Geochemical and Textural Consequences of Compaction

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9725394 Meurer Crystals that nucleate and grow in magma chambers can separate from the liquid and accumulate on the chamber floor. This process, termed fractional crystallization, is of fundamental importance in the study of igneous rocks. Rocks formed by the accumulation of crystals are called cumulates and provide a record of how fractional crystallization proceeds. Cumulates host significant economic minerals deposits including platinum group metals, chromium ore, and copper-and nickel-sulfides. The bulk of the ocean crust and most of the moon are also made of cumulates. During slow cooling, accumulated crystals can undergo compaction driven by the density contrast between the crystals and interstitial liquid. Compaction can expel liquid from the crystal pile or simply redistribute it within it. During compaction, recrystallization may take place changing the shape of grains and allowing them to pack more efficiently. Modern computer technology now allows quantitative textural study of cumulates. This study will provide the first large scale analysis that combines both chemical and textural data. By documenting the consequences of compaction we will further our understanding of fractional crystallization and hence the formation of cumulates and the mineral resources they host on the Earth and moon.