New Analyses of Eocene from the Olympic Peninsula, Washington

N. A. LYTTLE Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3]5 D. B. CLARKE Department of Geology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5

ABSTRACT 124° 123°

New chemical analyses have been made of a suite of recently col- lected samples of pillow , breccia, and minor intrusive rocks from the Olympic Peninsula. The rocks have been altered through addition of at least water and carbon dioxide, but the recalculated analyses show that these rocks are tholeiitic basalt rather than spi- lite as previously reported. A petrogenetic model, involving partial melting of mantle peridotite to produce a that underwent fractional crystallization of olivine and equilibrated near atmos- pheric pressure, accounts for the observed chemical features of the basalt. The characteristics and distribution of both the volcanic and associated sedimentary rocks suggests possible origin in an island- arc environment. Key words: igneous petrology, chemical analysis, Eocene, volcanic rocks.

INTRODUCTION

Geological Setting

The Olympic Peninsula is in northwestern Washington (Fig. 1). The Olympic Mountains form the nothern part of the western Washington and Oregon Coast Ranges, which developed during late Tertiary time. According to Snavely and Wagner (1963), an early Tertiary geosyncline extended from the southern end of Van- couver Island; through the Olympic Mountains, Coast Ranges, and Puget-Willamette lowlands of western Washington and Oregon; to Figure 1. The Olympic Peninsula and distribution of lower Tertiary vol- the northern end of the Klamath Mountains in southern Oregon. canic rocks (shaded areas). Early in Eocene time, a thick sequence of tholeiitic lava flows and breccia was erupted from numerous centers onto the floor of the some 100 km inland (Snavely and Wagner, 1963). Weaver subsiding geosyncline. These volcanic rocks are referred to as the (1945) estimated that a minimum value for the average thickness is Crescent Formation in western Washington and as the Siletz River 900 m and that their volume is greater than that of the Columbia and Tillamook Volcanics and volcanic rocks of the Umpqua For- Plateau basalt flows. According to Snavely and Wagner (1963), the mation in western Oregon. An early Eocene age was originally as- volcanic sequence totals more than 4,500 m in thickness on the signed to these rocks by Weaver (1937). On micropaleontological Olympic Peninsula where the base is exposed. evidence Rau (1966) reported them to be of early(?) or middle Most of the lava in the Coast Ranges was apparently erupted Eocene age. The base of the volcanic rocks is exposed only on the onto the sea floor. Well-developed pillow structures are common, Olympic Peninsula, where rocks of the Crescent Formation overlie along with volcanic breccia and intercalated marine sediment a relatively thin metasedimentary sequence, the base of which is a (Park, 1946), but Weaver (1945) also reported numerous small tectonic break (Cady and others, 1972a, 1972b; Tabor and others, vents and dikes that he believed were the source of much of the vol- 1970; Tabor and others, 1972). Throughout the Olympic Penin- canic material, at least on Vancouver Island. Snavely and Wagner sula and Coast Ranges, Eocene volcanic units intertongue com- (1963) also found interflow soil zones and interbedded, locally de- plexly with fossiliferous, tuffaceous siltstone that contains graded rived mud-flow breccia and conglomerate, indicating that volcanic beds of volcanic, feldspathic, and lithic wackes. Beds of chert and islands formed in places and that a part of the volcanic series was Globigerina-bearing limy siltstone occur locally (Snavely and erupted subaerially. Wagner, 1963). Throughout the Coast Ranges, intermittent volcanic activity and The Eocene volcanic rocks are believed to have formed a vast local uplift took place until about middle Miocene time, when fold- lava field that extended from Vancouver Island southward to the ing produced a series of northwest-trending structures. Tabor Klamath Mountains and from a line west of the present coastline to (1972) obtained a K-Ar age of 29 m.y. for the time of metamor-

Geological Society of America Bulletin, v. 86, p. 421-427, 6 figs., March 1975, Doc. no. 50318

421

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phism of rocks in the core of the Olympic Mountains. During late devitrification is more advanced, the glass has crystallized into Pliocene to early Pleistocene time, further folding took place spherulitic or feathery intergrowths of plagioclase and pyroxene. throughout Washington and Oregon (Weaver, 1937, 1945). Vesicles, when present, are generally filled with calcite and (or) chlorite; quartz, prehnite, and zeolites occur infrequently. Chlorite Present Work is invariably present, either in veinlets, vesicles, or as replacement for glass, olivine, pyroxene, and plagioclase. Calcite veinlets, and to The most recent petrological work on Eocene basalt in Washing- a lesser extent quartz veinlets, are common, and prehnite, with rare ton appears to be that of Glassley (1973) and this study based on a pumpellyite, is found in association with the calcite veinlets. collection of 95 samples, of which 53 were studied in thin section The mineralogy of pillows is identical to that of flows. The tex- and 24 were chemically analyzed. The objectives of this paper are tural features are those normally associated with pillows, namely, to (1) present the new chemical data on basaltic rocks from the increases in grain size away from the pillow margins and the de- Crescent Formation; (2) use the data to derive a petrogenetic model velopment of variolitic textures toward the interiors of the pillows. for the origin of the Crescent ; (3) use the data to re-assess the importance of spilite in the Olympic Peninsula; and (4) inter- Diabase pret the role that basalt has played in the Tertiary geological and tectonic evolution of western Washington. The generally poor outcrops of the Crescent Formation made the distinction between coarser grained interiors of thick flows and PETROGRAPHY diabase dikes difficult. For the purposes of this discussion, the medium-grained rocks with subophitic textures are termed diabase. The general petrography of the major types sam- The two distinct types that have been found are normal diabase pled on the Olympic Peninsula will be discussed as follows: basalt containing calcic plagioclase and albite diabase. (flows and pillows), diabase, and basaltic breccia. Sampling Several mineralogical and textural features are common to the localities are described in Appendix 1. two types of diabase. Generally fresh augite occurs in intergranular and subophitic relations with the plagioclase grains. Chlorite or Basalt (Flows and Pillows) pale-green actinolite are minor replacements of the augite along cracks and grain edges. Olivine is completely replaced by chlorite. Basalt is commonly an aphanitic, dark-green rock rich in Chlorite also occurs as abundant interstitial patches and veinlets. devitrified glass, with variolitic, intersertal, hyalopilitic, and inter- Prehnite is associated with calcite and chlorite in veins and also re- granular textures. Plagioclase occurs as microlites, as skeletal mi- places plagioclase. Epidote and pumpellyite are rare secondary crophenocrysts, or as subhedral to euhedral phenocrysts. Measured minerals. plagioclase compositions fell in the range An50 to An60. Colorless Apart from the composition of the plagioclase, the principal dif- to pale-brown clinopyroxene occurs as subhedral micropheno- ference between the two types of diabase is the degree of alteration crysts and as feathery intergrowths with plagioclase. It is generally of feldspar. Plagioclase in normal diabase is generally fresh, al- unaltered, although minor replacement by pale-green actinolite and though some kaolin and sericite are invariably present. Plagioclase chlorite occurs. Olivine is never abundant, but when present it in albite diabase is partly to completely replaced by sericite, kaolin, forms both euhedral and skeletal microphenocrysts that are invari- and in some cases, prehnite and chlorite. Also, partial replacement ably replaced by pseudomorphs of chlorite and (or) calcite. Small, by zeolite material in the albite diabase is occasionally found, and euhedral red-brown spinel is often found poikilitically enclosed laumontite was observed in one sample. within replaced olivine. Titanomagnetite is common throughout, either as subhedral or skeletal grains or as dense specks and rods in Breccia the groundmass. The groundmass may be dark-brown, fine-grained devitrified Volcanic breccia is represented mainly by two types: hyaloclas- glass, or lighter brown, partly spherulitic glass. Where tite breccia and mixed breccia. Hyaloclastite breccia is composed

TABLE 1. CHEMICAL ANALYSES

Sample no. 8 13 1411 16 171 23 30 34 38 40 43 47«

Oxides S102 51.9 47.1 46.6 47.8 47.8 49.2 45.8 46.7 46.6 45.4 49.1 45.8 T102 2.0 2.0 2.0 1.4 2.6 1.4 1.2 1.1 2.0 1.9 1.2 2.0 A120s 15.9 16.3 15.7 17.0 12.8 13.8 14.9 15.1 13.4 14.0 14.4 15.7 Fe20, 3.1 3.9 3.3 2.5 6.4 5.4 2.7 2.9 5.4 3.3 3.1 5.1 FeO 5.9 7.8 8.5 7.2 8.8 8.2 6.3 5.1 9.2 10.8 8.5 8.8 MnO 0.18 0.18 0.19 0.15 0.25 0.21 0.18 0.14 0.22 0.21 0.22 0.27 MgO 2.8 5.2 5.8 5.9 5.0 5.9 11.5 10.3 6.0 6.2 7.5 5.7 CaO 7.9 11.3 11.1 12.2 8.7 7.3 7.1 9.4 10.0 10.0 12.7 10.0 Na20 5.9 3.1 3.0 2.8 4.5 3.8 3.3 3.0 3.6 2.4 2.3 2.6 K20 0.07 0.38 0.53 0.41 0.17 1.0 1.0 0.88 0.11 0.07 0.18 0.36 P20s 0.72 0.18 0.19 0.13 0.27 0.15 0.31 0.18 0.26 0.18 0.11 0.29 C02+ 0.47 0.28 0.22 0.30 0.20 0.32 0.07 0.19 0.30 0.05 0.06 n.d. T H20 2.9 2.2 2.5 2.9 2.3 2.9 4.7 4.4 3.1 4.5 1.0 3.3 Total wrr 35TF 99.6 lOÙ.7 50~ 90~ 557T SO" 100,2 SO" 1ÖÖ.4 NOTTP.8s 0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Or 0.4 2.3 3.2 2.5 1.1 5.9 6.5 5.5 0.7 0.4 1.1 2.2 Ab 52.4 27.1 26.2 24.5 38.9 33.8 28.0 26.1 31.3 21.2 19.4 22.8 An 17.3 30.3 28.9 33.5 14.8 18.4 24.2 26.5 21.0 29.0 28.7 31.2 Ne 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.5 0.0 0.0 0.0 0.0 D1 12.8 19.6 20.7 21.3 21.9 13.5 8.3 16.2 22.3 18.1 27.4 15.2 Hy 6.6 4.9 2.1 4.0 0.2 11.2 0.0 0.0 0.8 20.1 13.3 13.0 01 0.0 6.2 9.5 7.4 11.2 9.6 24.7 18.6 15.5 1.9 3.6 5.7 Mt 4.6 5.2 4.9 3.8 6.1 4.3 4.2 3.9 3.8 5.1 3.9 5.2 11 4.0 4.0 4.0 2.7 5.1 2.9 2.5 2.3 4.0 3.8 2.3 4.0 Ap 1.7 0.4 0.5 0.3 0.7 0.4 0.8 0.4 0.6 0.4 0.3 0.7 Total TÔÔ7ÏÏ 100.0 T557B TÔÔ7ÏÏ TÔÔTÔ T5075 TÖO TÍO TSS7Ô TOTo TOO rara

* Analyst: H. Baadsgaard, University of Alberta. + Total H20.

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mostly of angular glass fragments that have devitrified into brown 20.0 spherulitic aggregates. Some fragments, as a result of hydration, are 150 * rimmed by a yellow-brown palagonite, and the most highly altered • ; i- i fragments have been completely replaced by bluish-green chlorite. AI O The mixed breccia consists of varying proportions of glassy 10.0 2 3 basalt fragments, glass fragments, and crystals of feldspar and pyroxene. The glass fragments have been altered similarly to frag- 20 0 ments in the hyaloclastite breccia. The basaltic fragments consist of dark, glassy fragments and often show fluidal orientation of 15.0 Total Iron plagioclase microlites. The glassy matrix may be fresh or totally re- placed by chlorite. The generally sericitized feldspar crystals are 10.0 i • as FeO more abundant than the pyroxene crystals, which tend to be quite fresh. 5.0

CHEMISTRY 15.0

In Table 1, 24 new chemical analyses of volcanic rocks from the 10.0 MgO Olympic Peninsula are presented. Most rocks have been altered by

the addition of HzO and C02, and some of these have probably suf- <" 5.0 0) fered addition of CaO and Na20. In view of the alteration of these TJ rocks, the subsequent normative calculations, variation diagrams, and projections use the analyses of Table 1 recalculated to 100 per- 15.0 cent on a total H20- and CaC03-free basis. Recalculation of the o 10.0 CaO analyses on a CaC03-free basis assumes that any CaO removed by the recalculation was introduced into the rocks in the form of 5.0 CaC03. In rocks such as samples 77, 32, and 10, all of which con- tain veinlets of calcite, this assumption seems reasonable. In the remaining rocks, the amount of CaO removal is so small that even 8.0 if the CaO was originally from within these rocks, its removal as 6.0 CaC03 does not significantly change the original analyses. To compensate for oxidation subsequent to eruption or intrusion, the 4.0 Na20 iron oxide ratios have also been readjusted by the method of Irvine 2.0 • • • . and Baragar (1971). The fact that the most altered rocks in Table 1 (namely, those with high Na 0, H 0, and C0 ) do not form a dis- 2 2 2 2.0 crete group on any of the variation diagrams (Fig. 2) indicates that this recalculation procedure is in order and that the adjusted K2O 1.0 analyses represent, as closely as can be determined, the original rock chemistry. Because of the mobility of the potassium ion » « • i under conditions of low-grade (Smith, 1968; 44 46 48 50 52 54 56 Hekinian, 1971), no significance is attached at this stage to the low potassium in some of the rocks. Si02(wt%) Most of the analyzed rocks are hypersthene normative and are Figure 2. Major-element variation, weight percent oxides versus weight therefore tholeiitic, in the terminology of Yoder and Tilley (1962). percent silica.

TABLE 1 (continued)

Sample no. 57 60 69 77 80 91 32C 32M 32E 10C 10M 10E

Oxides S102 51.4 46.3 49.0 44.7 50.2 49.7 45.0 46.5 48.6 44.2 49.8 50.9 T10¡ 1.9 1.1 1.9 2.6 1.5 1.5 1.1 1.1 1.1 0.69 0.74 0.75 A120, 12.4 16.0 14.4 10.6 16.3 13.0 12.4 13.6 14.8 12.2 13.0 13.7 Fe20i 6.7 3.0 3.4 9.4 5.4 6.5 4.5 5.2 4.1 6.1 4.9 4.4 FeO 7.9 6.7 8.6 8.9 5.8 6.9 4.0 3.7 4.4 6.2 7.2 7.8 MnO 0.14 0.17 0.14 0.29 0.17 0.22 0.15 0.15 0.16 0.20 0.22 0.22 MgO 4.3 9.4 6.8 5.8 4.0 6.4 6.7 5.0 6.9 6.9 7.4 7.5 CaO 7.0 8.9 8.3 11.1 6.9 10.5 14.2 13.0 10.4 14.0 10.4 9.7 Na20 6.1 2.5 3.6 3.6 5.4 2.3 3.5 3.9 2.8 2.9 3.2 3.1 KaO 0.04 1.2 0.53 0.14 0.28 0.08 0.46 0.62 1.5 0.25 0.30 0.38 P205 0.25 0.10 0.24 0.13 0.10 0.14 0.25 0.27 0.26 0.09 0.05 0.04 C02+ 0.41 0.07 0.25 0.89 0.14 0.13 4.0 3.4 1.2 3.2 1.2 0.54 T H20 1.9 4.8 3.0 1.9 3.1 2.1 3.4 2.6 3.0 2.9 1.9 2.0 Total 1ÛÛ.4 100.2 100.2 10Ô.1 90~ WT W7T 90~ wr 1ÛÔ.3 161.Ö G Norme Q 0.0 0.0 0.0 0.0 0.0 4.0 0.0 0.0 0.0 o.o • 0.0 0.0 Or 0.2 7.7 3.3 0.9 1.7 0.5 3.1 4.1 9.4 1.7 1.8 2.3 Ab 50.0 22.0 31.3 26.5 47.4 20.3 33.8 37.3 25.4 27.1 28.8 27.1 An 6.3 30.3 22.4 12.8 20.4 25.8 19.5 20.2 25.2 21.7 20.9 22.7 Ne 1.8 0.0 0.0 3.1 0.0 0.0 0.0 0.0 0.0 0.4 0.0 0.0 D1 21.1 11.8 13.9 32.0 11.3 21.7 24.7 21.5 16.2 26.9 20.4 18.6 «y 0.0 3.6 15.6 0.0 0.2 19.9 1.9 3.2 14.2 0.0 17.7 21.3 01 11.1 18.2 4.0 13.1 11.2 0.0 9.5 6.5 2.6 16.9 5.5 2.9 Mt 5.1 3.9 5.1 6.2 4.5 4.5 4.3 4.2 4.1 3.6 3.3 3.5 il 3.8 2.3 3.8 5.1 3.1 3.0 2.5 2.3 2.3 1.5 1.5 1.5 Ap 0.6 0.2 0.6 0.3 0.2 0.3 0.7 0.7 0.6 0.2 0.1 0.1 Total "TOOTS' TOOT TOOT TOOT T507ÏÏ TTO7ÏÏ TOOT "TOO TOTS' TOOT TOOT TOOT

§ Norms based on analyses recalculated to 100 percent on a total H20- and CaC03-free basis, with readjusted Iron oxide ratios.

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Samples 30, 34, 57, 77, and 10C are nepheline normative, but the strongly affected by soda metasomatism. The purpose of this sec- amounts of nepheline in samples 30, 34, and 10C are small enough tion is to examine to what extent the volcanic rocks of the Crescent to be within the limits of analytical error. Samples 57 and 77 may Formation can be regarded as spilite. be true alkali basalt, although the high Na20 in number 57 is prob- Yoder (1967) has illustrated the relation between basalt and a ably of metasomatic origin. portion of the anhydrous albite-diopside-clinochlore plane (the "spilite plane"), representative of the principal spilite mineral as- PETROGENESIS semblage. This spilite plane can also be constructed within the CMAS tetrahedron and is represented by the compositions diop- Two approaches were taken to examine the overall chemical side (CMS2)-clinochlore (M5AS3)-anorthite (CAS2), all of which lie character of the Olympic Peninsula volcanic rocks and to gain on the larger plane C2S3-M2S-A2S in the main tetrahedron (Fig. 5, some insight into the petrogenetic history of the parent magmas. inset). Spilitic and basaltic compositions have been recalculated in The first approach was to project the CIPW normative minerals terms of C, M, A, and S and then projected onto the spilite plane, into the basalt tetrahedron (Yoder and Tilley, 1962; Fig. 3). Several from the S apex of the tetrahedron. Figure 5 shows the field of pro- observations can be made: jection for published spilite analyses, with Na20 content equal to 1. All rocks plot close to the 1-atm cotectic line, as drawn by or greater than 4 percent by weight, onto this plane. The level of 4 Clarke (1968) using melting data on natural basalt (Tilley and percent Na20 is considered a convenient lower limit for spilite be- others, 1963, 1964, 1965, 1967). This suggests that the chemistry cause this value effectively separates them from basalt, which gen- of the metamorphosed Olympic Peninsula volcanic rocks is com- erally does not have a Na20 content much above 3.5 percent parable to fresh basaltic lava and that the Olympic volcanic rocks (Manson, 1967, Table V, VI). have equilibrated at low pressure. In addition to the field for published spilite analyses, we have 2. A restricted range of compositions is indicated for the Olym- also been able to delineate fields that enclose 12 published analyses pic Peninsula rocks. of Washington and Oregon basalt samples and 22 of the Olympic 3. There is a variation in the projected positions of different Peninsula rocks. Two of the latter analyses project well into the spi- parts of individual pillows, for example, samples 10 and 32, that is lite field, one of an albite diabase (analysis 8) and the other of a large relative to the variation in the province as a whole. gabbro with cumulus plagioclase (analysis 80). The three fields The second approach involves recalculation of the chemical overlap in projection, but the average of the Washington and analyses into the CMAS components (that is, CaO, MgO, A1203, Oregon field lies 3.3 percent Si02 above the spilite plane, the Olym- and Si02) using the method of O'Hara (1968). Once basalt pic Peninsula rocks 0.1 percent Si02 above the plane, and spilite analyses are recalculated into the pseudoquaternary system CMAS 0.6 percent Si02 below the plane. This indicates that the Olympic (Fig. 4A), they can be projected onto petrogenetically meaningful Peninsula rocks appear, at best, to have compositions intermediate planes within the tetrahedron and thus can be related to phase between Washington and Oregon basalt and true spilite. boundaries of experimentally studied natural and synthetic sys- tems. Figure 4C illustrates the projection of the Olympic Peninsula Environment of Volcanism rocks from diopside (CMS2) onto the plane C3A-M-S. The posi- tions of the phase boundaries have been taken from O'Hara The origin and environment of eruption of the lower to middle (1968). Eocene basaltic rocks of the Coast Ranges of western Washington Using Figure 4C, it is possible to consider a model for the forma- and Oregon are presently unresolved. Snavely and Wagner (1963) tion and evolution of the Olympic Peninsula magma. Partial melt- and Snavely and others (1968) described the environment of erup- ing of spinel peridotite at a pressure of 20 kb first produces a liquid at Bp The composition of this liquid then migrates out along the CPX boundary between olivine and orthopyroxene as the degree of par- tial melting is increased, and in so doing, the bulk composition of the magma changes its character from alkalic (nepheline norma- tive) to tholeiitic (hypersthene normative). Thus, all of the Olympic Peninsula rocks, including those that are nepheline normative, can be simply related to the range of partial melts through a process of olivine fractionation (control lines shown as bold arrows, Fig. 4C) by the magma en route to the surface as the olivine primary phase volume expands in response to falling pressure (O'Hara, 1968). In addition to this olivine fractionation, some degree of plagio- clase crystallization and (or) accumulation at low pressure is neces- sary to explain some of the compositions that lie in the plagioclase field at 1-atm pressure. This model does not preclude the formation of a primary magma at greater pressures, for example, liquid BH at 30 kb, but the occurrence of both tholeiite and alkali basalt in the Olympic Peninsula suggests that re-equilibration at intermediate pressures has taken place.

OLYMPIC PENINSULA: A CLASSIC SPILITE LOCALITY?

From the limited published data available (Park, 1946; Turner and Verhoogen, 1960) the impression could be gained that the metamorphosed volcanic rocks of the Olympic Peninsula are dom- Figure 3. Simple normative basalt tetrahedron (inset) and projection of inantly spilitic in character. Although most authorities today agree Olympic Peninsula rocks from quartz apex (filled circle) onto plane Cpx- that spilite is a type of metamorphosed basalt (Cann, 1969), it is Oliv-Plag. Triangle = pillow basalt; open circle = nepheline-normative distinct from most metamorphosed basalt in that it has been rocks.

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tion as being typically eugeosynclinal, whereas Glassley (1973) hypothesized that basalt of the Crescent Formation (at least, his lower member basalt) originated as part of the that was later subducted and incorporated onto the continent as a con- sequence of sea-floor spreading and collision of plates. If Glassley's hypothesis is correct, it might be expected that blueschist belts and tectonically emplaced slices of ultramafic rock (features commonly associated with subduction) be found in the Olympic Peninsula and possibly in other parts of the Coast Ranges. None has so far been described, although Tabor and others (1972) and Cady and others (1972a, 1972b) have indicated evidence for thrusting in the Olym- pic Peninsula. An alternative origin, namely an island arc origin, can be pro- posed for the early to middle Eocene basaltic rocks of the Coast Ranges. This proposal is based largely on the association of vol- canic rocks and interrelated sediment. In the Olympic Peninsula, where the base of the Crescent Formation is exposed, a sequence of clastic metasedimentary rocks (argillite and graywacke) conforma- bly underlie, and interfinger with, the Crescent Formation (Weaver, 1937; Rau, 1964). It is difficult to explain the presence of these metasedimentary rocks under the Crescent Formation if the vol- canic rocks were former oceanic crust. Also, sedimentary rocks within the Crescent Formation range from pelagic nannofossil limestone containing planktonic foraminifera and terrigenous clas- tic varieties, in the lower part of the formation, to shallow-water terrigenous clastic sediments containing benthonic foraminifera, in the upper part of the formation (Rau, 1964, 1966, 1967; Garrison, Figure 5. Spilite plane CMS2-M5AS3-CAS2 in relation to CMAS tet- 1967, 1972, 1973; Glassley, 1973). Rau (1964) has interpreted the rahedron (inset) and projected fields for spilite, Washington and Oregon basalt, and Olympic Peninsula rocks onto spilite plane. Spilite analyses change from dominantly planktonic foraminifera in the lower part from Bartrum (1936), Battey (19S6), Cann (1969), Gilluly (1935), Sunduis of the Crescent Formation to dominantly benthonic foraminifera in (1930), Wells (1923), Smith (1970), Nicholls (1958), Park (1946), Vallance the upper part as a change from open-sea conditions, prior to late (1960,1969), Aumento and Loncarevic (1969), and Melson and Van Andel early or middle Eocene time, to shallow bays in late early or middle (1966). Washington and Oregon basalt analyses from Park (1946), Waters Eocene time. This change would be in accord with the development (1955), and Snavely and others (1968). and gradual build-up of an island arc in the Olympic Peninsula re- gion, when open-sea conditions during early Eocene time would and the formation of mudflow breccia have all been described gradually give way to shallow-water conditions during middle (Snavely and Wagner, 1963; Snavely and others, 1968; Glassley, Eocene time, as the volcanic products accumulated within the 1973). Also, the associated calc-alkalic volcanism of Washington basin. and Oregon in early Cenozoic time (Waters, 1955) lends support to The pattern of early to middle F^ocene volcanism within the an island arc type of environment for the lower to middle Eocene Coast Ranges suggests the development of large volcanic edifices volcanic rocks, because both are related to an offshore subduction along an island arc, in that great local accumulations of basalt, zone. formation of basaltic islands with subaerial flows and soil horizons, ACKNOWLEDGMENTS s s A A B This research was supported by grants from Dalhousie Univer- /__\MS sity and the National Research Council of Canada and forms part / ¿S——\m2S of an M.S. thesis by N. A. Lyttle. We are grateful to D.G.W. Smith A / \ for his part in originating the project and to S. Abbey and D. F. Strong for their assistance with the chemical analyses. Finally, we C3A¿ ^M appreciate the valuable constructive criticism of R. W. Tabor, I. S. McCallum, and D.J.W. Piper in the preparation of this paper.

APPENDIX 1. FIELD RELATIONS AND COLLECTION LOCALITIES OF ANALYZED ROCKS For each rock, refer to Figure 6 for the map location of the sample.

Rock no. Field relations and collection localities 5. Extrusive, 15.2 m from upper sediment contact. Cushman Lake Road, 0.8 km west of Olympic National Park boundary. 8. Probably intrusive. Sample from center of sill. Cushman Lake Road, 0.6 km west of Olympic National Park boundary. M 10. Extrusive, pillow basalt. Cushman Lake Road, 2.1 km east Figure 4. A. CMAS tetrahedron. B. C3A-M-S plane in the CMAS tet- of Olympic National Park boundary. rahedron showing location of Figure 4C as stippled area. C. Projection of 13, 14. Intrusives(?) from massive unit of volcanic rocks. Cush- Olympic Peninsula rocks from diopside (CMS2) onto C3A-M-S plane. Sym- man Lake Road, 3.5 km east of Olympic National Park bols as in Figure 3. boundary.

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60. lntrusive(?) from exposure of volcanic rocks from the same locality as sample 57. 69. Intrusive(?) from massive unit of volcanic rocks 10.8 km from the southern end of Hurricane Ridge Road, south of Port Angeles. 77. Intrusive(?) from thick sequence of volcanic rocks 12.9 km from the southern end of Hurricane Ridge Road, south of Port Angeles. 80. Intrusive in sequence of volcanic rocks 0.3 km west of the eastern end of Lake Sutherland, west of Port Angeles. 91. Extrusive from large sequence of pillow lava and lava 7.2 km west of the eastern end of Lake Sutherland, on the shore of Crescent Lake, near Sledgehammer Point.

REFERENCES CITED

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