Abstract
Kimberlite intrusions from three localities, Nigerdlikasik, Pyramidefjeld and Midternæs, show closely comparable petrographicaI, mineralogical and geochemical features. They contain ultramafic gamet, spinel and phlogopite peridotite inclusions which appear to have been derived from the Upper MantIe, though scapolite granulite nodules in the Nigerdlikasik kimberlite must have originated in the lower crust. Garnet and spinel peridotite were sampled at successively higher levels by the kimberlite magma and micaceous peridotites wete produced by phlogopitisation of some of these inclusions during transport. Generation of the kimberlites took place during, the early Mesozoic and forms part of the Mesozoic pattern of igneous activity in South-West Greenland.
Highlights
Minor alkaline intrusive activity has recently been investigated in the Frederikshåb District, South-West Greenland
Walton (1966) described a series of NW-trending carbonatite lamprophyres at the coast near Frederikshåb, and Andrews (1969) in a preliminary note described a kimberlite dyke in the Nigerdlikasik area, 45 km east of Frederikshåb
The Nigerdlikasik dyke, Midternæs sills and Pyramidefje1d sheets are established, as true, though apparently non-diamondiferous kimberlites. Their similar petrography, mineralogy andgeochemistry suggests that the Frederikshåb district forms a province in which kimberlites have been emplaced as volatile-rich, xenocrystbearing magmas showing features suggesting the operation of fluidisation processes -
Summary
Minor alkaline intrusive activity has recently been investigated in the Frederikshåb District, South-West Greenland. The sheets are porphyritic with large olivines in a fine-grained matrix consisting of clinopyroxene, mica, opaques, perovskite, carbonate and serpentine. Mica occurs as small well-formed plates or as large poikilitic crystals enclosing perovskite, opaques, olivine and clinopyroxene. PaIe green serpentine occurs in two situations It is developed as the alteration producl of olivine and it appears as the last crystallising mineral in the groundmass where it is found as microcrystalline, sometimes fibrous, aggregates filling the 'paces between carbonate crystals The nodules consist of coarse- to medium-grained olivine crystals up to 4 mm diameter which interlock and occasionally are intergrown These are usually free from marked strain effects, they frequently contain strings and trails of bubblelike inc1usions partially filled by fluid Tie-lines join analyses from the same kimberiite or nodule; but note that the analyses Z-Z-Z refer to specimen 27703: the remaining diopsides from nodules are distinetly more calcic less calcic than diopsides from the kimberlites
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