Stress deflection in a tectonic compressional field: A model for the northwestern Iberian Chain, Spain

Abstract

By means of fault population analysis (using the right dihedra, y-R diagram and Etchecopar's methods), the states of stress in a number of sites of the Cameros Massff (Northwestern Iberian Chain, Spain) and nearby areas of the Ebro Basin have been determined. These states of stress have been used as a framework in order to infer a model of the actual stress field in that area during the main stage of the Alpine compression (Oligocene-lower Miocene). The three main compression directions obtained (NW-SE, NNE, NE-SW)can be explained by a single compression field with horizontal o, trending NNE and vertical 02, whose primary trajectories are deflected due to (1) largescale strike-slip faults or lateral ramps of thrusts or (2) frontal ramps of thrusts oblique to the main compressire axis. The reliability of this scheme has been checked by means of a two-dimensional mathematical model based upon the finite element method and applied on a sheet whose theological properties are similar to those of a standard limestone. This model simulates the main features of the regional stress field, and it was constructed after determining the average parameters of the possible external or "primary" field and simulating the major faults that could deflect the stress trajectories. INTRODUCTION Palaeostresses can be determined by means of analysis of fault populations on an outcrop scale. Several methods for this kind of analysis have been performed in the last l0 years [Angelier and Mechler, 1977' Armijo et al., 1982; Carey, 1979; Etchecopar et al., 1981; Sim6n G6mez, 1986]. These methods can be used in order to reconstruct both the orientation and shape of the local deviatoric stress ellipsoid. Using this analysis in a number of fault measurement stations within an area the state of stress responsible for the fault movements in each site can be determined. By integrating all the stress states of the same age we can draw a picture of the palaeostress field in this area during that time. An important condition for the correct determination of the palcostress field in a given area by means of microfault analysis is to determine the presence of geological structures of greater size, such as hectometric to kilometric strike-slip or reverse faults, that can deflect the stress trajectories. In the recent years some research has been made in order to define two-dimensional models of deviations in stress trajectories and magnitudes caused by these fractures in a given stress field [Rispoli, 1981; Xiaohan, 1983].These models have been made using real examples from map to outcrop scales and by means of mathematical simulation, usually based upon the finite element method. From these studies it can be seen that in certain areas, different stress tensors that had been previously interpreted as several primary stress episodes can be considered as deflections in the trajectories of an only regional stress field, caused either by deep or surface faults.In this paper, we make an attempt to draw a picture of the stress field that operated during the ...

Effect of predeformational basin geometry in the kinematic evolution of a thin‐skinned orogenic wedge: Insights from three‐dimensional finite element modeling of the Provo salient, Sevier fold‐thrust belt, Utah

“…The s s orientations tend to become parallel to the oblique ramp dip direction as the magnitude of stress increases. Stress trajectories of s 1 orientations indicated by map view 2-D plane strain models also show this tendency to become perpendicular to the strike of a preexisting oblique discontinuity [Casas et al, 1992;Homberg et al, 1997].…”

Paleostress Reconstruction from Striated Fault Data Sets in the Kirthar Fold Belt, Southern Pakistan

“…The present study utilized a sequence of three methods, whose joint usefulness has been broadly tested in the past (Casas et al, 1990(Casas et al, , 1992Arlegui, 1996;Arlegui and Sim6n, 1998). Each one provides a different approach to the stress determination problem, and allows the definition of stress tensors:…”

Effects of the hydrothermal circulation on the strain field of the Campanian Plain (southern Italy)

“…Thus, a major change in the direction of extension occurs. This feature may be due to: (a) the presence of faults with strikes making a low angle with the NE–SW strike of the far‐field extension (Casas et al ., 1992); (b) the occurrence of block‐rotations (Ron et al ., 1993); (c) the occurrence of a NW–SE extension that is parallel to the Apennine chain axis (Doglioni, 1991; Ferranti and Oldow, 1996); and (d) the presence, within the volcanic sector of the plain, of a zone with different rigidity with respect to the surrounding areas (Long and Zelt, 1991). We reject hypothesis (a) because the strike of the main faults of the Campanian volcanic area is the same as of the faults affecting the Apennines and Tyrrhenian Sea (Fig.…”