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Ordovician deformations in the Pyrenees; new insights into the significance of pre-Variscan ("Sardic") tectonics

J. M. Casas
Ordovician deformations in the Pyrenees; new insights into the significance of pre-Variscan ("Sardic") tectonics
Geological Magazine (September 2010) 147 (5): 674-689


Two deformational events which developed prior to the Variscan structures can be characterized in the Palaeozoic rocks of the Pyrenees: a Middle (?) Ordovician folding event and a Late Ordovician fracture episode. The Middle (?) Ordovician folding event gives rise to NW-SE- to N-S-oriented, metric- to hectometric-sized folds, without cleavage formation or related metamorphism. These folds can account for the deformation and uplift of the pre-Upper Ordovician (Cambro-Ordovician) sequence and for the formation of the Upper Ordovician unconformity. Ordovician folds control the orientation of the Variscan main-folding-phase minor structures, fold axes and intersection lineation in the Cambro-Ordovician sediments. The Late Ordovician fracture episode gave rise to normal faults affecting the lower part of the Upper Ordovician series, the basal unconformity and the underlying Cambro-Ordovician metasediments. Displacement of some of these faults diminishes progressively upwards of the series and tapers off in the upper part of the Upper Ordovician rocks, indicating that the faults became inactive during Late Ordovician times before deposition of the Ashgillian metasediments. Normal faults can be linked to the Upper Ordovician volcanic activity, which has been extensively described in the Pyrenees. The aforementioned deformation episodes took place after the Early Ordovician magmatic event, which gave rise to a large volume of plutonic rocks in the Pyrenees as in other segments of the European Variscides. This Middle Ordovician contractional event separated two extensional events in the Pyrenees from Early Ordovician to Silurian times. This event prevents us from assuming the existence of a continuous extensional regime through Ordovician and Silurian times, and suggests a more complex evolution of this segment of the northern Gondwana margin during the Ordovician.

ISSN: 0016-7568
EISSN: 1469-5081
Coden: GEMGA4
Serial Title: Geological Magazine
Serial Volume: 147
Serial Issue: 5
Title: Ordovician deformations in the Pyrenees; new insights into the significance of pre-Variscan ("Sardic") tectonics
Author(s): Casas, J. M.
Affiliation: Universitat de Barcelona, Departament de Geodinamica i Geofisica, Barcelona, Spain
Pages: 674-689
Published: 201009
Text Language: English
Publisher: Cambridge University Press, London, United Kingdom
References: 68
Accession Number: 2010-087339
Categories: Structural geologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., geol. sketch maps
N41°30'00" - N42°30'00", E00°00'00" - E03°30'00"
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Cambridge University Press. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201046
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