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Melts and fluids in planetary systems

Wednesday, July 15, 2020 - 09:30
Dr. Shantanu Keshav
University of Montpellier 2, France
Generation of melts (liquids/magmas) and fluids (e.g., gas), and their interactions in the Earth’s interior, are perhaps some of the most important of all planetary phenomena. Such activity is the principal mechanism by which planetary interiors differentiate chemically. The generally upward motion of magmas relative to solids can, and does, advect significant energy toward planetary surfaces.  Extrusion of magma on the surface and intrusion at shallow levels are the principal mechanisms by which planetary crusts form; these processes ultimately provide the raw material that is weathered, reworked, and remobilized by near-surface geologic processes; and in many cases, eruption of magma at the surface can have substantial nfluence on climate.
Here, from theoretical phase equilibria, thermochemistry, and experimental work, the most likely origin of magmas and fluids is discussed, with some focus on current/future work. On this aspect, fusion relations of the most plausible candidate materials (e.g., peridotite) with and without volatiles (for instance, water, H 2 O; carbon dioxide, CO 2 ), are examined in model systems as frameworks for visualizing, understanding, and analyzing igneous phenomena in more complex natural systems. Although these simple phase diagrams are incomplete models of actual magmatic systems, many of the processes that occur in natural systems can be understood by analogy with them, and most significantly, these phase diagrams often make it possible to visualize complex processes in relatively simple terms. Their staying power in earth-planetary sciences reflects the easy to understand yet powerful framework for interpreting and understanding complex natural phenomena that they provide.
On these bases, and without having misplaced notions tantamount to being presumptuous, some discussion, dominantly on fusion, derived on the basis of thermochemistry and experimental work, and how might it have “shaped” this planet, Earth, is presented. Attempt is made not to reach finalities, for such could be diagnosed as indicating my solipsism.
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