17 January 1973 Geological Information Group Meeting

Geological documentation problems and geosystems

31 January 1973 Ordinary General Meeting

Igneous Studies, held at the Linnean Society Lecture Room.

1. Demonstration on part of the Fiskenaesset complex, west Greenland. B. F. Windley, University of Leicester.

The Fiskenaesset layered intrusion is over 2900 m.y. old, has a strike length of at least 500 km, is bordered by meta-volcanic amphibolites and occurs as a conformable layer up to 2 km thick in high grade gneisses. It has been folded several times and recrystallized by granulite and amphibolite facies metamorphisms.

The intrusion has a well-preserved igneous stratigraphy passing upwards ideally through dunites, peridotites, pyroxenites, leuco-gabbros, minor chromiferous ultramafics, gabbros, leuco-gabbros, and anorthosites containing chromitites (up to 20 m thick). Mineral layering, cumulate textures, and grading are common. 70 whole rock XRF and 128 electron probe mineral analyses from one traverse demonstrate that the main differentiation trend of the body is intact, and that some cryptic chemical variations are preserved in olivine, orthopyroxene, hornblende, plagioclase, magnetite and chromite. The original high alumina basalt magma formed under a high water pressure which was responsible for the early crystallization of magnetite, primary igneous amphibole, a high calcium content in plagioclase (An96–80) and a thick sequence of late anorthositic fractionates. The igneous differentiation pattern of this layered intrusion has been only partly reorganized by subsequent, largely isochemical, metamorphic re-equilibration.

Field work for this study was carried out with the Geological Survey of Greenland. Co-authors of the petrochemistry are R.K.Herd,

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