Hostname: page-component-84b7d79bbc-g7rbq Total loading time: 0 Render date: 2024-07-29T18:35:41.175Z Has data issue: false hasContentIssue false
  • English
  • Français

‘Basalt fingers’ – origin of columnar joints?

Published online by Cambridge University Press:  01 May 2009

L. H. Kantha
L. H. Kantha*
Affiliation:
Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MarylandU.S.A.21218
Get access Rights & Permissions [Opens in a new window]

Summary

Thermal stresses due to contraction during cooling have been widely accepted as the origin of columnar structures in certain igneous rocks. It is proposed that these highly ordered structures could be the result of a double-diffusive convective process in the melt during cooling, a process analogous to salt fingers observed in the laboratory and the oceans. Salt fingers are driven by appropriate differences in heat and salt content at the top and bottom of a stably stratified water column. In molten basalts, temperature and chemical-compositional differences between the top and bottom of a stagnant melt could drive highly regular columnar ‘finger’ motions in the melt. When solidification takes place eventually, cracks due to contraction during cooling would then have preferred paths of propagation into the interior from the surface along the junctions of adjacent ‘basalt fingers’ giving rise to columnar jointing. Morphological evidence supporting the finger hypothesis is cited and useful ways of gathering further field data that would shed some light on the validity of the hypothesis are suggested. For the benefit of geologists not familiar with double-diffusive processes, an up-to-date review of these flow phenomena is included.

Type
Articles
Information
Geological Magazine , Volume 118 , Issue 3 , May 1981 , pp. 251 - 264
Copyright
Copyright © Cambridge University Press 1981

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Chen, C. F. & Turner, J. S. 1980. Crystallization in a double-diffusive system. J. Geophys. Res. (in the Press).Google Scholar
Huppert, H. E. & Linden, P. F. 1979. On heating a stable salinity gradient from below. J. Fluid Mech. 95, 431–64.CrossRefGoogle Scholar
Huppert, H. E. & Manins, D. C. 1973. Limiting conditions for salt-fingering at an interface. Deep Sea Res. 20, 315–23.Google Scholar
Kantha, L. H. 1980. A note on the effect of viscosity on double-diffusive processes. J. Geophys. Res. (in the Press).CrossRefGoogle Scholar
Linden, P. F. 1973. On the structure of salt fingers. Deep Sea Res. 20, 325–40.Google Scholar
Linden, P. F. 1974. Salt fingers in a steady shear flow. Geophys. Fluid Dynam. 6, 1–27.CrossRefGoogle Scholar
Linden, P. F. 1976. The formation and destruction of fine-structure by double-diffusive processes. Deep Sea Res. 23, 895–908.Google Scholar
Linden, P. F. 1978. The formation of banded salt finger structures. J. Geophys. Res. 83, 2902–12.Google Scholar
Macdonald, G. A. 1968. Extrusive basaltic rocks. In Basalts: Poldervaart Treatise on Rocks of Basaltic Composition, vol. 1 (ed. Hess, H. H., and Poldervaart, A.), pp. 40–5. John Wiley & Sons.Google Scholar
Magnell, B. 1976. Salt fingers observed in the Mediterranean outflow region (34° N 11° W) using a towed sensor. J. Phys. Ocean. 6, 511–23.Google Scholar
Shirtcliffe, T. G. L. & Turner, J. S. 1970. Observations of the cell structure of salt fingers. J. Fluid Mech. 41, 707–19.CrossRefGoogle Scholar
Spry, A. 1962. The origin of columnar jointing, particularly in basalt flows. J. geol. Soc. Austr. 8, 191–216.CrossRefGoogle Scholar
Stern, M. E. 1960. The ‘salt fountain’ and thermohaline convection. Tellus 12, 172–5.Google Scholar
Stern, M. E. & Turner, J. S. 1969. Salt fingers and convecting layers. Deep Sea Res. 16, 497–511.Google Scholar
Stommel, H., Arons, A. B. & Blanchard, D. 1956. An oceanographical curiosity: The perpetual salt fountain. Deep Sea Res. 3, 152–3.Google Scholar
Turner, J. S. 1967. Salt fingers across a density interface. Deep Sea Res. 14, 599–611.Google Scholar
Turner, J. S. 1973. Buoyancy Effects in Fluids. Cambridge University Press.Google Scholar
Turner, J. S. 1974. Double-diffusive phenomena. A. Rev. Fluid Mech. 6, 37–56.CrossRefGoogle Scholar
Turner, J. S. 1978. Laboratory models of double-diffusive processes in the ocean. Proc. of 12th Symp. on Naval Hydrodynamics, June 5–9, 1978.Google Scholar
Turner, J. S. 1980. Differentiation and layering in magma chambers. Nature, Lond. (in the Press).Google Scholar
Waters, A. C. 1960. Determining directions of flow in basalts. Am. J. Sci., Bradley Vol. 258A, 350–66.Google Scholar
Williams, A. J. 1974. Salt fingers observed in the Mediterranean outflow. Science, N.Y. 185, 941–3.CrossRefGoogle ScholarPubMed
Williams, A. J. 1975. Images of ocean microstructure. Deep Sea Res. 22, 811–29.Google Scholar