Preorogenic Folds and Syn‐Orogenic Basement Tilts in an Inverted Hyperextended Margin: The Northern Pyrenees Case Study

The Chaînons Béarnais (CB, North Pyrenean Zone) resulted from the Cenozoic contractional reactivation of the salt tectonics‐bearing, hyperextended margin that initiated at the Europe‐Iberia transition during the Early Cretaceous. In this tectonic scenario, assessing the relative contribution of exte...

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Bibliographic Details
Published in:Tectonics (Washington, D.C.) D.C.), 2020-07, Vol.39 (7), p.n/a
Main Authors: Izquierdo‐Llavall, Esther, Menant, Armel, Aubourg, Charles, Callot, Jean‐Paul, Hoareau, Guilhem, Camps, Pierre, Péré, Eve, Lahfid, Abdeltif
Format: Article
Language:English
Subjects:
Analytical methods
Cenozoic
Chaînons Béarnais
Cretaceous
Earth Sciences
hyperextension
inheritance
Isotherms
Mesozoic
Metamorphism
North Pyrenean Zone
Palaeomagnetism
Paleogene
Paleomagnetism
Pyrrhotite
Raman spectroscopy on carbonaceous material
remagnetization
Sciences of the Universe
Spectroscopy
Tectonics
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Summary:The Chaînons Béarnais (CB, North Pyrenean Zone) resulted from the Cenozoic contractional reactivation of the salt tectonics‐bearing, hyperextended margin that initiated at the Europe‐Iberia transition during the Early Cretaceous. In this tectonic scenario, assessing the relative contribution of extension and contraction to the present‐day structure is crucial to reconstruct the hyperextended margin geometry and to quantify the subsequent shortening. This study undertakes this issue by defining the relationship between folding and two bedding‐independent references: peak temperature isotherms and paleomagnetic data. Isotherms were reconstructed from 76 new measurements of Raman spectroscopy on carbonaceous materials (RSCM) and indicate temperatures at the time of peak metamorphism in the CB (110–85 Ma, end of extension). They are shallowly to moderately northwards dipping and cut across most of the folds deforming the Mesozoic units. Paleomagnetic data from 29 sites evidence a widespread remagnetization carried by pyrrhotite that was probably blocked during the early Paleogene (before the onset of continental collision) and postdated folding in the CB. Abnormal inclinations in this remagnetization suggest syn‐collision tilts up to 60° to the north in the back limb of the Axial Zone. Based on the presented data set, we propose that the folding of the cover above the evaporitic décollement was almost fully completed by the end of the Cretaceous extension, with ~85–100% of the dip of fold limbs being acquired before the remagnetization time. Cenozoic contraction reactivated the extensional faults in the shallow basement as top‐to‐the‐S thrusts, leading to the passive transport and northwards tilting of the folded cover. Key Points We propose a new methodological approach to reconstruct fold evolution in hot inverted basins Salt‐cored folding in the Chaînons Béarnais is mostly inherited from extensional stages Orogenic shortening in the Northern Pyrenees can be erroneously estimated if this preorogenic, salt‐controlled folding is discarded
ISSN:0278-7407
1944-9194
DOI:10.1029/2019TC005719