Anisotropic magnetic susceptibility record of the kinematics of the Boltaña Anticline (Southern Pyrenees)

Abstract

Anisotropic magnetic susceptibility (AMS) analysis of 1454 samples evenly distributed along an 1800 m section in the South Pyrenean Zone is presented. The sampled rocks are pre-and syn-tectonic limestones, marls and sandstones of Ypresian-Lutetian age. They are weakly deformed rocks sampled from both limbs of the N-S trending Boltaña Anticline (oblique to the WNW-ESE main Pyrenean trend). Rock magnetism analyses, including low temperature and high field magnetic susceptibility measurements confirm a dominant paramagnetic signal and hence allow the interpretation of AMS in terms of preferred rock fabric or finite strain orientation. Therefore, this study was focused on obtaining an independent kinematic information from a vast set of AMS data from particular structural positions. The three directional maxima for the maximum axis of the magnetic ellipsoid (K MAX , magnetic lineation) can be tentatively related to major tectonic events in the Central Pyrenees. A first stage (recording a N-S magnetic lineation) is related to an oblique ramp of the Cotiella Thrust, emplaced during Ypresian times. A pseudo-progressive variation turns into a second stage (linked to a NW-SE K MAX orientation maximum) that can be related to Pyrenean compression. Both stages witness a far-field imprint of active structures on the foreland sediments. Once the Boltaña Anticline was nucleated (during the Lutetian), a predominant, more constant NW-SE trend is observed, this near-field magnetic fabric being the only lineation imprinted in the rocks. A final stage arrived in the course of vertical axis rotation during the Late Lutetian-Bartonian. This latest event was responsible for the present configuration of the Boltaña Anticline (N-S).

The Ainsa Fold and thrust oblique zone of the central Pyrenees: Kinematics of a curved contractional system from paleomagnetic and structural data

“…Layer parallel shortening directions can be derived from axis parallel pressure solution cleavage (Figures and ) [ Holl and Anastasio , , ; Tavani et al ., ], fault assemblages, twinned calcite grains, and AMS. The maximum shortening direction is subperpendicular to the structural trend around the Ainsa Oblique Zone and westward, defining a radial pattern [ Parés and Dinarès‐Turell , ; Holl and Anastasio , ; Tavani et al ., ; Mochales et al ., ]. These observations rule out progressive curved models with parallel thrust slip.…”

“…[10] The oblique structures of the South Central Pyrenees have also been the focus for studies of internal strain [Holl and Anastasio, 1995a] and mesostructural analysis [Holl and Anastasio, 1995b;Tavani et al, 2006Tavani et al, , 2012, which together with recent studies on anisotropy of magnetic susceptibility (AMS) [Oliva-Urcia et al, 2009;Mochales et al, 2010] add further constraints in the understanding of the kinematic evolution of these structures.…”

Provenance of siliciclastic and hybrid turbiditic arenites of the Eocene Hecho Group, Spanish Pyrenees: implications for the tectonic evolution of a foreland basin

“…3; Lutetian to Late Bartonian; Pickering & Corregidor, 2005) to form the western boundary of the basin. However, the anticline grew during the latest stages of the turbidite filling of the basin (Mochales et al , 2007). Most of the turbidite systems of the Aínsa Basin can be traced basinward into the Jaca Basin (Muñoz et al , 1998; Muñoz, 2004), which probably represented a subtle submarine high during deposition of the Hecho Group turbidites (Dreyer et al , 1999).…”

Acquisition and blocking of magnetic fabrics in synsedimentary structures, Eocene Pyrenees, Spain

“…The main results obtained during these works show a pervasive magnetic lineation, parallel to the general structural Pyrenean orientation (NE, 090° to 110°) and Kmin normal to bedding. These fabrics have been interpreted to be pre‐folding acquired due to tectonic shortening in horizontal bedding (by means of reorientation of paramagnetic particles during incipient shortening—LPS, Parès et al 1999; Larrasoaña et al 2004; Parés 2004; Oliva et al 2009; Mochales et al 2010). In some cases, these fabrics do not seem to have been affected by later tectonic folding or cleavage development (Pueyo Morer et al .…”

“…These fabrics have been interpreted to be pre-folding acquired due to tectonic shortening in horizontal bedding (by means of reorientation of paramagnetic particles during 1016Ó. Pueyo Anchuela et al incipient shortening-LPS, Parès et al 1999;Larrasoaña et al 2004;Parés 2004;Oliva et al 2009;Mochales et al 2010). In some cases, these fabrics do not seem to have been affected by later tectonic folding or cleavage development (Pueyo Morer et al 1997;Larrasoaña et al 1997;Parès et al 1999;Oliva et al 2009).…”