Abstract
A dyke of presumed Gardar age on Igdlutalik island near Narsaq contains an abundance of ultramafic xenoliths. Both host rock and xenoliths have been metamorphosed and the original mineral assemblages largely replaced by tremolite, chlorite and magnetite. Textural and geochemical evidence suggests: (a) that the host rock was a part of the ultramafic lamprophyre suite known throughout the Tugtut6q-Ilimaussaq-nunataq lineament, and (b) that the xenoliths were mantle-derived peridotites (possibly garnetiferous), together with some glimmerites that may be analogues of MARID-suite xenoliths known from kimberlite occurrences.
Highlights
A dyke of presumed Gardar age on Igdlutalik island near Narsaq contains an abundance of ultramafic xenoliths
Textural and geochemical evidence suggests: (a) that the host rock was a part of the ultramafic lamprophyre suite known throughout the Tugtut6q-Ilimaussaq-nunataq lineament, a'nd (b) that the xenoliths were mantle-derived peridotites, together with some glimmerites that may be analogues of MARIDsuite xenoliths known from kimberlite occurrences
The Gardar alkaline igneous province in South Greenland comprises a wide range of mildly to strongly alkaline rocks erupted in mid-Proterozoic times across the southern part of the Greenland craton and the Proterozoic Ketilidian terrain to the south of it
Summary
Mineral analyses were made on a Cambridge Scientific Instruments Microscan 5 e1ectron-probe microanalyser at Edinburgh University using the wavelength dispersive method. The standards used were of pure elements, oxides or simple silicate compositions. Corrections were made for dead-time, atomic number, absorption and fiuorescence, using computer programs based on the methods of Sweatman & Long (1969). The whole-rock analyses were made at Edinburgh University using Philips PW1450 and PW1480 automatic XRF spectrometers. Major elements were determined on fused glass discs (Norrish & Hutton, 1969) with corrections applied for inter-element mass absorption effects. Trace elements were determined using pressed powder discs and corrected for mass absorption effects with coefficients calculated from the major element analyses. USGS and CRPG rock standards (Abbey, 1980) were used in the calibration of both major and trace elements. The precision and accuracy of the methods used have been described by Thirlwall (1979) and Fitton & Dunlop (1985)
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