Vertical Tectonics Associated with Rifting and Spreading [and Discussion]

Aseismic continental margins round the world have a much longer history as belts of subsidence than the lateral spreading which produced the oceans which they now flank. Additionally, they show a synchroneity of major development phases which appear to be in part independent of the opening of adjacent oceans. In many cases the margins coincide with areas which were prone to subsidence as far back as the Lower Palaeozoic; almost universally the rifting which began their main development dates back to the early Permian. In a majority of cases (not all) the main rift phase ended abruptly during the Lower Cretaceous to be succeeded by progradation and major unfaulted subsidence. In some regions (e.g. East Africa and south Australia) a further phase of major faulting continued until the Miocene, the time of a further globally controlled event. In this long history of vertical movement, extending back throughout the Phanerozoic the subsiding belts which became the sites of sutures between the major plates contrast sharply with East Africa and the Red Sea, often used as tectonic models. Additionally, there is a lack of evidence that oceanic rifting was preceded by anticlinal warping -- indeed, along many ocean edges both the faulting and the tilting towards the continent are demonstrably syn-sedimentary, associated with rotation of the marginal blocks as Permo--Triassic and later Mesozoic rocks accumulated.