Geology of the Mount Garibaldi Map-Area, Southwestern British Columbia, Canada

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 69. PP. 161-178. 2 FIGS.. 1 PL. FEBRUARY 1958

GEOLOGY OF THE MOUNT GARIBALDI MAP-AREA, SOUTHWESTERN BRITISH COLUMBIA, CANADA

PART I: IGNEOUS AND METAMORPHIC ROCKS

BY W. H. MATHEWS

ABSTRACT The Mount Garibaldi map-area is in the southern part of the plutonic complex com- prising the Coast Mountains of British Columbia. The oldest rocks of the map-area are metavolcanic and minor metasedimentary rocks of unknown age and structure. These are extensively invaded by a quartz diorite batholith, the earliest of the plutonic masses, which displays an unfoliated core, a margin with highly developed secondary foliation, and an intervening zone of primary foliation. Bedded rocks at least 20,000 feet thick, principally clastic sediments derived in part from the batholithic rocks, occur in fault blocks north of Garibaldi Lake. The rocks of one fault block rest uncomformably on the older quartz diorites and contain Upper Cretaceous fossils; those of the other fault blocks are thought to be slightly younger than the fossil-bearing beds. The bedded rocks have in turn been invaded by later quartz diorites which are partly contemporaneous with and partly later than the block faulting. Two post-tectonic and presumably post-Upper Cretaceous batholiths lie partly within the map-area.

CONTENTS TEXT Page Castle Towers batholith 174 Page Chemical compositions 175 Introduction 161 References cited 177 Location and access 161 Field work 162 TTCTW ATTrwc; Previous work 162 ILLtbl KAllONb Acknowledgments 162 Flgure Pase Geology of the igneous and metamorphic rocks 162 1. Tectonic map of the Mount Garibaldi Metavolcanic and metasedimentary rocks... 162 map-area; 163 Plutonic rocks 165 2. Variation diagram for the Coast intrusive General statement..'. 165 rocks o1' the Mount Garibaldi map-area Cloudburst quartz diorites 165 and the Vancouver area 177 Stratified rocks near Garibaldi Lake 168 Plate Facing page General statement 168 j Geology of the Mount Garibaldi map- Cheakamus Formation 169 area jyg Empetrum Formation 170 Helm Formation 170 Metamorphism 171 TABLES Internal relationships 171 Table Age and correlation 171 1. Stratigraphy 164 Plutonic rocks 172 2. Surface areas of map units 165 Younger quartz diorites 172 3. Chemical analyses and norms of the plutonic Squamish batholith 173 rocks 176

INTRODUCTION British Columbia, covers 380 square miles between Lat. 49°38' and 50°00' N., and Long. Location and Access 122°54' and 123°14' W. The town of Squamish, in the southwestern part of the map-area, lies The Mount Garibaldi map-area, in the at the head of Howe Sound, 41 miles by rail southern part of the Coast Mountains of north of the city of Vancouver. The Pacific 161

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Great Eastern railway extends northward past Stelck assistance and advice. The British Squamish through the western part of the Columbia Department of Lands and Forests map-area, and a few gravel roads serve the has made available maps and photographs. southwestern part. Elsewhere access is limited Mr. James T. Fyles rendered very valuable almost entirely to foot trails. assistance in the field during the season of 1946 and Mr. W. H. Genschorek during the follow- Field Work ing summer. Mr. John G. Fyles contributed much to the final report with his critical review. Most of the field work in the map-area was Laura Lu Mathews provided both encourage- carried on during the summers of 1946 and ment and aid in the editing. 1947, although previous work had been done during brief visits since 1936. Information was GEOLOGY OF THE IGNEOUS AND METAMORPHIC plotted in the field on manuscript maps (scale ROCKS 1:40,000, contour interval 100 feet) prepared by the British Columbia Department of Lands Mela-volcanic and Metasedimentary and Forests from photo-topographical surveys. Rocks Locations in the field were made by pace-and- compass traverses, by compass resections on Rocks mapped as metavolcanic and meta- identifiable landmarks, and by aneroid readings. sedimentary rocks are exposed over an area of Aerial photographs were limited to a few approximately 27 miles within the map-area, random obliques at the time of field mapping, principally near its southern end. They include but the entire area was covered by vertical such varied rock types as massive and bedded aerial photography in 1949, and these photos greenstone, chert, argillite, sandstone, con- have been used in the preparation and revision glomerate, and the schistose equivalents of of this report. these rocks. Crystalline limestone occurs as Contacts between the batholithic rocks and lenses generally only a few feet wide in the older schists and sedimentary rocks were northernmost part of the map-area. The crossed transversely at regular intervals, stratigraphy has not been worked out. generally along creeks or ridge crests; but as In the relatively few localities in which far as was practicable most of the contacts of stratification has been observed (Fig. 1) it the older rocks with the overlying Quaternary displays a general northerly strike but highly volcanic rocks were traced directly. variable dips, changing markedly in the in- competent argillites within an area of a few Previous Work square feet. Faults with displacements of tens of feet or more are common and make it im- Reference has been made in the literature to possible to establish the sequence of beds. the geology of parts of the area by O. E. LeRoy Although only two faults with mappable (1908), C. Camsell (1918), and F. C. Bell displacements have been recognized in the et al. (1932). E. M. J. Burwash included re- field—one west of Mount Baldwin (PI. 1), the connaissance observations from the Garibaldi other at the south edge of the map-area near Lake area in his doctorate dissertation (1918). the head of RaSuse Creek—it is possible that H. T. James (1929) has made a detailed survey the irregular outline of the areas of meta- of the Britannia Beach map-area which adjoins volcanic and metasedimentary rocks elsewhere the Mount Garibaldi map-area on the south. may be attributed in part to large-scale faulting. Full descriptions of mining properties on Ray Most of the rocks of this unit have undergone and Raffuse Creeks are given in the 1937 dynamic metamorphism with the development annual report of the Minister of Mines of of chlorite, but not biotite. Schistosity is most British Columbia by B. T. O'Grady (1938), marked in the vicinity of the quartz diorite and briefer descriptions of these and other intrusive rocks, and two areas remote from properties of the map-area are given in earlier these intrusive rocks—one northeast of Daisy annual reports of the same series. Lake, the other on Goat Ridge west of Sky Pilot Mountain—are notably unsheared. A Acknowledgments considerable area at the latter locality is, moveover, marked by nearly horizontal bed- The University of California gave financial ding. aid in the prosecution of this study, and Drs. At least a part of this map unit can be cor- F. J. Turner, Howel Williams, and C. R. related with the contiguous Goat Mountain

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LEGEND

^70 Strike ond dip of bedding -^"70 Strike and dip of foliation -*" vertical foliation M Migmatites '-"" Contact -accurately located Contact -ill defined, poorly •'" located, or concealed P" 1 Metovolconic ond metosedimentory rocks r^"3 Upper Cretaceous stratified rocks J J Plutonic rocks Foliated rocks - intensity of deformation indicated by density of line pattern, trends inferred from attitudes of the foliation Fault — located Fault — inferred

FIGUEE 1.—TECTONIC MAP OF THE MOUNT GARIBALDI MAP-AREA

Formation of the Britannia Beach map-area of these rocks has been found, other than that (James, 1929, p. 15-24), but it has not been they antedate the Cloudburst quartz diorites possible to recognize in the Mount Garibaldi which are themselves pro-Upper Cretaceous. map-area the three subdivisions of this for- Successions of metavolcanic and metasedi- mation. mentary rocks are common within southwestern The northernmost area of metavolcanic rocks, which differs from those farther south in con- British Columbia (Mathews, 1947, p. 34-37) taining lenses of limestone and in lacking in the upper Paleozoic, the Triassic, and the clastic beds, may be a distinct stratigraphic Jurassic, and the rocks of the Mount Garibaldi unit of a different age. map-area may correspond to one or more of No definite information on the age, or ages, these.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/69/2/161/3431746/i0016-7606-69-2-161.pdf by guest on 03 October 2021 TABLE 1.—STRATIGRAPHY Age Formation or Map Unit Lithologic Characters Thickness (feet)

Quaternary Alluvium, slide debris, lake beds Zero to several moraine, outwash hundred Terraced gravels and fanglomer- Zero to several ates, raised marine clays and hundred silts Garibaldi Group Andesite and basalt flows and Zero to several cinder cone; dacite flows, glow thousand ing avalanche deposits, and in trusives; rhyodacite intrusive Erosional unconformity Probably Post-Upper Castle Towers batho- Quartz diorite, trondhjemite, Cretaceous lith minor pegmatitic and other dikes (post-tectonic) Relations unknown Squamish batholith Granodiorite, quartz monzonite, minor pegmatitic and other dikes (post-tectonic) Relations unknown Post-mid-Upper Creta Younger quarts dio- Quartz diorite stock, dikes, sills, ceous rites major plutonic rock (syntectonic and post-tectonic) Intrusive contact Probably mid-Upper Helm Formation Cretaceous or later fifth member Paragneiss Several thousand (?) fourth member Principally slaty argillite, minor 3500± quartzite third member Conglomerate, quartzite, calcar- 2000± eous sandstone, sandy limestone, slaty argillite second member Slaty argillite, minor argillaceous 3250± quartzite first member Argillaceous quartzite, greenish 2000± arkose, conglomerate, argillite Fault contact Empetrum Forma- Metavolcanic rocks, limestone, Several thousand tion conglomerate, minor grit and argillite Fault contact Mid-Upper Cretaceous Cheakamus Forma- tion upper Greenish conglomerate, gray- 3000± wacke middle Stratified graywacke, arkose, ar- 1000± gillaceous and calcareous beds, locally fossiliferous Massive green graywacke 5000± lower Greenish and grayish conglomer- Few hundred to sev- ate, arkose, argillite. eral thousand (?) Erosional unconformity Pre-Upper Cretaceous Cloudburst quartz Major pluton or plutons of diorites quartz diorite, diorite; quartz feldspar porphyry; ortho- gneiss, augen gneiss, mylonite, green and white schists Intrusive contact Metavolcanic and Massive greenstone, breccia, metasedimentary conglomerate, slaty argillite, rocks limestone; green schist Base concealed 164

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Plutonic Rocks—Part 1 quartz diorites make up almost two-thirds of the exposed basement rocks. Two plutons, General Statement.—Granitic rocks underlie separated by a discontinuous belt of metavol- the greater part of the map-area and can be canic and metasedimentary rocks (Fig. 1) may subdivided into at least four map units. The be present, but it has not been possible to largest of these, a heterogeneous assemblage of recognize significant differences between the foliated and unfoliated quartz diorites1 and diorites, is clearly overlain unconformably by TABLE 2.—SURFACE AREAS OF MAP UNITS the mid-Upper Cretaceous Cheakamus formation and is referred to here as the Cloud- (Total area mapped—370 square miles) burst quartz diorites. Several bodies intrusive Percentage Percentage at into the Upper Cretaceous beds will be re- Map Unit at Present Pre-Gari- ferred to as younger quartz diorites. The Surface baldi surface western segment of another large pluton made up of quartz diorite and trondhjemite in the Lakes, Howe Sound 3.6 northeastern corner of the map-area will be Glaciers 6.1 referred to as the Castle Towers batholith. Moraines 1.0 Finally, a mass of quartz-rich granodiorite and Alluvium, slide debris 6.4 quartz monzonite in the southwestern part of Terrace gravels, fanglom- 1.7 the map-area will be referred to as the Squamish erate — batholith and a smaller body of the same rocks 18.8 near-by as its satellite stock. Although neither Garibaldi group rocks 15.7 the Castle Towers batholith nor the Squamish Younger plutonic rocks batholith and its satellite are in contact with Castle Towers batholith 3.5 5.4 the Upper Cretaceous beds, all have escaped Squamish batholith 7.6 11.6 the extensive deformation which has tilted and Younger quartz diorites 0.3 0.5 block faulted the stratified rocks and the plutonic rocks are, therefore, considered to be 11.4 17.5 younger than mid-Upper Cretaceous. Stratified rocks of the Gari- Most if not all of the plutonic masses of the baldi Lake area map-area can be grouped within the Coast Helm Formation 1.1 intrusions, to use the term now adopted by the Empetrum Formation 0.2 Geological Survey of Canada in place of the Cheakamus Formation 2.9 misleading title Coast Range batholith for the great plutonic complex exposed in and adjacent 4.2 6.4 to the Coast Mountains of British Columbia, Older plutonic rocks Alaska, and Yukon Territory. Should the term Cloudburst quartz diorites 40.9 62.4 Coast intrusions be restricted to pre-Tertiary Metavolcanic and meta- 7.4 11.3 plutonic rocks as proposed by Rice (1947, sedimentary rocks p. 33) in his original definition, or more specif- Migmatites of various ages 1.6 2.4 ically to syntectonic or pretectonic intrusions as suggested by Aitken (1955, p. 1701), the Castle Towers and Squamish batholiths would not be rocks on either side of the belt of metamorphic included nor would the quartz diorite stock on rocks, and all may be the product of a single the north shore of Garibaldi Lake. intrusion. The diversity in character and age of the Quartz diorite predominates in these older plutonic rocks of the map-area conforms to the plutonic rocks, but locally more basic rocks, observations of Cairnes (1924, p. 82-108), such as the diorite of Cheakamus Canyon, or Dolmage (1929, p. 85-87), Duffel and Mc- more siliceous rocks, such as the quartz- Taggart (1952, p. 78-83), and a few others feldspar-muscovite schist of Watson siding, are regarding the composite nature and extended important. Potassium feldspar is absent or age range of the granitic masses in the western nearly so in all rocks of this unit. In some areas part of the North American Cordillera. later stocks or dikes may be included, but all Cloudburst quartz diorites.—The cloudburst have apparently had a similar tectonic history. Three mutually gradational structural types 1 Lindgren's divisions are used in the classifica- can be recognized: (1) unfoliated quartz diorite, tion of the granitic rocks. (2) quartz diorite and diorite with a primary

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foliation, and (3) quartz diorite with secondary assemblage, sodic feldspar-epidote-chlorite- foliation locally converted to mylonite. Mig- quartz, from what was presumably the original matites of limited areal extent also occur. assemblage, andesine - hornblende - biotite - UNFOLIATED QUARTZ DIORITE: Unfoliated quartz, marks a response to a low grade of and relatively unaltered quartz diorites occur dynamic metamorphism, tending toward the on both sides of Squamish Valley above the greenschist facies. Thin sections suggest that mouth of Cheakamus River. They are this postconsolidation deformation became characterized either by biotite and hornblende more intense toward the northeast in the or by hornblende alone. No systematic dis- Cheakamus Canyon area. tribution of these two types is evident. The SECONDARILY FOLIATED QUARTZ DIORITES: oligoclase or andesine commonly displays in- Secondarily foliated rocks have been studied in cipient saussuritization. Similar fresh to most detail in a northwestward-trending belt slightly altered quartz diorites are present in up to 4 miles wide north and east of Cloudburst upper Mamquam valley, northwest, north, and Mountain where they are made up of sheared east of Mount Garibaldi and along the lower quartz diorites, augen gneisses, and mylonite. slopes of Squamish Valley below Cheakamus Probably no part of the quartz diorite of this River. belt has escaped some deformation. Intensity PRIMARILY FOLIATED QUARTZ DIORITES AND of shearing varies markedly within even a few DIORITES: Quartz diorites and diorites exhibit- feet, but it tends to increase toward the north- ing primary foliation are well displayed in east. Cheakamus Canyon for about 2}/£ miles along The least sheared of the quartz diorites in the Pacific Great Eastern Railway south of the this belt closely resemble the adjacent primarily Cheakamus bridge, and in adjacent areas east foliated rocks of the Cheakamus Canyon, but for almost 3 miles and northwest beyond the deformation and alteration has converted limit of the map-area. Strong preferred orien- original mafic minerals to ragged patches of tation of hornblende and biotite is obvious in chlorite. Where deformation has been more nearly all outcrops, and locally dark elongated intense the rock is an augen gneiss consisting of basic clots parallel this foliation. Planar struc- ellipsoidal to nearly spherical eyes of oligoclase ture is further emphasized in most thin sections in a fine-grained light to dark-gray matrix by a strong preferred orientation of the sub- consisting of granulated albite, quartz, musco- idiomorphic plagioclase crystals. The attitude vite, chlorite, and accessory minerals. The of the planar structure is rarely uniform for feldspar augen have neither the well-defined more than a few hundred to a few thousand crystal outline nor the strong orientation of the feet (Fig.l). Vertical air photos show on many plagioclase of the primarily foliated rocks. of the outcrops a fine-textured lineation paral- Chlorite occurs as minute oriented flakes leling the observed strike of the foliation. scattered through the groundmass or con- Abrupt changes in the trends of this lineation centrated into long subparallel or swirling occur at well-defined fracture traces. These trains, which, alone, render the foliation con- sharp changes in attitude and equally abrupt spicuous in many of the hand specimens. changes in rock texture and composition can Microscopic examination reveals similar trains best be attributed to widespread block faulting. of well-oriented muscovite flakes and of ran- Although the foliation here is ascribed to domly oriented quartz grains. Accessory movements of magma before complete con- minerals include sphene and apatite; epidote is solidation, all rocks studied in thin section not abundant; strongly zoned crystals of have undergone some later deformation. allanite occur in one thin section. Plagioclase grains commonly show undulatory Banded augen gneisses, consisting of streaks extinction, and their twin lamellae may be from 1 to 3 cm wide of chlorite-rich and chlorite- visibly bowed; biotite flakes are also commonly poor quartz diorite, occur in a few places. bent, and locally quartz is granulated and Neither field nor microscopic evidence indi- strung out along microscopic shear planes. At cates whether this banding has developed by least some epidote, which constitutes up to 8 some process of segregation during deformation per cent of the rock, may have developed or has been inherited from the original rock. during alteration of andesine to the oligoclase Should the direction of shearing parallel original which now predominates. Biotite is commonly banding, such banding could be retained, but green, and this mineral and to a less extent the should the two directions intersect the later hornblende are partly converted to chlorite. movement might destroy the earlier foliation. The incomplete development of a new mineral Chance parallelism of the two directions may

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explain the apparently irregular distribution of sive rocks are unknown. Banded migmatites are the banded augen gneiss. common in the Cloudburst quartz diorites of The structure and mineral assemblage of the northern, western, and southwestern these secondarily foliated rocks indicate intense slopes of Castle Towers Mountain where they low-grade dynamic metamorphism in which occur as bodies up to a mile long and a third of original quartz diorites, and perhaps mig- a mile wide. Both the migmatite bodies them- matites, have been converted to rocks of the selves and the banding within them have a muscovite-chlorite subfacies of Eskola's green- northerly to northwesterly trend. Migmatites schies facies (Turner, 1948, p. 96). The same also occur on the south face of Viking Ridge mineralogical alterations noted in their near the southwestern contact of the Castle incipient stages in the orthogneisses of Towers batholith. Many of the occurrences may Cheakamus Canyon are here essentially com- be relics of the former roof and wall rocks of plete. the plutonic rock; others such as that of Cloud- Sheared quartz diorites also occur in the burst Mountain, may be the foliated part of southern and central parts of the map-area on the Cloudburst quartz diorite itself migmatized either side of and along the extension of a belt during later intrusion of the unfoliated part. of older metavolcanic and metasedimentary Other migmatites within the belt of secondarily rocks. The quartz diorites are here so strongly foliated quartz diorites may have been partly sheared, and chlorite is so widely developed disguised by shearing. that many of the resulting rocks cannot be STRUCTURE OF THE CLOUDBURST QUARTZ distinguished in the field from metavolcanic DIORITES: The structure of the Cloudburst rocks, and only their general uniformity and the quartz diorite intrusive rock, though complex, absence of interbedded sedimentary rocks permits some generalizations. The quartz suggest a plutonic origin. Thin sections of these diorite is intensely sheared almost everywhere rocks reveal lenses of granulated quartz and along its contact with older rocks (Fig. 1). eyes of albite or oligoclase such as could form Such shearing extends locally as much as 4 from quartz diorites, or quartz-feldspar miles into the plutonic rock. The older bedded porphyries. Inasmuch as quartz porphyries are rocks are also sheared but only within a few not known in the unsheared metavolcanic hundred to a few thousand feet from the quartz rocks except as intrusive masses, the inclusion diorites. The sequence of rocks from wall to of these schistose green augen gneisses with core of the intrusive rock, best displayed along the plutonic rocks seems justified. Precise Cheakamus Valley, consists of (1) unsheared delineation of the contact between green greenstones and other constituents of the wall schists of plutonic origin and those of volcanic rocks, (2) green schist derivatives of the wall origin, however, remains far from satisfactory. rocks, (3) schistose quartz diorites, augen MIGMATITES: Migmatites are present in a gneisses, and mylonites developed from the few localities within both the foliated and intrusive rock itself, (4) primarily foliated unfoliated quartz diorites. The higher part of quartz diorite and diorite, and (5) unfoliated Cloudburst Mountain is an intrusion breccia quartz diorite. Here a general gradation exists consisting of migmatite in numerous angular between the first two and last three, but the unoriented blocks, from a fraction of an inch to contact between wall rocks and quartz diorites scores of feet across, frozen in a matrix of un- is concealed. Elsewhere the succession is foliated quartz diorite. The belts of ortho- similar except that primarily foliated rocks gneiss and secondarily foliated quartz diorite have not been detected, and in two localities extending across Cheakamus Valley are here the unfoliated quartz diorites are in direct truncated by the unfoliated quartz diorite, and contact with secondarily foliated quartz possibly many of the banded migmatites have diorites along a zone of intrusion breccia. In been developed from the foliated rocks. The some places belts of primarily foliated rocks relationships on Cloudburst Mountain are re- may have escaped detection. The contact peated on the southwestern slope of Tricouni between wall rocks and quartz diorite is Mountain, 1 mile north of the northwest corner commonly disguised by the intense shearing. of the map area (Fig. 1). Here, however, some The apparent gradation between unfoliated amphibolite is included in the migmatite and and foliated quartz diorites suggests that all possibly some of the metamorphic roof rocks were originally part of a single body of quartz may be present. Migmatites also occur on Brew diorite magma. Deformation affecting the wall Mountain, 2 miles northeast of Tricouni Moun- rocks and outer part of the intrusion had no tain, but here the relationships to younger intru- influence on the core but did give rise locally

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to primary foliation in an intermediate zone. sedimentary rocks. The time of plutonic in- Movements may have taken place when the trusion in the southern Coast Mountains is now outer part of the intrusive rock was completely known to extend back to the Middle or Lower solid, the intermediate zone partly consolidated, Jurassic (Duffel and McTaggart, 1952, p. 79), and the core still molten. Later, a part of the and in the absence of evidence of a still earlier molten core may have invaded the sheared age, the Cloudburst quartz diorites may margins to give rise to the internal disconform- tentatively be referred to the Jurassic or Lower ities, the intrusion breccias of Cloudburst and Cretaceous. Tricouni Mountains and of the southwestern If the cataclastically deformed marginal base of Brohm Ridge, and possibly the mig- phases of the Cloudburst quartz diorites are to matites of Cloudburst Mountain. Then move- be regarded as a product of autometamorphism ment ceased, and the central portion con- rather than an expression of external tectonic solidated without development of flow forces, there can be little other than age de- structures. terminations by radioactivity on which to base The localization of shearing around the correlations with other plutonic rocks in the margin of the pluton, the variations in its trend, Coast Mountains. In the "southwestern area and the absence of foliation in some of the of batholic rocks" of the Britannia Beach map- near-by wall rocks suggest that deformation area, however, James (1929, p. 45-49) finds a originated locally rather than from regional sequence of primary and secondarily foliated tectonic movements. These characteristics are granitic rocks which closely parallels that in like those of the Colville batholith of Washing- the Cheakamus Valley. He states: ton, with its protoclastic border, which Waters and Krauskopf (1941) attribute to stresses "the four specimens show that the nature of the granitic rocks varies as the contact is approached originating in the upward movement of the and that the variations are of a uniform and pro- batholith during emplacement. Three distinc- gressive type. Within the line of section all the rocks tions between the two plutons, however, are are foliated; but at 3,000 feet from the contact, noteworthy: (1) foliation in the Cloudburst the parallel orientation of the grains was brought about during the crystallization period of the magma quartz diorites of the Mount Garibaldi map- and is, essentially, a primary structure. As the area is almost invariably steeply dipping, contact is approached, this primary foliation is whereas in the Colville batholith it describes obliterated by a later shearing, which is parallel to broad domes and arches with dips only locally the primary structure, and which becomes more intense until the rock, at the very contact, is com- exceeding 30°, (2) foliation in the Mount pletely recrystallized." Garibaldi map-area locally cuts across the contact between intrusive and older rocks, He notes, too, the presence of sodic plagioclase whereas in the Colville batholith it almost in- in the sheared rocks and the development in a variably parallels this contact, and (3) no few localities of chlorite and sericite. These zone of swirled and porphyritic gneisses is de- rocks of the Britannia Beach map-area had a veloped in the Cloudburst quartz diorites as it similar geologic history to that of the Cloud- is in the Colville batholith. Notwithstanding burst quartz diorites and may be of the same these distinctions the two plutonic rocks may general age. have had a similar history. Some of the younger quartz diorites at the A possible objection to the hypothesis of northern edge of the map-area are also sheared deformation during, and by, intrusion lies in and closely resemble some of the Cloudburst the low grade of metamorphism in the sheared quartz diorites although clearly of a different rocks. Even in the orthogneisses showing in- age. The shearing of these younger rocks was cipient cataclasis biotite had become an un- probably accomplished by external forces stable mineral before movement ceased, and at which also tilted and faulted the adjacent the time these rocks were in the lowest or Upper Cretaceous sediments, and not by auto- chlorite zone of dynamic metamorphism where metamorphism. If so, the core of the Cloud- temperatures must have been relatively low. burst quartz diorites has escaped this later Such a condition is at least unexpected in the deformation, and the record of such deforma- broad marginal portion of a batholith pre- tions cannot be used as reliable age criterion. sumed to have a still-molten core not more than 2 miles distant. Stratified Rocks near Garibaldi Lake AGE AND CORRELATION: The Cloudburst quartz diorites cut metavolcanic and meta- General statement.—Stratified rocks, chiefly sedimentary rocks of uncertain age and are clastic sedimentary rocks, underlie most of the overlain unconformably by Upper Cretaceous map-area north and northwest of Garibaldi

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Lake. These are subdivided into three map found 1 mile to the north on the lower slopes units, here called the Cheakamus, Empetrum, of Rubble Creek valley and again on the hill- and Helm formations, which appear to be side southeast of Daisy Lake. Both grayish associated with one another in time and in and greenish tints prevail in the coarser beds. circumstances of origin as well as in present Many of the rocks, especially those with a spatial distribution. All three formations in- grayish argillaceous matrix, are highly sheared. clude conglomerate beds containing abundant Bedding is inconspicuous, and the few observa- granitic fragments, hence all three postdate tions indicate widely varying attitudes. In the first period of batholithic intrusion in or view of the relatively narrow width of this near the map area. All three formations are belt of rocks, however, probably not more than cut by later granitic rocks. Only the Cheaka- a few hundred feet of beds are present. mus Formation has to date yielded fossils, and The middle part of the Cheakamus Forma- the range of time over which these rocks were tion is an exceedingly uniform and massive being deposited remains unknown. The middle green graywacke in which stratification can part, and presumably all, of the Cheakamus only very rarely be detected. Much of this Formation is of mid-Upper Cretaceous age. graywacke might be confused in hand specimen This formation rests directly on the Cloudburst with greenstone but can be distinguished from quartz diorites and is probably the oldest of the latter rock with the aid of the hand lens the three units. The Empetrum and Helm by the abundance of minute quartz grains. formations may have been deposited later in Pebbles, generally less than 1 inch in diameter the Upper Cretaceous. occur at a few localities either singly or clustered Interpretation of the stratigraphic succession in small lenses. Observations on a few of these of these rocks is made difficult by the almost pebble lenses and on the rare and obscure complete absence of well-defined horizon stratification indicates that this member has a markers as well as by structural complexity. rather consistent easterly dip of 45°. This, and Few beds are sufficiently distinctive to be the observed outcrop width of approximately 1 traced in the field even in areas of good ex- mile, suggests a stratigraphic thickness of at posure, and these beds can rarely be followed least 5000 feet. The massive graywacke is for more than a few hundred feet before they overlain on the east by about 1000 feet of terminate abruptly, apparently against trans- similar greenish sandstones in which stratifica- verse faults. Most of the major subdivisions of tion is revealed by an alternation of beds pale the formations, however, have a much greater green noncalcareous and darker green with continuity, and probably most transverse faults calcareous cement commonly from 20 to 50 are small. A few larger discontinuities have feet thick, as well as by local color bands a few been recognized in the field, and several have inches thick. A few strata are rich in pebble been identified as either a single major fault bands or shell fragments or both. Brown- or a composite pattern of small faults. Con- weathering black argillaceous beds are locally ceivably other major discontinuities, notably present, and a bed of dark-gray coquina about those between the three formations, may be 20 feet thick occurs near the base of the West unconformities with marked overlaps. Bluff of The Black Tusk. Well-developed cross Changes in lithologic facies may also con- bedding and less common ripple marks exist tribute to difficulties in mapping, although in some of the sandstones. What is probably a few such changes can be demonstrated. single horizon extending north and northeast Cheakamus Formation.—The Cheakamus from The Barrier to the base of the West Formation, exposed on the eastern slopes of Bluff is marked by several fossiliferous out- Cheakamus Valley, after which it is named, crops yielding fragmentary to nearly complete consists mainly of green arenaceous and con- shells of large Inocerami. glomeratic beds having a general easterly dip. Thin sections of graywackes from the middle The base of the formation is exposed at one members of the Cheakamus Formation show locality, 1}.^ miles southeast of Garibaldi sta- that detrital grains of quartz and plagioclase tion, where massive conglomerate, made up of predominate in the rock. Fragments of mylo- boulders of granitic rocks and of greenstone up nite, like that in the secondarily foliated Cloud- to 2J-£ feet in diameter, rests directly on highly burst quartz diorites only a few miles to the sheared Cloudburst quartz diorite. Higher west are common. Grains of epidote, amphibole, parts of the succession are not exposed in this sphene, and black opaque minerals are also immediate locality, but similar conglomerates, present. Grains of allanite, like that in one interbedded with coarse sandstone, a gray- specimen of the Cloudburst quartz diorites, (13) wacke, and minor gray to black argillite, are were seen in one thin section. The source of

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scattered microcline grains on two thin sections schists are common, and pebbles in the con- is unknown. The matrix of the graywackes is glomerate and markedly distorted. The elonga- commonly chlorite, and it is this mineral which tion of the pebbles, a linear schistosity, and the contributes the green color to so much of the axes of small folds plunge 30-40° to the south- rock. Sericite forms the matrix of some of the east. No definite sequence can be recognized, lighter-colored beds. Cubes of pyrite are and repetition by folding, if not by faulting, is locally present. probable. The width of the formation measured The uppermost part of the Cheakamus For- perpendicular to the strike is at least 1 mile mation, exposed on the higher slopes south and dips average 45° to the northeast; up to and east of The Black Tusk and on the north- several thousand feet of beds may be present. western slopes of Panorama Ridge, consists of Helm Formation.—The Helm Formation is an alternation of greenish coarse pebble con- so named from its exposures on the south- glomerate and distinctly stratified greenish western, southern, and eastern margins of graywacke. Bedding dips eastward or north- Helm Glacier. This formation underlies a total eastward at from 10° to 55°, and as the width area of about 6 square miles of which about of this belt of rocks reaches \% miles a strati- 25 per cent is concealed beneath ice or Quater- graphic thickness of at least 3000 feet is indi- nary volcanic rocks. The succession of sediments cated. A massive sandstone member exposed on from Panorama Ridge on the southwest to the Garibaldi and Lesser Lakes and on the bench slopes above Cheakamus Lake on the north- half a mile to the north is not identifiable west east can be subdivided into 5 more or less of The Black Tusk. distinct members. A succession of grayish and greenish con- The lowest member, fully exposed on the glomerate and graywacke and lesser amounts of south face and west end of Panorama Ridge, is white to flesh-colored arkose and gray to black made up almost exclusively of arenaceous argillite is exposed in the northern part of the sedimentary rocks: bluish-gray argillaceous area mapped as Cheakamus Formation. These quartzites and less common pale greenish rocks are separated from the sequence already graywackes predominate; conglomerates, con- described by an easterward-trending fault, and taining granitic fragments, and argillites occur their stratigraphic position remains in doubt. in a few widely scattered beds. A thickness of Attitudes on bedding are highly variable but 2000 feet has been measured on the south face commonly high, and judging from the 1>£- to of the ridge. On the north face, where the 2-mile outcrop width, several thousand feet of contact with the Cheakamus Formation trun- sedimentary rocks may be present. Lithologi- cates the bedding, only the uppermost few cally they most closely resemble the lowermost hundred feet of this member are present; still few hundred feet of the Cheakamus Formation, farther north the member is absent. as typically developed near Rubble Creek and The second member, present but rather Daisy Lake, but the apparent differences in poorly exposed on and near the eastern end of thickness make this tentative correlation far Panorama Ridge, consists of massive argil- from certain. laceous quartzites and slaty argillites. The Empetrum Formation.—The Empetrum For- latter rock is subordinate to the quartzites in mation is confined to a triangular area 2 miles the lower part of the member but predominates long and 1 mile wide on Empetrum Ridge, in the upper part. Stratification is exceedingly after which the unit is named, and on the obscure throughout most of the succession, and neighboring ridge to the west. Much of the the few observations on argillaceous beds indi- formation is made up of greenstone and green- cate not only that these are highly and irregu- stone breccia derived in part from amygdaloidal larly contorted, but also that they bear no and porphyritic lavas and in part from tuffs or constant relation in attitude to slaty cleavage. graywackes. Lenses of white to cream-colored Three attitudes on stratification in quartzite limestone, commonly containing lime silicate are more consistent and indicate an easterly minerals and minor cream-colored dolomite, are dip averaging about 45°. This and the outcrop present throughout the succession. Conglomer- width of about 0.9 miles, indicate a strati- ates containing abundant partly rounded graphic thickness of about 3250 feet. granitic pebbles and boulders occur at several Most of the third member is concealed by localities near the northern end of Empetrum the eastern part of Helm Glacier, but limited Ridge. Argillite and coarse gray sandstone exposures occur near both source and terminus have been observed at one place in this same of this body of ice. At the base, near the east area. Much of the succession is highly sheared: tongue of Helm Glacier, a zone of conglomerate

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and quartzite rests with a sharp but apparently minerals, indicative of stress, the argillaceous conformable contact on the underlying argil- rocks southeast of Helm Peak contain un- lites of the second member; the corresponding oriented prisms of andalusite indicative of beds !'.£ miles southeast are quartzites and thermal rather than dynamic metamorphism. calcareous sandstones. The middle part of the Garnet locally present in the migmatites sug- succession consists of coarse sandstone charac- gests a higher grade of metamorphism than terized by grains of both clear and bluish- has been recognized elsewhere in the map-area. opalescent quartz and by abundant dark The Empetrum Formation is distinctly minerals, overlain by pale-grayish-brown cal- sheared, and the effects of deformation are careous sandstone and sandy limestone. A few noticeable in the squeezing of the pebbles in beds of slaty argillite are present. In the upper the conglomerates. The development of lime- part of the member, made up chiefly of dark silicate minerals and the preservation of dolo- argillaceous quartzite, slaty argillite is con- mite provide some limits to the grade of meta- spicuous, and at the contact with the overlying morphism. fourth member it becomes predominant. What Internal relationships.—The contact between appears to be a complete and relatively un- the Cheakamus and Helm formations is con- disturbed succession of beds of the third mem- cealed by moraine over much of its length and ber, half a mile to 1 mile northeast of Gentian by a small body of ice on the north wall of Peak, is about 2000 feet thick. Panorama Ridge. On the crest of the ridge The fourth member consists predominantly arenaceous beds near the base of the Helm of stratified argillite with minor quartzite. Formation are in contact with beds high in Bedding dips rather regularly at from 35° to the middle member of the Cheakamus Forma- 55° to the northeast and north across the full tion. Half a mile to the north argillaceous outcrop width, approximately 1 mile. The beds 2000 feet higher in the Helm Formation stratigraphic thickness is hence about 3500 adjoin conglomeratic beds of the Cheakamus feet. Formation also about 2000 feet higher in the Rocks still higher in the succession, exposed section than at the first locality. The stratifica- north and northeast of Corrie Peak, have been tion in the two formations is nearly parallel. dynamically metamorphosed, and their original If the contact between the formations is dep- character is uncertain. They now consist of ositional, a striking disconformity exists. A amphibole- and amphibole-biotite gneisses con- fault relationship is more probable, but the taining abundant quartz and plagioclase; the existence and attitude of the inferred fault has plagioclase occurs in some places as oligoclase not been established. porphyroblasts. Chlorite, epidote, sphene, The Empetrum Formation is separated from pyrite, and garnet are locally present. Both the upper part of the Cheakamus Formation amphibole and biotite exhibit a strong pre- by later intrusive rocks and by a cover of ferred orientation which with the larger-scale moraine and Quaternary volcanic rocks, and banding dip about 45° northeastward and from the middle part of the Helm Formation parallel the bedding in the slates to the south- by either an angular unconformity, or more west. If the banding in these altered rocks probably by an extension of the fault separating corresponds to bedding in original silica-rich the Helm and Cheakamus formations. If the sedimentary rocks a stratigraphic thickness of faulted relationship applies, the Empetrum at least several thousand feet may be present, Formation can best be regarded as intermediate and the upper limit has not been determined. in age between the Helm and Cheakamus for- Metamorphism.—The general metamorphism mations and eliminated by the fault everywhere of the Cheakamus Formation has been barely south of Empetrum Ridge. sufficient to recrystallize the chlorite occurring Age and correlation.—The age of the Cheaka- in interstices of the graywackes, conglomerates, mus Formation has been established by the and arkoses. Inocerami obtained from the upper part of the No significant metamorphism has been noted middle member of this formation at two lo- in the lower part of the Helm Formation on calities, one immediately northwest of The Panorama Ridge, but the higher part of this Barrier, the other a third of a mile west of the formation, southeast of Helm Peak, is distinctly west bluff of The Black Tusk. These were sub- metamorphosed, and the uppermost part, mitted for identification in 1947 to C. R. northeast of Corrie Peak, is extensively so. Stelck, then a Ph.D. candidate in paleontology Although the gneisses of the latter locality at Stanford University. Stelck found sufficient show strong preferred orientation of mafic material in the collection from the second

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locality, notwithstanding the distorted and Mountain Formation (James, 1929, p. 16). fragmentary preservation, to recognize two These isolated occurrences are not sufficient in species, ". . . Inoceramus cf. 7. vancouverensis themselves to justify the assignment of a Shumard and Inoceramus cf. /. schmidti post-mid Mesozoic age to these two formations. Michael..." These can be compared with The Mount Lomond arkose of this same area, specimens collected from Sucia Island, 80 however, is reported to contain an appreciable miles south of the occurrence in the Mount amount of detritus from granitic rocks (James, Garibaldi map-area. The former "species 1929, p. 9-10), and the possibility that this belongs to the widespread group of affiliated unit may correspond to the Cheakamus Forma- Inocerami referred to /. balticus and I. barabini, tion should be investigated. etc. occurring in the Senonian of Sucia Island, Japan, Europe, interior of North America". The Plutonic Rocks—Part 2 latter resembles species found in the Senonian of Europe and Japan, notably a Japanese form Younger quartz diorites.—The younger quartz 7. japonicus var 7 Nagao et Matumoto. "The diorites occur as several separate masses in and Senonian age is well established." adjacent to the Upper Cretaceous bedded rocks Although correlative rocks of Sucia Island of the northern part of the map-area. The body are part of the Nanaimo series (McLellan, which underlies at least 5 square miles near 1927, p. 121-122, Buckham, 1947, p. 461-462, Empetrum Ridge may extend over a very much Usher, 1952, p. 57-17), extending for 125 miles greater area and be genetically related to the northwestward, these two species of Inoceramus gneisses northeast of Corrie Peak. The three have not been reported at any other locality other masses of younger quartz diorite large in the vicinity. Lithologic correlation of the enough to be indicated on the map are exposed Cheakmus Formation and some part of the over a total area of only 0.45 square miles, Nanaimo series has not proven possible. No but an undetermined proportion of the stock volcanic rocks are known in the Nanaimo on the north side of Garibaldi Lake is concealed series that might correspond to the Empetrum by water. Formation. The younger quartz diorites are so similar No sedimentary successions of known Upper lithologically to some of the varieties of the Cretaceous age have hitherto been reported Cloudburst quartz diorites that, were it not from the southern Coast Mountains, and for their relationships to the stratified rocks, no paleontologic correlations with rocks of other age distinction would have been recognized. areas in this mountain chain are not possible. All the younger quartz diorites are notably de- The abundance of granitic debris in the ficient in potassium feldspar, as are their older Upper Cretaceous sediments of the map-area counterparts. Plagioclase is the predominant and its apparent absence in the older meta- mineral in all specimens, and quartz is con- volcanic and metasedimentary rocks probably spicuous. The chief original mafic mineral has local value as a basis for age determination. appears to have been hornblende, but in most Similar granitic debris is abundant in known places this has been altered to chlorite which Lower Cretaceous rocks, and occurs locally in only locally preserves the crystal outline of the Upper or Middle Jurassic rocks of the southern former mineral. Feldspar grains, some of which Coast Mountains and adjacent areas (Duffel are partly altered to epidote, generally present and McTaggart, 1952, p. 31); in still older their original euhedral form. Quartz has not rocks it is uncommon if present at all. The been notably brecciated. Discrete intersecting granite-bearing conglomerates of the Cheaka- shear planes are common between the crystals mus Formation, formerly thought to be Triassic of quartz and plagioclase and are rendered or older, have been used to support the con- conspicuous by films of chlorite or sericite or tention that pre-Triassic plutonic rocks were both. Locally, where these shear planes are once exposed in their vicinity (Schofield, 1941, numerous and subparallel, the rock breaks and others), but such a conclusion must now readily into platy fragments or flakes; in other be set aside. In the Britannia Beach map-area places where the shear planes may be widely a few plutonic fragments have been reported spaced and intersect at large angles the rock in conglomerate of the Britannia Formation breaks into irregular rhombohedral fragments. (LeRoy, 1908, p. 15) and in a lava flow of this The stock on the north side of Garibaldi Lake same unit (James, 1929, p. 13), and boulders is, however, undeformed, presents a simple of feldspar and quartz-feldspar porphyries are joint pattern, and contains unaltered horn- present in a conglomerate in the lower Goat blende and biotite. The quartz diorite of sills

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cutting the Helm formation around the margins part of Squamish Valley 4 miles northeast of of Helm Glacier and north of Helm Peak is also the town of Squamish. The "northwest area of undeformed. batholithic rocks" in the Britannia Beach That the younger quartz diorites are clearly map-area (James, 1929, p. 53-54) is a part of intrusive into the stratified Upper Cretaceous the Squamish batholith. (?) rocks is shown by the tightly frozen contacts As seen in hand specimen, the granodiorite truncating the bedding of the wall rocks, by and quartz monzonite contains abundant associated metamorphic zones, and in the quartz, in grains up to 10 mm in diameter, case of the stock at Garibaldi Lake, by apoph- conspicuously zoned plagioclase, white to pink yses penetrating the adjacent strata. The untwinned feldspar, and biotite. The rock is sills in the Helm Formation have not been homophanous and lacks gneissic banding. The traced into the quartz diorite mass of the texture is remarkably uniform from place to northern edge of the map-area and may or place, although near the margins of the plutons may not be offshoots of this intrusive. some finer-grained varieties and basic inclusions The quartz diorite body at the south end of exist. Pegmatite dikes are present but rare. Empetrum Ridge has been intruded along a Microscopic study reveals rounded and probable fault contact between the Empetrum fractured grains of quartz making up 18-35 per and Cheakamus formations, and is itself some- cent of the rock, euhedral crystals of zoned what sheared. The schistosity of this intrusive oligoclase making up 30-55 per cent, either strikes parallel to its contacts and dips steeply microcline or perthite or both as interstitial northward roughly parallel to the schistosity in grains making up 5-28 per cent, and biotite, the bedded rocks on either side; it may reflect with or without minor hornblende, making up continued movement along the fault zone 5-20 per cent. Accessory minerals include after emplacement of the quartz diorite. apatite, sphene, and black opaque material; The quartz diorite at the northern edge of muscovite and epidote occur in very minor the map-area intrudes the Empetrum and Helm amounts as alteration products. formations, but its age relationship to the Little is known of internal structure. No Cheakamus Formation is undetermined. It is primary foliation has been recognized, and faulted against this formation along part of the such variations in composition as have been contact; the contact between quartz diorite noted cannot be related to distance from the and metavolcanic rocks farther northwestward walls of the intrusive rock or to altitude within may be an extension of the same fault. A broad it. Jointing is simple, consisting of three or tongue of quartz diorite extends along the line four joint sets intersecting at large angles to of inferred faulting between the Empetrum form conspicuous rectangular or triangular and Helm formations as if it intruded a pre- patterns on exposed surfaces. Joints are as a existing fault zone. Secondary foliation in this rule widely spaced, in places tens of feet apart. quartz diorite mass, as much as 1J^ miles from The pattern has apparently been developed by its contact, tends to parallel schistosity in the a simple arrangement of stresses in a single Helm and Empetrum formations. This body period of fracturing, probably during the of quartz diorite, like the one south of Empe- initial cooling and with little or no externally trum ridge, was probably intruded during an applied force. The simple jointing and the extended period of faulting and shearing. lack of any detectable interruption in the The stock on the north side of Garibaldi Lake smooth northeastern contact of the batholith is, on the other hand, undeformed. It invades suggests no faulting after intrusion. both the upper part of the Cheakamus Forma- The Squamish batholith has not significantly tion and the lower part of the Helm Formation altered or deformed its wall rocks. Cloudburst with no sign of an offset along the inferred quartz diorite at its contact with the Squamish fault separating these two stratigraphic units. batholith between Squamish River and Fries Squamish batholith,—The Squamish batho- Creek is typical but for a lack of hornblende; lith, a major pluton consisting essentially of instead greenish biotite and some chlorite in fresh granodiorite and quartz monzonite, is large aggregates of fine-grained flakes make up exposed on both sides of lower Squamish Valley about 20 per cent of the rock. The bedded and upper Howe Sound. That part of the pluton rocks of Goat Ridge within a few hundred feet within the map area is 10 miles long and up to of the batholith are flat lying and apparently 7 miles wide, and covers an area of almost 40 undisturbed by faulting. Some partly assimi- square miles. An outlier of the same rock, lated masses of these older rocks are found one-half by 1J£ miles, is exposed in the eastern within the marginal part of the batholith.

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A characteristic topographic expression is quartz diorite differ from this one macroscopi- imparted to the granodiorite and quartz monzo- cally chiefly in the proportions of light and nite by the scarcity of jointing and the sim- dark minerals; the rocks tend to be richer in plicity of the joint pattern. Long smooth cliff mafic minerals near the margins of the batho- faces with hardly a foothold for vegetation are lith than toward the center. common, and some of the valley walls rival in A white rock consisting essentially of oligo- steepness and height those of Yosemite Valley clase and quartz with minor orthoclase occurs in California. The narrowness and depth of the on Parapet Peak. This rock, unlike anything fiord valley of Howe Sound may be attributed hitherto described from the Coast Mountains for the most part to the joint control of glacial except perhaps the "sodic granodiorite" of plucking, although the smoothness of some the Vancouver area (Phemister, 1945, p. 67), exposures has been enhanced by glacial abra- approaches in chemical and mineralogical sion. Postglacial streams and weathering have composition Goldschmidt's trondhjemite. Like had little effect on the rock and, although it is the original trondhjemite, this quartz-rich rock susceptible to disintegration, many ice-pol- is notably deficient in potassium feldspar, al- ished surfaces remain. Talus piles are small though the amount present in the mode, ap- even though characterized by blocks of enor- proximately 10 per cent, is more than in Gold- mous size. schmidt's specimens. Roughly rectangular Direct evidence of the age of the Squamish oscillatory-zoned crystals of oligoclase, many batholith is lacking, except that it postdates with corroded or myrmekitic borders, make up the highly fractured Cloudburst quartz diorites about 60 per cent of the rock, and flakes of and the Goat Mountain Formation of James biotite less than 5 per cent. Interstitial grains, (1929). The absence of marked deformation about 35 per cent of the rock, consist pre- during and after intrusion, however, strongly dominantly of quartz and minor orthoclase. suggests that it is younger than the tilted and Accessory minerals include sphene, apatite, block-faulted Upper Cretaceous sedimentary black opaque grains, and clinozoisite; alteration rocks 15 miles to the north. products present in very minor amounts in- Castle Towers batholith.—The Castle Towers clude sericite and chlorite. batholith, made up of quartz diorite and minor A few well-defined dikes cut both quartz trondhjemite, is situated near the northeastern diorite and trondhjemite and consist of fine- corner of the map-area. About 20.7 square grained basic and acid rocks as well as pegma- miles of the batholith lies within the map-area, tites. A specimen of pegmatite from Parapet but 7.7 square miles is concealed by glaciers. Peak consists of a graphic intergrowth of Its extent beyond the boundaries of the map- quartz and microcline with minor muscovite area are imperfectly known, but recent re- and garnet. connaissance mapping by the Geological Survey The contact between trondhjemite and of Canada (Roddick and Armstrong, 1957) quartz diorite is concealed by glacial ice at the plus indications of structure in distant views one point where it was crossed, but the gradual suggests it extends without interruption east- decrease in the dark mineral contact of the ward 8 miles beyond the map-area and south- quartz diorite as the contact is approached ward to the northern slope of Mamquam suggests that the two rocks may grade into Mountain. If so, it occupies a roughly circular one another. Recent mapping (Roddick and area about 10 miles in diameter and about 85 Armstrong, 1957) indicates that the more acid square miles in area. rock underlies an elliptical area 3 miles wide Most of the mapped area of the batholith extending 7 miles southeast from Parapet consists of quartz diorite, massive and homoph- Peak, and thus occupies about 16 square miles anous except near the margins where a or almost 20 per cent of the area of the pluton. faint flow structure, shown either by preferred Regular jointing is characteristic. Three orientation of minerals or by successive lighter joint sets are typical and define roughly rec- and darker bands, parallels the steeply dipping tangular blocks. Two of the joint sets are walls. One sample, from the ridge north of steeply dipping, one nearly parallel to the Sphinx Mountain and about half a mile from nearest part of the batholith wall, the other the western contact, consists of about 60 per nearly normal to it. The strike of the third cent oligoclase, 20 per cent quartz, 10 per cent set is almost parallel to the margin of the hornblende, and smaller amounts of orthoclase, intrusive rock and the dip is about 15° toward biotite, sphene, epidote, apatite, sericite, and this margin. These attitudes persist in the black opaque grains. Other specimens of entire northwestern part of the batholith with

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but slight variations and conform with a radial faults with displacements comparable to those symmetry. No displacement has been observed in the near-by Upper Cretaceous rocks are on the steeply dipping joints, but thin pegma- likely to be undetected. tite dikes occupying a few of the gently dipping Notable divergences between foliation in the joints in quartz diorite show slickensides paral- metamorphic rocks and the adjacent contact leling the direction of dip. None of these fault are known. In one locality 2% miles northeast planes has been seen cutting banded quartz of Castle Towers Mountain the trend of band- diorite, hence the direction and amount of ing in amphibolite veers sharply northeastward, movement is undetermined. northward, then northwestward away from the The Castle Towers batholith is bounded on contact to describe a vertical fold; one limb the northwest, west, and southwest by a belt parallels the contact, the other the regional of metamorphic rocks several hundred feet to trend. Similar variations in attitude have been almost half a mile wide. North of Sphinx seen south of Viking Ridge where steeply dip- Mountain these metamorphic rocks consist ping foliation strikes southeastward, south- mainly of medium- to fine-grained biotite ward, and southwestward with increasing gneiss which grades with no apparent break into distance from the batholith. Between these two the Cloudburst quartz diorites. Microscopic localities the regional trend of structure is study of the gneiss reveals numerous small nearly parallel to the local trend of the contact, undeformed biotite flakes, showing a strong and variations in the attitude of foliation are preferred orientation, in a matrix of oligoclase, neither observed nor expected. having randomly oriented twin lamellae, and The batholith has apparently escaped all quartz, also lacking obvious preferred orienta- external deformation since its intrusion judging tion. If this rock is a metamorphic derivative from the simple joint patterns and the lack of of the Cloudburst quartz diorites, it was first major faults. subject to deformation, by which the original Direct evidence of the age of the plutonic coarse texture was reducted and the orientation rock is limited. It cuts Cloudburst quartz pattern of the biotite developed, and was then diorites, of pre-Upper Cretaceous age. Most recrystallized, enabling quartz, feldspar, and significant is the lack of external deformation, biotite to reform in an unstrained state. Un- suggesting intrusion after the period of block oriented porphyroblasts of hornblende in the faulting which affected the Upper Cretaceous gneiss west of Sphinx Mountain provide addi- sedimentary rocks only a few miles away. tional evidence of post-tectonic recrystalliztion. Chemical compositions.—The compositions of South of Sphinx Mountain the Cloudburst the various batholithic rocks, early and late, quartz diorites, only locally deformed, are are indicated by the chemical analyses of six separated from the Castle Towers batholith by representative rocks from the map-area (Table a belt of amphibolite, biotite schist, and migma- 3). These six analyses and four analyses from tite, much of it apparently derived from vol- the Vancouver area (Phemister, 1945, p. 66) canic and sedimentary rocks. Foliation in the are illustrated graphically on a Harker varia- immediate vicinity of the Castle Towers tion diagram (Fig. 2). Although rocks of at batholith approximately parallels its walls. least two ages are included, nearly all the Vertical lineation is locally developed. No points fall on a single set of smooth curves. diagnostic minerals, other than biotite, have Only the Castle Towers trondhjemite (SiOz = been found to indicate the grade of metamor- 71.2) and the Caulfeild "sodic granodiorite" phism. (SiC>2 = 70.0) depart significantly from the The boundary between these metamorphic curves; both are distinctly richer in Na2O and rocks and the Castle Towers batholith is sharp, CaO and poorer in K2O and Fe2O3 than the and xenoliths of the former or apophyses of the average for corresponding silica contents. latter are lacking. The contact, both in small With one exception the rocks from the Van- exposures and on valley walls, is nearly vertical. couver area are slightly richer in K2O than the At one place west of Castle Towers Mountain corresponding rocks of the Garibaldi area. the contact is displaced several feet by an The analyses also demonstrate the marked eastward-dipping reverse fault, a marginal range in composition possible within a single thrust associated with the intrusion of the pluton, as for example the variation from 54.6 batholith. No other faults, large or small, have per cent SiOz to 69.4 per cent SiC>2 within the been observed at the contact and, although Cloudburst quartz diorite. scattered upthrusts of the scale of the one The alkali-lime index, that is the silica observed could readily be missed, no major content at which CaO = K2O + Na2O (Pea-

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TABLE 3.—CHEMICAL ANALYSES AND NORMS OF THE PLUTONIC ROCKS All analyses by W. H. Herdsman, Glasgow, Scotland i 2 3 4 5 6

SiO2 65.29 54.60 69.37 71.23 60.42 73.63 AlsOa 16.86 18.97 16.48 16.09 17.39 14.12 FeO 2.24 4.96 1.83 1.23 3.55 1.75 Fe2O3 1.96 2.34 .94 .47 1.90 .92 TiO2 .46 .84 .32 .21 1.02 .24 MnO .14 .13 .12 Traces .12 Traces CaO 5.18 8.08 3.23 3.88 7.26 1.62 MgO 2.06 4.35 1.02 .50 2.81 .51 K2O 1.12 .42 1.36 1.57 1.03 3.04 Na2O 3.18 3.39 3.37 4.44 3.62 3.52 H2O, -105°C .12 .07 .07 .05 .16 .07 H20, +10S°C 1.43 1.45 1.92 .32 .46 .43 CO2 Nil Nil Nil Nil Nil Nil P205 .17 .33 .13 .08 .22 .06 Total 100.21 99.93 100.16 100.07 99.96 99.91 Specific Gravity 2.74 2.82 2.67 2.65 2.78 2.63

Quartz 27.93 8.25 35.47 29.90 16.12 36.55 Orthoclase 6.62 2.48 8.04 9.27 6.08 17.96 Albite 26.89 28.67 28.49 37.55 30.61 29.76 Anorthite 24.58 35.31 15.18 18.72 28.17 7.64 Corundum 1.41 3.90 .23 2.24 Diopside 2.13 5.19 Hypersthene 7.13 15.83 4.82 2.77 7.97 3.33 Magnetite 2.84 3.39 1.36 .68 2.75 2.24 Ilmenite .87 1.59 .60 .40 1.94 .46 Apatite .39 .76 .30 .18 .51 .14 H2O+ 1.43 1.45 1.92 .32 .46 .43 H2O- .12 .07 .07 .05 .16 .06 Total 100.21 99.93 100.16 100.07 99.96 99.91

MgO/FeO in mafics 72/28 64/36 53/47 45/55 67/33 38/62 Ab/An in feldspar 52/48 45/55 65/35 67/33 52/48 80/20 1. Cloudburst quartz diorite, 1 mile north of Cheakamus station. 2. Cloudburst diorite, south end of Cheakamus Bridge, P.G.E. Ry. 3. Cloudburst quartz diorite, northwest side of Lake Lucille. 4. Castle Towers batholith—trondhjemite, Parapet Peak. 5. Castle Towers batholith—quartz diorite, half a mile northeast of Sphinx Mountain. 6. Squamish batholith—granodiorite, three-quarters of a mile northeast of Squamish.

cock, 1931), is 65.5 in the Garibaldi rocks, one alkali-lime index of the Katmai suite is 63.8 of the highest values on record and in accord (Peacock, 1931), of the Mount Lassen suite with the generally high lime content of other 63.9 (Williams, 1932), of the Oregon intrusive igneous rocks in the western part of the North rocks 61.6 (Buddington and Callaghan, 1936), American cordillera. For comparison the and of the Sierra Nevada intrusive rocks 60.8

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FIGURE 2.—VARIATION DIAGRAM FOR THE COAST INTRUSIVE ROCKS OF THE MOUNT GARIBALDI MAP-AREA (LARGE SYMBOLS) AND THE VANCOUVER AREA (SMALL SYMBOLS)

(Buddington and Callaghan, 1936). The alkali- morphism in the Cascade Range in Oregon: Am. Jour. Sci., v. 31, p. 421-449 lime index of the Cenozoic lavas of the North Burwash, E. M. J., 1918, The geology of Vancouver Island of New Zealand is 62.7 (Benson, 1941), and vicinity: Univ. Chicago Press, 106 p. and MacGregor's data (1938) on the composi- Cairnes, C. E., 1924, Coquihalla area, British tion of West Indian lavas when plotted suggest Columbia: Geol. Survey Canada Mem. 139, 187 p. an alkali-lime index as high as 66.5. Camsell, C., 1918, Reconnaissance along the Pacific Specific gravities, as listed in Table 3, provide Great Eastern Railway between Squamish an approximate index to the chemical composi- and Lillooet: Geol. Survey Canada Summary tions of rocks in the Garibaldi suite. If the data Rept, for 1917, pt. B, p. 12-22 Dolmage, V., 1929, Gun Creek map-area, British are plotted on a silica content-density diagram Columbia: Geol. Survey Canada Summary a straight line can be drawn such that no point Rept, for 1928, pt. A, p. 78-93 departs from it by more than 2 per cent in Duffel, S., and McTaggart, K. C., 1952, Ashcroft silica content or more than 0.02 in specific map-area, British Columbia: Geol. Survey Canada Mem. 262, 122 p. gravity. James, H. T., 1929, Britannia Beach map-area, British Columbia: Geol. Survey Canada Mem. REFERENCES CITED 158, 139 p. LeRoy, O. E., 1908, Preliminary report on a portion Aitken, J. D., 1955, Granitic rocks of northern of the main coast of British Columbia and British Columbia and southern Yukon—some adjacent islands included in New Westminster regional aspects: Geol. Soc. America Bull., v. and Nanaimo districts: Geol. Survey Canada 66, p. 1701 Rept. no. 996, 59 p. Bell, F. J., Graves, H., and Foster, W. W., 1932, MacGregor, A. G., 1938, The volcanic history and Garibaldi Park and contiguous area: Rept, petrology of Montserrat: Royal Soc. London to the Hon. Minister of Lands, Vancouver, Philos. Trans., ser. B, no. 557, v. 229, p. 1-90 British Columbia (mimeog.), 70 p. McLellan, R. D., 1927, The geology of the San Benson, W. N., 1941, Cenozoic petrographic Juan Islands (Washington): Univ. Washington provinces in New Zealand and their residual Pub. in Geology, v. 2, 185 p. magmas: Am. Jour. Sci., v. 239, p. 537-552 Mathews, W. H., 1947, Calcareous deposits of the Buckham, A. F., 1947, The Nanaimo coal field: Georgia Strait area (British Columbia and Canadian Inst. Min. and Metallurgy Trans., Washington): B. C. Dept. Mines Bull. 23, v. 50, p. 460-472 113 p. Buddington, A. F., and Callaghan, E., 1936, O'Grady, B. T., 1938, Silver-copper and silver- Dioritic intrusive rocks and contact meta- copper-lead-zinc deposits; Squamish area:

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Minister of Mines, B. C., Ann. Rept, for 1937, evolution of the metamorphic rocks: Geol. p. F20-F28 Soc. America Mem. 30, 342 p. Peacock, M. A., 1931, Classification of igneous Usher, J. L., 1952, Ammonite faunas of the Upper rock series: Jour. Geology, v. 39, p. 54-67 Cretaceous rocks of Vancouver Island, British Phemister, T. C., 1945, The Coast Range batholith Columbia: Geol. Survey Canada Bull. 21, near Vancouver, British Columbia: Geol. Soc. 182 p. London Quart. Jour., v. 101, p. 37-88 Waters, A. C., and Krauskopf, K., 1941, Proto- Rice, H. M. A., 1947, Geology and mineral deposits clastic border of the Colville batholith: Geol. of the Princeton map-area, British Columbia: Soc. America Bull., v. 52, p. 1355-1418 Geol. Survey Canada Mem. 243, 136 p. Williams, H., 1932, Geology of the Lassen Volcanic Roddick, J. A., and Armstrong, J. E., 1957, Pitt National Park: Univ. Calif. Pub. Bull. Dept. Lake, British Columbia: Geol. Survey Canada ' Geol. Sci., v. 21, p. 195-385 map 8-1956 THE UNIVERSITY or BRITISH COLUMBIA, VANCOU- Schofield, S. J., 1941, Cascadia: Am. Jour. Sci., VER, BRITISH COLUMBIA v. 239, p. 701-714 MANUSCRIPT RECEIVED BY THE SECRETARY or THE Turner, F. J., 1948, Mineralogical and structural SOCIETY, DECEMBER 3, 1956

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