An Archean fold-thrust belt in the northwestern Abitibi Greenstone Belt: structural and seismic evidence

1995 ◽  
Vol 32 (2) ◽  
pp. 97-112 ◽  
Author(s):  
S. Lacroix ◽  
E. W. Sawyer
Keyword(s):  
Greenstone Belt ◽  
Structural Evolution ◽  
Thrust Belt ◽  
Abitibi Greenstone Belt ◽  
Structural Style ◽  
Slip Event ◽  
Reflector Geometry ◽  
Mountain Belts ◽  
East West ◽  
Seismic Reflector

An integration of structural field data and Lithoprobe seismic reflection line 28 in the northwestern Abitibi Greenstone Belt (AGB) reveals a crustal-scale, south-to southwest-vergent thrusting event that developed "in sequence" above a shallowly (15°) north-dipping sole thrust at a mid-crustal level. Seismic reflector geometry above this décollement suggests a mid crust (6–20 km depth) dominated by low-angle thrusts with smooth trajectory ramps and culmination folds or antiformal stacks, similar to the structural style of neighbouring high-grade plutonic–gneissic (Opatica) and sedimentary (Pontiac) subprovinces. In contrast, low-to high-angle east–west-trending thrusts at the upper-crust greenstone belt level (6–9 km depth) are interpreted to be listric. They occur in two fault systems, the Chicobi and Taibi, that resemble "imbricate fan" systems. The contrasting structural geometry of the upper and mid crust is interpreted as variations in level through the thrust stack, and resembles Paleozoic mountain belts where the upper AGB would represent a ductile–brittle fold–thrust belt. However, the structural evolution of the AGB has been complicated by earlier intrusive–metamorphic contacts or set of thrusts beneath it, and (or) younger out-of-sequence thrusts with north-vergent backthrusts. Also, south-to southwest-vergent thrusts were reactivated, folded, and steepened during a younger dextral strike-slip event.

Central Superior Province geology: evidence for an allochthonous, ensimatic, southern Abitibi greenstone belt

1990 ◽  
Vol 27 (4) ◽  
pp. 582-589 ◽  
Author(s):  
S. L. Jackson ◽  
R. H. Sutcliffe
Keyword(s):  
Crustal Structure ◽  
Greenstone Belt ◽  
Superior Province ◽  
Low Grade ◽  
Simple Correlation ◽  
Abitibi Greenstone Belt ◽  
Structural Style ◽  
Metavolcanic Rocks ◽  
Crustal Model ◽  
Greenstone Belts

Published U–Pb geochronological, geological, and petrochemical data suggest that there are late Archean ensialic greenstone belts (GB) (Michipicoten GB and possibly the northern Abitibi GB), ensimatic greenstone belts (southern Abitibi GB and Batchawana GB), and possibly a transitional ensimatic–ensialic greenstone belt (Swayze GB) in the central Superior Province. This lateral crustal variability may preclude simple correlation of the Michipicoten GB and its substrata, as exposed in the Kapuskasing Uplift, with that of the southern Abitibi GB. Furthermore, this lateral variability may have determined the locus of the Kapuskasing Uplift. Therefore, although the Kapuskasing Uplift provides a useful general crustal model, alternative models of crustal structure and tectonics for the southern Abitibi GB warrant examination.Thrusting of a juvenile, ensimatic southern Abitibi GB over a terrane containing evolved crust is consistent with (i) the structural style of the southern Abitibi GB; (ii) juvenile southern Abitibi GB metavolcanic rocks intruded by rocks having an isotopically evolved, older component; and (iii) Proterozoic extension that preserved low-grade metavolcanic rocks within the down-dropped Cobalt Embayment, which is bounded by higher grade terranes to the east and west.

Orogen parallel and transverse shearing in the Opatica belt, Quebec: implications for the structure of the Abitibi Subprovince

1992 ◽  
Vol 29 (11) ◽  
pp. 2429-2444 ◽  
Author(s):  
Keith Benn ◽  
Edward W. Sawyer ◽  
Jean-Luc Bouchez
Keyword(s):  
Greenstone Belt ◽  
Regional Scale ◽  
Structural Evolution ◽  
Fault Zones ◽  
Crustal Thickening ◽  
Superior Province ◽  
Northern Margin ◽  
Abitibi Greenstone Belt ◽  
Ductile Shearing ◽  
Abitibi Subprovince

The late Archean Opatica granitoid-gneiss belt is situated within the northern Abitibi Subprovince, along the northern margin of the Abitibi greenstone belt. Approximately 200 km of structural section was mapped along three traverses within the previously unstudied Opatica belt. The earliest preserved structures are penetrative foliations and stretching and mineral lineations recording regional ductile shearing (D1). Late-D1 deformation was concentrated into kilometre-scale ductile fault zones, typically with L > S tectonite fabrics. Two families of lineations are associated with D1, indicating shearing both parallel and transverse to the east-northeast trend of the belt. Lineations trending east-northeast or northwest–southeast tend to be dominant within domains separated by major fault zones. In light of the abundant evidence for early north–south compression documented throughout southern Superior Province, including the Abitibi greenstone belt, D1 is interpreted in terms of mid-crustal thrusting, probably resulting in considerable crustal thickening. Movement-sense indicators suggest that thrusting was dominantly southward vergent. D2 deformation resulted in the development of vertical, regional-scale dextral and sinistral transcurrent fault zones and open to tight upright horizontal folds of D1 fabrics. In the context of late Archean orogenesis in southern Superior Province, the tectonic histories of the Abitibi and Opatica belts should not be considered separately. The Opatica belt may correlate with the present-day mid-crustal levels of the Abitibi greenstone belt, and to crystalline complexes within the Abitibi belt. It is suggested that the Abitibi Subprovince should be viewed, at the regional scale, as a dominantly southward-vergent orogenic belt. This work demonstrates that structural study of granitoid-gneiss belts adjacent to greenstone belts can shed considerable light on the regional structure and structural evolution of late Archean terranes.

Internal structure of the Cadillac tectonic zone southeast of Val d'Or, Abitibi greenstone belt, Quebec

1989 ◽  
Vol 26 (12) ◽  
pp. 2661-2675 ◽  
Author(s):  
François Robert
Keyword(s):  
Internal Structure ◽  
Fault Zone ◽  
Greenstone Belt ◽  
Strain Increment ◽  
Tectonic Zone ◽  
Abitibi Greenstone Belt ◽  
Detailed Structural Analysis ◽  
Major Fault ◽  
Wide Zone ◽  
East West

The Kirkland Lake – Larder Lake – Cadillac Break is a major fault zone of the Abitibi greenstone belt, well known for its spatially associated gold camps. A detailed structural analysis of this fault zone in the Val d'Or area has shown the presence of a 200 – 750 m wide zone of high strain, defined here as the Cadillac tectonic zone (CTZ), which includes the narrower schist zone generally regarded as the Cadillac Break. The boundaries of the CTZ, which coincide with major lithologic contacts, strike approximately east–west and dip 80° to the north.The internal structure of the CTZ is best analysed in terms of two increments of the same progressive deformation. The D1 strain increment is characterized by an east–west-striking, subvertical S1 foliation, at low angle in strike to the bound aries of the CTZ and containing subvertical elongation lineation. Primary lithological contacts have been transposed into S1 and folded by F1a folds. F1b intrafolial folds of S1 ranging from noncylindrical, subhorizontal folds to subvertical sheath folds, indicate dip-slip movements within the CTZ. The D1 strain increment records synchronous dextral transcurrent shearing, as required by the obliquity of S1 to the CTZ boundaries, and subvertical elongation, as indicated by elongation lineations and F1b folds. The D2 strain increment is chiefly characterized by the development of moderately to steeply plunging asymmetric Z-shaped F2 folds with associated S2 cleavage, recording dextral transcurrent shearing.The studied segment of the CTZ is best interpreted as a zone of dextral transpression, evolving from a zone with a significant shortening component (D1) into a zone increasingly dominated by a transcurrent shearing component (D2).

Timing and kinematics of post-Timiskaming deformation within the Larder Lake - Cadillac deformation zone, southwest Abitibi greenstone belt, Ontario, Canada

1999 ◽  
Vol 36 (4) ◽  
pp. 627-647 ◽  
Author(s):  
Lori Wilkinson ◽  
Alexander R Cruden ◽  
Thomas E Krogh
Keyword(s):  
Greenstone Belt ◽  
Deformation Zone ◽  
Greenschist Facies ◽  
Ductile Deformation ◽  
Magmatic Zircon ◽  
Lake Area ◽  
Abitibi Greenstone Belt ◽  
Terrane Accretion ◽  
East West ◽  
Greenschist Facies Metamorphism

The Larder Lake - Cadillac deformation zone is one of several anastomosing zones of high strain within the Abitibi greenstone belt. In the Kirkland Lake area, Ontario, the Larder Lake - Cadillac deformation zone is characterized by extensive carbonate and chlorite alteration, strong south-dipping foliations, and steep lineations. These features formed during two ductile deformation increments, D2 and D3, that occurred after deposition of Timiskaming assemblage sediments. D2 strain accumulation and greenschist facies metamorphism and alteration were localized within the deformation zone, facilitated by channelling of hydrothermal fluids within a preexisting structure, possibly formed during early D1 terrane accretion. During D2 north-south shortening, east-west-trending sectors of the deformation zone accumulated bulk coaxial strains, while southeast- and northeast-trending sectors experienced, respectively, dextral and sinistral transpressive deformations. Preservation of Timiskaming assemblage sediments in the footwall of the deformation zone indicates a component of south-over-north (reverse) displacement that is not recorded by D2 fabrics. Northwest-southeast D3 compression resulted in the formation of a regional, northeast-striking cleavage formed under regional greenschist facies conditions, and local dextral reactivation of suitably oriented sections of the Larder Lake - Cadillac deformation zone. The Murdoch Creek and Lebel stocks abut the Larder Lake - Cadillac deformation zone. Their internal structure and emplacement are interpreted to be a consequence of D2 north-south shortening. Magmatic zircon and titanite in the Murdoch Creek and Lebel stocks yield U-Pb geochronology ages of 2672 ± 2 and 2673 ± 2 Ma, providing a maximum age for D2 deformation. Hydrothermal titantite associated with S3 foliation in the Murdoch Creek stock gives an U-Pb age of 2665 ± 4 Ma, the maximum age of D3 deformation. Pluton emplacement, deformation, and coincident metamorphism occurred over a span of 1 Ma (from 2670 to 2669 Ma) to over 14 Ma (from 2675 to 2661 Ma), during a regime of north-south, followed by northwest-southeast, regional shortening.

Seismic reflection constraints from Lithoprobe line 29 on the upper crustal structure of the northern Abitibi greenstone belt

1995 ◽  
Vol 32 (2) ◽  
pp. 128-134 ◽  
Author(s):  
Gilles Bellefleur ◽  
Arthur Barnes ◽  
Andrew Calvert ◽  
Claude Hubert ◽  
Marianne Mareschal
Keyword(s):  
Crustal Structure ◽  
Greenstone Belt ◽  
Seismic Reflection ◽  
Volcanic Rocks ◽  
Seismic Profile ◽  
Median Filtering ◽  
Abitibi Greenstone Belt ◽  
Geological Information ◽  
Additional Constraints ◽  
East West

Detailed reprocessing of east–west Lithoprobe seismic reflection line 29 includes cross-dip analysis to improve the continuity of the reflectors and median filtering to attenuate shear wave refractions. The interpretation provides additional constraints on the tectonic models of northern Abitibi, but cannot be used to invalidate either of the two models recently presented for the area. However, the seismic profile defines a large east-dipping faulted contact between the Brouillan tonalite and the volcanic rocks exposed west of the intrusion. The moderate dip of the reflectors and their extensive lateral continuity, combined with geological information, provide evidence for an east-dipping thrust sequence and suggest an allochthonous origin for the Brouillan tonalite. The maximum thickness of the volcanic sequence in the northern Abitibi greenstone belt is 8 km, but could be as low as 4 km if Opatica orthogneisses are considered to underthrust northern Abitibi. The mid-crustal reflections confirm the east–west continuity of south-vergent imbrications also observed on a north–south reflection line (28) through northern and central Abitibi. Breakage and displacement of some mid-crustal reflectors may define a west-to-east thrust sequence of sense opposite to that which thrust the Brouillan pluton over the volcanic rocks.

Structural evolution of the eastern Amisk collage, Trans-Hudson Orogen, Manitoba

1999 ◽  
Vol 36 (2) ◽  
pp. 251-273 ◽  
Author(s):  
James J Ryan ◽  
Paul F Williams
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Detailed Structural Analysis ◽  
Vertical Extension ◽  
Deformational History ◽  
Flin Flon ◽  
Mountain Belts ◽  
Geochemical Studies ◽  
Early Late ◽  
East West

Deformation recorded in the Amisk collage in the central part of the Paleoproterozoic Flin Flon Belt (southeastern Trans-Hudson Orogen) is divided into pre-, early, late, and post-Hudsonian orogeny, distinguished by significant changes in metamorphic conditions and the orientation of structures. Detailed structural analysis, petrography, and high-precision geochronology, combined with previous mapping and geochemical studies, indicate a structural history spanning 180 Ma in the Amisk collage, and the database provides an excellent opportunity to study the structural evolution of Precambrian greenstone belts. Accretion of the 1.92-1.88 Ga tectono-stratigraphic assemblages in the Amisk collage began prior to 1.868 Ga. The deformational history records six generations of ductile structures (F1-F6), followed by development of brittle-ductile and brittle structures (F7), which may have continued as late as 1.690 Ga, during exhumation of the collage. The steep, generally north-northeast macroscopic structural grain is dominated by two regional foliations (S2 and S5), and contrasts strongly with the less steeply inclined, east-west grain in the adjacent Kisseynew Domain. Maximum displacements between tectono-stratigraphic assemblages occurred along early rather than late shear zones. Vertical extension was important in post-D1 deformations, even in the later stages. Postorogenic, low-angle extensional features that are common to many mountain belts appear to be absent, possibly indicating that erosion was the dominant unroofing mechanism.

Tectonic evolution of the northeast portion of the Archean Abitibi greenstone belt, Chibougamau area, Quebec

1990 ◽  
Vol 27 (12) ◽  
pp. 1714-1736 ◽  
Author(s):  
R. Daigneault ◽  
P. St-Julien ◽  
G. O. Allard
Keyword(s):  
Greenstone Belt ◽  
Local Stress ◽  
Shear Zones ◽  
Tectonic Zone ◽  
Abitibi Greenstone Belt ◽  
Vertical Extension ◽  
Regional Deformation ◽  
Deformation Phase ◽  
Deformation Event ◽  
East West

The Chibougamau area, occupying the northeastern part of the Abitibi greenstone belt is a large synclinorium of volcanic and sedimentary rocks enclosed within tonalitic gneisses. Several east–west–trending regional folds within this synclinorium are responsible for the vertical attitude of the strata. Synclinal structures, with youngest sediments within the core, possess axial-plane schistosity. Anticlines, on the other hand, either form domes with a core occupied by earlier tonalitic to dioritic plutons or are transected by a series of east–west-trending ductile faults (the Waconichi tectonic zone).An early deformation phase of low intensity (D1) generated broad, north–south folds without schistosity. The subsequent regional deformation, event D2, produced the large east–west folds. These deformations, in combination, produced the regional interference pattern of domes and basins. North–south horizontal shortening generated an east–west-trending schistosity associated with a vertical stretching lineation. Regional deformation at its climax produced a tightening of folds and rotation of fold axes parallel to the stretching lineation.Plutons deflected the regional east–west schistosity and formed concentric trajectories associated with "contact-strain aureoles." This produced small interaction zones or triple points characterized by strong vertical extension. These relations suggest an interference between a regional stress field, which produced north–south horizontal shortening, and local stress fields, controlled or deflected by granitoid plutons acting as competent bodies.East–west-trending ductile shear zones represent the final stage of the regional deformation. The observed northward and southward reverse movement along these east–west faults, their parallelism to the axial trace of folds, and the regional schistosity are probable evidence of a regime dominated by a coaxial strain.

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