The Origin and Interpretation of Spinel-Pyroxene Clusters in Peridotite

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Abstract
Lherzolite and harzburgite inclusions from the Green knobs kimberlitic diatreme on the Colorado Plateau have textures characterized by clusters of coarse-grained, intergrown enstatite, diopside, and spinel. The high molar fraction of spinel in these clusters indicates that they formed by reaction of olivine and garnet. Similar textures have been described from peridotite inclusions in basalt and from ophiolite complexes. The texture seems less common in inclusions examined from the Basin-Range province in the western United States than from the Colorado Plateau. The texture reflects transport of garnet peridotite through the garnet-spinel transition, and it suggests that mantle convection occurred to depths less than 90 km. The cluster texture should be explicitly described with modal data in descriptions of peridotite textures.