Orogenic Lherzolites and Mantle Processes: Editorial

Abstract

They contain vital information about melt transfer proThe papers in this Special Volume of the Journal of Petrology cesses related to the origin of mid-ocean ridge basalts. were presented at the Third International Lithosphere The Othris ophiolite, Greece, contains such spinel or Conference held in Pavia, Italy, in September 1999. The plagioclase lherzolites and Dijkstra et al. propose that meeting was attended by about 100 scientists who actively these shallow peridotites formed at a slow-spreading research mantle rocks and the processes of melt formation ridge. More significantly, they conclude that these rocks and extraction. The protoliths are garnet-, spinelor are the result of melt impregnation by mid-ocean ridge plagioclase-facies peridotites, rocks brought to the surface basalt (MORB) melts and that their ‘fertile’ compositions during the eruption of alkali to potassic volcanoes, diaare not primary. Similarly, an influx of melts of MORB tremes and maars. Mantle rocks are also exposed at the composition is proposed for the Horoman massif, Hoksurface of the Earth as a result of tectonic processes (i.e. kaido, by Saal et al. on the basis of Re–Os isotopic orogenic or alpine massifs) or mantle rocks are dredged data. Their data indicate a common petrogenesis for the or drilled on the ocean floor (i.e. abyssal peridotites). layered peridotite–pyroxenite sequence. In contrast, the Whereas the two previous lithosphere meetings in MontNikanbetsu plagioclase lherzolite from Hokkaido, Japan, pellier (1990) and Granada (1995) concentrated on orois believed by Takahashi to have experienced widespread genic massifs and xenoliths, the Pavia meeting dealt partial melting because of the evidence for incipient almost exclusively with the mineralogy, geochemistry and melting, melt migration and crystallization. experimental petrology of mantle rocks and their partial melt products.