Geochemical characteristics of hydrous basaltic magmas due to assimilation and fractional crystallization: the Ikoma gabbroic complex, southwest Japan
| Autor: | Katsuyuki Yamashita, Daisuke Ogawa, Naoko Koizumi, Takamoto Okudaira, Yoshimitsu Suda |
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| Rok vydání: | 2016 |
| Předmět: |
Basalt
Fractional crystallization (geology) 010504 meteorology & atmospheric sciences Geochemistry Magma chamber engineering.material 010502 geochemistry & geophysics 01 natural sciences Mantle (geology) Geophysics Geochemistry and Petrology engineering Plagioclase Mafic Petrology Ilmenite Geology 0105 earth and related environmental sciences Hornblende |
| Zdroj: | Mineralogy and Petrology. 110:639-662 |
| ISSN: | 1438-1168 0930-0708 |
| DOI: | 10.1007/s00710-016-0423-9 |
| Popis: | To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial 87Sr/86Sr ratios (SrI) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (SrI = ~0.7071) as the source material for the Ikoma gabbros. |
| Databáze: | OpenAIRE |
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