HR: 1330h
AN: T52A-0232    [PDF]
TI: Intraplate Stress Directions and Magnitudes Induced by an Orogenesis: Data From Pyrenean, Alpine and Appalachian Collisions
AU: * Muriel, R
EM: muriel.rocher@irsn.fr
AF: IRSN, BP 17, Fontenay-aux-Roses, 92262 France, Metropolitan
AU: St‚phane, B
EM: stephane.baize@irsn.fr
AF: IRSN, BP 17, Fontenay-aux-Roses, 92262 France, Metropolitan
AU: Marc, C
EM: edward.cushing@irsn.fr
AF: IRSN, BP 17, Fontenay-aux-Roses, 92262 France, Metropolitan
AU: Francis, L
EM: francis.lemeille@irsn.fr
AF: IRSN, BP 17, Fontenay-aux-Roses, 92262 France, Metropolitan
AB: Several studies indicate a nearly exponential decrease of orogenic stresses with the distance to the range. The aims of our study are (1) to determine the variations of the curves of decrease (speed of decrease, mean far field stress value, ...) from an orogenesis to another, and (2) to precise the meso-scale intraplate stress variations. In this study, we focussed on the Palaeozoic Appalachian stresses in the North American Plate, on the Mio-Pliocene Alpine stresses and Eocene-Oligocene Pyrenean stresses in the West European plate. Calcite crystals are primarily deformed by twinning at low temperature and confining pressure. The tectonic analysis of calcite twins allows to reconstruct both the directions and differential values of the stress tensors, from decimetre size samples. We thus used inverse analysis of calcite twin data, with an improved process from the Etchecopar's method, to determine paleostresses, along transects perpendicular to each range. Results from calcite twin inversion were validated with fault slip inverse analysis in sampled sites. The obtained results highlight various phenomena: 1- At a same distance to the collision front, the differential stress values of the three studied orogeneses are roughly the same. 2- When leaving the collision front to the far field, the compressional state of stress ($\sigma$3 vertical) is rapidly changing to a strike-slip regime ($\sigma$2 vertical), and then to a perpendicular extension ($\sigma$1 vertical) at far field. 3- Differential stress values rapidly decrease in the first 100 km from the thrust front then a more slowly decrease in the plate. 4- The trend of Pyrenean compression is nearly the same all over the plate (N-S), as for the Appalachians (WNW-ESE), whereas the intraplate Alpine compression is fan shaped, from E-W in southern France to NW-SE in Belgium-Netherlands. The fan shape can be attributed to the alpine indenter to the Jura Mountains. Induced stress directions are maintained in the plate, indicating that the intraplate crust performs as a rigid homogeneous material. 5- The intraplate differential stress values varies of $\pm$ 20 MPa. The invoked factors are (1) the crustal and lithospheric thickness variations, (2) the stresses at intrados and extrados of folds due to crustal and lithospheric flexuring, and/or (3) the stress relaxation in already fractured areas.
DE: 8030 Microstructures
DE: 8102 Continental contractional orogenic belts
DE: 8164 Stresses--crust and lithosphere
DE: 9335 Europe
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: 2003 Fall Meeting