Mantle xenoliths (fragments of mantle rock carried up intact within a host magma) are best preserved in magmas that ascend extremely rapidly from great depth, minimizing the time available for the xenoliths to react with, dissolve into, or thermally equilibrate with the surrounding melt.
Kimberlites are famous for their extremely rapid, deep-sourced ascent (originating in the mantle, sometimes below 150 km depth, and reaching the surface in a matter...
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