# Evolution of the Pyrenees during the Variscan and Alpine Cycles 1: Variscan Cycle and Cretaceous Rifting

Nicolas Saspiturry, Jessica Uzel, Alexandre Ortiz

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Nicolas Saspiturry, Jessica Uzel, Alexandre Ortiz. Evolution of the Pyrenees during the Variscan and Alpine Cycles 1: Variscan Cycle and Cretaceous Rifting. Wiley, 2024, Print ISBN:9781789451245 |Online ISBN:9781394306534. 10.1002/9781394306534 hal-04945362

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# Evolution of the Pyrenees
during the Variscan
and Alpine Cycles 1

*Variscan Cycle*
*and Cretaceous Rifting*

Coordinated by
**Nicolas Saspiturry**
Jessica Uzel
**Alexandre Ortiz**
Evolution of the Pyrenees during the
Variscan and Alpine Cycles 1
SCIENCES

*Geoscience, Field Director – Yves Lagabrielle*

*Dynamics of the Continental Lithosphere,*
*Subject Head – Sylvie Leroy*

**Evolution of the Pyrenees
during the Variscan and
Alpine Cycles 1**

*Variscan Cycle and Cretaceous Rifting*

Coordinated by
Nicolas Saspiturry
Jessica Uzel
Alexandre Ortiz

iSTE

WILEY
First published 2024 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd
27-37 St George's Road
London SW19 4EU
UK

www.iste.co.uk

John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
USA

www.wiley.com

© ISTE Ltd 2024

The rights of Nicolas Saspiturry, Jessica Uzel and Alexandre Ortiz to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.

Library of Congress Control Number: 2023942080

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN 978-1-78945-124-5

ERC code:

PE10 Earth System Science

PE10_5 Geology, tectonics, volcanology

PE10_7 Physics of earth's interior, seismology, volcanology
3.5. Discussion of the main scientific issues surrounding the kinematics of the Iberian plate .................................... 124

3.5.1. Deformation distribution at the Iberian-European plate boundary. ............................................ 124

3.5.2. Variscan inheritance and Late Variscan position of the Ebro, Sardinia and Corsica blocks. .................... 126

3.6. Acknowledgments. .................................................................................................................. 127

3.7. References .................................................................................................................................................. 127

## Chapter 4. Sedimentary Breccias Synextension in the North-Eastern Pyrenees. ........................................ 149

Tarik KERNIF, Thierry NALPAS, Romain BOUSQUET and Roman CHELALOU

4.1. Introduction. .................................................................................................................. 149

4.2. The breccias of the north-eastern Pyrenees ................................................................. 151

4.2.1. Geological background. .................................................................................... 151

4.2.2. Description and organization of the breccias. ............................................ 153

4.2.3. Interpretation. .................................................................................................... 158

4.3. Discussion ................................................................................................................................ 159

4.3.1. Implications of the interpretation that the Lower Agly breccias had on the evolution of the Pyrenees. .................... 159

4.3.2. Sedimentary breccias: markers of extension? .................................................... 160

4.4. Conclusion ................................................................................................................................ 162

4.5. References ................................................................................................................................ 163

## Chapter 5. The North Pyrenean Zone: Hyper-thinned Rift Crust and Exhumed Mantle .................................... 165

Yves LAGABRIELLE

5.1. The North Pyrenean Zone: introduction. ................................................................. 165

5.2. The NPZ: a surprising association of varied lithologies. ............................................ 168

5.2.1. Stratigraphy ................................................................................................................ 168

5.2.2. Cretaceous magmatism. .................................................................................... 173

5.2.3. Thermometamorphism. .................................................................................... 174

5.2.4. Fluids and metamorphism. .................................................................................... 179

5.2.5. Lherzolites ................................................................................................................ 180

5.2.6. The issue of polygenic breccias. ........................................................................ 184

5.2.7. Conclusion of section 5.2 .................................................................................... 187
<table><tr><td>5.3. Mechanisms of crustal thinning and mantle denudation in the NPZ – recent field data and modern models</td><td>188</td></tr><tr><td>5.3.1. Years 2008–2010: outcrop of mantle rocks at the axis of the future NPZ – evidence and preliminary models.</td><td>188</td></tr><tr><td>5.3.2. Mantle exhumation and thermal evolution in the core of the Pyrenean rift</td><td>196</td></tr><tr><td>5.3.3. Behavior of the cover, crust and mantle during exhumation.</td><td>200</td></tr><tr><td>5.3.4. Fluid flow, metamorphism and metasomatism during the formation of Cretaceous Basins in the NPZ</td><td>210</td></tr><tr><td>5.3.5. Exhumation of the mantle: synthesis of geological data and modeling.</td><td>215</td></tr><tr><td>5.4. Conclusion</td><td>221</td></tr><tr><td>5.5. Acknowledgments.</td><td>221</td></tr><tr><td>5.6. References</td><td>222</td></tr></table>

## Chapter 6. The Bay of Biscay Opening in the Frame of the Iberian-European Plate Boundary Formation

Julie TUGEND and Isabelle THINON

<table><tr><td>6.1. Introduction.</td><td>242</td></tr><tr><td>6.2. Structure and age of the Bay of Biscay</td><td>245</td></tr><tr><td>6.2.1. The North Biscay passive margin</td><td>246</td></tr><tr><td>6.2.2. North Iberia margin.</td><td>251</td></tr><tr><td>6.2.3. Eastern termination of the Bay of Biscay: the Aquitaine margin and Parentis Basin.</td><td>255</td></tr><tr><td>6.3. The Bay of Biscay and the Iberian-European plate boundary</td><td>258</td></tr><tr><td>6.4. Future challenges</td><td>260</td></tr><tr><td>6.5. Acknowledgments.</td><td>262</td></tr><tr><td>6.6. References</td><td>262</td></tr></table>

## Chapter 7. The Trimouns Talc-Chlorite Deposit

Michel DE SAINT BLANQUAT, Philippe DE PARSEVAL, Alexandre BOUTIN, Benoit QUESNEL and Marc POUJOL

<table><tr><td>7.1. The central place of Trimouns in the geology of the Pyrenees.</td><td>273</td></tr><tr><td>7.2. Pyrenean talc and its exploitation.</td><td>275</td></tr><tr><td>7.3. History of the work</td><td>279</td></tr><tr><td>7.4. Geological context.</td><td>281</td></tr><tr><td>7.5. Lithology, structure and microstructures.</td><td>284</td></tr><tr><td>7.5.1. The wall</td><td>285</td></tr><tr><td>7.5.2. The deposit.</td><td>286</td></tr></table>
<table><tr><td>7.5.3. The deposit-roof contact</td><td>292</td></tr><tr><td>7.5.4. The roof</td><td>292</td></tr><tr><td>7.5.5. Quaternary formations</td><td>295</td></tr><tr><td>7.6. Ore, mineralogy and fluids</td><td>295</td></tr><tr><td>7.6.1. Ore</td><td>295</td></tr><tr><td>7.6.2. Mineralogy</td><td>299</td></tr><tr><td>7.6.3. Origin of the fluids and formation conditions of the deposit</td><td>300</td></tr><tr><td>7.7. Geochronological data</td><td>302</td></tr><tr><td>7.8. Synthesis and formation model</td><td>305</td></tr><tr><td>7.9. Conclusions and perspectives</td><td>306</td></tr><tr><td>7.10. Acknowledgments</td><td>309</td></tr><tr><td>7.11. References</td><td>310</td></tr><tr><td>List of Authors</td><td>317</td></tr><tr><td>Index</td><td>321</td></tr></table>
# Preface

Nicolas SASPITURRY<fnref n="1" />, Jessica UZEL<fnref n="2" /> and Alexandre ORTIZ<fnref n="2" />

The Pyrenean Mountain belt is, without a doubt, one of the most emblematic of France’s geological “objects”. This mountain belt has long attracted many French and foreign scientists. Although its formation is relatively recent, the analysis of the innumerable variety of rocks composing it allows us to reconstitute the complex evolution of this area over the last 600 million years. The Pyrenees were studied extensively between 1960–1990 from a stratigraphic, sedimentological and tectonic point of view, through the realization of numerous PhD theses. The purpose of these theses was to produce the 1/50,000 scale geological maps published by the *Bureau de recherches géologiques et minières* (BRGM). The end of the geological BRGM mapping program caused geologists to lose interest in the Pyrenees in favor of the Alps. Indeed, the growth of knowledge concerning the formation of passive margins and sub-continental mantle exhumation at the ocean-continent transition has led many researchers to apply these concepts to the inverted Alpine passive margins, making them the emblematic fossil global standard for these objects. Nevertheless, the Pyrenees remain a first-class natural laboratory for better understanding of the Variscan and Alpine cycles.

Since the 2010s, Pyrenean research has experienced a significant boom, as evidenced by the many research projects that have emerged: (1) the ANR PYRAMID (2012–2016), (2) the Pyrenees project of the *Référentiel géologique de la France* (RGF) (2014-2019) and (3) the Convergence research program (2016–2020). The ANR PYRAMID, supported in part by the energy group TotalEnergies and BRGM, was entitled: “North PYRenees: Integrated assessment of fluid migration

<footnote n="1">¹ Géosciences Montpellier, CNRS, Université de Montpellier, France</footnote>

<footnote n="2">² Géosciences Rennes, CNRS, Université de Rennes 1, France</footnote>
history, rift inversion, the role of surface processes and deformation in the evolution of an orogenic retrowedge and its foreland basin". The goals of this ANR grant were to (1) understand the overall 3D structural style and architecture of the North Pyrenean foreland system, and define the role of crustal inheritance within it; (2) link sediment transfer, landform formation and exhumation to the evolution of the foreland basin; and (3) quantify fluid-rock interactions from pre-orogenic extension to compression. Following the success of the ANR PYRAMID, BRGM has decided to continue by re-initiating scientific research on the Pyrenees.

Developed by BRGM, the RGF program, following the 1:50,000 geological map of France program, aimed to constitute the new foundation of French geological knowledge. Selected for their societal and academic attributes, the Pyrenees and their northern foreland constituted the first territory to apply the concepts of the RGF program. The RGF program consisted of reusing, reinterpreting and unifying different sources of surface and subsurface data on a single map, whether they came from geological maps, the subsurface data bank or oil and geothermal drilling. The objective of the RGF was, in the long term, the multi-scale representation of the geological knowledge of France in three dimensions, taking into account the physical properties of rocks. A true strategic project for BRGM and the entire scientific community, the RGF was part of a mission to support public policies by offering a response to the problems of land use planning, natural resource management and seismic and flood risk prevention. The RGF Pyrenees project, which lasted five years, revisited the 600 million years of geological history of this mountain belt. The goal of the RGF Pyrenees project was to (1) revisit the knowledge of the Paleozoic basement of the Pyrenees, exhumation and denudation during the tertiary orogeny and (2) constrain the processes of formation of the North Pyrenean rift and the exhumation of the continental mantle during the Lower Cretaceous, of which the lherzolites lining the belt are relics.

Finally, the Convergence research program (2016–2020) is the result of a close collaboration between TotalEnergies, BRGM and CNRS. This national research program aimed to structure research activities on mountain ranges and their adjacent sedimentary basins. This major scientific program included two projects: OROGEN and SOURCE TO SINK. The SOURCE TO SINK project was designed to better understand the processes of landform creation and erosion that lead to the formation of sedimentary basins from their source to the depositional zone. At a larger scale, OROGEN was an integrated holistic geosciences research project coordinated by INSU, with the objective of pushing back the limits of knowledge in terms of understanding the mechanisms behind mountain formation, as applied to the Pyrenean belt. The Pyrenees represented an exceptional study area due to its geological singularities: (1) the passive margins inherited from the Cretaceous
rifting partially preserved during continental subduction and then collision, and (2) the variation of its deformation states, between the Bay of Biscay and the Gulf of Lion, allowing us to study, in detail, how this domain evolves during compression and postorogenic phases. The presence of preserved basins of Cretaceous age, accessible from the outcrop in the north of the axial zone of the chain, has allowed for the acquisition of a unique data set for this type of domain, in particular the continental crust thermal evolution during the rifting stage.

The works of the SCIENCES series by ISTE and Wiley on the Pyrenees thus report on the evolution of geological knowledge, from the Variscan cycle to the Alpine cycle, resulting from these three major scientific research programs: the ANR PYRAMID, the RGF Pyrenees project and the Convergence research program. These publications logically involve many of the leading scientific actors of these research programs. We would like to thank the authors of the chapters who participated in the construction of these works. We would also like to thank Yves Lagabrielle and Sylvie Leroy for trusting us to manage this edition on Pyrenean geology.

August 2023