Abstract

Sandstones from Ordovician sediments of the South Mayo Trough, western Irish Caledonides, show marked stratigraphic variation in their major and trace element geochemistry. High Cr, Ni, and Mg concentrations of ultramafic derivation succeed high Ti and Fe concentrations of mafic provenance This sequence is interpreted as the result of the progressive unroofing of an ophiolite. A possible sedimentary linkage with ophiolite lithologies in the Clew Bay Domain to the north would indicate minimal post-Arenig transcurrent displacement. The South Mayo flysch with its ophiolitic detritus is typical of Caledonian flysch sequences which pre-date the mid-Ordovician Taconic deformation, but differs in character from those of late Ordovician age.

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