Passive margins and their subsidence

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Abstract
Three main types of subsidence dominate the vertical tectonics of rifted inter-plume passive margins. These are the isostatic response to (1) stretching and thinning of the crust and lithosphere (syn-rift stage), (2) cooling and thickening of the lithosphere (mainly post-rift stage), and (3) sediment loading (both stages). Additionally, vertical movements occur at plume (hot spot) margins as a result of the anomalously hot underlying upper mantle, and emplacement and cooling of magma. Three examples demonstrate various features of subsidence at inter-plume passive margins. At the North Biscay starved margin, the subsidence history can be mainly explained by syn-rift lithospheric stretching followed by post-rift thermal subsidence. At the US Atlantic margin, the much greater overall subsidence results from the additional effect of sediment loading. The Tucano-Gabon graben system bordering the South Atlantic is an example of strongly asymmetrical extensional tectonics during the syn-rift stage which produced deep rifted basins within the adjacent continental borderland.