Abstract

Delamination of continental lithosphere in the core of active collisional orogens is a well-established process; however, evidence for its occurrence in ancient orogenic belts is less obvious. The contrasting Sm-Nd isotopic signature between pre– and post–Middle Permian mantle-derived mafic rocks from under the Iberian Massif suggests that most, but not all, of the subcontinental lithospheric mantle (SCLM) was replaced in latest Carboniferous to Permian time. Mantle replacement happened during and after the bending of the Variscan orogenic belt into the horseshoe-shaped Iberian-Armorican orocline. Delamination of thickened continental lithosphere in the core of the orocline triggered replacement of the ancient SCLM, thereby providing an explanation for the contrasting Sm-Nd isotopic characteristics of pre– and post–Middle Permian mafic rocks.

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