Gwenn Peron-Pinvidic

Continental Rifted Margins 1


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Congo Basin: (Crosby et al. 2010).

      This section lists the major tectonic structures and basin types encountered in rifts and rifted margins. Basic definitions and schematic diagrams are provided to clarify the main terminology used in the following chapters of this book and to avoid any misunderstanding.

      Note that this section does not aim to describe the details of all structural features that can be encountered in extensional settings. The descriptions below cover a biased and non-exhaustive selection of structures that are considered to be representative of rifts and rifted margins. For a proper primer in structural geology, the reader is referred to contributions specifically dedicated to this theme (see the Further reading sections, and, for example, Fossen 2010).

       1.3.1. Extensional mechanisms

Schematic illustration of the pure shear and simple shear deformation mechanism.

       1.3.2. Main structural geometries

      The following list contains most of the deformation structures that characterize extensional settings. Schematic figures are provided to relate each structural geometry with field and seismic examples in order to illustrate their typical identification and interpretation in rifted margin studies.

       1.3.2.1. Normal faults

      Fractures can be of various sizes (shear fractures, joints, faults, detachment faults) and geometries (high angle, low angle, listric or spoon-shaped, concave upward/downward), with large or little to no movement, and accommodate various types of displacements (normal, reverse, strike-slip and oblique-slip). The two blocks separated by the fault plane are called the hanging wall (above) and footwall (below).

      Depending on the overall geometry of the fault, additional terms can be used such as: 1) thrust faults are reverse faults with a dip under 45°; 2) listric faults are normal faults with a fault plane that curves with depth and flattens into a sub-horizontal layer often called decollement; 3) synthetic and antithetic faults describe minor or secondary faults associated with a major fault: synthetic faults dip in the same direction as the primary fault, whereas the antithetic fault dips in the opposite direction.

Schematic illustration of the three ideal Andersonian fault types.