CRYSTAL-MUSH FLOW DYNAMICS IN MIGRATING TUBES IN THE GLEN AULIN REGION OF THE TUOLUMNE INTRUSIVE COMPLEX

Magmatic structures, defined by compositional variations, form complex patterns and shapes that can be used to identify the flow direction, size, shape, and overall evolution of the magma melt. The Tuolumne Intrusive Complex (TIC) Eastern Sierra Nevada contains many of these structures, including plumes, troughs, stationary tubes, and migrating tubes, the latter of which can serve as a paleovertical tool as well as a marker for the rheology and evolution of crystal-mushes. Also called “ladder dikes”, migrating tubes tend to have a steep axis (>70^o) and internal mineral alignment, which provide insights into the local flow and younging directions inside the evolving magma chamber. Migrating tubes in the TIC tend to spatially cluster in relatively small regions ( ~1000 m²) one of which is in the Glen Aulin area. Migrating tubes in the Glen Aulin domain display variable younging but with a strong average movement direction towards 318^o, subparallel to one of the regional magmatic fabrics. This direction is opposite to that of regional younging defined by zircon crystallization ages. Three migrating tubes were grid mapped in detail, and 6 samples collected from grid mapped areas: 3 oriented samples from 2 different migrating tubes, and 3 samples of different compositional layers from the tube were collected. Major, minor, and trace element compositional analyses are presented to further define formation of the compositional diversity defining the tubes. Crystal fabric orientations in 2 thin sections from perpendicular faces of each oriented sample are under investigation using an Electron Backscatter Diffraction (EBSD) microscope, as well as traditional thin section analysis. Relationships between crystal orientation, size, and composition within the analyzed migrating tubes will provide insight into the flow dynamics in the tube.