The Origin of Amphibole in Lherzolite Xenoliths from Nunivak Island, Alaska |
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| Authors: | FRANCIS D M |
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| Institution: | Department of Geological Sciences, McGill University Montreal, Quebec H3C 3G1 Canada |
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| Abstract: | Ten lherzolite xenoliths collected on Nunivak Island, Alaska,contain interstitial chromian pargasitic amphibole. Of 2000lherzolite nodules examined from the maars of the island, however,50 per cent contain relics of such an amphibole in the formof fine-grained zones of euhedral diopside, olivine and spinelin a porous Al-rich glass. These nodules are believed to havebeen amphibole-bearing fragments of the upper mantle, that partiallymelted during their ascent to the surface in the Nunivak basalts.The textural intimacy and chemical zoning exhibited by the interstitialamphibole and spinel in the lherzolite xenoliths indicate thatalthough the amphibole predates the Nunivak basalts, it is asecondary aluminous phase. The amphibole was formed in the uppermantle during a pervasive metasomatic event caused by risingtemperature and the infiltration of alkali-rich fluid, priorto the introduction of basaltic magmas. |
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