Penetrative Deformation of Dolostones during Contact Metamorphism and the Forceful Emplacement of the Tungstonia Granite, Kern Mountains, Nevada

Abstract

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.