Deep seated magmas and their mantle roots: introduction

In the last decade there has been a considerable effort to better understand the joint evolution of mafic and ultramafic magmatic systems and their deep mantle roots, through integrated petrological and thermo-barometric studies. Magma generation is regarded as the result of complex processes including melting, creation of channels for melt transfer, and interaction with the wall-rocks. Complexities in magmatic systems involve metasomatism and the creation of metasomatic fronts, branching and splitting of magma volumes during their evolution, and variable compositional development during transfer to upper crystallizing horizons. Intrusions and formation of intermediate magmatic chambers in the upper mantle Moho or in the lower crust are often accompanied by melt differentiation according to Assimilation-Fractional-Crystallization processes (AFC). Splitting of polybaric magmatic systems brings the appearance of a wide spectrum of melt compositions. Each magmatic plume leaves its own tracers in the mantle, and can erase signs of preceding mantle magmatic events. Commonly, petrologists may focus on individual magmatic processes through the study of mantle rocks and mantle xenoliths, but there have been recent efforts to produce complex models that take into account the various aspects of such evolving magmatic system, particularly that take account of spatial and temporal changes. Such studies have also made links to modern and ancient geodynamics, and to questions of continental growth, structure of the mantle and modification of the sub-continental lithospheric mantle (SCLM).