Finger structures in the Lille Kufjord layered intrusion,Finnmark, Northern Norway

Highly irregular contacts are developed between peridotite and troctolite in layers forming the uppermost part of a transition zone between two of the cyclic units of the Lille Kufjord intrusion. The upwardly-directed peridotite fingers crosscut both the feldspar lamination and the feldspathic xenoliths in the troctolite and are interpreted as the result of the replacement of troctolite by peridotite. Similar structures are developed in the Rhum ultrabasic pluton. Replacement may have been caused by the migration of a more hydrous and magnesian magma trapped initially in olivine or olivine-clinopyroxene cumulates into plagioclase-olivine cumulates precipitated from a basaltic liquid.