Descriptive classification of dyke morphologies based on similarity to fracture geometries

Fractures (including faults and joints) are important pathways for magma in the upper crust. Two theories of dyke intrusion are generally accepted: dykes open pre-existing fractures or dykes inject propagating new fractures at their tips. Thus, there is a close interrelationship between dyke intrusion and fractures. We present a field-based study focused on geometric patterns of intrusions, because detailed descriptions and analyses of exposed dykes can provide useful complementary information regarding the roles of fractures as dyke formation pathways. Most non-planar dyke examples that we analyzed are from four areas (Geoje Island, Kori, Uljin, and Suncheon) of Korea. Some dykes show morphological similarities to fractures, such as branching, bending, and splaying. Therefore, we classified the intrusion patterns based on the equivalent terminology for fractures (e.g., tip, wall, and linkage), which is useful for describing dykes at the outcrop scale and for research into inter-relationships between dykes and fractures. This study improves our understanding for the role of fractures in guiding dyke emplacement.