Columbia River fault zone: southeastern margin of the Shuswap and Monashee complexes, southern British Columbia

1981 ◽  
Vol 18 (7) ◽  
pp. 1127-1145 ◽  
Author(s):  
Peter B. Read ◽  
Richard L. Brown
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Columbia River ◽  
Glacial Sediments ◽  
Monashee Complex ◽  
Southeastern Margin ◽  
Minimum Age ◽  
History Of ◽  
Slip Displacement ◽  
Fault Scarps

The Columbia River fault zone extends for 250 km from south of Nakusp, through Revelstoke, to north of Bigmouth Creek. It is a composite fault zone, which dips 20–30° easterly and separates major tectonic elements. The structurally lowest element is the Monashee Complex, which includes the culminations of Pinnacle Peaks, Thor–Odin, and Frenchman Cap. At Hoskins Creek, the Monashee décollement splays westward from the fault zone and then runs southward along the western margin of the Monashee Complex. On the east side, the Selkirk allochthon is a composite of four tectonic slices. Its western part consists of Clachnacudainn, Goldstream, and French Creek slices forming the hanging wall of the Columbia River fault zone. The remainder of the allochthon forms the highest and largest Illecillewaet slice, which may be composite.The fault zone retains evidence of a long history of movement extending from the mid-Mesozoic to Eocene. Early deformation formed a mylonite zone up to 1 km wide in which rocks recrystallized under greenschist facies conditions. The displacement truncated major folds and metamorphic isograds that had developed in the Middle Jurassic. Orientation of slickensides, fiber growth, and strain features in the mylonite indicates normal, dip-slip displacement with the slices of the hanging wall moving eastward. South of Revelstoke, the Galena Bay stock, dated at 150 Ma, apparently intruded the zone and gives a minimum age for early displacement that must be in the Late Jurassic.Late displacement caused intense fracturing, folding of mylonite, and development of gouge zones. These features are well exposed at the Revelstoke damsite, continue north of Revelstoke, but diminish in importance southward. Late movement was again normal, dip-slip with the hanging wall moving eastward; it probably ended in the Eocene. No fault scarps or disrupted drainages have been observed, and at several localities glacial sediments lie undisturbed across the fault zone, indicating a lack of postglacial movement.Metamorphic zones, juxtaposed along the fault, imply a minimum dip-slip displacement of 15–25 km. Displacement in this range poses stratigraphic and metamorphic problems, which are alleviated if displacement is in excess of 80 km. The tectonic slices east of the Columbia River fault zone are part of an allochthonous cover that was transported at least tens of kilometres eastward over the Shuswap and Monashee complexes during the Late Jurassic.

Brittle deformation in the Columbia River fault zone near Revelstoke, southeastern British Columbia

1984 ◽  
Vol 21 (5) ◽  
pp. 584-598 ◽  
Author(s):  
Larry S. Lane
Keyword(s):  
Fault Zone ◽  
Columbia River ◽  
Strike Slip ◽  
Fractured Zone ◽  
Displacement Vectors ◽  
Hydroelectric Dam ◽  
Slip Displacement ◽  
Shuswap Metamorphic Complex ◽  
Local Trend ◽  
East West

The brittle Columbia River fault zone forms part of the eastern margin of the Shuswap Metamorphic Complex, and for much of its 230 km length it coincides with the eastern exposure of the ductile Monashee décollement. The Eocene brittle fracturing and displacement are broadly parallel with, but cut and disrupt the middle Jurassic ductile mylonite zone. Excavations for a hydroelectric dam and a highway have facilitated a detailed analysis of fracture patterns at several localities along the fractured zone.Regionally, the brittle fault zone strikes 350° (locally 310–030°) and dips shallowly eastward. Over most of the studied part of the zone, the distributions of subsidiary fractures and displacement vectors demonstrate a normal dip-slip displacement consistent with subhorizontal east–west extension within the fractured zone, irrespective of the local trend of the zone. At Revelstoke damsite, where the zone trends 030° for 2 km, motion was towards the southeast, possibly indicating a localized clockwise rotation postdating dip-slip displacement.Fractures preserving both early dip-slip vectors and later strike-slip vectors demonstrate that minor north–south, strike-slip motion was superimposed on all parts of the zone, though no throughgoing strike-slip fault formed.In the damsite excavation, the fractured zone is largely confined to mylonites derived from footwall terrane. The Tertiary brittle offset was minor by comparison with the Jurassic ductile displacement.

Kinematic interpretation of mylonitic rocks in part of the Columbia River fault zone, Shuswap terrane, British Columbia

1982 ◽  
Vol 19 (3) ◽  
pp. 456-465 ◽  
Author(s):  
Richard L. Brown ◽  
Donald C. Murphy
Keyword(s):  
British Columbia ◽  
Fault Zone ◽  
Hanging Wall ◽  
Regional Metamorphism ◽  
Columbia River ◽  
Coarse Grained ◽  
Thick Section ◽  
Mylonite Zone ◽  
Relationship Of ◽  
Igneous Texture

Mylonitic rocks of the Columbia River fault zone have been examined in a 600 m thick section, 20 km north of Revelstoke, British Columbia. At this locality coarse-grained granite with well-preserved igneous texture lies in the hanging wall of the fault zone. Adjacent to the boundary of the mylonite zone the granite is foliated and mineral segregation gives rise to well-defined compositional layering. The foliation (Sf) is defined by oriented mineral grains and flattened porphyroclasts. In areas of intense strain compositional layering (Sc) is parallel to Sf. At the boundary of the mylonite zone and in weakly deformed areas within the mylonite zone Sc and Sf are inclined at angles up to 30°. Sf is taken to be a plane of flattening, and Sc appears to parallel a plane of shear. After correction for effects of late-stage flexural slip folding the angular relationship of Sc to Sf may be used to determine sense of shear in the mylonitc zone; the hanging-wall rocks have been displaced toward the east relative to the footwall. Formation of mylonitic fabrics and associated displacement of the Selkirk allochthon eastward relative to the underlying Monashee Complex occurred after the Middle Jurassic peak of regional metamorphism and before brittle reactivation and uplift in the Tertiary.

Distinguishing between Archean and Paleoproterozoic tectonism, and evolution of the Isortoq fault zone, Eqe Bay area, north-central Baffin Island, Canada

2003 ◽  
Vol 40 (8) ◽  
pp. 1111-1135 ◽  
Author(s):  
K M Bethune ◽  
R J Scammell
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Granulite Facies ◽  
Lower Grade ◽  
Baffin Island ◽  
Bay Area ◽  
Southeastern Margin ◽  
Greenstone Belts ◽  
Area North ◽  
Granitoid Intrusions

Structural, metamorphic, and U–Pb geochronological data bear on the distinction between Archean and Paleoproterozoic tectonism along the southeastern margin of the Rae Province on Baffin Island. Archean rocks include ca. 3.0–2.8 Ga gneiss, two greenstone belts of the Mary River Group, and various younger granitoid intrusions. In the greenstone belts, intermediate–felsic volcanism (2.74–2.725 Ga) was accompanied and outlasted by calc-alkaline plutonism (2.73–2.715 Ga). Deformation, low- to medium-pressure metamorphism, and peraluminous plutonism followed at ca. 2.7 Ga. Archean rocks and the locally overlying Piling Group (ca. 2.2–1.9 Ga) were deformed and metamorphosed together during development of the Paleoproterozoic Foxe fold belt. Tectonism is linked to the Isortoq fault zone, a major southeast-dipping structure marking an abrupt northwestward transition to granulite facies. Within a 5-km-wide zone, tight folds of the Archean Mary River Group give way down-section to moderately southeast-dipping, highly transposed, high-grade gneissic rocks. Several northeast- and north-striking ductile–brittle faults, some recording normal-sinistral oblique displacement, truncate early gneissosity and folds. This progression, along with U–Pb metamorphic ages, suggests early northwest-directed thrusting, starting at ca. 1.85 Ga, with peak metamorphism in the footwall at ca. 1.83–1.82 Ga. Later extensional displacement caused juxtaposition of lower grade on higher grade rocks. Archean ages of metamorphism (and deformation) are well preserved only in the hanging wall and the youngest metamorphic ages are restricted to the footwall. The data indicate that mountain building involved thrust-related thickening followed by gravitational collapse, a sequence characteristic of Phanerozoic orogens.

U–Pb geochronologic constraints on the cover sequence of the Monashee complex, Canadian Cordillera: Paleoproterozoic deposition on basement

1997 ◽  
Vol 34 (7) ◽  
pp. 1008-1022 ◽  
Author(s):  
James L. Crowley
Keyword(s):  
Hanging Wall ◽  
Crystalline Basement ◽  
Detrital Zircons ◽  
Canadian Cordillera ◽  
Metasedimentary Rocks ◽  
Monashee Complex ◽  
Minimum Age ◽  
Age Constraints ◽  
Unconformable Contact ◽  
Different Parts

The cover sequence in the Monashee complex is a platformal metasedimentary succession that occupies a nearly unique position in the Canadian Cordillera due to its unconformable contact with exposed crystalline basement. Zircon U–Pb data and field observations show that the lower part of the sequence contains Paleoproterozoic rocks, the oldest known metasedimentary rocks in the Cordilleran miogeocline, and the upper part of the sequence is Mesoproterozoic or younger. Maximum age constraints on the lower part are provided by 1.99 Ga detrital zircons from the basal unit and a 1862 ± 1 Ma orthogneiss upon which it was presumably deposited. Minimum age constraints are provided by rocks that intruded into the lower part: 1852 ± 4 Ma pegmatite, 1762 ± 6 Ma leucogranite, and 724 ± 5 Ma syenitic gneiss. The upper part of the sequence must be considerably younger than the lower part because it contains a detrital zircon dated at ~1.21 Ga. Other detrital zircons, dated at Neoarchean (2.95–2.86 Ga) and Paleoproterozoic (1.85–1.81, 1.75 Ga), suggest a source in the western Canadian Shield. These ages constrain the thickness of Mesoproterozoic and Neoproterozoic metasedimentary rocks in the cover sequence to be < 2 km. Combining these ages with previously interpreted Paleozoic deposition ages for the middle and upper parts of the sequence constrains the thickness to be <0.2 km, considerably less than that of coeval rocks above the Monashee complex in the hanging wall of the Monashee décollement. Such a contrast suggests that deposition above and below the décollement occurred in different parts of the Cordilleran miogeocline.

Thermal evolution of the southeastern Canadian Cordillera

1995 ◽  
Vol 32 (10) ◽  
pp. 1618-1642 ◽  
Author(s):  
Randall R. Parrish
Keyword(s):  
Thermal History ◽  
Thermal Evolution ◽  
Hanging Wall ◽  
Paper Analysis ◽  
Canadian Cordillera ◽  
Strong Argument ◽  
Metasedimentary Rocks ◽  
Late Tertiary ◽  
Monashee Complex ◽  
History Of

The eastern metamorphic culmination of the southern Canadian Cordillera is a composite core complex, which at low structural levels exposes the Monashee décollement, a major contractional fault with large Late Cretaceous to Paleocene east-directed displacement. The hanging wall of this fault, the Selkirk allochthon, is a sheared thrust sheet, recording metamorphic and deformational events spanning the period from ca. 170 to 60 Ma, with younger kinematic and thermal events recorded at progressively deeper levels. The Monashee complex, the footwall terrane of the Monashee décollement, consists of an Early Proterozoic crystalline basement complex overlain by Late Proterozoic and perhaps Phanerozoic metasedimentary rocks. The Monashee complex was significantly metamorphosed and deformed in Paleogene time (60–55 Ma), on the basis of U–Pb data presented in this paper. Analysis of U–Pb titanite data show that the duration of this metamorphic event was but a few million years at most, and it provides a strong argument that the heat source for this metamorphism was the overlying hot Selkirk allochthon. A ~1.85–1.90 Ga metamorphism also is recorded within the Precambrian basement. The tectonometamorphic chronology of the footwall and hanging-wall terranes of the Monashee décollement are very different, and only share Paleogene thermal–tectonic events when the two were structurally juxtaposed by deep-seated thrusting. Although this region is the hinterland of the foreland belt of the southern Cordillera, the thermal and tectonic history of the metamorphic core zone is analogous to that in a thrust belt setting where warmer rocks progressively override cooler rocks as displacement migrates toward the foreland. In such settings, a protracted and more complex thermal history of the hanging wall is juxtaposed with a simpler thermal history of shorter duration of the footwall. Seismic reflection and chronological information indicate that the Monashee décollement is the same structure as the basal décollement beneath the full width of the southern Rocky Mountains, representing its deep-seated continuation in the hinterland. Tectonic denudation resulting from Eocene extension and crustal-scale tilting, followed by late Tertiary erosion, brought these rocks to the surface for study.

Age and isotopic character of Early Proterozoic basement gneisses in the southern Monashee Complex, southeastern British Columbia

1991 ◽  
Vol 28 (8) ◽  
pp. 1159-1168 ◽  
Author(s):  
Dave Parkinson
Keyword(s):  
Fault Zone ◽  
Columbia River ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Early Proterozoic ◽  
Pelitic Schist ◽  
Monashee Complex ◽  
Gray Gneiss ◽  
Proterozoic Basement ◽  
Augen Gneiss

The southern Monashee Complex is a fault-bounded exposure of upper-amphibolite-grade basement gneisses (core gneisses) and unconformably overlying mantling metasedimentary gneisses. The eastern margin is marked by the Early Eocene ductile to brittle Columbia River fault zone; the western and southern margins are marked by the Monashee Decollement and structurally higher Selkirk allochthon.The basement gneisses are exposed in the cores of large, northeast-verging nappes that subsequently have been overprinted towards the east by the Columbia River fault zone. The basement gneisses are a supracrustal sequence intruded by at least two distinct orthogneisses: (i) a biotite granite gneiss ("gray gneiss") dated by U/Pb zircon at 1874 ± 21 Ma; and (ii) a ±hornblende–biotite K-feldspar augen gneiss dated by U/Pb zircon at 1934 ± 6 Ma.The supracrustal gneisses are predominantly heterogeneous biotite–quartz–feldspar gneiss interlayered with less common pelitic schist and calc-silicate gneiss. U/Pb zircon data on detrital zircon populations from this heterogeneous supracrustal sequence give 207Pb*/206Pb* ages of less than 2.2 Ga. Whole-rock Pb isotopic data indicate an age of approximately 2.0 Ga. Whole-rock Sm/Nd model ages on the two intrusive suites indicate separate sources, the 1874 Ma gneiss having been produced from similar-age juvenile Early Proterozoic material (TDM ≈ 2.2 Ga). In contrast, Nd data from the 1934 Ma augen gneiss clearly indicate interaction with a component of older (late Archean) material (TDM ≈ 2.8 Ga). Whole-rock Sm/Nd data from the supracrustal gneisses follow this same pattern, with one group (seven samples) similar to the 1874 Ma gneiss (with TDM ≈ 2.3–2.6 Ga) and a second group (five samples) showing provenance or derivation from an Archean source (TDM = 2.8–3.3 Ga). The age of the intrusive suites, combined with the Nd data, strongly argues for a correlation with the Early Proterozoic Wopmay orogenic belt in northern Canada.

scholarly journals Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 837-849 ◽  
Author(s):  
D. Díaz ◽  
A. Maksymowicz ◽  
G. Vargas ◽  
E. Vera ◽  
E. Contreras-Reyes ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Average Length ◽  
Sedimentary Cover ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Fault System ◽  
Surface Rupture ◽  
Thrust Tectonics ◽  
Rock Substratum ◽  
Fault Scarps

Abstract. The crustal-scale west-vergent San Ramón thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault surface rupture propagation, fault splays and fault segment transfer zones.

scholarly journals Seismic Activity of the Manisa Fault Zone in Western Turkey Constrained by Cosmogenic 36Cl Dating

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 451
Author(s):  
Nasim Mozafari ◽  
Çağlar Özkaymak ◽  
Dmitry Tikhomirov ◽  
Susan Ivy-Ochs ◽  
Vasily Alfimov ◽  
...  
Keyword(s):  
Fault Zone ◽  
Normal Fault ◽  
Vertical Displacement ◽  
Historical Records ◽  
Western Turkey ◽  
Slip Rates ◽  
Vertical Displacements ◽  
Surface Ruptures ◽  
Fault Scarps ◽  
Calculated Average

This study reports on the cosmogenic 36Cl dating of two normal fault scarps in western Turkey, that of the Manastır and Mugırtepe faults, beyond existing historical records. These faults are elements of the western Manisa Fault Zone (MFZ) in the seismically active Gediz Graben. Our modeling revealed that the Manastır fault underwent at least two surface ruptures at 3.5 ± 0.9 ka and 2.0 ± 0.5 ka, with vertical displacements of 3.3 ± 0.5 m and 3.6 ± 0.5 m, respectively. An event at 6.5 ± 1.6 ka with a vertical displacement of 2.7 ± 0.4 m was reconstructed on the Mugırtepe fault. We attribute these earthquakes to the recurring MFZ ruptures, when also the investigated faults slipped. We calculated average slip rates of 1.9 and 0.3 mm yr−1 for the Manastır and Mugırtepe faults, respectively.

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