Continental Rifted Margins 1. Gwenn Peron-Pinvidic
Чтение книги онлайн.

Читать онлайн книгу Continental Rifted Margins 1 - Gwenn Peron-Pinvidic страница 13

Название: Continental Rifted Margins 1

Автор: Gwenn Peron-Pinvidic

Издательство: John Wiley & Sons Limited

Жанр: Физика

Серия:

isbn: 9781119986911

isbn:

СКАЧАТЬ subsidence (the effect of the faulting events) and the thermal subsidence (see Chapter 2). Various hypotheses have been posited to explain these peculiar subsidence curves of intracratonic basins. The main theories include subsidence caused by density changes within the lower crust and lithospheric mantle due to mineral phase changes (Gac et al. 2012), thermal relaxation and subsidence due to (negative) dynamic topography (Heine et al. 2008), thermal relaxation of a thick lithosphere undergoing low strain rates (Armitage and Allen 2010), tectonic reactivation (Braun and Shaw 2001) and uplift followed by subaerial erosion (Burov and Cloetingh 1997). Cacace and Scheck-Wenderoth (2016) reviewed all these hypotheses and determined that the long life span and slow subsidence of intracratonic basins are the result of feedback effects between sedimentation and thermal re-equilibrium at deeper crustal and mantle depths.

      The basins of intracratonic rifts are often described as bowl-shaped depressions hundreds of kilometers across. The sedimentary successions correspond to terrestrial and shallow-water sediments (carbonates, shales, sandstones), typically exhibiting a layer cake infill architecture, supposedly thicker and more complete than in adjacent areas of the craton but still relatively thin. The accumulation rates are extremely slow (2–20 m/Ma), and sedimentation usually keeps pace with basin subsidence throughout the rift history. A key characteristic of intracratonic basins is that they preserve their stratigraphy over very long time periods.

      Other than the Congo Basin, other examples of intracratonic basins include the Michigan basin, the East Barents Sea and the Chad basin.

Schematic illustration of the intracratonic rift basin case.

       1.2.2.2. Rifts at convergent plate boundaries

      Sedimentary basins can also develop in close spatial and temporal relation to an active orogen in a convergent tectonic setting. These include basins in trenches, fore-arcs and foreland, intra-arcs, back-arcs/hinterland, retro-arcs/-foreland, pro-foreland and wedge-top regions. The list of basins in convergent settings is very long, often confusing and sometimes misleading. The various descriptors can identify the different structural settings in which the basins form (e.g. if the basin develops over the subducting plate, on the edge of the orogen, far from the orogen, within the orogen, etc.), and/or the different types of substratum (e.g. continental or oceanic crust). However, given the regular structural complexity of orogenic settings, the description of the basin into one category or the other is often not straightforward.

      In a post-orogenic context, the overthickened lithosphere tends to a re-equilibration of its gravitational and thermal status by lithosphere thinning and, hence, extension (e.g. Dewey 1988; Rey et al. 2001). This is the so-called orogenic collapse, a specific tectonic mechanism that can lead to the formation of extensional basins inside the orogen (see Chapter 2).

Schematic illustration of topographic map of central Africa showing the outline of the main cuvette of the Congo Basin. Schematic illustration of the back arc, forearc and trench basins related to a subduction zone.

      1.2.2.3. Rifts at divergent-plate boundaries