No abstract

The orthopyroxene-clinopyroxene. g a rne t-or t ho p y roxe ne gar n e t-cl in opyroxene geothermometers. and the garnetorthopyroxene-plagioclase. garnet-clino-

Potassium and rubidium values are reported for a suite of 181 metabasites from the amphibolite–granulite transition zone in the Precambrian Bamble sector of south Norway. Both alkalis are more abundant, and the K/Rb ratios lower, in the rocks from the amphibolite facies. Rubidium has been strongly fractionated with respect to potassium. The K/Rb ratios exhibit a regular and systematic variation and this defines a linear trend which is markedly different from established igneous fractionation trends. The chemical fractionation occurred as a result of the metamorphism, and the chemical changes are in keeping with the concept of a vertical chemical fractionation within the continental crust. Similar linear trends established in other high grade metamorphic terrains may have the same (metasomatic ?) origin.

No abstract

No abstract