Temporal evolution of enriched mantle sources in the southeastern Canadian Cordillera revealed by zircon geochronology and Hf isotopes in carbonatites

Abstract

Zircon from carbonatites and syenites of the Blue River area and Monashee Complex (southeast British Columbia, Canada) were analyzed for cathodoluminescence textures, trace elements, and Lu-Hf isotopic compositions. U-Pb geochronology reveals two distinct pulses of carbonatite magmatism: Early Cambrian (ca. 505 Ma) at Gum Creek, associated with continental margin extension, and Upper Devonian (ca. 358 Ma) at Howard Creek, linked to back-arc extension. Neoproterozoic to Cambrian samples from Perry River, Ren, and Gum Creek exhibit slightly enriched mantle Hf signatures, consistent with metasomatized mantle influenced by plume activity and early rifting along western Laurentia. In contrast, Devonian–Carboniferous carbonatites and syenites show a wider range of $\varepsilon$Hf values, reflecting depleted to very enriched mantle components. Mount Grace and Three Valley Gap carbonatites display enriched $\varepsilon$Hf (+3.5 to +7.6), suggesting derivation from a metasomatized mantle with minimal crustal input, while the Trident Mountain syenite and Howard Creek carbonatite yield negative $\varepsilon$Hf values (-3.7 to -1.1), indicative of enriched mantle and possible crustal sources. These results highlight a tectonic transition from homogeneous enriched mantle sources prior to subduction to increasingly heterogeneous mantle reservoirs during subduction-related extension, documenting evolving mantle dynamics beneath western Laurentia.