Finite strain variations along strike in mountain belts
In order to quantify finite strain from displacement fields derived from structural restorations in mountain belts, a simple technique using triangular elements (based on the finite element technique) is presented. This adequately describes the discontinuous displacement of a fold-thrust belt, whilst overcoming the difficulties posed by discontinuities which are integrated across appropriate elements for the purpose of strain calculation. The technique has been applied to two fold-thrust belts at contrasting scales, the Central Andes and the Neuchâtel region of the Jura mountains (Switzerland). In both cases, structural restorations have produced the finite displacement fields thought to be involved in their generation. Subsequent calculation of strain variation along strike shows that there is a strong relationship between first-order structure (the scale of major fold axes) and the trends of axis orientations. In spite of the contractional setting of both belts, strong along-strike extension is predicted but this is always in the context of a generally parallel to slightly convergent displacement field, and such extensions are generally related to differential shear accommodated on strike-slip or tear faults. Most elements showing along-strike extension are nevertheless predicted to undergo tectonic thickening. Second-order structures (faults necessary to accommodate local predicted deformation) are also calculated and the enormous difference between slip directions on small-scale faults and the regional ‘far field’ displacement direction is demonstrated. This is thought to be important when trying to infer large-scale tectonic information from very small-scale structures found in the field.
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New Insights into Structural Interpretation and Modelling
This title has arisen from the Geological Society of London conference of the same name. Since the publication of the predecessor of this book (‘Modern insights into structural interpretation, validation and modelling’, SP99, 1996, edited by Buchanan & Nieuwland) much progress has been made. This has been primarily thanks to the continuously increasing computing speed and computer memory capacity, which has positively affected all fields in structural interpretation, seismics and modelling, directly or indirectly.
‘New insights in structural interpretation and modelling’, presents a balanced overview of what the title promises. It is intended as a book that will serve the experienced professional as well as more advanced students in earth sciences, with a broad selection of topics ranging from classical field based studies to state of the art analogue and numerical modeling. The leaders of their fields have written some of the chapters, whereas younger authors with a fresh outlook and new ideas have written other chapters.