glacial lake camelsfoot a late wisconsinan advance stage proglacial lake in the fraser river valley gang ranch area british columbia in the gang ranch area british columbia interaction between the regional physiography and ice flow during the late wisconsinan fraser glaciation resulted in the formation of a proglacial lake confined to valleys of the fraser river and its tributaries lithostratigraphic and geomorphic evidence suggests that ponding was initiated in the big bar creek area where the fraser river is confined to a deep canyon in the camelsfoot range during ice advance a proglacial lake system developed that progressively deepened and reached a minimum upper elevation of approximately 710 m asl prior to being overridden by ice we propose that this system be formally named glacial lake camelsfoot a composite stratotype comprising lithostratigraphic units associated with glacial lake camelsfoot is described from eight reference sections along fraser river churn and lone cabin creeks in the gang ranch area additional geomorphic evidence indicates that at the fraser glaciation maximum the cordilleran ice sheet in th

finite element study of uplift and strain across vancouver island geological evidence for sudden coastal subsidence along the west coast of southern vancouver island points to the occurrence of great prehistorical subduction earthquakes contemporary uplift and crustal shortening patterns in southern vancouver island appear to indicate that the subduction megathrust fault is currently locked to understand better the dynamics of the observed surface deformation we develop a finite element model of earthquake cycles for the northern cascadia subduction zone across southern vancouver island using a linear viscoelastic rheology the model consists of the continental and oceanic lithospheres the asthenospheric mantle with a viscosity of 5 1019 pa s and a low viscosity 1018 pa s mantle wedge between the subducted oceanic plate and the overlying continental plate the shallow geometry of the subducted juan de fuca plate is well defined by the results of various geophysical surveys and the deep geometry is constrained by the results of seismic tomography the model me

on the difficulty of assigning crustal residence magmatic protolith and metamorphic ages to lewisian granulites constraints from combined in situ u pb and lu hf isotopes zircons from two granulite facies gneisses from the central region of the lewisian complex have been investigated by high spatial resolution ion microprobe u pb dating and laser ablation combined pb hf isotope methods the ion microprobe data reveal a complex pattern of zircon ages distributed along the concordia curve between the time of granulite facies metamorphism at c 2 5 ga and the oldest zircon in each sample respectively 2 89 ga and 3 04 ga this pb loss pattern complicates assignment of an unambiguous magmatic protolith age to the zircon although cathodoluminescence cl imaging is used to suggest a preferred age of c 2 85 ga for both samples with older grains being inherited in situ hf isotopes show a larger spread in the sample containing older grains which is also consistent with inheritance and further suggests that several crust extraction events are represented in the inherited population comparison of hf isotope compositions with plausible model evolution curves suggests that crustal precursors to the lewisian granulites were derived from their mantle source at c 3 05 3 2 ga

contrasting types of grenvillian granulite facies aluminous gneisses insights on protoliths and metamorphic events from zircon morphologies and ages abstract zircon morphology internal texture u pb age distributions and th u ratios are used to characterize aluminous gneisses in the canyon domain manicouagan area central grenville province from two contrasting supracrustal sequences metamorphosed at granulite facies one a package of paragneiss and the other a dominantly bimodal felsic mafic volcanic sequence the aluminous paragneisses yielded zircon with fragmental igneous cores overgrown by metamorphic rims these cores show a spread in ages between 1500 ma and 2700 ma consistent with a supply of detritus from the adjacent canadian shield in contrast a felsic gneiss with aluminous nodules inferred to represent a hydrothermally altered felsic volcanic rock of the bimodal sequence yielded well preserved igneous zircon dated at 1238 13 ma an age that integrated with previously published data links this volcanic sequence to a major episode of crustal extension in the central grenville province metamorphic zircon grains and rims from the paragneisses gave two groups of pre grenvillian ages that demonstrate the effect of major magmatic events on the country rocks in the canyon domain a 1391 1408 ma coeval with the emplacement of an older layered mafic to intermediate volcanic suite and b 1217 1260 ma coeval with the development of the 1238 ma bimodal felsic mafic volcanic sequence in addition metamorphic zircon from all the investigated aluminous gneisses records the high grade grenvillian metamorphism 1080 1040 ma

regional stratigraphy and age of chilcotin group basalts south central british columbia mio pliocene chilcotin group basalt flows form a 50 000 km2 lava plateau in south central british columbia two periods of eruptive activity at 2 3 and 6 10 ma are indicated by a compilation of available age data including 10 new k ar age determinations and basalts from these two periods are chemically indistinguishable the chilcotin group consists of thin crudely columnar jointed pahoehoe flows some thick tiered flows pillow lava and pillow breccia and rare silicic tephra layers the presence of many vesicle sheets and cylinders and collapsed pahoehoe toes suggests that the basalts were volatile rich known vents gabbro and basalt plugs for the basalt flows form a northwest trend along the axis of the lava plateau the plateau appears to have formed from the overlap of many low profile shield volcanoes and is similar in morphology to other plains basalts such as the snake river plain and parts of iceland glaciation has stripped off an unknown volume of the flat lying basalt flows

imaging and regional distribution of basalt flows in the faeroe shetland basin we demonstrate that the use of long offset seismic data allows wide angle reflections and diving waves to be recorded and that these can be used in conjunction with prestack depth migrations to constrain and to image the base of the basalt flows and the underlying structure in the faeroe shetland basin crustal velocity models are built first by inverting the traveltimes of the recorded reflections and diving waves using ray tracing methods finer details of the velocity structure can then be refined by analysis of the amplitudes and waveforms of the arrivals we show that prestack depth migration of selected wide angle arrivals of known origin such as the base basalt reflection using the crustal velocity model allows us to build a composite image of the structure down to the pre rift basement this has the advantage that the wide angle first arriving energy must be primary and not from one of the many multiples or mode converted phases that plague near offset seismic data this allows us to tag these primary arrivals with confidence and then to identify the same arrivals on higher resolution prestack migrations that include data from all offsets examples are drawn from the faeroe shetland basin with a series of regional maps of the entire area showing the basalt depths and the thickness of the basalt flows and underlying sediment down to the top of the pre rift basement the maps show how the basalts thin to the southeast away from their presumed source west of the present faeroe islands and also show the extent to which the structure of the pre rift basement controls the considerable variations in sediment thickness between the basement and the cap formed by the overlying basalt flows

new insights on the 1 7 1 0 ga crustal evolution of the central grenville province from the manicouagan baie comeau transect abstract integrated field relationships and u pb geochronology of rocks exposed along the southern part of the manicouagan reservoir central grenville province quebec provide insights into protolith formation and thermal events that range in age from ca 1 7 to 0 9 ga and share common features with the rest of the grenville province and beyond from presently lower to higher structural levels main findings include the recognition of a ca 1 70 1 75 ga granitic magmatism and metamorphism in the southern part of the parautochthonous gagnon terrane correlative in age with late stages of magmatism in the makkovik orogen to the northeast b a ca 1 69 gabbro anorthosite suite island domain which is inferred to represent the southwesternmost exposure of labradorian crust in the central grenville province c a 1 4 ga volcaniclastic sequence and associated plutonic rocks canyon domain which based on lithological association and age is inferred to represent the nne extension of the montauban island arc and d a ca 1 2 ga bimodal felsic mafic volcanic to intermediate volcaniclastic sequence banded complex inferred to have originated in an intra continental rift system contemporaneously with the composite arc belt southwestern grenville province and with widespread extensional magmatism elsewhere in the canadian shield in addition 1 3 ga granitoid plutons are documented to intrude labradorian units at the nw boundary of canyon domain the significance of these plutons is ambiguous as they may represent either stitching plutons marking the accretion of the 1 4 ga canyon domain to the laurentian margin or the first stage in the development of the ca 1 2 ga continental rift system the hinterland units island domain canyon domain and banded complex were metamorphosed under medium pressure granulite facies conditions during the culmination of the grenvillian orogeny between 1 08 and 1 04 ga this metamorphism was accompanied by ca 1 07 ga a type granitic magmatism in canyon domain in addition locally abundant ca 0 98 ga late tectonic felsic pegmatite and ultrapotassic dykes occur in canyon domain this event is coeval with titanite ages documented in a wide range of units the data on the grenvillian evolution suggest mantle derived magmatism and associated metamorphism in the hinterland during both the culmination and the waning stages of the grenvillian orogeny

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

new geophysical models for subsurface velocity structure in the nechako chilcotin plateau from 2 5 d waveform tomography1 seismic inversion is applied to generate physical property models p wave velocity and numerical attenuation for four profiles in the nechako chilcotin plateau region of south central british colu

the thickness of neogene and quaternary cover across the central interior plateau british columbia analysis of water well drill records and implications for mineral exploration potential abstract analysis of over 10 000 water well records has been used to produce new depth to bedrock maps for areas around five cities on the central interior plateau of central british columbia 100 mile house prince george quesnel vanderhoof and williams lake hitherto exploration for mineral and hydrocarbon resources has been hampered by a lack of basic knowledge of the thickness of neogene and quaternary lithologies interpretation of these new maps provides first order constraints on the localization of thick drift in pre late wisconsinan bedrock paleovalleys some of which are now buried basalt lavas of the chilcotin group are restricted to erosional remnants of previously extensive sheets emplaced onto an older peneplain our results confirm that the neogene and quaternary cover is primarily controlled by paleotopography and is generally thin and patchy across much of the region increased understanding of the three dimensional distribution of cover produces a corresponding increase in the utility of geological geochemical and geophysical exploration techniques and a reduction in the risk for future mineral exploration activities especially when combined with more sophisticated data sets

evolution of the subglacial hydrologic system beneath the rapidly decaying cordilleran ice sheet caused by ice dammed lake drainage implications for meltwater induced ice acceleration abstract a positive correlation between ice dammed lake drainage and ice acceleration at antarctic ice sheets ais and land terminating sections of the greenland ice sheet gris has been implicated in enhanced ice sheet decay however the paucity of direct measurements at the ice sheet bed restricts our understanding of subglacial drainage system evolution in response to transient water inputs we present evidence that two meltwater corridors on the former bed of the thin 600 m at last glacial maximum over the interior plateaus of british columbia and rapidly decaying cordilleran ice sheet cis were generated subglacially in response to the drainage of an ice dammed lake and operated as canals tunnel channels geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data reveal a simple event sequence that includes initial propagation of a broad at least 2 5 km wide floodwave inefficient drainage from an ice dammed lake over relatively short 3 24 km zones at the corridor heads that collapsed into efficient canals large up to 0 25 2 5 km wide channels incised down into the sediment bed and up into the ice downglacier canal formation on the southern fraser plateau involved synchronous along the full canal length system development including elements of headward erosion and plunge pool formation our data suggest that ice dammed lake drainage beneath a rapidly decaying thin ice mass that has an efficient antecedent drainage network is not conducive to large scale ice acceleration these data may aid better assessment of the role of ice dammed lake drainage on the dynamics of former as well as contemporary ice sheets

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

partial melting of metapelites in the gagnon terrane below the high pressure belt in the manicouagan area grenville province pressure temperature p t and u pb age constraints and implications metapelites of the parautochthonous gagnon terrane at the footwall of the high pressure high p belt in the manicouagan area central grenville province preserve an impressive textural record of partial melting reactions mainly in polymineralic inclusions within garnet the dominant textures were developed within the pressure temperature p t field of the continuous dehydration melting reaction biotite kyanite or sillimanite plagioclase quartz garnet k feldspar melt with sillimanite instead of kyanite in the southern part of the footwall inferred p t paths have a hair pin form in the range of 750 850 c and 1000 1500 mpa for the kyanite bearing rocks monazite crystallization ages are consistently late grenvillian either 995 or 985 ma and one sample contains monazite of both ages two of these samples also contain inherited monazite with ages of 1738 5 and 1719 30 ma indicative of an earlier metamorphic event tonalite and diorite from the same area yield archean zircon crystall

distribution of paleogene and cretaceous rocks around the nazko river belt of central british columbia from 3 d long offset first arrival seismic tomography across the nechako chilcotin plateau of british columbia the distribution of cretaceous sedimentary rocks which are considered prospective for hydrocarbon exploration is poorly known due to the surface cover of glacial deposits and tertiary volcanic rocks to constrain the subsurface distribution of these cretaceous rocks in 2008 geoscience bc acquired seven long up to 14 4 km offset vibroseis seismic reflection lines across a north northwest trending belt of exhumed sedimentary rocks inferred to be part of the taylor creek group p wave velocity models which are consistent with sonic logs from nearby wells have been estimated using three dimensional first arrival tomography to depths ranging from 1 to 4 km igneous basement can be identified on most lines using the 5 5 km s isovelocity contour which locates the top of the basement to an accuracy of 400 m where its depth is known in exploration wells there is no general distinction on the basis of seismic velocity between cretaceous sedimentary

genesis of an esker like ridge over the southern fraser plateau british columbia implications for paleo ice sheet reconstruction based on geomorphic inversion abstract robust interpretations of meltwater systems operating during ice sheet decay are integral to reconstructing deglacial patterns and style yet over reliance on meltwater landform morphology with limited attention to morpho sedimentary relationships and basin scale geomorphic and stratigraphic context can lead to unreliable geomorphic inversion based paleo ice sheet reconstructions this problem is illustrated by the evolution of young lake esker like ridge yler formed in the young lake basin ylb on bc s southern fraser plateau during decay of the last cordilleran ice sheet cis we integrate data from digital elevation models aerial photographs sedimentary outcrops water wells and shallow geophysics ground penetrating radar electrical resistivity tomography previous interpretations of yler as both an esker and an ice contact poorly sorted stratified deposit emplaced by westerly flowing meltwater imply an eastward retreating ice margin geophysical data from a flat topped component of yler reveal slipface and planar bedded sand and gravel overlying lacustrine sediments characteristic of a hjulstrom delta eastward dipping foresets in a gilbert delta exist at the eastern terminus contextually our observations suggest despite esker like morphology yler was not deposited within a subglacial ice tunnel instead it formed through deposition of subaerial outwash between and or on dead ice in front of a regionally backwasting ice margin the complex deglacial evolution of ylb including a drainage reversal and formation of two glacial lakes supports northwestward backwasting of the cis and dead ice within ylb we conclude that accurate geomorphic inversion of meltwater landforms for deglacial paleo ice sheet reconstruction requires knowledge of landform scale morpho sedimentary relationships and basin scale geomorphic and stratigraphic context

grenville front zone gagnon terrane southwestern labrador configuration of a midcrustal foreland fold thrust belt 1 evolution of a metamorphic fold thrust belt in archean and proterozoic rocks in the gagnon terrane northwestern grenville province involved underthrusting beneath a crustal scale orogenic wedge and metamorphism ranging from upper greenschist facies 600 100 mpa 450 50 c to upper amphibolite facies 1100 100 mpa 750 50 c during the terminal stages of the grenvillian orogeny structural and metamorphic data indicate that d1 structures formed at peak pressures during basal accretion to the overriding orogenic wedge whereas d2 structures developed within the wedge during its displacement toward the foreland in a sinistral transpressive setting the fold thrust belt developed sequentially on two levels a thin skinned cover dominated thrust system preceded and overlies a thick skinned basement dominated system the d3 cross folds postdated normal faulting at the top of the wedge and formed during gravitational collapse on the basis of this study characteristic features of midcrustal metamorphic thrust wedges include growth by basal accretion polyphase ductile deformation and noncoaxial strain dual level development extensive basement involvement and terminal gravitational collapse associated with cross folding

lithostratigraphic and tectonic framework of jurassic and cretaceous intermontane sedimentary basins of south central british columbia1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia the south central intermontane belt of british columbia has a complex architecture comprising late paleozoic to mesozoic volcanic and plutonic arc magmatic suites marine and nonmarine clastic basins high grade metamorphic complexes and accretionary rocks jurassic and cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential the geology is complicated by cretaceous to eocene deformation dismemberment and dislocation the eocene to neogene history of the southern intermontane belt is dominated by non arc volcanism followed by pleistocene to recent glaciation the volcanic and glacial cover makes this a difficult region to explore for resources much recent work has involved re evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis this paper summarizes the lithological and stratigraphic fra

mapping quaternary paleovalleys and drift thickness using petrophysical logs northeast british columbia fontas map sheet nts 94ithis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers the relatively subdued topography of british columbia s northern interior plains does not reflect the irregular buried bedrock surface many areas have been deeply incised by preglacial rivers tha

multistage metamorphic evolution and nature of the amphibolite granulite facies transition in lofoten vesteralen norway revealed by u pb in accessory minerals abstract the nature of the amphibolite to granulite facies transition zone exposed in the lofoten vesteralen islands of northern norway and the relationships between high grade metamorphism and the genesis of an anorthosite mangerite charnockite and granite suite amcg are studied with the help of id tims u pb dating of zircon monazite and titanite in polyorogenic gneisses the western part of the region is dominated by granulite facies gneisses intruded by a 1800 1790 ma amcg suite and characterized by a strong magnetic and gravity anomaly to the east this zone borders a crustal section with amphibolite facies gneisses migmatites and granites the transition has been considered to reflect the amphibolite to granulite facies metamorphic gradient of a palaeoproterozoic orogenic event the results of this study show that the region underwent multiple high grade events one in the late archean at ca 2640 ma one in the period slightly before

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

pleistocene reversal of the fraser river british columbia the fraser river in british columbia canada is the longest non dammed river on the west coast of north america and supplies 20 10 6 t yr of sediment to the pacific ocean abundant geomorphological evidence indicates that the fraser river reversed its course to southward flow in the recent geological past investigation of two volcanic dams at dog creek demonstrates northward flow of the fraser until at least 1 06 ma before reversal and erosion of the 270 km long fraser canyon we propose that the submarine nitinat fan off the coast of british columbia records the reversal and sudden input of coarse continental derived sediment ca 0 76 ma this study confirms reversal of the fraser river and places a firm constraint on the maximum age of that reversal reversal likely followed stream capture in response to enhanced glaciofluvial erosion and uplift of the coast mountains

towards a morphogenetic classification of eskers implications for modelling ice sheet hydrology abstract validations of paleo ice sheet hydrological models have used esker spacing as a proxy for ice tunnel density changes in crest type cross sectional shape along esker ridges have typically been attributed to the effect of changing subglacial topography on hydro and ice dynamics and hence subglacial ice tunnel shape these claims assume that all eskers formed in subglacial ice tunnels and that all major subglacial ice tunnels produced a remnant esker we identify differences in geomorphic context sinuosity cross sectional shape and sedimentary architecture by analysing eskers formed at or near the margins of the last cordilleran ice sheet on british columbia s southern fraser plateau and propose a morphogenetic esker classification three morphogenetic types and 2 subtypes of eskers are classified based on differences in geomorphic context ridge length sinuosity cross sectional shape and sedimentary architecture using geophysical techniques and sedimentary exposures they largely record seasonal meltwater flows and glacial lake outburst floods glofs through sub en and supraglacial meltwater channels and ice walled canyons general principles extracted from these interpretations are 1 esker ridge crest type and sinuosity strongly reflect meltwater channel type eskers formed in subglacial conduits are likely to be round crested with low sinuosity except where controlled by ice structure or modified by surging and contain faults associated with flank collapse eskers formed near or at the ice surface are more likely to be sharp crested highly sinuous and contain numerous faults both under ridge crest lines and in areas of flank collapse 2 esker ridges containing numerous flat crested reaches formed directly on the land surface in ice walled canyons unroofed ice tunnels or in ice tunnels at atmospheric pressure and therefore likely record thin or dead ice 3 eskers containing macroforms exhibiting headward and downflow growth likely record flood scale flows possibly glofs where a lake can be inferred these conclusions suggest that esker crest type sinuosity and geomorphic context when understood along with sedimentary architecture largely reflect formational position with respect to the ice surface reconstructions of ice sheet hydrology need to account for variation in esker morphology because basing hydrodynamic inferences on the presence or absence of an esker alone ignores encoded differences in water source supply flow magnitude and frequency and conduit position

the late wisconsinan deglacial history of the east central taseko lakes area british columbia late wisconsinan fraser glaciation retreat phase deposits and landforms in the east central taseko lakes area british columbia are used to demonstrate a four phase model of deglaciation during phase i at the onset of ice retreat the cordilleran ice sheet occupied much of the study area blocking southward drainage of fraser river phase ii was marked by the deglaciation of uplands and plateaux meltwater drainage patterns were controlled by stagnating glaciers confined to valleys phase iii commenced as remnant ice in the fraser valley downwasted to between 850 and 760 m elevation at this time interlobate glacial lakes formed in hanging valleys east of fraser river drainage of glacial lakes occurred subglacially and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys these events were followed by decreased sedimentation rates reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase iv postglaciation valley fill was subj

eocene and neogene volcanic rocks in the southeastern nechako basin british columbia interpretation of the canadian hunter seismic reflection surveys using first arrival tomography geological investigation of the near surface in the southeastern nechako basin is difficult shallow seismic reflection imaging is poor due in part to an extensive cover of eocene and neogene volcanic rocks outcrops of these volcanic rocks and the primarily cretaceous bedrock are commonly obscured by quaternary deposits and vegetation estimates of near surface p wave velocity are derived from the tomographic inversion of seismic first arrivals an effective tool when seismic imaging is poor tomographic model velocities are in agreement with sonic logs and laboratory samples except for those from the neogene chilcotin group cretaceous sedimentary rocks have velocities of 2800 4200 ms 1 the eocene endako and ootsa lake groups which have velocities of 3000 4200 ms 1 are not distinguishable based on velocity the velocity the character density focus and penetration depth of rays and ties with well and surface geology constrain the subsurface extent of the endako group adjacent to well b 82 c

neogene chilcotin basalts in south central british columbia geology ages and geomorphic history an extensive but generally thin mantle of basalt flows the chilcotin group covers much of the interior plateau of south central british columbia it provides material for dating and for reconstructing the original form of the paleosurface on which it was deposited k ar whole rock dates demonstrate that several ages of basalt are represented from early miocene or even late oligocene to early pleistocene with particularly abundant eruptions about 14 16 9 6 and 1 3 ma ago basalts of middle miocene and later ages if not the early miocene relics as well clearly rest on land surfaces of low local relief in places the low relief surfaces had been incised to depths of 100 200 m and the valleys backfilled with mid or late cenozoic sediments prior to burial by the basalts the low relief surfaces throughout the area are believed to have been developed close to a common base level and regional differences in their present elevation are thus largely a product of post basalt deformation this is recorded

the gang ranch big bar area south central british columbia stratigraphy geochronology and palynology of the tertiary beds and their relationship to the fraser fault tertiary rocks in the gang ranch big bar area south central british columbia consist of 1 early or middle eocene 50 ma lavas breccias and tuffs capped by a mappable unit of conglomerate a

correcting airborne gravity data for overburden thickness a case study from the nechako interior plateau british columbia large areas of bedrock in canada such as in the interior plateau of british columbia are covered by a thick glacial overburden lateral variations in overburden thickness can create spurious anom

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

chemical imprint of highly metamorphosed volcanic hosted hydrothermal alterations in the la romaine supracrustal belt eastern grenville province quebec the la romaine supracrustal belt and the southeastern end of the wakeham group in the eastern grenville province canada host a series of pinwarian 1 50 ga felsic dominated volcanic centres metamorphosed at amphibolite to granulite facies during the grenville orogeny the centres are interpreted as being related to the emergence of rhyolitic domes in shallow marine intra arc basins within the active pinwarian continental magmatic arc high grade metamorphosed hydrothermal alteration zones are intimately associated with pyroclastic deposits composing these volcanic centres and an overlying composite amphibolite unit they comprise layers of rhyolitic metatuff bearing networks of aluminous nodules and veins migmatized garnet biotite sillimanite gneiss with well preserved volcanic fragments and mottled quartz cordierite gneiss with textures similar to those of vuggy silica facies alteration zones of ironstone carbonate and calc silicate rocks garnetite diopsidite epidosite and sulphide mineralizati

the quaternary stratigraphic record of british columbia evidence for episodic sedimentation and erosion controlled by glaciation the terrestrial quaternary stratigraphic record of british columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion thick stratified quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the cordilleran ice sheet at glacial maxima till was deposited over large areas of low and moderate relief however at the same time much of the landscape was eroded by glaciers sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations on land the only important sediment accumulation sites during nonglacials have been lakes floodplains and fans however large amounts of sediment have accumulated offshore especially in fjords and basins such as the strait of georgia because of the restricted aspect of sedimentation during nonglacials the stratigraphic record of these periods is meagre in most places true nonglacial uni