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GEOLOGICAL SURVEY RESEARCH 1968
QUARTZ DIORITE-QUARTZ MONZONITE AND GRANITE PLUTONS OF THE PASAYTEN RIVER AREA, WASHINGTON- PETROLOGY, AGE, AND EMPLACEMENT By R. W. TABOR, J. C. ENGELS; and M. H. STAATZ, Menlo Park, Calif.; Denver, Colo.
ibstract.-Quartz diorite to granite plutons intrude Lower of plutonic igneous and metamorphic rocks. On the Cretaceous sedimentary and volcanic rocks lying between two blocks of metamorphic and granitoid rocks. As indicated by west is the core of the North Cascade crystalline block, K-Ar dates, the large Pasayten and Rock Creek dikes were and on the east is the Okanogan Highlands crystalline emplaced about 86 m.y. ago (based on dating of biotite and block (fig. 1). The Mesozoic strata, include andesitic hornblende). The Castle Peak stock was emplaced about 49.5 m.y. ago (biotite and hornblende), and the Monument Park pyroclastic rocks and ininor flows (member A of the stock about 48 m.y. ago (biotite). A concentration of rhyolitic dikes between the granite Monument Peak stock and the granitic Golden Horn batholith of the same age suggests that the stock 121°00' CANADA is a satellite of the batholith. The stock domed up the beds of f &,ri• · •·•,S•I»;• •Area of WASHINGTON the country rock and deflected regional fold axes. The Pasayten 1 and Rock Creek dikes parallel trends of concordant plutons in , - '211 11. .1 111 1 1 1%,1,12 .1 HIGHLANDSOKANOGAN the metamorphic block to the southwest, suggesting that the £6 \:::.:t ...t..... CRYSTALLINEBLOCK [likes may be the shallow extensions of a concordant pluton in 48°45' NORTH 0 metamorphic rocks beneath the sedimentary terrane. CASCADECORE ···· 0\· · ·XPA· ··· kcl· .. 0 CRYSTAILINE /r+ I'\'e..':Vi.'··: · 'k•/Goot'7 Pe"k BLOCK llc,·•\w·······.4lilI\·· Geologists working in the Pasayten River area, of lillI,·3 +''I:•+.-•'•¥':8· · · •»I · · northern Washington have found the geologic history ,--. 't-'r/)74.J ++++./·······»GOLDEN HORN · dimcult to interpret for many years. Early workers in- ..x9731 : . :BATH94'It' : . cluding Russell (1900), Daly (1912), and Smith and • fLACKJ'EAK-»''i•w : BATHOLITH ••\•--•• .•11•1.••. Calkins (1904) briefly described the Mesozoic sedimen- 13/ <, tary and volcanic rocks and noted the presence of in- TAN trusive plutons. J. D. Barksdale and geologists with the f»,-12./ •»$1Area of • • • Washington State Department of Conservation first A-'rlei3 eGEJ mapthis mapped the granitic rocks of the area, and showed their Glacier•-•13pea•,1•-7'/9>1 WASHINGTON work in simplified form on the Washington State geo- «...... logic map (Huntting and others, 1961). The present report stems from reconnaissance map- 0 10 20 MILES ping by the U.S. Geological Survey in 1965 and 1966 as part of a mineral evaluation of the North Cascade FIGUREreport.1.-SketchRandom mapdashesshowingUpper'theCretaceousgeologic settingand Tertiaryof this Primitive Area, under the directive of the 1964 Wilder- quartz diorite to quartz monzonite intrusions; crosses, granite intrusions; dots, Mesozoic volcanic and sedimentary ness Act. Potassium-argon ages were determined by rocks (including minor Tertiary rocks) ; and blank areas, Joan C. Engels. predominently gneiss, sehist, and granitoid plutons. Heavy lines are faults, and letters show relative up or down move- GEOLOGIC SETTING ment of rocks. Data are from J. D. Barksdale, Peter Misch, The plutons described in this paper were emplaced fiedand othersin thecompiledGlaeier Peakby Hunttingarea accordingand othersto (1961)Crowder; modi-and iii Mesozoic sedimentary and volcanic rocks exposed in others (1966), west of the area of figure 2 according to a northwest-trendingblock that lies between two blocks Mischto Libby(1966b(1964),) andandGrantnortheast(1966of). Glacier Peak according U.S. GEOL. SURVEY PROF. PAPER 600-C, PAGES C45-C52 C45 046 MINERALOGY AND PETROLOGY.
Pasayten Series of Daly, 1912, p. 481 ) along the east- nite is of intermediate composition ( CI=7-11). The ern initrgin of the central block, separated from the most silicic of the group is the Monument Peak stock of Okanogan I-Iigliltillds by a large fault. The volcanic graiiite ( CI = 2-4). rocks are overlain by tlie Pasayten Formation ( Smith Iii additioii to tliese large bodies tliere are numerous nrid Cal kins, 1904, p. 28-30 ), 11 thick sequence of inter- porphyritic aphanitic dikes. Hornblende-plagioclase bedded feldspathic to volcanic sandstone, black argillite, porpliyry dikes, mostly of dacitic composition, are par- and 11 few congloinerate beds ( members B to K of the ticularly abundant throughout the area. Sonic of these Pasayten Series of Daly, 1912, p. 481 ). Folds in the may be related to the quartz diorite-quartz inonzonite 3Iesozoic rocks are steel) ] imbed, subparallel, and trend plutons, but none were found connected to them. In nortliwest. Along tlie western margin of the sedimen- the Many Trails Peak area, biotite dacite dikes are tary block, iii fault contact witli tlie sandstone and argil- particularly abundant. lite, are greeiistone and cliert of probable Paleozoic age Quartz porphyry dikes of rhyodacitic to rhyolitic ( I-Iozonieen Series of Daly, 1912, p. 508 ). This unit com- composition are ·also abundant, and, since some of these poses the upper plate of tlie Jack Mountain thrust of stem from the Monument Peak stock, tliey will be dis- Miscli ( 1966b, p. 133-134). The Jack Mountain thrust cussed witll the stock. plate is iii part bordered 011 tlie west by the Ross Lake The ages of the plutons as based on field relations fault zone ( Misch, 1966b, p. 133-134)-a zone analogous and K-Ar analysis are, from oldest to youngest: to tlie fazilt separatiiig tlie eeiitral block from the crys- Pasayten dike and Rock Creek dike tal]ine Okanogan I-Iiglilands block on the east. How- Lost Peak stock ( age relative to tlie Pas:tyten and ever, the Ross Ltike fault zone lias been intruded by Rock Creek dikes zinknown) elongate plutons. To tlie soutli, tlie B] ack Peak batho- Monument Peak stock and Castle Peak stock. lit.li ( Adams, 1964; Miscli, 1966b, p. 134 ) has come up Pasayten dike and Rock Creek dike 111011% tliis sallie zoiie. In tlie sozithern part of the area The Pasayten dike has an avera (re widtli of 1 mile ( fig. 2 ) near Robiipson Afountain, Cretaceous red beds and a probable length of 1216 miles: The lithologically ( saiidstoiie, sliale, and conglomerate ), wliicli interfinger similar Rock Creek dike to the nortli-northwest is about witli over]ying massive :indesite breccia, are exposed in 036 016 miles long and lies along tlie saine trend as the 11783jor folds. Tliis is tlie Midniglit Peak Formation of Barksdale ( 1948, p. 173-174 ). Pasayten dike. The two dikes are the same age ( table 1 ) and may be connected at deptli. We did ilot deteriniize the exact stratigraphic se- The contacts of tlie Pasayten dike and Rock Creek quence or age of all the sedimentary rocks in the central dike are sliai·p, and near tliein the country rocks have block. Several fossil collectioiis, however, from the been tliermally inetamorphosed, commonly to ]iornfels satidstone-argillite sequence near Hurts Pass ( south of spotted with glomeroblastic biotite. Locally hornfelsed Slate Peak) indicate that the rocks are Early Creta- beds contain cordierite, andalusite, or garnet. Most rocks ceous in age ( D. L. Jones, written commun. 1965 ). Fos- at tlie contact are in the hornblende liornfels facies. A sils collected from similar rocks to tlie south have also few contacts along the Pasayten dike show coinplex been reported ( Barksdale, 1960, p. 2049 ) to be Early penetratioii of magma into ]iost rocks. For example, Cretaceous. Collections from a different part of this se- quence iii Canada ( Rice, 1947, p. 19 and 23; Coates, tlie nortliern border of the dike south of Wildcat Moun- tain is a migmatite consisting of narrow dikes and il·reg- 1966, p. 55 ) have been dated as Late Jurassic to Early ular masses of quartz diorite and pegmatite injected iiito Cretaceous. a hornfels spotted witll porphyroblasts of feldspar. DESCRIPTION OF THE INTRUSIVE ROCKS Along the southern margin of the Pastlyten dike in Eureka Creek the wallrocks are crisscrossed witli quartz The plutons of the Pasayten River area ( fig. 2 ) are diorite dikes and tlie pluton contains swarnis of hornfels of tliree principal types: quartz diorite to granodiorite, xeiioliths. Xeiiolitlis are abundant iii the Rock Creek granodiorite to quartz monzonite, and granite ( fig. 3 ). dike aloiig tlie western contact on the edge soutli of Rock The most mafia are the large nortliwest-trending Pasay- Creek. Such features would suggest :issimilation of ten dike ( extending from tlie Lost River to Pasayten tlle country rock in these areas; iii otlier areas, however, Peak) and Rock Creek dike (extending from the West as along the northeastern border of the Pasayten dike Fork of tlie Pasayten River to Chucliuwaiiteeii Creek ), iiortlieast of Robinson Mountain, the contact is sharp small pods and dikes of quartz-diorite to granodiorite aild the country rocks are overturned. The Pasayten dike (color index, iii percentage of mafic minerals-13-23 ), is intruded by the Monziment Peak stock on lower and the Castle Peak stock of grallodiorite ( CI=13-22). Eureka Creek, and its original hypidiomorphic texture Tlie Lost Peak stock of granodiorite to quartz monzo- has been recrystallized to a coarse granular mosaic. TABOR, ENGELS, AND STAATZ C47 120'45' CANADA BRITISH COLUMBIA 120°30' "4•' ••<'••,•'"•'k' 1 50 77 pee.%.4 GRANO- / 4-Monument1 Peak stock 2•F DIORITE C 2 //1 0/:. R / .' fLost Peak . )U A 2// stock --9- _L----* QUARTZ GRANITE Pasayten and MONZONITE 110 • Rock Creek dikes MAFIC PLAGIO- 35 35 K-FELDSPAR MINERALS CLASE FIGURE 3.-Ternary diagram showing modal composition of igneous rocks in the Pasayten River area. Triangles are Castle Peak stock; open, from Daly (1912, p. 494), solid, this report. TABLE 1.-K-Ar ages of dikes and stocks of the Pasayten River area, Washington [Samplelocationsonfigure 2] Name androck Mineral (percent)K20 *Arto (moles/g)1 AtmosphericAr (percent) Age (m.y.) Biotite______Pasayten dike; quartz diorite__ Biotite (replicate) __ 8. 11 1. 072X 10-10 9.7 87. 7• 2. 6 8.11 5.1. 60X046X10-1110-9 18 85. 3zt2. 6 Hornblende______. 429 4. 67X 10-11 17 86. 0a 2.6 Rock Creek dike; granodiorite-_. Biotite______Hornblende______. 358 6. 35X 10-10 42 49.86. 81af 2.61. 5 Castle Peak stock; granodiorite__ Hornblende______8.52. 688 5. 09X 10-11 2181 49. 5zE 1. 5 Monument Peak stock; granite____ Biotite______8.49 6. 08X 10-10 7.0 47. 9rE 1. 4 Golden Horn batholith; granite 2- - Biotite_____·______8.62 6. 007X 10-10 30 46. 6f 1.4 21SampleRadiogenicsuppliedargon.byPeterMisch; collected on State Route20, a short distance southof Cutthroat Creek (Miseh, oral commun., 1967). The Pasayten and Rock Creek dikes and sma.11 pods subhedral plagioclase, quartz, and mafic minerals. Bio- and dikes consist of a gray speckled, medium-grained, tite and, less commonly, hornblende are chloritized, and hypidiomorphic granular rock which ranges from in places the rock is crisserossed by small fractures filled quartz diorite to granodiorite. Modes are given in table with epidote and elllorite. 2. Hornblende and biotite a.re the principal mafia min- Lost Peak stock erals, the former being the most abundant. Accessory The Lost Peak stock is an oval-shaped body with an minerals are magnetite, ilmenite, apatite, sphene, a.nd exposed area of 12.6 square miles; Lost Peak stands zircon. Where plagioclase is fresh it appears to grade nearthe southeastern endofthestock. from andesine cores to sodic oligoclase rims. It shows The contact between the Lost Peak stock and the in- strong oscillatory zones and generally is partly altered truded sedimentary rocks is complex. To the southeast to sericite and caleite. Locally, coarse crystals of potas- of the Many Trails Peak, the hornfelsed country rock sium feldspar form a continuous mesostasis containing has been cut into numerous small blocks by qua,rtz di- TABOR, ENGELS, AND STAATZ C49 TABLE 2.-Modes 1 of igneous rocks in the Pasayten River area, 1Fashington Rock Castle Pasayten dike Pod 2 Creek Peak Lost Peak stock Monument Peak stock Constituents dike stock 1 2 3 4 567 8 9 310 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Quartz____-__- 17 15 25 21 20 17 20 18 17 18 26 26 26 26 24 26 20 37 43 35 35 36 32 35 32 Plagioclase__- __ 65 59 55 55 57 51 62 60 56 42 48 51 45 45 45 40 45 21 15 19 20 19 21 18 21 K-feldsp,ar__... 1 35 6 11 17 3 9 11 18 13 12 19 22 24 25 26 39 40 42 43 43 45 45 45 Mafic mineral 4- 17 23 15 18 12 15 15 13 16 22 13 11 10 7 7 9 9 3 2 4 2 2 2 2 2 Phenocrysts 40 13 12 23 Mnt.rir 60 87 88 77 1 All modes except 10 and 11 determined by Meade Norman on stained rock slabs by point count, 500 to 1,000 points. Phenocrysts determined by count and visual estimate. 2 Southernmost pod on ridge west of Lease Creek. 3 From Daly (1912, p. 494). 4 Mafic minerals include hornblende, biotite, chlorite, sphene, magnetite, and ilmenite. orite dikes of varying grain size. A similar army of ern margin. From the gorge of Lost River to the highest dikes cuts the sedimentary rocks on Many Trails Peak, peak, this stock is exposed over a vertical distance of but relationships are obscured by numerous dacite por- 5,100 feet. phyry dikes. The quartz diorite dikes are probably de- The Monument Peak stock is younger tlian any of the rived from the Lost Peak stock; the source of the dacite surrounding rocks. The sandstolle and argillite sequence porphyry dikes is not known. Locally, conditions fmvor- is thermally metamorphosed, and the Lost Peak stock ing the formation of pyroxene hornblende facies were conttiins much K-feldspar along its contact with the attained in the country rock. Along its southern margin, younger stock. Contacts of the .Monument Peak stock the Lost Peak stock has been intruded by the Monument are sharp, but numerous dikes and sills from it pene- Peak stock, and an arm of the latter separates the south- trate the hornfe]sed sedimentary rocks in a lit-par-lit ern tip of the Lost Peak stock from the main mass ( fig. fashion, especially along the western margin, where the 2). Innumerable dikes of granite porphyry, derived sills are so abundant that defining the outer limit of the from the Monument Peak stock, cut the Lost Peak stock stock is diflicult. Vuggy quartz veins are common in tlie on the northeast side of Mount Lago. Within a few margins of the Monument Peak stock and iii the nearby inches of the granite contact, the Lost Peak stock is country rock. Along Lost River tliese veins commonly flooded with K-feldspar, which replaces plagioclase, contain fluorite, a mineral which also occurs as an ac- quartz, and biotite. Farther from the granite contact the cessory mineral in the stock. In soine areas within the older pluton is cut by tiny veins of K-feldspar, quartz, granite a few feet from the contact are discontinuous and hornblende. narrow zones of pegmatite. The hornfelsed rocks usu- The Lost Peak stock is light gray to pinkish gray and ally contain biotite or hornblen(le, and locally cordierite hypidiomorphic granular, rarely porphyritic. Grain and garnet. size ranges from fine to medium over a distance of a few The Monument Peak stock is composed of a yellow- tens of feet. In composition the rock ranges from grano- ish-pink grallite, which for the most part is fine grained, diorite to quartz monzonite. Modes are given in Table 1. porphyritic, and locally miarolitic. In a small area near Biotite is generally more abundant than hornblende. Monument Peak, however, the granite is medium Accessory minerals are sphene, allanite, magnetite, il- grained, hypidiomorphic, and granulzr. Platy jointing menite, and zircon. Plagioclase occurs in fairly large subparallel to the contact is ubiquitous. In tlie por- crystals that commonly show oscillatory zoning, and phyritic granite, euhedral phenocrysts of K-feldspar, K-feldspar generally occurs as smaller intergranular quartz, and plagioelase are surrounded by a fine- i 1 crystals. Small fractures filled with chlorite and epidote grained, mainly xenomorphic matrix. Small areas of characterize the rock exposed in the southern tip of the 1Ilatrix of most of the granite are grallopllyrie, locally stock, and in this respect it resembles the Pasayten and grading into graphic granite. Modes are given in table Rock Creek dikes, but in other areas of the Lost Peak 1. The K-feldspar is perthitic, quartz is commonly re- sorbed, and plagioclase is unzoned. Most of the plagi- stock, joints are not chloritized. oclase is An15-20, although one specimen of medium- Monument Peak stock and associated dikes grained granular granite has a plagioclase of AnT042Dark- The Monument Peak stock is a circular intrusion some brown to green biotite is the only mafie mineral. Other 7 miles in diameter that is exposed between Eureka accessory minerals include apatite, zircon, sphene, tind Creek and Lost River ( fig. 2). It is here named after fluorite. The latter mineral, although rare, is present in Monument Peak, a prominent mountain near its west- most specimens. C50 MINERALOGY AND PETROLOGY Yellow-orange to pink quartz porphyry dikes are set in an aphanitic matrix. The matrix, which makes up common on all sides of the Monument Peak stock, but approximately 50 to 90 percent of the rock is typically are chiefly concentrated southwest of it (fig. 4). These spherulitic and (or) granophyric. Sodium col}altini- dikes, which cut the other plutons and the older dikes, trite staining indicates that a high proportion of the are from ·a, few feet to a few hundred feet across, and matrix is K-feldspar. Small amounts of chloritized bio- some are more than 2 miles long. Although most are tite and hematite make up the dark minerals, and traces lenticular, bra,nching and irregular-shaped dikes are of fluorite are present in a few dikes. Because the rock common as well. In the Lost River canyon, the quartz types cannot be accurately determined without a chem- porphyry dikes extend out from the porphyritic mar- ical analysis, these dikes are called quartz porphyries gin of the Monument Peak stock, and most are prob- after their most conspicuous phenocrysts. Many are ably offshoots of it. probably rhyolites or rhyodacites. The quaftz porphyry dikes consist of euhedral to sub- True granites are extremely rare in northwestern hedral quartz, K-feldspar, and plagioclaze phenocrysts Washington. The only other known granite body in this 120°30' 0 1 2 3 4 5 Mil.ES 4.f 83L___4,4 Data in mapped area from unpublished U.S. Geolog- \B\B* ical Survey field maps. \* Outline oftheGoldenHorn f \\»=P./ batholith from Huntting 4 and others (1961) .re«: 1/ 2' 4. W / 4.4 tf 1 /1/\ / lib1 9- i w:: 1 , 1- 2 C / ,\ r 41 MonumentPeak 1 1 \0\ 1 /-,-\\ \ MONUMENT \/ 1 1 : \\ 11 PEAK STOCK t1 {.: \ A ./ 1 . \\ 4 1I 48°45' - I. h %'6 \\ f /3 f , 4 \\ 4c<'036 .2 \ \ , 1 e \\ 9 4.. .//4. \\>\ C f,:2 44 . 4. \ 1/r '/J Q r <10 14\1< 1/ 1 •1-111111,«-f.-'...1-_«1111•111 4. \/\ ,/ i \ \ » 1 ..0 -111/ ///# 9/:/ .LL-'' - »-- West Fork t·4. / GOLDENBATHOLITHHORN : 3 160:rw fi&'*te·rs O Creek FIGURE 4.-Sketch map af quartz porphyry dike distribution. TABOR, ENGELS, AND STAATZ C51 general area is the alkaline and subalkaline Golden Horn tion has not been dated because specimens examined are batholith ( Misch, 1966a, p. 216; 1966b, p. 139 ), which not completely free of thermal metamorphism produced intrudes the western margin of the sedimentary belt by the nearby and younger Monument Peak stock. some 1042 miles southwest of tlie Monument Peak stock If the liypothesis that the Monument Peak stock con- ( fig. 1 ).A large number of satellitic rhyolite porphyry nects with the Golden Horn batholith at shallow depth dikes are associated with the batholitli. According to is correct, then the two plutons should be the same age, J. D. Barksdale ( oral commun; 1965), these dikes are that is, about 48 m.y. When this report was begun, the abundant between the dikes mapped by us and the two available biotite dates on the Golden Horn bat;ho- Golden Horn batliolith. The similarity of the rocks in lith, 38.8 m.y. and 48+2 m.y. ( Misch, 1964, p. 14) were these two plutons and the concentration of satellitic por- discordant. Consequently, a determination was made on phyry dikes between them suggests to us that the two a new stzmple supplied to us by Peter Misch. Tlie result- bodies connect at depth. ing age of 46.6=!=1.4 m.y. suggests that tlie older age is Castle Peak stock correct and substantiates the hypotliesis of a, connection The Castle Peak stock lies astride the Canadian bor- between the batholith and the Monument Peak stock. der ( fig. 2 ) and was named by Daly ( 1912, p. 492-499 ). However, an explanation for tlie anomalous 38.3-m.y. age has not been found. This oval-shaped intrusion is exposed over an area of about 10 square miles. MODE OF EMPLACEMENT Lawrence (1967) has described the petrology and contact relations of the stock in some detail. Contacts All the plutons in the Pasayten River area were dip sharply outwards and are discordant. A mafic bor- emplaced at relatively shallow depths, that is in the der phase, according to Lawrence ( 1967, p. 35-38 ) is epizone ( Buddington, 1959, p. 677-678 ), as shown by quartz diorite ; tlie central phase is predominantly their discordance, contact haloes, and lack of foliate granodiorite but ranges to quartz diorite. The color in- structures. The Monument Peak stock witli its por- dex ranges from 11 to 33 (Lawrence, 1967, p. 35-38 ). phyritic margins, vuggy veins, and hypabyssal dikes Biotite generally predominates over hornblende. Py- Was probably the shallowest. roxene, partially replaced by liornblende, occurs in the Daly ( 1912, p. 495 ) proposed that the Castle Peak marginal phase ( Lawrence, 1967, p. 42 ). stock was emplaced by iii situ stoping, but Miscli ( 1966b, p. 139-140) has shown that forceful intrusion played AGE OF THE PLUTONS an important role in the emplacement of this stock as The oldest o-f the plutons ( table 1 ) are the Pasayten well as the Golden Horn batholith. Lawrence ( 1967, p. 28 ) has sliown that GO percent of tlie area of tlie Castle and Rock Creek dikes, which have an age of about 86 million years ( Late Cretaceous). Locations of dated Peak stock can be accounted for by shouldering aside. We do not have sullicient structural data to evaluate samples are shown on figure 2. Although the sample of the mode of emplacement of all the plutons mapped the Pasayten dike lies within 3Ve miles of tlie younger by us. Our best data are on the Monument Peak stock Monument Peak stock, we believe that tliis sample is for which we have compiled a small structural contour probably unaffected by the second episode of heating map showing the shape of the roof and the outward because the biotite and hornblende ages are concordant. dips of the sedimentary rocks on and adjacent to it According to our data, the Monument Peak and ( fig. 5 ). This map clearly indicates that the Monu- Castle Peak stocks are analytically the same age ( tal)le ment Peak stock bowed up its roof, as it pushed its 1 ), about 48-50 m.y. ( Eocene). A K-Ar age of 46 m.y. way in. Bowing aside of the country rock is also sug- for the stock has been cited by J. A. Coates of the gested by the crowding of folds on the west side of Canadian Geological Survey as quoted by IAwrence the stock and the change in trend of the major fold ( 1967, p. 7). Altliough the age of the Monument Peak axes on the north, west, and southwest sides of the stock was determined by analysis of a single sample of Monument Peak stock ( fig. 2 ). Some of the deflection biotite, we do not know of any younger thermal events of structural lineaments might be due, however, to that might ha,ve altered the radiometric age. forceful intrusion of the Lost Peak stock and the It is readily apparent from these data that tliere is no Pasayten dikes. The lack of compressive features on simple correlation between the age and the composition the east side of the Monument Peak stock might be of these plutons. The oldest plutons are quartz diorite due to the rigidity of the Okanogan I-Iighlands crystal- to granodiorite, the youngest both granodiorite and line block, which prevented yielding in an easterly granite. The Lost Peak stock of intermediate composi- direction. C52 MINERALOGY AND PETROLOGY 120°30' Barksdale, J. D., 1948, Stratigraphy in the Methow quadrangle, Washington : Northwest Sci., v. 22, no. 4, p. 164-176. '22-ZI.= 3 MILES -1960, Late Mesozoic sequences in thenortheastern Cascade '07/»CR-'I 0 1 2 Mountains of Washington [abs.] : Geol. Soc. America Bull., -f»j -...1,11 CODNATOUUM'I't'•rAS•A,y'l"ET v. 71, no. 12, pt. 2, p. 2049. -- Buddington, A. F., 1959, Granite emplacement with special '' 2.------.- .... g reference to North America: Geol, Soc. America Bull,, v. C •ic. 70, no. 6, p. 671-747. \ Coates, J. A., 1966, Manning Park area, Cascade Mountains: , «' ..1 /(23.-3) » Canada Geol. Survey Paper 66-1, p. 55-56. 4.1/ \\\/701 3\ Crowder, D. F., Tabor, R. W., and Ford, A. B., 1966, Geologic -f I , ·. re 1...,/ map of the Glacier Peak quadrangle, Snohomish and Chelan 75 Counties, Washington: U.S. Geol. Survey Geol. Quad. Map / d GQ-473, scale 1 : 62,500. Daly, R. A., 1912, Geology of the North American Cordillera 48°45' - 559'•r--< CA1 \ A , 1.\1 \-C.5•.i'.' - at the forty-ninth parallel : Canada IGeol. Survey Menl. 38, ·<\L.1.\\ 1 \*-75 /.'' \i\23/,4 pts. 1-3, 857p. \\\ Grant, A. R., 1966, Bedrock geology of the Dome Peak area, Chelan, Skagit, and Snohomish Counties, Northern Cascades, --«»«•'•»h·"60 Washington: Washington Univ., Seattle, Ph. D. thesis, 306 p. Huntting, M. T., Bennett, W. A. G., Livingston, V. E., Jr., and FIGURE 5.-Contours drawn on the top of the Monument Moen, W. S., complies, 1961, Geologic map of Washington : Peak stock (patterned). Selected bedding attitudes Washington Div. Mines and Geology, scale 1: 500,000. (strike and dip symbols) show the bowing up of the Lawrence, D. P., 1967, Structure and petrology of the Castle country rocks (unpatterned). Dashed contours are less Peak stock, Northeastern Cascade Mountains, Washington: reliable than solid contours. Washington Univ., Seattle, M.S. thesis, 67 p. Libby, W. G., 1964, Petrography and structure of the crystaline Overturned beds adjacent to the contacts of the rocks between Agnes Creek and the Methow Valley, Wash- Pasayten and Rock Creek dikes suggest that forceful ington : Washington Univ., Seattle, Ph. D. thesis, 171 p. intrusion has played-a part in their emplacement. On Misch, Peter, 1964, Age determinations on erystalline rocks of the other hand, numerous xenoliths and migmatites Northern Cascade Mountains, Washington, in Kulp, J. L., alongthe contacts indicatethat some stoping and assim- senior investigator, and others, Investigations in isotopic geoehemistry : Palisades, N.Y., Columbia Univ., Lamont ilation may also have taken place. Geol. Observatory (U.S. Atornie Energy Comm. [Pub.] The northwest trend of the Pasayten dike and its NYO-7248), App. D, p. 1-15. probable extension, the Rock Creek dike, roughly par- -1966a, Alkaline granite amidst the calc-alkaline instrusive allels folds and some faults in the sedimentary belt of suite of the Northern Cascades, Washington [abs.] : Geol. the Pasayten area. The emplacement ma,y have been Soc. America Spec. Paper 87, p. 216. controlled by these structural elements, although we -1966b, Tectonie evolution of the northern Cascades of found no specific structure which could do so, such as Washington State-A wes't-Cordilleran ease history, in a fault along the trend of the dikes. However, the dikes Gunning; H. C.,ed., A symposium on teetonic history and also parallel concordant and elongate quartz diorite- mineral deposits of the 'Western Cordillera in British Colum- granodiorite plutons in the North Cascades farther bia and neighbouring parts of the United States: Canadian west, such as the probably Cretaceous Black Peak Inst. Mining and Metalurgy Spec. Paper, v. 8, p. 101-148. Rice, H. M. A., 1947, Geology and mineral deposits of the batholith (Adams, 1964; Misch, 1966b, p. 139).Perhaps Princeton map-area, British Columbia : Canada Geol. Survey the dike is the extension of a concordant pluton lying Mem. 243, Pub. 2477, 186B deeper in the metamorphic floor of the sedimentary Russell, I. C., 1900, A preliminary paper on the geology of the belt. Cascade Mountains : U.S. Geol. Survey 20th Ann. Rept., REFERENCES pt. 2, p. 83-210. Adams, J. B., 1964, Origin of the Black Peak Quartz Diorite, Smith, G. 0., and Calkins, F. C., 1904, A geological reconnaissance Northern Cascades, Washington : Am·. Jour. Sci., v. 262, across the Cascade Range near the forty-ninth parallel: no. 8, p. 290-806. 'U.S., Geol. Survey Bull. 285, 108 p. R