Aviva J Sussman1
(1) University of Arizona, Tucson, AZ
ABSTRACT: Development of Joint Systems in the Segre Oblique Zone, Southern Pyrenees,Spain
Located in the frontal portion of the southern Pyrenean orogenic system, the Segre oblique zone delineates the eastern boundary of the South Central Salient. This region is characterized by a series of thrust sheets striking SW-NE, and the doubly plunging Oliana anticline, which trends in a similar orientation. Rocks that have undergone deformation in the Segre oblique zone include pretectonic carbonates and syntectonic conglomerates. Joints within this area vary with respect to structural domain, mechanical stratigraphy, and surface morphology. In terms of structural domains, near-vertical joints trending NW-SE and NE-SW are prevalent along the limbs of the fold and in the thrust sheets. Joint density and size is controlled by the mechanical properties of the jointed rocks; the ratio of bed thickness to joint spacing is consistently ~1:1. A wide range of joint surface morphologies are present in the older lithologic units. For example, some of the systematic joints are open and have calcite vein material precipitated along them. Other joints are planar and many of the fractured conglomerate clasts contain plumose structures in similar orientations. On the other hand, younger syntectonics contain primarily planar joints with some exhibiting groove lineations. The distribution of surface morphologies is attributed to different amounts of overburden. As a whole, the data show a broad scatter when corrected for local structure, but are well organized when displayed unrotated suggesting that the development of joint systems in the Segre oblique zone occurred in the later stages of orogenesis.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado