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

Abstract

[1] The Pyrenean peridotites (lherzolites) form numerous small bodies of subcontinental mantle, a few meters to 3 km across, exposed within the narrow north Pyrenean zone (NPZ) of Mesozoic sediments paralleling the north Pyrenean Fault. Recent studies have shown that mantle exhumation occurred along the future NPZ during the formation of the AlbianCenomanian Pyrenean basins in relation with detachment tectonics. This paper reviews the geological setting of the Pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the Béarn region. Only two types of geological settings have to be distinguished among the Pyrenean ultramafic bodies. In the first type (sedimented type or S type), the lherzolites occur as clasts of various sizes, ranging from millimetric grains to hectometric olistoliths, within monogenic or polymictic debris flow deposits of Cretaceous age, reworking Mesozoic sediments in dominant proportions as observed around the Lherz body. In the second type (tectonic type or T type), the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses. Both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed Triassic rocks and have fault contacts with units of deformed Jurassic and Lower Cretaceous sediments belonging to the cover of the NPZ. These deformed Mesozoic formations are not older that the Aptian-early Albian. They are unconformably overlain by the Albian-Cenomanian flysch formations and have experienced high temperature-low pressure mid-Cretaceous metamorphism at variable grades. Such a tectonic setting characterizes most of the lherzolite bodies exposed in the western Pyrenees. These geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the Mesozoic cover in the preorogenic evolution of the Pyrenean realm. In the light of such evidence, a simple model of basin development can be inferred, involving extreme thinning of the crust, and mantle uprising along a major detachment fault. We demonstrate coeval development of a crust-mantle detachment fault and generalized gravitational sliding of the Mesozoic cover along lowangle faults involving Triassic salt deposits as a tectonic sole. This model accounts for the basic characteristics of the precollisional rift evolution in the Pyrenean realm. Citation: Lagabrielle, Y., P. Labaume, and M. de Saint Blanquat (2010), 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, 29, TC4012,

High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

“…Although the peridotites have risen to near-surface levels, there is no evidence for sedimentary reworking indicating their exhumation on the basin floor. Indeed, on the basis of their geological setting, it can be deduced that the mantle rocks have remained capped by the Mesozoic marbles together with small slices of continental crust, during their ascent along a detachment fault (Lagabrielle et al, 2010). There, the highest temperatures (500-600 • C) are recorded directly in marbles on top of the peridotite massif, confirming the general trend already suggested from the eastern domain.…”

“…At present, the Pyrenean domain is also considered as hosting relevant analogs of distal passive margins, and its pre-orogenic evolution is being intensely revisited (Lagabrielle and Bodinier, 2008;Jammes et al, 2009;Lagabrielle et al, 2010;Masini 2011;Clerc et al, 2012;Clerc et al, 2013;Masini et al, 2014;Tugend et al, 2014). Unlike the Alpine analog, the North Pyrenean domain did not undergo subduction, and the thermal pattern recorded in the pre-and syn-rift material has not been overprinted by major crustal overthrusts or subductions.…”

“…The zone affected by the HT-LP metamorphism is characterized by an intense ductile deformation -S1 of Choukroune (1972); Choukroune (1976) -first attributed to compression and later reinterpreted as resulting from syn-extensional or transtensional deformation (Golberg 1987;Golberg and Leyreloup, 1990;Lagabrielle et al, 2010;Clerc and Lagabrielle, 2014).…”

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

“…Manatschal 2004;Manatschal and Müntener 2009). Similar OCT sequences have been reported in the Pyrenees (Lagabrielle and Bodinier 2008;Lagabrielle et al 2010) but the recognition of OCT ophiolites in older orogenic belts has received less attention.…”

Plate kinematics in the Cantabrian domain of the Pyrenean orogen

“…In essence, Jammes et al (2009) made the simple consideration that seafloor spreading was only part of the Mesozoic breakup and spreading process, as an important role in the Mesozoic motion of Iberia was played by the exhumed continental mantle, which is exposed in the Pyrenean Mountain Range (e.g. Lagabrielle et al, 2010), and surrounds the oceanic crust of the North Atlantic and of the Bay of Biscay (e.g. Boillot et al, 1987;Sibuet et al, 2007).…”