The Eastern French and Spanish Pyrenees

A few weeks ago, I took a pseudo-holiday with the family to the eastern Pyrenees. The Pyrenees offers many (if not most) of the features seen in large collisional orogenies (e.g. Alps and Himalaya) but on a much smaller scale. Because of this, much of our understanding of orogenic basins and reactivated orogenic basement come from the very accessible, well exposed Pyrenean Orogeny. Additionally, the Pyrenees offer an unparalleled look at Medieval history (if you are into that kind of thing) with spectacularly preserved and often precariously perched castles and walled cities.

Top left: The Devil’s Bridge; top right: Foix Castle; bottom; walled city of Carcassonne
From Carcassone we drove south through the “Molasse de Carcassonne” which consists of synorogenic sediments filling the northern foreland basins. These fluvial sediments were deposited and subsequently deformed during the Pyrenean Orogeny.
Syn-orogenic sediments near Carcassone

Stepping further into the orogeny and crossing the transpressional North Pyrenian Fault we entered a series of nappes composed of sedimentary rocks deposited in the western Tethyan Ocean. Many of these sedimentary packages were nearly synchronous in deposition to those across the entire length of the Tethyan Ocean seen here in the Alps and here in the Himalaya.

Top left: arch cut into the Tethyan limestone; high peaks of the Early Cretaceous carbonates; bottom left: Camille posing with the subvertical overturned limestone; bottom right: deep gorge of Pierre Lys.
Overturned bedding and axial planar(?) cleavage
En echelon fracture array showing sense of shear top to the right

Beyond the supracrustals of the Tethyan Ocean is the Hercynian basement which is comprised of the granitoids and metamorphic rocks that were formed during an orogenic event which occurred ~300 million years prior to the Pyrenean Orogeny.

Mafic enclaves in the Variscan granites.
Top: migmatite and folded pegmatite in Cap de Creus, Spain; mid-left: boundary between sillimanite bearing schist and pegmatite; mid-right: in situ melting and intrusion of pegmatite; bottom: Tamariua beach.
Ductile folds in metapsammites, Cap de Creus.
“Le Train Jaune”
View from our B&B window in Jujols.

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