Interaction of Segments along Rifts that Separate Continents and Ridges that Spread Ocean Floors

Sammanfattning: The face of the Earth is constantly renewed by continental rifts that open and allow ridges to spread oceanic floor. Both types of these linear extensional structures are morphologically and structurally segmented. This thesis aims to provide insights into the interaction of such segments as they propagate and mature. It is based on the results of analogue models of evolving rifts and ridges together with field studies of populations of dilational normal faults in the active rift zone of Iceland. Linkage of initially separate segments along rifts and ridges leads to formation of through-going systems operating on a planetary scale. It is argued here that the processes of segment initiation and growth are effectively scale-independent and essentially the same in wide and narrow modes of extension and for shear and dilational failure. Three distinct types of segment coalescence are recognized; these involve tip-to-tip, one tip-to-sidewall and two tips-to-sidewalls segment linkage. The overall structural pattern, particularly the width of the extending domain and the range of displacements and orientations of smaller-scale internal extensional structures, is influenced by both the geometry of extension and the mechanical properties of the extending material. Types of segment linkage appear to be largely independent of localization of dilation or intensity of magmatic accretion. Instead they are controlled mainly by the relative distribution and orientation of interacting segments. A few orders of segmentation along global rift-ridge systems and arrays of dilational normal faults indicate that linear continuous structures accumulate extension in successive increments during which the segments change their geometries in semi-continuous interaction and coalescence.