Pyroclastic mechanisms for carbonatite intrusion: evidence from intrusives in the Fen central Complex, SE Norway.

Study of field relations and mesostructures of a heterogeneous intrusive body of ankeritic ferrocarbonatite and mafic silicate rocks (damtjernite) and their hydrothermally altered equivalent (roberg, ie hematite-calcite-dolomite carbonatite) in the Fen complex, SE Norway, reveals crosscutting contacts with wallrock gneiss, which demonstrates the intrusive nature of the ferrocarbonatite. Gradual transitions between the 2 units demonstrate their simultaneous emplacement. Ferrocarbonatite and damrjernite were emplaced as several pulses of fluidized material; and fluidization took place at a shallow level in the crust. The intrusion mechanism was pyroclastic, in principle analogous to that of kimberlite diatremes.-from Authors