OBSERVATIONS FROM THE FLOOR OF A GRANITOID PLUTON - INFERENCES ON THEDRIVING-FORCE OF FINAL EMPLACEMENT

An east-west profile across the tilted Bergell pluton exposes a 10-km- thick interval in terms of crustal depth. Consequently, the floor as w ell as the root and ''side'' of the main intrusive body of the pluton crop out at the surface and a tentative three-dimensional geometry is constructed. At the highest crustal level, the geometry and deformatio n features at the margin of the pluton indicate ballooning, whereas th e folded floor of the main intrusive body indicates synmagmatic shorte ning related to regional deformation. These contrasting features are b est explained by shortening of the base of the pluton which caused an expansion at a higher crustal level. Final emplacement of the pluton i nto higher crustal levels was, therefore, not driven primarily by buoy ancy, but rather by regional deformation within deeper levels of the c rust.