Geikielite and ilmenite in Archaean meta-ultramafic rocks, Fiskenaesset, West Greenland
Windley, Brian F.; Herd, Richard K.; Ackermand, Dietrich
European Journal of Mineralogy Volume 1 Number 3 (1989), p. 427 - 438
published: Jul 27, 1989
manuscript accepted: Mar 30, 1989
manuscript received: Jun 2, 1988
ArtNo. ESP147050103012, Price: 29.00 €
Abstract Geikielite and ilmenite occur in 10-15 m thick lenses of ultramafic rocks that are located along the top contact of the Fiskenaesset Complex with an overlying meta-volcanic amphibolite. There are several mineral assemblages reflecting differences in original bulk XMg, the most magnesian one consists of forsterite (XMg = 0.99) and spinel (XMg = 0.92) with minor diopside, clintonite, chlorite, carbonate, titanite, rutile and geikielite (XMg = 0.75). Where hornblende substitutes for diopside, ilmenite has XMg = 0.40. Ilmenite has the lowest XMg (0.20) where forsterite is substituted by enstatite. All geikielite/ilmenite has less than 2 mol % MnTiO3. In highly magnesian assemblages, the XMg order is: chlorite > clintonite (without hornblende) > diopside > forsterite > hornblende (without clintonite) > spinel > geikielite/ilmenite. In lower XMg assemblages, the order is: chlorite > diopside > hornblende > forsterite > enstatite > spinel > geikielite/ilmenite. The mineral assemblages of these geikielite/ilmenite and adjacent rocks formed during sillimanite-grade metamorphism in the amphibolite facies. However, the more Mg-rich geikielite/ilmenite occurring as inclusions in large forsterite porphyroclaste may represent higher-temperature relicts, either of the early metamorphic evolution or from a mantle stage.