Garnetiferous pelite (3D recon)

Images of a 1" (25 mm) core of garnet-filled pelitic schist. CT data provides an excellent means to image the three-dimensional size and spatial distribution of porphyroblasts. Such data can be used to deduce the mechanisms that control nucleation and growth of porphyroblasts during metamorphism. Further kinetic modeling based on these results allows estimation of physical parameters such as activation energies and diffusion constants that only have observable effects on geological time scales, and are thus problematic to measure in the laboratory. (Top left) A complete three-dimensional reconstruction of the scanned volume. Garnets appear as white circles in black-gray matrix of quartz, feldspar and mica. (Top right) A cubic subsection cut from the main volume. (Bottom left) A pseudocolor rendering of the subsection, showing matrix as blue-purple and garnets as yellow. (Bottom right) The matrix has been made fully transparent, allowing only the garnets to be seen. Measuring the size and location of this quantity of garnets in three dimensions by serial sectioning is impracticable, but becomes possible when CT data is combined with image processing techniques. Sample provided by Dr. John Ferry, Johns Hopkins University.

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