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TitleA Laurentian margin subduction perspective: Geodynamic constraints from phase equilibria modeling of barroisite greenstones, northern USA Appalachians
AuthorHonsberger, I W; Laird, J; Johnson, J E
SourceGeological Society of America Bulletin vol. 132, issue 11-12, 2020 p. 2587-2605,
Alt SeriesNatural Resources Canada, Contribution Series 20200642
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf; html
AreaUnited States of America
Lat/Long WENS -77.6419 -49.6767 52.8025 39.7069
Subjectsmineralogy; Science and Technology; geodynamics; magnesite; volcanic rocks; Appalachians
Illustrationslocation maps; geological maps; photomicrographs; cross-plots; diagrams; tables
Released2020 04 20
AbstractPhase equilibria modeling of sodic-calcic amphibole-epidote assemblages in greenstones in the northern Appalachians, USA, is compatible with relatively shallow subduction of the early Paleozoic Laurentian margin along the Laurentia-Gondwana suture zone during closure of a portion of the Iapetus Ocean basin. Pseudosection and isopleth calculations demonstrate that peak metamorphic conditions ranged between 0.65 GPa, 480 °C and 0.85 GPa, 495 °C down-dip along the subducted Laurentian continental margin between ~20 km and ~30 km depth. Quantitative petrological data are explained in the context of an Early Ordovician geodynamic model involving shallow subduction of relatively young, warm, and buoyant Laurentian margin continental-oceanic lithosphere and Iapetus Ocean crust beneath a relatively warm and wet peri-Gondwanan continental arc. A relatively warm subduction zone setting may have contributed to the formation of a thin, ductile metasedimentary rock-rich channel between the down-going Laurentian slab and the overriding continental arc. This accretionary channel accommodated metamorphism and tectonization of continental margin sediments and mafic volcanic rocks (greenstones) of the Laurentian margin and provided a pathway for exhumation of serpentinite slivers and rare eclogite blocks. Restricted asthenospheric flow in the forearc mantle wedge provides one explanation for the lack of ophiolites and absence of a well-preserved ultra-high-pressure terrane in central and northern Vermont. Exhumation of the subducted portion of the Laurentian margin may have been temperature triggered due to increased asthenospheric flow following a slab tear at relatively shallow depths.

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