6. Rotational kinematics of the Boltaña anticline - Instituto Geológico ...

Boltaña kinematics Mochales, 2011
1.1. Definition of this research
5
1. Objectives
This work deals with timing, kinematics and origin of oblique structure present in the
Southern Pyrenees using as a main tool paleomagnetism in its broadest sense; both as a dating tool and
as a way to obtain vertical-axis rotations. Moreover, analyses of the Anisotropy of the Magnetic
Susceptibility (AMS) have been performed to decipher additional details of the kinematics of
structures. These approaches have been especially focused on the Boltaña anticline and nearby areas.
The interest of this structure lies in its present orientation (N-S), oblique* with regard to the
dominating Pyrenean trend (ESE-WNW). The location of the Boltaña anticline, at the boundary
between the siliciclastic Tremp-Graus Basin and the turbiditic and molasse Jaca basin (the so-called
Aínsa basin), as well as its structural position at the western limit of the South Pyrenean Central Unit,
add interest to the interpretation of its complex evolution. The implications of the kinematics of the
Boltaña anticline in the evolution of the turbiditic Aínsa Basin (that is commonly used as a model of
turbiditic deposition in slope areas) has aroused the traditional interest of a broad number of scientists
and oil companies. The vast amount of studies here developed allows us for relying on a well-known
area whose temporal framework is not yet accurately unravelled.
The arrangement of this report has been done according to the disciplines used to establish the
kinematics of the Boltaña anticline and its temporal framework. Chapters two and three focus on the
geological setting based on previous investigations. The second chapter explains the geological frame
from the plate scale to the scale of thrust sheets. There, the crustal structure and the partitioning of the
Pyrenees are detailed. The third chapter is related to detailed stratigraphic and structural features of the
Aínsa Basin and the Boltaña anticline. Previous paleomagnetic studies involved in the study area are
overviewed in this chapter as well. The fourth chapter deals with the metholodogy applied in this
study. Here the paleomagnetic and magnetic fabric principles are centred on the relevant aspects for
this work.
Once focused the study area, the main body of PhD is developed in the following chapters.
The different kinds of new data produced in this work are described separately. The chapter number
five presents the magnetostratographic study carried out in the Aínsa Basin. It is based in the
continuous sampling performed throughout the Eocene rocks. It deals mainly with dating questions
and therefore paleomagnetism, biostratigraphy and mapping achieved special relevance in this chapter.
The sixth chapter analyzes the problem of the oblique structures of the South-Pyrenean Zone,
namely the western boundary of the South Pyrenean Central Unit (SPCU) where the Boltaña anticline
is located, from several points of view. From the kinematics point of view, the analysis of the
pretectonic, syntectonic and postectonic sequences by means of the study of Vertical Axis Rotations
(VAR) is performed.
*Oblique structure is defined as a structure with whose oblique to the main trend of a range.