01111nas a2200133   4500008004100000245008900041210006900130300001400199490000700213520065500220653001200875100002000887856007000907       1969                        eng d00aVariations of the K/Rb Ratio in Migmatitic Paragneisses of the Northwest Adirondacks0 aVariations of the KRb Ratio in Migmatitic Paragneisses of the No  a1203-12110 v333 a<p>Data for the migmatitic paragneisses of the Northwest Adirondacks indicate fractionation of potassium and rubidium during metamorphism and migmatization; total rock KRb ratios are controlled to a significant degree by modal composition. Biotite-poor granitic veins and lenses show KRb ratios averaging 431 in contrast to the host gneisses which have an average KRb ratio of 271. Paragneisses from the zone of granulite facies metamorphism show significantly higher (mean 307) KRb ratios than those from the amphibolite facies (231), indicating the possibility of regional depletion in Rb relative to K under intensive metamorphic conditions.</p>
10ageology1 aWhitney, P., R.  uhttp://www.sciencedirect.com/science/article/pii/0016703769900428