Pitt River, 30 km inland from. Vancouver, British Columbia at the southern margin of the Coast Mountains, links Fraser River estuary and Pitt Lake. Salt water seldom extends to within 10 km of Fraser - Pitt confluence; nevertheless, tides modulate Fraser flow and cause Pitt River to fluctuate 2 m and Pitt Lake as much as 1.2 m. There is an upstream movement of sediment in Pitt River from Fraser River, evidenced by identical mineralogy of Pitt River and Fraser River sediments, a decrease in grain size from the Fraser to Pitt Lake, and a predominance of flood-oriented bedforms in the river channel. A delta of 12 km2 area has accumulated at the lower (draining) end of the lake. The purposes of the study were to: (1) examine aspects of the hydrodynamics of Pitt River and Pitt Lake as a tidal system; (2) evaluate the effect of bidirectional flow on river and delta morphology; (3) determine processes of sediment movement in the river and of-sediment dispersal on the delta; and (4) estimate present sedimentation rate on the delta. Water Survey of Canada stage data from 3 locations in the system, used in conjunction with velocity measurements (profiles and tethered meter), revealed large seasonal and tidal variations in discharge. Calculations indicate that flood basal shear stress peaks early in the flow, whereas ebb currents have a lower basal, shear stress which peaks late in the flow. Thus, sediment moves farther forward on a flood flow than it moves back on the succeeding ebb. Studies of the river channel using hydrographic charts revealed regular meanders (^M = 6100. m) and evenly spaced riffles and pools which are scaled to the strongest flow (winter flood current, Qe). Meander point bars are accreting on the "upstream" side indicating deposition by the flood-oriented flow. The three dimensional geometry of the large-scale bedforms which cover the sandy thalweg of both river and delta channel was determined by echo sounding and side-scan sonar. Three distinct sizes (height/spacing = 0.8 m/10-15m; 1.5m/25-30 m; 3 m/50-60 m) of large-scale bedforms (sand waves) were found; their linear-relationship of height vs. spacing (XD) on log-log plot suggests a common genesis. The size appears to be related to channel geometry, not to depth of flow. Largest forms are found in reaches which shallow in the direction of water movement and smallest forms occur on relatively flat topography. The following tentative relationship is suggested for sandy meandering rivers: ^M/^B = Qe. Pitt delta morphology was studied with aerial photos and depth soundings. Its shape is considered an excellent example of sediment diffusion and deposition from a simple jet into a low energy lacustrine environment. Analysis of 190 sediment samples from river, delta, and lake bottom shows the sediment to be polymodal. Graphical partitioning of the cumulative probability plots reveals that sediments are composed of up to 4 log-normal distributions. Each distribution is interpreted as a population related to a process of sediment transport. Five subenvironments in the Pitt system are characterized by unique combinations . of these "process" populations. Cores in the delta topsets and lake bottom sediments reveal silt and clay rhythmites, interpreted as varves. The coarse layers are deposited during winter when discharge of Fraser River is low and tidally induced discharge in Pitt system is high. The fine layers are deposited during spring run-off when additional fines are added to the lake from the Pitt basin. 137Cs dating of sediments shows that as much as 1.8 cm/yr are accumulating in the active portions of the delta with an estimated 150 +/- 20 X 103 tonnes deposited annually. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Mara Lake, British Columbia, straddles the boundary between the Monashee Group on the east and the Mount Ida Group on the west. Both groups of rock have experienced four phases of deformation. Phases one and two are tight and recumbent, trending to the north and to the west respectively. Phases three and four are open to close and upright, trending northwest and northeast respectively. Second phase deformation includes large scale tectonic slides which separate limbs of major folds. These slide surfaces are folded by third and fourth phase structures and outline domal outcrop patterns. Peak metamorphism accompanied and followed phase two. Metamorphic grade is related to position within the second phase structure, increasing downward from greenschist to amphibolite facies. Greenschist conditions accompanied phase three while hydrothermal alteration characterizes phase four. Brittle fracturing and local faulting along a northeasterly trend followed phase four. Abrupt changes in metamorphic grade found at the northern end of Mara Lake are related to these late faults. Correlation of lithologies across the southern end of Mara Lake and the similar structural sequences indicate that no stratigraphic or structural distinction is necessary between the Mount Ida Group and the Monashee Group. On a regional scale similar structural sequences are observed in other areas of the Shuswap Metamorphic Complex. Microscopic deformation features are common in many mineral phases in the Mara Lake area. Amphibole rarely shows evidence of plastic deformation. To examine this apparent high strength characteristic, fifty samples of hornblendite (AM-2) were deformed in a large, solid-medium Griggs-type apparatus at 700° to 1000°C at strain rates from 10⁻⁴/sec to 10⁻⁶/sec and at 10 kb confining pressure. Talc, pyrophyl lite, and platinum jacketing were used to yary water content. From 700° to 850°C both mechanical twins (101) and translation glide (100) were observed. Twin development appears to be favored over glide at higher confining pressures, lower temperatures, and higher strain rate. Above 850°C subgrain development and recrystallization occur just prior to melting. A flow law, Є = ~ 1.5 x 10⁻¹ exp (-38/RT)σ[sup 4.8] describes steady state deformation from 750° to 910°C under wet conditions. Decreasing water and temperature are accompanied by increasing n values and perhaps increasing activation energy. At 750°C under dry conditions an exponential relationship, Є = 53 exp (.23 σ) best fits the data. From 910° to 950°C the amphibole structure "hardens" such that strain rate remains constant for a given load. This hardening is interpreted to be related to oxidation and distortion within the lattice. Uncertainty regarding the activation energy precludes effective extrapolation of the data to "geologic" strain rates. A tentative comparison of amphibole and quartz data reveals an order of magnitude difference in flow stress, suggesting that quartz will yield plastically before amphibole. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

No description available.

A more than 2000 m thick sequence of Hadrynian to Paleozoic Snowshoe Group metasedimentary rocks of the Omineca Belt (OMB) is exposed near Niagara Peak in the western Cariboo Mountains, central British Columbia. This package contains the northern extremity of the Shuswap Metamorphic Complex and lies 30 km northeast of the accretionary boundary with Intermontane Belt (IMB) Mesozoic sedimentary and volcanic rocks (Quesnellia Terrane) and Upper Paleozoic (?) ophiolitic and sedimentary rocks (Slide Mountain Terrane). Four phases of folding (D₁-D₄) are recognized. D₁ consists of isoclinal folds and transposed compositional layering. D₂ commonly forms southwest verging, open to close folds with subhorizontal axes and moderately northeast dipping axial surfaces. In the eastern part of the area, divergent fanning of D₂ axial surfaces and a reversal of vergence direction occur about a map-scale synform characterized by greater strain, bimodal fold style and a locally penetrative axial planar cleavage. D₃ and D₄ form orthogonal upright open buckles with respective northwest and northeast trending axes. Steeply dipping normal and minor reverse faults crosscut all fold structures, displaying minor offsets. Prograde regional metamorphism reached greenschist grade late in D₁. Staurolite and kyanite growth accompanied D₂, followed by postkinematic sillimanite generation under conditions of approximately 635° C and 5 kb. D₃ associated sericite-chlorite retrogression of porphyroblasts occurs in sub-sillimanite grade rocks in the western part of the area. Synmetamorphic veins represent polyepisodic hydraulic fracture development during progressive dewatering of a sedimentary pile by prograde metamorphism. Eastward obduction of Quesnellia and Slide Mountain Terranes onto theOmineca Belt took place in the Middle Jurassic. Shortly following this event, the IMB-OMB tectonic suture was deformed, forming map-scale folds of cuspate/lobate geometry. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Five phases of deformation are recognized in Shuswap metamorphics south of Vernon, British Columbia. Phase 1 and 2 deformations are isoclinal gently dipping folds which trend N and ESE respectively. Some thermal activity may have occurred prior to phase 2 deformation but metamorphism culminated in the amphibolite facies during and following phase 2. Metamorphism waned prior to the development of NE trending phase 3, folds of which are angular and moderately tight with one steep and one shallowly dipping limb. Phase 4 and 5 deformations trend NE and N respectively, and comprise open upright buckle folds and fractures which are contemporaneous with abundant hydrothermal alteration. The 42- 10 m.y. B.P. sr/Rb whole rock age date secured from a phase 2 sill probably represents thermal upgrading. Low metamorphic grade "Cache Creek" metasediments west of Vernon have undergone 4 recognized deformational phases. Phase 1 folds are tight, steeply dipping, and trend WNW. Phase 2 comprises E trending, angular mesoscopic folds. Phase 3 and 4 comprise NE and N trending fracture sets. A large amphibolite sill defines the "Cache Creek" albite-epidote-amphi-bolite facies metamorphic culmination. Metamorphic hornblendes from the amphibolite yield a 178 + 6 m.y. B.P. age date, using the K/Ar method. Hydrothermal activity occurred in association with phase 3 and 4 deformations. The final four phases of Shuswap deformation appear to correlate with respective "Cache Creek" phases, based on structural similarities. This suggests that the two complexes may be, at least in part, structural equivalents. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Metchosin Igneous Complex, a partial ophiolite exposed on southern Vancouver Island, is the most northerly exposure of the Eocene Crescent Terrane. The role of the Crescent Terrane in crustal genesis and Cordilleran tectonics would be affected by its tectonic setting, however that setting is in debate. Analysis of trace element compositions of basalt from the Metchosin Igneous Complex by ICP-MS was used to determine the tectonic setting in which the complex formed. REE and HFSE compositions are transitional between N-MORB and E-MORB and do not suggest a unique tectonic setting. Strong enrichments of Nb and Ta relative to N-MORB are contrary to formation in a subduction zone. In conjunction with existing plate motion data, this makes a rifted-margin origin unlikely. Interaction at a distance between the Yellowstone hot spot and the Kula-Farallon ridge is proposed to satisfy all the geological and geochemical data. Many studies of ophiolites have interpreted high-temperature phases as hydrothermal in origin despite high permeability and low temperatures in sea floor volcanics. Metamorphic assemblages and compositions of metamorphic minerals were used to determine if alteration in the Metchosin Igneous Complex was related to sea floor alteration or obduction. Chlorite geothermometry and amphibole compositions show that peak metamorphic temperatures increase from east to west across the complex. The metamorphic facies increase from prehnite-actinolite and greenschist in the east to amphibolite in the west, corresponding with the temperatures inferred from mineral compositions. The temperature gradient is perpendicular to stratigraphy, whereas hydrothermal patterns are expected to be parallel to stratigraphy. Therefore the pattern of alteration in the Metchosin Igneous Complex is unrelated to sea floor alteration. Metamorphism during obduction has overprinted any hydrothermal alteration patterns. The east-west thermal gradient is attributed to tilting of the complex, either by tectonic forces or by unequal exhumation due to orographic effects.

In northern British Columbia, the Sylvester Allochthon of the Slide Mountain terrane is the most inboard of Cordilleran suspect terranes, resting as a vast klippe upon miogeoclinal strata of the Cassiar Platform. The Sylvester is oceanic; it comprises gabbro, pillowed and massive basalt, banded chert, carbonate, argillite, ultramafics and minor arenite, which range in age from Late Devonian to Late Triassic. Internal structure in the Sylvester Allochthon is characterized as a stack of innumerable interleaved tectonic slices, bounded by subhorizontal, layer-parallel faults. These lithotectonic units are an order of magnitude smaller than the terrane itself and may consist of only a single or a few repeated rock types. The internal structure of the Sylvester is complex but not chaotic; small numbers of slices occur together in larger second-order packages which are also fault-bounded and lensoidal. However, tectonic juxtaposition of unrelated lithologies and older-over-younger faults are common. The "stratigraphy" of the Sylvester assemblage is thus tectonic. Sliver-bounding faulting within the Sylvester is known to have, at least in part, predated its post-Triassic, pre-mid Cretaceous emplacement. The Sylvester was emplaced onto North America as the roof thrust to a foreland-style duplex within underlying North American strata. vii viii The Sylvester Allochthon is the most inboard of accreted terranes, however it does not represent a simple marginal basin. New microfossil dating demonstrates that most rock types occur through the complete range of Sylvester ages. Coeval but depositionally incompatable lithologies must have accumulated in separate ocean floor paleoenvironments. Lithologies of the allochthon derive almost exclusively from layer 1, only the surface of oceanic crust. Thus, Sylvester slices are telescoped remnants detached from a vast area of ocean crust which ranged in age and width through the upper Paleozoic but which is now otherwise entirely consumed. Similarities of rock type, internal structure, age range, and regional tectonic setting have identified the Sylvester Allochthon as broadly correlative with a discontinuous series of terranes extending the length of the Cordillera. Together, these terranes may represent the remnants of what was once the late Paleozoic proto-Pacific ocean floor.

No description available.

Paleozoic rocks of Vancouver Island are exposed in three major belts: the China Creek-Saltspring, the Home Lake-Cameron River, and the Buttle Lake-Big Interior belts. Stratigraphic sequences in these three belts are grossly similar, though differing in detail. The Paleozoic rocks of each belt are correlated with the Sicker Group, originally defined in the southern part of the China Creek-Saltspring belt. Within the Sicker Group, two major lithological units are recognized, and are referred to as the Lower and Upper Divisions of the group. The base of the Sicker Group has not been seen. The upper contact of the group appears to be anpaunconformity, above which Upper Triassic volcanic and sedimentary rocks of the Vancouver Group occur. The Lower Division consists mainly of volcanic rocks and non-calcareous clastic rocks. In the Upper Division, limestones and thin-bedded cherty sediments predominate. The major unit within the Upper Division of the Buttle Lake-Big Interior belt is a limestone formation (named herein) of 1000 to 1100 feet maximum thickness. Thin-bedded, fine-grained non-calcareous rocks of unknown age, tentatively included within the Sicker Group Upper Division, conformably overlie the limestone at certain localities. A rich fauna of brachiopods, bryozoans, molluscs, corals and foraminifers has been found in the Upper Division. A meagre flora of algae and fragments of vascular plants is present in a locally-developed basal sandstone of the Upper Division. At least 42 genera, represented by 52 species, have been recognized in the Upper Division fauna; many fossils remain to be identified. Four of the brachiopod species are regarded as new. Faunas similar to that of the Upper Division of the Sicker Group have been listed or described from other northern Cordilleran regions. Correlation is thus suggested with the Permian Coyote Butte Formation of central Oregon, the Black Mountain Formation of northwestern Washington, part of the Cache Creek Group of mainland British Columbia, and parts of the Permo-Carboniferous successions of Alaska and Yukon Territory. Permian faunas of the Arctic Archipelago, Greenland, Spitsbergen and northwestern Russia contain many genera and some species in common with the fauna of the Sicker Group. Species of Hor-ridonia, Spiriferella and Kochiproductus are particularly significant in this regard, linking the Sicker Group fauna with the "Arctic Permian" and "Russian" boreal faunas. Despite the strong boreal affinities of the Vancouver Island fauna, however, relationships also with western Pacific equatorial faunas are suggested by certain brachio-pods and many of the bryozoans. The faunal relationships thus established, and the presence of certain diagnostic brachiopods and tentatively identified fusulinids, indicate the age of the Upper Division of the Sicker Group to be Early Permian (Wolfcampian-Leonardian). The evident mixing in the Permian fauna of Vancouver Island of elements of boreal and equatorial faunas prohibits conclusive bio-geographic analysis at the present stage of investigation. The present evidence of faunal distributions is also inconclusive with respect to the assessment of theories of continental drift and polar wandering. Lower Division rocks represent deposits of a moderately deep gulf or basin on the continental borderland, formed during a period marked by tectonic and volcanic activity. Diminishing crustal unrest culminated in the shoaling waters and carbonate deposits characteristic of the Upper Division. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate