Diffusion controlled evolution of reaction microstructures: potential geospeedometers for garnet granulite xenoliths from the lower crust.

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Garnet granulite xenoliths from the Bakony-Balaton-Highland Volcanic Field (Western-Hungary) provide excellent samples of the lower crust beneath the Pannonian Basin. Thesequence of mineral parageneses of these xenoliths testifies to an initial high temperaturehigh pressure stage followed by heating and decompression. This evidence can becorrelated very well with the Miocene tectonic evolution of the Pannonian Basin. Thexenoliths frequently contain symplectites and characteristic diffusion zoning of plagioclase.Both of these phenomena indicate diffusion controlled reaction kinetics and thus have greatpotential as geospeedometers. From the analysis of these phenomena we intend to derivetime scales and rates of the petrogenetic processes that were active in the deep crust duringthe Miocene evolution of the Pannonian Basin. The expected outcomes will allow to refinethe parameterization of geodynamic models of the coupled crust and mantle processes thatultimately shaped the present day topography. The intended research will involve detailedmineral chemical and microstructural/textural investigation with a focus on high spatialresolution techniques. It will also be concerned with the adoption of a generalized diffusiontheory to describe transport controlled reaction kinetics in geological materials.