Eastern Llano Uplift
Most of our research has been done in the eastern portion of the Llano Uplift. Major shear zones bound the domain boundaries and show tectonic transport to the northeast. The dominant fabrics and domain boundaries all dip to the southwest. See Reese and Mosher (2004). Rocks in the Packsaddle and Valley Spring domains overlap in age and are intruded by similar aged (1256-1232 Ma) granitic sills and small intrusive bodies. |
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The Coal Creek domain is thrust over the Packsaddle domain along the Sandy Creek shear zone, a 2-3 km wide zone recording high shear strains as shown by the ultramylonite of a granitic sills (upper left) (see Roback, 1996). The Packsaddle domain is thrust over the Valley Spring domain along a ductile shear zone (upper right); shear strains are lower but flattening strains are high (see Mosher et al., 2004). |
Deformation
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Five phases of synmetamorphic deformation produced multiple fabrics and associated folds. A regional composite S1/S2 fabric and associated isoclinal folds formed synchronous with discrete domain bounding and intra-domainal shear zones. Continued deformation folded the early fabrics and shear zones by three later phases of folding (Reese and Mosher, 2004). In the deepest structural levels of the Valley Spring domain (upper right), deformation is associated with partial melting forming leucosomes parallel to early foliations (Mosher et al., 2004).
For more information, see Nelis et al. (1989). Carter (1989), Mosher (1998), Reese and Mosher (2004), and Mosher et al. (2004) and theses by Nelis (1984), Carter (1985), Reese (1995), Zumbro (1999), and Hoh (2000). |
Metamorphism
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Dynamothermal metamorphism occurred under medium pressure conditions. End member Fe staurolite overgrows S2 fabric (upper right) and is found as inclusions in garnet (left - photomicrograph - crossed polars; lower right - photomicrograph -plane light close up). See Carlson and Nelis (1986); Carlson and Reese (1994). |
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A late low pressure Buchan metamorphism overprints the deformational fabrics and is associated with the late syn- to post-tectonic granites. Cordierite contains inclusions recording a preexisting crenulated foliation (above left); andalusite randomly overgrows the deformation fabrics (above right). For more information, see Carlson (1998); Carlson and Schwarze (1997); Carlson and Reese (1994); Carlson and Nelis (1986). |