AJ Sussman¹
(1) University of Arizona, Tucson, AZ

Abstract: Deformation history of the Segre oblique ramp, Southern Pyrenees, Spain

Many scale-independent lines of evidence suggest that material within fold-and-thrust belts is transported in three dimensions. Lines of evidence range from the arcuate topographic expression of active fold-and-thrust belts (or salients) to grain-scale strain patterns. Salients and the transport of material within them are often determined by several controlling parameters, including initial basin configuration, pre-existing weaknesses, plate geometry, and material properties of the deforming orogenic wedge. Because previous studies have delineated the effects of some of these parameters, the South Pyrenean orogenic system provides an outstanding opportunity to determine bulk-rock behavior. The convex-toward-the-foreland map pattern associated with the South Central salient in the Southern Pyrenees can be divided into three parts: the western oblique ramp associated with the Gavarnie Thrust, the frontal Serres Marginals thrust and the eastern oblique ramp of the Segre thrust. This investigation is based on field and microstructural studies from the hangingwall and footwall of the Segre thrust oblique ramp. Field analyses consist primarily of data from small-scale faults, fractures and veins, while thin-section analyses are comprised of data from calcite and quartz grains. Along with cross-cutting relationships, such analyses were extended in the stratigraphic column from the Triassic pretectonic assemblages up into the Eocene syntectonic conglomerates in order to determine a sequence of the primary bulk-rock mechanisms active throughout growth of the salient. Preliminary results suggest that the earliest phase of deformation is three-dimensional and dominated by plastic mechanisms, while later deformation regimes consist primarily of shear related motion along brittle faults.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana