Structural control of polygonal cracks in La Pedriza del Manzanares (Madrid)

Abstract

Polygonal cracks represent a common way of modeling granite whose origin and evolution continues under study not even existing a systematization of these diverse structures. Some authors explain their origin by internal geodynamic processes relating to movements of fracture planes in later stages of magmatic consolidation. Other authors attribute their formation and development to external factors related to climate regime. The great variety of polygonal cracks requires the use of a greater number of variables to define their different origins, the possible interrelations between external and internal factors, to explain the evolution of these structures and advance the classification of specific patterns. This work aims to contribute to systematize the mechanisms involved in the development of polygonal cracks. For that only polygonal cracks formed on flat vertical or subvertical fractures are studied. In particular relations are established between the presence of polygonal cracks with: the fracturing network, height of appearance, angle and tilt of the wall, plaque morphology and depth of incision of the perimeter cracks. Moreover it establishes relationships between internal geodynamic processes and external weathering processes.