strong> corridor are elongate to <strong>the</strong> NE <strong>in</strong>trude <strong>the</strong> <strong>Klamath</strong> Mounta<strong>in</strong>s (Table 1, fland<br />
SW, suggest<strong>in</strong>g NW-SE subhorizontal f23). This has two significant implications:<br />
extension. The sou<strong>the</strong>rn edge <strong>of</strong> <strong>the</strong> extended not only did arc magmatism cont<strong>in</strong>ue until<br />
corridor is <strong>the</strong> Salmon tectonic l<strong>in</strong>e <strong>of</strong> Irw<strong>in</strong> approximately 135 Ma, but metamorphism <strong>of</strong> <strong>the</strong><br />
(1985a, 1989), but a nor<strong>the</strong>rn, potentially country rock probably lasted <strong>in</strong>to Early<br />
more convoluted, boundary has not been Cretaceous time (see also Harper and o<strong>the</strong>rs,<br />
recognized or named. Both boundaries were 1993). Additional evidence for significant<br />
presumably transfer zones accommodat<strong>in</strong>g heat retention <strong>in</strong>to Cretaceous time comes<br />
differential subhorizontal extension, as from <strong>the</strong> Condrey Mounta<strong>in</strong> terrane (Fig. 1),<br />
hypo<strong>the</strong>sized for <strong>the</strong> Garlock fault <strong>in</strong> which yielded muscovite K/Ar ages <strong>of</strong> 125-143<br />
sou<strong>the</strong>rn California (Davis and Burchfiel, Ma and Rb-Sr isochron ages <strong>of</strong> 125-139 Ma<br />
1973). This hypo<strong>the</strong>sis might be tested by (Helper and o<strong>the</strong>rs, 1989).<br />
measur<strong>in</strong>g <strong>the</strong> orientation <strong>of</strong> comagmatic dikes<br />
associated with calc-alkal<strong>in</strong>e plutons <strong>in</strong> <strong>the</strong> DEFORMATION<br />
corridor and by <strong>in</strong>vestigat<strong>in</strong>g <strong>the</strong> structure<br />
<strong>of</strong> <strong>the</strong> Salmon tectonic l<strong>in</strong>e. Intraterrane deformation reveals<br />
aspects <strong>of</strong> <strong>the</strong> tectonic sett<strong>in</strong>g <strong>of</strong> <strong>in</strong>dividual<br />
Late <strong>Jurassic</strong> Events (-155 Ma) units, whereas <strong>in</strong>terterrane deformation<br />
provides <strong>in</strong>formation about <strong>the</strong> large-scale<br />
Plutonic and volcanic rocks <strong>of</strong> -155 Ma construction <strong>of</strong> <strong>the</strong> orogen. The emphasis<br />
are also restricted to a particular part <strong>of</strong> here is on <strong>the</strong> latter (Fig. 1). Motion on<br />
<strong>the</strong> <strong>Klamath</strong>s (Fig. 4d). The area is north <strong>of</strong> major faults structurally above <strong>the</strong><br />
slightly older Wooley Creek type events, Rattlesnake Creek terrane was Middle <strong>Jurassic</strong><br />
<strong>in</strong>dicat<strong>in</strong>g northward migration <strong>of</strong> magmatism (or earlier <strong>in</strong> <strong>the</strong> eastern <strong>Klamath</strong>s), whereas<br />
and cont<strong>in</strong>ued NW-directed extension. Rocks movement <strong>of</strong> faults far<strong>the</strong>r down section (more<br />
<strong>of</strong> this age <strong>in</strong>clude <strong>the</strong> Thompson Ridge westerly) was Late <strong>Jurassic</strong> (Wright and<br />
pluton, Grayback pluton, Ashland pluton, and Fahan, 1988; Harper and o<strong>the</strong>rs, 1993).<br />
Rum Creek metagabbro (Table 1, dl-d3, d13).<br />
Hypabyssal rocks <strong>of</strong> this age <strong>in</strong>trude <strong>the</strong> Displacement on <strong>the</strong> Siskiyou fault<br />
North Fork, Stuart Fork, Eastern Hayfork, placed <strong>the</strong> Central Metamorphic terrnne ~25 km<br />
Salmon River, Rogue, and Joseph<strong>in</strong>e units over <strong>the</strong> Stuart Fork and North Fork units<br />
(Table 1, d5-d13). The 155-Ma magmatism may (Davis and o<strong>the</strong>rs, 1965; Goodge, 1990).<br />
simply represent a northward shift <strong>of</strong> <strong>the</strong> Movement postdated deposition <strong>of</strong> Early to<br />
tectonic activity responsible for <strong>the</strong> Western Middle <strong>Jurassic</strong> chert <strong>in</strong> <strong>the</strong> North Fork unit<br />
<strong>Klamath</strong>/Wooley Creek magmatism. and predated emplacement <strong>of</strong> <strong>the</strong> 159-Ma<br />
Russian Peak pluton (Table 1, cl; Fig. 2).<br />
Latest <strong>Jurassic</strong> Events (-150 Ma)<br />
Displacement <strong>of</strong> <strong>the</strong> Stuart Fork terrane<br />
Yet ano<strong>the</strong>r notable change happened <strong>in</strong> over <strong>the</strong> Sawyers Bar terrane on <strong>the</strong> Soap<br />
<strong>the</strong> <strong>Klamath</strong> Mounta<strong>in</strong>s at 152-148 Ma, but <strong>in</strong> Creek Ridge thrust (Hotz, 1977) exceeds 35 km<br />
this case, <strong>the</strong> evidence comes from (Coleman and o<strong>the</strong>rs, 1988). Movement along<br />
metamorphic cool<strong>in</strong>g ages as well as from this fault predated cool<strong>in</strong>g <strong>of</strong> <strong>the</strong> Vesa<br />
, i<br />
"-,-c'"'-"'"<br />
I ,<br />
'_',,",H--"; cc'" -"",-"""~"~i,,t.,"" ,I '" "f, ,.,) ",jl' ,
Bluffs pluton at 165 Ma (Table 1, c9) and Ma, whereas Rb/Sr and K/Ar ages <strong>in</strong>dicate that<br />
postdated Middle <strong>Jurassic</strong> chert deposition <strong>the</strong> lower plate cooled through similar<br />
(Mortimer, 1984) <strong>in</strong> <strong>the</strong> footwall (Fig. 2). temperatures -20 Ma later (Helper and o<strong>the</strong>rs,<br />
These constra<strong>in</strong>ts, and those for <strong>the</strong> Siskiyou 1989). Rapid refrigeration <strong>of</strong> <strong>the</strong> upper<br />
fault, apply rigorously only to <strong>the</strong> central plate and prolonged cool<strong>in</strong>g <strong>of</strong> <strong>the</strong> lower<br />
<strong>Klamath</strong>s between about 41°N and 42°N. plate may be related to thrust<strong>in</strong>g <strong>of</strong> <strong>the</strong><br />
Condrey Mounta<strong>in</strong> terrane beneath <strong>the</strong><br />
Plutons <strong>of</strong> <strong>the</strong> Western Hayfork terrane Rattlesnake Creek terrane (Harper and o<strong>the</strong>rs,<br />
were crystalliz<strong>in</strong>g while that unit was thrust 1993).<br />
beneath <strong>the</strong> Sawyers Bar terrane along <strong>the</strong><br />
Wilson Po<strong>in</strong>t fault (Wright and Fahan, 1988), The Joseph<strong>in</strong>e ophiolite was thrust <strong>in</strong> a<br />
effectively constra<strong>in</strong><strong>in</strong>g <strong>the</strong> age <strong>of</strong> fault<strong>in</strong>g NNE direction over <strong>the</strong> still-active<br />
to -170 Ma (Fig. 2); displacement is at least Rogue/Chetco arc on <strong>the</strong> Madstone thrust<br />
20 km. between 146 and 152 Ma (Harper and o<strong>the</strong>rs,<br />
1990, 1993).<br />
The Salt Creek fault accommodated -60<br />
km <strong>of</strong> displacement <strong>of</strong> <strong>the</strong> Western Hayfork Most <strong>of</strong> <strong>the</strong> aforementioned faults are<br />
over <strong>the</strong> Rattlesnake Creek terrane (Coleman demonstrably thrust faults that place higher<br />
and o<strong>the</strong>rs, 1988), and postdated pressure and temperature rocks over lower<br />
crystallization <strong>of</strong> <strong>the</strong> 169 Ma Chanchelulla pressure and temperature assemblages. Some<br />
Peak pluton (Table 1, h4; Wright and Fahan, major faults <strong>in</strong> <strong>the</strong> Klamat~ Mounta<strong>in</strong>s,<br />
1988). The cessation <strong>of</strong> fault<strong>in</strong>g is not however, may have had normal-sense<br />
unambiguously constra<strong>in</strong>ed, but may have been displacement for at least part <strong>of</strong> <strong>the</strong>ir<br />
prior to crystallization <strong>of</strong> <strong>the</strong> Denny Complex history. In <strong>the</strong> Marble Mounta<strong>in</strong>s, <strong>the</strong><br />
at 167 Ma (Fig 4c; Wright and Fahan, 1988). typical north-south structural gra<strong>in</strong> <strong>of</strong><br />
These constra<strong>in</strong>ts, and those for <strong>the</strong> Wilson <strong>Klamath</strong> terranes is broken by an east-west<br />
Po<strong>in</strong>t fault, apply only to <strong>the</strong> <strong>Klamath</strong>s south trend<strong>in</strong>g contact between amphibolite-facies<br />
<strong>of</strong> about 41°N. Rattlesnake Creek terrane to <strong>the</strong> north and<br />
greenschist-facies Sawyers Bar terrane to <strong>the</strong><br />
The Rattlesnake Creek terrane south (Donato and o<strong>the</strong>rs, 1982). We<br />
(<strong>in</strong>clud<strong>in</strong>g <strong>the</strong> Preston Peak ophiolite) lies tentatively suggest that this structure, <strong>the</strong><br />
structurally above <strong>the</strong> Condrey Mounta<strong>in</strong> Marble Mounta<strong>in</strong>s fault (Hacker and o<strong>the</strong>rs,<br />
terrane along <strong>the</strong> Condrey fault, and on top 1992), is a south-dipp<strong>in</strong>g normal fault. The<br />
<strong>of</strong> <strong>the</strong> Joseph<strong>in</strong>e ophiolite and Galice Western Hayfork terrane, which is normally<br />
Formation along <strong>the</strong> Orleans fault. If <strong>the</strong> present as a thrust sheet between <strong>the</strong><br />
Orleans and Condrey faults are <strong>the</strong> same Rattlesnake Creek and Sawyers Bar terranes,<br />
structure, model<strong>in</strong>g <strong>of</strong> gravity data <strong>in</strong>dicates appears to have been excised along this<br />
that <strong>the</strong> Orleans/Condrey fault dips 10-25° structure; thus -5 km <strong>of</strong> structural thickness<br />
east and has -100 km <strong>of</strong> displacement (Jachens may have been cut out. In addition to<br />
and o<strong>the</strong>rs, 1986). Displacement on <strong>the</strong> changes <strong>in</strong> rock type and metamorphic grade,<br />
Orleans fault was toward <strong>the</strong> WNW, occurred <strong>the</strong> fault is marked by changes <strong>in</strong> foliation<br />
prior to crystallization <strong>of</strong> <strong>the</strong> 150-Ma Summit orientation and Ar/Ar cool<strong>in</strong>g ages. Ar/Ar<br />
Valley pluton (Harper and o<strong>the</strong>rs, 1990), and hornblende, biotite, and muscovite<br />
must postdate <strong>the</strong> Kimmeridgian Galice metamorphic ages north <strong>of</strong> <strong>the</strong> fault cluster<br />
Formation <strong>in</strong> <strong>the</strong> footwall. The Condrey fault tightly between 148 and 152 Ma (Figs. 2 and<br />
places high-temperature rocks <strong>of</strong> <strong>the</strong> 4). South <strong>of</strong> <strong>the</strong> structure, Ar/Ar igneous<br />
Rattlesnake Creek terrane over low- ages range from 175 to 140 Ma, and resett<strong>in</strong>g<br />
temperature rocks <strong>of</strong> <strong>the</strong> Condrey Mounta<strong>in</strong> <strong>of</strong> Ar isotopes dur<strong>in</strong>g metamorphism is not<br />
terrane. The fault zone preserves a -l-km- apparent. Foliation undergoes a marked<br />
thick <strong>in</strong>verted metamorphic gradient from change from steep ESE dips south <strong>of</strong> <strong>the</strong> fault<br />
greenschist upward <strong>in</strong>to partially melted to gentle and moderate southward or eastward<br />
amphibolite (Medaris, 1966; Barrows, 1969; dips to <strong>the</strong> north (Welsh, 1982; Donato, 1985;<br />
Burton, 1982). Gravity measurements suggest Ernst, 1987; Hacker, unpublished data).<br />
that <strong>the</strong> Condrey fault detached <strong>the</strong> Wooley Rocks on both sides <strong>of</strong> <strong>the</strong> fault are <strong>in</strong>truded<br />
Creek, Sl<strong>in</strong>kard, and Vesa Bluffs plutons by greenschist-facies metatholeiitic dikes<br />
(Barnes,. 1982; Barnes and o<strong>the</strong>rs, 1986; (Donato, 1985) that must postdate 150-Ma<br />
Jachens and o<strong>the</strong>rs, 1986). Syn-thrust<strong>in</strong>g amphibolite-facies metamorphism. The Marble<br />
leucosomes formed at <strong>the</strong> base <strong>of</strong> <strong>the</strong> Mounta<strong>in</strong>s fault postdated 172 Ma dikes <strong>in</strong> <strong>the</strong><br />
Rattlesnake Creek terrane dur<strong>in</strong>g <strong>in</strong>trusion <strong>of</strong> Rattlesnake Creek terrane (Table 1, b14) and<br />
<strong>the</strong> Sl<strong>in</strong>kard pluton; this suggests active predated <strong>in</strong>trusion <strong>of</strong> <strong>the</strong> 161-Ma ~loo1ey Creek<br />
fault<strong>in</strong>g at 161 Ma (Saleeby, 1990). Gneissic batholith (Table 1, c6). If <strong>the</strong> Western<br />
amphibolite from with<strong>in</strong> <strong>the</strong> Condrey fault Hayfork terrane was excised along <strong>the</strong> fault,<br />
zone yielded an Ar/Ar hornblende cool<strong>in</strong>g age fault<strong>in</strong>g must also postdate that 167-170 Ma<br />
<strong>of</strong> 152z1 Ma, suggest<strong>in</strong>g that amphibolite- period <strong>of</strong> magmatism (Fig. 2). The Marble<br />
facies metamorphism and co<strong>in</strong>cident thrust<strong>in</strong>g Mounta<strong>in</strong>s fault may be exposed <strong>in</strong> more<br />
ended by that time (Harper and o<strong>the</strong>rs, 1993). nor<strong>the</strong>rly parts <strong>of</strong> <strong>the</strong> <strong>Klamath</strong> Mounta<strong>in</strong>s too<br />
Widespread hornblende Ar/Ar and scattered (Fig. 4c).<br />
mica Ar/Ar ages <strong>in</strong> <strong>the</strong> upper plate <strong>of</strong> <strong>the</strong><br />
Condrey thrust suggest rapid cool<strong>in</strong>g at -150<br />
;: 1 "/, l,:'"'::"""f=~
SISKIYOU AND NEVADAN OROGENIES metamorphic ,pressures (Burton, 1982;<br />
Chambers, 1983; Rawson, 1984; Barnes and<br />
Lower Cretaceous sedimentary rocks o<strong>the</strong>rs, 1986; Lieberman and Rice, 1986;<br />
overly<strong>in</strong>g deformed Upper <strong>Jurassic</strong> rocks led Donato, 1989) substantiate <strong>the</strong> suggestion<br />
Blackwelder (1914) to suggest that a that <strong>the</strong> Siskiyou event occur~-ed with<strong>in</strong> an<br />
"Nevadian" <strong>orogeny</strong> affected <strong>the</strong> Sierra Nevada active magmatic arc (Coleman and o<strong>the</strong>rs,<br />
and <strong>Klamath</strong> Mounta<strong>in</strong>s. The Nevadan <strong>orogeny</strong> 1988).<br />
<strong>in</strong> <strong>the</strong> <strong>Klamath</strong>s <strong>in</strong>volved thrust<strong>in</strong>g along <strong>the</strong><br />
Madstone and Orleans faults (Harper and The Siskiyou metamorphic event can no<br />
o<strong>the</strong>rs 1990), deformation <strong>of</strong> Galice longer be conveniently pigeonholed <strong>in</strong>to a<br />
Formation as young as Kimmeridgian, and narrow time frame--<strong>the</strong> advectively supplied<br />
widespread metamorphism (Donato, 1985; Hill, heat requisite for metamorphism was probably<br />
1985). The m<strong>in</strong>imum age <strong>of</strong> <strong>the</strong> Nevadan spatially and temporally variable, as befits<br />
<strong>orogeny</strong> is -130 Ma, based on undeformed igneous activity <strong>in</strong> an arc. For example,<br />
Valang<strong>in</strong>ian sedimentary rocks that overlie amphibolite-facies metamorphism probably<br />
metamorphosed units (H<strong>in</strong>ds, 1934; Sliter and began at 167 Ma around <strong>the</strong> Hea<strong>the</strong>r Lake<br />
o<strong>the</strong>rs, 1984; Blake and o<strong>the</strong>rs, 1985). H<strong>in</strong>ds pluton and perhaps as late as 161 Ma around<br />
(1934) considered all Nevadan activity to <strong>the</strong> Wooley Creek pluton, but <strong>the</strong> area<br />
postdate <strong>the</strong> Mariposa Formation <strong>in</strong> <strong>the</strong> Sierra immediately north <strong>of</strong> both igneous bodies<br />
Nevada. The Galice Formation, <strong>the</strong> <strong>Klamath</strong> rema<strong>in</strong>ed above greenschist facies<br />
equivalent <strong>of</strong> <strong>the</strong> Mariposa, is as young as temperatures until 150 Ma. South <strong>of</strong> <strong>the</strong><br />
Kimmeridgian (pessagno and Blome, 1990); this Salmon tectonic l<strong>in</strong>e (Fig. 4c), <strong>the</strong> Siskiyou<br />
would bracket <strong>the</strong> age <strong>of</strong> <strong>orogeny</strong> as -155-130 event apparently was restricted to <strong>the</strong> time<br />
Ma. When isotopic data were first collected <strong>of</strong> Western Hayfork magmatism, or -167-170 Ma<br />
(Lanphere and o<strong>the</strong>rs, 1968), however, it (Wyld and Wright, 1988). North <strong>of</strong> <strong>the</strong> Salmon<br />
became clear that plutons <strong>in</strong>itially deemed tectonic l<strong>in</strong>e, <strong>the</strong> Siskiyou event lasted<br />
part <strong>of</strong> <strong>the</strong> Nevadan <strong>orogeny</strong> (H<strong>in</strong>ds, 1934) longer due to <strong>the</strong> heat provided by numerous<br />
were as old as Middle <strong>Jurassic</strong>. Lanphere and Middle and Late <strong>Jurassic</strong> plutons. Note that<br />
o<strong>the</strong>rs thus pushed <strong>the</strong> age <strong>of</strong> <strong>the</strong> Nevadan this north-south difference <strong>in</strong> <strong>the</strong> Siskiyou<br />
<strong>orogeny</strong> back to Middle <strong>Jurassic</strong>. Harper and event may be due to <strong>the</strong> exposure <strong>of</strong> deeper<br />
Wright (1984) <strong>in</strong>itially bracketed <strong>the</strong> age <strong>of</strong> structural levels <strong>in</strong> <strong>the</strong> north, ra<strong>the</strong>r than<br />
<strong>the</strong> Nevadan <strong>orogeny</strong> between 147 and 150 Ma on to any contrast <strong>in</strong> magmatic activity.<br />
<strong>the</strong> basis <strong>of</strong> deformed dikes <strong>in</strong> <strong>the</strong> Galice<br />
Formation as young as 150 Ma, and undeformed Thus, at this time, it seems<br />
plutons as old as 147 Ma. More recently, appropriate to abandon attempts to date <strong>the</strong><br />
(Harper and o<strong>the</strong>rs, 1993) extended <strong>the</strong> "Nevadan" and "Siskiyou" orogenies as though<br />
Nevadan <strong>orogeny</strong> to 135 Ma, based on cool<strong>in</strong>g <strong>the</strong>y were dist<strong>in</strong>ct <strong>the</strong>rmotectonic events that<br />
ages <strong>of</strong> deformed plutons and dikes. occurred synchronously throughout <strong>the</strong><br />
mounta<strong>in</strong> range, and to focus <strong>in</strong>stead on<br />
There is also evidence <strong>of</strong> metamorphism characteriz<strong>in</strong>g <strong>the</strong> ages and o<strong>the</strong>r<br />
and deformation <strong>in</strong> <strong>the</strong> <strong>Klamath</strong>s well before characteristics <strong>of</strong> <strong>the</strong> deformation,<br />
<strong>the</strong> Nevadan <strong>orogeny</strong> (Wright and Fahan, 1988). metamorphism, and volcanoplutonism <strong>in</strong><br />
Coleman and o<strong>the</strong>rs (1988) noted that different areas. It seems most likely that<br />
greenschist to amphibolite-facies rocks <strong>the</strong> "ages" <strong>of</strong> <strong>the</strong> Siskiyou and Nevadan<br />
stretch<strong>in</strong>g from <strong>the</strong> Soap Creek Ridge fault to orogenies are spatially variable and related<br />
<strong>the</strong> Orleans fault appear to be overpr<strong>in</strong>ted by to areas <strong>of</strong> <strong>in</strong>tense plutonism.<br />
aureoles <strong>of</strong> plutons such as <strong>the</strong> Wooley Creek,<br />
Vesa Bluffs, and Hea<strong>the</strong>r Lake, imply<strong>in</strong>g that REVISED TECTONIC HISTOkY<br />
a regiondl metamorphic event occurred prior<br />
to 167 Ma. They named this regional Although Davis and o<strong>the</strong>rs (1978)<br />
metamorphism <strong>the</strong> Siskiyou event. The Western cautioned aga<strong>in</strong>st fitt<strong>in</strong>g <strong>Klamath</strong> terranes<br />
Hayfork and Rattlesnake Creek terranes were <strong>in</strong>to a coherent plate tectonic sett<strong>in</strong>g,<br />
both affected by Siskiyou metamorphism, thus shortly <strong>the</strong>reafter Burchfiel and Davis (1981)<br />
<strong>the</strong>ir 168-170 Ma protolith ages (Table 1, b1- suggested that <strong>the</strong> Eastern Hayfork unit<br />
b7, b14) apparently constra<strong>in</strong> <strong>the</strong> Siskiyou formed <strong>in</strong> an accretionary wedge outboard <strong>of</strong><br />
event to 167-170 Ma. For this reason, K/Ar <strong>the</strong> Jura-Triassic volcanoplutonic arc <strong>in</strong> <strong>the</strong><br />
hornblende ages on amphibolite <strong>of</strong> -150 Ma eastern <strong>Klamath</strong>s. Wright (1981) added<br />
obta<strong>in</strong>ed by Lanphere and o<strong>the</strong>rs (1968) (Table fur<strong>the</strong>r <strong>the</strong> idea that <strong>the</strong> North Fork unit<br />
1, e4-e41) were discounted by Coleman and might represent fore-arc igneous crust and<br />
o<strong>the</strong>rs (1988) as too young. The large region sediments. This tectonic sett<strong>in</strong>g has been<br />
<strong>of</strong> 150 Ma cool<strong>in</strong>g ages reviewed <strong>in</strong> this paper modified slightly to <strong>in</strong>clude <strong>the</strong> Stuart Fork<br />
(Table 1, e25-e57) <strong>in</strong>dicate, however, that terrane as a somewhat older subduction<br />
"Siskiyou" metamorphic rocks rema<strong>in</strong>ed at complex (Goodge, 1990). Hacker and o<strong>the</strong>rs<br />
amphibolite-facies conditions well <strong>in</strong>to <strong>the</strong> (1993) proposed that <strong>the</strong> North Fork and<br />
Late <strong>Jurassic</strong>--about 10-20 m.y. after Salmon River units toge<strong>the</strong>r represent an<br />
crystallization <strong>of</strong> <strong>the</strong> supposedly post- immature magmatic arc.<br />
metamorphic Wooley Creek plutonic suite.<br />
These age relationships between plutons and Prior to Triassic time, radiolarians<br />
regional metamorphism and <strong>the</strong> low to moderate were deposited <strong>in</strong> <strong>the</strong> St Claire Creek unit<br />
c,~.."",.L""c'.""'-'_""i.d","~."..l.1 I ,ii,;, ;,<br />
.<br />
I
and plagiogranite crystallized <strong>in</strong> <strong>the</strong> Salmon fault was active at-this time, and <strong>the</strong> Salt<br />
River unit or its ophiolitic basement Creek, Soap Creek, Ridge, and Siskiyou faults<br />
(Sawyers Bar terrane). High-pressure may have been mov~ng as well.<br />
metamorphism<br />
terrane at<br />
occurred<br />
-219 Ma,<br />
<strong>in</strong> <strong>the</strong> Stuart<br />
and contemporaneous<br />
Fork<br />
1<br />
y,<br />
" -167-155 Ma<br />
radiolarians were deposited<br />
Hayfork and St Claire Creek<br />
<strong>in</strong> <strong>the</strong><br />
units.<br />
Eastern<br />
Melange Rift<strong>in</strong>g with<strong>in</strong> <strong>the</strong> Rattlesnake Creek<br />
formation <strong>in</strong> <strong>the</strong> Rattlesnake Creek terrane terrane led to formation <strong>of</strong> <strong>the</strong> Rogue/Chetco<br />
was followed by arc plutonism and volcanism arc and <strong>the</strong> <strong>in</strong>tra-arc prest?n Peak and<br />
that postdated Late Triassic limestone and Joseph<strong>in</strong>e ophiolites over <strong>the</strong> ~nterval 165predated<br />
212 Ma plutons. The North Fork, 160 Ma (Harper and wright, 1984; Wyld and<br />
Eastern Hayfork, and Western Hayfork units Wright, 1988; Harper and o<strong>the</strong>rs, 1990;<br />
conta<strong>in</strong> similar fossils and epiclastic rocks Saleeby, 1990). Contemporaneous with this<br />
<strong>of</strong> similar provenance-a persuasive was emplacement <strong>of</strong> <strong>the</strong> Wooley Creek suite and<br />
<strong>in</strong>dication that <strong>the</strong>y are not far traveled dike <strong>in</strong>trusion <strong>in</strong> <strong>the</strong> Sawyers Bar terrane<br />
(Wright, 1982). (Fig. 2). Large-scale NW-SE extension may<br />
have been accommodated by normal faults such<br />
-200 Ma as <strong>the</strong> Marble Mounta<strong>in</strong>s fault. 7he zone <strong>of</strong><br />
magmatic extension is apparently bounded on<br />
At roughly 200 Ma (earliest <strong>Jurassic</strong> <strong>the</strong> south by <strong>the</strong> Salmon tectonic l<strong>in</strong>e--a<br />
time), gabbroic plutons crystallized <strong>in</strong>- <strong>the</strong> cryptic, poorly def<strong>in</strong>ed feature named by<br />
Salmon River and Rattlesnake Creek units Irw<strong>in</strong> (1985a). Displacement on this feature<br />
co<strong>in</strong>cident with radiolarian deposition <strong>in</strong> <strong>the</strong> should- <strong>in</strong>crease from zero at its eastern end<br />
Eastern Hayfork and St Claire Creek units. to a maximum at its western end, expla<strong>in</strong><strong>in</strong>g<br />
The presence <strong>of</strong> -200 Ma plutons and <strong>the</strong> puzzl<strong>in</strong>g nature <strong>of</strong> <strong>the</strong> eastern end <strong>of</strong> <strong>the</strong><br />
associated volcanic rocks <strong>in</strong> <strong>the</strong> Rattlesnake feature noted by Irw<strong>in</strong> (Irw<strong>in</strong>, 1989). It is<br />
Creek and Salmon River units raises <strong>the</strong> possible that many contractional faults such<br />
possibility that <strong>the</strong>se now-separated units as Salt Creek, Soap Creek Ridge, Condrey, and<br />
were once contiguous--or at least Siskiyou faults may have been <strong>in</strong> motion<br />
tectonically related. The 200-Ma plutons <strong>in</strong> dur<strong>in</strong>g this same time frame.<br />
<strong>the</strong> Rattlesnake Creek terrane <strong>in</strong>trude an<br />
older basement <strong>of</strong> serpent<strong>in</strong>ite-matrix melange Recorded igneous activity <strong>in</strong> <strong>the</strong><br />
and volcaniclastic rocks. Coeval plutons <strong>in</strong> Joseph<strong>in</strong>e ophiolite ceased, and Galice flysch<br />
<strong>the</strong> Salmon River unit <strong>in</strong>trude diabase ra<strong>the</strong>r blanketed <strong>the</strong> Western <strong>Klamath</strong> terrane from<br />
than melange or volcaniclastic rocks, but -157-150 Ma, dur<strong>in</strong>g cont<strong>in</strong>ued activity <strong>in</strong> <strong>the</strong><br />
serpent<strong>in</strong>ite and mafic volcanic rocks are Rogue/Chetco arc. Far<strong>the</strong>r east <strong>in</strong> <strong>the</strong><br />
abundant nearby. Moreover, a Permo-Triassic central <strong>Klamath</strong>s, magmatism (Grayback,<br />
zircon age obta<strong>in</strong>ed from <strong>the</strong> Salmon River Thompson Ridge, Ashland plutons) shifted<br />
unit (Ando and o<strong>the</strong>rs, 1983) demonstrates northward from <strong>the</strong> region encompassed by <strong>the</strong><br />
that basement rocks older than 200 Ma are Wooley Creek suite, but covered <strong>the</strong> same<br />
present. If portions <strong>of</strong> <strong>the</strong> Rattlesnake east-west extent.<br />
Creek and Salmon River units represent a<br />
once-coherent, s<strong>in</strong>gle, -200 Ma arc, <strong>the</strong> -150 Ma<br />
presence <strong>of</strong> <strong>in</strong>terven<strong>in</strong>g Late Permian to Late<br />
Triassic Eastern Hayfork sedimentary rock Widespread contraction occurred aga<strong>in</strong><br />
mandates significant structural disruption. from about 155 to 146 Ma (Harper and Wright,<br />
It is unclear how volcanic rocks <strong>of</strong> 1984; Harper and o<strong>the</strong>rs, 1990). The still<br />
equivalent age <strong>in</strong> <strong>the</strong> Eastern <strong>Klamath</strong> terrane active Rogue/Chetco arc was thrust beneath<br />
are related to ei<strong>the</strong>r <strong>the</strong> Salmon River or <strong>the</strong> Joseph<strong>in</strong>e ophiolite along <strong>the</strong> Madstone<br />
Rattlesnake Creek units. thrust. The Joseph<strong>in</strong>e ophiolite, Galice<br />
Formation and Condrey Mounta<strong>in</strong> terrane were<br />
-170 Ma telescoped beneath <strong>the</strong> Rattlesnake Creek<br />
along <strong>the</strong> Condrey fault (Harper and Wright,<br />
At 177-169 Ma, <strong>the</strong> Western Hayfork arc 1984). The widespread -150 Ma coQl<strong>in</strong>g event<br />
formed; <strong>the</strong> basement <strong>of</strong> <strong>the</strong> Western Hayfork may be related to <strong>the</strong> onset <strong>of</strong> this thrust<strong>in</strong>g<br />
sensu stricto may have been <strong>the</strong> Rattlesnake (Harper and o<strong>the</strong>rs, 1993). Recognition <strong>of</strong><br />
Creek terrane (Wright and Fahan, 1988). cool<strong>in</strong>g <strong>in</strong> <strong>the</strong> Western <strong>Klamath</strong> terrane as<br />
Mafic igneous rocks <strong>of</strong> this age <strong>in</strong>trude <strong>the</strong> well as <strong>in</strong> <strong>the</strong> Rattlesnake Creek terrane at<br />
Eastern Hayfork, Condrey Mounta<strong>in</strong>, and this time suggests that <strong>the</strong> Condrey Mounta<strong>in</strong><br />
Rattlesnake Creek units, and may make up a terrane may have been subducted beneath <strong>the</strong><br />
large part <strong>of</strong> <strong>the</strong> Salmon River extrusive Western <strong>Klamath</strong> terrane.<br />
rocks. Moreover, <strong>the</strong> last phase <strong>of</strong> plutonism<br />
occurred <strong>in</strong> <strong>the</strong> eastern <strong>Klamath</strong> terrane at Cretaceous<br />
this time. The relationship between <strong>the</strong>se<br />
three Jura-Triassic magmatic events is a Volumetrically m<strong>in</strong>or arc magmati5m and<br />
conundrum, although <strong>the</strong> Middle Juras5ic m<strong>in</strong>or deformation lasted <strong>in</strong> <strong>the</strong> <strong>Klamath</strong><br />
<strong>in</strong>trusions <strong>in</strong> <strong>the</strong> Eastern <strong>Klamath</strong> terrane do orogen until 135 Ma, and was followed by<br />
not have arc-like trace-element compositions exhumation and post-orogenic sedimentation<br />
(Renne and Scott, 1988). The Wilson Po<strong>in</strong>t<br />
j;"'c!"'...c.l"""",*,"j.k..,.~,.;J." ,,: ::11';<br />
I
(Harper and Wright, 1984; Harper and o<strong>the</strong>rs, The Siskiyou and Nevadan orogenies car; .<br />
1993). no longer be 'assigned to specific, narrow<br />
time w<strong>in</strong>dows and may have outlived <strong>the</strong>ir<br />
CONCLUSIONS usefulness as currently def<strong>in</strong>ed.<br />
Geochronologic data are now numerous enough<br />
Abundant geochronologic <strong>in</strong>formation now to warrant def<strong>in</strong><strong>in</strong>g <strong>the</strong> ages and<br />
permits improved recognition <strong>of</strong> <strong>the</strong> spatial charact~ristic~ <strong>of</strong> specific. pl~tons,<br />
and temporal ranges <strong>of</strong> magmatic, metamorphic deformat~on fabr~cs, and metamorph~c m~nerals<br />
and deformational events associated with <strong>the</strong> <strong>in</strong> <strong>in</strong>dividual areas. Assumptions that<br />
formation <strong>of</strong> cont<strong>in</strong>ental crust <strong>in</strong> <strong>the</strong> <strong>Klamath</strong> metamorphism, deformation, and plutonism<br />
Mounta<strong>in</strong>s. Widespread magmatism began at occur throughout <strong>the</strong> <strong>Klamath</strong> o~ogen with<strong>in</strong><br />
-200 Ma. Two subparallel volcanoplutonic specific time ranges may no longer be valid.<br />
arcs were active around 170 Ma, and although<br />
probably related to one ano<strong>the</strong>r, <strong>the</strong>y are ACKNOWLEDGMENTS<br />
presently separated by an <strong>in</strong>terven<strong>in</strong>g and Our syn<strong>the</strong>sis relies heavily upon <strong>the</strong><br />
older accretionary wedge. From 167-159 Ma, earlier work <strong>of</strong> o<strong>the</strong>r geologists cited <strong>in</strong><br />
alternat<strong>in</strong>g extension and contraction Table 1. We have benefited from reviews by<br />
occurred along a NW-SE corridor <strong>in</strong> <strong>the</strong> Cal Barnes, Mary Donato, Greg Harper, and<br />
nor<strong>the</strong>rn <strong>Klamath</strong>s. Still to be determ<strong>in</strong>ed Dave Miller. Thanks to Mary Donato, Greg<br />
are details regard<strong>in</strong>g <strong>the</strong> relation between Harper, Jason Saleeby, and Doug Yule for<br />
contraction and extension and <strong>the</strong> ages and provid<strong>in</strong>g unpublished or <strong>in</strong> press radiometric<br />
senses <strong>of</strong> motion on major faults. This same data, and to Cal Barnes for provid<strong>in</strong>g rocks.<br />
area underwent pronounced cool<strong>in</strong>g at -150 Ma, This work was supported by <strong>Department</strong> <strong>of</strong><br />
perhaps as a result <strong>of</strong> deeper-level Energy grants DE-FGO3-90ER14154 and 8802-121.<br />
subduction.<br />
Table 1. Radiometric ages.<br />
Unit Age Intr:;des Reference [orig<strong>in</strong>al sample number]<br />
Figure 4A<br />
a1 Saddle Gulch pluton h 189:f:6 RC M.A. Lanphere <strong>in</strong> Irw<strong>in</strong> (1985a) ['?]<br />
a2 Bear Wallow pluton Z 193:f:? RC Wright (1981) [B~lJ<br />
a3 White Rock pluton (CA) Z 193:f:? RC Wright (1981) [WR-1J<br />
a4 Pole Corral Cr. pluton Z 198:f:? RC Wright (1981) [PCCKJ<br />
a5 Beegum pluton Z 207:f:? RC Wright (1981) [Beegum)<br />
a6 Rat Trap Ridge pluton Z 204t'? RC Wright (1981) [RT1)<br />
a7 "Somes Bar" pluton Z 208.1t? 207.3t? RC Gray (1985) [OMG-1, DOMG-2)<br />
a7" h 191.5t4.5 RC Gray (1985) [OMG..1J<br />
a8 "Somes Bar" pluton Z 193.7:1:? RC Gray (1985) [SB-7M,?)<br />
a9 "Horse Mtn" pluton H 200. 4t1. 4 SR Hacker and o<strong>the</strong>rs (1993) [Yr13)<br />
a10 LR gabbro block H 192t9 Ohr (1987) [LR 10J<br />
all LR gabbro block H 190t9 Ohr (1987) [LR 171J<br />
a12 LR gabbro block H 191t4 Ohr (1987) [LR 871)<br />
a13 LR gabbro block H 196t3 Ohr (1987) [LR 1273)<br />
a14 LR gabbro block H 199t4 Ohr (1987) [LR 1573)<br />
a15 LR volcaniclastic H 191t5 Ohr (1987) [LR 15J<br />
a16 LR plagiogranite Z -198 Ohr (1987) [LR 41)<br />
a17 PP amphibolite h 193t7 Gorman (1985) [2KL-338)<br />
a18 PP amphibolite h 190t14 Gorman (1985) [2KL-353)<br />
a19 Rum Creek metagabbro h 182t12 H.J.B. Dick <strong>in</strong> Garcia (1982) ['?)<br />
a20 metadiabase <strong>in</strong> Chetco h 197z5 Dick (1976) [Jl15-1)<br />
a21 Chetco metagabbro h 191:1:7 Dick (1976) [J103-19J<br />
a22 Chetco metagabbro h 202t17 Dick (1976) [J92-4)<br />
a23 blueschist chert block w 185t9 Irw<strong>in</strong> and o<strong>the</strong>rs (1985b) ['?)<br />
Figure 48<br />
bl Walker Po<strong>in</strong>t pluton Z -169 WH Wright and Fahan (1988) [WP-1J<br />
b2 Chanchelulla Pk pluton Z -169 WH EH Wright and Fahan (1988) [CP-2J<br />
b3 Bas<strong>in</strong> Gulch pluton Z -170 WH Wright and Fahan (1988) [BG-'lJ<br />
b4 Price Creek pluton Z -170 WH Wright and Fahan (1988) [89-1]<br />
b5 Ironside Mtn batholith Z 170t1 WH Wright and Fahan (1988) [IR-1, 2J<br />
b5" b 171t5 169t5 WH Lanphere and o<strong>the</strong>rs (1968) [65CLe 29,<br />
65CLe 33J<br />
b6 Pigeon Pt pluton h 169:1:1.2 171:1:1.8 WH Wright and Fahan (1988) [1058-184,<br />
1058-188J<br />
b6 Pigeon Pt aureole h 168:1:3.4 WH Wright and Fahan (1988) [1058-27)<br />
b7 WH volcaniclastics h 168t1.9 171t2.0 177t2.8 Wright and Fahan (1988) [16-109,<br />
1058-24, 1058-167)<br />
b8 Denny complex Z -167 EH Wright and Fahan (1988) [DC-1J<br />
b9 Forks <strong>of</strong> Salmon pluton Z -174 EH Wright and Fahan (1988) [FS-3J<br />
b9 t, h 171t5 EH Lanphere and o<strong>the</strong>rs (1968) [65CLe 17J<br />
L / "",.1 u "..
Table 1 cont<strong>in</strong>ued.<br />
bl0 CMS metagranodiorite Z 170tl CMS Saleeby and Harper (1993) [?]<br />
bll CMS orthogneiss Z 172t2 (n=2) CMS Helper and o<strong>the</strong>rs (1989) [?]<br />
bll " Rb/Sr 136-165 (n=3) CMS Helper and o<strong>the</strong>rs (1989) [?]<br />
bll" m 141-152 (n=5) CMS Helper and o<strong>the</strong>rs (1989) [?]<br />
b12 CMS metavolcanic Z 170tl CMS Helper and o<strong>the</strong>rs (1989) [?]<br />
b13 Hogback Mtn plutons p -169t5 (n=4) EK Renne and Scott (1988) [HMS]<br />
b14 "Ch<strong>in</strong>a Pk" dike complex Z 172t2 J.B. Saleeby <strong>in</strong> Hill (1985) [?]<br />
b15 Salmon River dike H 173.2t3.7 SR B.R. Hacker (unpub. data) [220M]<br />
b16 Salmon River dike H 174.6tl.3 SR B.R. Hacker (unpub. data) [190M]<br />
Figure 4C<br />
cl Hea<strong>the</strong>r Lake pluton<br />
c2 Russian Pk pluton<br />
H 167.0tO.6<br />
Z -159<br />
RC? EH SR<br />
NF SR SF<br />
B.R. Hacker (unpub. data) [Yr172]<br />
Wright and Fahan (1988) [RP-3, RPc2"<br />
c2"<br />
H 152.1tO.5<br />
b 144t2 147t2<br />
NF SR SF<br />
NF SR SF<br />
300]<br />
B.R. Hacker (unpub. data) [542M]<br />
Evernden and Kistler (1970) [KA955,<br />
c3 Sl<strong>in</strong>kard<br />
c3"<br />
pluton b 151t5<br />
h 157t5<br />
RC<br />
RC<br />
KA956]<br />
Lanphere and o<strong>the</strong>rs<br />
Lanphere and o<strong>the</strong>rs<br />
(1968) [66CLe 25]<br />
(1968) [66CLe 25]<br />
c3" Z 161=;4 RC Barnes and o<strong>the</strong>rs (Barnes .~nd o<strong>the</strong>rs,<br />
1986) [II, III, IV]<br />
c3" FTz 91:t10 RC Lewison (1984) (SL-10]<br />
c4 Sl<strong>in</strong>kard(?) pluton .H 156.2tO.7 RC Saleeby and Harper (Saleeby and<br />
c4" Z 160t2 RC<br />
Harper, 1993) [?]<br />
Saleeby and Harper (Saleeb~! and<br />
c5 RC leucosome<br />
c6 Wooley Creek pluton<br />
c6"<br />
Z 150-162<br />
h 156t5<br />
b 158t5 158t5<br />
WH EH RC<br />
WH EH RC<br />
Harper, 1993) [?]<br />
Saleeby and Harper (1993) [?]<br />
Lanphere and o<strong>the</strong>rs (1968) [66CLe 21]<br />
Lanphere and o<strong>the</strong>rs (1968) [66CLe 20,<br />
c6" Z 161_2 -+4<br />
WH EH RC<br />
66CLe 21]<br />
Barnes and o<strong>the</strong>rs (Barnes and o<strong>the</strong>rs,<br />
1986) [V,VI,VIII]<br />
c6" Z ~160 WH EH RC Wright and Fahan (1988) [WC-2]<br />
c6" FTz 91:t8, 94:t7 WH EH RC Lewison (1984) {WC1, WC3z]<br />
c6" FTa 22.2, 20.4:t3 WH EH RC Lewison (1984) [WC2, WC3a]<br />
c7 English Peak pluton Z ~164 EH NF SR Wright and Fahan (1988) [EP-l]<br />
c7" b 159t5 EH NF SR Lanphere and o<strong>the</strong>rs (1968) [66CLe 18]<br />
c7" h 161:t5 EH NF SR Lanphere and o<strong>the</strong>rs (1968) [66CLe 18]<br />
c7" H 154.5tl.4 EH NF SR M.M. Donato and C.G. Barnes (pers.<br />
comm., 1992) [EP176B]<br />
c7" B 154.3tO.8 EH NF SR B.R. Hacker (unpub. data) [365M]<br />
c7" H 153.3tO.3 EH NF SR B.R. Hacker (unpub. data) :365M]<br />
c7" H 160.4tl.4 EH NF SR B.R. Hacker (unpub. data) [EP141]<br />
c8 English Peak aureole H 162.6tl.4 EH NF SR B.R. Hacker (unpub. data) [506M]<br />
c9 Vesa Bluffs pluton H 165.1tO.4 RC EH NF SR B.R. Hacker (unpub. data) [FPV25]<br />
c9" M 148.2tO.3 RC EH NF SR B.R. Hacker (unpub. data) [FPV12]<br />
c9" h 164t4 RC EH NF SR Lanphere and o<strong>the</strong>rs (1968) [CM 29-60]<br />
c9" b 150t5 RC EH NF SR Lanphere and o<strong>the</strong>rs (1968) [CM 29-60]<br />
cl0 DE plagiogranite Z 164tl Wright and Wyld (1986) [DE-I, -2, -3]<br />
cll DE gabbroic clast H 160.5:t3.0 Harper and o<strong>the</strong>rs (1993) [OB-l]<br />
c12 DE gabbroic clast H 164.5t5.2 Harper and o<strong>the</strong>rs (1993) [OB-4]<br />
c13 JO plagiogranite Z 162tl Harper and o<strong>the</strong>rs (1993) [A88z]<br />
Saleeby and o<strong>the</strong>rs (1982)<br />
cI4 JO gabbro H 165.3:t3.5 Harper and o<strong>the</strong>rs (1993) [l':H-6]<br />
cIS Rogue tuff-breccia Z I57tI.5 Saleeby (1984) Harper and o<strong>the</strong>rs<br />
(1993) [?]<br />
c16 metagabbro <strong>in</strong> Rogue h 159t4 Dick (1976) [MGBSCS]<br />
c17 Rum Creek metagabbro Z 166t2? Saleeby (1984) Saleeby (1990) [?]<br />
c18 Chetco complex Z 155-160 (n=5) J.D. Yule (pers. comm., 1992) [?]<br />
c19 Chetco gabbro h 161t3 Dick (1976) [J69-3]<br />
c20 Chetco gabbro h 158t4 Dick (1976) [J94-8]<br />
c21 Preston Peak dike Z 164tl RC Saleeby and o<strong>the</strong>rs (1982)Saleeby<br />
(1990) [PP322]<br />
c22 Preston Peak aureole h I65t3 Saleeby and o<strong>the</strong>rs (1982) [PP580]<br />
c23 MC amphibolite H I62.0tl.4 M.M. Donato (pers. comm., 1992) [MC-<br />
154C-86]<br />
c24 dike cutt<strong>in</strong>g NF H I63.8tl.5 NF Hacker and o<strong>the</strong>rs (1993) [Yr84J<br />
c25 dike cutt<strong>in</strong>g NF H 164.8t2.2 NF B.R. Hacker (unpub. data) [601M]<br />
c26 dike cutt<strong>in</strong>g SR H 158.7t5.0 SR B.R. Hacker (unpub. data) [604M]<br />
c27 dike cutt<strong>in</strong>g JO h 163t5 JO Dick (1976) [J71-10] i<br />
c28 dike cutt<strong>in</strong>g JO h 158t3 JO Dick (1976) [J47-h]<br />
"""",11."_&"""",.;..,..""":::.,,,,,",;, ,.! ",:".,;,1111,
Table 1 cont<strong>in</strong>ued. ,c<br />
c29 dike cutt<strong>in</strong>g Rogue h 158t2 R Dick (1976) [J63-1]<br />
c30 dike cutt<strong>in</strong>g Rogue h 163t5 R Dick (1976) [J57-6]<br />
c31 dike cutt<strong>in</strong>g Rogue h 157t2 R Dick (1976) [J57-19]<br />
c31" b 125:t2 R Dick (1976) [J57-19]<br />
Figure 4D<br />
d1 Ashland pluton h 150z5 RC EH NF SR Lanphere and o<strong>the</strong>rs (1968) [CM77-63]<br />
d1" b 151:t5 136z4 RC EH NF SR Lanphere and o<strong>the</strong>rs (1968) [CM77-63,<br />
26-63]<br />
d1" h 170:t5 164z5 RC EH NF SR Hotz (1971) [46?]<br />
d1" b 147:t4 RC EH NF SR Hotz (1971) [46?]<br />
d1" h 155t? RC EH NF SR P.R. Renne (pers. comm., 1992) [?]<br />
d1" b 155t? RC EH NF SR P.R. Renne (pers. comm., 1992) [1]<br />
d1" H 152.2t1.2 RC EH NF SR M.M. Donato and C.G. Barnes (pers.<br />
comm., 1992) [AP48]<br />
d2 Thompson Ridge pluton H 153.2t1.2 RC B.R. Hacker (unpub. data) [TR4]<br />
d2 II H 153.0t1.0 RC B.R. Hacker (unpub. data) [TR16]<br />
d3 Grayback pluton H 157.3t1.4 RC AG M.M. Donato and C.G. Barnes (pers.<br />
comm., 1992) [GM24]<br />
d3" b 141:t4 RC AG Hotz (1971) [52]<br />
d3" h 153t5 153t5 RC AG Hotz (1971) [51, 52]<br />
d4 Russian Pk aureole H 154.0tO.8 NF SR B.R. Hacker (unpub. data) [584M]<br />
d5 dike cutt<strong>in</strong>g NF H 154.2tO.7 NF Hacker and o<strong>the</strong>rs (1993) [Yr19]<br />
d6 dike cutt<strong>in</strong>g SF H 155.9t1.6 SF Hacker and o<strong>the</strong>rs (1993) [Yr82]<br />
d7 dike cutt<strong>in</strong>g EH H 152.7tO.9 EH Hacker and o<strong>the</strong>rs (1993) [Yr61]<br />
d8 dike cutt<strong>in</strong>g SR H 155.5tO.7 SR Hacker and o<strong>the</strong>rs (1993) [448M]<br />
d9 dike cutt<strong>in</strong>g JO h 156t3 JO Dick (1976) [J123-2]<br />
d10 dike cutt<strong>in</strong>g JO h 156t12 JO Dick (1976) [J137-13]<br />
d11 dike cutt<strong>in</strong>g JO h 154t3 JO Dick (1976) [J41-d]<br />
d12 dike cutt<strong>in</strong>g Rogue h 154t2 R Dick (1976) [J61-9]<br />
d13 Rum Creek metagabbro Z 155t2 Saleeby (1984) [?]<br />
d14 Chetco gabbro h 154f5 Hotz (1971) [56]<br />
d15 Chetco gabbro(?) h 155t5 155f5 Hotz (1971) [1]<br />
d16 Chetco gabbro h 154t5 Hotz (1971) [57]<br />
d17 Briggs Cr amphibolite H 156.3tO.9 M.M. Donato (pers. comm., 1992) [216-<br />
GA-76]<br />
d18 MC amphibolite h 154t11 Kays and o<strong>the</strong>rs (1977) [T-112-70]<br />
d19 MC amphibolite H 154.2t2.1 M.M. Donato (pers. comm., 1992)<br />
d20 MC amphibolite H 153.3tO.8 M.M. Donato (pers. comm., 1992) [MC-<br />
41A-85]<br />
d21 MC amphibolite H 155.0t9.2 M.M. Donato (pers. comm., 1992) [MC-<br />
81A-85]<br />
Figure 4E<br />
e1 Bear Mounta<strong>in</strong> pluton Z 149-153 RC PP Saleeby and o<strong>the</strong>rs (1982) [PP567,<br />
PP572B]<br />
e1 II b 146f1 RC PP Snoke and o<strong>the</strong>rs (1981)<br />
e2 Ammon Ridge pluton Z 147-151 G Wright and Fahan (1988) [AR-1]<br />
e3 Glenn Creek pluton Z 147-151 G Wright and Fahan (1988) [GC-1]<br />
e4 Summit Valley pluton H 144.1fO.4 G RC Harper and o<strong>the</strong>rs (1993) [SV-1h]<br />
e4 II Z 150f1 G RC Harper and o<strong>the</strong>rs (1993) [4]<br />
e4 Summit V. pluton dike H 149f4 G RC Ohr (1987) [LR 82]<br />
e4 II H 148t1 G RC Ohr (1987) [D-LRO]<br />
e5 Bucksk<strong>in</strong> Peak pluton B 148.4tl.2 149.7tl.6 JO Harper and o<strong>the</strong>rs (1993) [66]<br />
e5" H 148.6t1.5 JO Harper and o<strong>the</strong>rs (1993) [66]<br />
e6 sill cutt<strong>in</strong>g G H 150.5t2.0 G Harper and o<strong>the</strong>rs (1993) [D24]<br />
e7 sill cutt<strong>in</strong>g G H 146.2f1.0 G Harper and o<strong>the</strong>rs (1993) [D26]<br />
e8 sill cutt<strong>in</strong>g G Z 150f2 G Saleeby and o<strong>the</strong>rs (1982) [PP582]<br />
e9 dike cutt<strong>in</strong>g G h 151t3 G Gray (1985) [LDB-9]<br />
e10 dike cutt<strong>in</strong>g JO H 148.9f2.6 JO Harper and o<strong>the</strong>rs (1993) [J98-12]<br />
e10" h 146z3 JO Dick (1976) [J98-12]<br />
ell dike cutt<strong>in</strong>g JO H 148.0f3.0 JO Harper and o<strong>the</strong>rs (1993) [J97-6]<br />
ell" h 151:t3 JO Dick (1976) [J97-6]<br />
e12 dike cutt<strong>in</strong>g JO h 147t6 JO Saleeby and o<strong>the</strong>rs (1982) [K20]<br />
e13 dike cutt<strong>in</strong>g JO Z 151t3 JO Saleeby and o<strong>the</strong>rs (1982) [C23]<br />
"e14 dike cutt<strong>in</strong>g JO h 150t3 JO Dick (1976) [J37-H]<br />
e1S dike cutt<strong>in</strong>g JO h 148t2 JO Dick (1976) [J39-B]<br />
e16 dike cutt<strong>in</strong>g JO h 150t3 JO Dick (1976) [J45-b]<br />
e17 dike cutt<strong>in</strong>g JO h 148t2 JO Dick (1976) [J49-j]<br />
"<br />
~".i-"",,-"""","--"~.c,...'(_."i",j.';.! :: " ,jj .11.<br />
~
.<br />
Table 1 cont<strong>in</strong>ued.<br />
e18 dike cutt<strong>in</strong>g JO h 146t2 JO Dick (1976) [J51-o]<br />
e19 dike cutt<strong>in</strong>g Rogue h 149t2 JO Dick (1976) [J61-3]<br />
e20 dike cutt<strong>in</strong>g Rogue h 147t3 JO Dick (1976) [J63-7]<br />
e21 dike cutt<strong>in</strong>g Rogue h 151t2 JO Dick (1976) [GFCJ]<br />
e21" b 124.t2 JO Dick (1976) [GFCJ]<br />
e22 dike cutt<strong>in</strong>g Rogue Z 151t2? R Saleeby (1984)Saleeby (1990) [?]<br />
e23 dike cutt<strong>in</strong>g SR H 149.3t1.7 SR Hacker and o<strong>the</strong>rs (1993) [Yr2]<br />
e24 dikes cutt<strong>in</strong>g EK w 149t6 (n=6) EK Brouxel and o<strong>the</strong>rs (1989)<br />
e25 JO s~le pegmatite Z 151t1 Harper and o<strong>the</strong>rs (1993) [5]<br />
e25 II M 146-150 Harper and o<strong>the</strong>rs (1993) [J113-7]<br />
e25" m 148.t3 Dick (1976) [Jl13-7]<br />
e26 JO sole metagabbro H 150.5t1.8 Harper and o<strong>the</strong>rs (1993) [J89-1]<br />
e26" h 154.t3 Dick (1976) [J89-1]<br />
e27 JO sole amphibolite H 152.8t1.7 Harper and o<strong>the</strong>rs (1993) [7-15-2k]<br />
e28 JO sole amphibolite H 151.9t1.8 Harper and o<strong>the</strong>rs (1993) [7-16-10b]<br />
e29 JO sole pegmatite m 148t3 Dick (1976) [J82-3]<br />
e30 JO sole amphibolite h 152t2 Dick (1976) [J87-6]<br />
e31 JO sole amphibolite w 148t2 Dick (1976) [Jl13-8]<br />
e32 Chetco metagabbro H 151.4t4.4 Harper and o<strong>the</strong>rs (1993) [LCHB]<br />
e32" h 156.t3 Dick (1976) [LCHB]<br />
e33 Pearsoll'Pk metagranite m 151t4.5 P.H. Hotz <strong>in</strong> Ramp (1984) [?]<br />
e34 RC amphibolite H 152t1 Saleeby and Harper (1993) [CMT-4a]<br />
e35 RC amphibolite h 148t3 Kays and o<strong>the</strong>rs (1977) [RdMtAg]<br />
e36 RC amphibolite H 153.0t2.2 M.M. Donato (pers. comm., 1992) [SV-<br />
1-85]<br />
e37 RC amphibolite H 146.9t2.1 M.M. Donato (pers. comm., 1992) [233-<br />
83]<br />
e38 RC amphibolite H 150.1t4.6 M.M. Donato (pers. comm., 1992) [GF-<br />
1-85]<br />
e39 RC amphibolite H 154.1t3.1 M.M. Donato (pers. comm., 1992)<br />
[MMD183-83]<br />
e40 RC amphibolite h 152t5 Lanphere and o<strong>the</strong>rs (1968) [CM 3-65]<br />
e41 RC amphibolite h 150t5 Lanphere and o<strong>the</strong>rs (1968) [CM 9-65]<br />
e42 RC amphibolite h 152.9t3.2 Gray (1985) [BM-120?]<br />
e43 RC amphibolite b 148t5 Welsh (1982)<br />
e44 RC amphibolite B 150.4tO.4 B.R. Hacker (unpub. data) [Yr131]<br />
e45 RC amphibolite B 148.8t2.6 B.R. Hacker (unpub. data) [Yr161]<br />
e46 RC amphibolite M 150.3tO.3 B.R. Hacker (unpub. data) [Yr179]<br />
e47 RC amphibolite H 147.8t2.3 B.R. Hacker (unpub. data) [Yr121]<br />
e48 RC amphibolite H 152.5t2.5 B.R. Hacker (unpub. data) [Yr165]<br />
e49 RC amphibolite H 152.1t4.7 B.R. Hacker (unpub. data) [Yr166]<br />
e50 RC amphibolite H 149.9tO.4 B.R. Hacker (unpub. data) [Yr151]<br />
e51 RC amphibolite H 150.3tO.6 B.R. Hacker (unpub. data) [Yr164]<br />
e52 RC amphibolite H 155-145 B.R. Hacker (unpub. data) [Yr157]<br />
e53 RC amphibolite H 150.8tO.6 B.R. Hacker (unpub. data) [Yr120]<br />
e54 RC amphibolite B 149.9tO.2 B.R. Hacker (unpub. data) [Yr154]<br />
e55 RC amphibolite h 146t? Welsh (1982)<br />
e56 RC amphibolite h 148t? Welsh (1982)<br />
e57 MC amphibolite B 147.8tO.7 M.M. Donato (pers. comm., 1992)<br />
[MC13B-87]<br />
I'iqure 41'<br />
f1 White Rock pluton (OR) b 141t4 MC G Hotz (1971) [54]<br />
f2 Grants Pass pluton h 139t4 G AG Hotz (1971) [53]<br />
f2" Z 139t2 G AG Harper and o<strong>the</strong>rs (1993) [1]<br />
f3 Gold Hill pluton b 145t4 AG Hotz (1971) [49]<br />
f3" h 142t4 AG Hotz (1971) [49]<br />
f4 Jacksonville pluton b 141t4 AG Hotz (1971) [48]<br />
f4" h 137t4 AG Hotz (1971) [48]<br />
f5 Bear Peak pluton h 142t? RC PP(?) C.G. Barnes (pers. comm., 1992) [?]<br />
f6 Coon Mtn complex Z 142t2 JO Saleeby and o<strong>the</strong>rs (1982) [J84z]<br />
f6" Z 145+1/-2 JO Harper and o<strong>the</strong>rs (1993) [2]<br />
f6" K 134.9tO.9 JO Harper and o<strong>the</strong>rs (1993, [J84z]<br />
f7 Pony Peak pluton Z 146t3 WH RC Harper and o<strong>the</strong>rs (1993) [3]<br />
f7" H 148. 5t2. 0 WH RC Harper and o<strong>the</strong>rs (1993) [K85-53]<br />
f7" H 147.9tO.1 WH RC Harper and o<strong>the</strong>rs (1993) [K85-26]<br />
f8 Yellow Butte pluton h 138t4 EK Hotz (1971) [?]<br />
f8" b 137t4 EK Hotz (1971) [7]<br />
£9 Craggy Peak pluton b 136t4 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 6]<br />
f10 Deadman Peak pluton Z 141-145 CMT SF Wright and Fahan (1988) [DP-1]<br />
f10" z 158.t6-167.t6 CMT SF Wright and Fahan (1988) [DP-1]<br />
f10" b 133t7 CMT SF Evernden and Kistler (1970) [RA957]<br />
;., uJicl.l ' "," ",'c<br />
i
Table 1 cont<strong>in</strong>ued. ,-<br />
f1C" H 136:1:2 CMT SF M.M. Donato and C.G. Barnes (pers.<br />
comrn., 1992) [DP353]<br />
f11 Caribou Mtn pluton b 136:1:? CMT Davis and o<strong>the</strong>rs (1965) [?]<br />
f11" H 138:1:2 CMT M.M. Donato and C.G. Barnes (pers.<br />
comm., 1992) [FPC10]<br />
f12 Sugar P<strong>in</strong>e pluton b 139:1:4 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 8]<br />
f12" h 137:1:4 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 8]<br />
f13 Horseshoe Lake pluton b 133:1:1 CMT Evernden and Kistler (1970) [KA828]<br />
f14 Canyon Creek pluton z 159z8 169z9 CMT Wright and Fahan (1988) [CC-1]<br />
f14" Z 141-145 CMT SF Wright and Fahan (1988) [CC-1]<br />
f15 East Fork pluton h 149:1:4 NF CMT M.A. Lanphere <strong>in</strong> Irw<strong>in</strong> (1985a) [?]<br />
f15" b 164z5 NF CMT M.A. Lanphere <strong>in</strong> Irw<strong>in</strong> (1985a) [?]<br />
f16 Shasta Bally batholith h 133:1:4 131:1:4 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 19,<br />
A-5]<br />
f16" b 130:1:4 134:1:4 135:1:4 EK Lanphere and o<strong>the</strong>rs (1968) '[65CLe 1,<br />
A-5, "Shasta Bally"]<br />
f16" Z 136:1:2 EK Lanphere and Jones (1978)<br />
f17 dike cutt<strong>in</strong>g NF h 134:1:2.1 NF Wright and Fahan (1988) [1058-158]<br />
f18 dike cutt<strong>in</strong>g WH h 134:1:1.4 WH Wright and Fahan (1988) [RCT-O]<br />
f19 dike cutt<strong>in</strong>g CMT h 136:1:1.5 CMT Wright and Fahan (1988) [1058-156]<br />
f20 dike cutt<strong>in</strong>g EH h 141:1:2.0 EH Wright and Fahan (1988) [1058-86]<br />
f21 dike cutt<strong>in</strong>g EH h 139:1:1.9 EH . Wright and Fahan (1988) [1058-127]<br />
f22 dike cutt<strong>in</strong>g SR H 142.6:1:1.7 SR Hacker and o<strong>the</strong>rs (1993) [Yr45]<br />
f23 dike cutt<strong>in</strong>g NF H 140.5:1:1.6 NF Hacker and o<strong>the</strong>rs (1993) [Yr52]<br />
f24 MC amphibolite H 145:1:7 Donato (1991) [152]<br />
f25 MC amphibolite H 145:1:2 Donato (1991) [158]<br />
f26 MC amphibolite H 145.4:1:7.3 M.M. Donato (pers. comrn., 1992)<br />
[MC152-86]<br />
f27 MC amphibolite H 144.7:1:2.1 M.M. Donato (pers. corom., 1992)<br />
[MC148-80]<br />
f28 MC amphibolite h 133:1:3 Kays and o<strong>the</strong>rs (1977) [T-42-68]<br />
f29 upper CMS Rb/Sr 134-139 (n=6) Helper and o<strong>the</strong>rs (1989) [?]<br />
f29" m 135-143 (n=6) Helper and o<strong>the</strong>rs (1989) [?]<br />
f30 CMS muscovite schist m 144:1:4 Lanphere and o<strong>the</strong>rs (1968) [CM 120f<br />
... f . 631<br />
Aq.. 0 Unc.rta~n S~qn~ ~canc.<br />
1 dike cutt<strong>in</strong>g JO k 25z0.5 JO Dick (1976) [J123-5]<br />
2 dike cutt<strong>in</strong>g JO h 85z1 JO Dick (1976) [J52-i]<br />
3 RC metadacite h 102z8 Welsh (1982)<br />
4 RC amphibolite h 118z8 Welsh (1982)<br />
5 MC amphibolite H 119.6z5.5 M.M. Donato (pers. comm., 1992) [MC-<br />
126-85]<br />
6 MC amphibolite H 125.4z2. 7 M.M. Donato (pers. comm., 1992) [MC-<br />
157-86]<br />
7 lower CMS RbISr 125-132 (n=5) Helper and o<strong>the</strong>rs (1989)?]<br />
7" m 125-134 (n=15) Helper and o<strong>the</strong>rs (1989)?]<br />
8 Bear Mounta<strong>in</strong> pluton h 129z4 RC PP Snoke and o<strong>the</strong>rs (1981)<br />
9 dike cutt<strong>in</strong>g JO h 130z8 JO Dick (1976) [J125-1]<br />
10 RC amphibolite h 131z8 Kays and o<strong>the</strong>rs (1977) [KTA-14-71]<br />
11 JO sole amphibolite h 138z5 Dick (1976) [J82-7]<br />
12 "Somes Bar" pluton h 142.2z5.8 RC Gray (1985) [KR-6]<br />
13 Chetco quartz diorite h 143z4 Hotz (1971) [58]<br />
14 dike cutt<strong>in</strong>g JO h 171z3 JO Dick (1976) [J39-A]<br />
15 dike cutt<strong>in</strong>g JO h 171z3 JO Dick (1976) [J119-2]<br />
16 dike cutt<strong>in</strong>g JO b 91z6 Dick (1976) [Jl19-2]<br />
17 Castle Crags b 162z5 167z5 132z4 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 1,<br />
65CLe 2, 65CLe 4]<br />
18 Castle Crags h 229z7 175z5 EK Lanphere and o<strong>the</strong>rs (1968) [65CLe 1,<br />
65CLe 4]<br />
19 Chetco metadiabase h 280z15 Dick (1976) [J90-7]<br />
20 Chetco(?) phyllonite w 236z5 282z6 Dick (1976) [J95-3]<br />
Quoted uncerta<strong>in</strong>ties are :1:10', except for Pb/U ages, which are :1:20'. Multiple analyses <strong>of</strong><br />
<strong>the</strong> same sample or pluton have <strong>the</strong> same number, "Intrudes" <strong>in</strong>dicates <strong>the</strong> host rock <strong>of</strong> plutons,<br />
dikes and sills. Italicized ages are not shown <strong>in</strong> Figure 4.<br />
Z: Pb/U zircon; z: Pb/Pb zircon; h: K/Ar hornblende; b: K/Ar biotite; k: K/Ar K-feldspar;<br />
p: K/Ar plagioclase; K: 40Ar/39Ar K-feldspar; M: 40Ar/39Ar muscovite; H: 40Ar/39Ar hornblende; B:<br />
40Ar/39Ar biotite; FTz: fission-track zircon; FTa: fission-track apatite.<br />
AG: Applegate terrane; CMS: Condrey Mounta<strong>in</strong> terrane; CMT: central Metamorphic terrane;<br />
DE: Devils Elbow remnant <strong>of</strong> Joseph<strong>in</strong>e ophiolite; EH: Eastern Hayfork unit; EK: Eastern <strong>Klamath</strong><br />
terrane; G: Galice Formation; JO: Joseph<strong>in</strong>e ophiolite; LR: Lems Ridge olistostrome; MC: May<br />
Creek terrane; NF: North Fork unit; RC: Rattlesnake Creek terrane; SF: Stuart Fork terrane; SR:<br />
Salmon River unit; WH: Western Hayfork terrane.<br />
'".c,.c':'.""", "..,*""""".,..."'",,"*ic',Ic, ,"II (, ",'"..,<br />
.<br />
I
- .<br />
REFERENCES CITED<br />
Albers, J.P. and Robertson, J.F.,<br />
Geology and ore deposits <strong>of</strong> East<br />
1961,<br />
Shasta<br />
Zimmerman, J.-L., 1989, Upper <strong>Jurassic</strong><br />
mafic magmatic rocks <strong>of</strong> <strong>the</strong> eastern<br />
<strong>Klamath</strong> Mounta<strong>in</strong>s, nor<strong>the</strong>rn California:<br />
Geol,ogy, v. 17, p. 273-2~6.<br />
copper-z<strong>in</strong>c district, Shasta County, B~rchf~el, B.C. and ,Dav~s, ~.A., 19~1,<br />
California: U.S. Geological Survey Triassic and Jurass~c tecton~c evolut~~n<br />
Pr<strong>of</strong>essional Paper 338, 107 p. <strong>of</strong> <strong>the</strong> <strong>Klamath</strong> Mts-Sierra Nevada geolog~c<br />
Ando, C.J., 1979, Structural and petrologic terrane,.i...n- W.G. Ernst, ed:, T,he<br />
analysis <strong>of</strong> <strong>the</strong> North Fork terrane central Geotectonic Development <strong>of</strong> Cal~forn~a:<br />
<strong>Klamath</strong> Mounta<strong>in</strong>s, California: Los Prentice-Hall, Rubey v. I, p. 50-70.<br />
Angeles, University <strong>of</strong> Sou<strong>the</strong>r,n Burton, W.C., 1982, Geology ,<strong>of</strong> th.e Scott Bar<br />
California,<br />
Ando, C.J.,<br />
(Ph.D.<br />
Irw<strong>in</strong>,<br />
dissertation],<br />
W.P., Jones,<br />
197 p.<br />
D.L., and<br />
Mounta<strong>in</strong>s,<br />
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