SALT FLOW AND DIAPIRISM RELATED TO EXTENSION AT CRUSTAL-SCALE

The analysis of the structure and history of salt diapirs in large anc ient evaporitic basins such as the southeastern North Sea basin sugges ts that diapirism is controlled by crustal-scale extension. Laboratory experiments on small-scale models designed to simulate configurations comparable to the southeastern North Sea basin show that diapirs, whi ch grow in a sedimentary cover during basement extension, can develop close to basement normal faults or at a significant distance from them , if the displacement on the basement faults is transfered horizontall y along the salt layer. For given values of salt viscosity, strain rat e and friction coefficient in brittle rocks, the pattern of salt diapi rism in a particular area depends on the ratio of cover thickness to s alt thickness, as well as the absolute thicknesses of cover and salt l ayers. The experiments give criteria for identifying different types o f diapirs and provide models of horizontal flow in a salt layer underg oing extension and diapir development. Some dynamic implications of th e experiments are applied to the southeastern North Sea basin.