The idea for a special publication on non-volcanic margins arose during Ocean Drilling Program (ODP) Leg 173 off West Iberia, prompted by ODP’s decision to cease publishing the scientific results volumes as hard copy. The Shipboard Scientific Party favoured an open scientific meeting and associated publication. But they did not want to produce a book that was a scientific results volume by another name, but rather contribute to a publication that had a much broader scope than just reporting results obtained off West Iberia. These thoughts, and many scientific discussions during the Leg, were influenced by the presence on board of scientists who also work on Alpine geology: hence the ‘evidence from land and sea’ approach that underlies the content of this publication.
However, when planning the meeting, we were very conscious of the fact that the West Iberia and Alpine examples might not be typical of other non-volcanic margins. We were keen, therefore, to ensure that margins in other parts of the world were discussed, including a margin that is active today, and that was visited by the JOIDES Resolution not long after Leg 173 took place (Leg 180: Woodlark Basin). We caution, therefore, that it may be premature to use models based on the Iberia and Tethyan margins as the paradigm for all non-volcanic margins.
The first paper in this book, by Boillot & Froitzheim, reviews the synergies that have occurred between investigations of the eastern Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the
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Non-volcanic continental margins may form up to 30% all present-day passive margins, and remnants of them are preserved in mountain belts. The papers in this volume demonstrate the benefits of integrating offshore and onshore studies, and illustrate the range of information obtained at different scales when comparing evidence from land and sea. Data sets collected across a range of spatial scales are evaluated: thin sections, cores, outcrops, seismic reflection profiles, and other geophysical data. The outcrop scale is crucial because it enables the spatial gulf to be bridged between DSDP and ODP cores and marine seismic data. There is also the problem that basins on land and beneath the sea inevitably have had different post-rift histories resulting in their contrasting present-day elevation. In mountain belts, portions of continental margins and oceanic crust are superbly exposed, but dismembered by subsequent compressional tectonics. Off present-day passive margins, extensional features have only been slightly deformed, if at all, by compressional movements, but are buried beneath significant thicknesses of post-rift sediments and so can only be sampled by ocean drilling at a small number of points.
The first paper reviews the synergies that have occurred between investigations of the eastern North Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the Alps, and some later papers return to this theme. However, papers describing margins from other parts of the world show that it may be premature to use models based on the Atlantic and the Alps as the paradigm for all non-volcanic margins. The following 25 papers in the book are grouped under the following headings: (1) Margin overviews; (2) Exhumed crust and mantle; (3) Tectonics and stratigraphy; (4)Numerical models of extension and magmatism.