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6918176 
Book/Book Chapter 
Oceanic plagiogranite revisited 
Coleman, RG; Donato, MM 
1979 
Elsevier Science 
New York, NY 
Trondhjemites, dacites, and related rocks 
149-168 
English 
Leucocratic rocks called plagiogranites are found in the upper parts of gabbros and in sheeted complexes of ophiolites, and represent small localized differentiates of subalkaline tholeiitic basalt. These rocks are composed of quartz and plagioclase, with accessory ferromagnesian minerals. Low-temperature hydrothermal alteration is evidenced by secondary minerals including epidote, chlorite, and actinolite.

Plagiogranites are characterized by unique low k2O contents; Na2O and CaO values are higher, and total iron contents are lower than most granites and rhyolites of continental affinities. Plagiogranites can be distinguished from continental leucocratic rocks by these and other chemical characteristics, including K/Rb, Rb/Sr, and rare-earth element values.

Normal compositional zoning of plagioclase and compositions of granophyric intergrowths indicate that these rocks are the product of igneous processes. Their low K2O character is not solely the result of post-crystallization hydrothermal alteration. However, strontium and oxygen isotope data show that interaction with seawater or meteoric water has taken place at some stage during the formation of plagiogranite. 
Barker, F 
Development in petrology, vol. 6 
9780444417657