Progressive metamorphism of Permian siliceous limestone and dolomite – a complete sequence around a monzonite intrusion, Marble Canyon, Diablo Plateau, west Texas

The Marble Canyon elliptical intrusion ranges in composition from syenite at the center to olivine-bearing monzonite with a discontinuous biotite gabbro border phase near the contact. The contact aureole contains the complete sequence of previously described anhydrous mineral phases resulting from temperature gradients in metamorphosed siliceous limestone and dolomite.

This is the first discovery in the United States of a complete sequence of minerals described by Bowen (1940) and Tilley (1923) as occurring with increasing temperatures in siliceous limestones and dolomites. The polymorphic forms of dicalcium silicate Ca 2 SiO4, a (bredigite), 13 (larnite), and y occur together in the contact zone in Marble Canyon and were described by Bridge (1966a, b).