The generation of felsic magmas in the oceanic crust: assimilation-fractional crystallization processes versus re-melting of the crust
Final Report Abstract
In our opinion the project was very successful and came up with some very good and important results. The sampling and analytical work went well and the two PhD students did a very good job collecting a large amount of data. The formation of felsic melts along the PAR and in the Troodos and Oman ophiolite show significant similarities and assimilation and fractional crystallization (AFC) of mafic magmas are the dominating processes. Significant volumes of mafic minerals and plagioclase are fractionated from the mafic magmas, most likely in very shallow melt lenses that appear to be abundant at fast spreading ridges. The AFC processes affect many incompatible element concentrations and apparently amphibole plays an important role in the crust. Fresh glassy lavas from the PAR show variable O isotope ratios and high Cl contents reflecting assimilation of hydrothermal material. Similar processes affect the O isotope compositions of quartz and zircon in felsic plutonic rocks from ophiolites implying that the interaction of stagnating magma with hydrothermally altered material is a typical process in the shallow oceanic crust. The shallow felsic intrusions in both ophiolites indicate multiple intrusions of magmas with different mantle sources that reflect the evolution of the ophiolite crust above a subducting slab.
Publications
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2013. Oxygen isotope evidence for the formation of andesitic–dacitic magmas from the fast-spreading Pacific–Antarctic Rise by assimilation–fractional crystallisation. Chemical Geology 347, 271-283
Freund, S., Beier, C., Krumm, S., and Haase, K.M.
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2014. Constraints on the formation of geochemically variable plagiogranite intrusions in the Troodos Ophiolite, Cyprus. Contributions to Mineralogy and Petrology, 167, 978
Freund, S., Haase, K.M., Keith, M., Beier, C. and Garbe-Schönberg, D.
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2015. Anatexis at the roof of an oceanic magma chamber at IODP Site 1256 (equatorial Pacific): an experimental study. Contributions to Mineralogy and Petrology
Erdmann, M., Fischer, L.A., France, L., Zhang, C., Godard, M., and Koepke, J.
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2015. Melts of sediments in the mantle wedge of the Oman ophiolite. Geology 43, 275-278
Haase, K.M., Freund, S., Koepke, J., Hauff, V. and Erdmann, M.
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Constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the Oman ophiolite. Contributions to Mineralogy and Petrology, May 2016, 171:46
Haase, K.M., Freund, S., Beier, C., Koepke, J., Erdmann, M., and Hauff, F.
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Experimental temperature cycling as a powerful tool to enlarge meltpools and crystals at magma storage conditions. American Mineralogist (2016) 101 (4): 960-969
Erdmann, M., and Koepke, J.
