Dynamothermal Metamorphism and Its Products

Abstract

Dynamothermal metamorphism is due to the co-operation of directed pressure and heat. The heat element facilitates recrystallisation; but the stress element not only promotes recrystallisation, but is powerful in deforming the rocks, and producing new structures. The new parallel textures and structures are usually orientated perpendicular to the direction of greatest stress, and parallel to that of minimum stress. The deformation may be regarded as due to the interaction of three processes, which may be designated as clastic, plastic, and blastic.¹ The clastic process is instrumental in actual fracture, rupture, and rolling-out of the minerals as detailed in Chapter XVII. Plastic deformation occurs when, under powerful confining pressure, rocks and minerals are made to stretch and flow by movement along cleavage and gliding planes without actual rupture (fractureless deformation), perfect cohesion being maintained during the movement. In a long series of experiments, F. D. Adams and his collaborators have shown that under sufficient pressure rocks and minerals can be deformed without fracture, and that such susceptible materials as marble can be forced to flow into, and fill, open spaces without loss of cohesion.