Reliability of magnetic fabric of weakly deformed mudrocks as a palaeostress indicator in compressive settings

The curved Magallanes fold and thrust belt: Tectonic insights from a paleomagnetic and anisotropy of magnetic susceptibility study

“…The AMS is controlled by individual grains in which the crystallographic orientation or grain shape orientation creates a preferred direction of magnetization [ Martin‐Hernandez et al ., ; Parés et al ., , for a review]. The application of AMS methods in sediments deposited in compressional tectonic settings has proved to be a reliable paleostress indicator, and AMS can be a very useful tool to unveil complex tectonic histories [ Kligfield et al, ; Borradaile and Henry, ; Parés et al, ; Robion et al, ; Soto et al, ; Roperch et al, ]. In undeformed rocks, the minimum axes of the AMS ellipsoid are well grouped and correspond to the bedding pole of the strata while maximum axes are dispersed within the bedding plane [ Borradaile and Henry, ].…”

Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

“…Such a progression has previously been identified in the Southern Pyrenean foreland basin (Parés et al, 1999). In the last stage of deformation, which corresponds to incipient metamorphism, the tectonic fabric developed during the initial (synsedimentary) phases of deformation is overprinted and lost, whereas it is preserved under small strains at low temperature (e.g., Parés, 2004;Larrasoaña et al, 2004;Soto et al, 2009). This implies that the finite strain inferred from AMS analyses of weakly deformed rocks can provide, in combination with structural geological analysis, fundamental constraints to study the tectonic regime (style and orientation)…”

“…Anisotropy of magnetic susceptibility (AMS) is a petrofabric tool able to determine the preferred orientation of magnetically-dominant minerals, and it is commonly used as a rock strain indicator (e.g., Jelinek, 1977;Hrouda, 1982Hrouda, , 1993Borradaile, 1988Borradaile, , 1991Jackson, 1991;Jackson and Tauxe, 1991;Rochette et al, 1992;Tarling and Hrouda, 1993;Sagnotti et al, 1994Sagnotti et al, , 1998Parés et al, 1999;Soto et al, 2009). In weakly deformed sedimentary rocks, AMS reflects the initial fabric produced during incipient deformation (mainly related to layer-parallel shortening) at the time of, or shortly after, deposition and diagenesis of the sediment (Sintubin, 1994;Sagnotti et al, 1998Sagnotti et al, , 1999Parés et al, 1999;Coutand et al, 2001;Cifelli et al, 2004Cifelli et al, , 2005Larrasoaña et al, 2004;Soto et al, 2009).…”

“…In weakly deformed sedimentary rocks, AMS reflects the initial fabric produced during incipient deformation (mainly related to layer-parallel shortening) at the time of, or shortly after, deposition and diagenesis of the sediment (Sintubin, 1994;Sagnotti et al, 1998Sagnotti et al, , 1999Parés et al, 1999;Coutand et al, 2001;Cifelli et al, 2004Cifelli et al, , 2005Larrasoaña et al, 2004;Soto et al, 2009). For this reason AMS analyses of weakly deformed sediments have frequently been used in orogenic settings to document the syn-sedimentary tectonic regime (Mattei et al, 1999; A C C E P T E D M A N U S C R I P T…”

“…Magnetic lineation has frequently been used to infer the nature (extensional vs. contractional) and orientation of the strain field, and draw conclusions on the local tectonic regime (e.g., Mattei et al, 1997;Larrasoaña et al, 2004;Soto et al, 2009;Gong et al, 2009). In this study, the magnetic lineations from the oldest (nonmetamorphic) units located in the most internal sectors of the Magallanes fold-andthrust belt have been analysed to constrain the kinematics of the earliest tectonic phases in the Fuegian Andes.…”