Late Devonian-Carboniferous detachment faulting and extensional tectonics in western Cape Breton Island, Nova Scotia, Canada

Lynch, G; Tremblay, Christian

doi:10.1016/0040-1951(94)90049-3

Cited by 32 publications

(17 citation statements)

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“…Further evidence of extensional faults are reports of widespread stratigraphic gaps within the well-defined stratigraphy of the Maritimes Basin (Howie and Barss 1975). The Margaree Shear Zone of western Cape Breton Island is a major shallowdipping extensional fault, which accommodated crustal thinning in Late Devonian time during the initiation of the basin (Lynch and Tremblay 1994). And, in New Brunswick, a thick zone of bedding-parallel shear and recumbent folding along Carboniferous evaporite deposits was described by Roberts and Williams (1993), who proposed that deformation occurred due to Mesozoic extension.…”

Section: 'mentioning

confidence: 96%

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

Lynch¹,

Giles²

1996

Can. J. Earth Sci.

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The Ainslie Detachment occurs near the base of the Carboniferous Windsor Group, forming a regional flat-lying extensional fault distributed across 10000 km2. New mapping has delineated the structure through southwestern Cape Breton Island and into central Nova Scotia. Shearing is concentrated at the top of the basal Macumber limestone along its contact with overlying evaporites and younger allochthonous units. The highly contrasting rheologies of the formations created an anisotropic zone of weakness which acted as an upper crustal stress guide, stratigraphically controlling the trajectory of the detachment through the basin. The detachment is characterized by an approximately 3 -10 m thick calc-mylonite zone, with an intense planar fabric featuring alternating very fine grained shear planes and coarser annealed layers. Coarser layers are boudinaged into pinch and swell structures, locally producing segmented augen. Highly strained intraclasts, ooids, and peloids, recrystallized carbonate boudins, and carbonate vein segments are included in the calc-mylonite as semirigid inclusions and rotated porphyroclasts. Thick zones of fault breccia straddle portions of the detachment and overprint the mylonite, demonstrating an evolution to brittle conditions during progressive shear. Listric faults in the hanging wall of the detachment feature a ramp and flat geometry, with an upper detachment occurring along the upper contact of the Windsor Group with the overlying Namurian Mabou Group. Locally up to 2 km of the stratigraphic succession has been removed, with faults cutting downsection in a westerly direction producing rollover in the hanging wall.RCsumC : Le detachement d'Ainslie apparait prBs de la base du Groupe de Windsor, il reprksente une faille rkgionale extensive, subhorizontale, distribuke dans une aire de 10 OOO km2. Un nouveau lev6 cartographique montre que cette structure s'btend au travers la rkgion sud-ouest de l'fle du Cap-Breton et dans la partie centrale de la ~ouvelle-~cosse. Une zone de cisaillements est concentrke au sommet du calcaire basal de Macumber, le long de son contact avec les Cvaporites sus-jacentes et les unitks allochtones plus jeunes. Le contraste trBs net des propriCtCs rhkologiques des formations a crkk une zone anisotropique de faiblesse, laquelle a semi i guider les contraintes dans la croCite supkrieure, et a contr6lC stratigraphiquement la trajectoire du detachement au travers le bassin. Le dCtachement est caractCris6 par une zone de mylonite calcareuse d'une puissance approximative de 3 i 10 m, avec une forte fabrique planaire exhibant des plans de cisaillement h grain trks fin et des couches recristalliskes i grain grossier. Les couches avec le grain le plus grossier sont boudinkes, elles foment des Ctranglements produisant localement une structure oeillCe segment6e. Des intraclastes ooydes et pCloYdes intenskment dkformCs, des boudins de carbonate recristallisks et des segments de filons de carbonate sont incorporks dans la mylonite calcareuse produisant des inclusions semi-rigide...

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Section: 'mentioning

confidence: 96%

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

Lynch¹,

Giles²

1996

Can. J. Earth Sci.

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“…Many hypotheses have been proposed for the cause of crustal melting and they involve one or more of the following: 1) injection of mantle-derived mafic magmas (Dorais and Paige, 2000;Shellnutt and Dostal, 2012;Tate and Clarke, 1995); 2) crustal thickening (Clarke et al, 1997); 3) decompressional melting Dallmeyer, 1987, 1995;Lynch and Tremblay, 1994); 4) the passage of a mantle plume beneath the crust (Keppie and Krogh, 1999;Murphy et al, 1999) or 5) radioactivity of anomalously U-enriched sediments (Chamberlain and Sonder, 1990). The presence of spatially and temporally associated mafic to ultramafic rocks with moderately depleted Nd isotope values indicates that mantle melting was occurring at the same time as the emplacement of the Late Devonian plutons and suggests the melting regime in the region was anomalously high however the reason for the elevated mantle temperatures is not constrained (Dorais, 2003;Dorais and Paige, 2000;Shellnutt and Dostal, 2012;Clarke, 1993, 1995).…”

Section: Introductionmentioning

confidence: 99%

Granodiorites of the South Mountain Batholith (Nova Scotia, Canada) derived by partial melting of Avalonia granulite rocks beneath the Meguma terrane: Implications for the heat source of the Late Devonian granites of the Northern Appalachians

Shellnutt

Dostál

2015

Tectonophysics

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“…On Cape Breton Island, however, sedimentological studies of broadly coeval basins suggest that they opened as a series of half-grabens (Hamblin and Rust 1989). More recently, Lynch and Tremblay (1994) have proposed that the basin evolved above a regional detachment fault (Margaree Shear Zone) that formed as a result of orogenic collapse following Acadian crustal thickening in the Devonian.…”

Section: Introductionmentioning

confidence: 99%

“…Following Fyson (1967), Lynch and Tremblay (1994) further proposed that extensional deformation within the Maritimes Basin is not limited to the Margaree Shear Zone, but reoccurred during the late Namurian-early Westphalian with the development of a regional fl at-lying extensional fault (the Ainslie Detachment) that developed within the basin fi ll. Located near the base of an evaporitic sequence of Viséan age (Windsor Group) and distributed across 10,000 km 2 , the detachment surface is held to be responsible for as much as 2 km of stratigraphic omission and 10-25 km of westward displacement (Lynch and Giles 1995).…”

Section: Introductionmentioning

confidence: 99%

Deformation of the Macumber Formation, Antigonish Basin, Nova Scotia: implications for the Ainslie Detachment

Thomas

Nance

Murphy

2003

atgeol

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The Antigonish Basin is one of several Carboniferous structural basins in northeastern Nova Scotia, the evolution of which have been cited as evidence for major detachment faulting within the Vis. Windsor Group of Maritime Canada. Evidence of extension in the Antigonish Basin takes the form of a major subhorizontal structure that closely follows the basin margins and has been interpreted as part of the regional Ainslie Detachment. Placed at the top of the basal Macumber Formation and reportedly characterized by several metres of calc-mylonite, the detachment is considered to have accommodated 10—25 km of westward transport of the evaporitic Windsor and overlying Mabou groups during the late Namurian-early Westphalian. However, deformation within the Macumber Formation limestone immediately beneath the detachment surface suggests local extension of Vis. age. Recumbent intraformational folds are overlain by depositional breccias that contain previously folded fragments and are themselves recumbently folded. These relationships suggest repeated movement that began soon after limestone deposition. Furthermore, fold asymmetry and the orientation of calcite veins and small-scale normal faults suggest variable directions of extension that converge on the centre of the basin located in St. Georges Bay. While these data do not preclude the existence of the Ainslie Detachment, they suggest that the Macumber Formation in the Antigonish Basin records an earlier episode of deformation that occurred in response to local gravity sliding rather than to movement on a regional detachment surface. RESUMÉ Le bassin d Antigonish constitue l un d une série de bassins structuraux du Carbonifère dans le nord-ouest de la Nouvelle-Écosse don t l évolution a été citée comme preuve d une dislocation importante par détachement à l intérieur du groupe viséen de Windsor dans les provinces Maritimes. On relève une preuve du prolongement dans le bassin d Antigonish sous la forme d une structure subhorizontale importante qui suit de près les limites du bassin et qui a été interprétée comme une partie du détachement régional d Ainslie. On estime que le détachement, situé au sommet de la Formation basale de Macumber et caractérisé, d après ce qu on dit, par plusieurs mètres de mylonite calcique, a permis le transport vers l ouest sur dix à 25 kilomètres des groupes sus-jacent de Mabou et évaporitique de Windsor au cours de la période du Namurien tardif-Westphalien précoce. La déformation à l intérieur du calcaire de la Formation de Macumber immédiatement au-dessous de la surface du détachement, laisse toutefois supposer un prolongement local à l époque du Viséen. Les plis intraformationnels couchés sont recouverts de brèches de sedimentation renfermant des fragments antérieurement pliés qui sont eux-mêmes repliés sur un plan axial horizontal. Ces rapports permettent de supposer un mouvement répété qui a débuté peu après la sédimentation du calcaire. De plus, l asymétrie des plis et l orientation des filons de calcite et des failles normales de petite échelle laissent supposer des orientations de prolongation variables qui convergent vers le centre du bassin situé dans la baie de St. Georges. Même si ces données n écartent pas la possibilité de l existence du détachement d Ainslie, elles permettent de supposer que la Formation de Macumber dans le bassin d Antigonish évoque un épisode plus hâtif de déformation, survenu à la suite d un glissement gravitationnel local plutôt que d un déplacement à la surface d un détachement régional.

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Late Devonian-Carboniferous detachment faulting and extensional tectonics in western Cape Breton Island, Nova Scotia, Canada

Cited by 32 publications

References 42 publications

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

Granodiorites of the South Mountain Batholith (Nova Scotia, Canada) derived by partial melting of Avalonia granulite rocks beneath the Meguma terrane: Implications for the heat source of the Late Devonian granites of the Northern Appalachians

Deformation of the Macumber Formation, Antigonish Basin, Nova Scotia: implications for the Ainslie Detachment

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