Contact metamorphism adjacent to a teschenite intrusion

Shale adjacent to the upper contact of an annular teschenite intrusion was converted to andalusite hornfels in an aureole 2–4 feet wide. At some points along the contact there is no evidence of anhydrous recrystallization. Rarely, magmatic reaction with small shale xenoliths resulted in formation of cordierite‐sillimanite (?) hornfelses, and locally a very small‐scale movement of magmatic constituents took place across the contact before consolidation of the teschenite. Very severe deuteric alteration of teschenite adjacent to the contact resulted in large losses of Si, Fe, Mg, alkalis, and probably Ca, some of which were recombined in clays and carbonates in the more porous shales and in joints, but analyses of uniformly fine‐grained shales indicate little change in bulk composition. Mineralogical evidence indicates a maximum contact temperature within the range 500°‐600° C, and a maximum intrusion temperature within the range 1000°‐1200° C.