Foliated dolostones surrounding the Tungstonia granite of eastern Nevada were investigated with the purpose of testing for models of forceful emplacement. Intragranular strains and lattice-preferred orientations (LPOs) define a zone of penetrative deformation that is narrow (<400 m) relative to the size of the Tungstonia granite (radius ~5 km) and coincident with its metamorphic contact aureole. Principle intragranular strains show shortening perpendicular to the granite-dolostone contact with maximum elongations that vary with position but are commonly parallel to the contact-parallel lineation. States of strain range from nearly pure flattening to plane strain. LPOs within ~50 m of the granite-dolostone contact exhibit c-axis maxima that are inclined to the foliation normal, indicating a sense of shear consistent with the ascent of the granite body relative to the surrounding carbonates. Penetrative deformation of dolostones is restricted to the contact metamorphic aureole with temperatures of ~300 to 710°C given by calc-silicate phase relations, calcite-dolomite geothermometry, and granite melting relations. Metamorphic constraints on peak temperatures and simple heat flow modeling suggest surprisingly short times of ~100 to 2,200 years for conductive heat exchange and pluton emplacement. Combined with constraints of temperature, pressure, strain, and grain size, strain rates near the granite-dolostone contact compare favorably with strain rates predicted by flow laws for dolomite evaluated at high strain rates in experimental studies. Penetrative deformation of dolostones closest to the granite-carbonate contact may involve a mixture of both dislocation and diffusion creep, while deformation further from the contact appears to be dominated by intracrystalline dislocation creep.
- Kronenberg, Andreas Professor, Michel T. Halbouty Chair