Extension and early orogenic inversion along the basal detachment of a hyper-extended rifted margin: an example from the Central Pyrenees (France)

Abstract

The North Pyrenean Zone inverts remnants of an Aptian–Cenomanian rifting during which subcontinental mantle was exhumed. These remnants contain a synrift HT–LP metamorphic domain, the Internal Metamorphic Zone. New field data, Raman spectroscopy on carbonaceous material data and structural cross-sections constrain the structural and metamorphic relationships between the Internal Metamorphic Zone and the underlying low-grade North Pyrenean Zone. The Internal Metamorphic Zone is a tectonic nappe that overthrusts the European margin along the 3M Fault. Along this contact, the Tuc de Haurades peridotite is surrounded by tectonic breccia composed of ductilely deformed carbonate and sparse lherzolite clasts that passes upward into foliated marbles. Marbles contain top-to-south ductile shear, recording continuing extensional deformation that marks the onset of HT metamorphism. During Early Cretaceous rifting, European Mesozoic sedimentary cover metamorphosed and its base brecciated as it slid basinward on Triassic salt onto exhumed mantle. As the exhumed mantle domain closed during early convergence, the detached metamorphosed cover was transported northward and thrust onto the distal European margin, sampling lherzolite tectonic lenses. This triggered the first tectonic loading on the European plate. This study highlights the role of the Internal Metamorphic Zone in the early Pyrenean orogenic phase and gives new insights into the east–west diversity of structural setting of the North Pyrenean Zone peridotites. Supplementary material : A table with Raman spectroscopy on carbonaceous material temperatures and original and high-quality photographs of the samples are available at https://doi.org/10.6084/m9.figshare.c.5539260