Tholeiitic magma series
The tholeiitic magma series (
Tholeiitic rock types tend to be more enriched in iron and less enriched in aluminium than calc-alkaline rock types. They are thought to form in a less oxidized environment than calc-alkaline rocks. Tholeiitic basalt is formed at
Geochemical characterization
Rocks in the tholeiitic magma series are classified as
The difference between these two magma series can be seen on an AFM diagram, a
The AFM plot distinguishes the intermediate members of the tholeiitic and calc-alkali magma series quite well. However, the felsic end members of the two series are nearly indistinguishable, so granitic rocks are generally assigned to the calc-alkali magma series. The mafic end members may be distinguished by the aluminium content, with tholeiitic basalts containing 12% to 16% Al2O3 versus 16% to 20% Al2O3 for calc-alkali basalts.[4]
Petrography
Like all basalt, the rock type is dominated by
Geologic context
Tholeiitic rocks are the most common igneous rocks in Earth's crust, produced by submarine volcanism at mid-ocean ridges and make up much of the ocean crust. Tholeiitic basaltic magmas are initially generated as partial melts of peridotite (olivine and pyroxene) produced by decompression melting of the Earth's mantle. Tholeiitic basalt constituting the oceanic crust is termed MORB: mid-ocean-ridge basalt. Throughout the process of igneous differentiation, the oceanic crust acts to reduce the magma, producing the tholeiitic trend.[2] In contrast, alkali basalts are not typical of ocean ridges, but are erupted on some oceanic islands and on continents, as also is tholeiitic basalt.[5] Because the Moon is extremely reduced, all of its basalts are tholeiitic.
Type locality
Tholeiite is named for its type locality near the municipality of Tholey, Saarland, Germany.[6]
See also
References
Citations
- ^ Le Maitre et al. 2002
- ^ .
- ^ Philpotts and Ague 2009, pp. 143-146
- ^ Philpotts and Ague 2009, p.144
- ^ a b "Polarized Light Microscopy Digital Image Gallery: Tholeiitic Basalt" (Accessed 4/1/06)
- ^ Mindat Location
Sources
- R. W. Le Maitre (editor), A. Streckeisen, B. Zanettin, M. J. Le Bas, B. Bonin, P. Bateman, G. Bellieni, A. Dudek, S. Efremova, J. Keller, J. Lamere, P. A. Sabine, R. Schmid, H. Sorensen, and A. R. Woolley, Igneous Rocks: A Classification and Glossary of Terms, Recommendations of the International Union of Geological Sciences, Subcommission of the Systematics of Igneous Rocks. Cambridge University Press, 2002. ISBN 0-521-66215-X.
- Philpotts, Anthony R.; Ague, Jay J. (2009). Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. ISBN 9780521880060.
- American Geological Institute. Dictionary of Geological Terms. New York: Dolphin Books, 1962.