Kristallisationsbedingungen von Karbonatiten und assoziierten Alkalimagmatiten
Zusammenfassung der Projektergebnisse
Samples from seven carbonatite complexes were investigated in the course of this project, including the Kaiserstuhl (Germany), Sokli (Finland), Kovdor (Russia), Oka (Canada), Magnet Cove (USA), Jacupiranga (Brazil) and Palabora (South Africa). Special focus was given on the petrological evolution of the Kaiserstuhl volcano. A K-basanitic magma produced the tephritic to phonolitic rock series, while an olivine melilititic magma is responsible for the nephelinitic to limburgitic rock series, the melilititic to haüynitic rock series and the carbonatites. Fractional crystallization at high redox conditions (ΔFMQ=+1 to+2) is the key process for the evolution of such magmas. In fact, carbonatites and associated silicate rocks at continental settings reveal on average significantly higher redox conditions (ΔFMQ≈+1.4) than alkaline complexes without carbonatites (ΔFMQ=-1.1). The redox variations of alkaline rocks presumably reflect the heterogeneity of the oxidation state of the mantle source. This is consistent with the prerequisite of a relatively oxidized, carbonate-bearing mantle for the formation of carbonatites, and may explain why carbonatites are absent at most agpaitic complexes. However, there are several further processes that have to be considered to relate the oxidation state of the mantle with its magmatic derivatives. At the Kaiserstuhl, we showed that carbonatite magma-wall rock interactions caused an increasing silica activity of the magma, and it seems likely that such processes may also affect the redox conditions. Variable melting degrees, degassing and fractional crystallization may also influence the oxidation state of a magmatic system. Thus, further work on such processes are appreciated in order to more precisely link the redox conditions of igneous rocks to their mantle source.
Projektbezogene Publikationen (Auswahl)
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The Petrology of the Kaiserstuhl Volcanic Complex, SW Germany: The Importance of Metasomatized and Oxidized Lithospheric Mantle for Carbonatite Generation. Journal of Petrology, 59(9), 1731-1762.
Braunger, S.; Marks, M. A. W.; Walter, B. F.; Neubauer, R.; Reich, R.; Wenzel, T.; Parsapoor, A. & Markl, G.
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Evidence for Magma–Wall Rock Interaction in Carbonatites from the Kaiserstuhl Volcanic Complex (Southwest Germany). Journal of Petrology, 60(6), 1163-1194.
Giebel, R. J.; Parsapoor, A.; Walter, B. F.; Braunger, S.; Marks, M. A. W.; Wenzel, T. & Markl, G.
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Do carbonatites and alkaline rocks reflect variable redox conditions in their upper mantle source?. Earth and Planetary Science Letters, 533, 116041.
Braunger, Simon; Marks, Michael A.W.; Wenzel, Thomas; Chmyz, Luanna; Guitarrari, Azzone Rogério & Markl, Gregor
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Interaction between mafic dike rocks and salt deposits in the Rhine Graben, southwest Germany. The Canadian Mineralogist, 59(3), 511-531.
Braunger, Simon; Scharrer, Manuel; Marks, Michael A.W.; Wenzel, Thomas & Markl, Gregor
