Geologische Rundschau

, Volume 85, Issue 4, pp 619–631 | Cite as

Inception and demise of a Neoproterozoic ocean basin: evidence from the Ougda complex, western Hoggar (Algeria)

  • J. Dostal
  • R. Caby
  • C. Dupuy
  • C. Mevel
  • J. V. Owen
Original Paper


The Neoproterozoic Ougda magmatic complex occurs within platformal carbonate rocks in the western part of the Pan-African fold belt of the Tuareg shield (NW Africa). It is composed of - 800 Ma old, relatively high P-T (i.e., Grt + Cpx-bearing: P > 5 kbar; T≈900'Q, tholeiitic mafic/ultramafic cumulates and related rocks intruded by intermediate to mafic calcalkali plutons (e.g., Cpx+Hbl-bearing gabbro) and dikes. Apparent contrasts in structural level of crystallization indicate that the calc-alkali rocks are significantly younger than the tholeiites, which temporally correlate with a period of regional extension in this part of Africa. Intrusion of the calc-alkali rocks may have occurred during the formation of an arc after the tholeiitic rocks had been (diapirically?) emplaced within the shelf carbonates, and prior to (> 630 Ma) the Pan-African orogeny. Data reported herein indicate that the Ougda complex records the inception and demise of a Neoproterozoic ocean basin. Similar crustal sections have been described from collisional (e.g., Aleutian islands) and extensional (e.g., Ivreä-Verbano zone) settings, indicating that processes operating in both environments can generate nearly indistinguishable igneous suites; the prevalence of shallow-level calc-alkali rocks in both settings may mask the presence of more mafic, tholeiitic rocks at depth.

Key words

Pan-African tectonics geochemistry crustal extension island arc tholeIIte calc-alkali gabbro 


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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • J. Dostal
    • 1
  • R. Caby
    • 2
  • C. Dupuy
    • 3
  • C. Mevel
    • 4
  • J. V. Owen
    • 1
  1. 1.Department of GeologySaint Mary's UniversityHalifaxCanada
  2. 2.Laboratoire de TectonophysiqueUniversite de Montpellier II, Sciences et TechniquesMontpellier, Cedex 05France
  3. 3.Centre Geologique et GeophysiqueUniversite de Montpellier II, Sciences et TechniquesMontpellier, Cedex 05France
  4. 4.Laboratoire de PetrologieUniversite P. et M. CurieParis, Cedex 05France

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