Re-Os, Pt-Os, Rb-Sr, and Sm-Nd isotope systematics in Kilbourne Hole lithospheric mantle xenoliths: implications for continental formation and stabilization

Constraining the timing and mechanisms of formation of the continental lithosphere has important implications for understanding the tectonic stabilization of the continents, the geochemical development of the continental crust, and mass balance across major mantle reservoirs. Mantle xenoliths brought to the surface by continental intraplate magmas present the most direct opportunity to assess SCLM formation. The Re-Os isotope system is a powerful tool to determine the timing of melt extraction from the mantle, as Re partitions more readily than Os into primitive melts and leads to 187Re/188Os fractionation and thus time-integrated 187Os/188Os melt depletion ages. Sub-continental lithospheric mantle is stabilized through the removal of partial melts, a process that is likely linked to the growth of continents. However, Re/Os systematics and the reliability of traditional isochrons can be obscured by metasomatism and melt-rock interaction subsequent to melt extraction. Analysis of both the Re-Os and Pt-Os isotope systems (e.g., 187Os/188Os and 186Os/188Os ratios) can distinguish between melt depletion and metasomatic signatures. The Kilbourne Hole maar, in the southern Rio Grande Rift, New Mexico, produced basanitic lavas with abundant xenoliths of both crustal and mantle origin. This classic xenolith locality is located off-craton on the 1.7-2.0 Ga Yavapai-Mazatzal crustal province; mantle xenoliths from this area can be assessed to determine the timescale of continental growth (i.e. single-phase melt depletion or localized growth pulses) and/or fingerprint metasomatic modification of the lithospheric mantle. We present coupled high-precision 186Os/188Os and 187Os/188Os measurements along with Rb-Sr and Sm-Nd isotopic data for a suite of peridotites and pyroxenites from Kilbourne Hole, with dunitic to lherzolitic bulk compositions. Peridotite 187Os/188Os (0.1165-0.1338) display a range that overlaps with Primitive Upper Mantle (Meisel et al., 2001), while Sr-Nd systematics of LREE-depleted clinopyroxene from the peridotite xenoliths reveal a range of 87Sr/86Sr (0.7020-0.7051) and 143Nd/144Nd (0.5129-0.5133) extending from DMM-like to more enriched values.