A new Rb-Sr isotopic parameter for metasomatism, At, and its application in study of pluri-fenitized gneisses around the Fen ring complex.

Abstract

Emplacement of the Fen peralkaline-carbonatitic ring complex 583 Ma ago in the c. 1105 Ma old Telemark gneisses caused mineralogical, chemical and Sr-isotopic changes, i.e., fenitization, in the country rocks. Fenitization involved at least two main phases of brecciation, creating pathways for the feitizing fluids, and at least two main phases of metasomatic alteration. The initial phase was dry and at high temperature, inducing melting and hybridization, producing true fenites close to the contacts with magmatic textures and fenitized gneisses farther from the contact.\r(Forkortet)