CHARACTERIZING THE WALLROCK STRAIN AND KINEMATIC VORTICITY OF HOT RISING BODIES, FROM THE PAPOOSE FLAT PLUTON TO METAMORPHIC CORE COMPLEXES

Art Sylvester’s pioneering work around the Papoose Flat pluton established a classic example of forceful pluton emplacement. As many students in the western United States have observed—often on fieldtrips with Art—Cambrian stratigraphy is greatly stretched (~90% vertically attenuated) around the Papoose Flat pluton. This deformation is driven by the hot buoyant ascent and emplacement of the pluton, which may be analogous to the development of gneiss dome-like metamorphic core complexes (MCCs) in the North American Cordillera. Here we examined the finite strain history and kinematic vorticity of the wallrock of the Papoose Flat pluton and 4 MCCs in the western US to establish quantitative strain characteristics of rising hot buoyant bodies. Our results show ~50-75% pure-shear strain in both the pluton emplacement and MCC settings, consistent with observations of significant stratigraphic attenuation. We show via numerical simulations that the advection of hot, buoyant viscous rocks drives significant pure shear strain along the margins of the rising diapir, whereas detachment faulting yields simple-shear kinematics. We suggest that pure-shear attenuation and kinematic vorticity numbers may be diagnostic features for deformation driven by buoyant, vertical advection in the crust. Our documented strain characteristics have implications that span from interpreting kinematic and dynamic development of metamorphic core complexes to the identification and interpretation of Early Earth dome-and-keel structures.