Mantle exhumation, crustal denudation, and gravity tectonics during Cretaceous rifting in the Pyrenean realm (SW Europe): Insights from the geological setting of the lherzolite bodies Yves Lagabrielle, Pierre Labaume, Michel de Saint Blanquat To cite this version: Yves Lagabrielle, Pierre Labaume, Michel de Saint Blanquat. Mantle exhumation, crustal denudation, and gravity tectonics during Cretaceous rifting in the Pyrenean realm (SW Europe): Insights from the geological setting of the lherzolite bodies. Tectonics, American Geophysical Union (AGU), 2010, 29, pp.TC4012. 10.1029/2009TC002588. hal-00512818 HAL Id: hal-00512818 https://hal.archives-ouvertes.fr/hal-00512818 Submitted on 30 Apr 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 29, TC4012, doi:10.1029/2009TC002588, 2010 Click Here for Full Article Mantle exhumation, crustal denudation, and gravity tectonics during Cretaceous rifting in the Pyrenean realm (SW Europe): Insights from the geological setting of the lherzolite bodies Yves Lagabrielle,1 Pierre Labaume,1 and Michel de Saint Blanquat2 Received 3 August 2009; revised 24 December 2009; accepted 17 February 2010; published 27 July 2010. [1] The Pyrenean peridotites (lherzolites) form development can be inferred, involving extreme numerous small bodies of subcontinental mantle, a thinning of the crust, and mantle uprising along a major few meters to 3 km across, exposed within the narrow detachment fault. We demonstrate coeval development north Pyrenean zone (NPZ) of Mesozoic sediments of a crust‐mantle detachment fault and generalized paralleling the north Pyrenean Fault. Recent studies gravitational sliding of the Mesozoic cover along low‐ have shown that mantle exhumation occurred along angle faults involving Triassic salt deposits as a tectonic the future NPZ during the formation of the Albian‐ sole. This model accounts for the basic characteristics Cenomanian Pyrenean basins in relation with detachment of the precollisional rift evolution in the Pyrenean tectonics. This paper reviews the geological setting of realm. Citation: Lagabrielle, Y., P. Labaume, and M. de Saint the Pyrenean lherzolite bodies and reports new detailed Blanquat (2010), Mantle exhumation, crustal denudation, and field data from key outcrops in the Béarn region. Only gravity tectonics during Cretaceous rifting in the Pyrenean realm two types of geological settings have to be distinguished (SW Europe): Insights from the geological setting of the lherzolite among the Pyrenean ultramafic bodies. In the first bodies, Tectonics, 29, TC4012, doi:10.1029/2009TC002588. type (sedimented type or S type), the lherzolites occur as clasts of various sizes, ranging from millimetric 1. Introduction grains to hectometric olistoliths, within monogenic or polymictic debris flow deposits of Cretaceous age, [2] The Pyrenees is a narrow, 400 km long and N110° trending continental fold‐and‐thrust belt that developed in reworking Mesozoic sediments in dominant proportions response to the collision between the northern edge of the as observed around the Lherz body. In the second Iberia Plate and the southern edge of the European Plate type (tectonic type or T type), the mantle rocks form during the Late Cretaceous‐Tertiary [Choukroune and hectometric to kilometric slices associated with crustal ECORS Team, 1989; Muñoz, 1992; Deramond et al., 1993; tectonic lenses. Both crustal and mantle tectonic lenses Roure and Choukroune, 1998; Teixell, 1998]. In the Pyrenean are in turn systematically associated with large volumes domain, Triassic and Jurassic rifting events preceeded the of strongly deformed Triassic rocks and have fault development of Cretaceous rifts which culminated in the contacts with units of deformed Jurassic and Lower crustal separation between the Iberia and European plates Cretaceous sediments belonging to the cover of the [Puigdefabregas and Souquet, 1986; Vergés and Garcia‐ NPZ. These deformed Mesozoic formations are not older Senz, 2001]. Continental rifting in the Pyrenean realm that the Aptian‐early Albian. They are unconformably occurred coevally with oceanic spreading in the Bay of ‐ Biscaye between Chron M0 and A33o (approximately 125– overlain by the Albian Cenomanian flysch formations 83 Ma), in relation with the counterclockwise rotation of and have experienced high temperature‐low pressure ‐ Iberia relative to Europe [Le Pichon et al., 1970; Choukroune mid Cretaceous metamorphism at variable grades. Such and Mattauer, 1978; Olivet, 1996; Sibuet et al., 2004]. a tectonic setting characterizes most of the lherzolite Rotation was achieved just before the Albian according to bodies exposed in the western Pyrenees. These geological recent paleomagnetic data collected onland [Gong et al., data first provide evidence of detachment tectonics 2008]. leading to manle exhumation and second emphasize [3] The northern flank of the Pyrenees is well known for the role of gravity sliding of the Mesozoic cover the occurrence of numerous small‐sized exposures of sub- in the preorogenic evolution of the Pyrenean realm. continental mantle rocks, mostly lherzolites, widespread In the light of such evidence, a simple model of basin within Mesozoic sedimentary formations forming the north Pyrenean zone (NPZ) (Figure 1). Since their early descrip- tions by Lacroix [1895], there was a more than 100 years 1Géosciences Montpellier, UMR 5243, Université Montpellier 2, CNRS, long debate relative to the origin and significance of these Montpellier, France. ultramafic remnants. Very recent field studies in the sur- 2LMTG, UMR 5563, Université Toulouse III, CNRS, Observatoire roundings of Etang de Lherz (central Pyrenees), the type ‐ Midi Pyrénées, Toulouse, France. locality of the lherzolite, have revealed that a large amount of mantle exposures do in fact represent fragments of sub- Copyright 2010 by the American Geophysical Union. 0278‐7407/10/2009TC002588 continental material reworked through sedimentary pro- TC4012 1of26 TC4012 LAGABRIELLE ET AL.: PYRENEAN LHERZOLITES, GRAVITY TECTONICS TC4012 Figure 1. Simplified map of the Pyrenean belt with the location of the main ultramafic bodies and out- crops of lower crust. S type (sedimented) and T type (tectonic) lherzolites are distinguished on the basis of their geological setting as discussed in text. The main mid‐Cretaceous basins are shown in italic. Location of Figures 2, 4, and 13 is indicated. cesses within Cretaceous basins of the NPZ [Lagabrielle Mesozoic sedimentary sequences, small tectonic lenses of and Bodinier, 2008]. This demonstrates that exhumation Variscan crustal units (including granulites) and, in some of subcontinental mantle occurred along the NPZ during localities, clastic ultramafic‐bearing sedimentary series of transtensional deformation linked to the separation between Cretaceous age. An important challenge is now to revisit the the Iberia and the European plates. Therefore, exhumation most representative exposures of lherzolites across the entire of subcontinental mantle following extreme continental belt, in order to extract a set of critical data constraining the thinning during the mid‐Cretaceous Pyrenean rifting event processes of mantle exhumation and crustal thinning. In this has been proposed as a general mechanism accounting article, we first make the point of the various geological for the presence of ultramafic material within the NPZ settings of the ultramafic bodies. We show that they can be [Lagabrielle and Bodinier, 2008]. In addition, interpretation classified into two distinct categories, based on few basic of geophysical profiles in the Aquitaine region by Jammes criterias relative to their geological environments. These et al. [2009], enriched with field data from the Mauléon criteria provide information not only on mantle exhumation basin, also concluded to extreme crustal thinning and finally processes, but also on the behavior of the Mesozoic sedi- to tectonic exhumation of both the lower crust and the mentary cover in response to the progressive thinning subcontinental mantle during the Aptian‐Albian period in of the continental crust during the preorogenic Pyrenean the western Pyrenees. In the light of these recent studies, evolution. mantle exhumation appears undoubtely as an important mechanism accompanying the processes of extreme thinning of the continental crust. Considering these new results 2. Pyrenean Mantle Bodies: Two Main Types should help improving our understanding of the preorogenic of Geological Settings evolution not only of the Pyrenees but also of nonvolcanic passive margins in general, where mantle rocks are exhumed [5] The Pyrenean peridotites form numerous small bodies during the preorogenic rifting stages. of subcontinental mantle, a few meters to 3 km across, scatterred within the North Pyrenean Zone (NPZ) of Mesozoic [4] A recent analysis of the geological setting of the Pyrenean lherzolites [Lagabrielle and Bodinier, 2008] sediments paralleling the North Pyrenean Fault [Monchoux, has shown that careful analysis of this setting