Geometry and distribution of regional joint sets in a non-homogeneous stress field: case study in the Ebro basin (Spain)
ABSTRACT Three regional joint sets striking N–S, E–W and WNW–ESE affect the Tertiary rocks of the central Ebro basin. From analysis of their chronological relationships and spatial distribution, it is concluded that they correspond to two different tectonic events. The N–S set (oldest) and the E–W set (younger) are present in the southern and central sectors, while the WNW–ESE joint set predominates in the northern one. The N–S joints propagated in response to joint-normal and fluid loads under an intraplate stress field with SHmax oriented near N–S (related to forces caused by the convergence of Africa, Iberia and Europe and rifting at the Valencia trough) during the sedimentary infilling of the basin. These joints are only present in the southern part of the area. The E–W joint set in the southern-central sector records the same fracturing event as the WNW–ESE set does in the northern one. Its orientation was modified by the presence of the older N–S set in the south, which perturbed the regional stress field. The younger WNW–ESE and E–W joint sets are interpreted as unloading joints. These propagated as a consequence of flexural uplift and exhumation related to isostatic rebound at the Pyrenees and the Ebro foreland basin. A numerical approach is used to explain the inhomogeneous distribution of the N–S joint set in terms of their absence being controlled by the depth of the water table at the time of their formation.
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ABSTRACT: The development of hybrid and faulted joints has not been studied in detail in natural outcrops. This field study in the Campo de Dalias (Betic Cordilleras) establishes the distinctive features of these structures as compared with those predicted by theoretical studies. Hybrid joints appear as two sets of vertical joints forming variable angles, but generally about 25°, with opening directions orthogonal to joint planes. Their development requires low differential stresses with a tensile minimum stress. The main criteria that indicate the existence of faulted joints are: (1) the presence of subvertical fault planes with oblique slip forming a complex pattern of dextral and sinistral faults developed under a single stress regime; (2) faults with similar geometries as joints in the same outcrop, showing an inconsistent cross-cutting relationship; and (3) the development of small basins with variable polarity of asymmetric wedge filling. A permutation in stress orientation since the Tortonian in the Campo de Dalias was responsible for the development of a faulted hybrid joint system, with a constant ENE-WSW extension trend and a switch of σ1 between NNW-SSE and vertical.Journal of Structural Geology 11/2004; 26(11):2025-2037. · 2.29 Impact Factor
- ACTA GEOLOGICA SINICA (English Edition). 07/2013; 87(12):139-141.
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ABSTRACT: An intense tectonic activity in eastern Sicily and southern Calabria (Italy) is well documented by the differential uplift of Late Quaternary coastlines and by the record of the strong historical earthquakes. The extensional belt that crosses this area is dominated by a well-established WNW-ESE-oriented stretching direction. However, this area is largely lacking of any structural analysis for defining the tectonics at a more local scale. The analysis of systematic extension joint sets affecting Pleistocene deposits presented in this paper allows to infer the causative tectonic stress tensor by means of a quantitative inversion technique. Local perturbations of the first-order regional stress field are consequently recognized. Such perturbations are interpreted as due to interferences between large active faults and their particular geometrical setting. These results contribute to the understanding of the Quaternary tectonic evolution and the present-day stress regime.Tectonics 03/2013; 32(2):239-251. · 3.49 Impact Factor