Solidification History of the KitdlÎt Lens: Immiscible Metal and Sulphide Liquids from a Basaltic Dyke on Disko, Central West Greenland

• Published in: Journal of Petrology
• Main Author: ULFF-MØLLER, FINN
• Format: Text
• Language: English
• Published: Oxford University Press 1985
• Subjects: Articles; Greenland; Kitdlît
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/26/1/64; https://doi.org/10.1093/petrology/26.1.64

A unique troilite-iron-cohenite-rich lens was found on a ledge in the sediment-contaminated Kitdlit dyke on Disko. The lens displays a mineralogical diversity and extreme liquid evolution not previously described from any single magmatic sulphide or metal liquid system. It was deposited at 1200 �C and fo2 = 10−13 as two immiscible liquids–a sulphide liquid and a C-rich metal liquid—which solidified from about 1100� to 300 �C as a closed system in a thermal gradient. The lower iron-rich half of the lens formed by crystallization of iron, cohenite, troilite, schreibersite and w�stite (in that order), with trace amounts of the phases found in the upper half of the lens. The approximate crystallization order of the upper troilite-rich half of the lens was: iron, cohenite, troilite, chromite, w�stite, fayalite (pseudomorphosed), high-T ‘chalcopyrite’, high-T ‘heazlewoodite’ (beta-(Ni, Fe, Cu, Co) 3+� S 2 ) and, finally, lead minerals. The latter comprise native lead, galena, altaite (PbTe), shandite (Ni3Pb2S2) and an unidentified phase. Additional immiscible liquids were formed during solidification. Oxysulphide liquid (roughly FeO with a minor FeS-component) exsolved from metal and sulphide liquid in equilibrium with iron and cohenite below 1100 �C. Later, FeO-rich silicate liquid, and Pb-rich liquid with Ni, Cu, S and Te, exsolved from the sulphide liquid. Segregation of oxysulphide and Pb-rich liquid may occur during core formation in planetoids, and there are thus important cosmochemical implications.