Abstract
The Pyrenees at the Iberia–Europe collision zone contain sediments showing Albian–Cenomanian high-temperature metamorphism, and coeval alkaline magmatic rocks. Stemming from different views on Jurassic–Cretaceous Iberian microplate kinematics, two schools of thought exist on the trigger of this thermal pulse: one invoking hyperextension of the Iberian and Eurasian margins, the other suggesting slab break-off. Competing scenarios for Mesozoic Iberian motion compatible with Pyrenean geology, comprise (1) transtensional eastward motion of Iberia versus Eurasia, or (2) strike-slip motion followed by orthogonal extension, both favoring hyperextension-related heating, and (3) scissor-style opening of the Bay of Biscay coupled with subduction in the Pyrenean realm, favoring the slab break-off hypothesis. We test these kinematic scenarios for Iberia against a newly compiled paleomagnetic dataset and conclude that the scissor-type scenario is the only one consistent with a well-defined ~35° counterclockwise rotation of Iberia during the Early Aptian. We proceed to show that when taking absolute plate motions into account, Aptian oceanic subduction in the Pyrenees followed by Late Aptian–Early Albian slab break-off should leave a slab remnant in the present-day mid-mantle below NW Africa. Mantle tomography shows the Reggane anomaly that matches the predicted position and dimension of such a slab remnant between 1900 and 1500km depth below southern Algeria. Mantle tomography is therefore consistent with the scissor-type opening of the Bay of Biscay coupled with subduction in the Pyrenean realm. Slab break-off may thus explain high-temperature metamorphism and alkaline magmatism during the Albian–Cenomanian in the Pyrenees, whereas hyperextension that exhumed Pyrenean mantle bodies occurred much earlier, in the Jurassic.
Highlights
The Pyrenees of southwestern Europe formed as a result of convergence and crustal thickening between Iberia and Eurasia since at least the Late Mesozoic (80 Ma)
A conspicuous phenomenon in the Pyrenees is the occurrence in the North Pyrenean Zone adjacent to the North Pyrenean Fault (Fig. 1) of low-pressure, high-temperature metasedimentary and alkaline igneous rocks with ages of ~ 110–90 Ma (Ubide et al, 2014; Clerc et al, 2015)
While the scissor-type scenario of Sibuet et al (2004) and Vissers and Meijer (2012a) successfully predicts the ~ 35° rotation of Iberia during the Aptian, we show that the consequent subduction and detachment during Aptian times of an oceanic domain in the Pyrenean realm is not falsified by mantle tomography
Summary
The Pyrenees of southwestern Europe formed as a result of convergence and crustal thickening between Iberia and Eurasia since at least the Late Mesozoic (80 Ma). One school of thought proposed that the HT–LP metamorphism is intrinsically related to the exhumation of the sub-continental mantle bodies, and that it serves as example of the temperature evolution associated with hyperextension at continental margins (Lagabrielle et al, 2010; Clerc and Lagabrielle, 2014; Clerc et al, 2015). A second school of thought, propounded that the metamorphism reflects the thermal response in the crust to the detachment of a subducted slab below the proto-Pyrenees (Vissers and Meijer, 2012a) and that the exhumation of the mantle peridotites is considerably older (Late Jurassic) than the HT metamorphism and associated magmatism
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