Marine geophysical study of the Eurasian-African plate boundary in the vicinity of Gorringe Bank
The Gorringe Bank region is located at the eastern end of the Azores-Gibraltar plate boundary, which plate kinematic studies show to progressively change from extension at the Azores, through pure right lateral strike slip at the Gloria fault to compression at Gibraltar. The region is dominated by high relief (4-5 km), highly deformed, uncompensated, ENE-WSW trending seamounts and intervening abyssal plains with basin sediment thicknesses in excess of 4 km and minimal surface deformation. Gorringe Bank, which was formed by overthrusting of the African plate upon the Eurasian plate at about 10 Ma along the plate boundary, is supported in part by exure of the Eurasian plate, as indicated by pre-loading sediments and basement to the north which are tilted towards Gorringe Bank. Broken plate models show the Eurasian plate to have an elastic thickness of about 35 km which is in agreement with that expected for the crustal age (130-135 Ma) at the time of loading. Coral Patch Ridge was formed by a combination of thrust faulting and whole crustal buckling resulting from the past 20 Ma compression and was partially uplifted before deposition of an olistostrome in the Middle Miocene. Recent compressional deformation is distributed over a wide region, as indicated by the dispersed shallow seismicity and has a trend which rotates from approximately N45oE to N70oE from west to east across the region, near perpendicular to westward verging plate motion vectors. The majority of extensional and strike-slip deformation is explained by a regional strike-slip strain ellipse model, including an antithetic NNE-SSW strike slip fault between Gettysburg and Hirondelle seamounts which marks the boundary between the Eastern and Western Horseshoe Basins. Isostatic models for the Madeira-Tore Rise, which initially formed at the Mid Atlantic Ridge, give an elastic thickness of approximately 15 km indicating that significant material was added to the Rise as it moved away from the Ridge.