Continental graben structures

Abstract

A continental graben structure or rift is a narrow, elongated, fault-bounded structure in the Earth’s crust (Fig. 3.1). Grabens consist of a central axial depression flanked by steep walls and elevated shoulders that plunge steeply into the rift axis and slope gradually towards the exterior (Fig. 3.2). The most famous example is the East African rift system. Rift systems may be cut and apparently offset by transform faults; examples include the Upper Rhine Graben in Central Europe and its southern continuation in the Bresse and Rhône grabens (see below). Graben structures occur in regions where the crust and lithospheric mantle are extended and thinned (Fig. 3.3). Broad regions of extension are typically expressed by numerous grabens and intervening higher horst blocks such as the Basin and Range Province in western North America. Graben systems also occur in oceanic crust along mid-ocean ridge systems and will be discussed in Chapter 5.