WILLIAM H. TAUBENECK Dept. Geology, Oregon State University, Corvallis, Ore. Cornucopia Stock, Wallowa Mountains, Northeastern O

WILLIAM H. TAUBENECK Dept. Geology, Oregon State University, Corvallis, Ore.

Cornucopia Stock, Wallowa Mountains,

Northeastern Oregon: Field Relationships

Abstract: The composite Cornucopia stock, a parts of different intrusions of cordierite trondhje- satellite of the Wallowa batholith, intrudes a mite. Taubeneck and Poldervaart (1960) defined heterogeneous assortment of eugeosynclinal sedi- Willow Lake-type layered rocks as being composed ments and volcanic rocks of greenschist-facies of alternating bands of felsic and mafic constituents regional metamorphism. Important field evidence in which the minerals are characteristically elonga- for emplacement of magmas is furnished by contact ted and oriented roughly perpendicular to the relationships, wall-rock deformation, and structural banding. Detailed mapping of Willow Lake-type features of the granitic rocks. The pluton contains layered rocks in Cornucopia stock was instrumental at least five distinct granitic rocks. A related series in belated field recognition of the composite of explosion breccias, intrusive breccias, and character of the trondhjemites. Elsewhere, Willow porphyry dikes forms part of the sequence. Lake-type layered rocks should also be useful in Willow Lake-type layered rocks are notable in a unraveling intrusive histories of some igneous biotite trondhjemite unit but are more striking in complexes.

CONTENTS Introduction . 1094 3. Geologic map of southeastern part of Cor- Acknowledgments . 10% nucopia stock 1098 General character of Cornucopia stock . . . . 1096 4. Map showing pattern of cross folds in limestone Location and topography . 1096 east of Little Eagle Creek 1099 Complexity and sequence of emplacement . 1096 5. Features of sills 1104 Geographic names . 1096 Structure of country rocks . 1098 Plate Following Structure of granitic rocks . 1100 1. Topography and rock relationships, Cornuco-] Planar structure . 1100 pia stock, Wallowa Mountains, Oregon . . Linear structure . 1101 2. Apophyses and contact relationships, Cornuco- Contacts between granitic rocks ... . 1101 pia stock, Wallowa Mountains, Oregon . . Contacts with country rocks . 1103 3. Contacts of Crater Lake cordierite trondhje- 1100 Apophyses in country rocks . 1104 mite, Cornucopia stock, Wallowa Moun- Boudinage of apophyses . 1105 tains, Oregon Aplite dikes . 1105 4. Sill and dike relationships, Cornucopia stock. Rocks of the regional terrain . 1106 Wallowa Mountains, Oregon Rocks of the thermal aureole . 1106 Modal data for granitic rocks . 1108 Facing Cordierite-bearing granitic rocks . 1109 5. Sill relationships, Cornucopia stock, Wallowa Willow Lake-type layered rocks . 1110 Mountains, Oregon 1108 Explosion and intrusive breccias , 1111 6. Aplite relationships, Cornucopia stock, Wallowa Porphyry dikes . 1111 Mountains, Oregon 1109 Field evidence for magmas . 1112 Table Other evidence for magmas . 1113 1. Modes of Cornucopia tonalite of the Cornuco- Conclusions . 1114 pia stock, Wallowa Mountains, Oregon . . 1108 References cited . 1114 2. Modes of tonalite from satellites of the Cor- nucopia stock, Wallowa Mountains, Oregon 1109 Figure 3. Modes of trondhjemites of the Cornucopia 1. Preliminary geologic map of southeastern stock, Wallowa Mountains, Oregon ... 1109 Wallowa Mountains, Oregon 1095 4. Mean and standard deviation for 11 specimens 2. Preliminary geologic map of most of Cornuco- of tonalite porphyry of the Cornucopia pia stock 1097 stock, Wallowa Mountains, Oregon . . . 1112

Geological Society of America Bulletin, v. 75, p. 1093-1116, 5 figs., 6 pis., November 1964 1093

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jemites of the Wallowa batholith and Cornu- INTRODUCTION copia stock are closely related, petrological REGIONAL SETTING: In the Wallowa Moun- discussions require a knowledge of rocks in tains of northeastern Oregon, a thick sequence both plutons. An understanding of trondhje- of Permian-Triassic and Lower Jurassic shale, mites in the Cornucopia stock depends es- limestone, graywacke, conglomerate, breccias, pecially on detailed field and laboratory studies and volcanic rocks is characterized by green- of related cordierite trondhjemites, explosion schist-facies regional metamorphism and is cut breccias, intrusive breccias, and ring structures by the composite Wallowa batholith and in the batholith. Mapping and studies of per- closely related satellitic stocks such as the tinent batholithic rocks are incomplete. There- Cornucopia igneous complex. The batholith, fore, presentation of current knowledge of the about 225 square miles in size, contains at least Cornucopia stock implies that several conclu- five small gabbroic units, four large zoned in- sions are somewhat tentative. Future revisions trusions of tonalite-granodiorite (Taubeneck, should be minimal, however, as emphasis here 1964a), and many small felsic bodies that include is on field relationships, to the exclusion of other a sequence of unique cordierite trondhjemites problems of importance to the petrogenesis of and cordierite trondhjemite porphyries. The the rocks. Field studies supported by adequate Cornucopia stock, 3-9 miles southeast of the mineralogical data must establish the identity, batholith (Fig. 1), is the largest satellite and sequence, and quantitative relationships of the the only one that contains representatives of Cornucopia series of plutonic and hypabyssal the cordierite trondhjemite series. Field evi- rocks before a controlling framework for dence (Taubeneck, 1955; 1959) suggests that theoretical and experimental treatment can be granitic rocks of northeastern Oregon are constructed. Hence, an introductory paper probably Early Cretaceous, but biotites from emphasizing field relationships is necessary. Craig Mountain and Pole Bridge plutons The goals of this paper are to: (1) mention (Taubeneck, 1964a) of the Wallowa batholith briefly progress in a long-range program in the give Late Jurassic K-Ar ages. Wallowa Mountains, (2) introduce field evi- After the granitic rocks were deroofed in the dence for magmatic origin of a sequence of Cretaceous, erosion prevailed until Miocene granitic rocks in Cornucopia stock, (3) focus and early Pliocene (Waters, 1962, p. 160) ex- preliminary attention on unique cordierite trusion of Columbia River Basalt buried topog- trondhjemites, (4) present data concerning raphy having a relief of several thousand feet. new discoveries of Willow Lake-type layered Major topographic features of northeastern rocks (Taubeneck and Poldervaart, 1960), and Oregon originated during Pliocene block fault- (5) provide a framework for later papers on the ing. Vigorous Pleistocene glaciation contrib- petrography and petrology of the rocks. uted to removal of most basalt from the higher PREVIOUS FIELD WORK: The only systematic part of the Wallowa fault block (Taubeneck, geological mapping in the southeastern Wal- 1963a), producing rugged mountains known in lowa Mountains was done in 1921 by Ross Oregon as the "Swiss Alps of America." (1938, p. 9) during a rapid reconnaissance in WALLOWA RESEARCH PROJECT: Eight Weeks difficult terrain that included the Cornucopia of back-pack reconnaissance in 1953 and 1955 stock as part of 500 square miles of complicated in the Eagle Cap Wilderness Area of the geology. The pioneer work of Ross is another Wallowa Mountains disclosed terrain admira- tribute in the early record of geologic explora- bly suited for structural and petrologic studies tions in the western United States. Numerous of granitic rocks. The Wallowa project, initi- interesting publications by Goodspeed ap- ated in 1956 to obtain additional knowledge peared between 1927 and 1959. Featuring of the granitic rocks, was soon expanded to in- metasomatic interpretations for rocks of the clude the geologic evolution of the Wallowa Cornucopia stock and adjacent areas, many Mountains. Field studies involve 700 square publications considered criteria for distin- miles in Joseph, Enterprise, Eagle Cap, Cornu- guishing magmatic from granitized rocks and copia, Sparta, Halfway, and Telocaset quad- thus contributed to higher precision in field rangles. Mapping at scales from 1 inch equals studies of granitic rocks. 4000 feet to 1 inch equals 1000 feet is four fifths METHODS: During the summers of 1957 complete in the batholith and one third com- through 1963, 36 weeks were spent in mapping plete in country rocks. and studying the area of Figure 1. As approx- PURPOSE: As tonalites and cordierite trondh- imately half the field work was in the Eagle

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LEGEND

70 Strike and d^p of beds (not Oal Alluvium and colluviun necessarily upright) X Strike of vertical beds X" 60 Strike and dip of overturned beds ", Qgm "| Glacial material _— -" Contact: Dashed where approximate, dotted where inferred FEETcrEEJ Columbia River Basalt •—- -•• Ma|0r Cenozoic fault: Dashed where approximate, dotted where concealed —x— Brown biotite isoqrod l

~~Figure 1. Preliminary geologic map of southeastern Wallovva Mountains, Oregon~~

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Cap Wilderness Area, horses were used to transport supplies to base camps accessible by trail GENERAL CHARACTER OF and to transport specimens to roads. Except for CORNUCOPIA STOCK 10 man-days of assistance by students in back- packing heavy loads of specimens to roads or Location and Topography base camps, the writer did the field work alone. Most of the Cornucopia stock is in the ex- Most of the Cornucopia stock was mapped at treme southeast portion of the Eagle Cap 1 inch equals 1000 feet, part at 1 inch equals quadrangle; the remainder is in the southwest 4000 feet; 917 specimens totaling about 5300 corner of the Cornucopia quadrangle. Any pounds were collected. About 1490 thin sec- part of the stock can be visited within a day tions were studied. from roads along glaciated canyons of East Modal anayses were determined by point- Eagle Creek on the west and Pine Creek on the counter (Chayes, 1949), using two to four thin east. sections (each 750-850 sq mm) from each rock. Cornucopia stock constitutes much of the At least 2000 points were recorded for each southeast corner of the uplifted Wallowa thin section. Mountain fault block (Taubeneck, 1963a). An attempt was made to record locations Eagle fault (Figs. 2 and 3) extends diagonally of significance. Elevations of locations should across the west-central portion of the stock and be accurate within 50 feet. roughly parallels the eastern half of the southern contact of the stock. Between 1 and 2 ACKNOWLEDGMENTS miles east of the stock, the Imnaha fault (Fig. The writer acknowledges with special grati- 2) extends northward. Displacements of several tude support from The National Science thousand feet on both faults contribute to Foundation in Research Grants G2415, prominent topographic features (Plate 1) of the G14553, and GP-472. eastern, central, and north-central portions of Much laboratory work was done at The the stock. The western third of the stock, Pennsylvania State University, particularly in rather heavily timbered, is down-dropped by- 1960-1961 during tenure of a National Science Eagle fault and is not visible for scores of miles Foundation regular postdoctoral fellowship. as is the remainder of the pluton; but steep The writer is especially indebted to members slopes and relief of several thousand feet pro- of the College of Mineral Industries, The Penn- vide many exposures. sylvania State University, for providing facilities and a stimulating environment for research. Complexity and Sequence of Emplacement Preparation of the manuscript at Oxford, Cornucopia stock contains at least five England, was possible by award of a Fellowship distinct tonalites and trondhjemites; each is a from the John Simon Guggenheim Foundation. separate injection. Prof. L. R. Wager kindly provided facilities The oldest and largest unit, here called at the Department of Geology and Mineralogy, Cornucopia tonalite, varies systematically in Oxford University. mineralogy from margin to core. The next During field trips in Wallowa Mountains, the oldest unit is named Tramway trondhjemite. writer benefited from discussions with C. E. The following unit, first in a series of three Brown, C. W. Chesterman, G. A. Chinner, cordierite trondhjemites, is Big Kettle cor- S. P. Clark, Jr.. John de Neufville, J. J. Fawcett, dierite trondhjemite, and the two subsequent R. F. Fudali, H. J. Prostka, J. F. Schairer, units are Pine Lakes cordierite trondhjemite W. F. Schreyer, T. P. Thayer, A. C. Turnock, and Crater Lake cordierite trondhjemite. O. F. Tuttle, and H. S. Yoder, Jr. Visits of Probably Crater Lake cordierite trondhjemite these men are held in warm remembrance. represents successive increments of two or For 1 or 2 days, assistance in back-packing three closely related magma pulses. many specimens to roads or base camps was A complicated series of explosion breccias, given by C. E. Wetherell, F. F. Greene, R. F. intrusive breccias, and porphyry dikes is part Morrison, H. J. Prostka, T. L. Vallier, and of the emplacement sequence. Bruce Nolf. To many other individuals, who contributed Geographic Names to recent advances in knowledge of rocks and The stock is named for Cornucopia (Fig. 1), minerals in the Wallowa Mountains, the writer since 1941 a languishing mining community expresses sincere appreciation. near the southeast corner of the pluton.

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For reference, parts of the stock and all eastern Wallowa Mountains have a prevailing satellites are assigned geographic names. The northeast trend. Oldest rocks are to the south- northerly projecting mass of cordierite trondh- east, youngest to the northwest. Three to eight jemite (Fig. 2) is Crater Lake salient, whereas miles east of Cornucopia, dips in Permian the eastward prong of tonalite (Fig. 3, vicinity strata are northwest at moderate angles.

~~R 45 E.~~

~~LEGEND~~

~~Qal { Alluvium and colluvium~~

~~"Qgm ^ Glacial material~~

~~:TcrEE| Columbia River Basalt~~

~~Rhyolite dike~~

~~Later intrusive breccia~~

~~Tramway trondhjemite~~

~~Tonalite porphyry dike~~

~~Early intrusive breccia~~

~~Cornucopia tonalite~~

~~Country rocks~~

SYMBOLS \ 70 Strike and dip of beds (not necessarily upright) •- Strike of vertical beds Strike and dip of overturned beds •\50 Strike and dip of planar structure x Strike of vertical planar structure — - Contact: Dashed where approximate —^ Fault: Dotted where concealed 2\~r~ Locality mentioned in text — — Secondary road ~~-*-~. Abandoned wagon road

~~0 1000 2000 Feel~~

~~Contour interval 400 feet Topography from 1954 U.S.G.S Cornucopia 15' quadrangle~~

~~R 45 E Figure 3. Geologic map of southeastern part of Cornucopia stock~~

and east of locations 1, 44, and 59) on the Average dips steepen and pass through vertical southeast is the Union Companion salient. as country rocks (Fig. 1) are crossed from The mass of tonalite (Fig. 3) from 0.1 to 0.4 southeast to northwest, where overturned miles northwest of the abandoned Red Jacket Upper Triassic beds dip southeast. Lower mine (Fig. 3, location 1, elevation 6120 feet) Jurassic fossils recently collected by Bruce Nolf is the Red Jacket satellite; the body of tonalite in the upper 2000 feet of the Triassic sequence about half a mile east of Red Jacket mine is in the northern Wallowa Mountains suggest the Coulter satellite; the much smaller tonalite that overturned Upper Triassic beds west and mass slightly more than half a mile N. 50° E. northwest of Cornucopia stock may also con- from the mine is the Last Chance satellite; tain Lower Jurassic strata. A major thrust of and the satellite (Fig. 1) of cordierite trondh- Middle (?) Jurassic age, best exposed (location jemite 1 mile north of Crater Lake salient is 2) 2 miles northeast of Crater Lake, is inter- the Corral Creek satellite. preted as separating older rocks on the east from younger, near-vertical to overturned STRUCTURE OF COUNTRY ROCKS rocks on the west. Elsewhere, several possible Permian-Triassic country rocks in the south- thrusts and associated tight folds create unre-

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solved structural complications. Accordingly, location 4, elevation 8170 feet, a few pebbles the geologic maps exclude facies changes, have ratios of 10; at location 5, elevation 7400 stratigraphic units, and principal structural feet, maximum elongation is 16; and at location features of Paleozoic and Mesozoic country 6, elevation 6560 feet, maximum elongation is rocks. Some attitudes may ultimately require 23. Average elongation is about half of the overturning, but no overturned beds are shown, maximum values. Directions of elongation except where confirmed. parallel the walls of the stock and lie in the Prevailing northeast trends show major de- planes of schistosity. In addition to flattening, viations (Fig. 1) near the Cornucopia stock. pebbles near the north contact are stretched Approaching the pluton from the north, one parallel to the a direction. Near location 6, pebbles are triaxial ellipsoids with the a axis between two and three times as long as the b axis. Changes in pebble dimensions, best seen on weathered surfaces, are well-defined west of the stock for about 1 mile between Sullivan Creek (Fig. 2, location 7) and Twin Canyon (location 8). About 1400 feet from the contact, few pebbles have length to width ratios greater than 2. Pebbles become more elongated nearer the contact, and rounded ends are converted to pointed terminations. Within 300 feet of the contact, many pebbles have elongation ratios between 6 and 9 on horizontal or vertical surfaces. The attitude of these flattened and elongated pebbles is reflected everywhere in the schistosity of the matrix between pebbles. Schistosity swings from N. 10° W. near Sullivan Creek to N. 5° E. at Twin Canyon, and dips are 75°-80° E., in accordance with the planar Figure 4. Map showing pattern of cross structure in adjacent tonalite. Pebbles can folds in limestone east of Little Eagle rarely be extracted in their entirety, but most Creek are disk-shaped where conglomerates are broken along planes of schistosity. However, evidence for some vertical lineation does occur, because finds that trends swing conspicuously around in 20 pebbles from an outcrop at location 9, the stock. South of the stock, deflected trends elevation 5050 feet, the vertical distance paral- have nearly reverted to their original northeast lel to a averages 1.4 times the horizontal dis- direction before they disappear under Tertiary tance. volcanic rocks. A prominent unit of limestone is absent on In contrast to the regional terrain, most the west and southwest sides of the stock in country rocks near the stock are foliated. Aside the same area of country rocks that is charac- from Crater Lake salient, country rocks gen- terized by flattened pebbles. At the northwest erally show incipient schistosity between 1200 corner of the stock near Big Kettle Creek and 2000 feet from the stock. Within 1000 feet (Fig. 2, location 10), the limestone is at least of the contact, schistosity is commonly distinct. 1700 feet thick. Limestone thins rapidly south- Pebbles in conglomerates become progres- ward and within 1 mile, pinches out at an sively flatter near the pluton, and intense elevation of 4600 feet near the bottom of flattening characterizes deformed country rocks Twin Canyon (location 8). Where the limestone along the north contact. In this area (Fig. 2), reappears near Little Eagle Creek (location 11) incipient schistosity first appears in phyllitic on the south-central side of the stock, outcrops rocks near location 3, about 2000 feet from the extending south define a series of S-shaped stock. Nearer the stock, pebble dimensions at cross folds (Fig. 4). The pattern of outcrops locations 3, 4, 5, and 6 indicate increasing de- is not controlled by topography and although formation. At location 3, elevation 8100 feet, the unit of limestone is partly concealed by some pebbles have elongation ratios of 4; at Columbia River Basalt, the explanation of the

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configuration of the unit requires a series of much of the Red Jacket satellite. In the Coulter cross folds. satellite, planar structure is evident in some Near the north and northeast margins of the talus blocks but is rarely detected in outcrops. stock, folds are pinched into a tight isoclinal East strikes and vertical to steep north dips sequence as they are traced southeast toward characterize three exposures with planar struc- the contact. The folds are in a thick clastic tures. Planar structure in the Last Chance formation (part of the "Lower Sedimentary satellite strikes east and dips 80° S.; the struc- Series" of Smith and Allen, 1941) that is ture is almost at right angles to the bedding in separated on the northeast by a probable thrust sharply transected country rocks. Almost all from an unnamed volcanic formation of older planar structure in the Red Jacket satellite age. The volcanic formation is massive green- strikes within 10° of N. 20° W. and dips 65°- stone composed mostly of submarine flows with 85° NE. In the vicinity of location 17, eleva- interbedded clastic rocks containing much tion 6800 feet, the tonalite is strongly gneissoid. volcanic detritus. Near the northeast corner of Faint to strong (vicinity of location 18, the stock, rocks of the "Lower Sedimentary elevation 6500 feet, to location 19, elevation Series" almost pinch out (location 12) against 7050 feet) planar structure defines a 135° arc hornfelsed greenstone. In this vicinity the throughout the central and north-central parts "Lower Sedimentary Series" is isoclinally of Tramway trondhjemite. Near the north con- folded and dips consistently 50°-70° NE. tact, planar structure is locally prominent. Remarkably preserved graded beds (best ex- Faint planar structure exists in many exposed near location 13, elevations 6100-6200 feet) posures in the east and north-central portions verify one zone of overturning. About 1 mile of Pine Lakes cordierite trondhjemite. Most northwest of location 13, open folds include two strikes are within 20° of north but northwest anticlines and an intervening syncline. The trends dominate. Dips are consistently 70°-85° synclinal axis is a few hundred feet southwest of E. location 3, and although some beds dip very All trondhjemites, except the Big Kettle steeply, none are overturned. Traced southeast, mass, contain prominent planar structure in the three folds are pinched into a tight isoclinal zones within 1-100 feet of most sequences or series dipping 50°-70° NE. Major shear zones disrupted sequences of Willow Lake-type best displayed between locations 14 and 15, layered rocks (Taubeneck and Poldervaart, and the fact that they are commonly conforma- 1960). In Tramway trondhjemite, for example, ble or nearly conformable with bedding planes a 1-10-foot zone is characterized by planar suggests that intense compression squeezed out structure accompanied by remnants of Willow some units during isoclinal folding. Lake-type layered rocks and persists almost continuously along the irregular contact between STRUCTURE OF GRANITIC ROCKS location 20, elevation 8000 feet, and location 21, elevation 6300 feet. In Pine Lakes and Crater Planar Structure Lake cordierite trondhjemites, planar structure Except in Union Companion salient where also exists as several zones generally less than planar structure is virtually absent, Cornucopia 40 feet wide, without Willow Lake-type tonalite in the stock exhibits strong planar layered rocks. Layered rocks similar to those structure (Fig. 2) in almost all rocks near con- described by Harry and Emeleus (1960) are tacts. Most marginal rocks are gneissoid, es- locally conspicuous in eastern (e.g., location 22, pecially in the western half of the stock. Planar elevation 8325 feet, and location 23, elevation structure disappears toward the east-center of 8600 feet) and central parts of Crater Lake the stock where tonalites possess a directionless cordierite trondhjemite. Figure 2 excludes fabric. attitudes of rocks mentioned in this paragraph. Some tonalite apophyses near the stock have In summary, planar structure is best de- planar structure at a high angle to bedding or veloped near contacts and closely approximates schistosity in schistose hornfels. An example on in orientation the gross trend of contacts re- the southwest occurs within 100 feet of the gardless of the attitude of bedding, schistosity, stock in a 20-inch-wide dike at location 16, or planar structure in adjacent wall rocks. elevation 5550 feet. Planar structure is most widespread in Cornu- In the 3 satellites of Cornucopia tonalite, copia tonalite and Tramway trondhjemite planar structure is poor in the Coulter body, where broad sweeping patterns are charac- good in the Last Chance mass, and excellent in teristic (Fig. 2).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/11/1093/3432058/i0016-7606-75-11-1093.pdf by guest on 27 September 2021 Figure 1. Northeast portion of stock in foreground and central portion in extreme right background. Contact between Kp and Kt is at location A. Contact between Kp and Kc is concealed behind small ridge on either side of location 47.

Figure 2. Looking southeast across Crater Lake. Numerous apophyses occur in vicinity of location B. An apophysis is also visible to left of white dot denoting location 41. TOPOGRAPHY AND ROCK RELATIONSHIPS, CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON See Figures 2 and 3 for symbols and position of numbered points; see text for description of points.

~~TAUBENECK, PLATE 1 Geological Society of America Bulletin, volume 75~~

~~Figure 2. Apophysis of Tramway trondh- Figure 4. Contact of Cornucopia tonalite jemite, location 27 and Pine Lakes cordierite trondhjemite~~

~~APOPHYSES AND CONTACT RELATIONSHIPS, CORNUCOPIA STOCK, VVALLOWA MOUNTAINS, OREGON~~

~~TAUBENECK, PLATE 2 Geological Society of America Bulletin, volume 75~~

~~Figure 2. Contact of Crater Lake cordierite trondhjemite and country rocks, location 38~~

~~CONTACTS OF CRATER LAKE CORDIERITE TRONDHJEMITE, CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON~~

~~TAUBENECK, PLATE 3 Geological Society of America Bulletin, volume 75~~

~~Figure 2. Diversely oriented xenoliths in dike of Crater Lake cordierite trondhjemite, location 40. Drawn from a photograph SILL AND DIKE RELATIONSHIPS, CORNUCOPIA STOCK WALLOWA MOUNTAINS, OREGON~~

~~TAUBENECK, PLATE 4 Geological Society of America Bulletin, volume 75~~

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difficult for the trondhjemite is slightly lighter, Linear Structure coarser in grain, and contains fewer inclusions Hornblende lineation characterizes two of country rocks. Furthermore, the trondh- widely separated areas of Cornucopia tonahte. jemite is characterized by a zone from 1 to 10 Along much of the western contact between feet wide of layered rocks, either directly Sullivan Creek (Fig. 2, location 7) and Big against the tonalite or within 40 feet of the Kettle Creek (location 10), prominent horn- tonalite. The layered rocks consist of alternating blende prisms lie in the planes of almost concentrations of biotite and felsic minerals; vertical planar structure and consistently larger biotite flakes are aligned in the plane of plunge steeply down-dip. Elsewhere, poor to layering. good lineation occurs near the east edge of the Shattering of the older rocks is best displayed stock at elevations from 6300 to 6800 feet on at elevations between 7500 and 8050 feet where steep cliffs near location 24. Most of these the prong (location 25) of tonalite projecting hornblende prisms plunge 45°-60° SE., virtu- into trondhjemite is interlaced with apophyses ally at right angles to the trend of planar struc- of trondhjemite. In the vicinity of location 26, ture. elevation 6550 feet, many tonalite blocks occur In some thin sections, many oriented horn- in trondhjemite. Near location 26 are numerous blende needles are broken so that an angle small blocks, mostly 2 feet across, of country of 10°-20° is common between cleavage traces rocks in the trondhjemite. and twin compositional planes of adjacent In the northeast corner of the stock near the fragments. The broken crystals indicate that end of the road along Pine Creek, several deformation, interpreted as protoclastic, oc- isolated exposures exhibit excellent contact re- curred after lineation developed. Primary lationships. From the end of the road, the origin of the lineation is also confirmed by most accessible exposure (location 27, elevation common resorption of hornblende. Many 5470 feet) is the first outcrop involving oriented crystals have scalloped and corroded granitic rocks along the foot trail to Pine Lakes. margins, whereas strongly resorbed crystals The trail crosses a 25-foot-wide basalt dike may occur as several detached pieces. These about 165 feet east of location 27. Much of this features warrant the conclusion that the horn- exposure, totaling about 950 square feet on the blende lineation represents flow lines and is not north side of West Fork Pine Creek is annually a secondary structure imposed on the rock after under water until mid-July. At the outcrop consolidation. Tramway trondhjemite cuts Cornucopia tona- Biotite lineation occurs locally in the Red lite containing numerous inclusions of country Jacket satellite where streaky biotite plunges rocks. Fifteen to twenty-two feet south of the steeply down-dip in gneissoid rocks near loca- trail, an inclusion of tightly folded country tion 17. This lineation is apparently secondary. rocks about 6 feet wide by 9 feet long is cut by In summary, tonalite in two areas of the a trondhjemite apophysis about 8 feet long. stock contains flow lines of hornblende that lie Much of this apophysis is shown in Figure 1 in the plane of the planar fabric and plunge of Plate 2. The apophysis crosscuts strata in steeply down-dip. lower left of the inclusion but is essentially parallel to bedding planes near the comb. Left Contacts between Granitic Roc/^s of the knife, a resistant sedimentary bed is CORNUCOPIA TONALITE AND TRAMWAY offset 1 inch by dilation. Figure 1 of Plate 2 TRONDHJEMITE: Contacts are distinct, except also shows a contact between tonalite and along the southwest margin of the trondhjem- lighter-colored trondhjemite about 1 foot ite, where location of the contact is extremely below the whisk broom. Texture of the tonalite difficult because tonalite in this vicinity carries is obscured by different polish on various water- no visible hornblende and approximates the worn surfaces and by a dark stain on one sur- trondhjemite in mineralogy, chemical com- face. Sloping tonalite surfaces above and below position, and texture. the broom are not stained as is the flat surface The best continuous contacts are along the in the vicinity of the broom. Between the southeast margin of the trondhjemite at eleva- broom and pocket comb, assimilation occurs tions between 6100 feet (near location 21) along the concordant contact of the tonalite and 8250 feet (near location 20). Most of this and inclusion. In contrast, concordant and dis- sharp and irregular contact is shown in Figure 1 cordant contacts of trondhjemite and inclusion of Plate 1. Recognition of the contact is not are sharp.

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Other pertinent contact relationships occur some trondhjemite apophyses extend more than at location 27. About 5 feet northeast of the 600 feet. knife (PL 2, fig. 1), an 8-inch trondhjemite dike Excellent brecciated contacts shown in cuts a 6-foot inclusion in tonalite, and irreg- Figure 1 of Plate 3 occur about half a mile ularities along opposite walls of the inclusion north of Pine Lakes near location 30, elevation can be fit into corresponding salients and in- 8060 feet. In this figure, the long direction of dentations. Twenty-three feet east of the peeled limbs of whitebark pine is parallel to knife (PI. 2, fig. 1), angular tonalite inclusions planar structure in the tonalite fragments. occur in another trondhjemite dike (PL 2, Four slivers of gneissoid tonalite near the fig. 2). Below the knife (PI. 2, fig. 2), a narrow center and left-center are not designated by tonalite inclusion is offset to the right. About peeled limbs. The upper tonalite inclusion is 5 feet to the east, the same dike cuts country cut by a leucocratic dike of cordierite trondh- rocks; inclusions (PL 2, fig. 3) can be fit into jemite rich in muscovite. Near the base of the the walls. In Figure 3 of Plate 2, lichens give a upper inclusion, a small triangular piece of blotchy appearance to the rounded surface of tonalite is offset 3/8 of an inch to the right by the outcrop. the leucocratic dike. The offset is 5 inches from As will be evident further on, contact rela- the lower end of the upper peeled limb and in tionships at location 27 are especially crucial in the direction that the limb points. The dark petrogenetic interpretations of Cornucopia blotches in the upper left are lichens. rocks. TRAMWAY TRONDHJEMITE AND PINE LAKES CORNUCOPIA TONALITE AND PINE LAKES CORDIERITE TRONDHJEMITE: Contacts between CORDIERITE TRONDHJEMITE: Tonalite in the these rocks, commonly difficult to locate, are interior of the stock contains no visible horn- best observed along the northeast margin of blende, and Pine Lakes cordierite trondhjemite Pine Lakes cordierite trondhjemite at eleva- contains little cordierite; hence the rocks are so tions between 7500 feet (location 31) and 6800 similar that contacts are not readily apparent. feet (location 32). This contact is characterized Along the southern margin of the trondhjemite, by brecciated Tramway trondhjemite cut by tonalite inclusions facilitate recognition of the numerous apophyses of Pine Lakes cordierite contact. Good planar structure, the presence of trondhjemite. Some apophyses are emphasized hornblende, and the higher color index of by dark selvages of biotite, iron ore, or cor- tonalite along the northwest boundary of the dierite. To a lesser extent, pods and irregular trondhjemite create perspicuous contacts (PL masses of pegmatite also characterize this con- 2, fig. 4). One can see in this figure that the tact. Location 33, elevation 7320 feet, is in- knife parallels the planar structure in the structive for Pine Lakes cordierite trondhjem- tonalite whereas the pencil parallels planar ite here contains inclusions of country rocks, structure (use magnifying glass) in the small Tramway trondhjemite, and gneissoid Cornu- tonalite inclusion. copia tonalite. CORNUCOPIA TONALITE AND CRATER LAKE PINE LAKES CORDIERITE TRONDHJEMITE AND CORDIERITE TRONDHJEMITE: Contacts between CRATER LAKE CORDIERITE TRONDHJEMITE: Con- these two rocks are sharp and readily discerni- tacts between these related units are located ble, especially where tonalite carries hornblende with difficulty. Crater Lake facies near the and has good to strong planar structure. Al- contact is slightly coarser, contains less biotite, though exposures are discontinuous, brecciated and carries at least a few cordierite crystals in tonalite along the contact about 1 mile west virtually every exposure, whereas scattered of Pine Lakes is particularly conspicuous in the cordierite is much less abundant in exposures vicinity of location 28, elevations 7300-7650 of the Pine Lakes facies. At location 34, eleva- feet. Relationships are better observed for tion 7660 feet, apophyses of Crater Lake facies half a mile southeast from the crest (location with considerable cordierite cut finer-grained 29, elevation 8415 feet) of a ridge shown in Pine Lakes facies in which cordierite is less Figure 1 of Plate 1. This contact is so irregular common. in detail that maps on the scale of Figure 2 BIG KETTLE CORDIERITE TRONDHJEMITE AND provide no concept of actual relationships. CRATER LAKE CORDIERITE TRONDHJEMITE: Con- Angular tonalite blocks in trondhjemite and tacts between these rocks are generally sharp. trondhjemite apophyses in tonalite create an The best and most accessible contact is along irregular contact zone as much as 300 feet wide; the western margin of the Big Kettle mass near

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location 35, elevation 7050 feet. As most narrow stringers of granitic material with small biotite of Big Kettle facies is fine-grained and porphyroblasts. the rock is darker than other trondhjemites, In the Coulter satellite, most contacts are one can identify this facies easily. An inclusion obscured by talus, but the north contact is of Big Kettle facies in Pine Lakes facies occurs well-exposed between elevations of 5500 and at location 36, elevation 7900 feet. 6000 feet. This blocky and irregular contact is sharp, without feldspathization of adjacent Contacts with Country Roc\s country rocks. Several blocky inclusions up to CORNUCOPIA TONALITE: Some contacts be- 20 feet across are at elevations between 5450 tween granitic rocks and country rocks are and 5600 feet. sharp, whereas others are gradational for as Precise contacts of the Red Jacket satellite much as 18 inches. Contacts, mostly concordant are exposed discontinuously on the southwest on a crude scale, dip within 20° of vertical, for about 40 feet at an elevation of 6650 feet except on the north where outward dips of 50° and locally on the west at an elevation of occur. 6950 feet. Concordant and discordant portions The most complex contact of the entire stock of the contacts are sharp and without porphy- and one of the most intricate granitic contacts roblasts in adjacent country rocks. in northeastern Oregon is on the north along Knife-edge contacts are exposed around most a remnant of tonalite (Fig. 2) that extends of the Last Chance satellite which is much for 0.6 mile between Tramway trondhjemite finer-grained than is tonalite anywhere in the on the east and Crater Lake cordierite trondh- stock and also has markedly higher 1C values jemite on the west. Sheets of tonalite several (Chayes, 1956, p. 72-73) than rocks of other feet wide alternate with country rocks in a satellites. On the west at an elevation of 5600 crude approximation of large-scale lit-par-lit feet, the tonalite tapers to a termination about involving a zone up to 500 feet wide. The sheets 2 inches wide, yet the granitic rock retains its are roughly parallel to bedding, but interlacing character even in this narrow extremity of the sheets enclose slices of country rocks. Features intrusion. Near the west-center of the satellite, of magmatic intrusion, intense deformation, the northward prong of tonalite contains a and granitization characterize this contact block of country rocks about 25 feet square. zone. Locally, excellent examples of small-scale Elsewhere, inclusions are uncommon. There is granitization occur. Many sheets contain no feldspathization near the tonalite, nor do slivers and digested streaks of country rocks the hornfelses noticeably increase in grain size in which feldspars (1-2 mm greatest dimension) near contacts. are probably porphyroblasts. Narrow stringers TRAMWAY TRONDHJEMITE: Contacts with of rocks influenced by feldspathization extend country rocks are sharp, and average grain size along some bedding planes. Borders of some of adjacent hornfelses and schists is less than sheets are gradational for 1-12 inches. Most 0.1 mm. There is little evidence of chemical country rocks within this zone, however, are reaction along the contacts. Diversely oriented not feldspathized and are no coarser in grain inclusions of country rocks are common near (less than 0.1 mm) than contact rocks elsewhere the north contact, where blocks up to 30 feet in the aureole. long are as much as 400 feet from the edge of In contrast, other contacts between tonalite the stock. At greater distances from the con- and country rocks generally are almost verti- tact, inclusions are not common. cal, and sheeting is minor or absent; thus rela- CRATER LAKE CORDIERITE TROXDHJEMITE: tionships are simplified. Sheeting is absent along Contacts with country rocks are generally discordant contacts such as east of Last Chance razor sharp, but some are gradational through mine (location 37, elevation 6880 feet) where as much as 2 inches. Almost all contacts dip the contact is well-exposed eastward to an ele- within 35° of vertical. Within 1-24 inches of vation of 5600 feet. Paucity of tonalite contacts, 27 specimens of country rocks from apophyses is noteworthy; only two extend widely separated areas have an average grain more than 100 feet from the contact. Most size of 0.07 mm and are not feldspathized. In- hornfelses and schists along this contact are less clusions of country rocks, rare more than 300 than 0.05 mm in grain size and show no feld- feet from contacts, almost invariably are spathization. Rare patches of feldspathized diversely oriented. Most contacts are dis- rocks occur, and a few bedding planes have cordant! About 0.7 mile N. 10° W. from Pine

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Lakes, the contact is more nearly concordant proximity to some pods (Fig. 5). Features ex- for 1500 feet. Even in this area, discordant hibited by the trondhjemite sills, including contacts alternate for short distances with pinching and swelling, are probably more wide- concordant contacts, as is apparent (Pi. 3, spread than the literature suggests. Tweto fig. 2) along a contact exposed continuously for (1951) described similar features in Tertiary 313 feet at location 38, elevation 8450 feet. porphyry sills in Colorado as did Hurlbut (1939, In this figure the contact is concordant for p. 1102) for some peripheral sills of the Shonkin 43 feet between A and B whereas concordancy prevails for 74 feet between C and D. Between B and C, 62.5 feet of strata are intersected along the alternately discordant and concordant contact. One thousand feet to the west along the upper portion of the contact of Figure 2 of Plate 1, 34 feet of strata are crossed in a vertical distance of 150 feet. Apophyses in Country Roc\s CORNUCOPIA TONALITE: Except for sheeting along part of the north contact, apophyses of tonalite are not as abundant in the country rocks as are sills and dikes of Tramway trondhjemite and Crater Lake cordierite trondhjemite. Dikes offset marker beds, whereas terminations of sills deflect bedding. Beyond the termination of some sills, pods of tonalite (Fig. 5) occur for many feet along a bedding plane. The isolated pods are mostly extensions of sills less than 3 inches wide or of thicker sills that taper to widths of a few inches before terminat- ing. Pods also occur in groups with no sill exposed laterally. Some larger pods show planar structure as concentric layers which parallel deflected bedding that swings around the pods. Figure 5. Features of sills. A, Cornucopia TRAMWAY TRONDHJEMITE: Apophyses of tonalite; B-G, Tramway trondhjemite; Tramway trondhjemite are numerous in the H, Crater Lake cordierite trondhjemite. country rocks and provide data concerning D and E are local irregularities in sills; extremities and terminations of sills. Figure 1 of other illustrations are terminations of sills. Plate 4 shows the edge of a 3.5-inch sill at loca- In B, regular continuity of narrow sill 2 tion 39, elevation 6600 feet, about 0.9 mile N. feet above pods indicates that pods are 61° W. from the end of the road along Pine not boudins. Creek. Figure 5 includes three field sketches from exposures near location 39. In all illustra- Sag laccolith in Montana. Pinch-and-swell tions, bedding planes are deflected around features generally are interpreted as products extremities of sills and around trondhjemite of deformation (Ramberg, 1955) or metasoma- pods. Pinching and swelling is typical near tism (Goodspeed, 1940), but examples in extremities of sills and is accompanied by Oregon, Colorado, and Montana suggest that equivalent adjustments in adjacent bedding at least some of the irregularities originate planes. Extending laterally from terminations, during intrusion of magma. isolated trondhjemite pods are common along Figure 1 of Plate 2 shows that the apophysis the bedding plane. In some bedding planes, of Tramway trondhjemite pinches and swells Tramway trondhjemite is restricted to one or near the interior of the contorted inclusion of more pods. Pronounced pinching and swelling country rocks. This apophysis is a dike where is generally confined to sills less than 6 inches it offsets with dilation the strata near the knife, wide, whereas no pods were found for sills more but strata are essentially parallel to the apo- than 4 inches wide. The pods are not boudins, as physis where pinching and swelling occurs. The shown by regular continuity of sills in close pinching and swelling of trondhjemite (PI.

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2, fig. 1) along a bedding plane is better ex- of apophyses or in the space between isolated hibited elsewhere. boudins. In addition, parts of boudinaged dikes CRATER LAKE CORDIERITE TRONDHJEMITE: are fringed by narrow zones of secondary Apophyses of Crater Lake cordierite trondh- schistosity at angles to schistosity of intersected jemite are abundant and provide many signifi- contact schists. cant relationships for the interpretation of Secondary schistosity and fillings of quartz in mechanisms of emplacement. At location 40, regions of low pressure occur about 9 feet from elevation 7750 feet, one example of diversely the stock along a 50-foot dike that shows oriented xenoliths, common in apophyses, is boudinage for 16 feet near E (PL 3, fig. 2). shown (see PI. 4, fig. 2). Movements of a few Boudinage of this dike is correlated with em- inches restore three slightly dispersed frag- placement of Crater Lake cordierite trondh- ments to their former positions as parts of one jemite in pulses as inferred by distribution of inclusion. Willow Lake-type layered rocks. Dikes commonly change to sills whereas off- shoots from some dikes extend laterally as sills. Aplite Dikes One instructive offshoot (location 41, eleva- Aplite dikes occur in Crater Lake cordierite tion 8400 feet) from a dike is near the distant trondhjemite, Pine Lakes cordierite trondh- contact in Figure 2 of Plate 1. Ten feet from jemite, Tramway trondhjemite, and Cornu- the stock, a sill extends upward from the dike. copia tonalite but are absent in satellites (Fig. Plate 5 shows features along the sill about 12 3) of tonalite. Most dikes are less than 5 inches feet above the dike. As details on the precipi- wide, but several up to 40 feet wide occur near tous exposure (PL 1, fig. 2) are photographed the east and southeast margin of the stock. at close distances, Plate 5 is drawn from several No dikes were seen in country rocks, except photographs. The thin marker horizon is a within a few hundred feet of Red Jacket mine lime-silicate bed with a center of flesh-colored (location 1, elevation 6120 feet). For evidence garnet fringed by green epidote. One can ob- of magmatic or metasomatic origin, the writer serve the offset marker bed, the matching walls gives special consideration to intersections of of the sill, and two fragments that fit back into dikes. walls. CORNUCOPIA TONALITE: Although not com- One thousand feet east of the skyline contact mon in most tonalite, aplite dikes are suf- of Figure 2 of Plate 1 some dikes and many sills ficiently numerous in the east quarter of the (PL 3, fig. 2) are within 200 feet of the contact. stock to provide many intersections. The The dikes and sills contain six inclusions that dilation offset of Figure 1 of Plate 6 is at loca- can be fit into the walls and nine examples of tion 42, elevation 6410 feet. An accessible area country rocks partly wedged away from walls. for observing many intersections is near loca- In Figure 2 of Plate 3, arrows along the sills tion 42 in the vicinity of location 43 at eleva- denote the locations of some of the displaced tions between 6650 and 6950 feet. In this area. inclusions or wedged-apart wall rocks. The sills 14 intersections have the prescribed offset of taper near extremities, as is typical of Crater magmatic dilation, whereas 3 intersections are Lake cordierite trondhjemite, and terminate inconclusive and could involve replacement. as slender stringers (Fig. 5) a fraction of an inch Apparent lack of dilation (Goodspeed, 1940, wide. p. 178) at the intersection of a porphyry dike and an aplite dike occurs (location 44, elevation Boudinage of Apophyses 6350 feet) in a weathered cut of an abandoned Minor boudinage occurs in several sills and wagon road about 35 feet from a switchback. along a few dikes of Tramway trondhjemite As evidenced by exfoliation in the photograph and Crater Lake cordierite trondhjemite. Most (Goodspeed, 1940, p. 178), the tonalite disin- examples are near the contact east of the skyline tegrates readily, and the exposure changed even ridge of Figure 2 of Plate 1. Commonly the during the interval between the years 1958 apophyses are only slightly disrupted; necking and 1963. The porphyry dike is vertical whereas of apophyses is more typical than occurrence of the curving aplite dike is 13° from horizontal separated boudins. at the point of intersection. Even after digging Unlike pinch-and-swell features, boudinage in the disintegrated tonalite to expose the is not restricted to terminal portions of sills or actual intersection, the writer could reach no dikes. Moreover, boudinage generally is dis- decisive conclusion regarding dilation or lack tinguished by deposits of quartz in necked parts of dilation, because the two dikes of similar

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strike are nearly at right angles, the exposure is Throughout the southeastern Wallowa Moun- poor, and the 9-inch-wide aplite dike is too tains, relict augite and calcic plagioclase persist wide to establish slight dilation that may exist in many metabasalts and meta-andesites and in along irregular porphyry walls. numerous dikes and small gabbroic intrusions. TRAMWAY TRONDHJEMITE: Relatively uncom- Foliation is absent, except along shear zones mon aplite dikes in Tramway trondhjemite and near intrusions. Identifiable fossils are have nearly consistent attitudes; hence inter- surprisingly abundant. sections are rare. At location 45, elevation ROCKS OF THE THERMAL AUREOLE 6250 feet, a 2-inch dike cuts an almost parallel 3/4-inch dike with offset. Another intersection In northeastern Oregon the outer edge of is at location 46, elevation 6120 feet, where a thermal aureoles (Taubeneck, 1958) is best 4-inch dike offsets a 3-inch sequence of Willow defined by the transformation of green biotite Lake-type layered rocks. of the regional terrain to brown biotite or by PINE LAKES CORDIERITE TRONDHJEMITE: Ap- the appearance of brown biotite where green lite dikes are common in the west-center of the biotite is absent. Two to four miles southwest Pine Lakes mass. Clearly documented offsets of the Cornucopia stock, regional metamorphism occur in the vicinity of location 47, elevation is of a lower grade than it is elsewhere within a 7560 feet. As shown in Figure 2 of Plate 6, similar distance of the stock, and a more re- aplite dikes also offset (e.g., location 48, eleva- fined subdivision of the outer aureole is pos- tion 7750 feet) contacts between Cornucopia sible (Prostka, 1962). tonalite and Pine Lakes cordierite trondhjem- To determine aureole width and gross ite. mineralogic features, samples were collected as CRATER LAKE CORDIERITE TRONDHJEMITE: indicated in Figure 1. As Wallowa bathohth is Aplite dikes in Crater Lake cordierite trondh- 4 miles northwest of the stock, no samples were jemite are commonly larger than in other collected in this direction. Northeast, south, trondhjemites; some are up to 2 feet wide. and southwest, the aureole is 5000-7500 feet Although scarce north of Crater Lake, dikes wide. The aureole extends southeast for 12,000- are more numerous elsewhere, and a superb 15,000 feet, but areas covered by Columbia dilation offset involving two dikes is at location River Basalt may conceal a satellitic intrusion 49, elevation 8650 feet. that could account for this greater width. In summary, most aplite-dike intersections in For a cross section of the aureole, 69 samples the Cornucopia stock show the requisite offset were collected1 from a traverse extending for emplacement of magma. northeast along or near the skyline ridge of Figure 2 of Plate 1. Metamorphosed silt- ROCKS OF THE REGIONAL TERRAIN stones, graywackes, and conglomerates domi- Country rocks in the southeastern Wallowa nate but conglomerates were excluded from Mountains are a heterogeneous assortment of samples. Contact schists and hornfelses occur eugeosynchnal deposits. Extensive volcanic within 1000 feet of the stock whereas horn- flows and detritus are mostly of andesitic and felses prevail at greater distances. Average basaltic compositions; common pillow structure grain size in the inner aureole varies from 0.02 suggests submarine extrusion. Volcanic rocks, to 0.08 mm but is larger in some graywackes particularly abundant in the east-central and from the outer aureole where metamorphism northeastern parts of the area (Fig. 1), are was not sufficient to recrystallize large clastic generally subordinate elsewhere near Cornu- plagioclase to a fine equidimensional mosaic. copia stock, and prevailing rocks are conglom- Throughout the inner aureole, hornblende, erate, graywacke, tuff, siltstone, shale, lime- cummingtonite, or both are present in almost stone, and minor chert. every section. Typical assemblages generally Judged by 143 thin sections of country rocks containing some quartz are: plagioclase-horn- from within the area of Figure 1 and 236 blende, plagioclase-cummingtonite, plagioclase- additional sections from within 50 miles of cummingtonite - hornblende, plagioclase - cum- Cornucopia, regional metamorphism is of mingtonite - hornblende - biotite, plagioclase- greenschist facies. Country rocks generally con- cummingtonite-biotite, and plagioclase-horn- tain at least a trace of green biotite, but rocks blende-biotite. Less common assemblages also of some areas, such as the southeastern part of the Cornucopia quadrangle, are devoid of 1 Clyde F.. Wethcrcll assisted for 2 days in back- biotite and belong to the chlorite subfacies. packing many specimens to a base camp.

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with quartz arc plagioclase-biotite and plagio- examples of cordierite - biotite - plagioclase- clase-hornblende-diopside. Iron ore and apatite quartz, cordierite - hornblende - biotite - plagio- are common accessories. Outward from the clase-quartz, and almandine(?)-biotite-plagio- stock, cummingtonite disappears beyond 1100 clase-quartz. feet, whereas green hornblende changes to blue In summary, marked contrast in grain size green. Locally, blue green hornblende occurs exists between medium-grained granitic rocks as near as 500 feet from the contact. A maxi- of the stock and fine-grained contact rocks. Of mum of four assemblages occur in a thin sec- 63 samples within 100 feet of contacts, 21 are tion, including one example with average grain within 1 foot of the contact of inclusions in size of 0.03 mm in a rock 5 feet from the con- Crater Lake cordierite trondhjemite, and 9 are tact. Repetition in thin section of two or three within 1 foot of the contact of inclusions in assemblages and rarely of four assemblages Cornucopia tonalite. The largest average grain reflects original composition differences in the size is 0.3 mm, and most are less than 0.1 mm. sediments and suggests isochemical meta- These contact rocks are schists and hornfelses morphism. rather than gneisses or migmatites. Toward the stock along the skyline (PL 1, Greenstones in the aureole are near the south- fig. 2), changes in the largest (1.5-3.0-mm) west corner of the stock and are almost con- plagioclase clasts portray increasing intensities tinuous east of the stock. Best exposures, in- of thermal and dynamic metamorphism. In the cluding some excellent pillow lavas, are on steep outer aureole, clasts are generally angular, rec- southwest slopes of Simmons Mountain within tangular, or almost cubic. Although most are half a mile northwest and southeast of location turbid, complex twinning and oscillatory zon- 50. Although the greenstones are hornfelsed to ing are conspicuous in many fragments. hornblende-hornfels facies, some retain con- About 3000 feet from the stock, boundaries spicuous plagioclase phenocrysts that commonly of clasts commonly are diffuse from inward occur as glomeroporphyritic rosettes of two or growth of randomly oriented amphibole more crystals. Rosettes in the aureole are rarely needles. Some needles develop entirely inside larger than half an inch. plagioclase. About 2500 feet from the contact, Greenstones containing glomeroporphyritic complex twinning and oscillatory zoning begin rosettes of plagioclase are the most distinctive to fade and are rarely detected within 300 feet country rock in the Wallowa Mountains. As of the stock. Additional growth of amphibole this attractive greenstone crops out on the and more intense recrystallization further northern edge of the mountains near Wallowa obscure boundaries of clasts. Within 1000 feet Lake State Park, specimens are distributed of the contact, flakes of biotite and needles of among many ranches and small communities in amphibole wind around relicts of turbid plagio- eastern Oregon. The rock commonly is used for clase that are commonly rounded and lenticu- decorative purposes such as for borders around lar. The relicts are also smaller than plagioclase flower beds. in the outer aureole. Changes in size and shape Microscopic evidence verifies the igneous originate from dynamic metamorphism con- origin of the rosettes. Outside the aureole verting large clasts into smaller pieces divided where recrystallization has not obliterated vol- by zones of mosaic plagioclase. Recrystallized canic textures in the groundmass, flow lines mosaics are water-clear in contrast to turbid bend around rosettes. Even several thousand relict plagioclase. Within 200 feet of the con- feet inside the aureole, individual crystals of the tact, small rounded grains (0.005 mm, too small rosettes retain complex twinning, oscillatory for microscopic distinction between plagioclase zoning, and rings of inclusions that coincide and quartz) appear in some relict plagioclase. with inner shells of some oscillations. These Thus some rocks near the contact with an features and the composite crystals are charac- average grain size of 0.03-0.05 mm have turbid teristic of igneous plagioclase (Phemister, 1934, plagioclase relicts up to 0.6 mm that resemble p. 545-555; Hills, 1936; fohannsen, 1937, p. porphyroblasts and contain inclusions of 163, 254; Turner, 1951; Gorai, 1951; Ross, amphibole and minute quartz or plagioclase. 1957, p. 655; Vance, 1961, p. 1099-1100), in These plagioclase relicts are not prophyroblasts, marked contrast to metamorphic plagioclase. nor did the writer see any near the contact Field evidence also confirms the igneous shown in Figure 2 of Plate 1. character of the white radiating or forked Other metamorphic assemblages elsewhere rosettes. In conglomerates composed mostly of in the aureole, excluding limestones, are rare volcanic rocks, cobbles and pebbles many

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miles outside the aureole commonly contain the Cornucopia stock are glomeroporphyritic rosettes of the same size as rocks within the aggregates of igneous crystallization. The aureole. Even more pertinent, numerous rosettes occur in hornfelsed greenstone, not in pebbles and massive greenstones of the region hornblende granulite or migmatite. exhibit larger rosettes (up to 1 inch across) than any found in the aureole. These relation- MODAL DATA FOR GRANITIC ROCKS ships provide insuperable difficulties for a Petrographic data concerning the granitic metasomatic interpretation. Moreover, raylike rocks are restricted here to summations of rosettes near the periphery of cobbles and modal analyses. pebbles are commonly truncated by the clast An attempt was made to collect adequate boundary which would not be true if the specimens for determination of systematic rosettes were glomeroblastic. These critical mineralogical variation that was suspected in features occur in many excellent exposures in Cornucopia tonalite after several traverses in

~~TAKI.K 1. Mom:s OF CORNUCOPIA TONAT.ITF. oi; Tun. CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON (In volume per cent)~~

Intermediate Border tonahtc tonalite Interior tonalite (38 specimens) (16 specimens) (22 specimens) Mean S.D. Mean S.D. Mean S.D. Potassium feldspar 0.20 0.31 0.26 0.49 0.69 0.59 Quart/. 21.07 1.77 24.71 1.7? 27.98 1.52 Plagioclase 66 . (, I 1 . 67 64.90 1.65 63.65 1.51 I lornblcndc 3.64 1.28 0 . S9 0 . 59 Hiotitc 6.7? 1.01 7.78 0.78 6.83 1.00 Opaque accessories 1.09 0.26 0.89 0.17 0.55 0.17 Nonopaque accessories 0.64 0.31 0.57 0.22 0.30 0.14

sections 5, 6, 8, and 9, T. 6 S., R. 46 E., an area 1957. Unfortunately, desired sampling density a few miles east of the geologic map (Fig. 1). rarely is apparent merely from field examina- Within the area of Figure 1, many exposures tion. Initial sampling of 1958 and 1959 was are about 4 miles N. 25° E. from Cornucopia, augmented after preliminary modal data within 700 feet of location 51. The most ac- permitted construction of contoured maps cessible pebbles outside the aureole, with (mineralogical isopleth maps) that revealed rosettes ol the same size as those in hornfelsed localities where additional samples were needed. greenstone of the inner aureole, are 2 miles Modal analyses were made of 152 thin sections northeast of Cornucopia at location 52, ele- from 76 rocks. The analyses warrant subdivid- vation 5950 feet, on the east side of Trail Creek ing Cornucopia tonalite into border, inter- within a few hundred feet of the stream. mediate, and interior rocks. Although feasible Mafic volcanic rocks in thermal aureoles subdivisions are possible using systematic commonly contain relict plagioclase pheno- variation of most minerals including many crysts in a reconstituted groundmass (Service, accessories (Taubeneck, 1963b) or on various 1937, p. 201-202). In the aureole of the Cor- mineralogical ratios, subdivisions in Table 1 nucopia stock, recrystallization of greenstone are defined by differences in hornblende per produced a hornblende-plagioclase mosaic in cent. Border rocks contain 6.1-1.6 per cent which original rosettes persist. As some rosettes hornblende, intermediate rocks 1.6-0.1 per enclose or partly enclose material of the ground- cent, and interior rocks have less than 0.1 per mass, recrystallization of fine-grained enclosures cent. Average modes and standard deviations produced inclusions that duplicate the features for 38 border tonalites, 16 intermediate tona- of the reconstituted groundmass. lites, and 22 interior tonalites are given in In conclusion, radiating or forked rosettes of Table 1. Accessory minerals are grouped in two plagioclase (Goodspeed, 1959, p. 239, Fig. 9) categories but are listed individually elsewhere in thermally metamorphosed mafic rocks near (Taubeneck, in prep.). Average modes and

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~~TAUBENECK, PLATE 5 Geological Society of America Bulletin, volume 75~~

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/11/1093/3432058/i0016-7606-75-11-1093.pdf by guest on 27 September 2021 Figure 1. Dilation offset of % inch at intersection of aplites, location 42. As surface at intersection is flat and neither dike curves, the dilation is real.

Figure 2. Dilation offset by aplite of contact between Cornucopia tonalite (rock No. 1) and Pine Lakes cordierite trondhjemite (rock No. 2), location 48. Planar structure in tonalite is at right angles to contact with trondhjemite. APLITE RELATIONSHIPS, CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON

~~TAUBENECK, PLATE 6 Geological Society of America Bulletin, volume 75~~

~~Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/11/1093/3432058/i0016-7606-75-11-1093.pdf by guest on 27 September 2021 MODAL DATA FOR GRANITIC ROCKS 1109~~

~~TABLE 2. MODES OF TONALITE FROM SATELLITES OF THE CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON (In volume per cent)~~

Coulter Red Jacket Last Chance (4 specimens) (3 specimens) (5 specimens) Mean S.D. Mean S.D. Mean S.D. Potassium feldspar 0.35 0.26 3.27 0.59 0.40 0.22 Quartz 26.92 1.49 33.20 0.10 26.44 1.51 Plagioclase 65.85 2.05 57.53 0.32 63.78 0.93 Biotite 5.95 0.82 5.47 0.66 8.74 1.30 Opaque accessories 0.45 0.21 0.33 0.15 0.34 0.09 Nonopaque accessories 0.48 0.33 0.20 0.10 0.30 0.12

standard deviations for four samples from the mineral, but it occurs in some volcanic rocks Coulter satellite, three samples from the Red and in various granitic plutons of which the Jacket satellite, and five samples from the Last Cape Town granite is perhaps most celebrated. Chance satellite are given in Table 2. Each No reason exists to exclude cordierite from the modal analysis of every tonalite is the average possible crystallization products of magmas of of two thin sections. proper bulk composition. Average modes and standard deviations for Cordierite is a characteristic and conspicuous 2 specimens of Big Kettle cordierite trondhje- component of a suite of plutonic and hypabyssal mite, 17 specimens of Tramway Trondhjemite, rocks in the Wallowa Mountains. Ring struc- 8 specimens of Pine Lakes cordierite trondhjem- tures involving porphyry dikes, explosion and ite, and 14 specimens of Crater Lake cordierite intrusive breccias, and a massive quartz dike trondhjemite are given in Table 3. Values re- are associated in the Wallowa batholith with corded in Table 3 represent modal analyses of intrusions of cordierite trondhjemite and at least three thin sections from every rock and cordierite trondhjemite-porphyry. Through- four thin sections from each specimen of Pine out Wallowa Mountains, explosion breccias and Lakes cordierite trondhjemite. intrusive breccias are related to cordierite- bearing granitic rocks. CORDIERITE-BEARING Close genetic relationship of plutonic and GRANITIC ROCKS hypabyssal rocks containing cordierite is One object of this paper is to focus attention especially apparent north of Crater Lake in on unique cordierite trondhjemites. Discussion vicinity of Corral Creek satellite (Fig. 1). is restricted to geological occurrence, some Cordierite trondhjemite in this satellite is salient features of the cordierite, and evidence virtually identical in major and minor elements for early magmatic crystallization of cordierite. to associated cordierite-bearing dike rocks in Cordierite is generally a metamorphic which the groundmass is too fine-grained for

~~TABLE 3. MODES OF TRONDHJEMITES OF THE CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON (In volume per cent)~~

Bis; Kettle Tramway Pine Lakes Crater Lake (2 specimens) (17 specimens) (8 specimens) (14 specimens) Mean S.D. Mean S.D. Mean S.D. Mean S.D. Potassium feldspar 0.20 0.20 2.69 1.17 1.32 0.87 2.26 1.50 Quartz 25.95 2.19 30.06 1.67 30.40 1.47 31.45 1.76 Plagioclase 66.80 1.84 60.63 1.77 62.10 1.72 59.85 2.08 Biotite 5.20 0.99 5.43 0.89 4.48 0.55 2.78 0.71 Muscovite 0.75 0.78 0.39 0.33 0.81 0.56 2.43 1.43 Opaque accessories 0.45 0.07 0.46 0.15 0 . 39 0.11 0.41 0.23 Nonopaque accessories 0.65 0.35 0.34 0.18 0.50 0.12 0.82 0.36

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modal analysis. Judged by statistical studies, reconstructing crystallization history and can distinctive zircons from the hypabyssal dikes provide the only clue to an otherwise obliterat- are identical with zircons from granitoid rocks ed stage of crystallization. of Corral Creek satellite. In cordierite trondhjemites, plagioclase con- Although reputedly difficult to recognize, tains no inclusions of augite or hornblende. In- cordierite in plutonic and hypabyssal rocks of stead, inclusions of cordierite up to 0.5 mm in Wallowa Mountains is the most conspicuous diamerter occur in oscillatory-zoned plagio- rock-forming mineral. Dark color, enhanced by clase. In these rocks cordierite was the first biotite rims that encase almost all crystals, mafic phase, in contrast to pyroxene and horn- facilitates identification. Crystals are euhedral, blende in most other granitic bodies in north- pseudohexagnoal prisms, commonly half an eastern Oregon. Further evidence supporting inch long in the Cornucopia stock and twice as early crystallization is partial replacement of long in the major trondhjemite body of the cordierite by biotite and the development of batholith. Excluding pegmatites, few crystals biotite rims. in the Cornucopia stock exceed 1 inch, but in Zircon studies also suggest early crystalliza- the batholith one crystal is 5 inches long. tion of cordierite. Vital to this reasoning is the Large size and scattered distribution create conclusion that zircons in granitic rocks of difficulties in determining percentage of cor- northeastern Oregon are of early formation dierite. If pinitization products are tabulated as (Taubeneck, 1957, p. 221). Zircons separated ;ordierite, 32 thin sections of Pine Lakes cor- from several pounds of cordierite are euhedral iierite trondhjemite contain 0.02 per cent with sharp terminations and duplicate the dis- cordierite, 42 sections of Crater Lake cordierite tinctive morphology of zircons of the bulk rock. trondhjemite have 0.39 per cent cordierite, 36 However, some zircons extracted from cor- sections of Corral Creek cordierite trondhjemite dierite are smaller than crystals separated from show 0.21 per cent cordierite, 20 sections of one the remainder of the rock. These zircons ap- intrusion in the batholith have 1.13 per cent parently were incorporated in cordierite before cordierite, and 44 sections of another batholithic termination of zircon formation, and they im- unit contain 1.09 per cent cordierite. The thin ply early crystallization of cordierite. sections represent randomly scattered samples from each intrusion. Percentages of cordierite WILLOW LAKE-TYPE are approximate but coincide with ratios in- LAYERED ROCKS volving counts of crystals per square yard in the Willow Lake-type layered rocks (Taubeneck respective trondhjemites and show that the and Poldervaart, 1960) are a notable feature of trondhjemites contain only a small percentage Tramway trondhjemite but are more strikingly of the most prominent mineral. displayed in parts of the various cordierite Evidence for early crystallization of cordier- trondhjemites. ite is preserved in cores of oscillatory-zoned Willow Lake-type layered rocks were orig- plagioclase. In plutonic rocks of northeastern inally regarded as unique (Taubeneck, 1957, Oregon, mafic inclusions in plagioclase are use- p. 191-192; Taubeneck and Poldervaart, 1960, ful in tracing crystallization history. For p. 1297), but recent papers (Emerson, 1963; example, granitic rocks that contain only a Preston, 1963a; 1963b; Loomis, 1963) and trace of augite not replaced by hornblende, many oral and written communications dis- everywhere have some inclusions of augite in close widespread occurrence in virtually the plagioclase. In the Hurricane Divide and Pole entire spectrum of igneous intrusives. Bridge plutons (Taubeneck, 1964a) plagioclase Minerals of Willow Lake-type layered rocks commonly contains inclusions of augite and crystallize inward from planar interfaces that hornblende, with the pyroxene concentrated separate consolidating rock from magma. near the center. In some rocks the only re- Feathery and elongated crystals at high angles maining augite is in plagioclase. A similar re- to layers are characteristic. Common brecciation lationship exists in tonalites near the center of of marginal layers in Cornucopia stock, in- the Cornucopia stock where the only remaining cluding isolation of layered autholiths in parts hornblende persists in plagioclase. This horn- of some trondhjemites and layers split asunder blende was enclosed in plagioclase before horn- by interfingering trondhjemite testify to blende became unstable during the late crystal- crystallization before consolidation of interior lization history of Cornucopia tonalite. Hence magma. Offset of disrupted layers by granitoid mafic inclusions in plagioclase are useful in trondhjemite and by intersecting aplites (e.g.,

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location 46, elevation 6120 feet) verifies that earliest explosive activity preceded emplace- the layered rocks are not late fillings of tension ment of satellites of Cornucopia tonalite. In- fractures but are part of the crystallization direct evidence involving transported breccia sequence of each trondhjemite. fragments in a series of distinctive porphyry In the Cornucopia stock, differences between dikes, some of which are also brecciated, sug- the three largest bodies of trondhjemite are gest up to seven episodes of explosive activity. subtle and were not detected until late in 1961. The most significant explosion and intrusive Originally the trondhjemites were regarded as breccias extend west-southwest for almost 4000 a gradational mass characterized by increasing feet in a composite zone from location 53 (PI. cordierite content westward, accompanied by 1, fig. 1), elevation 7880 feet, to location 54, slight systematic changes in most other con- elevation 7450 feet. Intrusive breccias between stituents. Field studies at conventional scales, locations 53 and 54 contain exotic fragments such as 1 inch equals 4000 feet, failed to dis- of metamorphic rocks as much as 6 feet across. close most of the history of the stock. Some The only source for such blocks is beneath the occurrences of Willow Lake-type layered rocks granitic rocks of the stock. Exotic fragments were noted, such as the impressive zone along in other intrusive breccias as well as xenoliths the contact between Cornucopia tonalite and in some late porphyry dikes confirm that at Crater Lake cordierite trondhjemite; but least part of the stock is floored. many significant occurrences were missed, and The best exposed and most instructive brec- the entire mass of distinctive Big Kettle cor- cias do not occur within a short distance of dierite trondhjemite was overlooked. Stimulat- Cornucopia. Both easily accessible breccias ed in 1961 by visitors to Wallowa batholith and (location 55, elevation 6850 feet, and location Cornucopia stock, the writer concluded that 56, elevation 6540 feet) near the abandoned more detailed field work was necessary to study wagon road (Fig. 3) are poorly exposed and not the layered rocks. Studies in the Cornucopia readily interpreted without knowledge of stock, where Willow Lake-type layered rocks breccias elsewhere. never occur in sequences wider than 6 feet and commonly are 1-24 inches wide, were re- PORPHYRY DIKES sumed in 1961 at 1 inch equals 1000 feet, con- A dike swarm (Fig. 3) of tonalite porphyry centrating on the layered rocks. occurs from 0.4 to 2.1 miles northwest of With three exceptions, two of which almost Cornucopia. The almost vertical dikes, general- certainly define contact zones between different ly less than 5 feet wide, have west to northwest magma pulses in Crater Lake cordierite trondhj - trends and transect country rocks and tonalites emite, Willow Lake-type layered rocks oc- of the Cornucopia stock, Coulter satellite, and cur at or near contacts shown in Figure 2. Red Jacket satellite. Two rare examples of a Although layered rocks are generally brecciated dike of Cornucopia tonalite cutting a porphyry and commonly missing along most parts of dike are at location 57, elevation 5400 feet, many contacts, mapping of these rocks was a and location 58, elevation 6280 feet. Near the key factor in locating contacts between the east end of the exposure at location 58, an different trondhjemites. apophysis from the main tonalite dike offsets Elsewhere, Willow Lake-type layered rocks the prophyry dike. At location 59, elevation should also be useful (Taubeneck, 1964c) in 6260 feet, a prophyry dike 5 inches wide offsets unraveling intrusive histories of some igneous a 2-inch aplite, but more commonly, aplites complexes, whatever their composition. offset porphyry dikes. As in some swarms in the British Tertiary province (Richey, 1932, p. EXPLOSION AND INTRUSIVE 122; Charlesworth, 1953, p. 170), overlapping BRECCIAS time relationships suggest that the dikes were In addition to Willow Lake-type layered not emplaced simultaneously. rocks, a complicated sequence of explosion and Most porphyry dikes show linear orientation intrusive breccias2 is invaluable in deciphering of hornblende needles that are vertical or al- much of the history of the Cornucopia stock. most vertical. With no apparent change in Four cycles of brecciation are established; mineralogy, dikes cut almost at right angles (Fig. 3) across strata that range in composition 2 Explosion and intrusive breccias are used in accord- from recrystallized cherts to rare calc-silicates. ance with the classification of Wright and Bowes (1963, Dikes intersecting the Red Jacket satellite p. 81-83). trend at high angles to planar structure. Where

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dikes cut country rocks, tonalite inclusions are Minor potassium feldspar occurs in micro- up to 500 feet (location 60, elevation 6600 feet) pegmatite of some dikes. Other minerals are from the nearest exposed tonalite. At location iron ore, apatite, allanite, sphene, zircon, epi- 57, schistosity in a fragment is almost 90° to dote, chlorite, prehnite, heulandite, chabazite, bedding in adjacent rocks. Rare inclusions of and white mica. Hornblende phenocrysts and country rocks and relatively common tonalite less commonly plagioclase are aligned, and laths fragments (e.g., location 61, elevation 7850 feet) of plagioclase in the groundmass locally show occur in dikes that transect tonalite. Porphyry flow alignment. Some elongated hornblende dikes that cut tonalite contain angular tonalite shafts are broken, and in a few places plagio- pieces, but walls of several dikes exhibit con- clase phenocrysts are also broken. Notable flicting relationships and are locally replaced by features in plagioclase phenocrysts are strong tonalite that extends inward for an inch or oscillatory zoning, complex twinning, inter- growths of two or more crystals, and small TABLE 4, MEAN AND STANDARD DEVIATION hornblende inclusions clustered near the center FOR 11 SPECIMENS OF TONALITE PORPHYRY OF THE of phenocrysts. No pyroxene relicts were noted CORNUCOPIA STOCK, WALLOWA MOUNTAINS, OREGON in hornblende phenocrysts, but bleached cores (In volume per cent) (Taubeneck, 1964b) suggest that pyroxene formerly existed. Biotite commonly rims and Mean S.D. replaces hornblende. Tonalite porphyries are the only pre-Ter- Potassium feldspar 0.19 0.29 tiary porphyry dikes3 in the Cornucopia tona- Quartz 8.83 2.64 lite and associated country rocks shown in Plagioclase 78.45 2.80 Hornblende 4.37 1.63 Figure 3. According to Goodspeed (1955, p. Biotite 6.82 2.29 148), porphyry dikes in the vicinity of locations Opaque accessories 0.87 0.46 1, 17, 44, 56, 58, and 59 include relict dikes, Nonopaque accessories 0.47 0.48 replacement dikes, and rheomorphic dikes. The writer emphatically disagrees. Moreover, the writer concludes that most more. Dikes (Fig. 3) are truncated where in aplites classified as replacement dikes (Good- contact with Tramway trondhjemite. speed, 1940) are apophyses of Tramway Two other swarms of tonalite porphyry also trondhjemite. Both examples of replacement with northwest trends occur in or near the aplites (Goodspeed, 1940, p. 179, Fig. 3) are of Cornucopia stock. One swarm of at least five the same dilation apophysis partly shown in dikes cuts Cornucopia tonalite near location Figure 1 of Plate 2. Most of the upper photo- 62, about 2 miles south of Crater Lake. The graph (Goodspeed, 1940, p. 179, Fig. 3) cor- other swarm of at least nine dikes clusters near responds with Figure 1 of Plate 2. Examples of the northwest side of the stock, mostly south- other dilation apophyses of trondhjemite (e.g., west and west of Crater Lake. Dikes of this PL 2, figs. 2 and 3) occur within 30 feet of the swarm are truncated and brecciated by Crater knife in Figure 1 of Plate 2. Lake cordierite trondhjemite. Other porphyry dikes, younger and different FIELD EVIDENCE FOR MAGMAS in mineralogical characteristics, are associated Some field evidence for magmatic origin of with the trondhjemite intrusions. Younger granitic rocks in the Cornucopia stock is as dikes are not discussed. follows: Table 4 provides average mode and standard (1) Pronounced deflection of regional trend deviation for 11 samples of tonalite porphyry, around the stock implies a three-dimensional including at least 2 specimens from each dike adjustment of country rocks to accommodate swarm. Potassium feldspar in micropegmatite intruding magma. occurs in 4 of the 11 dikes but is slightly more (2) Flattened and stretched pebbles near abundant than implied in Table 4 because of contacts of Cornucopia tonalite as well as con- 14 dikes sampled, 3 contain such fine-grained tact schists containing augen-shaped relicts of micropegmatite that modal analyses were clastic plagioclase indicate directed pressure precluded. during intrusion and expansion of the pluton. Under the microscope, hornblende and (3) Absence of massive limestone west and plagioclase phenocrysts are set in a groundmass of plagioclase, quartz, biotite, and hornblende. 3 Dikes of rhyolite (Fig. 3) are not porphyritic.

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southwest of the stock and buckling of the fragments of country rocks including exotic same limestone south of stock recalls similar types. Therefore, at least part of the Cornu- patterns produced in laboratory experiments copia stock is floored; this favors a magmatic involving forceful intrusion (Grout, 1945). origin for overlying granitic rocks. (4) Open folds pinched into tight isoclinal sequence as traced toward the northeast corner OTHER EVIDENCE FOR MAGMAS of the stock attests to forceful emplacement of As subsequent papers assume a magmatic magma. origin for granitic rocks of the Cornucopia (5) Low-grade regional metamorphic rocks stock, other supporting evidence for magmas is and superimposed thermal aureole of horn- recorded here for emphasis. Except as indica- blende-hornfels facies are present. ted, this evidence will receive no amplification (6) Contacts with country rocks and earlier for a number of years until completion of field granitic rocks are sharp. Some trondhjemite and laboratory studies of related rocks in the contacts are blocky and saw-toothed on a scale Wallowa batholith. The supporting evidence of scores of feet and cut strata of diverse com- for magmas is as follows: position without loss of sharpness. (1) This is a composite stock with various (7) Geometry of inclusions of country rocks units emplaced in a sequence of increasing and earlier granitic rocks indicates movement, silica content as shown by modal analyses and as does the presence of exotic inclusions. Some 18 chemical analyses. Cornucopia tonalite inclusions in Crater Lake (2) There is a compositional gradation of cordierite trondhjemite are more than 1 mile Cornucopia tonalite (satellites excluded) from from the nearest trondhjemite-tonalite contact. margin to core regardless of the character of Near contacts, inclusions commonly can be country rocks (Taubeneck, in prep.). fit into walls. (3) Distribution trends of trace elements in (8) Walls of apophyses show dilation, as do Cornucopia tonalite are systematic and in walls of intersecting aplites. accord with inward consolidation of magma (9) Internal foliation of different units (Taubeneck, in prep.). parallels external contacts with country rocks (4) Protoclastic texture in marginal Corn- or contacts with earlier units. Foliation in ucopia tonalite (Taubeneck, in prep.) signifies cross-cutting apophyses is at angles to schistosity plastic movement of consolidating crystal in country rocks. Linear flow structure in mush under high confining pressure. Cornucopia tonalite implies upward motion of (5) Textural and mineralogical character- moving crystal mush past confining wall rocks. istics (Taubeneck, in prep.) of Cornucopia (10) Tonalite porphyry dikes (Fig. 3) in tonalite are readily understood as a logical Cornucopia tonalite are truncated by Tramway interaction of phases in a crystallizing magma. trondhjemite. Similar dikes in country rocks (6) A remarkably small variation m chemical are cut by Crater Lake cordierite trondhjemite. composition of various cordierite trondhjemites (11) Willow Lake-type layered rocks (Tau- (17 chemical analyses) occurs throughout the beneck and Poldervaart, 1960, p. 1300-1303) Wallowa Mountains, inasmuch as this is a region are compelling evidence for igneous origin. of marked petrographic heterogeneity. (12) Regional association of cordierite (7) Statistical identity of zircon (e. g., trondhjemites with ring dikes and irregular Taubeneck, 1957, p. 216-221) and close similar- porphyry intrusions define epizonal levels ity of chemical composition, including trace where evidence of magmatic origin in most elements, in dikes of cordierite trondhjemite world terranes is clearly and consistently dis- porphyry and mass of cordierite trondhjemite played. constituting Corral Creek satellite (Fig. 1) sup- (13) Prevalence of a hypabyssal sequence of port recrystallization from a common magma. porphyry dikes, explosion breccias, and in- (8) Layered rocks in Crater Lake cordierite trusive breccias related to the emplacement of trondhjemite similar to some described by satellites of Cornucopia tonalite, intrusion of Harry and Emeleus (1960) indicate crystalli- Tramway trondhjemite, and intrusion of vari- zation from highly mobile magma. Sub- ous cordierite trondhjemites supports the con- horizontal (dips less than 30°) multiple- cept that the plutonic bodies represent injec- layered sequences with some graded layers tion at relatively shallow depths. suggest settling of crystals on the floor of an (14) Intrusive breccias west of location 53 upward-consolidating magma chamber. Other and porphyry dikes near location 54 contain layered sequences show current action.

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rvwT,-TTTCTr»xTc zonal to ePlzonal environment (Buddington, CONCLUSIONS ,959-, Not Qnly can wh0leSale granitization be The importance of field studies in petrology dismissed, but rocks near Cornucopia should has become less obvious in the last 15 years not be cited as examples of small-scale meta- because of the extraordinary growth of labora- somatic phenomena such as replacement dikes, tory and theoretical researches in geochemistry, relict dikes, rheomorphic dikes, rheomorphic but in any final analysis a complete story of breccias, replacement breccias, and small Cornucopia stock must commence with an granodiorite blocks formed by additive meta- adequate geologic map that includes the morphism. Wallowa batholith. Science is built on recognition and correction Magmatic origin of the Cornucopia stock is of mistakes. In subsequent papers involving the demonstrated by textbook examples of most Cornucopia stock, detailed attempts will be features associated with emplacement of mag- made to consider petrological problems ignored mas. Especially impressive and significant in this descriptive review of field relationships, evidence for magmas is furnished by contact Mistakes that may exist in these papers inevit- relationships, deformational structures in coun- ably will be recognized and duly corrected by try rocks, and flow fabrics in granitic rocks. The later workers en route to more precise corn- stock is an exceptionally well-defined product of prehension of igneous phenomena as exhibited a complicated sequence of intrusions in a meso- by rocks of the Wallowa Mountains.

REFERENCES CITED Buddington, A. F., 1959, Granite emplacement with special reference to North America: Geol. Soc. America Bull., v. 70, p. 671-747 Charlesworth, J. K., 1953, The geology of Ireland: London, Oliver and Boyd, 276 p. Chayes, F., 1949, A simple point counter for thin section analysis: Am. Mineralogist, v. 34, p. 1-11 1956, Petrographic modal analysis: New York, John Wiley and Sons, 113 p. Emerson, D. O., 1963, Orbicular and banded structures in diorite near Fisher Lake, Placer County, California, p. 38 in The Geological Society of America, Abstracts for 1962: Geol. Soc. America, Special Paper 73, 355 p. Goodspeed, G. E., 1940, Dilation and replacement dikes: Jour. Geology, v. 48, p. 175-195 1955, Relict dikes and relict pseudodikes: Am. Jour. Sci., v. 253, p. 146-161 1959, Some textural features of magmatic and metasomatic rocks: Am. Mineralogist, v. 44, p. 211-250 Gorai, M., 1951, Petrological studies on plagioclase twins: Am. Mineralogist, v. 36, p. 884-901 Grout, F. F., 1945, Scale models of structures related to batholiths: Am. Jour. Sci., v. 243A, p. 260-284 Harry, W. T., and Emeleus, C. H., 1960, Mineral layering in some granite intrusions of southwestern Greenland: Copenhagen, 21st Internat. Geol. Cong., pt. 14, p. 172-181 Hills, E. S., 1936, Reverse and oscillatory zoning in plagioclase feldspars: Geol. Mag., v. 73, p. 49-56 Hurlbut, C. S., Jr., 1939, Igneous rocks of the Highvvood Mountains, Montana, Pt 1, The laccoliths: Geol. Soc. America Bull., v. 50, p. 1043-1112 Johannsen, A., 1937, A descriptive petrography of the igneous rocks: Univ. Chicago Press, v. 3, 360 p. Loomis, A. A., 1963, Noritic anorthosite bodies in the Sierra Nevada batholith: Mineralog. Soc. America, Special Paper 1, p. 62-68 Phemister, J., 1934, Zoning in plagioclase feldspar: Mineralog. Mag., v. 23, p. 541-555 Preston, J., 1963a, A columnar crystallization of olivine and plagioclase: Geol. Mag., v. 100, p. 1-6 1963b, The dolerite plug at Slemish, Co. Antrim, Ireland: Liverpool and Manchester Geol. Jour., v. 3, p. 301-314 Prostka, H. J., 1962, Geology of the Sparta quadrangle, Oregon: Oregon Dept. Geology and Mineral Industries, Geol. Map Series 1 Rambcrg, Hans, 1955, Natural and experimental boudinage and pinch-and-swell structures: Jour. Geoloev, v. 63, p. 512-526 Richey, J. E., 1932, Tertiary ring structures in Britain: Geol. Soc. Glasgow Trans., v. 19, p. 44-140 Ross, C. P., 1938, The geology of part of the Wallowa Mountains: Oregon Dept. Geology and Mineral Industries, Bull. 3, 74 p.

~~Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/11/1093/3432058/i0016-7606-75-11-1093.pdf by guest on 27 September 2021 REFERENCES CITED 1115~~

Ross, J. V., 1957, Combination twinning in plagioclase feldspars: Am. Jour. Sci., v. 255, p. 650-655 Service, H., 1937, An intrusion of norite and its accompanying contact metamorphism at Bluff, New Zealand: Royal Soc. New Zealand Trans., v. 67, p. 185-217 Smith, W. D., and Allen, J. E., 1941, Geology and physiography of the northern Wallowa Mountains, Oregon: Oregon Dept. Geology and Mineral Industries, Bull. 12, 65 p. Taubeneck, W. H., 1955, Age of the Bald Mountain batholith, northeastern Oregon: Northwest Sci., v. 29, p. 93-96 1957, Geology of the Elkhorn Mountains, northeastern Oregon: Bald Mountain batholith: Geol. Soc. America Bull., v. 68, p. 181-238 1958, Argillites in contact aureole of Bald Mountain batholith, Elkhorn Mountains, northeastern Oregon (Abstract): Geol. Soc. America Bull., v. 69, p. 1650 1959, Age of granitic plutons in eastern Oregon (Abstract): Geol. Soc. America Bull., v. 70, p. 1685 1963a, Wallowa Mountain uplift, northeastern Oregon, p. 69 in The Geological Society of America, Abstracts for 1962: Geol. Soc. America, Special Paper 73, 355 p. 1963b, Distribution of accessory minerals in zoned granitic intrusions, northeastern Oregon, p. 97 in The Geological Society of America, Abstracts for 1962: Geol. Soc. America, Special Paper 73, 355 p. 1964a, Major plutons of the Wallowa batholith, northeastern Oregon, p. 295-296 in The Geological Society of America, Abstracts for 1963: Geol. Soc. America, Special Paper 76, 341 p. 1964b, Criteria for former presence of augite in granitic rocks containing hornblende, p. 295 in The Geological Society of America, Abstracts for 1963: Geol. Soc. America, Special Paper 76, 341 p. 1964c, Significance of Willow Lake-type layered rocks in field studies of igneous complexes, p. 227 in The Geological Society of America Abstracts for 1963: Geol. Soc. America, Special Paper 76, 341 p. Taubeneck, W. H., and Poldervaart, Arie, 1960, Geology of the Elkhorn Mountains, northeastern Oregon: Pt. 2. Willow Lake intrusion: Geol. Soc. America Bull., v. 71, p. 1295-1322 Turner, F. J., 1951, Observations on twinning of plagioclase in metamorphic rocks: Am. Mineralogist, v. 36, p. 581-589 Tweto, Ogden, 1951, Form and structure of sills near Pando, Colorado: Geol. Soc. America Bull., v. 62, p. 507-532 Vance, J. A., 1961, Polysynthetic twinning in plagioclase: Am. Mineralogist, v. 46, p. 1097-1119 Waters, A. C., 1962, Basalt magma types and their tectonic associations: Pacific northwest of the United States, p. 158-170 in Macdonald, G. A., and Kuno, H., Editors, Crust of the Pacific Basin: Geophysical Monograph 6, 195 p. Wright, A. E., and Bowes, D. R., 1963, Classification of volcanic breccias: A discussion: Geol. Soc. America Bull., v. 74, p. 79-86

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