Gorringe Bank thrust sheet

Gorringe Bank thrust sheet
Name	Gorringe Bank thrust sheet
Type	submarine thrust sheet
Location	Northeast Atlantic Ocean, west of Gibraltar, southwest of Portugal
Coordinates	32°N 12°W (approx.)
Region	Iberian Peninsula margin, Azores–Gibraltar Transform Fault zone
Age	Cenozoic (Oligocene–Miocene to present)
Orogeny	Alpine orogeny

Gorringe Bank thrust sheet is a major submarine tectonic feature formed by compressional emplacement on the northeastern margin of the Atlantic Ocean near the Iberian Peninsula. It represents a large-scale nappe and thrust complex associated with plate boundary interactions involving the African Plate, Eurasian Plate, and the Iberian microplate. The feature has attracted multidisciplinary study from researchers at institutions such as the Instituto Hidrográfico de Portugal, Geological Survey of Spain, International Ocean Discovery Program, and universities including University of Lisbon, University of Porto, Universidad Complutense de Madrid, and University of Southampton.

Geologic Setting

The thrust sheet lies within the broader plate boundary region defined by the Azores Triple Junction, the Gibraltar Arc, and the Eurasia–Africa plate boundary, adjacent to the Tagus Abyssal Plain and the Gulf of Cadiz. Regional tectonics link it to the Alboran Domain, the Betic Cordillera, and the Atlas Mountains via far-field compressional stresses from convergence between the African Plate and Eurasian Plate. The bathymetric high is positioned near transform and fracture systems including the Gloria Fault and the Marquês de Pombal fracture zone, and is mapped in surveys by GEBCO, EMODnet, and national hydrographic offices.

Structure and Morphology

The thrust sheet exhibits a complex morphology of imbricated thrusts, large-scale folds, and an uplifted bedrock massif rising from abyssal depths to shallow seafloor highs. Multibeam sonar from research vessels such as RV Belgica, RRS James Cook, and RV Maria S. Merian reveal fault scarps, aligned ridges, and landslide complexes similar to structures documented in the Calabrian Arc and the Hellenic Trench systems. Structural mapping correlates a hanging wall nappe, basal décollement surfaces, and transported blocks comparable to thrust sheets in the Alps and Apennines.

Stratigraphy and Lithology

Exposed lithologies include Mesozoic carbonate platform sequences, Cretaceous pelagic limestones, Paleogene turbidites, and Neogene hemipelagic units, with igneous intrusions and seafloor basalts attributed to earlier Atlantic rifting episodes. Drill cores and dredge samples obtained during campaigns by the Ocean Drilling Program and the International Ocean Discovery Program show limestone, marl, chert, sandstone, and serpentinite clasts analogous to units in the Iberian Massif and the Betic Cordillera. Mineralogic assemblages contain calcite, dolomite, clay minerals, and serpentine phases comparable to those in ophiolite complexes such as the Semail Ophiolite.

Tectonic History and Formation

The thrust sheet formed during late Cenozoic compressional reorganization associated with the closure of the eastern Atlantic and the westward migration of the Alboran microplate. Episodes of subduction initiation, slab rollback, and continental collision influenced emplacement, with kinematic links to the Messinian Salinity Crisis timeframe and ongoing post-Messinian adjustments. Proposed models invoke low-angle thrusting, strike-slip partitioning along the Gloria Fault, and indentation from the African Plate producing large-scale nappe transport comparable to processes in the Himalaya-frontal thrust systems and the Zagros Mountains.

Seismicity and Geophysical Studies

The area is seismically active, producing earthquakes such as events recorded by networks including the International Seismological Centre, Instituto Português do Mar e da Atmosfera, and Instituto Geográfico Nacional (Spain). Geophysical investigations using seismic reflection, wide-angle refraction, gravity, and magnetic surveys by platforms like RRS Discovery and institutions such as Ifremer and BGR reveal a complex crustal architecture with high-amplitude reflectors, accreted slices, and thin-skinned thrust stacks. Tomographic models and focal mechanism studies link activity to regional events such as the historic 1755 Lisbon earthquake and more recent seismicity beneath the Gulf of Cadiz.

Hydrocarbon Potential and Mineral Resources

Sedimentary traps associated with thrust-related folds and syn-tectonic basins have been evaluated for petroleum potential by energy companies and national agencies including Petrobras, Repsol, and Galp Energia. Geochemical analyses of organic-rich intervals and basin modeling indicate limited but locally significant maturation analogous to other passive margin thrust belts like the Jura Mountains and parts of the North Sea Basin. The uplifted massif exposes massive sulfide occurrences and serpentinite-hosted mineral assemblages that attract interest for polymetallic sulfide and cobalt-rich crust exploration similar to deposits investigated in the Mid-Atlantic Ridge and Azores region.

Marine Ecology and Oceanographic Context

The Gorringe thrust sheet forms an ecological oasis for pelagic and benthic communities, hosting hard-substrate habitats colonized by deep-sea corals, sponges, and gorgonians comparable to those on seamounts such as Great Meteor Bank and Porcupine Bank. Biological surveys by organizations including WWF, Oceana, and the European Marine Observation and Data Network document fisheries interactions with species like bluefin tuna, swordfish, and deep-water demersals targeted by fleets from Portugal, Spain, Morocco, and France. Oceanographic dynamics are modulated by currents such as the Portugal Current, the Iberian Poleward Current, and mesoscale eddies linked to the Azores Current, influencing nutrient flux, larval dispersal, and biogeographic connectivity with the Mediterranean Sea and the North Atlantic Ocean.

Category:Seamounts Category:Geology of the Atlantic Ocean Category:Thrust faults