Field trips

The A Coruña region sits at the doorstep of two Variscan allochthonous complexes, Cabo Ortegal and Malpica-Tui, which together preserve a remarkable record of Late Palaeozoic subduction and exhumation along the northern Gondwana margin. These two complexes form the geological backbone of the IEC-16 field programme.

The setting of the Variscan Orogeny in NW Iberia

The Variscan orogen records the Late Palaeozoic assembly of Pangaea, resulting from the convergence and collision of Gondwana and Laurussia during the Devonian and Carboniferous. In northwestern Iberia, this history is preserved in an allochthonous nappe pile emplaced onto the Iberian autochthon, comprising oceanic and continental affinity units that were subducted to high-pressure conditions before being exhumed and tectonically transported to their current position.

The region around A Coruña exposes two well-preserved and extensively studied segments of this nappe system: the Cabo Ortegal Complex in the north, and the Malpica-Tui Complex to the south. Together, they offer a cross-section through the Variscan subduction zone, and have contributed substantially to our understanding of high-pressure metamorphism, exhumation mechanisms, and Variscan geodynamics. Notably, the allochthonous complexes of NW Iberia preserve multiple high-pressure metamorphic belts recording successive subduction events spanning much of the Devonian, making this region a key reference for reconstructing the polyphase accretionary history of the orogen (e.g., Arenas et al., 2016, Novo-Fernández et al., 2024).

The Cabo Ortegal Complex

The Cabo Ortegal Complex occupies the northwestern tip of the Iberian Peninsula and represents the upper part of the Variscan allochthon. It comprises a stack of thrust sheets exposing a varied assemblage of high-pressure rocks, including eclogites, high-P granulites, high-P migmatitic paragneisses, high-P peridotitic massifs, and a serpentinitic mélange with high-P blocks, all along with spectacular coastal cliff sections that reveal the structural relationships between these units.

Kyanite-bearing eclogite from the Upper Units

High-pressure granulite from the Upper Units

High-pressure ultramafic rocks from the Upper Units

High-pressure metavolcanic block from the Somozas Mélange

The Malpica-Tui Complex

The Malpica-Tui Complex extends from the Atlantic coast near Malpica de Bergantiños southward to the Portuguese border at Tui. As the structurally lowest unit of the allochthonous pile, it exposes blueschists and blueschist-facies rocks, eclogites and high-pressure orthogneisses, preserving a contrasting and complementary record to that of Cabo Ortegal.

Retrogressed blueschists with pseudomorphs of lawsonite from the Basal Units

Boudin of retroeclogite within orthogneisses from the Basal Units

Blueschist-facies metapelite from the Basal Units

Eclogite alongside kyanite-bearing vein from the Basal Units

Field trip programme

The quality of a geological field trip depends on keeping group sizes small enough for genuine scientific exchange at the outcrop. Anticipating strong demand for both destinations, we have chosen to run each field trip twice rather than once, with a maximum of 50 participants per departure. This arrangement allows us to maintain the standard of experience the community expects while ensuring that as many participants as possible can take part.

IEC-16 therefore offers four field trip departures across the two complexes described above: the Cabo Ortegal Complex, over three days, and the Malpica-Tui Complex, over two days. Each runs once before and once after the conference.

Contact: iec16.contact@gmail.com

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