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1 Department of Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara, Italy (e-mail: clt@unife.it)
2 Laboratoire Dynamique Terrestre et Planétaire, UMR-CNRS 5562, Observatoire Midi-Pyrénées, 31400, Toulouse, France
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In the foreword of the volume Mantle Metasomatism by Menzies & Hawkesworth (1987), Boettcher stated that the concept of mantle metasomatism has been of immense heuristic value for Earth scientists. At that time, metasomatism was still strongly related to allochemical metamorphism, where chemical composition of the rock is changed by the additional or removal of material. However, the concept of modal or patent (where a new phase is petrographically evident) and cryptic (where chemical enrichment is not accompanied by the presence of a newly formed phase) metasomatism had already been introduced by the pioneering works of Harte (1983), Menzies (1983) and Dawson (1984).
Outstanding progress has characterized the past two decades, and the processes and agents of metasomatism are now much better understood, in part as a result of the significant advancements of in situ microanalytical techniques such as secondary ionization mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The in situ analyses substantially deepened knowledge of intermineral and solid–liquid partitioning coefficients as well as identifying the geochemical features of metasomatizing agents recorded by secondary paragenesis, (namely, clinopyroxenes, amphiboles and glasses), which are the main acceptors of trace elements within the mantle.
Glasses were initially interpreted as the product of host basalt infiltration and their petrological importance was disregarded. During the 1990s, the importance of identifying the geochemical features of the metasomatizing agents was properly highlighted and the study of glasses represented an important improvement in the understanding of metasomatic processes. Irrespective of their origin as products of (1) reaction (Coltorti et al. 2000), (2) in situ melting (Chazot et al. 1996; Yaxley et al. 1997), (3) decompressional melting (Francis, 1976; Gamble & Kyle, 1987) or (4) partial melting (Draper & Green, 1997), the glasses'
