Alkaline Rocks and Carbonatites of the World

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Frederikshabs Isblink

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Occurrence number: 
063-00-029
Country: 
Greenland
Location: 
Longitude: -50, Latitude: 62.07

Nephelinite, olivine nephelinite, melilitite, phonolite and carbonatite are found in the vicinity of Frederikshabs Isblink as 0.5-2 m thick, vertical, north-south-trending dykes as well as some flat-lying sheets. A carbonate breccia occupies a 'blow' along one dyke (Hansen, 1980, p.145). Clinopyroxene is the dominant mineral and is present as phenocrysts, while in the more evolved rocks magnetite, apatite and possible leucite, now present as pseudoleucite, form phenocrysts. Other phases include melilite, melanite-schorlomite, amphibole, perovskite and sphene. The carbonatitic rocks are mainly composed of calcite, phlogopite, magnetite, apatite, garnet and melilite. Some dykes carry a little matrix K-feldspar. Analyses of rocks, clinopyroxenes, magnetite, garnet, olivine and phlogopite will be found in Hansen (1980), details of Sr istotope chemistry in Hansen (1981) and of REE in Hansen (1984).

Age: 
K-Ar ages on separated biotite (?phlogopite) from three dykes ranged from 116±4 to 138±5 Ma (Hansen and Larsen, 1974). Estimated ages by Rb-Sr on nephelinite are 130 Ma and on carbonatites 150 Ma (Hansen, 1981, Table 2).
References: 
HANSEN, K. 1980. Lamprophyres and carbonatitic lamprophyres related to rifting in the Labrador Sea. Lithos, 13: 145-52. HANSEN, K. 1981. Systematic Sr-isotopic variation in alkaline rocks from West Greenland. Lithos, 14: 183-8. HANSEN, K 1984. Rare earth abundances in Mesozoic undersaturated alkaline rocks from West Greenland. Lithos, 17: 77-85. HANSEN, K. and LARSEN, O. 1974. K/Ar age determinations on Mesozoic lamprophyre dykes near Ravns Storo, Fiskenaesst region, southern West Greenland. Rapport, Gronlands Geologiske Undersogelse, 66: 9-11
Fig. 99 Location of nephelinitic, melilititic and carbonatitic dykes in the Frederikshabs Isblink area (after Hansen, 1980, Fig. 1).
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