Gwenn Peron-Pinvidic

Continental Rifted Margins 1


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extending – this one is called the “aulacogen” (Burke 1977; Şengör and Burke 1978) (Figure 1.6). Aulacogens are often reactivated in the post-rift stages under renewed extension or compression. A well-studied example is the Benue Trough, that extends from the equatorial Atlantic Ocean into the continental hinterland of Nigeria (Figure 1.7). It formed in the Early Cretaceous as a major rift arm accommodating the separation of South America from Africa (Olade 1975; Robert 2008).

Schematic illustration of topographic map of the East African Rift system with indication of some of the major segments. Schematic illustration of an Aulacogen. Schematic illustration of maps locating the Benue Trough aulacogen in the South Atlantic plate tectonic evolution.

       Case example: The Basin and Range Province

Schematic illustration of the wide rift mode.

      The tectonic reason for the formation of the province is interpreted to be due to crustal buoyancy forces and stress changes at plate boundaries (Sonder and Jones 1999). The entire region is characterized by high heat flow, slightly thinned continental crust (27–35 km) and a relatively flat Moho with reduced upper mantle P wave velocities (7.5–8.0 km s-1) (Holbrook 1990; Gilbert 2012). Structurally, the region displays distinct modes of deformation (high-angle faulting, low-angle detachment and metamorphic core complexes) and the rocks have experienced syn-deformational high-grade metamorphism (amphibolite, granulite, eclogite facies) (Axen et al. 1993). The observations led to the development of the simple shear model (Wernicke 1981, 1985) (see Chapter 2) where a detachment surface separates an upper plate setting (hanging wall) from a lower plate setting (footwall), which are mostly made of upper crust dissected into blocks by high-angle normal faults and highly-deformed lower crust, respectively (Davis and Lister 1988; Lister and Davis 1989).

Schematic illustration of topographic map of the Basin and Range Province.

      Intracratonic rifts

      The basins of intracratonic rifts