The object of this study is to establish the stratigraphy, structure, and petrology of early Tertiary rocks in the White Lake area near Penticton, British Columbia. This is achieved by field mapping and laboratory work. Early Tertiary rocks of the White Lake area, thought to be mainly Eocene age, consist of five main stratigraphic division; 1. discontinuous beds of basal breccia and conglomerate, 2. a thick and widely distributed succession of volcanic rocks of diverse composition - mainly phonolite, trachyte, and andesite lavas, 3. discontinuous volcanic beds - mainly rhyodacite lava, 4. locally thick volcanic sandstone and conglomerate beds inter-digitated with lahar and pyroclastic deposits, 5. local deposits of slide breccia and some volcanic rock overlain by fanglomerate beds. Each division rests with some angular or erosional unconformity on older rock. Aggregate thickness of the Tertiary strata, where best developed, is about 12,000 feet. These rocks are regionally downfaulted accounting, in part, for their preservation from erosion. Greatest downward movement is near the Okanagan Valley where, in places, it is estimated that basal beds exceed depths of -5,000 feet (m.s.l.). In general, beds are tilted easterly as if rotated downward forming a trap-door-like structure. Locally, folds are developed but these are without regional pattern and may be the result of simple flextures in the basement rocks. Petrographic and chemical data indicates a three-fold division of igneous rocks: 'A' series - mainly plagioclase porphyries; lavas of rhyodacite and andesite composition; 'B’ series - mainly two feldspar porphyries with co-existing plagioclase and sanidine; lavas of trachyte and trachyandesite composition; 'C’ series - mainly anorthoclase porphyries; lavas of phonolite composition and some tephrite. Phase diagrams and subtraction plots indicate that rocks of 'A' and 'C’ series were probably formed by crystal fractionation. In the case of 'A' series, precipitation of mainly plagioclase and pyroxene from andesite produces rhyolite; and for 'C’ series, precipitation of mainly pyroxene and some biotite from tephrite produces phonolite. Rocks of 'B’ series are intermediate in composition to 'A' and 'C’ and were probably formed by mixing of magmas. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Fatty Basin and Useless Inlet result from modification by water and ice erosion of depressions caused by Early Tertiary faulting. Uplift of the land due to post-glacial rebound is in excess of 6 m (20 ft) for the last 7000 years. Shallow entrance sills cause the inlets to act as traps for organic detritus brought in by tidal action. The rate of deposition of fine-grained suspended debris is in the range of 900 g/m² /year, with maximum deposition during late summer, when phytodetritus is most abundant. Five sedimentary environments exist in Fatty Basin, namely mud zones, rock slopes, beaches, deltas, and zones of strong currents. In addition to boulder accumulations and bedrock exposures, general categories of sediments are pebbles and gravels, terrestrial sands, shell debris, muds, and shell-gravel mixtures. Statistical analysis of the size distribution of 125 samples resulted in recognition of 8 groups of sediments, which were then subdivided into 13 types on the basis of composition and grain shape. Olive-green mud rich in organic matter covers almost three-quarters of the bottom surface in the Basin. Coarse terrestrial sands are derived mainly from bedrock exposures within about 300 ft of the shore, whereas most of the fine sands, silts, and clays originate from glacial sediments. The source area for glacial debris is in the Henderson Lake region, underlain dominantly by Karmutsen basalts. Shell debris, notably barnacle plates and calcareous worm tubes, is essentially confined to the rock-slope environment, where it accumulates in a narrow zone along the base of steep slopes. The rock-slope environment represents a preferred habitat for lobsters, because it offers better shelter and food supply than the other environments. In Fatty Basin, the total area most suitable to lobsters amounts to about 38,000 m² (=7% of the bottom surface), in Useless Inlet, this area covers 135,000 m² (= 5% of the bottom surface). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Wreck Bay is located on the west coast of Vancouver Island at 49°00'N, I25°38'W. It is roughly crescent shaped with a small cuspate foreland named Sand Point in the middle, and measures 2½ miles (2.17 kilometers) between the enclosing headlands of Quisitis and Wya Points. Rocks exposed along the coast are indurated, unmetamorphosed, impure sandstones and mudstones of late Jurassic to early Cretaceous age. They were derived from the hinterland northeast of Wreck Bay, and were rapidly deposited into a trough which extended parallel to the present-day coastline. The contact between these sediments and the source rocks is thought to lie beneath a thick cover of Pleistocene material which now overlies the Estevan Coastal Plain; the southwestern edge of the paleotrough, from seismic evidence, appears to lie 5 - 6 miles (4.35 - 5.22 kilometers) seaward from the present-day coastline. Infilling of both sides of this paleotrough with Pleistocene and Recent sediments has resulted in a narrow, arcuate, present-day trough on the continental shelf adjacent to Wreck Bay. The Pleistocene sediments, consisting of cohesive grey clay and glaciofluvial outwash, were also derived from the mountainous hinterland to the northeast, and recent sediments derived therefrom are dispersed across the bay and inner shelf. Boulders and gravel freed from the retrograding sea cliff behind the beach have settled to the base of wave erosion in the bay, and this coarse "mat" is covered by a thin veneer of very well sorted fine sand which becomes progressively finer further away from shore. A nearshore surface current transports clay, silt and some of the sand southeastwards to Wya Point and the offshore trough. During the summer, breaker heights in the bay vary from 0.75 - 4.00 feet (0.23 - 1.27 meters), and it is calculated that during winter storms, wave heights exceed 19 feet (5.75 meters). The foreshore in summer consists of fine, light-coloured sand, and slopes gently seaward at less than 2.6°. Profile changes on the foreshore result from three controlling factors: the breaker height, the breaker incident angle, and the position of the water table on the beach. The direction of littoral drift near the middle of the beach changes with tide level, but generally it is towards Sand Point and very strong; near Quisitis and Wya Points it is weak, and consistently away from them; elsewhere, it is weak and variable in direction. Transverse profiles were found to be most sensitive to tidal range where the brisker incident angle was small and consistent; they were virtually insensitive where the breaker incident angle was small and variable. In winter, the foreshore is generally less steep than in summer, and near Sand Point the surface material of the beach is reduced to coarse gravel as sand is carried out to the middle of the bay; northwest and southeast from here, the beach surface consists of dark-coloured medium sand; adjacent to the two headlands, the light-coloured fine sand of summer remains. Profile changes in winter are determined by breaker heights only, the other two controlling factors becoming insignificant. Runnels, or incipient beach cusps, tend to form wherever littoral drift is not too strong, and their spacing is apparently related to the thickness of the swash wedge. The cliffbase along the northwest half of Wreck Bay very closely approximates a log-spiral curve in plan due to the angular relationship between prevailing wave fronts and the coastline; the southeast half, however, does not, because a complex wave pattern is created in the lee of islands located in the middle of the bay. The value of gold contained in the backshore near Lost Shoe Creek is calculated to be $10,650. An offshore placer deposit at 20 fathoms (36,6 meters) depth is indicated by a great increase in the amount of magnetite and other heavy minerals there, together with the fact that a small mode of very fine sand, which contains most of the heavy minerals onshore, reappears in samples collected from this bathymetric level. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The southern extension of the Quesnel Lake Gneiss lies approximately 10 km northeast of the Intermontane-Omineca Belt tectonic contact in the southwestern Cariboo Mountains, British Columbia. The aim of this thesis is the investigation of the structural development and style at a deep structural level relative to the 1MB-OB contact, and to determine the nature origin of the southern extension of the Quesnel Lake Gneiss. Omineca Belt rocks in the Quesnel Lake region are the Late Proterozoic to Late Paleozoic Snowshoe Group metasediments. The Snowshoe Group rocks in this study area comprise a package of variably micaceous schist, quartz-biotite gneissose schist, calcareous metasandstone, marble and amphibolite which represent deformed and metamorphosed continental margin deposits. The Quesnel Lake Gneiss is a predominately subalkaline granodioritic intrusive into these sediments that has been modified by subsequent deformation and metamorphism. High Sr content, low initial ⁸⁷Sr/⁸⁶Sr ratios and an alkalic component imply a mantle source although possible Pb inheritance in zircons and regional Sr data suggest a certain amount of assimilated continental crust A U-Pb zircon age on the Quesnel Lake Gneiss indicates intrusion in Mid-Paleozoic, probably Devonc—Mississippian time. A regional metamorphic event affecting the entire sedimentary and intrusive package is interpreted to have occurred in the Middle-Jurassic as suggested by sphene U-Pb geochronometry and regional stratigraphic relations. The structural sequence observed in this area is composed of five phases of folding followed by a brittle fracturing and faulting phase. The entire sequence of deformation is seen in both the Snowshoe Group and the Quesnel Lake Gneiss. A pervasive metamorphic foliation defines the compositional layering (S0/1) and is axial planar to isoclinal first phase folds in both rock packages. Syn-metamorphic second phase deformation is evidenced as tight similar-style folds with an axial surface penetratively developed at a low angle (10-15°) to the compositional layering. Syn- to post-metamorphic third phase deformation produced southwest verging folds with only locally penetrative axial surfaces developed at approximately 40° to SO/1 compositional layering and northwest plunging fold axes nearly coaxial with F2 folds. The Quesnel Lake Gneiss shows a lack of F3 macroscopic folds. Fourth and fifth phase folds are brittle, broad warps that are only locally developed in the more micaceous units. A series of ť vs. α plots on second and third phase folds in both rock types indicates a ductile regime associated with high shear strain during F2 deformation with decreasing shear strain and less ductile behavior during the third phase of deformation. This change in behavior corresponds with the waning of metamorphism. At least one regional metamorphic episode has affected this area in association with the deformational sequence outlined above. The metamorphic peak occurs post-F2 and pre- to syn-F3 deformation producing Barrovian-type assemblages of the amphibolite facies. Metamorphic temperatures of approximately 590° C at 5.5 kb were determined by garnet-biotite geothermometry in sillimanite-bearing schists northeast of the Quesnel Lake Gneiss. A tectonic history for the rocks in this map area began with the deposition of the Snowshoe Group sediments in a continent margin basin from the Late Proterozoic to the Early Mississippian. Intrusion into this package by the Quesnel Lake granitic body occurred between 317 and 400 Ma ago. The first phase of deformation recognized in the Snowshoe Group and Quesnel Lake Gneiss is absent in the Quesnellia and Slide Mountain rocks and may also be of Paleozoic age. The accretion of Quesnellia onto the continental margin in Early Jurassic time is inferred to have initiated the subsequent deformation and regional metamorphism. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Okanagan Valley is the boundary between the Okanagan Metamorphic and Plutonic Complex of the Omenica Belt to the east and the Intermontane Belt to the west. The Okanagan Metamorphic and Plutonic Complex consists of greenschist to amphibolite grade paragneiss and large areas of massive, gneissic, and mylonitic granitic rock. The Intermontane Belt consists of tectonically scrambled late Paleozoic to Triassic eugeosynclinal rocks, intruded by large Jurassic plutons and locally by plutons of mid-Cretaceous age. These are overlain by Eocene non-marine volcanic and sedimentary rocks, capped by fanglomerate breccias and gravity slide megabreccias. The thesis area contains all of these elements. In particular, the mid-Jurassic Oliver pluton is composed of three separate intrusive phases. The oldest phase is a heterogeneous biotite-hornblende diorite, which was intruded by the most extensive phase: a porphyritic biotite granite. The youngest phase is a garnet-muscovite granite. The intrusion of this last phase created the porphyritic biotite granite from an originally more mafic, hornblende bearing granodiorite. The mineralogy of the garnet-muscovite granite suggests that it might be of S-type. Several geochemical plots contradict this and suggests it is a highly evolved I-type magma. Previous geochronometry indicates that the tectonic boundary between the Okanagan Metamorphic and Plutonic Complex and the Intermontane Belt separates: 1) gneisses on the east that consistently yield K-Ar dates of 40-60 Ma, typically 51 Ma for hornblende and 48-50 Ma for biotite, from 2) intrusive rocks on the west that yield Jurassic K-Ar and Rb-Sr dates and Eocene volcanic rocks, erupted largely between 53 and 45 Ma. U-Pb dating of zircons indicates the presence of early Jurassic to mid-Jurassic plutons both east (granite of Anarchist Mtn., 160Ma; gneiss of Osoyoos, 201Ma deformed) and west (Similkameen granodiorite, 170Ma; Olalla Syenite, 18O-190Ma; undeformed) of the Okanagan Valley. East of the Okanagan Valley there are also mylonitic gneisses of Cretaceous age (gneiss of Skaha Lake, 105-120Ma; gneissic sill of Vaseaux Lake, 97Ma), as well as metamorphosed and deformed Eocene intrusives (Rhomb Porphyry, 51Ma). The interpretation is thaL although there are Jurassic plutons and early Mesozoic deformation in both the Okanagan Metamorphic and Plutonic Complex and the Intermontane Belt, there are also Cretaceous and Tertiary intrusive bodies within the Okanagan Metamorphic and Plutonic Complex that have been highly deformed in late Cretaceous to early Tertiary time. Regional geochronometry summarized on time versus blocking temperature graphs emphasizes the large (10 km) and rapid (1-4 mm/yr) unroofing needed to bring the gneisses east of the Okanagan Valley to near surface temperatures in Eocene time. Field evidence for a low angle west dipping detachment fault (Okanagan Valley fault) which juxtaposes brittle disrupted Eocene and older rocks against unannealed mylonitic rocks with Eocene K-Ar dates justifies comparison of the Okanagan Metamorphic and Plutonic Complex with other Cordilleran metamorphic core complexes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

In late Proterozoic to early Paleozoic time, continent-derived clastic sediment and minor carbonate of the Snowshoe Group were deposited in a continental slope to shelf environment, and shallow marine elastics and carbonates of the Cariboo Group were deposited nearer to the shore of North America. The Snowshoe Group is divided into a lower sequence of micaceous quartzite, pelite, and minor amphibolite, all interlayered with quartz diorite sheets; and an upper sequence of micaceous quartzite, pelite, and carbonate with minor calc-silicate and amphibolitic rocks. Early isoclinal (F1A) and NE-verging tight folds (F1B) formed together with a metamorphic foliation. Tight to normal, cylindroidal second phase (F2) folds, characterized by SW-vergence and NW plunge, formed during the mid-Jurassic Columbian orogeny at about the same time as accretion of suspect terranes southwest of the map area. Prograde metamorphism in the Barrovian series of amphibolite facies was synkinematic to postkinematic to F2 folding, with maximum metamorphic recrystallization outlasting deformation. Garnet-biotite geothermometry indicates temperatures of 525 ± 20°C for pelites near the kyanite to sillimanite zone isograd. Garnet-aluminosilicate-ilmenite geobarometry limits P to less than 7 kb. Grossular-anorthite-aluminosi1icate geobarometry gives P = 5.5 ± 0.7 kb. Retrograde metamorphism and F3 kink-folding occurred during uplift, followed by broad warping (F4) with NE trend. The low-angle, postmetamorphic Little River Fault emplaced chlorite to biotite zone phyllite and carbonate of the Cariboo Group, in the hanging wall, against staurolite-kyanite to sillimanite schists and gneisses of the Snowshoe Group, in the footwall, with latest movement of the hanging wall in an ESE direction. A Rb-Sr model depositional age of approximately 750 Ma, assuming an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.708, was obtained for Snowshoe Group metasedimentary rocks. Paleozoic plutonism is indicated by a Rb-Sr whole-rock isochron date of 530 ± 94 Ma with initial ⁸⁷Sr/⁸⁶Sr ratio of 0.706, and U-Pb dates on zircon, indicating a minimum age of 335 Ma and maximum age of about 450 Ma, for quartz dioritic gneiss intrusive into the Snowshoe Group early in its deformational history, pre-F1B folding. Late- to post-metamorphic pegmatite cooled through 400-500°C at 86 ± 3 Ma. The age of the Little River Fault is bracketed between intrusion of pegmatite and a Miocene(?) erosion surface. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The "Cache Creek Group" as previously mapped in the Kamloops area actually consists of two sequences of different ages, the Late Paleozoic Harper Ranch Group (new name), and the Upper Triassic Nicola Group. The lower part of the Harper Ranch Group is a 5 km-thick sequence of hemipelagic mudstone and redeposited tuff with rare lenses of shallow marine limestone which yield fossils of Late Mississippian to Middle Pennsylvanian age. This sequence is disconformably overlain by several hundred metres of Lower Permian limestone forming the upper part of the group. Only the lower 2.3 km of the section were studied in detail. In this portion, andesitic to dacitic tuffs consist of ash produced by shallow marine eruptions, then reworked and redeposited in deep water by turbidity currents and high concentration subaqueous flows. A thin Upper Mississippian bioclastic limestone with a diverse marine fauna is found near the base of the sequence. It accumulated during a period of volcanic quiescence and shallowing of the basin floor. The Harper Ranch and Chilliwack Groups were probably parts of a Late Paleozoic volcanic arc which formed above an east-dipping subduction zone. East of the arc was an "oceanic" back-arc basin bounded on the east by orogenic lands formed by the Late Devonian to Mississippian Caribooan orogeny. This orogenic terrane supplied the lithic-rich elastics of the Late Paleozoic Anarchist Group, Mt. Roberts Formation, and the Eastern assemblage of Monger (1977). Pre-Late Triassic deformation and low grade metamorphism of the Late Paleozoic eugeoclinal rocks of southern British Columbia may have been caused by Permo-Triassic closure of the back-arc basin, and collision of the arc with the old orogenic terrane to the east. A new volcanic arc formed in the Late Triassic is represented by volcanic flows and breccias of the Nicola Group west of Kamloops. East of Kamloops, the Nicola Group consists of 3 km of sediments and volcaniclastics which accumulated in deep water within a back-arc basin. Pelagic and hemi-pelagic mudstones dominate the section, but are interbedded with redeposited tuff, lithic sandstone and conglomerate, and limestone, all of which were deposited by turbidity currents and high concentration density flows. Massive and pillowed basaltic or andesitic volcanic flows occur near the base and top of the sequence, which has been subdivided into five lithologic units. Conodonts extracted from limestones yield Karnian ages. Redeposited tuffs in the Nicola Group were probably derived from the volcanic arc to the west, and also from submarine volcanoes in the basin to the east. Lithic sandstones and conglomerates contain sedimentary and volcanic detritus, including abundant chert and cherty mudstone. These may have been derived from accreted oceanic rocks of the Cache Creek Group, exposed in the emergent Pinchi geanticline west of the volcanic arc. Detrital blue amphiboles in fine-grained turbidite limestones suggest this sediment was also derived from shallow waters surrounding the Pinchi terrane. The Nicola volcanic arc therefore seems to have been built on an east-facing paleoslope. The back-arc basin was floored by older eugeoclinal rocks, and stretched from the arc eastward to the miogeocline. The Harper Ranch and Nicola Groups are separated by a northwest-trending vertical fault, probably of Late Mesozoic or Early Tertiary age. East of the fault the lower Harper Ranch Group forms an east-facing homocline with few discernible mesoscopic folds. To the west, lithic units in the Nicola Group outline a pair of faulted northwest-trending folds: an upright syncline on the east, and a westward-overturned anticline on the west. Deformation probably took place during the Latest Triassic to Earliest Jurassic Inklinian orogeny. The Triassic rocks are intruded by the Paul Peak Stock, a zoned intrusion ranging from pyroxenite to granite in composition. This pluton is similar to zoned Alaskan-type mafic-ultramafic intrusions in composition and tectonic setting, and is probably part of the 200 m.y. plutonic suite of southern British Columbia. Numerous andesitic to rhyolitic dikes of probable Eocene to Oligocene age cut all other rock units. Prehnite-pumpellyite facies metamorphism has affected all rock units in the area, including the dikes. Alteration of volcaniclastic rocks in the Harper Ranch Group is much more complete than in the younger rocks, suggesting that the Paleozoic rocks were affected by the Permo-Triassic low grade metamorphic event recorded elsewhere in southern British Columbia. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Cache Creek Group in the type area is characterized by oceanic rocks such as radiolarian chert, fusulinid limestone and pillow basalt. Three divisions have been made in the Cache Creek Group in this study: 1) structurally lowest is the melange unit (which has been identified as a subduction complex); 2) an overlying greenstone unit; and 3) the Marble Canyon Formation. Emplacement of the Marble Canyon Formation and greenstone unit on the underlying melange unit is believed to have occurred in the Early to Mid-Jurassic along a shallow dipping thrust fault. This emplacement may have caused soft sediment deformation features in the Early to Mid-Jurassic Ashcroft Formation. Felsic volcanic rocks and associated tuffs and volcaniclastic sediments are found mainly along the east side of the Cache Creek Group. These felsic rocks have been called the Nicola(?) Group and based on lithological correlation are of probable Late Triassic age. The Nicola(?) Group is correlated both with the western belt of the Nicola Group as described by Preto (1977) and the Pavilion beds as described by Trettin (1961). Blocks of Nicola(?) Group tuffs have been found in the Cache Creek Group melange unit. This indicates that in Late Triassic time the Cache Creek Group and Nicola(?) Group were adjacent to one another. Paleoenvironmental and geochemical evidence indicate an ocean island or platform depositional environment for the Cache Creek Group. Tropical shallow seas covered most of these islands. Lack of continental sediments indicates that the Cache Creek Group was distant from any major land masses. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Fission track dating of zircon and apatite has been used to determine the Cenozoic uplift history of the British Columbia Coast Mountains from 50°-55°N. 115 dates were obtained from rocks of variable geographic location and altitude, and the resulting date pattern constrains the movement and deformation of the fission track retention isotherms (175°C for zircon, 105°C for apatite) within the crust. Because date-altitude correlations (apparent uplift rates) cannot always be used confidently to estimate actual rates of uplift, a finite difference numerical scheme was formulated to construct models of heat flow, uplift, denudation, and cooling that satisfy not only fission track dates, but also present heat flow, other isotopic dates, geologic considerations, and fission track-derived estimates of paleo-geothermal gradient. In most cases, apparent uplift rates derived from apatite date-altitude correlations are very close to modeled rates of uplift. Zircon-derived apparent rates, however, often exceed modeled rates and reflect post-orogenic cooling a,nd relaxation of isotherms. The relationship of the movement of isotherms to rates of uplift and fission track-derived apparent uplift rates is quantified and discussed. Orogenic rapid cooling and uplift occurred from Cretaceous to Eocene time in most of the Coast Mountains. Rates during orogenic uplift were near 1.0 km/Ma, causing setting of K-Ar clocks in biotite and hornblende. Uplift rates during the middle Cenozoic ranged from 0.2 km/Ma in the axial region of the mountains between 52° and 55°N to less than 0.1 km/Ma south of 52°N. The moderate rates north of 52°N were likely the result of gradual erosion of crust thickened during Eocene orogeny. A thermal origin for this northern uplift is not likely. Rates of uplift south of 52°N were low despite arc-related volcanic activity during the Oligocene and Miocene. Accelerated uplift in the Late Miocene near Bella Coola-Ocean Falls was probably the result of passage of the transverse Anahim Volcanic Belt or hotspot beneath the area about 10 Ma ago, after which uplift slowed. Rapid Pliocene-Recent uplift south of 52°N at rates of up to 0.75 km/Ma elevated a broad region creating the present southern Coast Mountains and deforming 7-10 Ma lavas erupted on the mountains' east flank. It is suggested that this uplift resulted from thermal expansion in the mantle related to a westward jump in the locus of late Neogene arc volcanism. The extent of this rapid Pliocene-Recent uplift correlates with the area above the Juan de Fuca-Explorer subducted slab and confirms a relation between continental uplift and plate tectonic setting. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Spuzzum Batholith underlies an area northwest of Hope, B.C. It is nearly 60 km. long in a northerly direction and 10 to 20 km. across. The southern part of the body is zoned from pyroxene diorite in its core, through hornblende diorite, to biotite-hornblende tonalite. Tonalite forms about two thirds of the pluton's area, forming a nearly continuous rim. The pluton intrudes upper Paleozic Chilliwack Group, the Cretaceous (?) Giant Mascot Ultramafic Body, and Settler Schist of unknown age. K-Ar ages for tonalite and diorite range from 76 to 103 m.y. Diorite consists of subhedral orthopyroxene and plagioclase (An₆₂ to An⁴¹), with variable amounts of hornblende and clinopyroxene. Tonalite is largely composed of anhedral quartz and biotite, and subhedral hornblende and plagioclase (An⁵⁰ to An₃₂). Tonalite and some diorites are foliated. These rocks are locally hornblendized, resembling hornblende gabbro. Pods of directionless hornblendite are common in hornblendized rocks. Foliations and mineralogical zonation outline a crude tongue-like structure, modified by later deformation. Spuzzum diorite appears to have intruded the main part of the Giant Mascot Ultramafic Body but some hornblendites are younger than diorite. The Giant Mascot Ultramafic Body, 2 by 3 km., is zoned from dunite or peridotite, through pyroxenite, to a rim of hornblendite up to 100 m. across. Hornblendite occurs also as dykes. Orthopyroxenes of Spuzzum diorite are weakly aluminous hypersthene; those of the contact with Giant Mascot pyroxenite are bronzite. Clinopyroxenes of the same rocks are somewhat more aluminous salites and diopsides. Hornblendites from Spuzzum diorite and the Giant Mascot Ultramafic Body resemble alkali basalt in composition. Hornblende analyses fall into three categories: edenite, pargasite-common hornblende, and thirdly, more iron-rich common hornblende. It is concluded that Spuzzum diorite and tonalite originated by crystal settling from quartz diorite magma at depth, followed by diapiric rise of a zoned pluton composed of residual tonalite liquid cored by drawn-up dioritic cumulate. A mathematical test shows the compositions of diorite and tonalite to be consistent with this hypothesis. The rising pluton subsequently engulfed the Giant Mascot Ultramafic Body. Hornblendites may have formed by metasomatism of these rocks and adjacent diorite or tonalite as a consequence of the second boiling of tonalite and the coursing of resultant hydrothermal fluid through the nearly solid pluton. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate