Archean diamonds from Wawa (Canada): samples from deep cratonic roots predating cratonization of the Superior Province

  • Thomas Stachel
  • Anetta Banas
  • Karlis Muehlenbachs
  • Stephan Kurszlaukis
  • Edward C. Walker
Original Paper


With an age of ca. 2.7 Ga, greenschist facies volcaniclastic rocks and lamprophyre dikes in the Wawa area (Superior Craton) host the only diamonds emplaced in the Archean available for study today. Nitrogen aggregation in Wawa diamonds ranges from Type IaA to IaB, suggesting mantle residence times of tens to hundreds of millions of years. The carbon isotopic composition (δ13C) of cube diamonds is similar to the accepted mantle value (− 5.0‰). Octahedral diamonds show a slight shift (by + 1.5‰) to isotopically less negative values suggesting a subduction-derived, isotopically heavy component in the diamond-forming fluids. Syngenetic inclusions in Wawa diamonds are exclusively peridotitic and, similar to many diamond occurrences worldwide, are dominated by the harzburgitic paragenesis. Compositionally they provide a perfect match to inclusions from diamonds with isotopically dated Paleo- to Mesoarchean crystallization ages. Several high-Cr harzburgitic garnet inclusions contain a small majorite component suggesting crystallization at depth of up to 300 km. Combining diamond and inclusion data indicates that Wawa diamonds formed and resided in a very thick package of chemically depleted lithospheric mantle that predates stabilization of the Superior Craton. If late granite blooms are interpreted as final stages of cratonization then a similar disconnect between Paleo- to Mesoarchean diamondiferous mantle lithosphere and Neoarchean cratonization is also apparent in other areas (e.g., the Lac de Gras area of the Slave Craton) and may suggest that early continental nuclei formed and retained their own diamondiferous roots.


  1. Akaogi M, Akimoto S (1977) Pyroxene–garnet solid-solution equilibria in the systems Mg4Si4O12–Mg3Al2Si3O12 and Fe4Si4O12–Fe3Al2Si3O12 at high pressures and temperatures. Phys Earth Planet Inter 15:90–106CrossRefGoogle Scholar
  2. Appleyard CM, Viljoen KS, Dobbe R (2004) A study of eclogitic diamonds and their inclusions from the Finsch kimberlite pipe, South Africa. Lithos 77(1–4):317–332CrossRefGoogle Scholar
  3. Aulbach S (1999) The chemistry of syngenetic mineral inclusions in diamonds from Venetia and the stable isotope composition of diamonds from Mwadui and the Kankan district. MSc thesis, J.W. Goethe University, 104 ppGoogle Scholar
  4. Ayer JA, Wyman DA (2003) Origin of diamondiferous Archean Lamprophyres in the evolution of the Michipicoten and Abitibi greenstone belts. In: Extended abstracts of the eighth international kimberlite conference, Victoria, BC, Canada, 5 pp (CD, not paginated)Google Scholar
  5. Bleeker W (2003) The late Archean record: a puzzle in ca. 35 pieces. Lithos 71(2–4):99–134CrossRefGoogle Scholar
  6. Boyd SR, Mattey DP, Pillinger CT, Milledge HJ, Mendelssohn M, Seal M (1987) Multiple growth events during diamond genesis: an integrated study of carbon and nitrogen isotopes and nitrogen aggregation state in coated stones. Earth Planet Sci Lett 86(2–4):341–353CrossRefGoogle Scholar
  7. Boyd SR, Kiflawi I, Woods GS (1994) The relationship between infrared absorption and the A defect concentration in diamond. Philos Mag B 69(6):1149–1153CrossRefGoogle Scholar
  8. Boyd SR, Kiflawi I, Woods GS (1995) Infrared absorption by the B nitrogen aggregate in diamond. Philos Mag B 72(3):351–361CrossRefGoogle Scholar
  9. Brenker FE, Brey GP (1997) Reconstruction of the exhumation path of the Alpe Arami garnet-peridotite body from depths exceeding 160 km. J Metamorphic Geol 15:581–592CrossRefGoogle Scholar
  10. Capdevila R, Arndt N, Letendre J, Sauvage JF (1999) Diamonds in volcaniclastic komatiite from French Guiana. Nature 399(6735):456–458CrossRefGoogle Scholar
  11. Cartigny P, Stachel T, Harris JW, Javoy M (2004) Constraining diamond metasomatic growth using C- and N-stable isotopes: examples from Namibia. Lithos 77(1–4):359–373CrossRefGoogle Scholar
  12. Davies RM, Griffin WL, O’Reilly SY, Andrew AS (2003) Unusual mineral inclusions and carbon isotopes of alluvial diamonds from Bingara, eastern Australia. Lithos 69(1–2):51–66CrossRefGoogle Scholar
  13. Davies RM, Griffin WL, O’Reilly SY, Doyle BJ (2004a) Mineral inclusions and geochemical characteristics of microdiamonds from the DO27, A154, A21, A418, DO18, DD17 and Ranch Lake kimberlites at Lac de Gras, Slave Craton, Canada. Lithos 77(1–4):39–55CrossRefGoogle Scholar
  14. Davies RM, Griffin WL, O’Reilly SY, McCandless TE (2004b) Inclusions in diamonds from the K14 and K10 kimberlites, Buffalo Hills, Alberta, Canada: diamond growth in a plume? Lithos 77(1–4):99–111CrossRefGoogle Scholar
  15. Davis WJ, Jones AG, Bleeker W, Grütter H (2003) Lithosphere development in the Slave craton: a linked crustal and mantle perspective. Lithos 71:575–589CrossRefGoogle Scholar
  16. Deines P (2002) The carbon isotope geochemistry of mantle xenoliths. Earth Sci Rev 58(2002):247–278CrossRefGoogle Scholar
  17. Deines P, Harris JW (2004) New insights into the occurrence of C-13-depleted carbon in the mantle from two closely associated kimberlites: Letlhakane and Orapa, Botswana. Lithos 77(1–4):125–142CrossRefGoogle Scholar
  18. Doroshev AM, Brey GP, Girnis AV, Turkin AI, Kogarko LN (1997) Pyrope-knorringite garnets in the earths mantle: experiments in the MgO–Al2O3–SiO2–Cr2O3 system. Geol Geofiz 38(2):523–545Google Scholar
  19. Ernst WG, Liou JG (1999) Overview of UHP metamorphism and tectonics in well-studied collisional orogens. Int Geol Rev 41(6):477–493CrossRefGoogle Scholar
  20. Evans T, Harris JW (1989) Nitrogen aggregation, inclusion equilibration temperatures and the age of diamonds. In: Ross J et al (eds) Kimberlites and related rocks. GSA Spec Publ 14, vol 2. Blackwell, Carlton, pp 1001–1006Google Scholar
  21. Griffin WL, O’Reilly SY, Ryan CG (1999) The composition and origin of subcontinental lithospheric mantle. In: Fei Y, Bertka CM, Mysen BO (eds) Mantle petrology: field observations and high pressure experimentation: a tribute to Francis R. (Joe) Boyd. The Geochemical Society, Houston, pp 13–45Google Scholar
  22. Griffin WL, O’Reilly SY, Davies RM (2000) Subduction-related diamond deposits? Constraints, possibilities, and new data from Eastern Australia. Rev Econ Geol 11:291–310Google Scholar
  23. Griffin WL, Win TT, Davies R, Wathanakul P, Andrew A, Metcalfe I, Cartigny P (2001) Diamonds from Myanmar and Thailand: characteristics and possible origins. Econ Geol 96(1):159–170Google Scholar
  24. Grütter HS (2001) The genesis of high Cr/Al garnet peridotite, with implications for cratonic crust–mantle architecture. In: The Slave–Kaapvaal workshop, Merrickville, Ontario, 3 pp Google Scholar
  25. Gurney JJ (1984) A correlation between garnets and diamonds in kimberlites. In: Glover JE, Harris PG (eds) Kimberlite occurrence and origin; a basis for conceptual models in exploration, vol 8. Geology Department & University Extension, University of Western Australia, pp 143–166Google Scholar
  26. Gurney JJ (1989) Diamonds. In: Ross J et al (eds) Kimberlites and related rocks. GSA Spec Publ 14, vol 2. Blackwell, Carlton, pp 935–965Google Scholar
  27. Gurney JJ, Harris JW, Rickard RS (1984) Silicate and oxide inclusions in diamonds from the Orapa Mine, Botswana. In: Kornprobst J (ed) Kimberlites II: the mantle and crust–mantle relationships. Elsevier, Amsterdam, pp 3–9Google Scholar
  28. Harris JW (1992) Diamond geology. In: Field JE (ed) The properties of natural and synthetic diamond, vol 345–393. Academic, London, pp 345–393Google Scholar
  29. Harris JW, Stachel T, Leost I, Brey GP (2004) Peridotitic diamonds from Namibia: constraints on the composition and evolution of their mantle source. Lithos 77(1–4):209–223CrossRefGoogle Scholar
  30. Hoffman PF (1989) Precambrian geology and tectonic history of North America. In: Bally AW, Palmer AR (eds) The geology of North America—an overview, vol A. The Geological Society of America, Boulder, pp 447–511Google Scholar
  31. Irifune T (1987) An experimental investigation of the pyroxene–garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle. Phys Earth Planet Inter 45(4):324–336CrossRefGoogle Scholar
  32. Irifune T, Hibberson WO, Ringwood AE (1989) Eclogite–garnetite transformation at high pressure and its bearing on the occurrence of garnet inclusions in diamond. In: Ross J et al (eds) Kimberlites and related rocks. GSA Spec Publ 14, vol 2. Blackwell, Carlton, pp 877–882Google Scholar
  33. Irifune T, Kurio A, Sakamoto S, Inoue T, Sumiya H, Funakoshi K (2004) Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature. Phys Earth Planet Inter 143–144:593–600CrossRefGoogle Scholar
  34. Kaminsky FV, Zakharchenko OD, Khachatryan GK, Shiryaev AA (2001) Diamonds from the Coromandel Area, Minas Gerias, Brazil. Rev Bras Geoci 31(4):583–596Google Scholar
  35. Kirkley MB, Gurney JJ, Otter ML, Hill SJ, Daniels LR (1991) The application of C isotope measurements to the identification of the sources of C in diamonds: a review. Appl Geochem 6(5):477–494CrossRefGoogle Scholar
  36. Leahy K, Taylor WR (1997) The influence of the Glennie domain deep structure on the diamonds in Saskatchewan kimberlites. Geol Geofiz 38(2):451–460Google Scholar
  37. Lefebvre N, Kopylova M, Kivi K, Barnett RL (2003) Diamondiferous volcaniclastic debris flows of Wawa, Ontario, Canada. In: Eighth international kimberlite conference, Victoria, BC, Canada, 5 pp (CD, pot paginated)Google Scholar
  38. Lefebvre N, Kopylova M, Kivi K (2005) Archean calc-alkaline lamprophyres of Wawa, Ontario, Canada: unconventional diamondiferous volcaniclastic rocks. Precambrian Res 138(1–2):57–87CrossRefGoogle Scholar
  39. Leost I, Stachel T, Brey GP, Harris JW, Ryabchikov ID (2003) Diamond formation and source carbonation: mineral associations in diamonds from Namibia. Contrib Mineral Petrol 145(1):15–24CrossRefGoogle Scholar
  40. Logvinova AM, Zedgenizov DA, Sobolev NV (2001) Pyroxenite paragenesis of abundant mineral and probable fluid inclusions in microdiamonds from the Mir kimberlite pipe, Yakutia. Dokl Earth Sci 380(7):795–799Google Scholar
  41. Magee CW, Taylor WR (1999) Diamond and chromite geochemical constraints on the nature of the Dachine complex, French Guiana. In: Experimental Petrology Group, annual report 1999, Research School of Earth Sciences, ANU, Canberra, 1 pGoogle Scholar
  42. Mc Kenna N, Gurney JJ, Klump J, Davidson JM (2004) Aspects of diamond mineralisation and distribution at the Helam Mine, South Africa. Lithos 77(1–4):193–208CrossRefGoogle Scholar
  43. Meyer HOA (1987) Inclusions in diamond. In: Nixon PH (ed) Mantle xenoliths. Wiley, Chichester, pp 501–522Google Scholar
  44. Navon O (1999) Diamond formation in the Earth’s mantle. In: Gurney JJ, Gurney JL, Pascoe MD, Richardson SH (eds) The P.H. Nixon volume, Proceedings of the VII international kimberlite conference, Red Roof Design, Cape Town, pp 584–604Google Scholar
  45. Navon O, Hutcheon ID, Rossman GR, Wasserburg GJ (1988) Mantle-derived fluids in diamond micro-inclusions. Nature 335(6193):784–789CrossRefGoogle Scholar
  46. Orlov YL (1977) The mineralogy of the diamond. Wiley, New York, p 235Google Scholar
  47. Pearson DG, Shirey SB, Bulanova GP, Carlson RW, Milledge HJ (1999) Re–Os isotope measurements of single sulfide inclusions in a Siberian diamond and its nitrogen aggregation systematics. Geochim Cosmochim Acta 63(5):703–711CrossRefGoogle Scholar
  48. Phillips D, Harris JW, Viljoen KS (2004) Mineral chemistry and thermobarometry of inclusions from De Beers Pool diamonds, Kimberley, South Africa. Lithos 77(1–4):155–179CrossRefGoogle Scholar
  49. Pokhilenko NP, Sobolev NV, Reutsky VN, Hall AE, Taylor LA (2004) Crystalline inclusions and C isotope ratios in diamonds from the Snap Lake/King Lake kimberlite dyke system: evidence of ultradeep and enriched lithospheric mantle. Lithos 77(1–4):57–67CrossRefGoogle Scholar
  50. Poujol M, Robb LJ, Anhaeusser CR, Gericke B (2003) A review of the geochronological constraints on the evolution of the Kaapvaal Craton, South Africa. Precambrian Res 127(1–3):181–213CrossRefGoogle Scholar
  51. Promprated P, Taylor LA, Anand M, Floss C, Sobolev NV, Pokhilenko NP (2004) Multiple-mineral inclusions in diamonds from the Snap Lake/King Lake kimberlite dike, Slave craton, Canada: a trace-element perspective. Lithos 77(1–4):69–81CrossRefGoogle Scholar
  52. Richardson SH, Gurney JJ, Erlank AJ, Harris JW (1984) Origin of diamonds in old enriched mantle. Nature 310(5974):198–202CrossRefGoogle Scholar
  53. Richardson SH, Erlank AJ, Harris JW, Hart SR (1990) Eclogitic diamonds of Proterozoic age from Cretaceous kimberlites. Nature 346(6279):54–56CrossRefGoogle Scholar
  54. Richardson SH, Harris JW, Gurney JJ (1993) Three generations of diamonds from old continental mantle. Nature 366(6452):256–258CrossRefGoogle Scholar
  55. Ringwood AE (1967) The pyroxene–garnet transformation in the Earth’s mantle. Earth Planet Sci Lett 2(3):255–263CrossRefGoogle Scholar
  56. Ringwood AE, Major A (1971) Synthesis of majorite and other high pressure garnets and perovskites. Earth Planet Sci Lett 12:411–418CrossRefGoogle Scholar
  57. Robinson DN (1979) Surface textures and other features of diamonds. PhD thesis, University of Cape Town, Cape Town (South Africa), vol 1: 221 pp, vol 2: 161 ppGoogle Scholar
  58. Ryan CG, Griffin WL, Pearson NJ (1996) Garnet geotherms—pressure–temperature data from Cr-pyrope garnet xenocrysts in volcanic rocks. J Geophys Res 101(B3):5611–5625CrossRefGoogle Scholar
  59. Sage RP, Lightfoot PC, Doherty W (1996) Bimodal cyclical Archean basalts and rhyolites from the Michipicoten (Wawa) greenstone belt, Ontario: geochemical evidence for magma contributions from the asthenospheric mantle and ancient continental lithosphere near the southern margin of the Superior Province. Precambrian Res 76(3–4):119–153CrossRefGoogle Scholar
  60. Scott HP, Hemley RJ, Mao HK, Herschbach DR, Fried LE, Howard WM, Bastea S (2004) Generation of methane in the Earth’s mantle: in situ high pressure–temperature measurements of carbonate reduction. Proc Natl Acad Sci USA 101(39):14023–14026CrossRefGoogle Scholar
  61. Shirey SB, Harris JW, Richardson SH, Fouch MJ, James DE, Cartigny P, Deines P, Viljoen F (2002) Diamond genesis, seismic structure, and evolution of the Kaapvaal-Zimbabwe craton. Science 297(5587):1683–1686CrossRefGoogle Scholar
  62. Sobolev NV (1977) Deep-seated inclusions in kimberlites and the problem of the composition of the upper mantle. Translated from the Russian edition, 1974. AGU, Washington, p 279Google Scholar
  63. Sobolev NV, Lavrent’ev YG, Pokhilenko NP, Usova LV (1973) Chrome-rich garnets from the kimberlites of Yakutia and their paragenesis. Contrib Mineral Petrol 40(1):39–52CrossRefGoogle Scholar
  64. Sobolev NV, Logvinova AM, Zedgenizov DA, Yefimova ES, Lavrent’ev YG, Usova LV (2000) Anomalously high Ni admixture in olivine inclusions from microdiamonds, the Yubileinaya Kimberlite pipe, Yakutia. Dokl Earth Sci 375(9):1403–1406Google Scholar
  65. Sobolev NV, Logvinova AM, Zedgenizov DA, Seryotkin YV, Yefimova ES, Floss C, Taylor LA (2004) Mineral inclusions in microdiamonds and macrodiamonds from kimberlites of Yakutia: a comparative study. Lithos 77(1–4):225–242CrossRefGoogle Scholar
  66. Spetsius ZV, Belousova EA, Griffin WL, O’Reilly SY, Pearson NJ (2002) Archean sulfide inclusions in Paleozoic zircon megacrysts from the Mir kimberlite, Yakutia: implications for the dating of diamonds. Earth Planet Sci Lett 199(1–2):111–126CrossRefGoogle Scholar
  67. Stachel T, Viljoen KS, Brey G, Harris JW (1998) Metasomatic processes in lherzolitic and harzburgitic domains of diamondiferous lithospheric mantle: REE in garnets from xenoliths and inclusions in diamonds. Earth Planet Sci Lett 159(1–2):1–12CrossRefGoogle Scholar
  68. Stachel T, Brey GP, Harris JW (2000) Kankan diamonds (Guinea) I: from the lithosphere down to the transition zone. Contrib Mineral Petrol 140:1–15CrossRefGoogle Scholar
  69. Stachel T, Harris JW, Tappert R, Brey GP (2003) Peridotitic diamonds from the Slave and the Kaapvaal cratons—similarities and differences based on a preliminary data set. Lithos 71(2–4):489–503CrossRefGoogle Scholar
  70. Stachel T, Blackburn L, Kurszlaukis S, Barton E, Walker EC (2004a) Diamonds from the Cristal and Genesis volcanics, Wawa area, Ontario. In: Abstracts of the 32nd annual Yellowknife geoscience forum, Yellowknife, NWT, Canada, pp 74–75Google Scholar
  71. Stachel T, Viljoen KS, McDade P, Harris JW (2004b) Diamondiferous lithospheric roots along the western margin of the Kalahari Craton—the peridotitic inclusion suite in diamonds from Orapa and Jwaneng. Contrib Mineral Petrol 147(1):32–47CrossRefGoogle Scholar
  72. Stott GM (1997) The Superior Province, Canada. In: de Wit MJ, Ashwal LD (eds) Greenstone belts. Clarendon Press, Oxford, pp 480–507Google Scholar
  73. Sung J (2000) Graphite → diamond transition under high pressure: a kinetics approach. J Mater Sci 35(23):6041–6054CrossRefGoogle Scholar
  74. Tappert R, Stachel T, Harris JW, Shimizu N, Brey GP (2005) Mineral inclusions in diamonds from the Panda kimberlite, Slave Province, Canada. Eur J Mineral 17(3):423–440CrossRefGoogle Scholar
  75. Taylor WR, Jaques AL, Ridd M (1990) Nitrogen-defect aggregation characteristics of some Australasian diamonds: time–temperature constraints on the source regions of pipe and alluvial diamonds. Am Mineral 75(11–12):1290–1310Google Scholar
  76. Taylor WR, Bulanova GP, Milledge HJ (1995) Quantitative nitrogen aggregation study of some Yakutian diamonds: constraints on the growth, thermal and deformation history of peridotitic and eclogitic diamonds. In: Sixth international kimberlite conference, Novosibirsk, Russia, pp 608–610Google Scholar
  77. Taylor LA, Snyder GA, Crozaz G, Sobolev VN, Yefimova ES, Sobolev NV (1996a) Eclogitic inclusions in diamonds: evidence of complex mantle processes over time. Earth Planet Sci Lett 142(3–4):535–551CrossRefGoogle Scholar
  78. Taylor WR, Canil D, Milledge HJ (1996b) Kinetics of Ib to IaA nitrogen aggregation in diamond. Geochim Cosmochim Acta 60(23):4725–4733CrossRefGoogle Scholar
  79. Thurston PC (2002) Autochthonous development of Superior Province greenstone belts? Precambrian Res 115(1–4):11–36CrossRefGoogle Scholar
  80. Turek A, Smith PE, Vanschmus WR (1984) U–Pb zircon ages and the evolution of the Michipicoten plutonic volcanic terrane of the Superior Province, Ontario. Can J Earth Sci 21(4):457–464CrossRefGoogle Scholar
  81. Turek A, Sage RP, Vanschmus WR (1992) Advances in the U–Pb zircon geochronology of the Michipicoten greenstone-belt, Superior Province, Ontario. Can J Earth Sci 29(6):1154–1165CrossRefGoogle Scholar
  82. Vaillancourt C, Ayer JA, Zubowski SM, Kamo SL (2004) Synthesis and timing of Archean geology and diamond-bearing rocks in the Michipicoten greenstone belt: Menzies and Musquash townships. Summary of field work and other activities 2004, Ontario Geological Survey, Open file report 6145, pp 6.1–6.9Google Scholar
  83. Wang WY, Sueno S, Takahashi E, Yurimoto H, Gasparik T (2000) Enrichment processes at the base of the Archean lithospheric mantle: observations from trace element characteristics of pyropic garnet inclusions in diamonds. Contrib Mineral Petrol 139(6):720–733CrossRefGoogle Scholar
  84. Westerlund K, Shirey SB, Richardson SH, Gurney JJ, Harris JW (2003) Re–Os isotope systematics of peridotitic diamond inclusion sulfides from the Panda kimberlite, Slave Craton. In: Extended abstracts of the eighth international kimberlite conference, Victoria, BC, Canada, 5 pp (CD, not paginated)Google Scholar
  85. Williams HR, Stott GM, Heather KB, Muir TL, Sage RP (1991) Wawa Subprovince. In: Geology of Ontario, Special volume 4. Ontario Geological Survey, Sudbury, pp 485–539Google Scholar
  86. Wilson AC (2004) Diamond exploration targets, Michipicoten greenstone belt. CIM Bull 97(1077):41–46Google Scholar
  87. Wood BJ, Pawley A, Frost DR (1996) Water and carbon in the Earth’s mantle. Philos Trans R Soc Lond Ser A Math Phys Eng Sci 354(1711):1495–1511CrossRefGoogle Scholar
  88. Wyman DA, Kerrich R (1993) Archean shoshonitic lamprophyres of the Abitibi Subprovince, Canada—petrogenesis, age, and tectonic setting. J Petrol 34(6):1067–1109CrossRefGoogle Scholar
  89. Wyman DA, Kerrich R, Polat A (2002) Assembly of Archean cratonic mantle lithosphere and crust: plume–arc interaction in the Abitibi–Wawa subduction–accretion complex. Precambrian Res 115(1–4):37–62CrossRefGoogle Scholar
  90. Yamaoka S, Komatsu H, Kanda H, Setaka N (1977) Growth of diamond with rhombic dodecahedral faces. J Cryst Growth 37(3):349–352CrossRefGoogle Scholar
  91. Yaxley GM, Green DH (1994) Experimental demonstration of refractory carbonate-bearing eclogite and siliceous melt in the subduction regime. Earth Planet Sci Lett 128(3–4):313–325CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Thomas Stachel
    • 1
  • Anetta Banas
    • 1
  • Karlis Muehlenbachs
    • 1
  • Stephan Kurszlaukis
    • 2
  • Edward C. Walker
    • 3
  1. 1.Earth and Atmospheric SciencesUniversity of AlbertaEdmontonCanada
  2. 2.Exploration DivisionDe Beers Canada Inc.TorontoCanada
  3. 3.Petrologic Inc.LakefieldCanada

Personalised recommendations