Review of the stratigraphic divisions of the kakortokite and lujavrite in southern Ilímaussaq

Abstract

Kakortokite and lujavrite constitute the lower sequence of the stratified Ilimaussaq intrusion. Detailed field work in recent years has allowed the extension and refinement of the stratigraphy so that the idealised section from the south-east part of the intrusion (fig. 1) presents the current state of knowledge. The kakortokite and lujavrite accumulated on the floor of the magma chamber which was probably formed by a major cauldron subsidence of at least 1600 m. The exposed thickness of these two rock types is nearly 1000 m; however the deeper levels and substratum are unknown. By the time the exposed part of the bottom sequence started to accumulate, the 800 m thick roof sequence had aiready solidified. At this time the magma chamber was roofed by naujaite and insulated from the wall rocks by a shell of early-formed marginal pegmatite (Andersen et al., 1981).