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TitleAccretion, soft and hard collision: similarities, differences and an application from the newfoundland appalachian orogen
Authorvan Staal, CORCID logo; Zagorevski, AORCID logo
SourceGeoscience Canada vol. 47, no. 3, 2020 p. 103-118, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200493
PublisherGeological Association of Canada
Mediapaper; on-line; digital
File formatpdf; html
AreaIndia; Canada; United Kingdom of Great Britain and Northern Ireland
Lat/Long WENS 55.0000 67.0000 29.0000 23.0000
Lat/Long WENS-131.0000 -120.0000 52.0000 44.0000
Lat/Long WENS 149.0000 168.0000 -1.0000 -11.0000
SubjectsScience and Technology; sedimentology; tectonics; deformation; sedimentary rocks; volcanic rocks; subduction zones; Appalachian orogen
Illustrationslocation maps; cross-sections
Released2020 09 28
AbstractWe argue there is no distinction between accretion and collision as a process, except when accretion is used in the sense of incorporating small bodies of sedimentary and/or volcanic rocks into an accretionary wedge by off-scraping or underplat-ing. There is also a distinction when these terms are used in classifying mountain belts into accretionary and collisional orogens, although such classifications are commonly based on a qualitative assessment of the scale and nature of the accreted terranes and continents involved in formation of mountain belts. Soft collisions occur when contractional deformation and associated metamorphism are principally concentrated in rocks of the leading edge of the partially pulled-down buoyant plate and the upper plate forearc terrane. Several young arc-continent collisions show evidence for partial or wholesale subduc-tion of the forearc such that the arc is structurally juxtaposed directly against lower plate rocks. This process may explain the poor preservation of forearcs in the geological record. Soft collisions generally change into hard collisions over time, except if the collision is rapidly followed by formation of a new subduction zone due to step-back or polarity reversal. Thickening and metamorphism of the arc’s suprastructure and retro-arc part of upper plate due to contractional deformation and burial are the characteristics of a hard collision or an advancing Andean-type margin. Strong rheological coupling of the converging plates and lower and upper crust in the down-going continental margin promotes a hard collision. Application of the soft hard terminology supports a structural juxtaposition of the Taconic soft collision recorded in the Humber margin of western Newfoundland with a hard collision recorded in the adjacent Dashwoods block. It is postulated that Dashwoods was translated dextrally along the Cabot-Baie Verte fault system from a position to the north of Newfoundland where the Notre Dame arc collided ca. 10 m.y. earlier with a wide promontory in a hyperextended segment of the Laurentian margin.

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