| Title | A Laurentian margin subduction perspective: Geodynamic constraints from phase equilibria modeling of barroisite greenstones, northern USA Appalachians |
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| Author | Honsberger, I W; Laird, J; Johnson, J E |
| Source | Geological Society of America Bulletin vol. 132, issue 11-12, 2020 p. 2587-2605, https://doi.org/10.1130/B35456.1 |
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| Year | 2020 |
| Alt Series | Natural Resources Canada, Contribution Series 20200642 |
| Publisher | Geological Society of America |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Area | United States of America |
| Lat/Long WENS | -77.6419 -49.6767 52.8025 39.7069 |
| Subjects | mineralogy; Science and Technology; geodynamics; magnesite; volcanic rocks; Appalachians |
| Illustrations | location maps; geological maps; photomicrographs; cross-plots; diagrams; tables |
| Released | 2020 04 20 |
| Abstract | Phase 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. |
| GEOSCAN ID | 327914 |
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