The Mantle Source for Olivine Nephelinite, Basanite, and Alkaline Olivine Basalt at Fort Selkirk, Yukon, Canada |
| |
| Authors: | FRANCIS DON; LUDDEN JOHN |
| |
| Institution: | Geological Sciences, McGill University 3450 Rue Universit?, Montr?al, Qu?bec H3A 2A7 Canada and Dept. de G?ologie, Universit? de Montr?al CP 6128 "A", Montreal, Quebec H3C 3J7, Canada |
| |
| Abstract: | Olivine nephelinite, basanite, and transitional alkaline basaltlavas of the Quaternary Fort Selkirk volcanic complex in thecentral Yukon represent three distinct alkaline magma serieswhich have evolved along diverging paths. They cannot be relatedby low-pressure crystal-liquid fractionation, and systematicisotopic differences make it difficult to derive them by variabledegrees of melting of a common mantle source. Field evidencerequires, however, that these three magma series are intimatelyrelated in time and space, and they share a number of anomalouschemical characteristics including low Ca/Na ratios with respectto the majority of terrestrial equivalents. When the effectsof differential olivine fractionation are ignored, the compositionalspectrum of the Fort Selkirk lavas approximates a binary mixingline between transitional alkaline basalt and olivine nephelinite.A population gap along this mixing line, located between thecompositions of the nephelinite and basanite lavas, coincideswith the compositions of amphibole and/or amphibole–garnet–clinopyroxeneassemblages observed in mantle xenoliths. This compositionalgap may represent a thermal divide separating two minimum-meltcompositions in a mantle source consisting of a lherzolite hostcut by amphibole–garnet–clinopyroxenite veins. Theolivine nephelinite endmember may have been derived by earlymelting in the amphibole–garnet–clinopyroxeniteveins, whereas the transitional alkaline basalt would representmore extensive melting of the host lherzolite. |
| |
| Keywords: | |
| 本文献已被 Oxford 等数据库收录！ |
|
