Deformation associated with mantle exhumation in a distal, hot passive margin environment: New constraints from the Saraillé Massif (Chaînons Béarnais, North-Pyrenean Zone)

Abstract

International audienceThe Chaînons Béarnais ranges (North-Pyrenean Zone, west-central Pyrenees) display a fold-and-thrust structure involving the Mesozoic sedimentary cover, decoupled from its substratum at the Keuper evaporites level and associated with a few peridotite bodies and scarce Palaeozoic basement lenses. In the western part of the Chaînons Béarnais, the newly described recumbent fold of the Saraillé massif comprises a peridotite body and several lenses of Palaeozoic basement wrapped by the Triassic to Aptian sedimentary cover. This structure represents a remnant of the distal portion of the Pyrenean paleo-rifted margin where mantle rocks have been exhumed during Albian–Cenomanian times. In this paper, we present the first detailed mapping and microstructural analysis of the Saraillé massif, providing new geological basis for reconstructing the evolution of this part of the paleo-margin. Our mapping (i) shows that the pre-rift Mesozoic cover forms a recumbent fold cored by mantle and crustal rocks and (ii) confirms that the prerift cover was detached from its bedrock along a layer of Triassic evaporites and slid onto the exhumed mantle rocks. Sliding of the prerift cover was associated with extreme crustal thinning and mantle exhumation along a major detachment fault, together with intense metasomatism affecting both the continental basement and the sedimentary cover. We show for the first time (1) that the Mesozoic pre-rift sediments experienced syn-metamorphic ductile thinning during mantle exhumation, and (2) that during its extreme attenuation, the continental basement was reduced to tectonic lenses some ten meters thick by ductile shearing

Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

“…In agreement with the ductile model cited above, Teixell et al (2016) (Corre et al, 2016). It must be underlined that the Triassic is a pre-rift salt, and the model requires a certain lateral continuity for regional detachment.…”

“…This interpretation is guided by the limited depth extent of the present-day subducted lower crust imaged by receiver functions (Fig. 7), and by the occurrence of only mid-upper crustal rocks in the continental fragments intermixed with the peridotite slices in the Chaînons Béarnais area (Lagabrielle et al, 2010;Corre et al, 2016). As an alternative, it may be argued that the PYROPE receiver function profiles do not image the true depth reached by the subducted lower crust, which may have arrived at greater depths beyond detection.…”

The crustal evolution of the west-central Pyrenees revisited: Inferences from a new kinematic scenario

“…In parallel with extreme stretching and gliding, temperatures up to 300-350°C were attained in the Jurassic-Cretaceous sediments (Clerc et al, 2015). The fragments of upper crustal rocks and mantle lherzolites were collected along the Triassic décollement (Lagabrielle et al, 2010;Corre et al, this volume) during the extensional and/or the later contractional gliding.…”

The pull apart-type Tardets-Mauléon Basin, a key to understand the formation of the Pyrenees

“…8B). The recent models involving this denudation commonly consider that the process could be regional, multi decakilometre-scale and closely related to one or several detachment faults shallowly dipping towards the north (Jammes, 2009;Masini, 2011;Masini et al, 2012;Corre et al, 2016;Teixell. et al, 2016).…”

“…This collision could have occurred through the Cenozoic inversion of an old rift opened during the Cretaceous period (Puigdefabregas and Souquet, 1986). Generating an extreme N-S crust thinning with detachment faulting, this opening could have led to the creation of oceanic crust (Stampfli, 2011;Vissers and Meijer, 2012), and even to a wide exhumation of the peridotitic upper mantle (Lagabrielle and Bodinier, 2008;Jammes, 2009;Jammes et al, 2009;Lagabrielle et al, 2010;Masini, 2011;Clerc et al, 2012;Masini et al, 2012;Corre et al, 2016;Teixell et al, 2016;Saint-Blanquat et al, 2016). The considered studies commonly suggest that the Mauléon, Baronnies, Ballongue, Aulus and Saint-Paul de FenouilletBoucheville basins (for location, see Fig.…”