The Chamrousse Ophiolite (Western Alps, France): Relict of a Devono‐Carboniferous Ocean

ABSTRACT The Chamrousse ophiolite (Western Alps, France) is one of the best‐preserved Variscan relicts of Cambro‐Ordovician oceanisation within the northern Gondwana margin. This study presents new in situ U–Pb isotope analyses on zircon grains from that ophiolite, revealing that the oceanic stage in Chamrousse has occurred 150 Ma later than estimated. The metabasite unit, previously interpreted as the ophiolite volcanic layer, yields Cambro‐Ordovician zircon ages (460–520 Ma) with few Proterozoic inherited grains, suggesting a continental origin. Meanwhile, zircon grains from the ultramafic, gabbro and basaltic dike units yield new igneous U–Pb ages at 350–360 Ma. The Chamrousse ophiolite may thus be the relict of a marginal basin formed in a back‐arc setting, at the onset of the Variscan collision, as are other Devono‐Carboniferous ophiolites of the Variscan belt.