Modeling fractional crystallization of basalts on the island of Hawaii
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Date
2017-12
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The Ohio State University
Abstract
The island of Hawaii is the youngest, largest and most volcanically active island of the Hawaiian island chain. Located in the Central Pacific and fed by a mantle plume, Hawaii makes an excellent location to study oceanic island basalts. The objective of this thesis was to study the effects of fractional crystallization of Hawaiian basalts at Mauna Loa, Mauna Kea, Kilauea and Puna Ridge at various conditions of pressure and H2O. Modeling of basalt compositions at each location was done using the PETROLOG software and high MgO melt compositions were selected at each location as parent compositions. The calculated compositions of melts produced by fractional crystallization were then compared to the compositions of the natural samples to determine the most likely conditions for which the calculated path of crystallization for the liquids agrees with the compositional trends for the natural samples. The pressures of crystallization range between 1 atm and 3 kbar at Mauna Loa, Mauna Kea, Kilauea and Puna Ridge, and when these pressures are converted to depths in km, the range in depth is 0 km to 10.55 km. The effect of addition of small amounts of water (>0.5 wt. %) is to shift Al2O3, FeO and TiO2 contents relative to those in liquids formed under anhydrous conditions, but water has little effect on the SiO2, CaO, and Na2O contents of calculated liquids. The results are consistent with generation of Hawaiian tholeiitic lavas by fractional crystallization at relatively low pressures (≤3kbar) with relatively low water contents (≤3 wt. %).
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Keywords
Hawaii, Magma Plumbing System, Petrolog, Fractional Crystallization, Hydrous Conditions, Anhydrous Conditions