An Example of Consequent Mantle Metasomatism in Peridotite Inclusions from Nunivak Island, Alaska

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Abstract
Many of the coarse-grained peridotite inclusions in basanites from Nunivak Island, Alaska, contain amphibole and a smaller fraction also contain phlogopite and apatite. All of these peridotites have light REE/heavy REE abundance ratios greater than chondrites and many have abundances of K, Rb, Sr, Ba and light REE which exceed estimates for primitive mantle. On the basis of mineral textures and compositions we infer that the clinopyroxene, amphibole, phlogopite and apatite equilibrated with a metasomatic fluid. Isotopic (Sr and Nd) ratios and parent-daughter abundance data for the coarse-grained peridotites constrain the age of the metasomatism to be less than 200 million years.

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