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

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.

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

1988 ◽  
Vol 25 (11) ◽  
pp. 1725-1739 ◽  
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.

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

1975 ◽  
Vol 12 (4) ◽  
pp. 595-605 ◽  
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.

Structural evolution of basement gneisses and Hadrynian cover, Bulldog Creek area, Rocky Mountains, British Columbia

1988 ◽  
Vol 25 (10) ◽  
pp. 1687-1702 ◽  
Author(s):  
Michael R. McDonough ◽  
Philip S. Simony
Keyword(s):  
British Columbia ◽  
Structural Evolution ◽  
Rocky Mountain ◽  
Strike Slip ◽  
Normal Faulting ◽  
The West ◽  
Kinematic Indicators ◽  
Thrust Sheets ◽  
Dextral Strike Slip ◽  
Southern Rocky Mountain

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.

Imbricated terranes of the Cariboo gold belt with correlations and implications for tectonics in southeastern British Columbia

1986 ◽  
Vol 23 (8) ◽  
pp. 1047-1061 ◽  
Author(s):  
L. C. Struik
Keyword(s):  
British Columbia ◽  
Continental Shelf ◽  
Rocky Mountains ◽  
Rocky Mountain ◽  
East Central ◽  
Pillow Basalt ◽  
Shelf Sediments ◽  
Kootenay Lake ◽  
Southern Rocky Mountain ◽  
Bounded Sequences

The Cariboo gold belt of east-central British Columbia is divided into four fault-bounded sequences of distinct stratigraphy. They are, from east to west, the Cariboo (continental-shelf sediments), Barkerville (continental-shelf sediments and intercalated volcanics), Slide Mountain (rift-related submarine pillow basalt, chert, and diorite) and Quesnel (island-arc sediments and subaqueous volcanics) terranes. Each is separated from others by thrust faults. Grit, phyllite, limestone, and volcanics of the Barkerville terrane may be correlative with the Eagle Bay Formation near Adams Lake and the Lardeau Group near Kootenay Lake. Barkerville terrane may be part of a more regional rock package, Selkirk terrane, which is defined to include Kootenay terrane, Badshot Formation, and Horsethief Creek and Hamill groups. Selkirk terrane is (i) separated everywhere by a low-angle fault from the overlying age-equivalent but stratigraphically and structurally different Cariboo terrane and (ii) separated by a system of faults in the general location of the Southern Rocky Mountain Trench from the age-equivalent but stratigraphically and structurally different North American terrane of the Rocky Mountains.

Proterozoic gneisses of the Malton Complex, near Valemount, British Columbia: U–Pb ages and Nd isotopic signatures

1991 ◽  
Vol 28 (8) ◽  
pp. 1202-1216 ◽  
Author(s):  
Michael R. McDonough ◽  
Randall R. Parrish
Keyword(s):  
British Columbia ◽  
Rocky Mountain ◽  
Granite Gneiss ◽  
Canadian Shield ◽  
Crustal Material ◽  
East Side ◽  
Complex Span ◽  
Late Proterozoic ◽  
Zircon Crystallization ◽  
Southern Rocky Mountain

Proterozoic gneisses of the Malton Complex in the vicinity of Valemount, British Columbia, occur in a series of lithologically and structurally complex, fault-bounded slices of crystalline basement and interleaved cover. Gneisses of the Malton Complex span the Southern Rocky Mountain Trench and underlie the western part of the Rocky Mountain fold and thrust belt and the eastern part of the Omineca Belt of the Canadian Cordillera. Structural and stratigraphic relationships indicate that they formed the basement upon which an enigmatic quartzite unit and the Late Proterozoic Windermere Supergroup were deposited.The Yellowjacket and Bulldog gneisses, on the east side of the Rocky Mountain Trench, have yielded four U–Pb zircon crystallization ages of ca. 1870 Ma, with εNd(T) values of −2.6 to −3.4. The Hugh Allan gneiss, also on the east side of the trench but separated from the Yellowjacket gneiss by a major thrust fault, includes leucocratic granite gneiss having a zircon U–Pb age of [Formula: see text], which has intruded an older (undated) lithologically heterogeneous assemblage of gneiss. The basal Windermere succession of the Valemount region is inferred to be younger than ca. 740 Ma, since these intrusions are not found within the Late Proterozoic stratified rocks.Augen granitoid orthogneiss of the Malton Range on the west side of the Rocky Mountain Trench has been dated as [Formula: see text] using zircons. A second sample yields data suggesting an age between 2050 and 2100 Ma, but its interpretation is uncertain because of scatter in analyses and possible zircon inheritance. The latter sample has an εNd(T) at 1990 Ma of −2.6. Nd model ages for the Malton, Yellowjacket, and Bulldog samples range from 2.45 to 2.56 Ga, indicating that the igneous protoliths were derived from a source that probably had some component of Archean crustal material involved.The U–Pb ages and Nd model ages are quite similar to those of rocks underlying portions of Alberta and the western Canadian Shield, specifically the Fort Simpson terrane, the Great Bear magmatic zone, and parts of the Thelon–Taltson arc. This evidence, as well as structural and stratigraphic arguments, links the Malton Complex gneisses with those of the Canadian Shield, precluding their derivation by large-magnitude displacements from the southwestern United States. Structural analysis indicates that they restore to locations 100–200 km southwest of their present exposure.Structural, stratigraphic, and isotopic data indicate that the Southern Rocky Mountain Trench is not a suture.

Sign in / Sign up

Export Citation Format

Share Document