ORIGINAL PAPER The origin of coarse garnet peridotites in cratonic lithosphere: new data on xenoliths from the Udachnaya kimberlite, central Siberia Luc S. Doucet • Dmitri A. Ionov • Alexander V. Golovin Received: 6 July 2012 / Accepted: 12 January 2013 / Published online: 12 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract We report new textural and chemical data for 10 garnet peridotite xenoliths from the Udachnaya kim- berlite and examine them together with recent data on another 21 xenoliths from the 80–220 km depth range. The samples are very fresh (LOI near zero), modally homoge- neous and large ( [ 100 g). Some coarse-grained peridotites show incipient stages of deformation with \ 10 % neoblasts at grain boundaries of coarse olivine. Such microstructures can only be recognized in very fresh rocks, because fine- grained interstitial olivine is strongly affected by alteration, and may have been overlooked in previous studies of altered peridotite xenoliths in the Siberian and other cra- tons. Some of the garnet peridotites are similar in com- position to low-opx Udachnaya spinel harzburgites (previously interpreted as pristine melt extraction residues), but the majority show post-melting enrichments in Fe and Ti. The least metasomatized coarse peridotites were formed by 30–38 % of polybaric fractional melting between 7 and 4 GPa and B1–3 GPa. Our data together with experimental results suggest that garnet in these rocks, as well as in some other cratonic peridotites elsewhere, may be a residual mineral, which has survived partial melting together with olivine and opx. Many coarse and all deformed garnet peridotites from Udachnaya underwent modal metasomatism through interaction of the melting residues with Fe-, Al-, Si-, Ti-, REE-rich melts, which precipitated cpx, less commonly additional garnet. The xenoliths define a complex geotherm probably affected by thermal perturbations shortly before the intrusion of the host kimberlite magmas. The deformation in the lower lithosphere may be linked to metasomatism. Keywords Garnet peridotite Á Mantle xenolith Á Craton Á Melting residue Á Metasomatism Á Deformation Introduction Garnet peridotites are by far the most common rock type in cratonic mantle, particularly in the depth range 80–250 km (Boyd 1989; Lee et al. 2011; Pearson et al. 2003). Understanding their origin is essential to get a better insight into the origin of cratonic lithosphere. Garnet peridotites are usually considered to be residues of high degrees of melt extraction that experienced a range of post-melting chemical and modal enrichments commonly referred to as metasomatism and/or ‘‘re-fertilization’’ (Carlson et al. 2005; Ionov et al. 2010; Pearson et al. 1995; Shimizu et al. 1997; Simon et al. 2003), in many cases accompanied by deformation (Boyd and Mertzman 1987). This intrinsic complexity of the origin of garnet peridotites makes it difficult, on the one hand, to define their melting conditions (because of variable metasomatic imprints) and, on the Communicated by T. L. Grove. Electronic supplementary material The online version of this article (doi:10.1007/s00410-013-0855-8) contains supplementary material, which is available to authorized users. L. S. Doucet (&) Á D. A. Ionov Universite ´ J. Monnet (Member of PRES Universite ´ de Lyon), 42023 Saint Etienne, France e-mail: luc.serge.doucet@univ-st-etienne.fr L. S. Doucet Á D. A. Ionov UMR 6524 ‘‘Magmas et Volcans’’, CNRS, 42023 Saint Etienne, France A. V. Golovin V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia 123 Contrib Mineral Petrol (2013) 165:1225–1242 DOI 10.1007/s00410-013-0855-8