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 to granulite fades assemblages (Chapter 12). Occurrences ofeclogitesand gamet peridotites in exposed crustal metamor phic terrains have been interpreted in the past as exotic tectonic blocks of deeper (largely mantle) origin, because of their apparent difference in metamorphic grade compared with the encompassing rocks. Only in recent years have metamorphic petrologists begun to recognise that such crustal terrains sometimes preserve co-facial (eclogite fades), high pressure mineral parageneses in other spatially associated lithologies such as metapelites and metagranitoids. Placed in a modern, global geotectonic context, it is now apparent not only that eclogites can be expected to be stabilised in oceanic crust subducted at continental plate margins (Chapter 9), but also that eclogite fades mineral parageneses may be stabilised in a wider range ofcontinental crust lithologies, where substantial tectonic thickening has occurred in continental plate collision zones (Chapters 8-10). Recent exciting evidence from the Western Alps(Chapter 10)suggeststhat continental crust may be subducted to depths approaching 100km and iyet exhumed during subsequent orogenic uplift.

My book Metamorphic Rocks and Metamorphic Belts (in Japanese) was published by Iwanami Shoten, Publishers, in Tokyo in 1965. A few years later, Mr D. Lynch-Blosse of George Allen & Unwin Ltd contacted me to explore the possibility of translating it into English. Thus, translation accompanied by rewriting of substantial parts of the book was made in subsequent years, resulting in the present book Metamorphism and Metamorphic Belts. This title was chosen to emphasize the tectonic Significance of metamorphic belts. Metamorphic geology has a long history. The microscopic description and classification of metamorphic rocks began in the late nineteenth century. The theory of equilibrium mineral assemblages began in the first half of the twentieth century. Detailed mineralogical studies and the experimental determination of the pressure-temperature conditions of metamorphism began in the 1950s. The importance of metamorphic petrology in our understanding of the tectonic processes has been realized only in the past decade. This book is intended to synthesize the mineralogic, petrologic" and tectonic aspects of metamorphism. Advanced treatment of the thermodynamic and structural aspects is not intended.