Advertisement

Contributions to Mineralogy and Petrology

, Volume 57, Issue 3, pp 305–316 | Cite as

Model for the Closed-System Fractionation of a Dike Formed by Two Pulses of Dolerite Magma

  • Kenneth F. Steele
  • Paul C. Ragland
Article

Abstract

Elemental variations along a profile perpendicular to strike of an exceptionally wide (342-m) dolerite dike near Pageland, South Carolina, USA, were studied in order to determine the crystallization history of the dike. Although the modes show no systematic variation across the dike, the elemental concentrations generally exhibit overall trends about the approximate center of the dike with several superimposed subsidiary anomalies. The initial changes in concentration of the elements in the outer two meters of the dike margins are thought to represent a gradation from the chilled magma to the first differentiate. The other subsidiary inflections are interpreted as representing mixing of two magma pulses.

A closed-system fractionation model for each pulse of magma can be tested by assuming the chemical composition of the final solid to be that of the final liquid and determining the composition of the “solids” (including entrapped magma) at various percentages of crystallization. The liquid line of descent can be back-calculated until the original magma composition is determined — simply a weighted average composition for that pulse. The calculated initial composition of each pulse and the composition of rocks from the dike margins compare quite favorably, indicating that the dike is the result of two magma pulses with essentially the same composition that have each undergone crystal fractionation as a closed system, with minor mixing at the boundaries between the two. It appears that the dike composition at the present level of erosion is representative of the overall composition.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Hopkins, H.R.: A diabase dike near Afton, Virginia, (abst.) Va. J. Sci. 7, 328 (1956)Google Scholar
  2. 2.
    Justus, P.S.: Modal and textural zonation of diabase dikes, Deep River Basin, North Carolina. M.S. thesis, University of North Carolina, Chapel Hill (1966)Google Scholar
  3. 3.
    Ragland, P.C, Rogers, J.J.W., Justus, P.S.: Origin and differentiation of Triassic dolerite magmas, North Carolina, USA. Contrib. Mineral. Petrol. 20, 57–80 (1968)CrossRefGoogle Scholar
  4. 4.
    Chayes, F.A.: Petrographic modal analysis, 113 p. New York: John Wiley and Sons 1956Google Scholar
  5. 5.
    Yoder, H.S., Tilley, C.E.: Origin of basalt magmas. J. Petrol. 3, 342–532 (1962)CrossRefGoogle Scholar
  6. 6.
    Condie, K.C., Barsky, C.K., Mueller, P.A.: Geochemistry of Precambrian diabase dikes from Wyoming. Geochim. Cosmochim. Acta 33, 1371–1388 (1969)CrossRefGoogle Scholar
  7. 7.
    Green, D.H., Ringwood, A.E.: The genesis of basaltic magmas. Contrib. Mineral. Petrol. 15, 103–190 (1967)CrossRefGoogle Scholar
  8. 8.
    Ragland, P.C., Butler, JR.: A model for magmatic crystallization of the West Farrington Pluton, North Carolina. J. Petrol. 13, 381–404 (1972)CrossRefGoogle Scholar
  9. 9.
    Nockolds, S.R.: The behavior of some elements during fractional crystallization of magma. Geochim. Cosmochim. Acta 30, 267–278 (1966)CrossRefGoogle Scholar
  10. 10.
    Damon, P.E.: Behavior of some elements during magmatic crystallization. Geochim. Cosmochim. Acta 32, 564–567 (1968)CrossRefGoogle Scholar
  11. 11.
    Burns, R.G.: Mineralogical applications of crystal field theory. Cambridge: Cambridge Press 1970Google Scholar
  12. 12.
    Weigand, P.W., Ragland, P.C.: Geochemistry of Mesozoic dolerite dikes from eastern North America. Contrib. Mineral. Petrol. 29, 195–214 (1970)CrossRefGoogle Scholar
  13. 13.
    Ragland, P.C, Brunfelt, A.O., Weigand, P.W.: Rare-earth abundances in Mesozoic dolerite dikes from eastern United States. In: Activation analysis in geochemistry and cosmochemistry. p. 227–235. Oslo: Scandinavian University Books 1971Google Scholar

Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • Kenneth F. Steele
    • 1
  • Paul C. Ragland
    • 2
  1. 1.Department of GeologyUniversity of ArkansasFayettevilleUSA
  2. 2.Department of GeologyUniversity of North CarolinaChapel HillUSA

Personalised recommendations