Abstract

The basic-ultrabasic complex of Belle-IsIe-en-Terre (northwestern part of the Armorican Massif, France) has been dated at 602+4−1 m.y. by the U-Pb zircon method. The calc-alkaline trend of the metabasic rocks and the geologic context suggest that this ophiolite-like complex is related to a back-arc orogenic setting similar to the geodynamic environment that has been proposed for Pan-African calc-alkaline ophiolite-like complexes of late Proterozoic age around the West African craton. Our results are compatible with the closing, in late Proterozoic time, of a “Channel ocean” north of the basement and formed during the Cadomian orogeny, rather than with possible Caledonian or Hercynian subduction.

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