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Late Carboniferous Tectonostratigraphy in the Avalon Terrane of Southern New Brunswick R

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Late Carboniferous Tectonostratigraphy in the Avalon Terrane of Southern New Brunswick R Document generated on 09/28/2021 10 p.m. Atlantic Geology Late Carboniferous Tectonostratigraphy in the Avalon Terrane of Southern New Brunswick R. Damian Nance Volume 22, Number 3, December 1986 Article abstract Development of the basement-involved, fold-thrust belt in coastal southern New URI: https://id.erudit.org/iderudit/ageo22_3art07 Brunswick is attributed to dextral transpression associated with regional. CarbonlCerous strike-slip displacements. In the vicinity of Saint John, See table of contents deformation strongly influenced Westphalian sedimentation in the penecontemporaneous Lancaster and Balls Lake Formations and reflects sustained NW-SE shortening that coincides with a major compressive bend in Publisher(s) the E-W, Cobequid-Cbedabucto fault system which records significant, right-lateral Pennsylvanian displacement. Atlantic Geoscience Society Purple conglomerates and lithic wackes of the Balls Lake Formation record syntectonic. NW-progradation of an alluvial fan in response to the uplift of a ISSN source to the SB and display facies depicting proximal to ndd-fan. mid-fan, and distal settings. Locally interfingering and laterally equivalent, grey lithic 0843-5561 (print) arenites of the Westpbalian Lancaster Formation are the product of major, NE- 1718-7885 (digital) flowing, meandering streams partially influenced by the prograding distal fan. Initial deformation (Dj) produced NW-directed, basement-involved thrusts that Explore this journal structurally invert regional stratigraphy. Associated lower greenschlst facies metamor-phism accompanied development of a widespread, SB-dipping fabric (Sj). variably expressed as a slaty cleavage, protomylonitic solution cleavage and Cite this article orthomylonitic foliation. The fabric locally bears a strong but variably oriented mineral lineation (L^) and is axial. planar to NW-vergent, isoclinal ndcrofolds Nance, R. D. (1986). Late Carboniferous Tectonostratigraphy in the Avalon and regional overturned structures (Fi) that plunge gently NE and SW. Renewed Terrane of Southern New Brunswick. Atlantic Geology, 22(3), 308–326. thrusting (D2) and back-thrusting (D3) produced conjugate fold sets coaxial with Fj that verge both NW (F2) and SB (F3). Associated axial planar crenulation cleavages (S2 and S3) overprint S\ and dip SB and NW respectively. On-strike variations in deformational style and timing, coupled with the presence of steeply dipping, en echelon zones of Intense deformation, suggest the fold-thrust belt is segmented by right-stepping, convergent wrench faults synthetic to the deeply listric, Cobequid-Cbedabucto system. These faults may shallow into thrusts to form positive flower structures, and locally terminate in thrusts associated with anomalous NW-SE trends in D^ and D2. Thrust uplift in response to transpression on locally downward-steepening, en echelon faults subparallel to the Fundy shore Is proposed to account for the source area of the syntectonic Balls Lake fan. Further displacement and telescoping resulted in structural inversion of regional stratigraphy and deposition of the Balls Lake and Lancaster Formations in advance of an overriding allochthon to the south. All rights reserved © Atlantic Geology, 1986 This document is protected by copyright law. Use of the services of Érudit (including reproduction) is subject to its terms and conditions, which can be viewed online. https://apropos.erudit.org/en/users/policy-on-use/ This article is disseminated and preserved by Érudit. Érudit is a non-profit inter-university consortium of the Université de Montréal, Université Laval, and the Université du Québec à Montréal. Its mission is to promote and disseminate research. https://www.erudit.org/en/ Maritime Sediments and Atlantic Geology Vol. 22 December, 1986 No. 3 Late Carboniferous Tectonostratlgraphy In the Avalon Terrane of Southern New Brunswick R. Damian Nance Department of Geological Sciences Ohio University, Athens, Ohio 45701 Development of the basement-involved, fold-thrust belt in coastal southern New Bruns­ wick is attributed to dextral transpression associated with regional. Carboniferous strike-slip displacements. In the vicinity of Saint John, deformation strongly influenced Westphalian sedimentation in the penecontemporaneous Lancaster and Balls Lake Formations and reflects sustained NW-SE shortening that coincides with a major compressive bend in the E-W, Cobequid-Chedabucto fault system which records significant, right-lateral Pennsylvanian displacement. Purple conglomerates and lithic wackes of the Balls Lake Formation record syntectonic, NW-progradation of an alluvial fan in response to the uplift of a source to the SB a n d display facies depicting proximal to mid-fan, mid-fan, and distal settings. Locally interfingering and laterally equivalent, grey lithic arenites of the Westphalian Lancaster Formation are the product of major, NE- flowing, meandering streams partial­ ly influenced by the prograding distal fan. Initial deformation (Dj) produced NW-directed, basement-involved thrusts that struc­ turally invert regional stratigraphy. Associated lower greenschist facies metamor­ phism accompanied development of a widespread, SE-dipping fabric (Si), variably expressed as a slaty cleavage, protomylonitic solution cleavage and orthomylonitic foliation. The fabric locally bears a strong but variably oriented mineral lineation (Li) and is axial planar to NW-vergent, isoclinal microfolds and regional overturned structures (Fi) that plunge gently NE and SW. Renewed thrusting (D2 ) and back- thrusting (D3 ) produced conjugate fold sets coaxial with Fi that verge both NW (F2 ) and SE (F3 ). Associated axial planar crenulation cleavages (S2 and S3 ) overprint § 1 and dip SE and NW respectively. On-strike variations In deformational style and timing, coupled with the presence of steeply dipping, en echelon zones of Intense deformation, suggest the fold-thrust belt is segmented by right-stepping, convergent wrench faults synthetic to the deeply listric, Cobequid-Chedabucto system. These faults may shallow into thrusts to form positive flower structures, and locally terminate in thrusts associated with anomalous NW-SE trends in D^ and Dy. Thrust uplift in response to transpression on locally downward-steepening, en echelon faults subparallel to the Fundy shore is proposed to account for the source area of the syntectonic Balls Lake fan. Further displacement and telescoping resulted in structural inversion of regional stratigraphy and deposi­ tion of the Balls Lake and Lancaster Formations in advance of an overriding allochthon to the south. On impute le dAveloppement d'une zone orogAnique chevauchante solidaire du socle au littoral du Nouveau-Brunswick meridional A une transpression dextre accompagnAe de dAcrochements rAgionaux carbonifAres. PrAs de Saint John, la deformation, qui a fortement marque la sAdi mentation westphalienne dans les formations syncbrones de Lancaster et de Balls Lake, provient d'un raccourcissement soutenu NW-SE ayant coincide avec un important coude en compression dans le systAme de failles E-W de Cobequid-Chedabucto. Ce dernier reprAsente un coulissage A droite de grande valeur d'age pennsylvanien. Les poudingues pourpres et les wackes lithiques de la Formation de Balls Lake soulignent la progradation syntectonique NW d'un cdne de dejection et traduisent la MARITIME SEDIMENTS AND ATLANTIC GEOLOGY 22, 308-326 (1986) Received April 9. 1986 0711-1150/86/030308~19$3.85/0 Revision Accepted August 25. 1986 309 Nance proximity de reliefs dmergds au SE; les facias tdmoignent de regimes proximaux k milieux de cone, de milieux de cone, et distaux. Les ardnites lithiques grises de la Formation de Lancaster, du Westphallen, en sont iEquivalent lateral et s'y interdigitent par endroits. Elies sont, pour leur part, le produit de grands cours d'eau k mdandres coulant vers le NE sous 1 'Influence partielle du cone distal progradant. Des nappes de socle de direction NW Inversent structuralement la stratlgraphie rdgionale et tdmolgnent d'une deformation tnitiale (Dj). Le ddveloppement largement rdpandu d'tme fahrique (S^), pentde SE et prenant l'aspect variable d'un clivage ardoisier, d'un clivage sous solution protomylonltique et d'une foliation orthomylonitique, fut accompagnd d'un mdtamorphisme dans le facids schistes verts infdrieur. Localement, la fahrique acquiert une lindation (Lj) forte mais variable, soulignde par 1 ' orientation de mindraux dana le plan axial de microplis isoclinaux k vergence NW et de structures rdgionales retoumdes (F5 ) qui plongent gentiment vers le NE et le SW. S'y associent des clivages de crdnulation de plan axial (S2 et S3 ), pentds respectivement SE et NW, qui se superposent sur Sj. Des variations longitudinales dans le style et l'dpoque de la ddformation, coupldes k la prdsence de zones intensdment ddformdes, en dchelon et fortement pentdes, suggdrent que la zone orogdnlque chevauchante est scindde par des ddcrochements vertlcaux ddcalds k droite, qui convergent et sont, eux-memes, synthdtiques du systdme fortement Ustrique de Cobequid-Chedabucto. Ces failles se couchent vers la surface pour devenir des chevauchements qui engendrent des structures en fleur positives; elles s'estompent par endroits en des chevauchements associds aux orientations anormales NW­ SB dans et D 2 . On explique la source du cone syntectcnique de Balls Lake par la surrection des paquets chevauchants sous le jeu en transpression de failles en dchelon subparalldles k la cote de Fundy et dont les pendages se redressent localement
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