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Ultrapotassic igneous rocks
Additional recommended knowledge
Ultrapotassic rocks are defined by molar K2O/Na2O >3 in much of the scientific literature. In other papers written as recently as 2005, they are defined as rocks with weight percents K2O/Na2O >2. Hence, caution is indicated in interpreting use of the term "ultrapotassic", and the nomenclature of these rocks continues to be debated.
Genesis of these ultrapotassic rocks has been much discussed. The magmas probably are produced by a variety of mechanisms and from a variety of sources. The magma production may be favored by the following:
Many of these possibilities were discussed by Foley and Peccerillo (1992) and by other authors in directly following papers of that journal issue.
Mantle sources of ultrapotassic magmas may contain subducted sediments, or the sources may have been enriched in potassium by melts or fluids partly derived from subducted sediments. Phlogopite and/or potassic amphibole probably are typical in the sources from which many such magmas have been derived. Ultrapotassic granites are uncommon and may be produced by melting of the continental crust above upwelling mafic magma, such as at rift zones.
Types of ultrapotassic rocks
The economic importance of ultrapotassic rocks is wide and varied;
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ultrapotassic_igneous_rocks". A list of authors is available in Wikipedia.|