Geochemische und petrologische Untersuchung zur Evaluierung der Hauptelement-Flüsse in Vulkanbogen und die sich daraus ergebenden Konsequenzen für den globalen Stoffkreislauf

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The elemental outflux from volcanic arcs is a key variable in the global geochemical cycle, the quantification of which requires the knowledge of the arc growth rate, i.e. the volume added to the arc crust per time increment. The arc growth rate is commonly determined by volumetric methods. However, these methods often yield uncertain numbers, because so much of the material is actually erupted explosively and is either quickly eroded or deposited far from the volcanic site. Analysis of distal tephra fallout permits a more rigorous evaluation of eruption frequency, as well as the chemical composition, which should correlate to first order with crustal growth. Therefore, I propose to establish quantitative links between the composition of arc volcanic rocks and the arc growth rates. The approach builds on the systematic global variations of the arc major elements observed by Plank and Langmuir (1988), that indicate an inverse relationship between the crustal thickness and the degree of subarc mantle melting, and implicate the arc growth rate. To test the Plank and Langmuir (1988) model, I propose carrying out selected case studies in the well-investigated Mexican Volcanic Belt and the Izu Bonin Island arc, using modern microanalytical methods (e.g. LA-ICPMS, ion probe), and in-depth evaluation of published data on arc volcanic rocks. Finally, models will be developed to derive arc growth rates by a combination of volumetric and geochemical methods.