Adcumulates

Adcumulates form when the intercumulus liquid is similar in composition to cumulate crystals and results in additional growth of cumulus grains of similar composition. Adcumulates are essentially monomineralic, although the growth boundary between the original cumulate grain and later adcumulus growth is recognizable.

The exact way in which the cumulus crystals became enlarged by material of similar composition is still not certain, but it must have taken place at the same temperature as the formation of the cumulus crystals because of the similarity in the solid solution composition. By such growth the intercumulus liquid would gradually be pushed out.

adcumulates.jpg

open-system exchange between the intercumulus liquid and the main chamber (plus compaction of the cumulate pile) allows components that would otherwise create additional intercumulus minerals to escape, and plagioclase fills most of the available space. Some liquid is trapped and forms the small intercumulus pyroxenes, etc. After Wager and Brown (1967).



Bibliography



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Optical Mineralogy : The Nonopaque Minerals by Phillips / Griffen
• Eric A.K.Middlemost (1985): Magmas and Magmatic Rocks. Longman, London
• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore
• K.G.Cox, J.D.Bell & R.J Pankhurst (1979): The interpretetion of igneous rocks. George Allen&Unwin editori.
• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori


Photo
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Plagioclase crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
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Plagioclase crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
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Plagioclase and Orthopyroxene crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
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Plagioclase and Orthopyroxene crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
cumulite2012(6).jpg

Plagioclase crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
cumulite2012(7).jpg

Plagioclase and Orthopyroxene crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
cumulite2012(8).jpg

Plagioclase crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
cumulite2012(9).jpg

Plagioclase and Orthopyroxene crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)
cumulite2012(10).jpg

Plagioclase crystals in a Adcumulate. XPL image. 2x (Field of view = 7mm)