Lithospheric Metasomatism

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New frontiers have been broken within the past years in our understanding of the upper mantle through theoretical and applied geophysical and geochemical programs. While the structure and composition of the upper mantle remain topics of debate, and whereas a considerable gap continues to exist between geophysical and geochemical models, discrepancies for the subcontinental, subcratonic upper mantle are approaching consensus, mainly because models can be geochemically constrained by direct measurements of upper mantle-derived xenolith suites. Five research topics are identified that will further constrain the mineralogy, petrology and geochemistry of the upper mantle, including source regions and repositories for large-ion- lithophile-elements relevant to the geochemical modelling of alkali and basaltic magmas in the upper mantle. The emphasis is the titanate minerals and associated silicates of metasomatic origin, and of eclogites and diamonds that have evolved in upper mantle metasomes. Regional lithospheric metasomatism and exotic titanates are recognized in Africa, China, Venezuela, Siberia and Australia. With the seminal discoveries of titanates as diamond inclusions, and of LILE in coated diamonds, revised models for the genesis of diamond are required. Principal techniques to be employed in this study are optical and SEM microscopy, electron and ion-probe, and XRF analyses. The results will provide an improved definition of the subcratonic lithosphere, mineralogically, petrologically and geochemically.//