Effects of H2O on Phase Relations during Crystallization of Gabbros in the Kap Edvard Holm Complex, East Greenland

Abstract

In the Kap Edvard Holm Complex of East Greenland, layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences. In some olivine gabbros host numerous small, discordant bodies of ultramafic cases, partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late-magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates. Similar repile, resulting in resorption of cumulus minerals, crysplacive rocks are also present as large semi-conformable sheet-like tallization of intrusive or replacive bodies, and rebodies within the layered gabbro sequence. Replacive bodies of all distribution of mass within the intrusion (e.g. Robins, sizes are spatially associated with xenoliths of metabasaltic lava: 1982; Butcher, 1985; Butcher et al., 1985; Helz, 1987; the small bodies cluster around xenoliths, and the large bodies host Irvine, 1987; Boudreau, 1988; McBirney & Sonnenthal, swarms of xenoliths. The replacive bodies are inferred to have formed 1990; Larsen & Brooks, 1994; Scoon & Mitchell, 1994; by reaction of gabbroic cumulates with pore liquids that were Mathez, 1995; Meurer et al., 1997; Boudreau, 1999). In enriched in H2O by degassing or dehydration melting of the other cases, partially molten cumulates are inferred to metabasalts. As these liquids migrated through the cumulus pile, have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies. Where the truded the cumulus pile, resulting in the development liquids came to rest, they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite-rich gabbro. The most evolved pore liquids cumulates with intruding magmas (e.g. Morse et al., 1987; segregated to form hornblende-rich pegmatitic dikes of roughly dacitic Bedard et al., 1988; Tegner & Wilson, 1993; Tegner & composition, suggesting that hydration and possibly oxidation of the Robins, 1996). Because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc-alkaline trend. These inferences imply that contamination of mafic intrusions, recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems. into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust. Near the western margin of the Kap Edvard Holm