Primary igneous load-cast deformation structures in the Fongen-Hyllingen layered basic intrusion, Trondheim Region, Norway

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Abstract
Summary Load-cast structures in the Caledonian, synorogenic, Fongen-Hyllingen layered basic complex closely resemble those deformations resulting from reverse density stratification in experimentally studied, water-saturated sediments. The mushroom-shaped structures are apparently restricted to a single horizon within an interlayered, metamorphosed, dunite–troctolite sequence. They generally have a symmetrical form, revealing a polygonal pattern in the plane of the layering. The density contrast between an olivine-rich crystal mush overlying a plagioclase-rich crystal mush, both very close to the igneous sediment–magma interface, is believed to have caused the deformation. Subsequent consolidation occurred by adcumulus growth.