Direct Evidence For Dextral Strike - Slip Displacement From Mylonites in the southern Rocky Mountain Trench near Valemount, British Columbia

Two gneiss bodies are contained in thrust sheets on the west edge of the Rocky Mountain Main Ranges near Valemount, British Columbia. The Bulldog Gneiss comprises Aphebian or older paragneiss and amphibolitic gneiss intruded by Aphebian orthogneiss sheets. The Yellowjacket Gneiss is granodioritic orthogneiss of unknown age. Both gneiss bodies are basement highs with thin Hadrynian metasediment cover sequences. The cover sequences are assigned to the lower Miette Group and are correlated with Horsethief Creek Group.Internal shortening of gneiss thrust sheets is expressed by recumbent folding and stacking of thin thrust sheets of gneiss and cover. The Bulldog Gneiss and its cover were carried on the postmetamorphic Purcell Thrust. The Yellowjacket Gneiss and its cover were carried on the pre- to synmetamorphic Bear Foot Thrust. Northeast and northwest displacement is documented on the moderately southwest-dipping Bear Foot Thrust, and a dextral oblique-slip – thrust model is proposed to explain the duality of thrust and dextral strike-slip kinematic indicators in mylonite from the fault. An estimate of shortening in the fore-land suggests that basement thrust sheets were translated more than 200 km to the northeast.Correlation of gneisses and cover with the westerly adjacent Malton Gneiss and its cover precludes major dextral strike-slip motion on the Southern Rocky Mountain Trench (SRMT) during and after thrusting. The SRMT was the locus of post-thrusting and postmetamorphic, Eocene(?), brittle, west-side-down, normal faulting.

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Tertiary extension in the central British Columbia Intermontane Belt: magnetic and paleomagnetic evidence from the Endako region

Canadian Journal of Earth Sciences ◽

10.1139/e00-070 ◽

2001 ◽

Vol 38 (4) ◽

pp. 657-678 ◽

Cited By ~ 6

Author(s):

Carmel Lowe ◽

Randolph J Enkin ◽

Lambertus C Struik

Keyword(s):

British Columbia ◽

Strike Slip ◽

Paleomagnetic Data ◽

Magnetic Data ◽

Euler Deconvolution ◽

The West ◽

Near Surface ◽

Dextral Strike Slip Fault ◽

Slip Displacement ◽

Dextral Strike Slip

New magnetic and paleomagnetic data for central British Columbia support and quantify the hypothesis that the area underwent significant Tertiary-age transtensional deformation. Paleomagnetically determined tilts in Eocene rocks indicate that four fault-bounded pits, which constitute the Endako molybdenum mine, were displaced on a series of normal (probably listric) faults that have separations of less than a kilometre. The interpretation also suggests there can be little vertical offset on the Denak West Fault, which separates the Denak East and Denak West pits. Regional paleomagnetic data indicate a predominance of easterly directed tilts to the east of the Casey Fault, but to the west a large variation in the orientation and magnitude of tilts is observed. Results at one site proximal to the Casey Fault indicate a component of dip-slip displacement on this dominantly dextral strike-slip fault. Mapped northeast- and northwest-trending faults commonly correspond to linear zones of steep magnetic gradient and near-surface magnetic sources. Several additional northwest- and northeast-trending lineaments are imaged in the magnetic data where no faults are mapped (particularly over massive and lithologically homogeneous phases of the Endako batholith). Euler deconvolution solutions confirm most such lineaments are also associated with shallow magnetic sources. In profile, they have either a fault or dyke character and are interpreted to be unmapped faults, some locally intruded by mafic dykes, which cut the region into a series of fault-bounded blocks.

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Dextral strike-slip faulting in the Cariboo Mountains, British Columbia: a natural example of wrench tectonics in relation to Cordilleran tectonics

Canadian Journal of Earth Sciences ◽

10.1139/e02-017 ◽

2002 ◽

Vol 39 (6) ◽

pp. 953-970 ◽

Cited By ~ 6

Author(s):

L F Reid ◽

P S Simony ◽

G M Ross

Keyword(s):

British Columbia ◽

Rocky Mountain ◽

Strike Slip ◽

Strike Slip Fault ◽

Fault System ◽

Fault Systems ◽

Dextral Strike Slip Fault ◽

Deformation Event ◽

Step Over ◽

Dextral Strike Slip

The Cariboo Mountains, British Columbia, contain an intracontinental dextral strike-slip fault system that crosscuts the regional fold structures. This fault system accounts for a minimum of 120 km and a maximum of 200 km of dextral strike-slip displacement. This probably accommodates some of the motion associated with the southern termination of the Northern Rocky Mountain Trench Fault and is part of a step-over zone between the Northern Rocky Mountain Trench Fault and the Fraser River Straight Creek fault systems. The Isaac Lake Synclinorium is a kilometre-scale Jurassic fold structure that is bounded by the dextral oblique Isaac Lake and Winder strike-slip faults. These faults are part of the regional strike-slip fault system that is found throughout the Cariboo Mountains. Deformation associated with the strike-slip faults is complex and is partitioned into motion along the faults and into the formation of kilometre-scale folds that are found in areas between the faults. The angular relationship between the strike-slip faults and folds conforms to models developed for dextral strike-slip fault systems with drag on high-friction faults. We interpreted these structures to have formed during a continuous deformation event. Timing constraints indicate that faulting started by the Late Cretaceous and may have had a long and protracted history into the Tertiary.

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Walker Creek fault zone, central Rocky Mountains, British Columbia-southern continuation of the Northern Rocky Mountain Trench fault zone

Canadian Journal of Earth Sciences ◽

10.1139/e00-038 ◽

2000 ◽

Vol 37 (9) ◽

pp. 1259-1273 ◽

Cited By ~ 6

Author(s):

M E McMechan

Keyword(s):

Fault Zone ◽

Late Cretaceous ◽

Lateral Displacement ◽

Shear Bands ◽

Rocky Mountain ◽

Strike Slip ◽

Fault System ◽

Early Eocene ◽

Fold And Thrust Belt ◽

Slip Displacement

Walker Creek fault zone (WCFZ), well exposed in the western Rocky Mountains of central British Columbia near 54°, comprises a 2 km wide zone of variably deformed Neoproterozoic and Cambrian strata in fault-bounded slivers and lozenges. Extensional shear bands, subhorizontal extension lineations, slickensides, mesoscopic shear bands, and other minor structures developed within and immediately adjacent to the fault zone consistently indicate right-lateral displacement. Offset stratigraphic changes in correlative Neoproterozoic strata indicate at least 60 km of right-lateral displacement across the zone. WCFZ is the southern continuation of the Northern Rocky Mountain Trench (NRMT) fault zone. It shows a through going, moderate displacement, strike-slip fault system structurally links the NRMT and the north-central part of the Southern Rocky Mountain Trench. Strike-slip motion on the WCFZ occurred in the Late Cretaceous to Early Eocene at the same time as northeast-directed shortening in the fold-and-thrust belt. Thus, oblique convergence in the eastern part of the south-central Canadian Cordillera was apparently resolved into parallel northwest-striking zones of strike-slip and thrust faulting during the Late Cretaceous to Early Eocene. The change in the net Late Cretaceous to Early Eocene displacement direction for rocks in the Rocky Mountain trenches from north (56-54°N) to northeast (52-49°N) suggests that the disappearance of strike-slip displacement and increase in fold-and-thrust belt shortening in the eastern Cordillera between 56° and 49°N is largely the result of a north-south change in relative plate motion or strain partitioning across the Cordillera, rather than the southward transformation of right-lateral strike-slip displacement on the Tintina - NRMT fault system into compressional deformation.

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Structural geology of the Lardeau Group near Trout Lake, British Columbia: implications for the structural evolution of the Kootenay Arc

Canadian Journal of Earth Sciences ◽

10.1139/e92-104 ◽

1992 ◽

Vol 29 (6) ◽

pp. 1305-1319 ◽

Cited By ~ 6

Author(s):

Moira T. Smith ◽

George E. Gehrels

Keyword(s):

British Columbia ◽

Shear Zone ◽

Structural Evolution ◽

Strike Slip ◽

Ductile Deformation ◽

Lower Paleozoic ◽

Trout Lake ◽

Facies Metamorphism ◽

Dextral Strike Slip ◽

Greenschist Facies Metamorphism

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic eugeoclinal strata present in the Kootenay Arc in southeastern British Columbia. It is in fault contact with lower Paleozoic miogeoclinal strata for all or some of its length along a structure termed the Lardeau shear zone. The Lardeau Group was deformed prior to mid-Mississippian time, as manifested by layer-parallel faults, folds, and evidence for early greenschist-facies metamorphism. Regional constraints indicate probable Devono-Mississippian timing of orogeny, and possible juxtaposition of the Lardeau Group over miogeoclinal strata along the Lardeau shear zone at this time. Further ductile deformation during the Middle Jurassic Columbian orogeny produced large folds with subhorizontal axes, northwest-striking foliation and faults, and orogen-parallel stretching lineations. This deformation was apparently not everywhere synchronous, and may have continued through Late Jurassic time northeast of Trout Lake. This was followed by Cretaceous(?) dextral strike-slip and normal movement on the Lardeau shear zone and other parallel faults. While apparently the locus of several episodes of faulting, the Lardeau shear zone does not record the accretion of far-travelled tectonic fragments, as sedimentological evidence ties the Lardeau Group and other outboard units to the craton.

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Dextral Strike - Slip Faulting and Associated Extension Along the southern Portion of the Louscoone Inlet Fault System, southern Queen Charlotte Islands, British Columbia

10.4095/132536 ◽

1991 ◽

Cited By ~ 1

Author(s):

P D Lewis

Keyword(s):

British Columbia ◽

Strike Slip ◽

Fault System ◽

Queen Charlotte Islands ◽

Dextral Strike Slip

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Geochemistry of the gneissic basement complex near Valemount, British Columbia: further evidence for a varied origin

Canadian Journal of Earth Sciences ◽

10.1139/e88-164 ◽

1988 ◽

Vol 25 (11) ◽

pp. 1725-1739 ◽

Cited By ~ 4

Author(s):

V. E. Chamberlain ◽

R. St J. Lambert ◽

M. J. M. Duke ◽

J. G. Holland

Keyword(s):

British Columbia ◽

Rocky Mountain ◽

Small Scale ◽

Basement Complex ◽

X Ray ◽

Low Magnesium ◽

Upper Proterozoic ◽

Four Blocks ◽

Southern Rocky Mountain ◽

Representative Samples

Rare-earth elements and other trace elements have been determined by activation analysis and X-ray fluorescence for representative samples from each of the four blocks of basement gneisses near Valemount, eastern British Columbia. Patterns in mafic and tonalitic gneisses are generally as expected, but the granite–gneisses have very large negative europium anomalies, up to Eu*/Eu = 18, indicating multistage histories involving plagioclase fractionation. Modelling shows that plagioclase fractionation alone is insufficient to account for these anomalies without intervention of other phases: apatite control is suggested, among other possibilities. The granite–gneisses also contain exceptionally low magnesium (0.1–0.2%), phosphorus (<300 ppm), scandium (<0.07 ppm), and cesium (<0.5 ppm). After partial melting is considered as a possible mode of origin, it is concluded that the granite–gneisses are final, small-scale fractionates from enriched tholeiite magmas. These might be associated with upper Proterozoic rifting processes. Previously published conclusions regarding the protolith of each subset of the gneisses are confirmed; likewise, the earlier conclusion that the gneisses cannot be correlated across the Southern Rocky Mountain Trench is substantiated in detail.

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Late Paleozoic and Mesozoic terrane interactions in north-central British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e91-086 ◽

1991 ◽

Vol 28 (6) ◽

pp. 947-957 ◽

Cited By ~ 37

Author(s):

Hubert Gabrielse

Keyword(s):

British Columbia ◽

North America ◽

Middle Jurassic ◽

Subsequent Development ◽

Structural Data ◽

Strike Slip ◽

Granitic Rocks ◽

Late Triassic ◽

North Central ◽

Dextral Strike Slip

Five clearly defined terranes, comprising from northeast to southwest, Ancestral North America, Slide Mountain, Quesnellia, Cache Creek, and Stikinia, are the dominant tectonic elements of north-central British Columbia. Stratigraphic, sedimentological, plutonic, metamorphic, and structural data show that the Slide Mountain Terrane evolved as a subduction, accretion, and island-arc complex during Permian time. Sedimentological data hint at the demise of the Slide Mountain and Cache Creek oceanic environments in the Permian or Early Triassic and Late Triassic, respectively. Subduction led to the development of volcanic–plutonic island arcs on Stikinia, Quesnellia, and locally on the Cache Creek Terrane in Late Triassic to Middle Jurassic time. Marked inter- and intra-terrane contraction in the Middle Jurassic resulted in the south westward thrusting of the Cache Creek Terrane onto Stikinia, the subsequent development of the Bowser Basin on Stikinia, and possible coeval culmination of the emplacement of Quesnellia and the Slide Mountain Terrane onto Ancestral North America. Deformation, metamorphism, and plutonism along the western margin of Ancestral North America closely followed these events. Contraction was succeeded by a dextral strike-slip regime during the mid-Cretaceous accompanied by the intrusion of voluminous potassic, silica-rich granitic rocks in Ancestral North America. The emplacement of Early to mid-Cretaceous plutons postdated the development of broad, open, regional anticlinoria and synclinoria, perhaps during Early Cretaceous time. The plutonic episode coincided approximately with initiation of the Sustut Basin. Dextral strike-slip faulting further disrupted Ancestral North America until post-Eocene time.

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Structure and Dynamics of the Southern Rocky Mountain Trench near Valemount, British Columbia, Inferred from Local Seismicity

Seismological Research Letters ◽

10.1785/0220200350 ◽

2021 ◽

Author(s):

Joshua C. S. Purba ◽

Hersh Gilbert ◽

Jan Dettmer

Keyword(s):

British Columbia ◽

Correlation Coefficients ◽

Rocky Mountain ◽

Earthquake Catalog ◽

P Waves ◽

Local Seismicity ◽

Subsurface Structures ◽

Level Of Activity ◽

And Shifts ◽

Southern Rocky Mountain

Abstract Stretching nearly the extent of the Canadian Cordillera, the Rocky Mountain trench (RMT) forms one of the longest valleys on Earth. Yet, the level of seismicity, and style of faulting, on the RMT remains poorly known. We assess earthquakes in the southern RMT using a temporary network of seismometers around Valemount, British Columbia, and identify active structures using a probabilistic earthquake catalog spanning from September 2017 to August 2018. Together with results from earlier geological and seismic studies, our new earthquake catalog provides a constraint on the geometry of subsurface faults and their level of activity during a year of recording. The tectonic analysis presented here benefits from the catalog of 47 earthquakes, including robust horizontal and vertical uncertainty quantification. The westward dip of the southern RMT fault is one of the prominent subsurface structures that we observe. The seismicity observed here occurs on smaller surrounding faults away from the RMT and shifts from the east to the west of the trench from north to south of Valemount. The change in distribution of earthquakes follows changes in the style of deformation along the length of the RMT. Focal mechanisms calculated for two earthquakes with particularly clear waveforms reveal northeast–southwest-oriented thrusting. The seismicity reveals a change in the pattern of deformation from narrowly focused transpression north of Valemount to more broadly distributed activity in an area characterized by normal faulting to the south. Six sets of repeating events detected here produce similar waveforms whose P waves exhibit correlation coefficients that exceed 0.7 and may result from the migration of fluids through the fractured crust.

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Late Quaternary Sediments and Geomorphic History of the Southern Rocky Mountain Trench, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e75-054 ◽

1975 ◽

Vol 12 (4) ◽

pp. 595-605 ◽

Cited By ~ 20

Author(s):

John J. Clague

Keyword(s):

British Columbia ◽

Short Duration ◽

Late Quaternary ◽

Lacustrine Sediments ◽

Rocky Mountain ◽

Quaternary Sediments ◽

Glacier Recession ◽

History Of ◽

Cordilleran Ice Sheet ◽

Southern Rocky Mountain

The southern Rocky Mountain Trench was a major outlet valley of the Cordilleran Ice Sheet. Quaternary sediments underlying the floor of the trench in southeastern British Columbia consist mainly of glacial, glaciofluvial, and glaciolacustrine materials deposited during the Fraser (Pinedale) Glaciation, and fluvial and lacustrine sediments deposited during the preceding interglaciation.Deposits of three stades and two intervening nonglacial intervals are recognized. Interglacial sediments which contain wood dated at 26 800 ± 1000 y B.P. underlie drift of the early stade. During the interval between the early and middle stades, the Rocky Mountain Trench in southeastern British Columbia probably was completely deglaciated, and sediments were deposited in one or more lakes on the floor of the trench. In contrast, glacier recession between the middle and late stades was of short duration and extent; glaciolacustrine sediments were deposited only along the margins of the Rocky Mountain Trench, and apparently residual ice remained in the center of the valley. Final recession of the trunk glacier occurred prior to 10 000 y B.P. with no major halts and without significant stagnation of the terminus.

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