Syn-Acadian emplacement model for the South Mountain batholith, Meguma Terrane, Nova Scotia: Magnetic fabric and structural analyses

Benn, K.; Horne, R. J.; Kontak, Daniel J.; Pignotta, Geoffrey S.; Evans, Neil G.

doi:10.1130/0016-7606(1997)109<1279:saemft>2.3.co;2

Cited by 57 publications

(33 citation statements)

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“…Thus the transition from shallow-marine to subaerial environment recorded by the Torbrook Formation may reflect the onset of the deformation. The 400-377 Ma age range of the early cleavage development is also consistent with the observation that some of the folds in the Meguma Group are truncated by the~380-370 Ma granitoid plutons Dallmeyer 1987, 1995;Benn et al 1997). On the other hand, later cleavage development is recorded in shear zones within the 380-370 Ma granitoid plutons and in the~360 Ma high-grade dextral and normal shear zones (Keppie and Dallmeyer 1987;Williams and Hy 1990).…”

Section: Age Of the Cleavagesupporting

confidence: 80%

Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data

Keppie

Murphy

2002

Can. J. Earth Sci.

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Many auriferous veins dated at~370 Ma in the Meguma terrane of Nova Scotia are concentrated in tight domes, and conical fold hinges that are transected by 378 Ma low-pressure and high-temperature metamorphic isograds and 380-370 Ma granitoid plutons. Published experiments suggest that such folds are diachronous initiating at inhomogeneities and propagating both in amplitude and along their length. Thus fold terminations are typically conical in geometry and record only the youngest increment of folding. The northeastern termination of the Oldham anticline is characterized by (1) a conical fold, (2) saddle reef auriferous veins, (3) divergent and convergent cleavage fans, (4) a downdip lineation on the slaty cleavage defined by biotitic mineral aggregates inferred to have developed during fold growth. The age of the biotitic mineral aggregates is bracketed between peak metamorphism at > 600°C, defined by a nearly concordant 378 Ma U-Pb monazite age from a xenolith in lamprophyre dyke, and~366 Ma 40 Ar/ 39 Ar muscovite-biotite ages, recording cooling through~400-300°C. This suggests that the conical termination of the Oldham anticline grew between 378 and 366 Ma, an observation that reconciles the empirical structural control of the saddle reef auriferous veins with the~370 Ma age dating of vein minerals. Application of this conclusion to saddle reef auriferous veins in domes suggests that mineralization was related to the youngest increment of fold amplification.Résumé : Plusieurs veines aurifères datant de~370 Ma dans le terrane de Meguma de la Nouvelle-Écosse sont concentrées dans des dômes serrés et des charnières de plis coniques qui sont recoupées par des isogrades de métamorphisme de basse pression et haute température datant de 378 Ma et par des plutons granitoïdes datant de 380-370 Ma. Des expériences publiées suggèrent que de tels plis soient diachroniques, débutant aux non-homogénéités et se propageant à la fois en amplitude et suivant le sens de la longueur. Ainsi, la géométrie de la terminaison des plis est typiquement conique et n'enregistre que la plus jeune amplification du plissement. La terminaison nord-est de l'anticlinal d'Oldham est caractérisée par : (1) un pli conique, (2) des veines aurifères apicales, (3) des éventails de clivage divergents et convergents, (4) une linéation en aval-pendage sur le clivage schisteux défini par des agrégats de minéraux à biotite, lesquels se seraient développés durant la croissance du pli. L'âge des agrégats de minéraux biotiques est placé dans la fourchette entre le métamorphisme de pointe à > 600 ºC tel que défini par un âge U-Pb de 378 Ma sur de la monazite provenant d'un dyke de lamprophyre et des âges de~366 Ma 40 Ar/ 39 Ar muscovite-biotite qui enregistrent un refroidissement de~400-300 ºC. Cela suggère que la terminaison conique de l'anticlinal d'Oldham ait crû entre 378 et 366 Ma, une observation qui réconcilie le contrôle empirique structural des veines aurifères apicales avec l'âge de~370 Ma pour les minéraux dans les veines. L'application de cette c...

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Section: Age Of the Cleavagesupporting

confidence: 80%

Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data

Keppie

Murphy

2002

Can. J. Earth Sci.

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“…We interpret that the Karlshamn pluton was folded with the metamorphic host rocks and that the magnetic lineations (magnetite mineral lineation), which are fold-axis parallel, record some stretching of the magma parallel to the fold axes during magmatic deformation. Magnetic lineations in granite plutons emplaced and magmatically deformed in folding metamorphic terrains have also been documented in at least three other well studied cases, in the Devonian Meguma Terrane, Canada (Benn et al 1997;Pignotta and Benn 1999), in the Cretaceous Mt. Stuart batholith, Washington state (Benn et al 2001) and in the Sveconorwegian granites of southern Norway (Bolle et al 2003).…”

Section: Directional Datamentioning

confidence: 93%

Emplacement and deformation of the ca. 1.45 Ga Karlshamn granitoid pluton, southeastern Sweden, during ENE-WSW Danopolonian shortening

Cecys

Benn

2006

Int J Earth Sci (Geol Rundsch)

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Anisotropy of magnetic susceptibility and structural geology of the ca. 1.45 Ga Karlshamn pluton (southern Sweden) are used to study its emplacement and structural evolution. The Karlshamn pluton is one of the largest metaluminous A-type granitoid intrusions in southern Sweden. It is a multiphase body made up of two suites that differ in composition but which have similar crystallization ages. The magmatic foliation, ductile shear zones and granite-pegmatite filled fractures were mapped as well as the metamorphic foliation and extension lineation in the metamorphic host rocks. The anisotropy of magnetic susceptibility was used to map the magnetite petrofabric of the pluton, providing a larger data set for both the magmatic foliations and lineations, which could not be mapped in the field. The fabrics within the pluton are continuous with the metamorphic fabrics in the country rocks. Both the pluton and the country rock fabrics were folded during ENE-WSW compression, while the pluton was still a magma mush. The stress field orientation during cooling of the pluton is determined on the basis of magmatic, ductile and brittle structures in the Karlshamn pluton that formed successively as the pluton cooled. The compressional event is referred to as the Danopolonian orogeny and therefore the Karlshamn granitoids, and other plutons of similar composition and age in central and southern Sweden, on the Danish Island of Bornholm, and in Lithuania, may be considered as syntectonic intrusions and not as anorogenic, as was previously thought.

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“…Examples include syntectonic plutons related to compressional (Ingram and Hutton 1994;Davidson et al 1992;Paterson et al 1991;Benn et al 1997), extensional (Hutton et al 1990; Aranguren and Tubía 1992) or different strike-slip settings (e.g. Guineberteau et al 1987;Morand 1992;Tikoff and Teyssier 1992).…”

Section: Introductionmentioning

confidence: 99%

Exhumation, strain localization, and emplacement of granitoids along the western part of the Central Bohemian shear zone (Bohemian Massif)

Scheuvens

Zulauf²

2000

International Journal of Earth Sciences

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Syn-Acadian emplacement model for the South Mountain batholith, Meguma Terrane, Nova Scotia: Magnetic fabric and structural analyses

Cited by 57 publications

References 0 publications

Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data

Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data

Emplacement and deformation of the ca. 1.45 Ga Karlshamn granitoid pluton, southeastern Sweden, during ENE-WSW Danopolonian shortening

Exhumation, strain localization, and emplacement of granitoids along the western part of the Central Bohemian shear zone (Bohemian Massif)

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