Chapter 1 - Rifts and rifting

Abstract

Rifts are linear structures on the crust that are involving or have involved the lithosphere in their dynamics. In other words, they are penetrative structures. They are the loci of crustal extension occurring in various tectonic settings ranging from cratonic crust to orogenic settings, meaning that although they are generally considered to be extensional features on the crust, they can also be associated with earlier, contemporaneous, or later compression settings. Rifts occur as narrow (50–100km wide), elongated (up to 1000km long) structures and are often segmented. Geomorphologically, rifts are defined as elongated depressions, bounded by normal faults. They are, in many parts, characterized by abnormally high heat flow, causing some parts of the rifts to raise in order to achieve isostatic equilibrium. The elevation of the thermal bulge varies with the activity of the rift system but is usually about 1.5–2km above the regional average.