Metasomatism in oceanic and continental lithospheric mantle: Introduction
M. Coltorti, M. Grégoire, 2008. "Metasomatism in oceanic and continental lithospheric mantle: Introduction", Metasomatism in Oceanic and Continental Lithospheric Mantle, M. Coltorti, M. Grégoire
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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.
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Metasomatism in Oceanic and Continental Lithospheric Mantle
Twenty years have passed since Menzies & Hawkesworth extended the concept of metasomatism to mantle processes. The aim of this book is to gather together progress made on this topic since then. Most of the 14 papers reported in the volume rely on in situ major and trace element analyses of minerals and glasses in mantle xenoliths, and deal with different kinds of metasomatic agents at variable fluid/rock ratios in tectonic settings as different as intra-plate, mid-ocean ridge (ophiolites) and supra-subduction. The book contributes to the wide debate on the nature of the fluids migrating into the mantle wedge, as well as on the different residential times of the subduction signature. In addition papers on intra-plate settings deal with the problem of relating various metasomatic signatures to one single metasomatic event through an infiltration-reaction process.