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    Laurentian crustal recycling in the Ordovician Grampian Orogeny : Nd isotopic evidence from western Ireland

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    Draut Laurentian.pdf (497.8Kb)
    Date
    2004-04-21
    Author
    Draut, Amy E.  Concept link
    Clift, Peter D.  Concept link
    Chew, David M.  Concept link
    Cooper, Matthew J.  Concept link
    Taylor, Rex N.  Concept link
    Hannigan, Robyn E.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/211
    As published
    https://doi.org/10.1017/S001675680400891X
    DOI
    10.1017/S001675680400891X
    Keyword
     Grampian Orogeny; Western Ireland; Continental crust; Nd isotopes; Laurentia; Iapetus Ocean 
    Abstract
    Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at [similar] 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of [varepsilon]Nd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using [varepsilon]Nd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.
    Description
    Author Posting. © Cambridge University Press, 2004. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Geological Magazine 141 (2004): 195-207, doi:10.1017/S001675680400891X.
    Collections
    • Geology and Geophysics (G&G)
    Suggested Citation
    Geological Magazine 141 (2004): 195-207
     

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