Tectonic Evolution of the Moroccan High Atlas: A Paleomagnetic Perspective: Magnetic Techniques (Anisotropy of Magnetic Susceptibility and Paleomagnetism) Applied to the Understanding of the Evolution of an Intra-Plate Mountain Chain

666 Pages·2023·49.294 MB·English

by  Pablo Calvín, Antonio M. Casas-Sainz, Teresa Román-Berdiel, Juan J. Villalaín

Springer Geology
Pablo Calvín · Antonio M. Casas-Sainz ·
Teresa Román-Berdiel ·
Juan J. Villalaín   Editors
Tectonic Evolution
of the Moroccan High
Atlas: A Paleomagnetic
Perspective
Magnetic Techniques (Anisotropy
of Magnetic Susceptibility
and Paleomagnetism) Applied
to the Understanding of the Evolution of
an Intra-Plate Mountain Chain
Springer Geology
Series Editors
Yuri Litvin, Institute of Experimental Mineralogy, Moscow, Russia
Abigail Jiménez-Franco, Barcelona, Spain
Tatiana Chaplina, Institute of Problems in Mechanics, Russian Academy of
Sciences, Moscow, Russia
The book series Springer Geology comprises a broad portfolio of scientific books,
aiming at researchers, students, and everyone interested in geology. The series
includes peer-reviewed monographs, edited volumes, textbooks, and conference
proceedings. It covers the entire research area of geology including, but not limited
to, economic geology, mineral resources, historical geology, quantitative geology,
structural geology, geomorphology, paleontology, and sedimentology.
· ·
Pablo Calvín Antonio M. Casas-Sainz
·
Teresa Román-Berdiel Juan J. Villalaín
Editors
Tectonic Evolution
of the Moroccan High Atlas:
A Paleomagnetic Perspective
Magnetic Techniques (Anisotropy
of Magnetic Susceptibility
and Paleomagnetism) Applied to
the Understanding of the Evolution
of an Intra-Plate Mountain Chain
Editors
Pablo Calvín Antonio M. Casas-Sainz
Instituto Geológico y Minero de Department of Earth Sciences, Geotransfer
España (IGME), Zaragoza unit, Consejo Research Group (IUCA)
Superior de Investigaciones Universidad de Zaragoza
Científicas (CSIC) Zaragoza, Spain
Zaragoza, Spain
Juan J. Villalaín
Teresa Román-Berdiel Department of Physics
Department of Earth Sciences, Geotransfer Universidad de Burgos
Research Group (IUCA) Burgos, Spain
Universidad de Zaragoza
Zaragoza, Spain
ISSN 2197-9545 ISSN 2197-9553 (electronic)
Springer Geology
ISBN 978-3-031-16692-1 ISBN 978-3-031-16693-8 (eBook)
https://doi.org/10.1007/978-3-031-16693-8
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Dedicated to all paleomagnetists, geologists,
geoscientists, researchers and lovers of the
amazing nature of the Atlas Mountains
Foreword
I feel deeply honoured to have been given the chance to introduce this Springer
Geology Special Volume unravelling the amazing geological structure of the
Moroccan High Atlas. This book summarizes almost 15 years of extensive fieldwork,
countless hours of laboratory measurements, novel data processing protocols and
thorough geological interpretations leading to a unique picture of the Central High
Atlas in the geological past. The application of rock magnetic techniques, mainly
paleomagnetism and magnetic anisotropy, has proven extremely useful for discussing
the possible origin of many controversial structures in the High Atlas Basin. To me,
this book is probably the most complete and interesting work utilizing rock magnetic
methods, in conjunction with “classical” techniques of structural geology and sedi-
mentology (presented in Chapters “The Geological Setting of the Moroccan High
Atlas and Its Plate Tectonics Context” and “Structure of the Central High Atlas
(Morocco). Constraints from Potential Field Data and 3D Models”), applied in a
single orogenic chain.
Here, quite naturally, an average reader from among the geological public may
wonder what exactly these somewhat mysterious rock magnetic techniques are and,
more importantly, what additional pieces of information they are able to convey in
understanding the geological history of our area of interest. Well, in a very simplified
way, paleomagnetism studies a record of the Earth’s magnetic field locked, under
certain conditions, in rocks since the time they were formed. This is because the
preferred orientation of magnetic moments of very fine-grained magnetic minerals.
Like a “frozen compass needle”, paleomagnetic record provides probably the only
way for tracking the relative movements of different-scale rock units throughout the
geological history.
The other important rock magnetic technique is based on anisotropic behaviour of
magnetic properties, most frequently anisotropy of magnetic susceptibility. Magnetic
anisotropy results from the integrated anisotropic contributions of entire populations
of rock-constituent mineral grains and quite precisely reflects their crystallographic
or shape preferred orientation. Using magnetic anisotropy, one can, in a very fast,
cost-effective and non-destructive way, obtain invaluable information about principal
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structural directions even for rocks that show no apparent fabric on the macroscopic
scale.
In the course of this study, the authors obtained an astonishing number of more than
six thousand precisely oriented and localized specimens and subjected them to both
paleomagnetic and magnetic anisotropy investigations. At the earliest stages of the
research, it turned out that the Jurassic rocks of the Central High Atlas had been widely
remagnetized and their original paleomagnetic record had been altered or completely
reset in the Cretaceous time (Chapter “Magnetic Properties of the Jurassic Sedimen-
tary Rocks of the Central High Atlas Affected by a Regional Chemical Remagne-
tization”). Only after the remagnetization was understood, the authors were able to
reconstruct, step-by-step, how the Central High Atlas had been built and how the
Atlas Basin looked like in the pre-compressional stages (Chapter “Paleomagnetism
of the Central High Atlas. The Widespread Cretaceous Remagnetization and Struc-
tural Implications”). The paleomagnetic research was complemented by the tectonic
interpretation of magnetic fabric in terms of principal strain directions which, in
turn, provided a notion of how the rocks were deposited, deformed and over-thrusted
to build the present-day Atlas chain (Chapter “Kinematics of Structures and Basin
Evolution in the Central High Atlas. Constraints from AMS and Paleomagnetic
Data”).
What makes this book different from the previous and similar works? One of its
strengths is doubtless the geological subject. This is nicely reflected in countless
photographs that illustrate the book. Another interesting point is the accurate presen-
tation of data that will allow future researchers to perform new interpretations of this
huge data set in the light of new paradigms. Besides being an excellent regional study,
this book, due to its thorough and precise conception, provides valuable guidelines
about how the magnetic techniques could be used in other sedimentary basins.
I travelled to the Moroccan Atlas only briefly, many years ago, visiting mostly the
crowded touristic highlights. But even then, I noticed that not many areas in the world
show the fantastic features that every visitor (with or without a geological vision) is
amazed with if given a chance to wander around its ranges and valleys. I wish I had
had this book with me then. By deciphering the paleomagnetic record, the authors
were able to create a stunning “time-lapse image” of the Atlas Mountains that, in its
time frame, far exceeds our relatively short lifetime.
I am confident you will enjoy reading this book as much as I did.
September 2022 Dr. Martin Chadima
AGICO Inc. & Institute of Geology
of the Czech Academy of Sciences,
Brno, Czech Republic
Preface
Mountain building and mountain/basin evolution are major issues in Earth Sciences.
To solve the jigsaw puzzle containing the different pieces (many of them missing)
is a never-ending issue stimulated by new data and new perspectives. Answers to
some questions give rise to new ones and so on. On the other hand, seeking such
understanding in the company of friends is always much more rewarding.
This book is the result of a casual friendship that arose after two researchers with
common interests, J. J. Villalaín and A. M. Casas-Sainz, met at a scientific congress
several years ago. This encounter led them to work together in search of answers about
the rotation of Iberia, bringing together a comprehensive view of plate tectonics and
paleomagnetism. However, a regional remagnetization affecting the rocks they had
decided to study did not allow them to obtain data to solve the problem of the rotation
of Iberia, but it allowed them to open a novel line of research, consisting in using
paleomagnetic data to perform palinspastic reconstructions of inverted sedimentary
basins to the pre-compressional state, an issue difficult to perform and quantify
without the help of paleomagnetism. Together with R. Soto and C. García-Lasanta,
this technique was initially applied in several Mesozoic basins of the Iberian Penin-
sula, and later on in the Central High Atlas, with the development of the doctoral
theses of S. Torres-López, B. Moussaid and P. Calvín.
In parallel, T. Román-Berdiel had been using magnetic fabrics to understand the
tectonic context in which several Variscan granitic plutons were emplaced, while A.
M. Casas-Sainz had focused his study on inverted intra-plate basins. The union of
these two strands allowed them to develop, together with B. Oliva-Urcia, a research
line consisting of the study of magnetic fabrics in order to understand the tectonic
evolution of the Mesozoic sedimentary basins of the Iberian Peninsula first, with the
development of the doctoral thesis of C. García-Lasanta, and later on in the Central
High Atlas, together with B. Moussaid and P. Calvín.
The third leg of this bench came by the hand of Rui Dias, from the Univer-
sity of Evora, who, through the development of long-term geological activities in
Morocco, brought together the teams of the University of Meknès (led by Hmidou
el-Ouardi) and the already cooperating University of Burgos-University of Zaragoza
system. This book can be considered as the result of the fruitful collaboration between
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x Preface
the Meknès and Zaragoza-Burgos teams (subsequently involving the University of
Casablanca when Bennacer Moussaid moved to the latter).
This book tries to bring together these different visions to give some answers to
what happened during the last 200 Ma in the Central High Atlas. For this, with the
participation of 21 researchers from different Spanish and Moroccan institutions that
make up the list of authors of the different chapters, it has been possible to make this
book. Despite being divided into different chapters, authored by different scientists,
it is important to consider this book as an only work, though at the same time the
different chapters can be understood independently from one another. Far from the
“obligations” generated in today’s science, in which scientific papers have to be
quick and categorical, and it is hardly allowed to stop at a priori minor examples, but
which are part of the whole, this book seeks to go quietly through the structure and
the magnetic features (i.e., rock magnetism, paleomagnetism and magnetic fabrics)
of the Jurassic rocks of the Central High Atlas. Special mention should be made of
the last chapter, which in the same quiet and reflective line, analyzes the different
processes that have given rise, in a complex way, to the Atlas chain that we observe
when we are lucky enough to visit it.
Zaragoza, Spain Pablo Calvín
July 2022