Advertisement

Mineralogy and Petrology

, Volume 65, Issue 3–4, pp 249–275 | Cite as

Petrogenesis of the Wadi Dib alkaline ring complex, Eastern Desert of Egypt

  • W. Frisch
  • A. M. Abdel-Rahman
Article

Summary

The Wadi Dib magmatic complex is the oldest known alkaline ring complex in the Egyptian part of the Pan-African orogenic belt. Rb-Sr isotope data for seven samples suggest a Vendian age of 578±16 Ma, and a87Sr/86Sr initial ratio of 0.7048±0.0010. The igneous complex has a diameter of 2 km and was emplaced within granodioritic Pan-African host rocks at the intersection of two faults. It shows distinct concentric compositional zoning with several syenitic outer ring sheets, a mainly trachytic intermediate ring sheet, and a quartz syenite inner ring sheet with a granitic core; relative ages decrease from margin to core. The mineralogical and chemical features are characteristic of within-plate (A-type) magmatic complexes. Major and trace element patterns underline the co-magmatic origin of the suite but indicate three stages of evolution with several pulses of emplacement. A common feature of element distribution patterns is the small systematic change in the early lithologies, but a distinct evolution trend in the late quartz-bearing rocks.

We propose that an alkali-basaltic parent magma was emplaced within deep or middle levels of the juvenile Pan-African crust. Differentiation mainly occurred by fractional crystallization of olivine, clinopyroxene, plagioclase, and apatite. During the late stages of evolution, limited assimilation of island-arc magmatic rocks may have occurred. Emplacement took place along ring fractures at a subvolcanic level and was probably related with formation of a caldera during emplacement of the trachytic lithologies. The anorogenic character of the magmatic suite indicates consolidation of the Pan-African crust of NE Africa at the time of emplacement of the alkaline body.

Keywords

Eastern Desert Trace Element Pattern Magmatic Complex Element Distribution Pattern Magmatic Suite 
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.

Petrogenese des alkalischen Wadi Dib ringkomplexes, Östiche Wüste Ägyptens

Zusammenfassung

Der Wadi Dib-Komplex ist die älteste bekannte Ringstruktur im ägyptischen Teil des Panafrikanischen Orogengürtels. Rb-Sr Isotopendaten von sieben Proben ergeben ein vendisches Alter von 578±16 Ma and ein initiales87Sr/86Sr-Verhältnis von 0,7048±0,0010. Der magmatische Komplex besitzt einen Durchmesser von 2 km und hat am Schnittpunkt zweier Störungen innerhalb panafrikanischer Granodiorite Platz genommen. Er weist eine konzentrische Zonierung mit mehreren syenitischen äußeren Ringen, einem vorwiegend trachytischen mittleren Ring und einem quarzsyenitischen inneren Ring mit einem granitischen Kern auf; die relativen Alter der Gesteine nehmen vom Rand zurn Kern hin ab. Mineralogische and chemische Charakteristika sind die von Intraplatten- (A-Typ-) Komplexen. Haupt- and Spurenelementmuster weisen auf eine ko-magmatische Entstehung hin, zeigen aber eine Entwicklung in drei Stadien mit mehreren magmatischen Pulsen auf. Charakteristika der Elememverteilungen sind wenig systematische Änderung in den älteren Lithologien, aber ein gerichteter Entwicklungstrend in den späten, quarzführenden Lithologien.

Wir schließen, daß ein alkali-basaltisches Magma in ein tiefes oder mittleres Niveau der jungen panafrikanischen Kruste intrudierte. Differentiation erfolgte im wesentlichen durch fraktionierte Kristallisation von Olivin, Klinopyroxen, Plagioklas und Apatit. Während später Entwicklungsstadien gab es vermutlich begrenzte Assimilation von Inselbogen-Kruste. Die Platznahme erfolgte entlang von Ringbrüchen in einem subvulkanischen Stockwerk und war vermutlich mit der Bildung einer Caldera während der Platznahme der trachytischen Lithologien verbunden. Der anorogene Charakter der magmatischen Folge zeigt an, daß die panafrikanische Kruste Nordost-Afrikas zur Zeit der Platznahme der alkalischen Intrusion bereits konsolidiert war.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Abd El-Naby HH (1998) Geology, petrochemistry and tectogenesis of the Wadi Um Ghalaga area, Eastern Desert, Egypt. Tübinger Geowiss Arb A46: 1–137Google Scholar
  2. Abdel-Rahman AM (1994) Nature of biotites from alkaline, calc-alkaline, and peraluminous magmas. J Petrol 35: 525–541Google Scholar
  3. Abdel-Rahman AM, Doig R (1987) The Rb-Sr geochronological evolution of the Ras Gharib segment of the northern Nubian Shield. J Geol Soc Lond 144: 577–586Google Scholar
  4. Abdel-Rahman AM, Martin RF (1987) Late Pan-African magmatism and crustal development in northeastern Egypt. Geol J 22: 281–301Google Scholar
  5. Abdel-Rahman AM, Martin RF (1990a) The Mount Gharib A-type granite, Nubian Shield: petrogenesis and role of metasomatism at the source. Contrib Mineral Petrol 104: 173–183Google Scholar
  6. Abdel-Rahman AM, Martin RF (1990b) The Deloro anorogenic igneous complex, Madoc, Ontario. 11. Evolution and Post-eruption metasomatism of the volcanic units. Can Mineral 28: 267–285Google Scholar
  7. Bonin B (1990) From orogenic to anorogenic settings: evolution of granitoid suites after a major orogenesis. Geol J 25: 261–270Google Scholar
  8. Bonin B, Giret A (1984) The plutonic alkaline series: the problem of their origin and differentiation, the role of mineralogical assemblage. Phys Earth Planet Int 35: 212–221Google Scholar
  9. Bowring SA, Erwin DH (1998) A new look at evolutionary rates in deep time: uniting paleontology and high-precision geochronology. GSA Today 8/9: 1–8Google Scholar
  10. Collins WJ, Beams SD, White AJR, Chappell BW (1982) Nature and origin of A-type granites with particular reference to southeastern Australia. Contrib Mineral Petrol 80: 189–200Google Scholar
  11. Cox KG, Bell JD, Pankhurst RJ (1979) The interpretation of igneous rocks. Allen and Unwin, London, 450 pGoogle Scholar
  12. deGruyterPD, Vogel TA (1981) A model for the origin of the alkaline complexes of Egypt. Nature 291: 571–574Google Scholar
  13. Eby GN (1992) Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20: 641–644Google Scholar
  14. El-Ramly MF, Hussein AAA (1985) The ring complexes of the Eastern Desert of Egypt. J Afr Earth Sci 3: 77–82Google Scholar
  15. Engel AEJ, Dixon TH, Stern RJ (1980) Late Precambrian evolution of Afro-Arabian crust from ocean arc to craton. Bull Geol Soc Am 91: 699–706Google Scholar
  16. Faure G (1977) Principles of isotope geology. John Wiley & Sons, New York, 464 pGoogle Scholar
  17. Floyd A, Winchester JA (1978) Identification and discrimination of altered and metamorphic volcanic rocks using immobile elements. Earth Planet Sci Lett 27: 211–218Google Scholar
  18. Francis MH (1972) Geology of the basement complex in the North Eastern Desert between latitudes 27°30′ and 28°00′ N. Ann Geol Surv Egypt 2: 161–180Google Scholar
  19. Frisch W (1982) The Wadi Dib ring complex, Nubian Desert (Egypt), and its importance for the upper limit of the Pan-African orogeny. Precamb Res 16: A20Google Scholar
  20. Frisch W;Al-Shanti A (1977) Ophiolite belts and the collision of island arcs in the Arabian Shield. Tectonophysics 43: 293–306Google Scholar
  21. Gass IG (1977) Evolution of the Pan-African crystalline basement in north-east Africa and Arabia. J Geol Soc Lond 134: 129–138Google Scholar
  22. Gass IG (1982) Upper Proterozoic (Pan-African) cafe-alkaline magmatism in north-eastern Africa and Arabia. In:Thorpe RS (ed) Andesites. John Wiley & Sons, New York, pp 591–609Google Scholar
  23. Goldsmith JR (1981) The join CaAl2Si2O8-H2O (anorthite-water) at elevated pressures and temperatures. Am Mineral 66: 1183–1188Google Scholar
  24. Harris NBW (1985) Alkaline complexes from the Arabian Shield. J Afr Earth Sci 3: 83–88Google Scholar
  25. Henderson P (1984) Rare earth element geochemistry. Elsevier, Amsterdam, 510 pGoogle Scholar
  26. Hussein AA, Monir MA, El-Ramly MF (1982) A proposed new classification of the granites of Egypt. J Volcanol Geotherm Res 14: 187–198Google Scholar
  27. Kerr A, Fryer BJ (1993) Nd isotope evidence for crust-mantle interaction in the generation of A-type granitoid suites in Labrador, Canada. Chem Geol 104: 39–60Google Scholar
  28. Landoll JD, Foland KA, Henderson CM (1994) Nd-isotopes demonstrate the role of contamination in the formation of coexisting quartz- and nepheline syenites at the Abu Khruq complex, Egypt. Contrib Mineral Petrol 117: 305–329Google Scholar
  29. Leake BE (1997) Nomenclature of amphiboles: report of the subcommittee on amphiboles of the International Mineralogical Association, Commission on new minerals and mineral names. Can Mineral 35: 219–246Google Scholar
  30. Loiselle MC, Wones DR (1979) Characteristics and origin of anorogenic granites. Geol Soc Am Abstr Programs 11: 468Google Scholar
  31. Longerich HP, Jenner GA, Fryer BJ, Jackson SE (1990) Inductively coupled plasma-mass spectrometric analysis of geological samples: a critical evaluation based on case studies. Chem Geol 83: 105–118Google Scholar
  32. Miyashiro A (1978) Nature of alkalic volcanic rock series. Contrib Mineral Petrol 66: 91–104Google Scholar
  33. Morimoto N (1989) Nomenclature of pyroxenes. Report of the subcommittee on pyroxenes, Commission on new minerals and mineral names, International Mineralogical Association. Can Mineral 27: 143–156Google Scholar
  34. Nedelec A, Stephens WE, Fallick AE (1995) The Panafrican stratoid granites of Madagascar: alkaline magmatism in a post-collisional extensional setting. J Petrol 36:1367–1391Google Scholar
  35. Pearce JA, Harris NBW, Tindle AG (1984) Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J Petrol 25: 956–983Google Scholar
  36. Sabet AH, Abdel-Maksoud MA, Nabrovenkov US (1978) Geological setting and petrography of Wadi Dib ring intrusion, northern Eastern Desert, Egypt. Geol Surv Egypt Report 16pp (unpublished)Google Scholar
  37. Serencsits CMcC, Faul H, Foland KA, Hussein AA, Lutz TM (1981) Alkaline ring complexes in Egypt: their ages and relationship in time. J Geophys Res 86: 3009–3013Google Scholar
  38. Skjerlie KP, Johnston AD (1992) Vapor-absent melting at 10 kbar of a biotite- and amphibole-bearing tonalitic gneiss: implications for the generation of A-type granites. Geology 20: 263–266Google Scholar
  39. Taylor SR, McLennan SM (1985) The continental crust: its composition and evolution. Blackwell, Oxford, 312ppGoogle Scholar
  40. Vail JR (1985a) Alkaline ring complexes in Sudan. J Afr Earth Sci 3: 51–59Google Scholar
  41. Vail JR (1985b) Pan-African (Late Precambrian) tectonic terrains and the reconstruction of the Arabian-Nubian Shield. Geology 13: 839–842Google Scholar
  42. Vail JR (1990) Geochronology of the Sudan. Overseas Geology and Mineral Resources 66: 58ppGoogle Scholar
  43. Wilson M (1989) Igneous petrogenesis. Unwin Hyman, London, 466 pGoogle Scholar

Copyright information

© Springer-Verlag 1999

Authors and Affiliations

  • W. Frisch
    • 1
  • A. M. Abdel-Rahman
    • 2
  1. 1.Institut für Geologie und PaläontologieUniversität TübingenTübingenGermany
  2. 2.Z Department of GeologyAmerican University of BeirutBeirutLebanon

Personalised recommendations