An Experimental Investigation of Melt Inclusion Formation, Phase Equilibria and Trace Element Partitioning in Anorthitic Feldspar in Natural Mafic Systems

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9903137NielsenOne of the most important sources of data used in the development of models of mantle processes is the diversity of lava compositions we observe on the surface of the earth. Obtaining such information is hampered by the processing that magmas undergo during transport. Unmodified magmas may be sampled from melt inclusions in crystals that form early in the history of the magma. Melt inclusion data has demonstrated that there is a wide range of magma compositions generated in the mantle. However, there is still much that we do not understand about how melt inclusions were trapped, and how the composition of melt inclusions relate to the magmas. This investigation will focus on three issues: (1) The compositional effects of the process of formation re-heating on melt inclusions; (2) The phase equilibria of anorthitic feldspar in natural basalt. Feldspar is one of the most common minerals in ocean floor lavas, yet our understanding of the conditions and compositions under which they form is still very poor; and (3) To address the first two issues, and to model the formation of the oceanic crust, we need data on how elements distribute themselves between feldspar and magma. These issues will be addressed in a series of experiments designed to develop a means for creating synthetic melt inclusions, and to create basaltic melts that mimic the near-primary magmas represented by the melt inclusions.