Contributions to Mineralogy and Petrology

, Volume 100, Issue 4, pp 510–527 | Cite as

Metasomatised and veined upper-mantle xenoliths from Pello Hill, Tanzania: evidence for anomalously-light mantle beneath the Tanzanian sector of the East African Rift Valley

  • J. B. Dawson
  • J. V. Smith


Peridotite xenoliths from the Pello tuff cone in the Rift Valley of northern Tanzania, bear witness to upper mantle veining and metasomatism. Veins of katungite composition, with an asthenospheric signature, have imposed K, Fe, Ti, OH and REE metasomatism upon previously depleted peridotite. Chemical and mineralogical gradients are present in the peridotite wall rocks, and hydrous phases developed in the peridotite are generally lower in Ti and Fe, but higher in Mg and Cr, than those in the veins. The metasomatism has reduced the density of affected peridotite by up to 4.5%, supporting earlier geophysical models for low-density mantle beneath the Rift Valley. Age constraints for the metasomatically-induced density decrease permit correlation with Recent faulting in the Rift Valley, but not with the major upwarp of the Kenya Dome in the late Tertiary.


Mineral Resource Wall Rock Rift Valley Density Decrease Hydrous Phasis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. Arima M, Edgar AD (1983) High pressure experimental studies on a katungite and their bearing on the genesis of some potassium-rich magmas of the western branch of the African Rift. J Petrol 24:166–177Google Scholar
  2. Baker BH, Mohr PA, Williams LBJ (1972) Geology of the Eastern Rift system of Africa. Geol Soc Amer Spec Pap 136Google Scholar
  3. Banks RJ, Swain CJ (1978) The isostatic compensation of East Africa. Proc R Soc A364:331–352Google Scholar
  4. Bertrand P, Mercier J-C (1985) The mutual solubility of coexisting ortho- and clinopyroxene: toward an absolute geothermometer for the natural system? Earth Planet Sci Lett 76:109–122Google Scholar
  5. Best MG (1970) Kaersutite peridotite inclusions and kindred inclusions in basanitic lavas. Grand Canyon, Arizona. Contrib Mineral Petrol 27:25–44Google Scholar
  6. Best MG (1973) Amphibole-bearing cumulate inclusions, Grand Canyon, Arizona, and their bearing on silica-saturated hydrous magmas in the upper mantle. J Petrol 16:212–236Google Scholar
  7. Brey G (1978) Origin of olivine melilitites — chemical and experimental constraints. J Volcanol Geotherm Res 3:61–88Google Scholar
  8. Chapman NA (1976) Inclusions and megacrysts from undersaturated tuffs and basanites, East Fife, Scotland. J Petrol 17:472–498Google Scholar
  9. Cohen RS, O'Nions RK, Dawson JB (1984) Isotope geochemistry of xenoliths from East Africa: implications for development of mantle reservoirs and their interaction. Earth Planet Sci Letts 68:209–220Google Scholar
  10. Dautria JM, Liotard JM, Cabanes N, Girod M, Briqueu L (1987) Amphibole-rich xenoliths and host alkali basalts: petrogenetic constraints and implications on the recent evolution of the upper mantle beneath Ahaggar (central Sahara, southern Algeria). Contrib Mineral Petrol 95:133–144Google Scholar
  11. Dawson JB (1964) Carbonatite tuff cones in northern Tanganyika. Geol Mag 101:129–137Google Scholar
  12. Dawson JB (1980) Kimberlites and their xenoliths. Springer, Berlin Heidelberg New York, p 252Google Scholar
  13. Dawson JB (1984) Contrasting types of upper mantle metasomatism? In: Kornprobst J (ed) Kimberlites II. Elsevier, Amsterdam, pp 289–329Google Scholar
  14. Dawson JB (1987a) Upper mantle metasomatism: chemical and physical consequences. In: Fuchs K, Froidevaux C (eds) Composition, structure and dynamics of the lithosphere-asthenosphere system. Amer Geophys Union Mon (Geodynamics Ser) 16:155–159Google Scholar
  15. Dawson JB (1987b) Metasomatic harzburgites in kimberlitic and alkaline magmas: enriched restites and “flushed” lherzolites. In: Menzies M, Hawkesworth CJ (eds) Mantle metasomatism. Academic Press, London, pp 125–144Google Scholar
  16. Dawson JB, Powell DG (1969) The Natron-Engaruka explosion crater area, northern Tanzania. Bull Volcanol 33:791–817Google Scholar
  17. Dawson JB, Smith JV (1973) Alkalic pyroxenite xenoliths from the Lashaine volcano, northern Tanzania. J Petrol 14:113–131Google Scholar
  18. Dawson JB, Powell DG, Reid AM (1970) Ultrabasic lavas and xenoliths from the Lashaine volcano, northern Tanzania. J Petrol 14:113–131Google Scholar
  19. Dawson JB, Delaney JS, Smith JV (1979) Aspects of the mineralogy of alnöitic breccia, Malaita, Solomon Islands: comparison with continental kimberlites. Contrib Mineral Petrol 67:189–193Google Scholar
  20. Dawson JB, Smith JV, Jones AP (1985) A comparative study of the bulk rock and mineral chemistry of olivine melilitites and associated rocks from East and South Africa. Neues Jahrb Mineral Abh 152:143–175Google Scholar
  21. Delaney JS, Smith JV, Carswell DA, Dawson JB (1980) Chemistry of micas from kimberlites and xenoliths — II Primary- and secondary-textured micas from kimberlite xenoliths. Geochim Cosmochim Acta 44:857–872Google Scholar
  22. Dickey JS (1968) Eclogitic and other inclusions in the Mineral Breccia Member of the Deborah volcanic formation at Kakanui, New Zealand. Amer Mineral 53:1304–1319Google Scholar
  23. Droop GTR (1987) A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric data. Mineral Mag 51:431–435Google Scholar
  24. Eggler DH (1987) Solubility of major and trace elements in mantle metasomatic fluids: experimental constraints. In: Menzies MA, Hawkesworth CJ (eds) Mantle metasomatism. Academic Press, London, pp 21–41Google Scholar
  25. Fairhead JD (1976) The structure of the lithosphere beneath the Eastern Rift, East Africa, deduced from gravity studies. Tectonophysics 30:269–298Google Scholar
  26. Fairhead JD, Reeves CV (1977) Teleseismic delay times, Bouguer anomalies and the inferred thickness of the African lithosphere. Earth Planet Sci Lett 36:63–76Google Scholar
  27. Francis DM (1976) Amphibole pyroxenite xenolithe: cumulate or replacement phenomena from the upper mantle, Nunivak Island, Alaska. Contrib Mineral Petrol 58:51–61Google Scholar
  28. Frey FA (1984) Rare earth element abundances in upper mantle rocks. In: Henderson P (ed) Rare earth element geochemistry. Elsevier, Amsterdam, pp 153–203Google Scholar
  29. Frey FA, Green DH (1974) The mineralogy, geochemistry and origin of lherzolite inclusions in Victorian basanites. Geochim Cosmochim Acta 36:1023–1059Google Scholar
  30. Frey FA, Prinz M (1978) Ultramafic inclusions from San Carlos, Arizona: petrological and geochemical data bearing on their petrogenesis. Earth Planet Sci Lett 38:129–176Google Scholar
  31. Frey FA, Green DH, Roy SD (1978) Integrated models of basalt petrogenesis: a study of quartz tholeiites to olivine melilitites from south-eastern Australia utilizing geochemical and experimental petrological data. J Petrol 19:463–513Google Scholar
  32. Guest NJ (1953) The geology and petrology of the Engaruka-Oldoinyo Lengai-Lake Natron area of northern Tanganyika Territory. PhD thesis. Sheffield UniversityGoogle Scholar
  33. Harte B (1977) Rock nomenclature with special reference to deformation and recrystallisation textures in olivine-bearing xenoliths. J Geol 85:279–288Google Scholar
  34. Hervig RL, Smith JV, Steele IM, Dawson JB (1980) Fertile and barren Al-Cr-spinel harzburgites from the upper mantle: ion and electron probe analyses of trace elements in olivine and orthopyroxene: relation to lherzolites. Earth Planet Sci Lett 50:41–58Google Scholar
  35. Hervig RL, Smith JV, Dawson JB (1986) Lherzolite xenoliths in kimberlites and basalts: petrogenetic and crystallochemical significance of some minor and trace elements in olivine, pyroxenes, garnet and spinel. Trans Roy Soc Edinburgh: Earth Sci 77:181–201Google Scholar
  36. Irving AJ (1974) Megacrysts from the Newer Basalts and other basaltic rocks of southeastern Australia. Bull Geol Soc Amer 85:1503–1514Google Scholar
  37. Irving AJ (1980) Petrology and geochemistry of composite ultramafic xenoliths in alkalic basalts and implications for magmatic processes within the mantle. Amer J Sci 280A:389–426Google Scholar
  38. Ito M, Suwa K, Winani P (1981) Peridotite xenoliths in kimberlite from Nyanza, western Kenya. 6th Prelim Rpt African Stud. Nagoya Univ, pp 101–110Google Scholar
  39. Jones AP, Smith JV, Dawson JB, Hansen EC (1983a) Metamorphism, partial melting and K-metasomatism of garnet-scapolite-kyanite granulite xenoliths from Lashaine, Tanzania. J Geol 91:143–165Google Scholar
  40. Jones AP, Smith JV, Dawson JB (1983b) Glasses in mantle xenoliths from Olmani, Tanzania. J Geol 91:167–178Google Scholar
  41. Jordan TH (1979) Mineralogies, densities and seismic velocities of garnet lherzolites and their geophysical implications. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. Amer Geophys Union, Washington DC, pp 1–14Google Scholar
  42. Kempton PD (1987) Mineralogic and geochemical evidence for the differing styles of metasomatism in spinel lherzolite xenoliths: enriched mantle source regions of basalts? In: Menzies MA, Hawkesworth CJ (eds) Mantle metasomatism. Academic Press, London, pp 45–89Google Scholar
  43. King BC (1970) Volcanicity and rift tectonics in East Africa. In: Clifford TN, Gass IG (eds) African magmatism and tectonics. Oliver and Boyd, Edinburgh, pp 263–283Google Scholar
  44. Kovalenko VI, Solovova IP, Ryabchikov ID, Ionov DA, Bogatikov OA (1987) Fluidized CO2-sulphide-silicate media as agents of mantle metasomatism and megacrysts formation: evidence from a large druse in a spinel-lherzolite xenolith. Phys Earth Planet Inter 45:280–293Google Scholar
  45. Kramers JD, Roddick JCM, Dawson JB (1983) Trace element and isotope studies on veined, metasomatic and “MARID” xenoliths from Bultfontein, South Africa. Earth Planet Sci Lett 65:90–106Google Scholar
  46. Lawless PJ, Gurney JJ, Dawson JB (1979) Polymict peridotites from the Bultfontein and De Beers Mines, Kimberley, South Africa. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. Amer Geophys Union, Washington, DC, pp 145–155Google Scholar
  47. Leake BE (1978) Nomenclature of amphiboles. Amer Mineral 63:1023–1052Google Scholar
  48. Le Maitre RW (1984) A proposal by the IUGS Subcommission on the systematics of igneous rocks for the chemical classification of volcanic rocks based on the total alkali silica (TAS) diagram. Austr J Earth Sci 31:243–255Google Scholar
  49. Lloyd FE, Bailey DK (1975) Light element metasomatism of the continental mantle: the evidence and the consequences. Phys Chem Earth 9:389–416Google Scholar
  50. MacIntyre RM, Dawson JB, Mitchell JG (1974) Age of fault movements in Tanzanian sector of the East African rift system. Nature 247:354–356Google Scholar
  51. Maguire PKH, Khan MA (1980) The deep structure and dynamics of the East Africa Plateau, the Kenya Dome and the Gregory Rift. Proc Geol Assoc 91:25–31Google Scholar
  52. McIver J, Ferguson J (1979) Kimberlite, melilitite, trachytic and carbonatite eruptives at Saltpeterkop, Sutherland, South Africa. In: Boyd FR, Meyer HOA (eds) Kimberlites, diatremes and diamonds: their geology, petrology and geochemistry. Amer Geophys Union, Washington DC, pp 111–128Google Scholar
  53. Menzies M, Kempton P, Dungan M (1985) Interaction of continental lithosphere and asthenosperic melts below the Geronimo volcanic field, Arizona, USA. J Petrol 26:663–693Google Scholar
  54. Menzies MA, Rogers N, Tindle A, Hawkesworth CJ (1987) Metasomatic and enrichment processes in lithospheric peridotites, an effect of asthenosphere-lithosphere interaction. In: Menzies MA, Hawkesworth CJ (eds) Mantle metasomatism. Academic Press, London, pp 313–361Google Scholar
  55. Mercier J-C, Carter NL (1975) Pyroxene geotherms. J Geophys Res 80:3349–3362Google Scholar
  56. Mitchell RH (1986) Kimberlites. Plenum Press, New York, p 442Google Scholar
  57. Mitchell RH, Bell K (1976) Rare earth element geochemistry of potassic lavas from the Birunga and Toro-Ankole regions of Uganda, Africa. Contrib Mineral Petrol 58:293–303Google Scholar
  58. Mysen BO (1983) Rare earth element partitioning between (H2O+CO2) vapor and upper mantle minerals: Experimental data bearing on the conditions of formation of alkali basalt and kimberlite. Neues Jahrb Mineral Abh 146:41–65Google Scholar
  59. Nixon PH, Rogers NW, Gibson IL, Grey A (1981) Depleted and fertile mantle xenoliths from southern African kimberlites. Annu Rev Earth Planet Sci 8:285–309Google Scholar
  60. Norry MJ, Truckle PH, Lippard SJ, Hawkesworth CJ, Weaver SD, Marriner GF (1980) Isotope and trace element evidence from lavas, bearing on mantle heterogeneity beneath Kenya. Phil Trans Roy Soc A297:259–271Google Scholar
  61. Porcelli DR, O'Nions RK, O'Reilly SY (1986) Helium and strontium isotopes in ultramafic xenoliths. Chem Geol 54:237–249Google Scholar
  62. Reid AM, Donaldson CH, Brown RW, Ridley WI, Dawson JB (1975) Mineral chemistry of peridotite xenoliths from the Lashaine volcano, Tanzania. Phys Chem Earth 9:525–543Google Scholar
  63. Ridley WI, Dawson JB (1975) Lithophile trace element data bearing on the origin of peridotite xenoliths, ankaramite and carbonatite from the Lashaine volcano. N Tanzania. Phys Chem Earth 9:559–569Google Scholar
  64. Roden MF, Frey FA, Francis DM (1984) An example of consequent mantle metasomatism in peridotite inclusions from Nunivak Island, Alaska. J Petrol 25:546–577Google Scholar
  65. Shimizu N (1975) Geochemistry of ultramafic inclusions from Salt Lake Crater, Hawaii and from Southern African kimberlites. Phys Chem Earth 9:655–669Google Scholar
  66. Simkin T, Smith JV (1970) Minor element distribution in olivine. J Geol 78:304–325Google Scholar
  67. Suess E (1891) Die Brüche des östlichen Afrika. Denksch Akad Wiss, Wien 58:555–584Google Scholar
  68. Suwa K, Yusa Y, Kishida N (1975) Petrology of peridotite nodules from Ndonyuo Olnchoro, Samburu District, central Kenya. Phys Chem Earth 9:273–286Google Scholar
  69. Taylor SR, McLennan SM (1985) The continental crust: its composition and evolution. Blackwells, Oxford, p 312Google Scholar
  70. Tilley CE, Yoder HS (1968) The pyroxenite facies conversion of volcanic and subvolcanic melilite-bearing and other alkali ultramafic assemblages. Carnegie Inst Washington Yearbk 66:457–460Google Scholar
  71. Varne R (1968) The petrology of Moroto Mountain, eastern Uganda, and the origin of nephelinites. J Petrol 9:169–190Google Scholar
  72. Wakita H, Rey P, Schmitt RA (1971) Abundances of the 14 rareearth elements and 12 other trace elements in Apollo 12 samples, five igneous and one breccia rocks and four soils. Proc 2nd Lunar Sci Conf, pp 1319–1329Google Scholar
  73. Wilkinson JFG, Le Maitre RW (1987) Upper mantle amphiboles and micas and TiO2, K2O and P2O5 abundances and the 100 Mg/(Mg+Fe2) ratios of common basalts and andesites: implications for modal mantle metasomatism and undepleted mantle compositions. J Petrol 28:37–73Google Scholar
  74. Willis B (1936) East African plateaus and rift valleys. Carnegie Inst, Washington, DCGoogle Scholar
  75. Wilshire HG, Neilson Pike JE, Meyer CE, Schwarzman EC (1980) Amphibole-rich veins in lherzolite xenoliths, Dish Hill and Deadman Lake, California. Amer J Sci 280-A:576–593Google Scholar

Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • J. B. Dawson
    • 1
  • J. V. Smith
    • 2
  1. 1.Department of GeologyUniversity of SheffieldSheffieldUK
  2. 2.Department of Geophysical SciencesUniversity of ChicagoIllinoisUSA

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