Geochemical and isotopic characteristics of lithospheric mantle beneath West Kettle River, British Columbia: Evidence from ultramafic xenoliths

A group of spinel peridotite xenoliths from West Kettle River, British Columbia, represents essentially undepleted to moderately depleted lithospheric mantle rocks in terms of major and compatible trace elements. Whole rock Sr isotopic composition for most of these xenoliths, and whole rock Sm‐Nd isotopic composition and LREE contents for some of them, seem to have been perturbed by near‐surface processes. Sr and Nd isotopic results for acid‐cleaned clinopyroxenes separated from these spinel peridotites reveal an isotopically mid‐ocean ridge basalt (MORB)‐like mantle. Seven spinel Iherzolites gave Nd model ages of 1.5–3.6 Ga, similar to MORB, and on a Sm‐Nd isotope diagram plot close to a reference Nd isochron with an age of 0.7 Ga and an initial εNd of +7. These features likely resulted from multiple mantle depletion. The isotopic similarities of these xenoliths with MORB suggest that this area is underlain by oceanic lithospheric mantle, possibly accreted to North America during the mid‐Jurassic. The Nd isochron age could record the time when the oceanic lithosphere was isolated from the asthenosphere. Recent enrichment event may have acted on such a depleted mantle, as indicated by the low Sm/Nd ratios of two spinel harzburgites.