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    Wyoming craton mantle lithosphere: reconstructions based on xenocrysts from Sloan and Kelsey Lake kimberlites

    Ashchepkov, I.V. and Downes, Hilary and Mitchell, R. and Vladykin, N.V. and Coopersmith, H. and Palessky, S.V. (2013) Wyoming craton mantle lithosphere: reconstructions based on xenocrysts from Sloan and Kelsey Lake kimberlites. In: Pearson, D.G. and Grütter, H.S. and Harris, J.W. and Kjarsgaard, B.A. and O’Brien, H. and Chalapathi Rao, N.V. and Sparks, S. (eds.) Proceedings of the 10th International Kimberlite Conference. Springer, pp. 13-27. ISBN 9788132211693.

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    Abstract

    Book synopsis: The structure of the lithospheric mantle of the Wyoming craton beneath two Paleozoic kimberlite pipes, Sloan and Kelsey Lake 1 in Colorado, was reconstructed using single-grain thermobarometry for a large data set (>2,600 EPMA analyses of xenocrysts and mineral intergrowths). Pyrope compositions from both pipes relate to the lherzolitic field (up to 14 wt% Cr2O3) with a few deviations in CaO to harzburgitic field for KL-1 garnets. Clinopyroxene variations (Cr-diopsides and omphacites) from the Sloan pipe show similarities with those from Daldyn kimberlites, Yakutia, and from kimberlites in the central part of the Slave craton, while KL-1 Cpx resemble those from the Alakit kimberlites in Yakutia that sample metasomatized peridotites. LAM ICP analyses recalculated to parental melts for clinopyroxenes from Sloan resemble contaminated protokimberlite melts, while clinopyroxenes from KL-1 show metasomatism by subduction fluids. Melts calculated from garnets from both pipes show peaks for Ba, Sr and U, and HFSE troughs, typical of subduction-related melts. Parental melts calculated for ilmenites from Sloan suggest derivation from highly differentiated melts, or melting of Ilm-bearing metasomatites, while those from Kelsey Lake do not display extreme HFSE enrichment. Three P-Fe# (where Fe# = Fe/(Fe + Mg) in atomic units) trends within the mantle lithosphere beneath Sloan have been obtained using monomineral thermobarometry. At the base, the trends reveal melt metasomatized (possibly sheared) peridotites (Fe# = 13–15 %), refertilized peridotites (Fe# = 10–11 %) and primary mantle peridotites (Fe# = 7–9 %). Anomalous heating was found at depths equivalent to 4.0 and 3.0–2.0 GPa. The mantle section beneath KL-1 is widely metasomatized with several stages of refertilization with dispersed Ilm–Cpx trends. The step-like subadibatic heating in the mantle column beneath the Sloan pipe is strong in the base and the middle part and weaker within 2–3 GPa. Heating beneath the KL-1 pipe is more evident in the base and middle part from 7.0 to 3.0 GPa.

    Metadata

    Item Type: Book Section
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Sarah Hall
    Date Deposited: 17 May 2016 16:34
    Last Modified: 17 May 2016 16:34
    URI: http://eprints.bbk.ac.uk/id/eprint/15212

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