 |
| Titel |
Precisions on the structure of the Basque Arc (western Pyrenees, Spain):
preliminary results from magnetic fabrics from the Biscay Synclinorium |
| VerfasserIn |
Nestor Vegas, Aitor Aranguren, Lidia Rodriguez-Méndez, Julia Cuevas, Jose María Tubía, José Julián Esteban |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145427
|
| Publikation (Nr.) |
 EGU/EGU2017-9365.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Mesozoic Basque-Cantabrian basin (western Pyrenees) was inverted during the Alpine
Orogeny in late Cretaceous-Eocene times. The central sector of the basin, the Basque Arc is
characterized by the existence of large folds (80 km long) that outline an arc. This study
focuses on the interpretation of AMS fabrics in rocks from the Biscay Synclinorium, a major
fold system of the Basque Arc that verges to the NE, with sub-horizontal, N110˚ E trending
axes and axial planes striking to N110˚ E and dipping steeply to the SW (Calvo-Rathert et
al., 2007). The aim of this contribution is characterize the deformation around the Biscay
Synclinorium. For this reason we combined fieldwork with magnetic fabric analysis of 95
cores in Upper Cretaceous sedimentary rocks of the Biscay Synclinorium. 68 cores
come from the Calcareous formation (marls, sandy limestones and limestones of
Cenomanian to Campanian age) that makes part of the northeastern limb of the
synclinorium and the remaining 27 cores from the Detrital-calcareous flysch (a
multilayer sequence with sandy limestones and marls of Maastrichtian age) that
crops out in the synclinorium core (Garrote et al., 1991). In the Upper Cretaceous
Calcareous formation there is a penetrative cleavage that mainly strikes to N110˚
E dipping 50˚ to 60˚ to the SW (S1). In the Detrital-calcareous flysch of the
core, the best-preserved planar structure is the bedding and only locally an axial
planar cleavage is observed. Intersection lineations are sub-horizontal and N110˚
E-trending.
The measurements of the magnetic susceptibility provide low k values ranging between
99x10−6 and 403x10−6 SI. The anisotropy of the magnetic susceptibility, P, reaches values of
1.213, pointing to the overprinting of tectonic deformation on primary magnetic fabrics of
sedimentary origin. The magnetic foliation shows a fairly uniform arrangement that
is nearly coincident with the dominant planar structures of the rocks, S0 or S1in
the core and the limb of the synclinorium respectively. The magnetic lineation,
instead, yields complex patterns, as evidenced by the finding of two main sets of
magnetic lineations: 1) weakly plunging N110˚ E-trending lineations; 2) steeply
plunging N200˚ E-trending lineations. In both cases the magnetic fabric reflects
a tectonic origin but with different geological meaning. The first set, dominant
in the core of the synclinorium, is characterised by magnetic lineations parallel
to the intersection lineation between S0 and S1. In contrast, the other set come
from sites located along the limb of the synclinorium, where lower deformation
would be expected. However, owing to the steep plunging of the magnetic lineation
and to fact that the highest P values are obtained along this limb, we consider that
the second set of magnetic fabrics reflects the existence of a major shear zone at
the regional scale, with a top-to-the-NE motion, that has remained unknown until
now.
Calvo-Rathert, M., Cuevas, J., Tubía, J.M. et al. Int J Earth Sci (Geol Rundsch) (2007)
96: 1163. doi:10.1007/s00531-006-0149-8
Garrote, A., García, J., Fernández, J., Cerezo, A., Tijero, F. and Zapata, M. (1991).
Memoria Hoja nº 63-III (Eibar), 1:25.000. Ente Vasco de la Energía-EVE. , pp. 1-50 |
|
|
|
|
|
|