Spilite and Diabase, with Minor Chert, and (2) Piagogranite Hornblende Gabhro, Cum'ilate Gahbro An'3

AN ABSTRACT OF THE THESIS OF

SCOTT GARRET VAIL for thedegree of DOCTOR OFPHLLOSOPHT

in GEOLOGY presented on February 4, 1977

Title: GEOLOGY AND GEOCHEMISTRY OF THE OREGON

MOUNTAIN AREA, SOUTHWESTERN ORECON AND NORTHERN CALIFORNIA

Abstract approved: Signature redacted for privacy.

The Oregon MDuntain area contains ai oihiohic asernb.ee ef rocks which can he divided iato two majorzones on thea ci' iit1 ology:(1) spilite and diabase, with minor chert, and (2) piagogranite hornblende gabhro, cum'ilate gahbro an'3. cnmulatt ultramaficrccs The two zones have a total estimated thickness of ahcut 4. 6 kmThe lower contact of the cumulatezone is gradational into the 3osephi.ne Peridotite, an extensive body of alpine-type harzburgite, Thetipper- most spilites are depositionally overlain by the Galice Forma ien (Jurassic, Kimmeridgi.an). Rocks in the diabase-spilitezone have unde rgone metamorphism similar to sea -floor burial metancrphirn. Metamorphic grade progresses from zeolite facies through chlorite, epidote and actinolite zones of the greenschist facies to amphibolito facie s.Prehnite -purnpel]yite facie s me arnerphi sm has been superimposed on the lowest temperature assemblages. probably owing to later burial by- the Galice Formation. The plutonic zone consists of a sequence of ultramaEic and rnafic cumulate rocks which culminates in a residue of granophyric plagiogranite.Hornbiende gabbro, in part cumulate and in part intrusive, occurs near the top of the sequence. The Josephine Peridotite consists of olivine-rich harzburgite and minor amounts of dunite, chromitite and pyroxenite, all with tectonite textures.It is essentially indtmguishable from other occurrences of alpine-type harzburgite. The Galice Formation is predominantly slaty shale.Lithic graywacke and pebbly cong].omerate are volumetrically minor corn-- ponents. The gray-wacke contains abundant auartz,roicanic fr.agmens with minor feldspar, mafic minerals and metamorphic fragments which indicate a mixed continental and volcanic arc provenance. Rocks of the Oregon Mountain area chemicall'r resemble other well known and well studied ophiolites. Major eler.cert variations in the diabase-spilite zone are interpretable in terms of sea water inter-- acton with mid-ocean ridge tholeiite.Increases in 3iO, Na20, H2O and FeC and decreases in CaO and MgO relative to mid-ocean ridge hasaits were. observed in most specimens. Lrs consistent changes occur in K20, A1Z03, TiO. and MnO. Titanium and zirconirn abundances suggest affinities to mid- ocean ridge basalts, but there is some evidence of mobilization of these elements. Rare earth element distributions in rocks from the di.abase- spilite zone appear to have been generally unchanged during ineta- morphism although modification of Ce abundance has evidently occurred in one specimen. The distribution patterns are typicallfiat (La/Lu = 1- 1.5) with low abundances (ay. La = 15x chronditic abundance)indicating that basaltic rocks from the Oregon Mountain area have a.ffithties with mid-ocean ridge basalts and arc tholeiitcs. Theoretical models indicate that a 15 to 20 percent melt of mantle source rock with a REE abundances about 2 to 3 times those of chondrites is a reasonable mechanism to produce the observed REE distributions. The ophiolite exposed in the Oregon Mountain area apparently formed as oceanic crust in a marginal basin environment during Jurassic time prior to the Nevadan Orogeny. The marginal basin probably lay between the Rogue-Galice island arc and the western continental margin. Nevadan deformation telescoped the arc-marginal basin terrain and caused accretion of the Jurassic rocks onto the continental margin. Geology ard Geochemistry of the Oregon Mountain Area, Southwestern Oregon and Northern CaUfornia

by Scott Garret Vail

A. THE3iS submitted to Oregon State Univeri:y

in partial fulfillment of the requirements for the degree of Doctor of PhilosopI'r Completed Febr;ary 4, i)77 Cnmencerr.Lar'.t June 1977 ACKNOWLEDGEMENTS

I am indebted to many peouie for encouragement and assistance during the course of this investigation.Richard A. Weisner, Karleen E. Davis, C. Stewart Eldridge arid Robert Dorsett gave able assistance and companionship in the field. chnical assistance in analytical procedures was given by Roberta L. Connard, Takaaki Fukuoka, Kathleen Heide, Kenneth F. Scheidegger, Roman A. Schmitt and Ronald G. SerAechai at Oregon State University, and Gary Cunningham at the University of Oregon.I am particularly thankful to Michael 0. Garcia at U.C.L.A. for the electron microprobe analyses included herein.Early drafts of the thesis were typed and photography was done by Janice M. Stevens.The final draft was typed by Lyndal'u Sikes.The illustrations were drafted by Barbara Priest. Discussions with many ieople helped formulate my ideas and direction for research; however responsibility for errors, of course, is mine.In partuiaI thank Drs. Hans G. Aye? Lallemant, Robert G. Coleman, Henry J. B. Dick, Cyrus VT. Field, Michael 0. Garcia,

Clifford A.. Hopson, William P. Leean and Thomas P. Thayer.I am especially indebted to Len Ramp for suggesting an appropriate area for study. I have received much helt .1ro. the members of my thesis committee -J. Granvilie Johnson. Robert A. Lawrence and William H. Taubeneck.I am especiaUy grateful to my advisor E Julius Dasch for his encouragement and admirable patience during my work. I thank the Geological Society of America for three Penrose Research Grants, and the Oregon Department of Geology and Mineral Industries for providing a vehicle for the field portion of this investigation.Without the assistance of these two agencies I would have been unable to complete this project. Most importantly, I am grateful o my parents who have never faltered in their. faith in my azrbitions, encouragement and financial support. TABLE OFCONTENTS

INTRODUCTION 1 Purpose I Location and Accessibility I Ophiolites and the Ophiolite Problem 3

PREVIOUS WORK 9

REGIONAL GEOLOGY 11 Introduction 11 Western Paleozoic and Triassi.c Belt ii Western. Jurassic Belt 11 Nevadan Orogeny 17 Coast Range Province .18 PETROGRAPHY OF THE MAFIC COMPLEX 20 General Statement 20 Contact Relations 20 Distribuior and Thickness 21 Diabase-Spilito Zone 21 Hornb.iende Gabbro and Quartz Diorite 32 Cumulate Rocks 36 Norite Dikes a'-id Rodingite 49

JOSEPHINE PERIDOTITE 52 Introduction 52 Harzhurgite and Dunite 52 Ciinopyroxene -Rich Lherzolite Veins S5 Orthoprroxenite Veins 56 Se rpentinization 56

C-ALICE FORMATION AND LATE JURASSIC DIKES 57 Galice Formation 57 Late Jurassic Dikes 59 STRUCTURAL GEOLOGY 61 General Statement 61 Early Structures 61 Nevadan Structures 62 Post-Orogenic Uplift 62 Age of the Mafic Complex 64

GEOCHEMISTRY 6 Introduction 65 Methods 65 Major Element Chemistry 68 TraceElement Geochemistr,r REE Models of Oregon Mountain Area Petrogenesis 103

DISCUSSION 113 Regional Relationships n9

BIBLIOGRAPHY 121

APPENDIX I: Location and Description of Analyzed Samples 136 APPENDIX Ii: Chemical Analyses 143

APPENDLX III, Parameters Used in Neutron Activation AnaLyses

APPENDIX IV: Microprobe Analyses of Minerals From Mafic Complex Cumulate Rocks 156

APPENDIX V: Distribution Coefficients Ued in Trace Element Models 158

VITA 159 ILLUSTRATIONS Lre Page Sketch map of southwestern Oregon and Northern California showing the Oregon Mountain area and areas of pertinent previous investigations. 2 Comparison of the stratigraphic th. ckriess of igneous units from various ophiolite masses with the geophysical estimate of the oceanic crustal layers of Hess and Shor and Rait. 4 Generalized geologic map of the Kiamath Mountains. 12 Generalized geology of the northern part of the western Jurassic belt southwestern Oregon and northern California. 13 Stratigraphic sections of Permian arid Mesozoic rocks in the Kiamath Mountains. 15 Composite section through the mafic complex, Oregon Mountain area. 22 Basalt pillows in diabase-spilite zone; Shelly Creek. 24

JP 326, spilite. 26 JP 416, epidosite. 28

JP 366, diabase. 29

ii. JP 340, porphyritic quartz keratophyre. 31 12. JP 318, altered plagiogranite. 34 13. Distribution of minerals in the cumulate zone of the mafic complex. 38 Figure Pao'e C1inopyroxeneo1ivine cumulate s; north slope of Oregon Mountain. 39 Mine ra1graded layering in orthopyroxerte - olive cumulates, Whiskey Creek. 40 JP 178, clinopvroxene-orthopyroxene orthocumulate. 41

JP 322, norite adcumulate, 42 Part of the pyroxene quadrilateral showing analyzed ciinopyroxene s, or thopyroxene s, and olivines from Oregon Mountain area cumulates. 45 Branching rodingite dike and veinlets in cumulate harzburgite; Whiskey Creek, 51 Banded harzburgite cut by serpentine v- ns; Cook Trail, north of Bain Station. 54 FeO*/MgO vs major element oxides in rocks from the diabasespilite zone, Oregon Mountain area. 70 Si02 and Na70 vs H2O in diabase- spilite zone rocks, Oregon Mountain area. Na20 + K20 in rocks from the diabase-spilite zone, Oregon Mountain area. 73 A.FM comparison plot for diabase-spilite zone rocks, Oregon Mountain area. 74 AFM comparison plot for plutonic rocks, Oregon Mountain area. 81 26. Ti vs Zr discrimination plot of sea-floor basalts. 83 re ae Ti vs Zr discrimination plot of Oregon Mountain area diabase-spi1ite zone rocks. 66 Rare earth element patterns of island arc tholeiites, mid--ocean ridge tholeiites and caic-alkaline, shshonitic and aikalic rocks of island arcs. 88 Rare earth element patterns for rocks from the diabase-.spilite zone, Oregon Mountain area. 90 Rare earth element pattern for a sill (JP 391) in the Galice Formation near the top of the diabase-spilite zone, Oregon Mountain area. 93 Rare earth element patterns for keratopy:re (JP 340) and the average a. 12 basaltic rocks from the diabase.-spilite zone, Oregon Mountain area. C./ ' Rare earth element patterns for plutonic rocks, Oregon Mountain area. 97 Rare earth element patterns for two rodingite dikes which cut cumulates on Oregon Mountain. 1 00 Rare earth element pattern for ande site dike which intrudes a fault zone in the Josephine Pe ridotite, Oregon Mountain area. 102 Rare earth element model for 90 percent crystallization of a liquid with 5.5 times chondritic REE abundances. 108 Rare earth element model of partial melting in an undepieted oi-opx-cpx mantle. 111 Diagramatic interpretation of the tectonic setting of major units in the western Jurassic belt prior to and after he Nevadan Orogeny. 115 LISTF TABLES

Table I. Rare earth element compositionof chondrite meteorites.. 68

2. Average chemical composition ofdiahase- spilite zone rock types compared to sea- floor basaits. 75

PLATES

Plate Geology of the Oregon Mountain area, southwe stern Oregon and north.e rn California. in pocket Structural cross sections through theOregon Mountaia rca, 3outhwetern Ortgonand northern Caiiiorna. in pocket GEOLOGY AND GEOCHEMISTRY OF THECRECCN MOUNTAIN AREA, SOUTHWESTERN OREGON AND NORTHERN CALIFORNIA

INTRODUCTiON

Purpose

The purpose ofthis investigation is to pursue the origin and

evolution ofophiolitic rocks which are exposed on the eastern margin of the alpine-type Jose2hine Peridotit3, along the Oregon-California boundary.Geologic mapping, petrographic studies and major element and trace element geochenica1 methods havebeen combined to investigate the ectonic setting, emplacementand metamorphism of the ophiolite complex. The results of these inquiries will be helpful in improving our knowledge of the tectonic history of the Kiamath Mountains, which in turn is critical to our understanding of the history of the western cordillera.Further, it is hoped that this study will contribute to our understanding of the origin and significance of alpine mafic-ultramaf'ic rock associations.

Location and Accessibility

The Josephine Peridotites a large mass of alpinetype ultramafic rock which crops out in southweitern Oregon and northern

California (Figure 1),Exposed along theeastern margin is a 3equence 0 Grunts Pis

We! Is, e t (.i 949

I 7 0 ( sncs. _L/ g 1972

Figure 1.Sketch map of outhwesrn Oregon and Northern California showing the Oregon Mourtain area and areas of pertinen: previous inreshgaion. Shaded areas indicate epcsures of ultramafic rock. 3 of mafic plutonic and volcanic rocks which structurally overlie the peridotite. An area of about 140 kTnwithin the peridotie and the rnafic complex was mapped indetail(Figure 1, plate J).The mapped area was selected because it contains a relatively cornpletsection through the rnaiic complex in a managable small area.The terrain is rugged and hilly, with a maximum relief of 740 meters. Deep soil and heavy brush hamper work in the mafic complex, hut exposures arc fair to excellent ii peridotite. Access to the eastern margin of the area is from U. S. 199. A network of logging roads places most parts of the areawithin atwo mile walk.

lites and the Ophiolite Problem

Ophiolites are assemblages of peridotite, gabbro, and spilitic volcanic rocks which occur within manj eugeosynclinal orogenic belts (Anonymous, 1972).In a strict seise all three rock types must be present to warrant the use of the term ophiolite.Figure 2 (Coleman, 1971) shows schematic sections and correlations through several of the best known ophiolites.There is a remarkable lithic similarity among ophiolites although stratigraphic thicknesses vary greatly. This can he partly explained if portions of the sequence in many regions have been removed by faulting. 4

CC Aic GRUT- MANTLE OP H 0 L rs

LAYER 2 VOURI NJU

M. C&NYN MT.

SEPNufTE BRO AA LT -'., O F TNjTO ZO?E GABarc) '-lEw::LE:oiAL GAllj 6$ K''/$Ac r i TE-JM. E CUt33O PRGXE4TC\ I LS rTMOH C' V C I PZrut.(rTTE I

PERCTlTE T

--I

-12

Figure 2.Comparison of the strati-zraphic thickness of igneous units from various ophiolite masses with the ophysica1 estimate of the oceanic crustallayers cHess(1962) and Shor and Raitt (1969); (from Coleman, 1971). D

Peridotite

The basal and commonly the thickest section of an ophiolite consists of peridotite- -in general olivine-rich harzburgite (divine (Fo 90-93), enstatite (En 90-93), and chromian spinel).Typically the peridotite has a strongly developed tectonite fabric (Aver Lafle- mant, 1976; Lone.y and Hin-imelburg, 1976).Vein-like and irregular bodies of d'nite and pyroxenite are common, hut genera11r are voiu- metrically ninor.Duni.te is a significant component near the top of the peridotite. Chromite deposits with cumulate layering are common within oohiolitic dunite (Thayer, 1969).

Gabbro

Gabbroic rocks overlie the peridotite zone in typical ophiolites. Where the section is relatively complete there is a transition zone a few hundred meters thick consisting of cumulate wehrlite (cpx and 01). Clinopyroxene and piagioclase are the dominant primary phases. Orthopyroxene and olivine occur within many of the lower gabbros. Reddish-brown hornblende is a common phase in all hit the lowest gabbros. Hopson et al,, (1975a) discuss cumulate textures and cryptic layering in gabbros of the Poi:t Sal ophiolite in considerable detail. Uppermost gabbro3 corr.o!-iv contain abundant hornblende and have hypidiomorphic granular to diabasic textures.Minor volumes of 6 tonalite and 'p1agiogranite, n araiiophyric textured :ock in which the essential phases are aibite atdqiarLzCoi.eman and Peterman, 1975), occur at the top of the piutonic init.

Basaltic Zone

The upper zone of ophiolites consists of diahase and spilite. Diabase forms a sheeted complex of dikes in the lower part of the zone and grdes into spilitized pillow basalts which characterize the upper part of the zone (Moores and Vine, 1971; Hopson et al., 1975a). Eugeosynclinal s edirnentav rocks, particularly radiolarian che rt, overlie the basn3tic zone -in ophi.olites in which the top of the zone is exposed (Dewey and Bird, 1970; Hopson et al., 1975b), Massive Cu- Fe-Zn sulfide deposits may occur near the sedimentary-volcanic con-- tact (Anderson, 1969; Clark, 1971).Rocks of the basaltic member are generally altered to low to moderate grade metamorphic mineral assemblages, hut tpica1ly do not show evidence cl penetrative defor- inaton. Metasomatm of the basaltic rocks is common, marked chemically by increases in Na?O. Fe,03, S'i02 and H20, and a decrease in GaO and 'eO relative to unaltered rnid-cean ridge basalts. Aburiances of MgO and KZO commonlye variable.

OjioiiLe Origin

Steinman (1926) first used the term ophiolite and popularized the 7 theory that ophiolite s originally were intrusions beneath geosynciines. This theory conflicted, however, with repeated observations that ophiolites do not have contact metamorphic aureoles, but rather are invariably fault-bounded at the lower contact. At upper contacts there is abundant evidence that ophi.olitic rocks are extrusive rather than intrusive and that they predate the superjacent sediments. DeRoever (1957) and Hess (1962) proposed that ophiolites represent fragments of fosi.i oceaflic crust, faulted onto the continents during orogenesis. With the advent of plate tectonic theory, this concept has beccrne very popular because it affords a link between geo- synclinal theory and plate tectonic theory and makes it possible to construct more meaningful mechanistic models for the tectonic history of major orogens (Dickinson, 1971; Coleman, 1971; Dewey and Bird, 1970, 1971). The strength of the oceanic crust hypothesis lies partly in the compatibility between the lithic sequence (and thicknesses of the nore massive ophiolites) and the seismic structure of oceanic crust (Figure 2) (Coleman, 1971; Shor and Raitt, 1969).Also, dredge hauls from the sea floor, particularly along fracture zones, consistof essentially the same rock types found in ophiolites (Quon and Ehiers, 1963; Melson, et al., 1968; Aumento, 1969; Miyashio et al., 1970, 1971; Cann, 1970, 1971). 8

Recently a new class of volcanic rocks,hesiand arc tholeiite suite, has been recog:aized Lii island arcs (Jakeand Gill, 1970). Basalts in this series chemically are very similar to ocean floor basalts and in some respects to ophiolitic spilite (Jake and Gill, 1970; Jakeand White, 1971).Ewart and Bryan (1972), Miyashiro (1973) and Dick (1976) proposed that many if not all ophioliies are the lower parts ci ancient iland itrcs rather than oceanic crust.Support for this hypothesis comes from the abundance of certain silicic volcanic rocks (keratophyres) in some ophiolites, which are rare on the sea floor, close association of some ochiolites and island arc volcanic rocks, and marked chemical differences betveen many ophiolitic ba.saitand sea-fioor basaits. 9

PREVIOUS WORK

The pioneering geologic investigation of southwestern Oregon was by Joseph Diller (1907).His investigations covered thousands of square miles, and he named the major rock units of the area and established their basic stratigraphic relations. Francis Wells and coworkers mapped much of southwestern Oregon and parts of northern California including the Kerby Quadrangle (Wells et al., 1949) and the Gasquet Quadrangle (Cater and Wells, 1953) within which the Oregon Mountain area lies (Figure. 1). In recenL years, detailed investigations of parts of the western Jurassic belt of the Klamath Mountains have been the subject of several graduate theses, Ramer (1967) investigated the petrology of a portion of the Josephine Peridotite near Cave Junction.Jorgenson (1970) studied the petrology of the Illinois River Gabbro (Figure 4). Snoke (1972) mapped ophiolitic and granitic rocks around Preston Peak, northern California. Dick (1976) investigated the geochemistry, petrology and structure of the northern part of the Josephine Peridotite and associated metamorphic rocks.Garcia (1976a) investigated the chemistry and petrology of the Rogue Formation and Galice volcanic rocks (Figure 1). The Kalniopsis Wilderness has been mapped recently by Ramp (1975) (Figure 1).The petrology and structural geology of the peridotite on Vulcan Peak at the northwestern edge of the Josephine Peridotite was studied by Himmelburg and L1oney (1973) and Loney and HimmeL. burg (1976).Coleman et al. (1976) have discussed the petrology of amphibolite and probable ophiolitic 'ocks north of the Josephine Peridotite, within the Galice Quadrangle (Figure 4). REGIONAL GEOLOGY

Introduction

The Josephine Peridotite lies within the Western Jurassic Belt

(WJB) of' the Kiamath Mountains Province (Figures 3, 4).The WJB is the westernmost of the four major allochthons which compose the Kiamath Mounains, as defined by Irwin (1960).The WJB is overthrust on the east hy the older Western Paleozoic and Triassic Leit, and is thrust over the late Jurassic-C retaceous Dothan and Franciscan formations of the Coast Rartges on the west.

Wesiern Paleozoic and Triassic Belt

The Western Pa1eozoc and Triassic Belt (WPTB) (Figure 3) consisspr lmariiy ci nterbedd metamorphosect eugeosynclinal volcanic and sedimentary rocks, and serpentinized peridotite (Wells et al., :1949; Wells,1956;Irwin, 1966, 1972; Snoke, 1972).Irwin (1972 has interpreted the WPTB as an island arc which collided with. the continent durin-: the late Triassic.

Western Jurassic Belt

The WesternJ urassic Belt is an arcuate belt of eugeosynclinal sedimentary, volcanic and ultramafjc rocks which extends for over 12

I 124c .IJZ° EJ.PLANATON SEtIMEiiTARV .4140 VOLC'NC ROCKS 43 J..b.1t )' Co 'ir - J Ijai Poic o4 obdI Ia.

.riiCoot.,l o.phioi >

_S )

z ) '. i

a1tto

0 rh0t f4t pI.

C 10 20M;liS '

Figure 3.Generalized geologic map of the Kiamath Mountains (from Irwin, 1964). 13

Figure 4.Generalized geology of the northern part of the western Jurassic belt southwestern Oregon and northern Califona. 14

350 km. along the western margin of theKlarrLathMountains (Figure

34).The major units within the WJB are the Rogue and Galice formations and the Josephine Peridotite (Wells et al., 1949; Cater and Wells, 1953; Wells and Walker, 1953; Irwin, 1964, 1966). Kimmeridgian (middle upper Juras sic) pelecypods (Buchia concentrica) are present in the Galice sedimentary member, hut the Jurassic age of the underlying voicani.c units is speculative (Figure 5).The WJ}3 was extensively deformed during the Nevadan orogeny (Wells ct al.,

1 949).

Rogue Formation

The Rogue Formation as defined by Wells and Walker (1953) is a sequence of metavolcanoclastic and voicanoclastic rocks which crops out in a band north oi the Josephine Peridotite, within the WJF (Figure 4).The principal rock types are chemically intermediate to silicic tuffs, flow rocks and agglomerates. The rocks have undergone meta- moroktsm which ranges in grade from incipient to greenschist facies. RecrysLallization characteristically is more intense than in the Galice Formation.The age of the Rogue Formation is not well known except that it undo rliethe Galice Formation (Garcia,1 976 a).The petrology and origin of the Rogue Formation have been recently investigated by Garcia 1976a, 197'ih). 15

Age (my.) Statlgraphc Stratigraphic cournns time scale of Klamth Mourt3ns Western C..) rt of Eastern Kamath belt 0 Ktarnatt 0 Mountains z Strata younger than Great Valley sequence are not shown Ei5

Strataf the 100 Great Valley seuuerce Franciscan and C) DoThn Fcrrnotici 132 :gi-ENDhce/// OF, NEVADAN OROENY -

170 .4'PoternFm. 7/ EtagleyAndesite Cl .//A Arvisori Fm. 190 _L..::_... Modin Fm. -OO £rock shale Hosselkus Ls. m' PitFm. Bully Hill Rhyolite oo,i Dekkas Anesite Nosom Fm.

280 MClcud L5.

Figure 5.Stratigraphlcsections of Permian and Mesozoic rocks in the Klarnal:h Mou-itis (modified from Lanphere et a].., 1968). Galice Formation

The Galice Formation (Kimme rid ian; ias been des crihed by Wells et al., (1949).It consists of a v3lcanic member which is partly interstratified with hut mainly overlain by a thicker sedimentary member. The volcanic member consiats of chemically intermediate flow rocks and flow breccias with subordinate basalt and rhyolite.Tuff- aceous rocks are present. but riot as abundantly as in the Rogue For- mation.In many placi the volcanic rocks have been metamorphosed to lower greenschit facies. However, unaltered rocks are common. The sedimentary member is mostly shale and siltstone, which in places have slatey cleavage. Sandstone and fine grained conglom-- crate, thoug1 not voluminous, are uniquitous throughout the unit.

Josephinee rioti to

The Josephine Peridotite, with an outcrop area over 1000 km.,2 forms an arcuate band 75 km long and averaging 14 km. wide along the western margin c.the WJL, Outliers of the peridot:ite extend over anothe500 arzburgite tectonite is by far the dominant rock type.flunite and minor chromite occur locally.Clinopyroxene- rich. lherzoiite and orthopyrcxenite veins are minor but widespread throughout the mass. The petroiogy and structure ef the Josephine 17 Feridotite have been discussed by Dick (1976), }immelburg and. Loney (1973), and Loney and Hirnmelburg (1976).

Nevadan Orogeny

The Nevadan Orogeny was a major late Jurassic deformational and metamorphic event within the K]amath Mountains (Dott, 1965; Lanphere at al., 1968).Within the WJB, Nevadan thrusts and high angle reverse faults are closely spaced.Nearly all contacts are faults and stratigraphic relations are difficult to interpret.Tight foldin parallels major fault trends within the Galice Formation. Regional metamorphism was generally moderate but wide spread throughout the WJB (Wells et al., 1949).Slatey cleavage is crnnmon in the sedimentary rocks and most of the volcanic rocks have at least incipient prehnite-pumpellyite or greenschist facies mineral assemblage s.Serpentiniza.tion, possibly related to emplacement, is ubiquitous within the ultraniafic rocks. A seemingly anomalously high-grade amphibolite (the Briggs Creek amphibolite) occurs in the northern part of the belt.This unit recently has been interpreted as the product of metamorphism deep within an island arc (Coleman, etal., 19 Intrusive rocks, related in time to the Nevadan Orogeny, are common in the WJfSRock types range from hornhlertde gabbro to quartz rnonzonite.Potas iin feldspar-poor types are most voluminous (Wells et al,, 1949; Jorgenson, 1970; Garcia, 1976). Numerous intermediate to mafic dikes intrude the WJB, commonly along faults (Dick, 1973, 1976). The Nevadan Orogeny continued through much of the late Jras- sic.Tithonian strata of the Great Valley sequency and Myrtle Group unconformably overlie the deformed Galice Formation (Kimmeridgian) indicating that deformation ceased by Tithonian time (Irwin, 1964; Figure 5).:Piutcnism attributed to the Nevadan Orcgeny was esen- tially cc.ntiuous from the mid-Jurassic to the early Cretaceous (Dott, 1965; Laxtphere et al., 1968; Dick, 1973, 1976).Nevadan metarnorphc ages have a smaller range (Lanphere et aL, 1968), mainly falling near 150 m. y. beie the present (Kinimeridgian)

Coast Rarge Province

The Coast Ranges structurally urideruie the. WJB on the west, and are separated from it by the South Fork Mountai. Thrust (Figure 3; Irwin, 1966).The Coast Range Proviice can he divided into a eugeosynclinal fades and a miogeoync1inal facies Bai1ey et al.,

1964). The eugeosynclinal facies is repreLented by the Franciscan. Formation in Catilornia and the Dothan and Otter Fout fot'mations in Oregon. The rocks consist of graywacke, mudstcn, chert and mafic volcanic rocks which have been extenuiveiy ared into a 19 chaotic me'lange and metamorphosed to the zeolite arid blueschist facies (Bai1eet al., 1964; Dott, 1971).Withri the eugeosrnc1inal fades are a large number of tectonic blocks arid thrust outliers of older rocks. Among these are the Colebrooke Schist (Coleman, 1972), outliers of the Galice Formation (Dott, 197!), peridotite (Medaris, 1972), and numerous exotic blocks of ecologite and blueschist (Cole- man and Lanphere, 1971; Gherit and Coleman, 1973).The miogeo- synclinal or shelf facies consists of graywacke, shale and minor conglomerate represented by the Great Valley sequence, the Myrtle Group, and snal1 erosional remnants within the Kiamath Mountains (Bailey et al. , 1964; Irwin, 1966; Dott, 1971).The two fades are coeval and probably formed as a continental margin subduction complex (Bailey et al., 1964).They now are separated by major thrust faults and in California by the Coast Range Ophiolite (Bailey et al.. 1970). 20

THE MAFIC COMPLEX

General Statement

The mafic complex in the Oregon Mountain area consists of a sequence approximately five l-n, thick which passes dowz'ward from volcanic and hypabyssal rocks through gabbro and cumulate ultramafic ro:ks. The sequen.e can be divided into three zones, the dials.e spilite zone, the gabbroic zene and the ultramafic zone.Transiti.c.s between the three zones are gradational.

Contact Relations

The mafic complex is overlain by the Galice Formation. The contact is clearly exposed in several road cuts below Lone Mountain and along Shelly Creek. At these localities siatyshale lies directly on pillow basalts with little or no evidence of differential movement. No indication of a weathering borLon or of chert deposition was observed along the contact.It is ir.terpreted that the mafic complex forms the basement to the GaUce Formation, in this area, and that sedimentation began during or soon after eruption of the basalts.

The base of the Anafic complex is the Josephine Peridotite No sharp lower contact with the peridotite could be found.Rather, cumulate text:2res in harzburgite and dunitof the ultramafic-cumulate 21 zone become increasingly vague northvaci (down dip) from exposures along Whiskey Creek (Plate I).Evidently the cumulate zone is gradational into ultramafitectonities of the Josephine Pe ridotite.

Distribution and Thickness

Rocks of the mafic complex occur in a belt extending from Lone Mountain to Monkey Ridge on the eastern side of the mapped area and in a broad area between Whiskey Creek and Diamond Creek (Plate 1). A continuous section through the complex was not found, but a compilation oi short sections suggests that the mafic complex is about 4. 6 km. thick (Figure 6).Faulting disrupts the sequence in many p1acs and stru'-ura1 attitudes could be determined in few locations.Therefore,he composite. section should be regarded as tentative.

Introduction

Diabase and spilite form a thick sequence of rocks at the top of the mafic complex.Spilite is most abundant at the top of the sequence, where it is accompanied by minor keratophyre and radiolarian chert.Diabase is uncommon near the top but dominates in 22

UNlI UTHOLOCY

Galice groywacke Formal ion shale (dote)

spiUte, chart (;eclite, prehnte- purnp& lyife fccies)

Ciobe diabase (greenschist lucies)

piagiogranite hornblendc çchbro

Gab brc ougitegubbro

norite U!trcrncfic wehrlite Cumulotes dunite horzbrgite Tectonized dunite- chrornile Harz burg te harz hurçi t

Figure 6.Cornposi.e section through the mafic complex, Oregon Mountain area. 23 the lower half o. the zone.The se of the diabase-spilite zone is a fault in most sections.However, diahase grades downward into hornblende gabbro and quartz diorite on Lone Mourtain and Monkey Ridge. Metamorphism and poor exposures made distinction of diabase and spilite difficult in the field.Therefore, the two rocks were mapped as a single unit.

PrimaryFeatures

Spilitized basalt pillows Figure 7) were the oniy volcanic features observed in outcrop.Pillows are well exPosed near the Turner-Aibright Mine and along Shellv Creek. Diabase dikes cutting cumulate gabbro were observed in a roadcut east of Baker and sheeted diabase is exposed near the toof Monkey Ridge.Excdllnt exposures of sheeted diabase dikes occur in similar rocks in the Smith River Canyon, west of Gasquet, about 25 km. southwest of the mapped area,Buff colored, porphyritic keratophvre was observed near the head of Shelly Creek. No volcanic textures were found in the keratophyres. Sedimentary rocks occur in a few places within the diabase- spilite zone. Lenses of tuffaceous radiolarian chert crop out near Blue Creek and at the Turner-Aibright Mine.Pyrite-bearing chert underlain by a layer of congiomeratic, metamorphosed graywacke occurs near the head of Shelly Creek (Plate I). 24 25

Relics and pseudomcrphs of primary mineris are common in both spilite and diabase.Most spilites were originally glassy and. contained phenocrysts of plagioclase and augite. A few fine-grained holocrystalline spilites were observed.Olivine was found in only one thin section.Diabases from the mafic complex have suhoph-itic textures. P1aoclase and augite were the only primary minerals identified in the diabasic rocks.

Metamorphism

Introduction.All rocks in the diabase-spilite zone have been metamorphosed. The observed mineral assemblages and a general lack of schistosity suggest that the rocks have undergone low pressure burial metamorphism as described by Miyashiro (1973, p. 70).The metamorphic mineral assemblages follow a progression downward from zeolite and prehthte-pumoellyite facies, through greenschist facies to incipient amphibolite facies. No epidate- amphibolite assemblages were observed.Sea-floor metamorphic assemblages (Meison, Thomoson and van Andel, 1968; Melson and van Ande11968; Miyashiro et al., ],971; Cann, 1971) are similar in many respects, although prehnite-pumpellyite assemblages are rare in the sea floor rocks (Miyashiro et al., 1971). Zeolite Facies.The lowest temperature assemblages contain abundant sinectile, which has replaced glass (Figure 8).Prehoite, 26

Figure 8.JP 326, spilite.Pumpellyite replacing groundrnass zeolites and smectite adjacent to zrnectite filled amygdule. Fine grained pumpellyite aio occurs in he groundmass; width of field 1 mm. ; plain polarized light. 27 pumpellyite, quartz, calcite and zeolite minerals are present in amydules and in the groundmass. though nc all in the same thin section.Plagioclase phenocrysts are replaced by albite, but albite was not observed in the groundmasst this metamorphic stage. Greenschist Facies.Greenschist facies rocks in the diabase- spilite zone can be grouped into three assemblages--chlorite - quartz + albite; epidote + quartz±aibite;andact-inolite+albite. The chlorite - quartz - albite assemblage occurs mostly in altered volcanic rocks, and is superimposed on zeol.ite facies mineralogies in some specimens.Pumpellyite commonly occurs with chlorite but not with higher temperature. minerals.Prehnite is common in many greenschist facies samples. The second major greenschist facies assemblage consists mostly of granoblastic and crystailoblastic epidote-quartz .-alhite rocks (Figure 9).Generally, the original texture of the rock ha been completely destrove. The mineralogy suggests that large metasomatic changes have occurred, particularly an influx of silica. Chlorite occurs in a few rocks.Fine grained rutile and sphene are abundant. The highest temperature assemblages are found only in the diabasic rocks. Primary textures generally are well preserved and relict augite is common (Figure 10).The dominant metamorphic mineral assemblage is albite + actinolite.Chlorite, quartz, prchnUe, 28

Figure 9.JP 416, epidosite. Quartz and elongate epidote, width of field 1 mm.,plain polarized light. 29

Figure 10.JP 366, diabase.Albite, actinolite and augite; augite has high relief; width of field 3 mm.; plain polarized light. 30 epidote and sphene are comrno access3riesActinolite occurs as both fibrous aggregates and pseudomorphs of augite. Amphibolite Fades. Green-brown hornbiende occurs in several specimens from the lower part of the diabase zone.It is gradational, or nearly so, into pieochroic actinolite.Feldspar compositions of hornblende-bearing rocks could not be determined, owing to intense sausseritization. Many of the amphibolites appear to be the result of retrograde (deuteric) alteration of the primary rocks. Me ratophrre.Keratophyre is a minor component of the diabase-. spilite zone which probably formed as submarine tuffaceous deposits. The keratophyres examined in thin section have a fine grained grouncbnass of quartz and white mica.Relict euhedral phenocrysts of potassium feldspar are common (Figure 11).

The Turner-Aibright Mine

The Turner-Aibright Mine is a massive Fe-Cu-Zn sulfide deposit.It was first explored in the early 1900's for gold (Wells et al., 1949); it presently is inactive.The deposit occurs in pillow basalts within the diabase-spilite zone, associated with lenses of chert.The chert contains recrystallized radiolarian tests and tuffaceous material and probably formed during a lull in volcanism. Sulfide ore occurs in silicifi.ed veins in brecciated volcanic rocks. No mineralization has been observed within the ultrarnafic rocks or 31

Figure 11.JP 340, porphyrihc quartz keratophyre.Quartz, muscovite, a1bitied K -feldspar phenoc rysts; width of field I inrn.; crossed nichols. 32 in nearby fault zones.There is no obvious hydrothermal alteration of the host rocks, nor is there any ohviou nearby pluton which could have acted as a source of metals and heat.The deposit probably is of volcanogenic origin, and may have formed by the interaction of hot volcanic rocks and sea water. A similar inter- pretatiori bas been made for mas.ive sulfide deposits in the Troodos Ophiolite (Clark, 1971; Corliss, 1977). The Turner-Alhright deposit currently is being studied in more detail by Cynthia Taylor Cunningham of Oregon State University.

Hornblende Gabbro and Quartz Diorite

Distribution and General Character

Hornblende gahhro and quartz dioritic rocks crop out: near Bain Station, on the west flank of Monkey Ridge and on Gilligan Butte (Plate 1).These rocks form a transition zone between cumulate gahbro and diabase,The transition is gradual; hence it was not possible to map hornblende gabbroseparately. Two small dioritic bodies are shown on Plate 1 as uplagiogranite" which includes both tonalite (mafic quartz diorite) and albite granite after the terminology of Coleman and Peterman (1975).In most outcrops however, only the most leucratic quartz diorites (albite granite) can be distinguished from horrblende gabbro. 33

Hornblende Gabbro and Tonalite

Hornblende gabbro and tonalite are mediurngrained (1-10 rnm) rocks which have a hypidiornorphic-granular texture.Finer grained varieties grade into diabasic textures.Essential minerals are plagioclase, augite, green-brown hornblende and quartz.P1agio clase grains have a pronounced zoning.Composition of feldspars from these rocks has not been determined owing to sausseritization and a lack of albite twinning. Rims on plagioclase grains commonly are clear, unaltered albite.Hornblende is mostly pseudomorphuus after augite which remains as ragged cores. Quartz is a common interstitial constituent of gabbro, and it occurs in large, irregular grains and granophyric intergrowths with albite in some tonalife samples. Apatite and intergrowths of magnetite and ilmenite are the only common accessory minerals.

Albite Granite

Albite granite is a term applied to quartz diorites in which essentially the only feldspar is albite (Coleman and Peterman, 1975).Rocks of this type crop out on Gilligan Butte and the west side of Lone Mountain. Aibite granite from the study area has a hypidiomorphic to nearly idiomorphic granular tthLre (Figure 12). The bulk of the rock is composed of large 1 to 2 cm.) blades of 34

Figure 1Z. JP 318, altered plagiogranite.Altered plagioclase laths, quarz-albite granophyric intergrowth and indistinct patches of actnoiite; width of field,1 mm. crossed nichols. 35 albite and granophyric intergrowths of quartz and albite.Pale red amphibole is the only primary rnafic phase observed and, unlike the amphibole in tonalite and gabbro, iL forms iender, sheaf 4ike aggregates.Intergrowths of magnetite and ilmenite and minor apatite, sphene, rutile, and py-rite are present as accessories. Attempts to recover zircon from these rocks for radiometric age determination were unsucce s sful.

Alteration

Most hornblende gabbro and piagiogranite specimens have been considerably altered.Secondary minerals are largely those found in upper greenschist facies diahases.Textures and mineral parageneses observcd in the plutonic rocks suggest that the a1tera tion can be described as retrograde-deuteric recrystallization. Alteration minerals include actinolite, chlorite, fine-grained sausserite minerals, sphene and patches and veins of prehnite.

Discussion

Hornblende gabbro and plagiogranite apparently are the differentiates of the gabbroic magma which produced the underlying cumulate rocks.These rocks are intrusive into diabase (particularly evident on Gilligan Butte) and are cut by diabase dikes.I believe that the diabase-spilite zoie formed the roof under which the cumulate 36 series crystallized, but that injectiot of di.abae continued after crystallization of the underlying plutonic rocks.

Cumulate Rocks

Textures

Gabbroic and ultramafic plutonic rocks of accumulative origin occur in the headwaters of Diamond Creek, on the western slopes of Monkey Ridge and on Oregon Mountain (Plate I).Ciinopyroxene gabbro, wehrlite and dunite are the most abundant rock types observed.Norite, clinopyroxenite, harzburgite and chroniitite are present in subordinate amour.ts.Evidence for the accumulative nature oi these rocks includes phase layering, sedimentary features in outcrop, cumulate microtexlure s, and cryptic layering.

Phase Layeg

Phase layering refers to the succession of minerals in a cumulate sequence.Faulting has greatly disrupted the cumulate sequence in the Oregon Mountain area, but it is possible to reconstruct qualitatively, a composite sequence on the basis of partial sequences and the observed mineral assemblages (Figure 13).The proportion of a given mineral fluctuates greatly within its stratigraphic range, resulting in a diversity of rock types, particularly near the transtion 37 from ultramafic to gabbroic cumulates. One or two rock types, however, predominate in each interval, as indicated by the unit names in figure 13.

Sedimentary Features

In many outcrops there is a pronounced layering of the ultrarnafic cumulate rocks and lower gabhros (Figure 14).This layering is produced by abrupt variation in either the grain size, or pro portions of settled minerals.In most places the margins of individual layers are sharply defined.Mineral-graded layering (Figure 15) was oherved but is uncommon except within cumulate harzburgite. Indivual layers generally are not continuous for nore than a few meters,Rather, they are disrupted by shallow cross bedding, slump structures, clastic pyroxenite dikes and small faults.Layering become5 indistinct upward into the gabbroic sequence, as the proportion of pyroxene to plagioclase becomes relatively constant.

Microtexture s

Observed mi c rotexture s vary fromorthocumulate (idiomorphic) in very mafic gabbros to adcumulate (allotriomorphic) in mono- mineralic dunite and pyroxeriite and in leucocratic gabbro (Figures 16, 17), using the classification of Wager and Brown (1968). 38

I ' C C C UNIT ) ., I:' C > C ° 'C (not tscale) = , a 0 0 a I

Hornbtende Gobbro 63

Cpx Gobbro 45 89

Cpx Goib 47 89 cnd Norite 90 St5249 91 Wehdife arid Pyroxenite (-Ariorfhosjt)

C (+ Duni'e C hrornite)

Figure 1 3.Distribution of minerals in the cumulatezone of the rnafic complex. Numbers represent measured values of Fo content in olivine, En content in orthopyroxene, Mg/(Mg+Fe+ca) in clinopyroxene and An content in plagioclas e. 39

Figure 14.Clinopyroxene-olivine cumulates; pyroxene stands out in relief; olivine is rpentinized.North slope of Oregon Mountain. 40

Figure 15.MineraJ-graded layering in orthopyroxene-olivine cumulates. Pyroxene stands out in relief. Whiskey C reek. Figure 16.JP 178, clinopyroxene-orthopyroxene orthocumu].ate. Interstitial filling is hydrogarnet replacing plagioclase; width of field 3 mm.; crossed nichols. 4

Figure 17.JP 322, norite adcumulae. AnorthiLe, orthopyroxene and minor clinopyroxene; width of field 3 mm.; crossed nicho. 43 Poikilytic clinopyroxene overgrowths up to 10 cm. in maximurn dimension frequently are developed around olivine and clinopyroxene prirnocrysts.Igneous lamination, characterized by foliation of tabular crystals, is common in plagioclase or clinopyroxene-rich layers. Cryptic i.4arig

Cryptic layering1Edefined aa continuous change in mineral composition upward through a cumulate sequence (Wager and Brown,

1968).it icharacteristic of layered mafic intrusions and has been recognized in the ophiolite at Point Sal, California (Hopson et a]..,

1 975a). Electron rnicroprobe analysis was used to investigate the possi- bility of cryptic. layering in cumulate minerals from the Oregon Mountain complex. Microprobe data summarized in Anpendix IV, were obtained by M. 0. Garcia (pers. comm. ,1976) at the University of California at Los Angeles.Precision for major elements in the minerals analyzed is approximately + 2 weight percent, except for FeO and Na20, which probably have uncertainties of about 5 to 10 percent.Data for elements with abundances less than 1 weight percent have much larger uneertainties.Precision was determined by comparative analysis of mineral standards and by multiple analysis of samples (Appendix IV). 44 Mineral compositions are shown in Figure 13 and rnafic mineral compositions are plotted on the pyroxene quadrilateral diagram in Figure 18.Feldspar compositions vary from An91 to An64.Plagioclase more calcic than An90 is rare in terrestrial rocks other than ophiolite s.Clinopyroxene, orthopyroxene and divine compositions are very magnesian. becoming slightly more iron rich upward in the sequence. Due to a poor choice of specimens the analyzed suite represents only the lower cumulate section.The data,nevertheless, suggest that cryptic variation is present.The mineral compositions are similar to those of minerals in equivalent positioin the Point Sal cumulate sequence (Hopson et al., 1975).

Plagi ocla s e

Plagioclase compositions ranging from An91 to An64 have been observed in cumulate series rocks (Figure l3)Plagioclase first appears in wehrlite cumulates rocks as intercumulus material and as crossbedded anorthosite layers a few cm. thick.This early- formed plagioclase is almost totally replaced by hydrogarnet. Where plagioclase occurs as a primary cumulus phase, it commonly displays extensive adcumulate overgrowth.Zoning is absent, except in the highest gabbros in the series Figure 18. Part of( the pyroxene quadrilateral Ehowing), and olivmes ana1yed ( clinopyroxenes ( ) from Oregon Mountain area. cumulates. Ana1yt ), orthopyroxenealvi. 0. Garcia. 46

Cli.nopyroxene

Clinopyroxene is magnesian, low alumina augita in the lower cumulates, and becomes increasingly iron-rich upward in the sequence (Figure 1 3).It is pale green and occurs as tabular pri.mo- crysts and as coarse poikilytic patches. Most grains have a pronounced diallage parting

Olivine

Olivine varies in composition from Fo91 to Fo80 n the grains analyzed.Its original compositional range probably was greater, but in most samples no fresh olivine remains, and the full variation probably has not been established. Most olivine graths have been extensively cut by serpentine. Well formed serpentine pseudomorphs in some samples of gabbro indicate that euhedral olivine once was present. 2oxae

Orthopyroxene is the least abundant primary silicate mineral in the cumulate series.It occurs in cumulate harzburgite where it has a measured composition of En91 and in two-pyroxene gabbro and norite,One .mafic gabhro sample contains bronzite with a 47 composition En82.Most grains aro. neariy eb.edral.Orthopyroxene was not observed as an intercumulus mineral.

Chromian Spinel

Chrornian spinel is common in the ultramafic zone on1below the first appearance in the sequence of clinopyroxene, with which it apparently has a reaction relaticr..Isolated irregular grains are disseminated throughout harzburgite and duni.te layers.in thir. section, chromian spinel occurs as small (<1 mm.) translucent red grains.Within the lowest dunites in the section, chrornite is concentrated in layers, which have in places been explored by prospec- tors.Individual layers are discontinuous and at most a few cm. thick. No chrome 1roduction has come from the mapped area, although elsewhere in the Josephine Peridotite, chrome deposits have been mined (Ramp, 1961).

Alteration

AU of the cumulate rocks observed have been at least slightly altered.In the less altered rocks, alteration is selective, affecting only one or two minerals, Pseudomorphs are common. With increasing alteration, original textures become vague. Ultramafic rocks are altered primarily to the serpentine group minerals crysotile and lizardite,In early stages of serpentinizatipn 48 olivi.ne andenstatitegrains are cut by crysotile veinsthen later replaced by fine grained lizardite.Clinopyroxene is destroyed only in the most altered rocks.Brucite veins and fine grained, secondary magnetite accompany serpentinization.Dunite is particularly succeptible to serpentini.zation. No dunite observed in the cumulate sequence contains more than 25% relict oIly-me. Calcium is mobilized during serpentinization and migrates into adjacent gabbroic rocks and into intercumuius plagioclase ca sing extensive c-icium meta somatism (rodingitization; Coleman,

1967).Plagioclase within the ultramafic sequence therefore is recrystallized to a fine gralned nearly isotropic mass of garnet, probably hdrogrossular, accompanied by minor clinozoisite and prehnite. Much of the alteration in the gabbroic rocks examined is retrograde, suggesting that late magmatic and deuteric processes rather than regional metamorphism are responsible for the alteration. Clinopyroxene is relatively resistant to alteration but has a complex paragenesis where altered.In several specimens, the first stage of dlinopyroxene alteration is a rimming by pale, red brown hornhlende.In later stages pseudomorphs of hornblende after augite are evident. Apparently the hornbiende is early post- magmatic. Actinolite replaces both augite and hornblende particularly in rocks near the top of the cumulate sequence.It is pseudomorphous 49 in places, but in more altered specimens iforms fibrous, radiating masse-s.Pale green chlorite occurs in minor amounts in many gabbros where IL is found asmall -patches in mafic minerals or inclusions in plagi.oclase.Plagioclase is relatively unaltered i-n many of the lower gahbros.Flecks of wMte mica occualong cleavage planes or randonly in some plagioclase grains.in gabbros from within and near the ultramafic zone, rodingitization is extensive.Plagioclasin rocks from near the top of the cmuiate series are sausseritized to assemblages of aibite a-nd fine grained clinozoisite(?), mica or bath. Very altered plagioclase grains from the top of the cumulate sequence have nearly opaque sauserite cores and rims of unaltered albite. Orthopyroxene alters along fractures to pale red, fibrous amphibole in many of the gabbroic rocks.In ultramafic rocks and tnafic gabbros, orthopyroxene is replaced by- peeudomorphs of pale yeflowgreen serpentine (bastite).Olivine in gabbros is extensively replaced by serpentine. Iron-titanium oxides are commonly altered to patchy, irregular, grains of sphene (leucoxene).ifl some specimens skeletons of iirnenite occur surrounded by red, fine grained iron hydroxides.

Norite Dikes and Rodingite

Coarse grained norite dikes, a few centimeters to about one 50 meter thick, occur in rrany places s:itJ.n he ultramafic cumulate zone and the upper part of the peridoite.Essential minerals are plagioclase (An5), orthopyroen and augite.Pale brown hornblende partially replaces someii:e and forms fibrous rims around orthopyroxeneThese rock can be distinguished from cumulate layers by their hypidiomorphic granular texture and distinctly zoned, relatively sodic plagiociase.In the field, smaller dikes typically are branched (Figure 19).Larger dikes are somewhat zoned, with large pyroxne crvals (up to 10 cm.) con.ceiitrated along the margins of the dike aid elongated perpendicular to the dike margin. The original mineralogy in the majority of riorite dikes is not preserved.Typically, the dike rocks have been recrystallized to fine grained assemblages of hydrogarnet, prehnite and epidote group minerals, presumably by the influx of calcium released during serpentinization of the surrounding ultramafic rocks (Coleman,

1967).Such rocks are termed rodingites.In outcrop they are white and commonly marked by relict, red, pyroxene grains.In thin section they are mostly fine grained hydrogarnet cut by prehnite veins. Many of the gabbroic cumulate rocks are similarly rodingit- ized. 51

Figure 19.Branching rodingitdike and veiilets in cumulate harzburgie; Whiskey Creek. JOSEPHINE PERIDOT1TE

mt roduc hon

The Josephine Peridotite is an extensive allochthonous mass which forms the basement of the Oregon Mountain mafic complex.

The peidotite covers an area of about 1100 km2 along the western margin of the Kiamath Mountains province. Kim (1974) has estini- ated the thickness of the allochthon to be approximately 2 km.on the basis of a rconnaisance gravity survey in northern CaIifornia Texturally and mineralogically the Josephine Peridotite close1 resembles other alpine-type peridotite masses (Himmelburg and Loney, 1973; Dick, 1976).Olivine-rich harzburgite with a tectonite fabric is the dominant rack type, accompanied by perhaps five percent of dunite and minor pyroxerzite arAd chromitite.Serpentthiza- tion typically has been intense, but unaltered peridoti.te occurs locally.rrhorough discussions of the petrology and structural geology of the Josephine Peridotite, on the basis of detailed mapping and analytical work, have been published by Himmelburg and Loney (1973), Loney and Hi'iimeiburg (1976) and Dick (1976).

Harburgite and Dunite

In. tjpica1 wcihored outcrops, harzburgite has a coarseir banded appearance marked by reddish orthopyr.x.ene -rich layers and buff coloredlayers rich inolivine (Figure 20).These layers vary from about 1 cm. to perhaps 30 cm. in thickness; are generally steeply dipping, and strike NNE, parallel to regional structural trends.Individual bands are distinctively duni:ic or pyroxeni.tic in places; in most outcrops, however, the banding is vague. I)unite occurs as irregular masses up to a few hundred in. in maximun dimension.,as concordant bands within the harzburgite, and as veins of crosscutting harzburgite. The veins commonly are 2 to 5 cm. in width and may be either straight or isoclirially folded. Segregations of chromian spinel occur at the centers of a few veins. Economically significant accumulations of chromite occur only near the base of the cumulate series, and were not observed within the tctonito peridotite. Such a relation is typical of alpine peridotite- chrornite associations (Thayer, 1969). Under the microscope, harzhurgi:e and dunite are similar in appearance, although dunite has less pyroxene and contains a slightly larger content of chomian spinel than harzburgite. The rocks have a xcnomorphicgranular texture, excett where primary textures have hen destroyed by serpentinization. Most of the olivine apparently originally occurred as large grains 2 to 5 mm. I!diameter.IKinking, polygonization and serpen- tizaoon have greatly reducedtie grain size.All grains examined 54

Figure 20.Banded harzburgite cut by serpentine veins; Cook Trail, north of Bain Station. 55

have a very high optic angle.Their composition is probablytthe range Fo90Fo93 as determined by electron probe analysis for olivine grains from the northern part of the Josephine Peridotite (Dick, 1976; Himrneiburg and Loney, 1973). Orthopyroxene grains are subidoblastic and rary in dimensions from about 2 to 10 mm. Excolution lamellae of clinopyroxe:aeare abundant within orthopyroxene.Bent and kinked cleavage traces and exsolution lanxe11ae also are common. Chromian spinel occurs asmall grains ( < 1 mm.) disseminated through the rock or concentrated in the centers of dunite veins. In some outcrops trains of spinel grains define a foliation.In thin section, spinel grains are deep red, irregular in outline, and occupy intergranular positions between larger olivine and pyroxene grains.

2Uroxene-Rich Lherzoiite Veins

Clinopyroxene-rich lheroiite (01+ opx4 cpq veinsre found at a few iocaU±ies in the mapped area, notably along the north fork of

I Whisky Creek. The veins are approximately 10 cm. wide or less, coarse grained and generally have diffuse borders. Similar veins near Chetco Peak to the north have been described in detail by Dick (1975, 1976), who interprets them as ultramafic pegmatites resulhng from low degrees of partial melting of the per.dotite. 56

Orthopyroxenite Veins

Coarse veins of orthopyroxenite a few cm. in width are common in peridotite outcrops.These veins crosscut the handing in the host rock.One vein was examined in thin section; he ortho pyroxene was found almost completely replaced by fibrous tremolite, interspersed with talc and chlorite.The tremolite fibers were extensively folded and kinked, indicating that replacement occurred prior to he final emplacement of the peridotite.

S erpentini zation

Ultramafic cumulate rocks and the Josephine Peridotite are extensively serpentinized within the study area. Some pyroxerites are nearly free of serpentine, but most rocks are 25 to 75 percent altered.Dunites are everywhere intensely altered to serpentine. Serpentine mineralogy and textures observed are essentially iden- tical to those described frrn other serpentinized alpine ultramaf±c masses (Hostelier et al,1966; Page, 1967; Coleman and Keith,

1970).Fibrous crysotile and platy lizai'dite are the prevalent .serpentirie polyrnorphs recognized in the mapped area although atitigorite occurs in the contact aureole of a dioritic pluton which crops out near the western margin of the mapped area (C. S. Eldridge, pers. comm., 19'?). GALICE FORMATION AND YOUNGER DIKES

Galice Formation

Sedimentary rocks of the Galice Formation, depositionally overlie the mafi.c complex. The Galice sedimentary rocks are tightly folded ad slatey cleavage locally is well developed. Recrys- tallizaticn in these rocks is only weakly developed in contrast to that in the underlyiz metavolcanic rocks.Slatcy shale and lithic graywacke were the only sedimentary rock types observed. Two mafic hornblende-hearir.g sills were the only igneous rocks found cutting the sedinienta-y secuence.Shale invariably is the lithology found at the base of the unit, and remains dominant throughout the sedi- nientary section.The petrography of the slate was not examined. Strata of sandstone, mostly le.s than 3 m. thick, first occur approximately 100 rn. above the base of the Formation and continue sporatically through the sequence. The total volume of sandstone probably does not exceed 10 percent of the Galice formation in the study area. Grain size in the sandstones varies from about 0. 05 mm. to 5.0 mm., although sorting is generally fair within a single hand sample. The coarser varieties are more properly termed pebbly coilomcrate.Individual smaller grains a re vpically angular to suhangular.Grains larger than I mm. commonly are subrounded. 58 Graded bedding was not observed. The sandstones iii the mapped area can be classified as lithic wackes. Visual estimate of the modal composition of two typical sandstones indicates approximately 45 percent quartz, 2.5 percent lithic fragments, 10 percent plagioclase and other minerals and perhaps 1S percent fine matrix. Minor and trace minerals are mainlyhornhlende,microcline, micas. and augite.The lithic fragments consist mostly of silicified volcanic fragments and basalt. Fragments of sedimentary chert, rnudstone, and metamorphic rocks are also present.In the oebhly conglomerates, litbic fragments make up at least 75 percent o.f the rock.Typically, the fragments are tabular and parallel to the bedding. A sill (JP 391, Appendix IIC) which intrudes the Galice Foma- tion resembles diabases of the upper di.abase.-spilite zone, except that it contains magmatic (? ) hornblende, which is not typical of diabasic rooks.The origin of this sill is not known.It may have resulted from a rnafic-compiex magma which was chemically altered after intrus:oo into wet sediments. Alternatively, it may postdate the tectonic emplacement of the inafic complex and the Galice. Dickinson (I 974a. 1 974b) has discussed the provenance relations of sandstone in orogen:ic areas, He concluded that feldspar-rich, quatz-poo graywacke s are characteristic of a volcanic, particularly an is1andarc, provenance.Abundant quartz and metamorphic liftic 59 fragments indicate a conti.nental provenance. The presence of volcanic fragments mixed with metamorphic fragments and quartz suggests that there were two source terrains for the Galice, one a young volcanic terrain and the other somewhat older eroded continental crust.A. similar conclusion was reached by Coleman (1972) on the basis of Galice exposures north of the mapped area.The mixed provenances are consistant with a hypothesis that the Galice was deposteci in a marginal basin between the continent and island arc.

Late Jurassic Dikes

Altered igneous dikes up to several in. thick are common within the peridotife, especially along shear zones.They consist mineralogically of randomly oriented, brown hornblende laths, altered plagioclase and quartz.Chlorite, sausserite, prehnite and sphene are the common alteration productsPumpellyite is abundant in one rock,The few samples that were examined in thin section were andesitic; dacic and basaltic types were also observed in the field. The hornblende-bcaring dikes are clearly distinguishable from diabase of the mafic compie:. They lack augite and diahasic textures and they have undergone a lower grade of metamorphism. The mafic-corapiex diahase does not contain euhedral hornblende laths rj as the later dikes do. Dick (1974, 1976) has obtained potassium-argon radiometrc dates that cluster around 150 m. y. (Kimmeridgian) for lithically similar dikes a few km. north; thus the emplacement of the complex apparently predates this age.Serpentinization of the peridotite occurred prior to intrusion of the dikes, as the dikes have baked margins, but show no evidence of rodingitization.Rodingite corn- monlv forms in fe1dpathic rocks adacent to ultramafic rocks during serpentinization of the ultramafic rocks (Coleman1967). 61

STRUCTURAL GEOLOGY

General Statement

The structural geology within the Oregon Mountain area is complex and poorly understood. Three structural episodes are recognized: deforma:ion associated with the formation of the ophio lite, the Nevadan Orogeny, and post-orogen.ic uplift.The Coast Range Orogeny probably constitutes a fourth episode, but its effects could nct be distinguished n the mapped area from those of the Nevadan Orogeny

Earl,r Structures

The dcveior.ment of a tectoii.te fabric in the Josephine Peridotite and small scale fuiting in the diabase..spilite zone are attributed to deformation during the formation of the ophiolite. The tectonite fabric is the result of syntectonic recrysalliza- tics of the peridoite and has been discussed in detail by Dick (1976) ant-i by Loney and Hirnirelhurg (1976).Such fabrics are thought to form in the mantle beneath a spreading ridge (Aye' Laileniant and

Carter, 1970; Ave Latk-mant,I 976) The diabase-sr,ilite zone is cut br many faults with displace- rnents up to perhaps scveral Iudred rn.These faults could not be 62 mapped, but were evident in that textures and metamorphic grade of rocks in the diabase-spilite zone chtnged abruptly in many traverses. Normal faulting characterizes oceanic spreading ridges (Cann, 1967); therefore, I believe that many of these faults predate the tectonic emplacement of the complex and result, instead, from extension at a spreading center.

Nevadan Structures

The ophiolite complex in the Oregon Mountain area was tectoni- cally emplaced within its present setting during the Nevadan deformational event, Emplacement occurred as a complex west-directed movement along thrust faults and NNE-trending, high angle reverse faults accomoau:ied by folding of the overlying sedimentary rocks, These faulcs are the major recognizable structures within the mapped area.The high angle faults (the Illinois River fault srstem of Wells et al., 1949) and thrusts probably were not greatly separated in time; however, cross cutting relations (Plate 1) indicate that thrusting predated the high angle faults.Dick (1973) has obtained K-Ar dates of ahcyit 150 m. y. from dikes which intrude similar, probably related faults in the northern part of the peridotite.This age provides an upper limit to the time of faulting and the time of emplacement o± the ophiolite..Relatively small northwesterly- trending fau1tcut the doniinant faults.The age of these smaller 63 faults is unknown. The combined effect of the two fault systems within the mapped area is an extensive dismemberment of the ophioiiteThe displace- ment on any particular fault could not be determined. On major high angle faults, displacements may be several thousand xneers, estimated on the basis of juxtaposed ophiolitic zones. The thrusts may have horizontal displacements of up to several kilometers; however, there appears to be no obvious means by which this dis- placement can be determined.Plate 2 shows structural cross sections through the Oregon Mountain area which summarize the relations of the major faults. The Galice Forrnatioii, in the mapped area, is tightly folded along trends parallel .o the major faults.This folding is discussed by Wells et al., (1949) and hCater and Wells (1953).It is probably reasonable to assume that the folding is related in time tthe emplacement of the ophiolite.

Post-O rogenicift

The WJB including the Oregon Mountain area was uplifted and eroded in several stages following the Nevadan and Coast Range orogeriles.The best developed erosion surface is the Klamath PeneplairL (Eocene). Many flat top ridges in the region at a present 64 elevation of about 100(1 rn.,nciuding Oregon Mountain are remnants of this surface (Diller, 1902).

Age of the Mafic Complex

The age of the Oregon MountaIn ophiolitic rocks is known only within wide limits.Attempts to separate zircon from plagiogranite for uranium-1ead radiometric dating were unsuccessful.The ophio.- lite underlies the Galice Formation, and is therefore older than. Kimmeridgian (m±ddle-late Jurassic). A similar limit is imposed by 150 m. y., potassium-argon dates of the dikes which crosscut; the Josephine Peridotite (Dick, 1973). A lower age limit fcr the ophiolite is difficult to establish.Triassic or older rocks and evidence for T riassic deformation are not known in the western Jurassic belt, which suggests that the ophiolite is probably at least as young as the early Jurassic. M. A. Kays (pers. comm., 1976; H. J. B. Dick, analyst) has obtained a potassium-argon date of 177 m. y. (early Jurassic) from hornblende in gahhro of probable ophiolitic origin associated with the Josephine Perdct:ite about 50 km. north of the Oregon Mountin area. Owing to widespread alteration and metamorphism in the region a single pctassiurn-agon date should be regarded with sus- picion; nonetheless, the 177i.y. date for the age of ophiolif:ic rocks in the western Jurassic belt is the best presently available estimate. 65

GEOCHEMISTRY

Introduction

Chemical analyses of a suite of samples from the mafic complex were obtained to develop a more definitive model for the origin of the Oregon Mountain area ophiolitic rocks. Whole-rock samples were analyzed for major elements and selected trace elements, particularly the rare earth elements (REE), Ti and Zr to provide a comparison between the mafic complex and related rocks in other ophiolites, to investigate the chemical effects of metamorphism in the upper zone of the complex, to test the hypothesis that the mafic complex formed as oceanic crust, and to provide a basis for trace element modeling of magmatic processes possibly involved in evolution of the mafic complex.

Methods

Major element oxides except Na20 were determined by X-ray flourescence spectrometry (XR5) using a method mdiCied slightly from that described by Norrish and Hutton (1969).Counting statistics and analysis of U. S. Geological Survey rock standards (Appendix II) indicate an analytical uncertainty of ± 2 percent for most elements. Data for MnO for most standards analyzed are 00 precise to within± 5 percent of the acceped value (Flanagan, 1973)

I except for one anomalousdeterminationfor 3CR-i. Zirconium and strontium were determined by XRF using pressed powder pellets backed with boric acid. U S. G. S. standard rocks G-2, W-1 and 3CR-i were used as working standards. Data were reduced and interference corrections made by a computer pro- gram written by G. Cunningham at the University of Oregon. Multiple analysis of standard.s and counting statistics indicate that precision is on the order of percent of the accepted abundance for both elements. Sodium and magnesium were determined by atomic absorption spectrophotometry using the method of Ornang (1967) for about half of the samples analyzed.For the remaining samples, cothurn was determined by instrumental neutron activation analysis (INAA) and magnesium by XRF. Analysis of 3CR-i indicates that uncertainties

are on the order of + 1 percent for Na20 and±10 percent for MgO. Rare earth element concentrations and Na20 abundances were determined primarily by INAA usi.ng methods similar to that of Gordon et a].., (1968). Samples and standards were irradiated in the OSU-TRIGA reactor and their gamma-ray spectra obtained with

a high resolutionGe(Li)scintillation detector and a 2048 or 4096 channel pulse -height analyzer.Important analytical parameters and estimations for REE concentrations given in the appendix are 67 applicable to sampLe conceritration. about ten times those in chondritic meteorites (Table 3).Below this value, instrumentally determined rare earth values may be subject to much larger errors. Deter!rlination of very low abundances of REE in two pyroxenites (JP 178, JP 352) necesMtated i'adiochernical neutron activation analytical procedures. The method used is surnmerized by Boynton et al. (1977).In brief, previously activated samples are fuzed with an unactivated REE carrier.Repetitive hydrod.de and fluoride precipitations were used to extract the REE from the dissolved rock to improve peakto-background ratios for counting.Experimental yield is determined by reactivation to determine the percentage of the carrier recovered during extraction.The percentage recovery of REE in the sample is taken as equal to the recovery of the carrier, The results (Appendix TiC) have a precision which is within± 10 percent of the indicated value, estimated on the basis of counting statistics, except for Ce abundances which have a precision of about ± 20 percent. Rare earth e]ernenk data are presented graphically by dividing the abundances in the samples by the respective abundances in an average of 29 chondritic meteorites (Table 1) given by Wakita et al.,

(1970) 68

Table 1.Average rare earth e1ment comoiion of 29 chondrite meteorites (Wakita et al., 1970). Element ppm

La 0.32 Ce 086 Pr 0.11 Nd 0.59 Sm 0.196 Eu 0.071 Gd 6.25 Tb 0. 048 Dy 0. 31 Ho 0.071

1 r 0.20 Tm 0.031 Yb 0.19 Lu 0. 033

Major Element Chemistry

Diaba se -Slite Zone

Results,Analytical results for major element analyses of rocks from the diabase.spi1ite zone are tabulated in Appendix hG and arc presented graphically in Figures 21 and 24. Abundances of major elements expressed as wddes are plotted against FeO*!MgO where FeO* represents total Fe as ferrous oxide.The FeO*/MgO ratio is used because it is a sensitive indicator o crystal fractionation and, is relatively undisturbed by metasoniatism, as compared to other ratios or ccncentrations cf specific oxides. Thedata are grouped according to three mineralogi:ally based classes of rocks: (1) low temperature assemblages (mostly originally glassy); (2) epidote-quartz-albite greerischist assemblages; and (3) chlorite- quartz and actinolite-albite greenschist and amphibolite facies assemblages (mostly diahases).One keratophyre (JP 340) and a sill in the Galice Formation (JP 391) were alsO analyzed. Definite trends were distinguishable for a few elements. Abundances of MgO decrease with FeO/MgO, whereas Tb, and FeO* generally increase with FeO*/MgO. Abundances ofother oxides do not shcw dc±inite trends withFeO*/MgO. The sample of keratophyre, TP 340, (Appendix hG) is chemically distinctfrom the three classes of metabasaltic rocks.In particular it has higher Si02 and K20 and lower MgO, FeO* and T102 abundances. Relative to sea floor basalts (Table 2) metahasaltic rocks from the Oregon Mountain area are enriched in SiO, Na20, and H20,and depleted in T102, Al203, FeO, MgO and GaO; relative abundances of K20 are variable, Several cheinica3. trcnds can he discerned which are apparently related to the metamorphic niineralogr of the rocks.Originally glassy basalts, now in the zeolite fades, are low in S1O,particularly low in MgO, and enriched in FdO and HO, refkcting their abunciaiit 70

Figure 21. FeO*/MgO vs major element oxides in rocks from the diabase-.spilite zone, Oregon Mountain area. Low temperature assemblages (0); quartz-epidote-.albite green. schists (); actinolite-albite greenschists and amphibolites (a); keratophyre (.a ); mid-ocean ridge basalt (MORB); tholeiitic rocks (Thol.); caic-alkaline rocks (C-A); alkalic rocks (Alk.).Fields and trend lines are from Miyashiro (1973). // C-A, 41k. / e 60 / (N 0 0 0 0 (I)5Q 0_-__--- 0 Thol. / 40

0(N H

0 8 I 0 0 O 16 .0 0 .. . Ga I 0 4 .0 0 2

. 0 00 0 0 G . / Thol, 8 I. -.- (I)*0 6 G .. OLL4Lii 0 x o 2 A 0

0 I 8 (9 :..I 0.0 SI 0

2 G 00

0 0 0 0 o .0 0 8 0 06 I 04a 0 0 0 2 A 0

8 0 06 I 0 I 0 0 ' 0 II A 0

(1.6) I I.0 0 0 (N I 0 .5 . 0 0 t: 0. 0 0 0 2 3 FeO*/ MgO 72

)o0

wi:% 1120

Figure 22.SiO and Na20 in diabase-spilie zone rocks, Oregon Mountain area. Symbols as in Figure 21. j UZ' 23.Na0 :0:esf0th0 Spjji Zcle0IgO 'e1cj Odified j et aj(l9);SYb3 21. Na20 Figure 24. AFM comparison KOfield from Bailey and Blake, (1974); symbols as in Figure 21. plot for diabase-spilite zone rocks, Oregon Mountain area. MORB -4 75

Table 2.Average chemical composition of rock t'rpes in the diabae spilite zone, Oregon Mountain area, compared to sea- floor basalts.(1) average of 8 sea-floor basalts from Carmichael et al. (1974)(2) zeolite facies rocks; (3) chorite-quartz greensohist facies rocks (4 samples); (4) quartz-epidote-aibte greenschist facies rocks (6 samples); (5) actinolite-a1bite ar.ci aniphibolite facies rocks (12 samples

1 2 3 4 5

Si02 48.79 49.15 54,67 59.04 54,84 TIC2 1.47 1.36 086 0.90 0.84 A?703 16.23 15.35 15.01 15.28 15.16 FeO 9.73 10.07 8.45 6.82 7.86 MnC 0.15 0.15 0.15 0.13 0.15 MO 8.07 4.12 5.13 2.90 6.05 CaO 11.17 9.71 6.90 6.36 6.64 Na20 2.72 2.87 4.58 4.42 4,43 1(20 0.24 0. 34 0.27 0. 15 0.43 P70 0.15 0.14 0.11 0.15 0.14 H2 0 1.30 4. 19 3.90 2. 33 2.71 To;aJ 100. 02 97, 45 100.03 98.48 99' 25 76 zeolite and Fe-rich smectite mineraiogsr. Abundances of GaO, Na20 and K20 are variable in this group (Appendix hG) owing, in part, to variable amounts of calcite and aibite in the rocks. Quartz-epidote-albite greenschist fades rocks are considerably enriched in SiO., and somewhat enriched in Na 0. Most of the other 2 oddes are depleted in this group. Chlorite and actinolite greenschist fades and amphibolite fades rocks have similar, although less pronounced trends as the quartz-epdote-albite rocks; however, K20 an.d H20 are somewhat enriched in the former groups. DiscussionIt is apparent that the chern.Lstry ot roLks from the diabase-spilite zone is controlled more by metamorphism than by magmatic processes. These rocks differ significantly from mid- ocean ridge basalts in their major element chemistry (Figure 22, 24; Table 2), but are similar in both chemistry and mineralogy to basaltic rocks from other ophiolites (Bailey and Blake, 1974) and to metamorphosed rocks which have beeii recovered from many locations on the sea floor (Melson and Thompson, 1966; Melson et al., 1968; Cairn and Funnel, 1968; Cann, 1969, 1971; Miyashiro et al., 1971; S. R. Hart et al., 1974; Valance, 1974.). Sea-floor metamorphism is a low pressure type of burial metamorphism, represented by zeolite fades, greenschist facies and arnphibolite facies mineral assemblages (Can, 1969; M,yashiro et I'I a!,, 1971).Recent experimental work (Motti &t aL, 1974; Bisehoff et al., 1975; Hajash, 1975) indicates that the observed sea-floor metamorphic assemblagescan be ex-rIained in termsof the nter- action of seawater hydrothermal solutions and basalt. Chemically, metamorphosed sea-floor basalts cn be grouped into three types, which correspond to the three groups of basaltic rocks in the Oregon Momtain area. Sea-floor :ocks which were originally glassy (weathered basalts, zeolite fades rocks, chlorite- quartz greenschist fades rocks) aregenerally depleted in SiO, CaO, K20, and Al203, and enriched in FeO, MgO and H20. Na20 is depleted in originally aphyric rocks andenriched in zeolite-bearing and albitized porphyritic rocks (Cann, 1969; Miyashiro et al., 1971; S. R. Hart et al., 1974).Holocrystalline basalts arid diabases from the sea floor in the upper greenschist facies and lower amphiholite fades, contrastingJ.y, are enriched inSiO2 and Na20 and show less pronounced changes in other elements, compared to unaltered basalts and altered glassy basalts.Quartzepidote rocks from the sea floor are characteristically Si02 rich and depleted in most other elements

(Cann, 1969). Chemical trends for aliered sea-floc: basaits and rocks from the Oregon Iviountain diabase-spilite zone are similar in many vespects.In general, however, Oregon Mountain area rocks are richer in Sb, and depleted in Al203, TiC)? and MgO relative to 78 altered sea-floor rocks. These differences may he ctrdy primarysince Al203 arid Tb2 are regarded to be relatiF stable during low temperature metamorphismThe SiO. er-irnent is,n part, onl,r appalenr, because most Oregon Mountain samples are from. originally holocrystalline rocks; glassy rocks, which are prevaient in the sea-floor studies, alter to very hydrous, low silica minerals (smectite and zeolites),It may also be that the Oregon Mountain rocks are, overall, n-iore intensely altered than analyzed sea-floor metabasalts, owing to more intense hydrothermal activity, greater age, or greater depth of bnrial.Despite these differences, the broad similarities in the mineralogy and chemistry of Oregon Mountain diabase-spilite zone rocks and metamorphosed sea-floor rocks indicate that the two have undergone similar histories.it is possible to construct a qualitative model to account for the observed chemical and mineralogical trends of both groups. The low temperature assemblages form at shallow depths in the volcanic pile, from mostly glassy basalts. Alteration near the seawater-basalt interface initially results in replacement of glass by smectite and of calcic plagioclase by aihite. At successively greater burial depths zeolite fades and chlorite-quartz greenschist facies assemblages appear.Temperatures at.... ch these assern-- blages form are probably less than2000C (Motti et al. ,1974; 79 Bischoff et al., 1975; Hajash, 1975; Miyashiro et aL, 1975). Deeper in the crust, the rocks are mostly holocr'rstalline diabases.Temperatures can be expected to be in the range of3000 to5000C (Hajash, 1975; Miyashiro, 1975), ow.ng to high heat flow at oceanic ridges.At these temperatures the rocks recrystallize to albite-actinolite greenschist and amphibolite facies assemblages. Seawater hydrothermal solutions are important to all parts of the metamorphic sequence, as they are the medium by which the observed metasomatic changes take place. Where seawater interaction is particularly intense, the metallic elements are leached from the rock leaving a silica-rich residuum represented by the quartz-epidote-albite rocks. Massive sulfide deposits such as the Turner-Aibright deposit fcrm by the precipitation of metals from the enriched hythoteriria]. solutions at or near the sea floor.Similar models for metamorphism and metallogenesis in the oceanic crust and in ophiolites have been presented by several authors (Anderson, 1969; Clark, 1971; Hart, 1973; Motti et al. ,1974; Bischoff et al., 1975; Miyashiro, 1975; Hajash, 1975; Corliss, 1977). Plutothc Rocks. Analyses of cumulate gabbros, ultramafic rocks, hornblerde gabbros and quartz diorites are tabulated in

Appendix 11G.Figure 25 is an AFM plot showing the trends of the rnafic- complex plutonic rocks. Whole-rock chemistry of cumulate rocks is of limited usefulness because mineral proportions and hence 80 compositions vary widely over short distances in outcrop, and thus do not represent the composition of the p rent liquid.The data do, however, serve to demonstrate a close similarity between Oregon Mountain area plutonic rocks and plutonic rocks from the sea floor (Bailey and Blake, 1975). Hornblende gabbro and tonalice crop out with diabasic rocks, and chemical data for these rocks occupy a similar compositional fields (Figures 24, 25).The compositions and textures of many of the hornblende gabbros (Appendix IIC) are much like that of the high temperature class of diabases.Because of these similarities it is probable that these gabhros are coarse grained equivalents of diabase, rather than differentiates of the cumulate series. Abun- dances of Si02, Na20 and H20 in the hornblende gabhros probably have been increased by metasomatism. The analyzed albite granite (JP 316) plots near the alkali apex of Figure 25, reflecting the leucocratic nature of the sample.It is silica rich (66 percent) and low in K20 (0. 22 percent).The tonalites and albite granite (collectively plagiogranites) have similar textures; they vary mainly in their contained abundances of dark minerals. The plagiogranites are interpreted as the end products of differentiation and hence are probably related to the underlying cumulate rocks. N 120 Figure 25. AFM comparison plot for plutonic rocks, Oregon Mountain area. publishedrocksK20 (*); analyses cumulate of gabbros (. ); hornbiende gabbros ( ca-floor plutonic rocks (Bailey and Blake, l74 ); plagiogranites (0). Fields represent MgOUltramafic 82

Trace Element Geochemistry

Introduction

Metasomatism has altered the major element chemistry of the ophiolitic volcanic and hypabyssal rocks to such an extent that their magmatic affinities cannot be determined by analysis of major elements alone. A number of studies have appeared in recent years which attempt to solve the problem of ophiolite origin by application of trace element method3.It has been shown that, in particular, Ti, Zr, Y, Cr, and the rare earth elements are relatively immobile during low temperature metamorphism and that they are potentially valuable tracers for distinguishing between rocks of mid-ocean ridge, arc tholeiite, and calc-alkalj.ne affinities (Pearce and Cann, 1971, 1973; Pearce, 1975; Hart et al., 1974; Kay and Senechal, 1976;Smewingetal., 1975).

Ti-Zr

Pearce and Cairn (1971, 1973) have used Ti and Zr abundances to distinguish mid-ocean ridge, calc-alkaline and arc-tholeiitic rocks. They established fields on Ti vs Zr diagrams which were characteristic for each of the three groups of rocks (Figure 26).The fields overlap consIderably, however, and the overlap limits the utility of 83

8 0 0 008060 e o r' o ''8°

0 E 0. 0.

50 00 50 200 Zr, ppm

Figure 2.6.Ti vs Zr discrimination plot of sea-floor basalts.Arc tholelites (A, B); caic-alkaline basalts (B, C); sea- floor basaits (B, D).Data points are for published analyses of sea--floor basalts. Redrawn from Pearce and Cann(1973). 84 this type of graphic anaJ.-i.Pearce arid Crin (1971, 1973), Miyashiro (1973), Pearce {1975), Smewing et al. (1975) and Kay and Senechal (1976) have disc:.s .ed application of Ti-Zr correlation methods to rocks of the Troodos complex. These workers considered the data to be inconclusive in determining the affinities of the Troodos rocks. Most of them (Miyashiro excepted), however, felt that the Troodos data suggested an affinity with sea-floor basalts. Despite the partial overlap in Ti. .. Zr distributions for rocks from different tectonic settings, some distinctions ar evident. There is strong positive correlation between Ti and Zr in sea- floor hasalts.Contrastirgly, very little TI enrichment occurs at high Zr abundances in caic-aikaline rocks. Arc-tioleiitic rocks show little eiirichment in eihor Ti or Zr.It is suggested that the slope of the Ti-Zr distribution for a suite of related rocks is a more sensitive means of dter!nin±ng provenance than the position of individual points.Data from Pearce and Cairn (1973) (Figure 26) were teaTruned with this poshiLy in mind, onTi/iOfls Zr diagram, data for sea.-fioor ha salts follow a trend with basalts a positive slope of about 0.6. Application of the slope method is advantageous in that alter.. ation of a few Ti. or Zr points within a larger population of data will not greatly affect calculated slopes.Plots of Ti02 vs ieOiMgO from the Toodos Massif (MiyashIro,1973)and the Oregon Mountain 85

area (Figure 21) do not corrzlate well with either thoieiitic01' caic-alkaline trends, suggesting t':iat some mobilization of Ti may have occurred.In the O:re;zon Mountain area, quartz-epidote metasomatic rocks have particularly low Tb2 abundances for a given value of FeO*/MgO (Figure 21). Spilite and diabase from the Oregon. Mountain area were analyzed for Ti and Zr (Appendix hG).Ratios of these data plot with some scatter but define an apparent trend of Ti and Zr enrichment (Figure 27), Many of the points within the caic-aika].ine field of Pearce and Cairn (1973), hut the overall distribution resembles that of sea-floor ba5alts. Thus the data are inconclusive with respect to this type of analysis. A least squares fit of these data yields a slope of 0. 60, suggestive of an affinity with sea-floor basa1tsalthough the Oregon Mountain distributions are considerably displaced toward higher Zr abundances.

Rare Earth Geoches!r

Introduction.The rare earth elements (REE) are particularly useful tracers of magmatic processes. The 14 REE have similar ionic radii, and a3+valence under most geologic conditions. Under 4+ some conditions Eu may be reduced to2+or Ce oxidized to which may result in anomalous values of these two elements,relative to the REE as a whole, Because of their similarities, the REE behave 36

20,000

15,000 E CL CL . 10,000 H-

5,000

I 0 50 100 150 200 Zr% ppm

Figure 27.Ti vs Zr discrimination plot of OregonMountain area diabase-spilite zone rocks.Basaltic rocks (o); keratophyre (A ); fields as in Figure 25. Aleast squares fit of sample distributionhas a slope of 0. 60 with a correlation coefficient of 0. 6S 87 coherently in geologic processesRelative variability in concentration within the group is fairly small, compared to variability within other element groups (eg. the alkali elements) and abundances vary smoothly with ionic radius (or atomic number). Rareearth element abundances customarily are normalized against average respective abundances in chondritic meteorites, which are thought to have the apprwdrnate REE composition of the earths mantle. Normalization produces smooth curves on the commonly used REE (Sample)/REE (Chondrites) vs atomic number plot.The shape arid graphical position of these curves indicates relative and absolute chemical fractionation within the group.Different classes of rocks generally have distinctive REE patterns and total REE abundances by which they can be characterized. The REE have been shown to be immobile during metamorphism and metasomatism of ophiolitic rocks of up to amphibolite grade (Montigny et al., 1973; Kay and Senechal, 1976).Evidence for minor changes in REE abundances during sea-floor weathering has been published by Nicholls and Islam (1971), Frey et al. (1974), and Herrmann et al. (1975).ft general, however, it appears that the REE are relatively stable under most metamorphic conditions encountered in ophiolites. Basaltic Rocks. Sea-floor basalts have REE patterns which are typically flat to somewhat depeted inh.e Iiht REE (Figure 28) 88

o Ce Pr Nd Sm Eu G Tb Dy )o Fr Tm Y

Figure 23. Rare earth element patterxs of island arc tholeiites (vertical stipies), midocean ridge tholeiites (shaded) and caic-alkaline, shoshonitic and aikalic rocks of arcs btwen dashed lines); (fromJake and Gill, 1970). 89 with abundances which average about 10 times those in chox.drites

(Frey, 1968; Kay et al. ,1970; Schilling, i97l1975).Light REE- enriched rocks have been reported from a few mid-ocean ridge sites (Schilling, 1971; Nicholls and Islam, 1971), and from the Lau Basin (S. R. Hart et al., 1972; Gill, 1976). Caic-alkaline rocks from island arcs are sigthficantly enriched in light REE relative to sea-floor basalts (Taylor, 1969;JakeX and White, 1971).Island arc tholeiites have REE distribution fields which are very similar to, and overlap, the field for sea-floor basalts (Figure 31). Rare earth data for arc tholeiltes, however, have a greater compositional range and are commonly light REE enriched relative to sea-floor baalts. Miyashiro (1973), Jake and Gill (1970) and Kay and Senechal (1976) have pointed out the similarity n REE distributions between sea-floor basalts and arc tholelites.Both suites are readily distinguished from rocks of the caic-alkaline suite on the basis of REE distribution. A siite of rocks from the diabase-spilite zone was analyzed for the REE. Analytical results, representing a range of metamorphic and c1mcal rock types, are listed in Appendix IIC and are suinmaried in Figure 29. Data for ten samples form a tight group. These samples exhibit fiat, slightly La-enricied distributions (Av. La/Lu = 1.5) and low absolute abundances (ay. La:15 x chondritic abundances). 90

30 20 O--- JP4O7

C') JP 135 U 345 JP35t -I---- L a: z0 o 30

()20 JP416 Li iP34I Li JP 313 a: tO JP347

I _j__J LiJ 0 30 (')20 Li J P359 U -" J P 358 WJP 366 JP 306b

LaCe SrnEu Tb YbLu REE BY ATOMIC NUMBER

Figure 29.Rare earth element patterns for rocks from the diabase- spiite zone, Oregon Mountain area.Top, low temper- at-tire metamorphic rocks; middle, quartz-epidote.-albite greenschi st facie s rocks; bottom, actinolite -albite greenscbist facies rocks. 91

A few sample s appear to have a slight negative Eu anomaly, butthe anomaly Is uncertain owing to the poor precision for Tb analyses. No distinction can be made between diabases and extrusive rocks on the basis of the REE. The close grouping of REE data from the basalts and diabases suggests that they belong to a single, relatively primative, magma type, rather than that they are successful members of acrystal fractionation series.The lack of a strong Eu anomaly suggests that piagiociase, which preferentially incorporates Eu, was not removed in large amount5 from the parent liquids. A limited amount of differentiation cannot he ruled out however. Hence it is concluded that these basalts and diabases are not differentiates of the liquids which were parental to the underlying cumulates. Field evidence is supportive of this conclusion in that one sample (JP 359; Figure 29) is froma dike which crosscuts and thus post-datesthe cumulate sequence. One saxnple SP 407) is considerably enriched in the REE's (La ZOx chondritic abundances) compared to the majority ofthe samples.It may be that this rock resulted from a smaller degree of partial melting of parent rock, than the other basalts or that this particular basalt has been significantly enriched in REE through crystal fractionation.Conversly, sample JP 306h, a diabase, has low abundances of REEs, a fairly low FeO/MgO ratio (0. 861 and 92 low Ti (6200 ppm) and Zr (33 ppm) c3ntens.It was evidently produced by a relatively iargc degree of melting of parent rock. Diabasic rock JP 39! (Figure 30) is unique in that it has a negative Ce anomaly. This rock conies from a sill in the Galice Formation a few hundred meters above the Galice-mafic complex contact.The chemistry and mineralogy of this sample is like those of mafic complex diabases except for the Ce anomaly (and the presence of green-brown hornblende),It is interpreted that low temperature alteration of the sill by sea water caused wddation of +3 +4 Ce to Ce which facilitated removal of Ce, perhaps as chloride complexes. A similar interpretation has been made for spilites with negative Ce anomalies in the Pt. Sal ophiolite (Martin Menzies, pers. comm., 1976).Evidence for mobilization of REF's during alteration of sea-floor basaits has been aiscussed by Frey et al.

(1974).The presence of horublende is not understood. Most sea-floor basalts are somewhat depleted in light REF's. It has been interreted that the mantle under mid-ocean ridges has undergone previous partial melting events which depleted the source rocks in the more volatile elements, including light REE's (Kay et al.., 1970; Schilling, 1971, 1975).Basaltic rocks from the Oregon Mountain area are moderately enriched in light REE;s and have abundances within the published range.s of ocean floor and island arc rock suites.It is interpreted that the magma s which formed the 93

LUU)

20 czZ0 tio-.-- 10 JP391 LLJ

1 t_-1 La Ce Sm Eu Tb Yb Lu REE BY ATOMIC NUMBER

Figure 30.Rare earth element pattern for a sill (JP 391) inthe Galice Formation near the top of the diabase-spilite zone, Oregon Mountain area.Note negative Ce anomaly. 94 mafic complex were ri :-nelts o.Z rx.antlmaterial which was undepleted, compared to the parent mantle material for most ocean- floor basalts

Rare earth patternsof basaltic rocks from the Oregon Moun- tain area preclude a calc-alkaline affinity; the patternscannot be used, however, to distinguish between an arc-tholeiite orocean- floor provenance. Abundances o2 Ti and Zr in Oregon Mountain basalts suggest a sea-floor origin but do not indicate affinity with arc tholeiites.The REE and Ti-Zrtracers collectively indicate that the Oregon Mountain area basaltic rocks resemble ocean-floor basalts much more closely than arc-tholeiitic or caic-alkalire rocks. Keratophyre. Quartz keratophyre (JP 340) from the diaba'e- spilite zone has a strongly light REE enriched pattern (Appendix IIC; Figure 31).This rock has low Ti(800 ppm) high SIC2 (72 percent) and high K20 (1.6 percent).These abundances haveprobably been changed somewhat by- metasomatism,but,nevertheless, are quite different from the composition of basaltic rocks from the diabase- spilite zone. A caic-alkaline affinity is indicated for this rock on the basis of its composition.It is suggested that JP 340 was an air fall or ash flow which was erupted, presurnab1y from the nearby

Rogue island arc. Rocks with similar,light REE enriched patterns typical of the calc-aikaline trend have been reported from the Rogue

Formation (Garcia,1976). 95

100 (I)

<0z - avD-S Io JP340

I______LaCe SmEu Tb Yb Lu REE BY ATOMIC NUMBER

Figure 31.Rare earth element patterns for keratophyre (JP340) and the average of 12 basaltic rocks from the diabase- spilite zone, Oregon Mountain area.Shading indicates the range of diabase-spilite zone analyses. 96 Keratophyres are ab'andaritin some ophio1:ite(Thayec and Hi.rnrnelburg, 1968; Thayer, 1968; Hopsonet1., 1975a) but i know of none from the sea floor.The interpretation given for sample JP 340 may he applicable to keratophyres in other ophiolites.Rocks of possible island arc origin commonly are associated with ophiolites

(Schweickert and Cowan, 1975; Thayer, 1974; Dewey and Bird1971; Monger eal., 1972). Some light colored rocks which have been called keratophyres (Bailey and Blake, 1975; Hopson et al., 1975a) have a mineralogy of the quartz-epidote ty-pe described herein and bsr Cann (1969).These rocks probably result from advanced metasomatism of basalt, Plutonic Rocks.Rare earth distributions were determined tom 13 rocks from the cumulate sequence of the mafic complex (Appendix HC). Chondrite-normalized analytical results are summarized in Figure 32.Distributions for two chemically and mineralogically similar gabbros (JP 0029 JP 042) and three similar plagioclase pyroxenites (JP 039, JP 041, JP 043) are p1oted as averages. The remaining samples are more distinctive in mineralogy and REE contents and are plotted individuaUy Rare earh diributions for cumulate rocks from the Oregon Mountain area emble tiose frothe Troodos complex (Kay and Senechai, 1976, the Piidooptdolitc (ontiguJ et al., 1973) and thc mid-Atlantic Ridge (Masa Jibiki, 1973) Sa-uple JP 3529 97

I0O

-S JP316 liito I- JO -----a i---A JP442 zc:i JP129 0 G 2gihbros __- ___-' JP 322 uJ o-- 3 pxites

o--o JPF?9

JP352

LaCc SmEu Tb Dy Ho Yb Lu REE BY ATOMIC NUMBER

Figure 32. Rare earth element patterns for plutoric rocks, Oregon Mountain area.Pyroxenites (o); gabhros (); norite dike (4 ); plagiogranites (). Gadolinium points (not identified) interpolated to emphasize Eu anomalies. 98 a pyroxene adcumuiate rock contains the lowest REE abundances and most light-REE depleted pattern of the samples analyzed. Samples with progressively greater REE abundances have progressively flatter patterns. Crystal-liquid distribution coefficients (D elementconc. solid/conc. liquid) for the REE's are considerably less than unity for most minerals (Phiipotts and Schnetzler, 1970, 1972).Therefore it can be expected that trapped intercurnulus liquid will contribute a significant part of the REE content of cumulate rocks (Kay and Senechal, 1976).Accordingly, rare earth abundances in samples JP 322 (adcumuj.ate norite) and JP 352 (adcumulate pyrocenite) are lower than REE abundances in the ortho- and mesocurnulate gabbros and pyroxenites which were analyzed. Adcumulate rocks contain little crystallized trapped liquid owing to secondary growth of settled cumulus minerals (Figure 17).Ortho- and mesocumulate rocks may contain up to 50 percent trapped liquid (now crystalline).Samples JP 322 and JP 352 have pronounced positive and negative Eu anomalies respectively in accord with the large DE for plagioclase and small DE for clinopyroxene (Philpotts and Schnetzier, 1970). Tonalite (JP 442) and albite granite (JP 316) have patterns which are slightly enriched in the light REE. These two rocks are interpreted as crystallized differentiates of the cumulate series. Their light REE enrichment is consistant with a progressive change 99 in liquid composition, as light REE depleted crystals are removed. Sample JP 316 has a pronounced negative Eu anomaly which indicates that the magma was depleted in Eu by crystallization of plagioclase The contrast between the REE distributions of albite granite in JP 316 and keratophyre JP 340 (Figure 31) is further evidence that the kertophyre was not derived by differentiation of the basaltic magmas which produced most of the rocks within the mafic cornp1ex The history of norite sample JP 129 (Figure 32) is proble- matical in that it has a positive Eu anomaly, suggestive of plagioclase accumulation; however, it has a hypidiornorphic-granular texture and strcngl zoned plagioclse (cores = An 57)--features which are not typical of cumulate rocks.Rodingite samples JP 01and JP 026 have similar REE patterns to JP 129 (Figure 33).Apparently the rodingites have not been greatly altered with respect to the REE. All three specimens came from dike.4ike bodies near the base of the pyroxenite section, within se rpentinized ultramafic cumulate s. Many of these dikes, averaging about 1Q cm. in thickness, occur on Oregon Mountain.Coniinonly these dikes are highly branching (Figure 19).The positive Eu anomalies would seem to preclude an interpretation that these dikes are feeders from the underlying mantle.Therefore it is suggested that JP 129 formed by the pressing

out of intercumulus liquid frorr. a mushy,clinopyroxene-rich cumulate. The rodingites are evidently altered equtvalents of this 100

Ui H aQ to 2: J P026 0 ------G 0T JPOL5

LU Ui

I.0 La Ce SmEu Dy Yb Lu REE BY ATOMIC NUMBER

Figure 33. Rare earth element patterns for two rodingite dikes (JP 015, JP 026) which cut cumulates on Oregon Mountain.Gadolixilutm points (not identified) interpolated to emphasize Eu anomalies. 101 gabbro.Indeed, there 5eems to be a gradation between fresh gabbro and rodingite.Fo: example, gabbro JP 016 (Appendix IIC) is chemically and petro graphically intermediate between rodingite s JP O1S and JP 026, and gabbro JP 129. Somewhat analogously Hopson et al. (1975a) reported norite dikes from the lower portion of the Point Sal ephiolite which they, however, considered to be feeders for the overlying volcanic rocks, on the basis of major element chemistry. All of the analyzed plutonic rocks have REE patterns which are light-REE enriched relative to equivalent rocks from the Troodos complex (Kay and Senechal, 1976) and the Pindos ophiolite (Montigny et al., 1973).This characteristic is consistent with the relatively light-;REE enriched patterns of the Oregon Mountain mafic complex compared to both ophiolites and typical mid-ocean ridge basalts. Rare earth elements were determined for one sample from a hornblende-rich dike that cuts the Josephine Peridotite (JP 142, Appendix IIC).The REE distribution for this dike (Figure 34) is considerably light REE enriched (La/Lu = 2.6) relative to mafic complex diabase.This pattern has abundances within the range of caic-alkaline andesites (Figure 29).Apparently such dikes are unrelated to the ophiolihc rocks as was concluded on the basis of ft.eir occurrence and mineralogy 102

JP39

7 1 La Ce SmEu Tb YbLu REE BY TOMC NUMBER

Figure 34.Rare earth element pattern for andesite dike which intrudes a fault zone in the Josephine Peridoti.te, Oregon Mountain area. Compare pattern with range of caic- alkaline rocks shown in Figure 28. 103

REE Models of Ore or'. Mountain Area Petrogenesis

Introduction

Recent improvements in our understanding of thetheoretical basis for trace element partitioning (Gast, 1968; Shaw, 1970) and the availability of precisely determined partition coefficients (Phil- potts and Schnetzler, 1970) permit the construction ofquantitative models for trace element behavior during magmatic processes. Such models can provide considerable insight into the origin of a suite of rocks, if they are interpreted in light of field relationsof the rocks, their petrography and their major element chemistry. The relative concentration (CE) of an element E between a liquid and a co-existing solid is given by the Nernst expression for the distribution coefficient:

crystal E liquid CE which is temperature dependent.If a number of minerals crystallize simultaneously, a bulk distribution coefficient can bedetermined

D JXiD1 104 th where Xi is the mole proportion of the imineral erystailizing.If the appropriate DE values are known, itis possible to calculate the behavior of dispersed (trace) elementsduring petrogenetic processes. Trace element behavior duringcrystallization has been treated theoretically by Gast (1968). Two limiting cases maybe considered-- surface equilibrium, in which crystals areremoved continuously from the liquid as they form (eg. bysettling or zoning), and bulk equilibrium in which the crystals andliquid remain in equilibrium throughout crystallization.Conditions of surface equilibrium are more appropriate forfractional crystallization andcrystal settling and therefore are used here.It should be stated, however,that some degree of bulk equilibrium generallyprevails during crystallization; the relative importance of the twoconditions cannot be precisely determined. The appropriate expressions forvariation of an element during surface equilibrium crystallization havebeen given in a convenient form by Murali, et al. (1977) and Leemanet al. (1977):

CL =F' and 1-F C 0

and under bulk equilibrium conditions:

D__ I and C F+D(l-F) - F±D(1-F) 0 0 105

Where CL in the concentration of the element in the aggregateliquid, Co is the initial concentration of the element in theliquid, F is the fraction of original liquid remaining, Cs is the concentrationof the element in the residual solid, and D is the bulk distributioncoefficient. An expression for trace element behavior duringpartial melting has been given by Shaw (1970):

1 C D+F(l-P 0

where P is a bulk distribution coefficient that isweighted according to the proportions in which mantle phasesmelt and F is the weight fraction of melt formed. The distribution coefficients used herein aretaken from the compilation of Murali et al., (1977). A temperatureof 1300° C is assumed for partial melting and1200°C for fractional crystallization (Murali et al., 1977).Therefore distribution coefficients for the two processes differ somewhat.

Fractional Crystallization Models

Most of the basaltic rocks analyzed for REEhave very similar abundances, which suggests that they have not beengreatly fractionated.Crystallization of small amounts (< 10 percent;)of plagioclase and clinopyroxene is reasonable to explain, respectively,the small 136 negative Eu anomali.dnd mode rate iighJ REE enrichment which occur in some sample;, and these two rninrals are com:mon as phenocrysts in spiites from the diabase.-spilite zone. !)iabase JP 306b and spilite JP 407 hnve, respectiveli, 1:he lowest and highest RE abundances of the basaltic rocks analyzed. Models were constiucted to determine if these two rocks might be related to the other basaltic rocks through cr'ctal fractionation processes Crystallization of about 50 percent olivi.nend minor plagio-. clase and clinopyroxene from a liquid with the REE content of JP 06b would produce a liquid with REE abundances like those in the majority of the. basalts.Such. a model requires that rock JP 306h initi1iy was an ult:amafic liquid; this hypothetical constraint is n supported bi the chemistry and petrography of the sample. The REE abundances in spilite JP 40'? can be produced by crystallization of plagioclase from liquids with REE contents similar to those of the majorit,r of the basaltic rocks.This process how ever, would introduce a substantial negative Eu anomaly, which the sample does not exhibit. Rare earth element modeling was used to investigate the possible crystallization history of the cumulate series.The models generted were subject to the constrairte that the albite granite differentiate is volumetrically less than !0 percent oi the cumulate 107 series, and olivine, clinopyoxene and piagiociase arethe most abundant cumulus minerals in the layered sequence.It was assumed that the initial liquid had flat or slightly light REE-enrichedpatterns like those of rocks in the diabase-spilite zone It was found that upon 90 percent crystallization,liquids with the REE composition of albite granite (3P 316) wereproduced by removal of piagioclase and clinopyroxerte in approximately atwo-to- one ratio; the proportion of olivineremoved is variable, depending upon the total REE content of theinitial liquid.If surface equilibrium is assumed, an initial REE concentration of about5. 5 times chondritic abundances is required (Figure 35).If some degree of bulk equilibrium is allowed, higher initial concentrations canbe assumed since bulk equilibrium results in less enrichment inthe REE. Basalts with 5. 5 times chondritic REEabundances are unusual. Hence it is likely that a considerable degreeof bulk equilibrium was obtained, especially during the latter stages ofcrystallization when crystal settling would probably be relatively inefficientowing to increased visäosity of the magma.

Partial Melting Models

To develop a model for partial melting, one mustidentify the mantle conditions under which melting takes p1ac. Inparticular the initial mineralogy, the proporticnin which the miner.s melt, 108

100 rr phase proportion U, .1 w 90% cryuUi2CtiOn ploq. .5 -50 cpx .3 a: urfocc equil. liquid z0 0 bulk equil. liquid

0 // uJ w a:

-JLu Initial comoositian: 5.5 x chondrites equii solid

(1) - rface equiLsolid Lu Lu a:

I I La Ce SrnEu Tb Yb Lu REE BY ATOMICNUMBER

Figure 35.Rare earth element model for 90 percent crystallization of a liquid with 5.5 times chondritic REE abundances. Mineral proportions were chosen to provide best surface equilibrium fit to albite granite (JP 316) in Figure 33. Gandolinium points (not indicated) interpolated to emphasize Eu anomalies. [09 and the initial abundances and DE values for the modeled elements must be specified. Although these factors have not been established unequivocally, certain limitations can be imposed Geophysical and petrologic studies (Ringwood, 1975) collectively indicate that the mantle is mostly of peridotitic composition. Ring- wood (1975) has conceived and promoted a rather narrow range of model mantle composition (pyrolite) which may occur as lherzolite (ol to px + cpx± spinel) at moderate depths in the mantle (70 km., or 20 kb.); and a 10 to 30 percent partial melt of pyrolite yields tholeiitic magmas, leaving a residuum of olive-rich harzburgite (01 + opx + spinci). Melting relations in the svstem forsterite - diopside-enstatite, have been investigated by Kushiro (1969). At 20 kb. the first liquid produced has a composition of about Fo0. 15, Di = 0. 65, En = 0. 20, a estimated from the ternary phase diagram. These proportions can he taken as a rough estimate of the melting proportions of olivine, clinopyroxene and orthopyroxene, re spectively. The REE composition of the mantle is not known with certainty and is likely to vary somewhat, both geographically and vertically. iflundepleted mantle, however, the REE composition is believed to be similar to chondrite meteorites (Ringwood, 1975).The mantle in oceanic regions probably is somewhat depleted in REE, particularly the light REE owing to melting events prior to the eruption of bacalts 110 that presently compre tie oceani erut (Kay et al. ,1970; Schilling, 1975). If we accept the proposition that alpine-type harzburgite is the residuum of partial melting at mid-ocean ridges (Menzies, 1976), a model undepleted mantle mineralogy must be chosen which will leave a harzburgie residuum on partial melting. For the models tested, proportions of ol:opx:cpx of about 0. 6:0. 3:0. 1 worked most satisfactorily (Figure 36).But a considerable range of mineralogy, and hence composition can produce acceptable models; the results vary only slightly as long as no phase is depleted.The mineral assemblage used in Figure 36 provides for the elimination of cpx at about 23 percent melting, which is within the probable melting interval for producing tholeiitic magma (Pingwood, 1975). Further melting of olivine and orthopyroxene would lower the REE content of the melt without greatly changing the shape of its pattern. The results indicate that a 15 to 20 percent melt of an olivine- orthopyroxenec1inopyroxene mantle with an initially flat REE pattern would yield liquids with light REE-enri.ched liquids and patterns slightly flatter (La/Lu1.2) than those in diabase-spilite-zone rocks (Figure 36).To match more closely the oberved patterns, it is necessary to lower the degree of melting, while increasing the REE content of the mantle, assume a light REE enriched mantle, or allow for a few percent crystallization of clinopyroxene and plagioclase. J..L..-i1 1

i00 I modcT Tcj ihuse pro rlon properfloi ;j

3% op 25 .2 50 5 .65 - 5% ..._

'5% 2Z-- - t 23% mehng cpx is dpeted

nitii composiflon = 2.5 x chondr3tes

3 ------

oo/.

Lu Ce SmEu Tb Yb Lu REE BY ATOMIC NUMBER

Figure 36.Rare earth element model of partial melting in an undepleted ol-opx-cpx mant.'le.Upper lines indicate successive liquids; lower lines indicate successive residua. Heavy line average REE composition of 12 diabase- spilite zone metabasaltic rocks. ia The latter speculative process seems most practicable. To match absolute abundances, it is neces3ary that the model mantle have initial abundances approximately 2.. 5 times those in chondrites. An approximately 25 percent melt (hyond depletion of cpx) of this model is a reasonable approximation for the production of the REE-depleted pattern in diabase JP 306B. A relatively low degree of melting may be responsib].e for the REE enriched pattern of spilite JP 407. Summary. Rare earth element models based on REE patterns of rocks from the Oregon Mountain area suggest that the primary magmas which formed the ophiolitic complex wereproduced by a moderate degree (10 to 25 percent) of rneltiug of mantle rock which initially had REE abundances roughly 2 5 times those of chondrites. The d!abase-spflite-zone rocks result from small amounts of crystallization of plagioclase and clinopyroxene from the primary magma type.The cumulate sequence results from extensive fractional crystallization of the same primary magma type; the diabase-spilite zone and the cumulate sequence, however, are apparently notrelated through crystal fractionation. u3

DISCUSSION

In the preceeding sections it was established that the Oregon Mountain mafi.c complex is a coherent assemblage of igneous rocks that grades downward into the Jcsephine Peridotite. Comparison of rnafic complex lithology and the generalized description of ophiolites given in the introduction strongly i2dicates chat the Josephine Pen- dotite and the Oregon Mountain mafic complex constitute an ophiolitic suite. In the past few years ophiolites have been interpreted by many geologists as fra ments of oceanic li.thosphere emplaced on continental ms.rgins (Thayer, 1968; Coleman, 1971; Moore.s and Vine, 1971; iDewey and Bird, 1s71).I propose that the opuolitic assemblage in the Oregon Mountain area is such a remnant of oceanic crust and that it formed abovc upper mantle-.-the Josephine iridoti.te. Many ophiolites have bedded radiolanian chert above the volcanic zone.This rock is believed to be deposited in the deep ocean directly on an ophiolite which forms at a mid-ocean nide, distant from scirces 0 clastic sedircnt ar.d oclow the lysocline (Hopson et al., IT/Sb). lrrgnlar masses of radio1aian client occur wihuii the volcanic zone or the Oregon Munt.in maiic co:mplex, but have not been observed at the top oz the zone.Rather, pillow lavas of the mafic complex arc overlain by slightly inetamorpho sod shale of the LI

Galice Formation.. ino inc caicn of faulting at the conact The Galice Formation, estimated to hover 5000 m. thick in southwestern Ocegon (Wells ci al., 1949), consists of shale and minor sandstone.The sandstone is composed largely of volcamc detritus, but contains a significant continentally derived component.. The Rogue Formation aid the volcanic member of the Galice Fom.aiion are faulted agaLnst the 3osn,hine Peridotite north ofthe Oiegon Mountain area. The se rocks have recently been shown to have island- arc chemical and petrologic affinities (Garcia, 1976a, 1976b). On the basis çf these ob,ervations it i.s proposed the Oregon Mountain opbiitic complex formed in Jurassic time as a marginal basin behLnd Rogue-Galice island arc and adjacent to the con- tthental margm (Figure7). The rnechanim of m.aginai basin formation and back-arc spreading has been discussed b Karig (1971) and by Masuda and

T5yeda (97O) A marginal basin is thought to form by sea-floor pradJng behind an island arc, which causes the arc to migrate t:ocrard the t enc Dcwey and T3ird[971) have proposed that thick ciritar uance are deposited above ophiolite swhich. form in marginal oasins.Lack o cherts attributable o the eariy oret oi clastic sedirneniahon owi to the :J.r9xmitv of he arc and con- .TflCflt soce tcrars. In cord:ratsto the Oreon bountain area., the Coao Range ophiolite haa iver of about 25 rn. of chert.Ihe 115

Loca t lc'rt

Grc',ts Piss 0

LEGEND Pltfonic rocks, moinly lHinoi River Gabur.

ORE.

CALIF. Rogue, Gal ice :::J volcanic rocks, LIiArnphibolite Ophiolitic metavofcani ro'k Ophiolitic gabbro. UItrornafc roci(S.

Figure 37.Diagramatic intarpretation of the tectonic setting of major units in the western Jurassic belt prior to(a) and after (b) the Nevadan Orogeny. Heavy stiples,oceanic crust; light stipls, island arc crust;dark, Galice For- mation; horizontal :uiing, Franciscan andGreat Valley rocks; white, ultrarnafic rocks; crosses,continental c rust; 116 Coast Range ophiolite has been interpreted to have formed at a mid- ocean ridge (Hopson et al,, 1975b). Pumpellyite and prebnite are common in Oregon Mountain spilites, but have each been reported from only one location from the sea floor (Melsonand van Andel, 1966; Miyashiro et al., 1971). Prehnite-purnpellyite facies mineralogy may have formed in response to the thick sedimentary cover of the Galice Formation. The California Coast Range ophiolite (Hopson et al,1975a; Bailey and Blake, 1975), which is overlain by the Great Valley sequence, also contains prehnite and pumpellyite-bearing mineral assembiages Pumpellyite typically replaces smectite in Oregon Mountain spi1ites which suggests that the prehnite .punipeliyite facie s metamorphism post-dates sea-floor burial metamorphism (Figure 8).Pumpellyite was also observed within aniygduies, however, so its paragefletic significance is not clearcut, Recently stated objections to the oceanic crust hypothesis of ophiolite orig.n are. based oi the observation that many features of at least some ophiolites might alternatively be interpreted as relict features of island arcs (Eart arid Bryan, 1972; Miyashiro, 1973, 1975a, 1975b; Dick, 1975, 1976). Kay and Senechal (1976) have reviewed argm.ents regarding the origin of the Troodos Massif and concluded, mainly on chemical grounds, that there are no simple means deterirdne une.uivoca1ly the tectotic setting in which an 11.7 ophiolite formed.Ic would seem that each cphiolite must he considered separately with particular attention paid to field relations, regional tectonic setting and judiciously applied geochemical parameters. As the subject of ophiolite origin is, controversial, I will review the arguments that support my interpretations: The composite section through the mafic complex is approximately 4. 6 km.. thick, similar to the seismically determined thickness of ocean crust. Volcanic rocks in the area are predominantly pillow' basalts; fragmental volcanic rocks are rare A zone of sheeted diabase dikes underlies the volcanic rocks. The presence cf these di.kesuggests that the mafic complex formed in a tensional environment characterized by fis sure eruotioi. The basaltic and diabasic rocks have undergone a style of burial metamorphism which is similar in mineralogy and chemical trends t-o sea-floor metamorphismPrehnite- pumpellyite fades burial metamorphism is superimposed on the sea-floor metanirphism. The second alteration probal:lv occurred in respouse to burial of the ophiolitic rocks beneath the Galice Forrn.tion. 118 The rare earth e:tenzct, Ti.,nd Zr distributions of rocks from the diabae-spilite zone are mggestive of a sea-floor origin. Quartz keratophyres with trace element abundances indicative of caic-aikaline rocks are minor components of the diabase- spilite zone.These rocks are interpreted as altered tuffaceous deposits from a nearby island arc. Plutonic rock types of the Oregon Mountain area include harzhurgite, cumulate ultramafic rocks, cumulate gabbro, hornhlende gabbro and piagiogranite, all of which have been identified from the ocean floor. The Galice Fo:maticn depositionally overlies the mafic complex, Craywacke from the formation contains quartz and metamorphic clasts indicative of a continental provenance and abundant volcanic clasts suggestive of a volcanic arc provenance. Bedded cher, which is indicative of abyssal sedimentation, is lacking at he too of the ophiolitic sequence, suggesting that the ophiolite formec near sources oZ clastic sediment. Rocks vthin th western J'irassi.c belt, including the Oregon Mointain area, are not known to be deposited on Trias sic or older continental basement, 119

Regional_Relationships

Ultramafic rocks and volcanic rocks of Jurassic age are exposed discontinuously along the we stern margin of the continent from British Columbia to theootbills of the Sierra Nevada (Monger, et al,, 1972; McKee, i972; Irwin, 1966; Clark, 1960).Several authors have proposed Lhat these rocks are remnants of a Jurassic. Andean-type., east-dippi::tg subduction system which was disrupted. by the Nevadan Oroge.tiy (Dott, 196!.; Hamilton, 1969; Monger et al., 1972; Burchfiel and Davis, 1972; Dickinson, 1972).Schweikert and Cowan (1975) proposed that the Logtowri Ridge and Mariposa formations in the Sierra-Nevada foothills were pcoiced within a late Jurassic island arc complex which formed above a separate west.dippiig subduction zone.These. two authors suggesL that the. island-arc system extended northward into the western Kamath Mountains, as the Logtown Ridge and Mariost formations are correlative with the Rogue and Galice fr,rrnatjons (Wells et al . 1949; Clark, 1960).. The hyDothesis of a Jurassic island arc in northern California and southern Oregon is in agreen,ent with conclusions presented herein as well as those of Garcia (l976' and Coleman et al., (1976). However, the chrcction of' dip on the associated subduction zone remains specuLative; no remnants of a pre-Franciscan sbduction me.ange are known in southwestern Oregon, although exotic, ISo m.y. 120. bluschist blocksiti ± DothaF ra ;iscan terrain (Coleman and Lanphere, 1971) may be relicts of this earlier subdutiorL system. It is perhaps more likely that the Rogue Ga1ice arc formed over an east-dipping subduction zone (Figure 37).Modern marginal basins have been shown to form behind an island arc-trench system, above the su:bduc tion zone (Karig, 1971). It isossib1e that a separate Andean-type subduchon system exstea aiong the continental margin, east of the ltogue-CAalice arc- trench system, but evidence for this is scarce.Plutons in the western Paleozoic and Trias sic belt give isotopic dates in the range of 140-166 m. y, (late Jurassic) and ruiddle Jurassic Volcanic rocks occur above Triassle reeks in the southern Kiarnath Mountains (Albers and Rcertson, 1961).In the northern Klarnaths, however, Jurassic volcanic rocks are unknown outside of the western Jurassic belt. Causes of the late Jurassic Nevadan Orogeny are not well understood. However, it can be concluded that the orogeny greatly changed the tectonic framework of the region, causing in particular: (I) closure of the marginal basin; (2) accretion of western Jurassic belt rocks onto the continental margin; (3) development of the Franciscan subduction system; and (4) an eastward shift in magma- tisrn, away from the western Jurassic belt. 121

BIBLIOGRAPHY

Albers, J. P., and Robertson, J. F,, 1961, Geology and ore deposits of the East Shasta copper-zinc district. Shasta County, Cali- fornia:U. S. Geol, Survey Prof. Paper 338, 107 p. Anderson, C. A., 1969, Massive sulfide deposits and volcanism: Econ. Geology, v. 64, p. 129-146. Anonymous, 1972, Penrose field conference (on) Ophiolites: Geo- times, v.17,p. 24-25.

Aurnento, F., 1969, Diorites from the mid-Atlantic ridge at 45°N: Science, v.165, p. 1112.

AveLal1ernat. H. C., 1976, Structure of the Canyon Mountain (Oregon) ophiclite and its implication for sea.fioor spreading: Geol, Soc. America Spec. Paper, 1973 Av'Laliamant, IL C.and Carter,N. L, ,1970, Syntectonic recrystallization and rnoues of flow in the upper mantle: Geol, Soc. America BulL, v. 81, p. 2203-2220.

Bailey, E. H.,and Blake, M, C,,Jr. ,1974, Major chemical characteristics of Mesozoic Coast Range ophiolite in. California: (1.S. Geol. Survey Jour. Research, v.2,p. 637-656.

Bailey, E. H,, Blake, M. C., and Jones, D, L., 1970, Qn land Mezozoic oceanic crust in California Coast Ranges: U. S. Geol, Survey Prof. Paper 70(L.C, p. 70-81.

Dailey, F. H,Irvin, W, P., and. Jones, I). L,1964, Franciscan and related rocks:California Div. Mines Geol. Bull. 183, 84 p.

BIschoif, J. L, and Dickson, F. W,, 1975, Seawater-basalt interaction at 200°C andOO bars: lmDlications tar the origin of sea- f1oi heavy metal deposits and regulation of seawater chemis try: Earth and. Planetary Sci, Letters, v, 25, u, 385-397.

Blake, M, C,,Irwin, W. P., and Coleman, R. C.1967, Upside- down rnetamorphini in the blue;chit fades along a regional thrust in CaiiiSornia and, Oregon: L S. Geol, Survey Prof. Parie.r 575...ç:, C1-C9, 122 Boynton, W. V., Conard. R. L. Curtis, D, B,, and Schmitt, R. A,, 1977, The precise determination of the fourteen rare-earth elements and barium and strontium by radiochemical neutron activation analysis:in preparat'on.

Burchfiel, B. C,,and I)avis, C. A. ,1972, Structural framework and evolution of the southern part of the Cordilleran orogen, western United States: American Jour, Sci., v. 272, p. 971l8, Cann, J., 1968, Geologic processes at mid-ocean ridge crests: Geophys, Jor, Royal Soc0 London, v.15, p. 331-341. Cann, J., 1969, Spilites from the Carlsberg Ridge, Indian Ocean: Jour. Petrology, v,10, p. 1-19. Cana, J, R., 1971, Petrology of basement rocks from Palmer Ridge, N. E, Atlantic: Phil. Transactions, Royal Soc. London, ser. A, v. 268, p. 605-617,

Cann, J. R0, and Funnll, B, M,,1967, Palmer Ridge: a section through the upper part of the oceanic crust?: Nature, v, 213, p. 661 -664. Carmichael. I,5. E'., Turner, F. J., and Verhoogen, J., 1974, lgneous Petrology: McGraw Hill, New York, 739 p. Carter, F. W., and Wells, F. G., 1954, Geology arid mineral resources of the Gasquet quadrangle, California - Oregon: U. S. Geol, Survey Bull., 995-C, p. 79-133.

Clark, L, D., 1971, Volcaogenic ores: Comparison of cupriferous pyrite deposits of Cyprus and Japanese Kuroko deposits: Soc. Mining Geol, Japan, Sec, Issue 3,p. 206-215. Clark, L,. D.1964, Stratigraphy and structure of part of the western Siarra Nevada metamorphic belt, California: U. S. Ge&. Survey Prof. Paper 410, 70 p.

Colnan. R, C., 1967, Low temoerature reaction zones and alpine ultamafic rocks o Ca!ifornia. Oregon and Washington: U. S. Geol. Survey Bull, 1247, 49 p.

Coleman, R, C., 1971.Plate tectonic emplacemont of upper mantle peridotites aorig continental edgs: Jour. G& phys. Research, v80, piO99-J108, 123

Coleman, R. G. ,1972, The Colebrooke sehist of southwestern Oregon and its relation to the tectonic evolution of the region: U. S. Geol. Scvey Bull. 1339, 61 p. Coleman, R. C., and Keith, T. E., 1971, A chemical study of serpentinization - Burro Mountain, California: Jour. Petrology, v12, p. 311-328. Coleman, R. G., Garcia, M. 0., and Anglin, C., 1976,The amphibolite of Briggs Creek:a tectonic slice of metamorphosed oceanic crust in southwestern Oregon: Geol. Soc. America Abs. with Programs, v.8,p. 363. Coleman., R. G., and Lanphere, M. C., 1971, Distribution and age of ih grade blueschists, associated eciogites and amphibolites from Oregon and California:Geol. Soc. America Bull,, v, 82, p. 2397-2412, Coleman, R. G. and Peterman, Z. E.1975, Oceanic Plagiogranite: Jour. Geoohys. Research, v. 80,p. 1099-1108, Corliss, J. B., 1977, Seawater hydrothermal system and the formation of ore deposits: Geol. Soc. America Bull., In press. Davies, H. L., 1971, Peridotite-gabbro complex in eastern Papua: an overthrust plate of oceanic mantle and crust:Australian Bureau of Mineral Resources Bull. 128, 48 p. Davis, G. A., 1969,Tectonic correlations Kiamath Mountains and western Sierra Nevada: GeoL, Soc. America Bull., v, 80, p. 1095-1108. deRoever, W. P., 1957, Sind die aipinôtypen peridotit massen viel- le±cht tectonisch ver fractete Bruchstke der peridotiteschale? Geologishe Rundschau,, v. 46, p. 137-146.

Dewey, J, ,ind Bird, J,, 1970, Ivlountain belts anthe new global. tectonics: Jour, Ceophys. Research, v. 75, p. 2625-2647.

Devey, J.,and Bird, J,,1970, Origin and emplacement of the ophiolite suite: Appalachian ophoitei.n New foundiand: Jour, Geophrs. Research, v, 76, 3179-3206, 124 Dick, H. 3. B,, 1973, K-Ar dating of intrusive rocks in the Josephine Peridotite and Rogue Formation west of Cave Junction, Oregon: Geol. Soc. America Abstracts with Programs., v. 5,p. 33-34. Dick, H. J. B., 1976, The origin and emplacement of the Josephine Peridotite of southwestern Oregon: Ph. D. Dissertation, Yale University, 409 p. Dickinson, VT. R., 1970, Relations of andesites, granites and derivi- tive sandstones to arc-trench tectonics: Reviews of Geophys. and Space Physics, v.8,p. 813-860. Dickinson, VT. R., 1971, Plate tectonics in geologic history: Science, v.175, p. 107-113. DickiusonVT. R., 1974a, Plate tectonics and sedimentation: in Plate Tectonics and Sedimentation, Dickinson, W. R., ed., Soc. Econ, Paleontologists and Mineralogists Spec. Pub. 22, p. 1-27. Dickthort, VT. R.1974h, Sedimentation within and besideancient and modern magmatic arcs: inDott, R, H., Jr., and Shaver, R. H., eds,, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 19, p. 230-239.

Diller, 3. S., 1902, Topographic development of the Klamath Mountains: U.S. Geol. Survey Bull, 196, 69 p. Diller, J, S., 1907, The Mesozoic sediments of southwestern Oregon: American Jour, Sci,, 4th ser. ,v. 23, p. 401-421. Donnelly, T,, Melson, VT. ,Kay, R. ,and Rogers, 3., 1973, Basalts and dolerites of late Cretaceous age from the central Caribbean: in Yeats, R,, S, Hart, S. R., et al,, Initial reports of the deep sea drilling oroject, v,15, Washington, U. S. Government Printing Office. p. 989-1012. Dott, R. H. .1965, Mesozoic tectonic history of the southwestern Oregon coast in relation to the Coralleran orogenesis: Jour Geophys. Research, v, 70, ,4587-4707. Dymond, 3., Corliss, J, B, ,Heath, G. R., Field, C. W. ,Dasch, E. 3., and Veeh, H. H. ,1973, Origin of metallifercus sediments from the Pacific Ocean: Geol. Soc. America Bull., v. S4 p. 3355-3372. 125 Frey, F, A., Bryan. W B., and Thompson. G..,1974, Atlantic ocean floor: geochemi.trv atd petrology of hasalts from legs 2 and 3 of the deep-sea. drilling project:Jour. Geophys. Research, V. 79,p.550,7 -5S27, Engel, C. E., and Fisher, R. L., 1969, Lherzolite, anorthosite, gabbro and basalt dredged from the mid-Indian Ocean Ridge: Science, v. 166, p. 3281-3298. Ewart, A,. Bryan, W. B., and Gill, J,, 1973, Mineralogy and geochemistry of the younger volcanic islands of Tonga, S. W. Pacific: Jour. Petrology, v.14, p. 429-465.

Ewart, A. , Bryan, W. B., 1972, Petrography and geochemistry of igneous rocks from Eua, Tongan Islands: Geol, Soc, America BuLl,, v. 83, p. 3281-3298, Ewart, A., Taylor, S. R, and Capp, A. C,, 1968, Trace and minor element geochemistry of the rhyolitic volcanic rocks, central North Island, New Zealand: Contributions Mineralogy and Pet- rology, v. 18, p. 7104. Flanacan, F. J,, 1973, 1972 values for international geochemical reference samples: Gcochim.et Cosmochim. Acta, v. 37, p. 1189-120C, Frey, F. A,, Bryan, W. B,, and Thompson, G., 1974, Atlantic ocean floor: Geochemistry and petrology of basaits from Legs 2 and 3 of the Deep Sea Drilling Project: Jour, Geophys. Research, v, 79, p. 5507-5528.

Frey., F. A.,Haskin, M. A,, and Poet, J,, 1968, Rare-eart:h abundances in some basic rocks Jour. Ceophys. Research, v, 73, p. 6085-6098. Garcia, M. 0,, 1976a, Petrology of the Rogue River Area, Klamath MountainsOregon: Problems in the identification of ancient volcanic arcs: Ph.D. )issertation, University of California Los Angeles, 185 p. Garcia, M, 0., 1976b, Rogue River island a:rc complex, western Jurassic belt, Kiamath Mountains, Oregon: Geci, Soc. America Abs. with Programs. v, 8, p. 375. 126 Gass, 1. G., and Srnewing, 3. D. ,1973, Intrustion, extrusion and metamorphismat constructive margins: Evidence from the Troodos Massif, Cyprus: Nature, v. 243, p. 26-29. Gass, I. G., et aL, 1975, Comments on 'The Troodos ophiolitic complex was probably formed in an island arc' by A. Miyashiro and subsequent correspondence by A. Hymes and A. Miyashiro: Earth and Planetary Sci, Letters, v. 25, p. 346-238. Gast, P. W., 1968, Trace element fractionation and the origin of the tholeiitic and alkaline magma types: Geochim, et Cosmochim. Acta, v, 32, p. 1057-1086, Ghent, E. D., and Coleman, R. G., 1973, Eclogites from southwestern Oregon: Geol. Soc. America Bull, v. 84, p. 2471-2488. Gill, 3, B., 1976, Composition and age of Lau Basin and Ridge volcanic rocks: implications for evolution of an interarc basin and remnant arc: c;eol, Soc. America Bull, v, 87, p. 1384-1395. Gordon, G. i. ,et al, ,1968, InstrumentaL activation analysis of standard rocks with high resolution I -ray detectors: Geochim. et Cosomochirm, Acta, v. 32, p. 369-396. Graf, 3. L. ,Jr., 1976, Rare earth elements as hydrothermal tracers during the formation ofmassive sulfide deposits and associated iron formaIons in New Brunswick: Submitted to Econ. Geol. Hamilton, W, E., 1969. Mesozoic California and the underfiow of Pacific mantle: Geol, soc, America Bull,, v, 80, p. 2409-2430, Hajash, A., 1975, Hydrothermal processes along mid-ocean ridges: an experimental investigationContrib, Mineralogy and Petrol-

ogy, v. 53.,p. 205-226.

Hart. R. A., 1973, A model for chemical exchange in the basalt-. seawater system of oceanic layer II:Canadian Jour. Earth Sci,, v,10, p. 799-816, Hart, S. R. ,1971, K, Rb, Cs, and Ba contents and Sr isotope ratios of ocean floor basalts: Philosophical Trans. Royal Soc London ser. A, v, 268, p. 573-587. 127 Hart, S. R.Erlank, A. J,and Kable, E. S. D.. 1974, Sea-floor basaltalteration:Sot-ne chemical and Sr isotope ei:fects.: Coatrib. Mineralogy and Petrology, v, 44, p.. 219-240, Haskin, L. ,Frey, F. A.., Schmitt, R. ,and Smith R., 1966, Meteoritic, solar and terrestrial rare-earth distributions:in Ahrens, L. H., etaL,eds., Physics and Chemistry of the Earth, V. 7, p. 167-321, Fergammon, New York.. Hawkins, J, VT,, 1974, Geology of the Lau Basin, a marginal sea end the Tor'c. a ,i'urk, C P , and Drake, C L,eds The geology of continental margins: Springer-.Verlag Heidelberg, p5O552O.

Hawkins, .J. W.1076,Petrology and geochemistryof ba;altic rocks ofthe Lau Basin: EarthandPlanetary Si. Letters, v48, p. 283-297. Herrmann, A., Potts, M., and Drake, D., 1974, Geochemistry of .ha rare earth elements in soliites from the oceanic and continental crust: Contrib. Mineralogy and Petrology, v, 44, p. 1-16. Hess, H. H. ,192 History of the ocean basins:GeoLSoc.. Ametica, Buddington, VoL I 9-62O Hinetherg C. R. ,aid Lonoy, IL A. ,1973, Petrology the Vulcan Peak alpine-type peridotite, southwestern Oregon: Geol. SOC. America Bull. , v. 94u. i585--1600.

Hc.psonC. Franno, C. J., Pessagno, E., and Mattirson, S. M, 1975a, P.elimuiary report and geologic guide to theJurassic ophiolite ne ..r Pt. So. Caiifrrni.a coast: GeoL Soc. America CordilIer.n Sections, FieldtriuGuidebook, 36 p. HOpSOn. C. A. , Mattircn, J. M.and Pessagno, E.197, cord em av'ui a pr mdni,C1ifornia Coa3tRnrcs Geoll SOC Ameri:a Abs. with Programs, v7, p. 326. Hostetler, B, Colem an, It. C., Muirmoton, F. A., and Evans, B,W., 196, Brucite inalpine serpentines:Arner.car Mineralogist, V. 51, .75-9'.

Hotz, P.. E, 197 , Putonic rocics of the K1.amath Mountains, California and C)egort U. S.. teoL. Survey Proi, Paper 8-i3, p. 128

Hypes, A, 1975, A discussion on'the Troodos Ophiol.ite Complex was probably formed in an island arc' byA. Miyashiro: Earth and Planetary Sci.. Letters, v. 25, p. 213-216. Irwin, W. P., 1960, Geological reconnaissance of the northernCoast Ranges and K.lamath Mountains, California with a summary of the mineral resources: California Div. Mines Bull. 179, 80 p. Irwin, W P. ,1964, Late mesozoic orogenies in the ultramafic belts of northwestern California and southwestern Oregon: U. S. Geol. Survey Prof. Paper 501-C, p. Ci-C9. Irwin, W. P.., 1966, Geology of the Klamath Mountains province: in Geology of Northern California, Bailey, E. H, ed,: California Division Mines and Geol. Bull..190, p. 19-38, Irwin, W, P. ,1972, Terrains of the western Paleozoic and Triassic belt in thsouthern Kianiath Mountains, California: U. S. Geol. Survey Prof. Paper 501C, p.1-9. Jakes, P.and CJi, J., 1970, Rare earth elements and theisland arc. Tholeiitic series: Earth and Planetary Sci. Letters, v.9, p. 17 -.28, Jake, P., and White, A. J, R. ,1972, Major and trace element abundances in volcanic rocks of orogenic areas: Geol. Soc.America Bull., v, 83, p. 29-40. Jorgenson, D, B. ,1970, Petrology and origin of the Illinois River Gabbro, a part of the Jocph±ne oeridotite -gabbro complex Kiamath MountainsSoutL.west.e rn Oregon: Ph. D.. Dis sertation Univ. of LaLiforoia atar,ta 3arbara, 195 p. Karig.. 1). E. ,i97i, Origin and development of marginal basinsin the western Pacific: Jour Gcophys. Research, v. 7, p.2542-2561. Kay 11., HubbardN, J, and Gast, P. W., 1970, Chemical characteristics and origin of ocerdc ridge volcanic rocks:Jour.. Geophys. Research, v. 75, p. 1585-1b14. Kay, R. W., and Sen e.'hal. R. G., 197, The rare earthgeochemistry of the Troodos ophiollte comp'ex: Jour. Geophys.Research, V.. 81, p. 964.970. 129 Kays, M. A. ,1968, Zones of alpine tectonism and metamorphism, Kiamath Mountains, southwestern Oregon: Jour, Geol,, v. 76, p. 17-36. Kim, C. K., 1974, A gravity investigation of the Weed Sheet, northwestern California: Ph. D. Dissertation, University of Oregon, 120 p. Kushiro, 1., 1969.The system forsterite-diopside-silica with and without water at high pressure: American Jour, Sd,, Schairer VoL ,v, 267-A, p. 269-294, Lanphere, M, A,, Irwin, W. P. and E-Iotz, P. E., 1963, Isotopic age of the Nevadan Orogeny and older plutonic and metamorphic events in the Kiamath Mountains, California: Geol. Soc. America Bull, v. 79, p. 1027-1052, Leeman, W. P., Murali, A, V., Ma, M. -S, and Schmitt, R, A., 1977, Mineral constitution of mantle rource regions for Hawaiian basalts - rare earth elemnnt evidence for mantle heter- ogeneity: Proc. of the Chapman Conference on Partial Melting in the Manlie (American Geophys. Union), Oregon Dept. of Geol, and Mineral industries Bull,, in press. Loney, Ft. A. ,arid Hiinmeihurg, G. R. ,1976, Structure of the Vulcan Peak aipinevpe peridotite, southwestern Oregon: Geol. Soc. America Bull,v87, p. 259-274.

McKee, B.,1972, Cascadia: McGraw-Hill, New York, 394 p. Masuda, A., and Jibiki, IL, 1973, Rare-earth patterns of mid- Atlantic Ridge gabbros: continental nature?: Geochem. Jour., v. 7?'55-65. Masu.da, T., and Uyeda, S. ,1971, On the Pacific type orogeny and its model-extention ol the onired belts concept and possible origin of marginal seas: Tectonnphysics, v.ii, p. 5-27, Medaris, L. G. ,1972, High pressure perdotites in southwestern Oregon: Geol, Soc. America Bull. ,v, 83, p. 41-53, Melson, W. G. ,and van Andel, T. A,, 1968, Metamorphism in the mid-Atlantic ridge, 220 N. latitude: Marine Geology, v, 4, p.3.6.5-186. 130

Melson, W. G., Thompson, C., and van Andel, T. I-I.,1968? Volcanism and metamorphism in the inidAtiantic ridge, 22 N latitude: Jour. Geophy. Research, v. 73,p. 5925S941.

Melson, W. G., and Thompson, G., 1970, Layered basic complex in oceanic crust, Romanache fracture, equatorial Atlantic Ocean: Science, v. 168, p. 817-820. Menzies, M., 1975, Rare earth geochemistry of fuzed ophiolitic alpine lherzolites - I. Othris, Lanzo and Troodos: Geochim. et Cosmochim, Acta, v. 40, p. 645-656. Miyashiro, A., 1961, Evolution of metamorphic belts: Jour, Petrology V.2,p. 277-311, Miyashiro, A.1972, Metamorphism and related magmatism in plate tectonics: American Jour, Sci., v. 272, p. 629-656, Miyahiro A., i3, The Troodos ophiolite was probably formed in an island arc: Earth and Planetary Sci, Letters, v.19, p. 218- 224:, Miyashiro, A.., 1975a. Origin of the Troodos and other ophiolites: A reply to Hynes: Earth and Planetary Sci, Letters,V.25, p. 217-222. Miyashi.ro, A., 197 Sb, Origin of the Troodos and other ophiolites: a reply to Moores: Earth and Ptanetary Sci. Letters, v. 25, p. 217-235.

Miyashiro, A., Shido, F.,and Ewing, M, ,1971, Metamorphism in the mid-Atlantic ridge near 240 and 30° N: Philosophical Trans- actions Royal Soc. London, Se r. A.,v. 268, p. 589-603. Monger, S. VT, H., Souther, J. G., and Gabrielse, H., 1972, Evolu- tion of the Canadian Cordiliera: plate tectonic model: American Jour, Sd. v272, p577-602

Montigny R.,Bougault, H., Bottinga, Y.and Ailegre, C. J., 1973, Tia-c lemen.. gecoerr / and geneisi tie Pindos ophiolitic suite: Geochim, et Cosmoschim. Ata, v, 37, p. 2 135-2147. Moorehouse, W. W., 159, The study of rocks in thin section: Harper and Row, New York, 514 p. 131 Moores, E0 M,, 1969, PetroLogy and strcctaie of the Vourinos ophi litic complex of northern Greece: GeoL Soc. America Spec, Paper 118, 74 p. Moores, E. M,, 1975, DiscussIon of 'Origin of Troodos and other ophiolites as oceanic crust: Evaluation and implications: Philosophical Transactions Royal Soc. London, SerA., 268,p. 443-466.

Motti, M. J., Corr, R. F, ,and Holland H. D., 1974, Chemical exchange between sea water and mid-ocean ridge basalt during hydrothermal alteration: an experimental study: Geol. Soc. America, Abs. with Programs, v, 6, p. S79880 MuraU, A. V.Leeman, W. P., Ma, M. -S., and Schmitt, R. A., 1977, Evaulation of fractionation and hybridization models for Kilauea erupions and probable mantle source of Kilauea and Macna Lca tholeiitic hasalts, Hawaii - a trace element study: Jour.'et°otogy, in press. Nicholls, C. D.. and siam, M. R.1971, Geochemical investigations of basalts and asocjated rocks from the ocean floor and their implications: Pliosophica1 Transactions Royal Soc0. London, Ser, A, v,68, p. 469-486,

Norrish, K., aicl Hutton, J. T., 1969, An accurate X-ray spectro- grapiiic ni;thod .for he analysis of a wide range of geological samples: Geochim, et Costnachim, Acta, v, 33, p. 431-453, Omang, S. H.l96', A rapid fusion method for the decomposition and comprehensive analysis o± s;Llicates by atomic absorbsion spectrophotornetry: Analvtica Chim, Acta, v. 46, p. 225-230,

Page, N. J,, 1966, Mineraegy and chemistry of the serpentine group nitri als ''J t erntin. nr Ce3P D Jniversity or Caifcnia, 3erk1°, California, 341p Faster, T. P. cei). :..d L, A 1974, Th )VIC 0.. .CU e cr2:0 ei: 'tt!.On of he 'era.rt-1 s;- .-_-j- Act&,

Pearce, J. A.,1975, Basalt geochemistrysecl to investigate past e.tonic'roli nesl Cvp cu co' phc, 5, p41 67. 132

Pearce, J. A., and Cairn, J. R., 97), Ophiolite origin investi..:ated by discriminant analysis using Ti, Zr and Y: Earth and Pnei- ary Sci. Lettersv,12, p. 339-349. Pearce, J. A,, and Cann, J. R., 1973, Tectonic setting of basic volcanic rocks determined using trace element analysis: Earth and Planetary Sci, Letters v. 19,p. 290-300,. Philpotts, J. A., and Schnetzler, C, C. and Hart, S. R., 1969, Submarine basalts: some K, Rb, Sr, Ba, rare-earth, H20 and CO2 data bearing on their alteration, modification by plagio-. clase and possible source materials: Earth and Planetary Sci, Letters, v, 7,p. 293-299.

Philpotts, J. A., and Schnetzler, C. C., 1972, Large trace cation partitioning in igneous )rocesses: 24th International Geol, Congress, Section 10,p. 52-59. Quon, S. H., and Ehiers, E. C., 1963, Rocks of the northernpart of the mid-Atlantic ridge: Geol. Soc. America Bull.,v, 74p.

Ranier, A. R., 1967, The petrology ofa portion of the Josephine øeridotite sheet, southwestern Josephine County, Oregon: Unpublished University of Oregon M, S. Thesis, 121p, Ramp, L., 1961, Chromite in southwestern Oregon: Oregon Dept. Geol, and Miera1 industries Bull. 52, 169p. Ramp, L. 1969, Dothan? iossiis discovered: Ore Bin,v. 31, p. 245-246. Ramp, L., 1975, Geology and mineralresources of the upper Chetco drainage, including he K!miopsi Wilderness and Big Craggies otanicai areas, Oregon: Oregon Dept. Cool, and Mineral Industries Bull, 8$, 79p.

Ringwood. A E., 1974, The petrological evolution of island arc systems: Jour, Geol, Soc. London, v,130, .183-204, Ringwocd, A. E., 1975, Composition and petrology ofthe Earth's mantle: McGraw Hill, New York, 618p.

Rittriiann, A., 1962, Volcanoes and their actirit.r: John Witey and Sons, New york, ,153-i4, 133 Roeder, D. H. ,1973, Subduction acid Orogeny: Jour, Geophvs. Research, v. 78, p. 5005-5024. Schilling, J. -G. ,1971. Sea-floor evolution: rare-earth evidence: Philosophical Transactions Royal Soc. London, 5cr, A, v, 268, p. 663-706. Schilling, J..G., 1975, Rare-earth variations across norma1 seg- ments of the Rekjanes Ridge,600 530 N, mid-Atlantic ridge, 29°S, and East Pacific Rise, 2- 19°S,and evidence on the composition of the underlying low velocity layer: Jour. Geophys. Research, v. 80, p. 1459-1473, Schnetzler, C. C. and Philpotts, J. A. ,1970, Partition coefficients of rare-earth elements between igneous matrix material and rock forming minerals - II:Geochim, et Cosmochim. Acta, v. 34, p. 331-340. Schweickert, R. A., and Cowan, D. S., 1975, Early Mesozoic tectonic evolution of the western Sierra Nevada, California: Geol. Soc. .Anerica Bull, ,v, 86, p. 1329-1336. Sclater5, G., Hawkins, J. W,, Mammerickx, J., and Chase, C. G., 1972, Crustal extension between the Tonga and Lau Ridges: Petrologic and geophysical evidence: Geol. Soc. America Bull. v, 83, p. 505-518. Shaw, D. M.1970, Trace element fractionation during anatexis, Geochirn. et Cosmochim, Acta, v, 34, p. 237-243. Shor, G, G., Jr, and Raitt, R. W., 1969, Explosion seismic refraction studies of the crust and upper mantle in the Pacific and Indian Oceans: in the Earth's Crust and Upper Mantle, Wiley, P. J., cci,, GeophyMonograph 13, American Geophysical Union, Washington .D. C., p. 225-230. Smewing, J. D. ,Simonian, K. 0. and Gass, I. G., 1975, Meta- basalts from the Troodos Massif, Cyprus: Genetic implication deduced from petrographr and trace element geochemistry: Contrib, to Mineralogy and Petrology, v, 51, p. 4964.

Snoke, A. W.,1972, Petrologr and structurc of the Preston Peak area, DeJ. Norte County CaLiforna: Ph D, Dissertation, Stanford Univeisity, 274 p. 1.34 Steinmann, C. ,1926, Die ophiolitischen zonen in den Mediterranean kettengebirgen: 14th International Geol. Cong., v. 2, p. 636- 668, Strand, R. G. (Compiler), 1962, Geologic Map of California, Weed sheet Olaf P. Jenkins edition: California Div. Mines and Geol. Taiwani, M., LePichon, X. and Ewing, Me, 1965, Crustal structure of mid-ocean ridges, 2, computed model from gravity and refraction data: Jour. Geophys. Research, v. 70, p. 341-352, Taylor, S. R, 1969, Trace element chemistry of andesites and related caic-alkaline rocks:in Proc. of the Andesite Conf. A. R. McBirney, ed. Oregon Dept. Geol, and Mineral Industries Bull, 65, p. 43-63, Thayer, T. P., 1969a, Peridotite-gabbro complexes as keys to the petrology of mid-oceanic ridges: Geol. Soc. America Bull. v. 80, p. 1515-1522. Thaver, T. P. ,1969h, Gravity differentiation and magmatic re-emplacement of podiform chromite deposits: in Wilson, H. D. B.,ed,, Magmatic ore deposits, Econ, Geol. Mono- graph 4, p132-146. Thayer, T. P., arid Himmelburg, G. R., 1968, Rock succession in the alpine-type mafic complex at Canyon Mountain, Oregon: 23rd International Geol. Cong., v,1, p. 175-186. Thompson, G, 1973, A geochemical study of the low-temperature interaction of sea-water and oceanic igneous rocks: American Geophys Union Transactions., v. 54, p. 1015-1019, Thompson, G,, Shido, F., and Miyashiro, A., 1972, Trace element distributions in fractionated oceanic basalts: Chem, Geology, v, 9, p. 89-97, Vail, S. G, 1975, Jurassic ophiolitic rocks in southwestern Oregon: Oregon Academy of Sci. Abs. ,in press. Valiance, T. C., .1974, Spilitic degradation of a tholeiitic basalt: Jour, Petrology, v,15. p. 79-96. Wager, L. R.and Brown, C. R, 1968, Layered Igneous Rocks: Freeman and Co., San Franc:c, 588 p 135 Wakita, H,, Schmitt. R. A., and Rev, P., i970. Elemental abundances of major and trace elenents in Apollo 11 lunar rocks) soil and core sampie: Proc. Apollo II Lunar Sci. Conf. Geochim, et Cosmochim, Acta Suppi. 2, .2,p. 1685-1717. Walker, B. M,, Vogel, T. A., and Ehrlich, R., 1972, Petrogenesis of oceanic granites from the Ayes Ridge in the Caribbean Basim Earth and Planetary Sd. Letters, v.15, p. 133-139. Wells, F. G., Hotz, P. E., and Cater, G. W., 1949, Preliminary description of the Kerby quadrangle, Oregon: Oregon Dept. Geol. and Mineral Resources Bull, 40, 23p.

Wells, F. C.,ar.d Walker, G. W.,1953, Geologic map of the Galice quadrangle, Oregon: U. S. Geol. Survey map GQ-25. Wells, F. G., 1955, Preliminary geologic map of southwestern Oregon west of meridian 1ZZwest: U. S. Geol, Survey Mineral investigations Field Studies Map MF-38. APPENDICES 136

APPENDIX I

Location and Description of Analyzed Samples

Listed below are tEe locations, the more pronounced textural features and the mineralogy of rocks for which chemical data are given in Appendix II.Minerals are U.sted in order of decreasing abundance.Relatively minor abundances of a mineral in indicated by parentheses. 137

APPEND]X I

Location and Description of Analyzed Samples

Diabase Zone

Zeolite, ?rehnite -.Pumpellyite and Chlorite_Greenshist Facte sReeks

JP 135Spilite; Oregon, SE 1/4 S.10, T. 4 iS., R. 9W. Chlorite, prehnite, pumpellyite, zeolites, calcite, elongate albite, fine grained g round mass. JP 136Diabase; Oregon, SW 1/4 5. 15, T. 41S., R. 9W. Albite, epidote, chlorite, quartz, (augite). JP 310Spilite; Oregon, NW 1/4 S. 2, T. 41S., R. 9W. Albite, chlorite, quartz. prehnite, pumpellyite (augite), JP 326Spilite; California, NE 1/4 S.5, T. 18 N., R. 4E, Smectite, prehnite, pumpellyite, quartz, chlorite, zeolite s, (augite). JP 334Spilite; Oregon, SE 1/4 S.16, T. 41 S. ,R. 9W. Albite, chlorite, prehnite, pumpellyite, epidote, calcite, (augite). JP 345Spilite; California, SW 1/4 S. 3, T. 18N. ,R. 3E. Augite, plagioclase (albitized),. chlorite, purnpellyite, zeolites, (clinozoisite?), fine grained ground mass, JP 351SpiLie; California, NE 1/4 S.5, T. 18N. ,R. 4E. Smectite, chlorite, albite, quartz, pumpellyite.(augite). JP 407Pillcw spilite; CaUiorn.ia, NW 1/4 S.liT. 1SN,, R. 3E Porthyritic; augite, plagioclase (albitized), epidote, irehnite, quartz, chlorite, calcite, fine grained groundrnas s. 138

Epidote -Quartz -Albite Greenfacie Rocks

JP 174Epidosite; Oregon, SW 1/4 S. 12, T. 41S,, R. lOW. C rystalloblastic; quartz, epidote, chlorite. JP 313Metabasalt; Oregon, NE 1/4 S.10, T. 4 iS., R, 9W. Chlorite, epidote, albite, actinolite, quartz. JP 341Epidosite; California, NE 1/4 S3, T, 18N.., R. 3E. C rystalloblastic; quartz, epidote, chlorite. Jp 34'?Diabase; California, SW 1/4 S. 8, T, 18N., R, 4E. Albite, chlorite, epidote, quartz. JP 344Metabasalt; California, NE 1/4 S. 3, T. 18N., R. 3E, Crystalloblastic; albite, epidote, quartz, chlorite. JP 416Epidosite; California, sw 1/4 S.2, T. 18N. ,R. 3E. C rystailoblastic; epidote (idioblastic), albite, quartz.

Ke rat ophyre

JP 340Quartz keratophyre; California, NW 1/4 S. 3, T. 18N,, R. 3 E. C rystallobiastic; quartz, mus covite, albite, K -feldspar, phenocrysts (abitized), (biotite).

Metamorphosed Sill iF 391Mafic sillinGalice Formation; California, NE 1/4 S.11, T. l8N., R. 3 E. Albite, hornhlende, epidote, chlorite, calcite, quartz, (pumpellyite). 139

3pper Greenschist Faie' Rocks

JP 306A Diabase; Oregon, SE 1/4 S.34, T. 40S., R. 9W. Albite, actinolite, chlorite, prehnite,(green hornblende). JP 306B Metabasalt; Oregon, SE1/4 S. 34, T. 405,, R. 9W. .Albite, actinolite, chlorite. JP 307A Metabas alt; Oregon, NW 1/4 S2, T. 4 iS., R. 9W. Albite, actinolite, chlorite, p rehnite. JP 307B Diabase; Oregon, NW 1/4 S. 2,T. 415., R. 9W. Hornblende, aI.bite, epidote, prehnite. JP 314Diabase; Oregon, NW 1/4 S. 10, T. 41S,R, 9W. Plagioclase, hornblende, chlorite, whitemica (augite) JP 343Diabase; California, NE 1/4 S. 3, T.1SN., R. 3E. Albite, actinolite, epidote, quartz,chlorite, (prehnite). JP 348Diabase; California, NW 1/4 S. 8, T.18N., R. 4E. Albite, hornhlende, actinolite. JP 349Diabase; California, NW 1/4 S. 8, T18N,, R. 4E. Albite, actinolite, quartz, chlorite,epidote. JP 358Diabase; California, NW 1/4 S. 9, T.18N., R. 3E. Albite, actinolite, (chlorite),(prehnite), (calcite), (augite). JP 359Diabase; California, NW 1/4 S.5, T. 18N., R. 3E. Plagioclas e, augite, chlorite, prehnite. JP 366Diabase; California, NW 1/4 S. 12, T.18N., R. 3E. Plagioclas e, augite, ho rrblende, chlorite.

JP 377Diabase; Oregon, SW 1/4 S. 35, T.40S., R. 9W. Albite, actinolite, chlorite. 140

Hornblende Gabbro and Paiog ranite

JP 137Gabbro; Oregon, NE 1/4 S. 3, T. 41S., R. 9W, Diabasic texture; plagioclase, augite, hornblende (red-brown), chlorite. JP 197Gabbro; California, NW 1/4 S. 2, T. 18N., R. 3E. Diabas ic texture; p].agioclas e, augite, hornblende, actinolite, chlorite, prehnite. JP 316Albite granite; Oregon, NE 1/4 S.10, T. 41S., R. 9W. Granophyric; plagioclas e, hornblende. JP 318Tonalite; Oregon, NE 1/4 S. 10, T. 41S., R. 9W. Granophyric; plagioclase (zoned, altered), hornhlende, quartz (grains and granophyric intergrowths with albite), augite, (actinolite), (chlorite), (s e ricite). JP 368Tonalite; California, NW 1/4 S.12, T. l8N, R. 3E. Hypidiomorphic -granular; plagioclase , augite, hornblende, quartz, actinolite, chlorite, (s aus s e rite). JP 432Gabbro; Oregon, SE 1/4 S. 34, T. 40S., R. 9W. Hypidiomorphic granular; plagioclas e, augite, hornblende, actinolite, JP 442Gabbro; Oregon, SE 1/4 S. 13, T, 41S,,, R. lOW, Hypidiomorphic granular; plagioclas e, augite, hornblende, quartz, chlorite,

Cumulate Gabbros

JP 119Gabbro; Oregon, NW 1/4 S.17, T. 41S., R, 9W. Adcumulate; plagioclase (sausseritized), augite, JP 132Gabbro; Oregon, SW 1/4 S.18, T, 41S,, R. 9W. Adcumulate; plagioclase (An 89), augite, (sausserite). JP 158Gabbro; California, NW 1/4 S.12, T. 18N., R 3E. Mesocumulate; plagioclase (An 63), augitehornbiende, (actinolite), (oli.vine). 141 JP 162Gabbro; California, NW 1/2 5. 1, T, 13N, R. 3E. Mesocumuiate; augite, piagioclase. (An 91), orthopyroxene, olivine, hornhlende, (tremolite), JP 165Gabbro; California, NE 1/4 S. 2, T. 18N., R. 3E. Adcumulate; plagioclase (An 89), augite, hornblende, serpentine (replacing orthopyroxene?), (tremolite), (white rnic a). JP 222Gabbro; California, NW 1/4 S. 4, T. 18N,., R. 3E. Adcurnulate; plagioc].ase, augite, serpentine (replacing orthopyroxene?). JP 224Norite; California, NW 1/4 S. 4, T. 18N., R. 3E. Adcuniuiate; plagioclase (An 89), augite, serpentine (replacing orthopyroxene and olivine). JP 322Norite; Oregon, SW 1/4 S. 10, T. 41S., R. 9W. Adcumulate; plagioclase (An 90+), orthopyroxene. augite, (ac tinolite). JP 63 Gabbro; California, NW 1/4 S. 12, T. 18N,, R. 3E, Mes ocurnulate; plagioclas e, augite, hornblende. JP 410Gabbro; California, NW 1/4 S.1, T. 18N., R. 3E. Mesocumulate; plagioclase (zoned), augite (relict cores), hornblende, (actinolite), (serpentine), (prehnite) JP 042Gabbro; California, NW 1/4 S. 3, T. 18N., R. 3E. Orthocumulate; augite, plagioclas e (replaced by hydrogarnet), olivine, (serpentine).

Ultramafic Rocks

JP 039Pyroxenite; Oregon, SE 1/4 S.18, T. 41S., R. 9W. Coarse hete radc urnulate; clinopyroxene, olivine, (serpentine). JP 041Wehrlite; Oregon, SW 1/4 S. 7, T. 41S,, R. 9W. Gr3nular, serpentine, cLinopyroxene, (olivine). 142 JP 043Pyroxenite; Oregon, SW 1/4 S.13, P. 41S,, IL lOW, Mosocurnulate vne, thopvroxene, htogarnet, hornblende, (erpitine), (ch.rie). JP i7 Pyroxenite; Oregon, NW 1/4 S.17, T. 41S., IL 9W. Orthocurnulate; clinopyroxene, olivine, (serpentine), (hydrogarnet). JP 352Pyioxenite; Oregon, SE 1/4 S.18, T. 41S,, R. 9W. Orthocumulate; clinopyroxene, olivine.

Norite and Rodite Dikes

JP 015Rodingite; Oregon, NE 1/4 S.IS, T. 41S., IL 9W Granoblastic; hydrog ross ular, prehziite. JP 016Norite; Oregon, SE 1/4 S.18, T. 43S, IL 9W. Hypithoirorphic -gramilar, aogiteort yroe iwdro grossular, hornblende, JP 026Rodig.te; Oregon, SW 1/4 S.17, T. 41S., IL 9W Granoblastic; hydrogrs sular, prehnite, zosite, iF 129Norite; Oregon. NE 1/2 S.18,T.. 413. ,R, 9W. t-oidiomorphi- granular, pLagiocht" - (An 57)atgie, orthopyroxene, hornblende, (trenmiLte), (clinozoisite), (white mica), (prehnite), (hiotite).

Post-Ophioli.te Dikes

JP 142Mafic Dike; Oregon, NW 1/4 S. 4, T. 418., It 9W. Pagioc1ase (albitized), hornblende (elongate, brown), (prehnite), (pumpellyite).

JP 170Mafic dike; Oregon, NE 1/4 3,1,T. 413,, R. 10W. i-fornbknde, Diagoclase, (preLriite). 143

APPENDIX II

Chemical Analyses A?PENI)IX hA. Analysis oI Major Element Rock Standards. BCR-1i3 AGV-1.A This Report AGV-1B PCC-1A PCC-1B flCR-1 F1ann (1973) MW-i PCC-1 T1O,,Sb2 BCR-IA55,07 2.14 54.25 2,2- 59.94 1.06 59.93 1.08 42.35 0,03 41.93 0.05 54.50 2.20 59.00 1.04 41.90 0.015 FeO*MrO 12.0213.570,19 12.4413.66 0.10 16.89 0.105.99 17.12 0,106.28 0.147330,60 0.190.647.73 12.0613.61 0, 18 17.250.0976.08 0.0.74 127.72 Na,OCaOMgO 3.376,913,41 nd3.137.08 nd5.001.41 nd5,061,36 44.08 nd0.59 43.46 nd0.61 6.923.463.27 4.264.901.53 43.18 0.510,O'h$ pK Q 0 -I 0.341.78 0.361.76 2.960.45 rid0.482.97 rid0,010.02 nd0.000.04 0.361.701.57 0.492.890.97 00O20.0045,20 *H0 Tc1nd, not i'e thte2rniQed. a FeO nd nd nd 145

APPENDIX IIB.Trace Eierneiit Analysis of Rock Sta.rd,5

Tht5 Report Flanagan ( l973 BCR-1 G-2 w-1 3CR-i G-2 W-i

Sr* 334 483 187 330 479 190

Zr 195 316 98 190 300 105

La 26 26

Ce 60 54

Sm 6.4 6.6

Eu 1.91 1.94

Tb ISO 1.0

Py 6. 1 6.3

Yb 3.28 3.36

Lu 0.52 0.55

* AU values in ppm. APPENDIX I1C. Chemtcal Analyses of Rooks from the Oregon Moimtain JP 1)S JP 326 JP 310 JP 334 Area. JP 345 JP 351 JP 407 jP 136 49. 12 48. 75 55.98 Low Temperature AssembIgs 52.66 54.71 53.55 43.56 55.31 1. 34 FeOA,OTz02 16.66 7.441,03 10.4012.97 1.36 16.240.968.54 13.65 7.850.54 15.650.607. 13 14.600.677,45 12.16.42 :36 10.14,31 23 CaCMgOMO 10,424,520.13 12.90 3.410.21 74.490.16 27 7.867.400.11 7.5,110.15 14 8.335.400.14 5.4,420.12 80 5.333.500.16 4.200.12016 0,120.010.28 0.573.580.13 0.144.680.09 0.185.660.08 0.165. 100,09 0.644. 120.17 0.140,174.39 TiTotalP0 2500 97,02 8200 95.67 5800 102.49 4.57 3200 98.48 3.2 3600 99.30 2.89 2100 98.38 29 10100 99.64 4.14 8000 99. 77 4.83 SrZrCcLa 100 10.767 4.02.6 7418 131 7 6745 178 6210.8 4.9J.76 115 5512.1 2.15.1 232132 16.94.36,9 6479 YbTbEuLu 0.292.40.50.90 0.290.60.691.7 0.280.50.691.8 0.3.50.9 391.35 APPENDIX fTC. JP174 (Cont.) JP313 JP341 JP344 JP347 JP416 JP340 JP391 Ti02Sf02 61.56 1.10 62.83 0.74 Metabasalts: Epidote-Quartz.-Albite Greenhist 58.99 0.74 54.04 0.70 54.58 0.99 62.22 1.10 Keratophyre 71,96 0.13 46.53Dike 1.52 MuOFeC)A1703 13.570.125.36 15.480.095.45 14.910.096.92 18,190.117.73 15.860.219.63 13.640.145.81 15.680.061.29 10.9616.920.19 Na20CaOMgO 3.666. 101.91 8.003.322.29 9.063.001.38 3.436.263.29 4.053.557.88 6.515.522.88 3.070.411, 17 3.778,084.80 H20P205K20 0.280. 101.97 0.0.26 171.90 2.430. 1218 4.220.080. 14 2.670. 110.04 0,800. 1519 2.830.061.63 0. 1714 TiTotal 6600 95.73 4400 100.53 78 4400 9497.82 4200 134 98.20 5900 7799.57 6600 9198.97 780104 98,29 9100 125 94,8.' SmCeLaSr 59.12.1 2.64.9 274 12.52.65.2 357 215 10.42.24.6 9616.43.15.5 285 2517.3 3.1 596 4.48.85.2 YbTbEuLu 0.370.60.811.5 0.422.20.60.96 0.330,50.781.91 0.432.40.70.98 0.200.850.341.3 0,360.71.41.1 APPENDIX JIC. (Corit.) JP 306A JP 3063 JP 307A JP 3073 JP 314 jP 343 Ti02Si02 54.69 0.64 Metabasalts and Diabases: Albite Actinolite Greenschist and Above 55.46 0.41 57.64 0.82 54.96 0.78 53.45 0,65 55.24 0.86 MnOFAl203 cO 15.670.128.08 13.810.147.02 14.76 0.176.48 16.72 0.196,98 15. 12 0.147,33 15. 76 0.137.67 Na2OCMgO aO 5,966.105.91 4.536.248.22 5.477.194.64 3.675.365.70 2.877,937,75 6.124.495,67 HOP0K20 252 2.460,080.20 2.040.050.28 0.100.231.13 3.530.101,06 0.8730,09 44 2.580.120.10 ZrTiTotal 3800 99.9168 6200 98.2083 4900 7198.64 4700 9699.06 3900 6999.70 5200 7798.74 SmCeLaSr 237 21 6.02.41.2 102 384 191 97 Lu.LuYbTb 0,260,30.441.4 A PPENDDC IIC (Cont.) JP 348 Metabasalts and Diabases: Albite Actinolite Greenschist and Above JP 349 JP 358 jP 359 JP 366 it' 377 A1,OTiOS102 60.j5 56 3 1.09 58.15. 52 35 0.43 14.9451.52 0.89 14.51.51 15 1.71 14.6951.04 1.16 15.6353. 13 0.60 MgOMi0FeO 0.067.t;7 7.0.095.87 12 0.218.79 10.91 0.21 0.169.ii 83.42 0. 9 NaOCaO 2 3.845.303.26 2.756.58 4.865.377.83 5.646.344.79 3.639.426.33 4.336.317.81 HOP205KO 0.230.67 2.680.070.71 3.950.100,50 2.960.170.30 2.380,100.24 3.0.070,05 14 ZrTiTotal 6S00 124100.28 2600 100.18Si 5300 7399.26 10200 116 98.69 6900 8398.25 3600 4699.69 CeSmLaSr 262 17 9812.32.34.6 13.923 2.86.0 182 10.5 2.54.2 65 LuYbTbEu 0.342.20.50.8 0.372,30.70.97 0.322.250.50.75 APPENDIX TiC. (Cont.) JP 137 JP 197 JP 316 JP 318 JP 368 JP 432 JP 442 S!02 50. 12 1.45 50.60 1.85 Hornblende Gabbros and Quartz Diorites 66.66 0.92 54.66 0.45 54.90 0,43 51.15 0.45 53,94 0,61 FcCM'iOA1,03 10.0315.05 0.16 11.9313.790.21 15.55 0.021.28 16.87 0,126.45 15.370.115.00 15.670,097.56 17. 020.157. 14 Na,OC;O 'lgO 8.626.64 7.815.01 4.111,43 7.526.93 10.446,29 10,292.8%9.03 3,135.33 Fc,o 2 5 0.150.284,35 0.170.164.67 0.270.227.64 3.430.051.09 0.080.423.00 0.040. So 0.08C.2.95 24 TiTotulP 0 100.38 3.54 - 99.43 3.23 99.37 1.27 99.69 2.11 97.53 1.49 100, 12 2.47 98.48 2.27 CesuLa 3412. 1 10.3 3. 51.9 TbLuYb 0,766.366141.7 0.450.340.741,9 APEND1X TIC. (Cout.) Si02 49.39JP 119 JP 51.132 14 Curnu3 ate Cahbrs Jp50. 58 53 47,51JR 162 47.06JR 165 48.60JR 222 FeCAl203Ti02 13,09 3,450.04 15. 66 5.090.28 17. 035.790.19 10,29 7.380.19 21. 17 3.980.08 4,626.0.13 46 CaOMgOMnO 17,3612,64 0,10 12.4310.89 0.06 11.559.670.13 11.5518.76 0.16 12,44 8.870.08 16.10,02 14 C. 11 P205K20Na20 0.500.920.00 0.030.351.52 0.010.262.03 0.030.260.64 0.630.011,76 0.000.040.99 TiTotalHO 9.64 2.15 99. 11 1.69 99.45 2.25 98. 14 1.38 98. 14 2.07 98.68 1, .57 SriCeLaSrZr LuYbTbEu APPENDIX IIC. (Cont.) JP 224 JP322 Cumulate Gabbros JP 353 JP 410 JP 002 Jp 042 Al203Ti02Sb9 48.14. 79 89 0,09 47.9418. 30 0.22 50.3417. 17 0.19 46.9718.52 0,31 MgOMnOFeO 11.99 0,5.31 12 9.590.136.45 9,910.126.21 7.0.155.55 12 CaONa 0 14.26 0,130.67 13. 73 0,270.99 11. 69 0.211.94 11.97 0.262.19 TotalH20 98.74 0,02 98.32 0.670.02 99.76 0.031.95 94.31 0.081. 19 TbEuSmCeL 0.130.280.0.5 5 0.370.971.0 0.250.720.54 LuYbHoPy 0.130.74 0.220.871.21 0.201.181.16 AP1'EDIX flC. (Cont.) Si02 48.09JP 178 JP 52,47352 oxenites and Harzf JP 41,28354 ie JP 039 31' 041 JP 043 FeCTb2Al203 2.790.085.67 0.043.321.51 7.980.530.05 CaCMgOMrO 23.7714.570. 14 20.8218.33 0. 17 42,05 0.770.18 NaOP205K20 0.010.111.12 0.000.050.12 0.010.050.03 LaTotalH90 99.35 2.99 97.69 0.87 97.22 4.30 0.08 TbCeEuSm 0.1000.210.0500.40 0.0440,150.0310.13 0,16014 0.120.260.09 0.100.12 DyLuYbHo 0,0220.0.035 128 0.0130.0.024 076 0,39 0.470.560.06 0.380.061.9 APPENDiX UC. (Cont.) JP 015 JP 016 Rodinites and Norite JP 026 JP 129 JP 142 Post-OphioliteDilces JP 170 Al,03Tb2SiO,, 38.0413.31 0.77 45.9416.02 0,16 13.0237.81 0.73 50,8117,45 1.07 46.8513.55 1.32 MnOFeQ 5.050.5.00 14 10.28 0.4.89 13 5.350.5.27 13 4.220,9,41 13 10,69 8.960.24 K20Na20CaOM0 34.39 0.100.04 17.09 0.350.36 34.74 0.060.10 0.296.256.34 11.04 0.423.61 Total110P205 100.22 3,320.06 97.86 2.620.03 98,23 0.940.09 99.45 3.280.19 97,92 0.171.08 ZrTiLaSr 1,6 322 60 2,1 9.2 NdCeEuSm U20 631.1 3, 30.671.3 0.717.01.6 26 3.51,27 YbDyTbLu 0.141.201,5 0.212,01.3S 0.230. 41,6 0.412.60. 8 APPENDIXEiemeit III. Parameters UsedIsotope in Neutron Activation Analysis. HiU Life Energ (KEV) Duration Neutron Flux** Delay* Counting Time EstimatedPrecision CeLaNa 140141 24 40,2h32.Sd15.OIi 15961369 145 3-6h 30.2 14d 7d6h 6-12h2-6h 16m 10% 5% EuSmNd 152153147 47. Oh11.Od 1408 103531 3-6h 6h 3 14d 7d 2-6h 6h 20% 3%59 DyTb 165160 72.3dl2.7y2.35h 298 95 3.6h Sm6h 0.053 14d 4h 6-12h612h 20m 50%1094 YbHoLi t 166177176 2.8h 6.7d-4. 19d 208396 80.6 3-6h 33 7did 2-6h6-12h 50%20% 594 ** Delay from irradiatior to counting PreconNeutronsHoto improve detected estimated cm peakradiochemically to at backgroundapproximately only ratio. lOx chondritic abundances. -2 sec -1 x 10 12 APPEMMX N. Microprobe Analysis of Minerals From Mafic Complex Cumulate Rocks. JP 352 SiC 45.9JP 132 JP 162 46.2 Pta ioclase JP 165 46.2 JP 224 45.9 JP 52.4110 JP 16254.0 JP 52.8165 Cloxene JP 53.178 7 JP 52.9224 54, 8 F'F eQ j) 34.4 33.8 34.5 34.2 4.22.3 5.0 5.2.50.23 7 4.2. 12 6.2.0.22 1i 2.91.4 MgOMr() 18.9 18.9 18.4 18.6 0.5 22.217.4 0.11 21.317.4 22. 716.8 22.18. 1 1 0, 17 22.416.2 22.319. 0 KNa 0/Cr 0 O,,*2 2 1.15 0.071.02 0.30 0.011.23 0.20.60 0. 318 0.550. 1 CompositionTctai 100.4An 100.0An 100.4An 100.4 An 98.6CaMgFe 100.4 CaMgFe 100.7 CaMgFe 100.4 CaMgFc 100. 4 CaMe 101.0 Ca1Fe Anaiy* K20 in Piagioclase; Cr2O3in Pyroxenes. M. 0. Garcia, U. C. L.A. 90 91 89 89 444907 434908 454708 445006 464509 435205 APPENDIX W. (Cont. Si02 jP 39.4162 JR 40.178 7 Olivine JR 40.8352 JR 42.4354 55,4JR 162 57,6JR 354 FeOAl2OTi02 17.6 12. 7 9.6 9,0 10.60,97 Qoxn 5.81. 1 CMgOMnO aO 42.9 47.6 50.3 50.2 30. 7 1.3 33. 7 1.6 TotalCr203Na20 99.9 101.0 100,7 101.6 99.0 100,4 0,6 Aoi1vst, M. 0. Garcia, U. C. L.A. Fo81 Fo87 90Fo 91Fo 85En 91En 1 SS

A?PENDX V. Drib'idon Cc fir Ud, Ci:zl at1or Mcdl(12000C).

Eie Cliv 7l.z.g Cpx CPx

0,01 0.19 0.10 0.02 Ce 0.01 0,12 0.15 0.03 s C. UI '3.07 0,30 0.05 Eu 0,01 0.25 0.51 o. Os 0.01 0.05 0.65 0.2 0,02 0.04 0.65 0.23 Yb 0.02 C. 04 0.52 0.34 Lu 0.03 u.04 0.56

'ibjti 111 et Je! h Mitth; M:eis (1300° CL

Cliv Opx Cpx

0,007 0.00S 0,C9 Ce 0.0 O,QS 0,098

Sm 0,007 0.013 0.260

Eu 0. 'Y37 0.014 0.260 Tb 0.009 0.021 0.310 O.Oil 0.037 0.300 0.014 0.056 0.290 0,016 0. 063 0.280

Dis'ibuticii cceilcients u.ed inaceiement models fter Murali e in press) 159 VITA

Scott Garret Vail vas born December 2, 1948 tD RaiFL E Vail and Margaret Rose Vail, in VancouverWashington. He graduated from Santa Fe High Scboo], Santa Fe, New Mexico in i9? artd from New Mexico Institute of Mining and Technology in l97. H- began graduate studies at Oregon State University in i972.

Permanent address: 228 Spruce Street

Santa Fe, New Mexco 7SOi