International Journal of Earth Sciences

, Volume 92, Issue 6, pp 873–890 | Cite as

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

  • Asfawossen AsratEmail author
  • Pierre Barbey
Original Paper


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.


A-type granite Ethiopia Mozambique Belt Ordovician Post-collisional 



We are grateful to C. Spatz, D. Mangin and M. Champenois for technical assistance. Our sincere gratitude goes to T. Nardos and D. Hailu for their invaluable assistance during the field work. The two anonymous referees are thanked for their valuable comments that contributed to improve the manuscript. We are indebted to the Department of Geology and Geophysics, Addis Ababa University, for the logistical support during the field work. This work was supported by a research grant from the French Ministry of Foreign Affairs and financial support from INSU-Ethiopie-2000 Project.


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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

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