The high pressures necessary for the stabilisation of eclogites in metabasic rocks andgarnetperidotitesinultrabasic rocks havebeen long recognised and experimentally established. Xenoliths of such rocks brought up in volatile charged alkaline magmas, such as kimberlites, are widely accepted to be mostly ofupper mantle derivation (Chapter 13). Eclogites are predicted to be thermodynamically stable also in the lower crust beneath cratonic regions. However, xenolith suite studies indicate that kinetic and/or compositional factors limit their distribution in the lower continental crust relative...