International Journal of Earth Sciences

, Volume 92, Issue 6, pp 873–890

Petrology, geochronology and Sr–Nd isotopic geochemistry of the Konso pluton, south-western Ethiopia: implications for transition from convergence to extension in the Mozambique Belt

Original Paper

Abstract

Granites were shown to be excellent geochronological, structural and geodynamic markers. Among several generations of granites described in the Neoproterozoic of Ethiopia, we studied the post-tectonic Konso pluton to characterise the post-Pan-African evolution of the Mozambique Belt (MB) of southern Ethiopia. The Konso pluton is a composite intrusion of slightly peraluminous and ferro-potassic, bt (biotite)–leucogranites, bt–hbl (hornblende)–granites and subordinate coeval metaluminous monzodiorites, intruded into high-grade gneiss–migmatite associations of the MB. The whole suite displays chemical features of A-type granites. It is LIL- and HFS-elements enriched with Y/Nb and Yb/Ta≥1.2. The granites and leucogranites show non-fractionated to fractionated REE patterns [(La/Yb)N=0.3–9.4] with strong negative Eu anomalies. The monzodiorites show fractionated REE patterns [(La/Yb)N=5.5–7.4] with negligible negative Eu anomaly. The low initial (87Sr/86Sr)450 ratios (0.70113–0.70441) and positive εNd(450) values (+1.8 to +3.3) suggest an isotopically primitive source. The Konso granites are likely to be derived from a basaltic parent, with minor contamination by crustal material with high Y/Nb and low Sr initial isotopic ratios. Age of pluton emplacement is constrained by a Rb–Sr isochron and zircon U–Pb data at 449±2 Ma. The Konso pluton is, therefore, the witness of an Ordovician A-type magmatic event, which marks a change from convergence, related to the Pan-African collision, to extension in the Mozambique Belt of southern Ethiopia.

Keywords

A-type granite Ethiopia Mozambique Belt Ordovician Post-collisional 

References

  1. Alene M, Barker AJ (1993) Tectonometamorphic evolution of the Moyale region, southern Ethiopia. Precambrian Res 62:271–283CrossRefGoogle Scholar
  2. Anderson JL, Smith DR (1995) The effects of temperature and f O2 on the Al-in-hornblende barometer. Am Mineral 80:549–559Google Scholar
  3. Asrat A (1997) Geology and geochemistry of the Negash Pluton and their metallogenic significance, central Tigrai. MSc Thesis, Addis Ababa University, EthiopiaGoogle Scholar
  4. Asrat A, Barbey P, Gleizes G (2001) The Precambrian geology of Ethiopia: a review. Afr Geosci Rev 8:271–288Google Scholar
  5. Asrat A, Barbey P, Gleizes G, Reisberg L, Ludden J (2002) Structure, géochimie et âge du pluton Negash (nord Ethiopie): implications sur la nature du Bouclier Arabo-Nubien (ANS) et ses relations avec la Chaîne Mozambique (MB). RST-19, 9–12 April, Nantes, Résumés, pp 51–52Google Scholar
  6. Asrat A, Gleizes G, Barbey P, Ayalew D (2003) Magma emplacement and mafic-felsic magma hybridization: structural evidence from the Pan-African Negash pluton, Northern Ethiopia. J Struct Geol 25:1451–1469CrossRefGoogle Scholar
  7. Ayalew D, Barbey P, Marty B, Reisberg L, Yirgu G, Pik R (2002) Source, genesis, and timing of giant ignimbrite deposits associated with Ethiopian continental flood basalts. Geochim Cosmochim Acta 66:1429–1448CrossRefGoogle Scholar
  8. Ayalew T, Gichile S (1990) Preliminary U–Pb ages from southern Ethiopia. In: Rocci G, Descamps M (eds) Recent data in African earth sciences. CIFEG Occasional Publ 1990/22:127–130Google Scholar
  9. Ayalew T, Bell K, Moore JM, Parrish RR (1990) U–Pb and Rb–Sr geochronology of the western Ethiopian Shield. Geol Soc Am Bull 102:1309–1316Google Scholar
  10. Barbarin B (1999) A review of the relationships between granitoid types, their origins and their geodynamic environments. Lithos 46:605–626CrossRefGoogle Scholar
  11. Boher M, Abouchami W, Michard A, Albarède F, Arndt NT (1992) Crustal growth in West Africa at 2.1 Ga. J Geophys Res 97:345–369Google Scholar
  12. Bonavia FF, Chorowicz J (1993) Neoproterozoic structures in the Mozambique orogenic belt of southern Ethiopia. Precambrian Res 62:307–322CrossRefGoogle Scholar
  13. Bouchez JL, Hutton DHW, Stephens WE (eds) (1997) Granite: from segregation of melt to emplacement fabrics. Kluwer, DordrechtGoogle Scholar
  14. Brueckner HK, Elhaddad MA, Hamelin B, Hemming S, Kröner A, Reisberg L, Seyler M (1995) A Pan-African origin and uplift for the gneisses and peridotites of Zabargad Island, Red Sea: A Nd, Sr, Pb, and Os isotope study. J Geophys Res 100:22283–22297Google Scholar
  15. Clemens JD, Holloway JR, White AJR (1986) Origin of an A-type granite: experimental constraints. Am Mineral 71:317–324Google Scholar
  16. Collins WJ, Beams SD, White AGR, Chappell BW (1982) Nature and origin of A-type granites with particular reference to southeastern Australia. Contrib Mineral Petrol 80:189–200Google Scholar
  17. Creaser RA, White AJR (1991) Yardea dacite-large-volume, high-temperature felsic volcanism from the Middle Proterozoic of South Australia. Geology 19:48–51CrossRefGoogle Scholar
  18. Creaser RA, Price RC, Wormald RJ (1991) A-type granites revisited: assessment of a residual-source model. Geology 19:163–166CrossRefGoogle Scholar
  19. Davidson A (1983) The Omo River project: reconnaissance geology and geochemistry of parts of Illubabor, Keffa, Gemu Gofa and Sidamo, Ethiopia. Ethiopian Institute of Geological SurveysGoogle Scholar
  20. Deloule E, Alexandrov P, Cheilletz A, Laumonier B, Barbey P (2002) Zircon U–Pb ion-probe dating of the orthogneisses from the Canigou–Carança massif (eastern Pyrenées, France): irrelevance of the Cadomian basement/Paleozoic cover model. Int J Earth Sci 91:398–405CrossRefGoogle Scholar
  21. DePaolo DJ (1988) Neodymium isotope geochemistry, an introduction. Springer, Berlin, Heidelberg New YorkGoogle Scholar
  22. de Wit MJ, Chewaka S (1981) Plate tectonic evolution of Ethiopia and the origin of its mineral deposits: an overview. In: Chewaka S, de Wit MJ (eds) Plate tectonics and metallogenesis: some guidelines to Ethiopian mineral deposits. Ethiopian Inst Geol Surv Bull 2:115–129Google Scholar
  23. Eby GN (1990) The A-type granitoids: a review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26:115–134Google Scholar
  24. Eby GN (1992) Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20:641–644CrossRefGoogle Scholar
  25. Ewart A, Griffin WL (1994) Application of proton-microprobe data to trace-element partitioning in volcanic rocks. Chem Geol 117:251–284Google Scholar
  26. Ferré EC, Caby R, Djouadi MT, Bouchez JL (1998) Pan-African, post-collisional, ferro-potassic granite and quartz–monzonite plutons of eastern Nigeria. Lithos 45:255–280CrossRefGoogle Scholar
  27. Frost BR, Barnes CB, Collins WJ, Arculus RJ, Ellis DJ, Frost CD (2001) A geochemical classification for granitic rocks. J Petrol 42:2033–2048Google Scholar
  28. Gichile S (1992) Granulites in the Precambrian basement of southern Ethiopia: geochemistry, P–T conditions of metamorphism and tectonic setting. J Afr Earth Sci 15:251–263CrossRefGoogle Scholar
  29. Harris NBM (1996) Radiogenic isotopes and the interpretation of granitic rocks. Episodes 19:107–113Google Scholar
  30. Harrison TM, Watson EB (1984) The behaviour of apatite during crustal anatexis: equilibrium and kinetic considerations. Geochim Cosmochim Acta 48:1467–1477Google Scholar
  31. Heltz RT (1976) Phase relations of basalts in their melting ranges at PH2O=5 kbar. II. Melt compositions. J Petrol 17:139–193Google Scholar
  32. Henderson P (1982) Inorganic geochemistry. Pergamon, OxfordGoogle Scholar
  33. Höhndorf A, Meinhold KD, Vail JR (1994) Geochronology of anorogenic igneous complexes in the Sudan: isotopic investigations in north Kordofan, the Nubian Desert and the Red Sea Hills. J Afr Earth Sci 19:3–15CrossRefGoogle Scholar
  34. Kazmin V, Shiferaw A, Balcha T (1978) The Ethiopian Basement and possible manner of evolution. Geol Rundsch 67:531–546Google Scholar
  35. Key RM, Charsley TJ., Hackman BD, Wilkinson AF, Rundle CC (1989) Superimposed Upper Proterozoic collision-controlled orogenies in the Mozambique Orogenic Belt of Kenya. Precambrian Res 44:197–225Google Scholar
  36. Kröner A, Linnebacher P, Stern RJ, Reischmann T, Manton W, Hussein IM (1991) Evolution of Pan-African assemblages in the southern Red Sea Hills, Sudan, and in southwestern Arabia as exemplified by geochemistry and geochronology. Precambrian Res 53:99–118CrossRefGoogle Scholar
  37. Küster D (1993) Geochemistry and petrogenesis of Permo-Jurassic oversaturated alkaline complexes of northern Kordofan, central Sudan. In: Thorweihe U, Scheandelmeier H (eds) Geoscientific research in NE Africa, Rotterdam, pp 197–201Google Scholar
  38. Küster D, Harms U (1998) Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review. Lithos 45:177–196CrossRefGoogle Scholar
  39. Küster D, Utke A, Leupolt L, Lenoir JL, Haider A (1990) Pan-African granitoid magmatism in northeastern and southern Somalia. Berliner Geowiss Abh A 120:519–536Google Scholar
  40. Lenoir JL, Küster D, Liégeois J-P, Utke A, Haider A, Matheis G (1994) Origin and regional significance of late Precambrian and early Paleozoic granitoids in the Pan-African belt of Somalia. Geol Rundsch 83:624–641Google Scholar
  41. Ludwig KR (1991) Isoplot, a plotting and regression program for radiogenic isotope data. US Geophys Soc Openfile Report 91-445Google Scholar
  42. McGuire A, Stern RJ (1993) Granulite xenoliths from western Saudi Arabia: the lower crust of the late Precambrian Arabian–Nubian Shield. Contrib Mineral Petrol 114:395–408Google Scholar
  43. Michard A, Gurriet P, Soudant M, Albarède F (1985) Nd isotopes in French Phanerozoic shales: external vs internal aspects of crustal evolution. Geochim Cosmochim Acta 49:601–610Google Scholar
  44. Mock C, Arnaud NO, Cantagrel JM, Yirgu G (1999) 40Ar/39Ar thermochronology of the Ethiopian and Yemeni basements: reheating related to the Afar plume? Tectonophysics 314:351–372CrossRefGoogle Scholar
  45. Nakamura N (1974) Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary chondrites. Geochim Cosmochim Acta 38:757–775Google Scholar
  46. Nédélec A, Stephens WE, Fallick AE (1995) The Pan-African stratoid granites of Madagascar: alkaline magmatism in a post-collisional extensional setting. J Petrol 36:1367–1391Google Scholar
  47. Nédélec A, Madison Razanatseheno M, Rakotondrazafy M, Ralison B (2002) Le magmatisme potassique tardi-pan-africain de Madagascar. RST-19, 9–12 April, Nantes, RésumésGoogle Scholar
  48. Otten MT (1984) The origin of brown hornblende in the Artfjället gabbro and dolerites. Contrib Mineral Petrol 86:189–199Google Scholar
  49. Paquette JL, Nédélec A (1998) A new insight into Pan-African tectonics in the east–west Gondwana collision zone by U–Pb zircon dating of granites from Central Madagascar. Earth Planet Sci Lett 155:45–56CrossRefGoogle Scholar
  50. Pearce JA, Harris NBM, Toille AG (1984) Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J Petrol 25:956–983Google Scholar
  51. Peccerillo A, Taylor SR (1976) Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey. Contrib Mineral Petrol 58:63–81Google Scholar
  52. Pik R, Deniel C, Coulon C, Yirgu G, Hofmann C, Ayalew D (1998) The northwestern Ethiopian plateau flood basalts: classification and spatial distribution of magma types. J Volcanol Geotherm Res 81:91–111Google Scholar
  53. Pouchou JL, Pichoir F (1991) Quantitative analysis of homogeneous or stratified microvolumes applying the model ‘PAP’. In: Heinrich KFJ, Newbury DE (eds) Electron probe quantitation. Plenum, New York, pp 31–75Google Scholar
  54. Rapp RP, Watson EB (1995) Dehydration melting of metabasalt at 8–32 kbar: implication for continental growth and crust–mantle recycling. J Petrol 36:891-932Google Scholar
  55. Shackleton RM (1979) Precambrian tectonics of northeast Africa. In: Al Shanti AMS (ed) Evolution and mineralization of the Arabian–Nubian Shield, vol 2. Pergamon, Oxford, pp 1–6Google Scholar
  56. Spear FS (1981) An experimental study of hornblende stability and compositional variability in amphibolite. Am J Sci 281:697–734Google Scholar
  57. Stern RJ, Abdelsalam MG (1998) Formation of juvenile continental crust in the Arabian–Nubian shield: evidence from granitic rocks of the Nakasib suture, NE Sudan. Geol Rundsch 87:150–160CrossRefGoogle Scholar
  58. Stern RJ, Dawoud AS (1991) Late Precambrian (740 Ma) charnockite, enderbite, and granite from Jebel Moya, Sudan: a link between the Mozambique Belt and the Arabian–Nubian Shield? Geology 99:648–659Google Scholar
  59. Sun SS, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders AD, Norry MJ (eds) Magmatism in the ocean basins. Geol Soc Spec Publ 42:313–345Google Scholar
  60. Tadesse T, Hoshino M, Sawada Y (1999) Geochemistry of low-grade metavolcanic rocks from the Pan-African of the Axum Area, northern Ethiopia. Precambrian Res 99:101–124CrossRefGoogle Scholar
  61. Tadesse T, Hoshino M, Suzuki K, Iizumi S (2000) Sm–Nd, Rb–Sr and Th–U–Pb zircon ages of syn- and post- tectonic granitoids from the Axum area of northern Ethiopia. J Afr Earth Sci 30:313–327Google Scholar
  62. Teklay M, Kröner A, Mezger K, Oberhansli R (1998) Geochemistry, Pb–Pb single Zircon ages and Nd–Sr isotope composition of Precambrian rocks from southern and Eastern Ethiopia: implications for crustal evolution in East Africa. J Afr Earth Sci 26:207–227CrossRefGoogle Scholar
  63. Vail JR (1976) Outline of the geochronology and tectonic units of the basement complex of northeast Africa. Proc R Soc Lond 350A:127–141Google Scholar
  64. Vail JR (1985) Alkaline ring complexes in Sudan. In: Black R, Bowden P (eds) Alkaline ring complexes in Africa. J Afr Earth Sci 3:51–59CrossRefGoogle Scholar
  65. Vail JR (1989) Ring complexes and related rocks in Africa. J Afr Earth Sci 8:19–40Google Scholar
  66. Watson EB, Harrison TM (1983) Zircon saturation revisited: temperature and compositional effects in a variety of crustal magma types. Earth Planet Sci Lett 64:295–304Google Scholar
  67. Whalen JB, Currie KL, Chappell BW (1987) A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib Mineral Petrol 95:407–419Google Scholar
  68. White AJR, Chappell BW (1983) Granitoid types and their distribution in the Lachlan Fold Belt, South Western Australia. Geol Soc Am Mem 159:21–34Google Scholar
  69. Wiebe RA (1996) Mafic-silicic layered intrusions: the role of basaltic injections on magmatic processes and the evolution of silicic magma chambers. Trans R Soc Edinb Earth Sci 87:233–242Google Scholar
  70. Woldehaimanot B, Behrmann JH (1995) A study of metabasite and metagranite chemistry in the Adola region (South Ethiopia): implications for the evolution of the East African Orogen. J Afr Earth Sci 21:459–476CrossRefGoogle Scholar
  71. Worku H, Schandelmeier H (1996) Tectonic evolution of the Neoproterozoic Adola Belt of southern Ethiopia: evidence for a Wilson Cycle process and implications for oblique plate collision. Precambrian Res 77:179–210CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Department of Geology and GeophysicsAddis Ababa UniversityAddis AbabaEthiopia
  2. 2.CRPG-CNRS54501 Vandoeuvre-lès-Nancy CedexFrance

Personalised recommendations