Strain path partitioning during forceful emplacement of the Papoose Flat pluton, Inyo Mountains, CA

• Main Author: Morgan, Sven Soren
• Other Authors: Geology
• Format: Others
• Language: en
• Published: Virginia Tech 2014
• Subjects: LD5655.V855 1992.M674; Rock deformation > California > Inyo Mountains
• Online Access: http://hdl.handle.net/10919/43474; http://scholar.lib.vt.edu/theses/available/etd-06302009-040224/

Sedimentary units in the Inyo Mountains of eastern California can be traced into the aureole of the Papoose Flat pluton where, due to intense crystal-plastic deformation, they are thinned to less than 10% of their original stratigraphic thickness. This deformation is constrained by textural relationships to have occurred during contact metamorphism. The strain within the dominantly S>L tectonites is partitioned by lithology. The deformation is in bulk, noncoaxial, but examination of individual lithologic units reveals large components of either pure shear or simple shear deformation. C-axis fabric analysis of quartz tectonites within veins in the gneissic border of the pluton, and quartzites within the pluton aureole, indicate that quartz tectonites deformed under approximately simple shear deformation, and suggest that the pluton/wall rock contact is the zone of highest strain. C-axis fabrics measured from the quartz tectonites are distinctly different between the veins and the quartzites. Veins display a higher maximum concentration of c-axes per uniform distribution and fabrics are characterized by single girdles. Quartzites display decreasing maximum concentrations of c-axes with increasing distance from the pluton/wall rock contact and fabrics are characterized by asymmetric cross girdles. Structural and field relationships indicate that; 1) pure shear deformation was dominant within the deformed border of the pluton, 2) flattening (chocolate tablet boudinage) occurred locally at the pluton/wall rock contact, 3) dominantly pure shear deformation produced the porphyroblast-matrix relationships within the aureole schists and, 4) pure shear plane strain (symmetrical boudinage) occurred locally within the aureole marbles. The direction of maximum extension within the boudinaged marbles is parallel to a stretching lineation which is well developed throughout the deformed western margin of the pluton, and is associated with the simple shear deformation observed in the quartz tectonites. Both pure shear and simple shear deformation are believed to be occurring concurrently with intrusion. Porphyroblast-matrix relationships within the aureole schists indicate that andalusite porphyroblasts have not rotated with respect to compositional layering. In sections viewed parallel to lineation and perpendicular to foliation, a constant angular relationship is observed between planar porphyroblast inclusion trails and matrix foliation traced around the western margin of the pluton. Unwrapping of the matrix foliation, from concordancy with the pluton margin into a planar reference frame, "unspins" the planar inclusion trails into a parallel and constant geographic orientation. This relationship, along with inclusion trail geometry, suggests that initial metamorphism was static, and that penetrative deformation did not occur until late in the growth history of andalusite. Deformation is recorded in the rims of andalusite porphyroblasts as a curvature of inclusion trails into parallelism with the matrix foliation. Inclusion trails begin curving at the same point in porphyroblast rims where inclusions coarsen in grain size and decrease in abundance, therefore a second ‘stage’ of metamorphism is believed to be synchronous with deformation. The strong component of pure shear deformation (plane strain and flattening) observed within various lithologic units, the variation in strain around the pluton/wall rock contact, and the synchroneity of the second stage of metamorphism with deformation suggest that the Papoose Flat pluton was forcefully emplaced. The deformation is believed to be a result of a complex path of forceful inflation, where inflation is not symmetrical as a balloon, but is heterogeneously developed and possibly directed more in the orientation of the lineation. A regional deformational event may, or may not, have occurred synchronously with forceful emplacement. === Master of Science